BIOLOGY

LIBRARY

G

Plate L

FIG. 1.

4«*

r

)

FIG. 2.

FIG. 1. — Human blood-corpuscles, fresh ; magnified 840 diameters, -fV inch homogeneous oil-
immersion-objective by Zeiss, original negative amplified twice (Stratford).

FIG. 2. — Blood of Guinea-pig, spread and dried on glass cover; magnified 1,450 diameters, jV
inch homogeneous oil-immevsion-objective by Zeiss, and Tolles's amplifier (Sternberg).

A TEXT-BOOK OF

HUMAN PHYSIOLOGY

BY

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

PROFESSOR OP PHYSIOLOGY AND PHYSIOLOGICAL ANATOMY IN THE BELLEVUE HOSPITAL MEDICAL COLLEGE
NEW YORK ; CONSULTING PHYSICIAN TO BELLEVUE HOSPITAL ; VISITING PHYSICIAN TO THE INSANE
PAVILION, BELLEVUE HOSPITAL ; CONSULTING PHYSICIAN TO THE INSANE ASYLUMS OF
NEW YORK CITY ; FELLOW OF THE NEW YORK STATE MEDICAL ASSOCIATION ;
CORRESPONDENT OF THE ACADEMY OF NATURAL SCIENCES OF PHILADEL-
PHIA ; MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, ETC.

WITII THREE HUNDRED AND SIXTEEN FIGURES IN THE TEXT, AND THREE PLATES

FOURTH EDITION, ENTIRELY REWRITTEN

NEW YORK

D. APPLETON AND COMPANY

1901

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,C , - - u . * I * « C t 4 » * ' *,

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, 1875, 1879, 1881, 1888,
D. APPLETON AND COMPANY.

BIOLOGY

LIBRARY

G

'-I,

PEEFAOE.

THE present edition of this treatise has been rewritten ; and while the
general arrangement of subjects is retained, but little remains of the
original text. Although the third edition, published in 1880, is still
much used as a text-book, for several years I have not been able to follow
it closely in public teaching ; and its defects have become so important
that it has seemed to me impossible to remedy them without making a
new book.

I have thought it advisable to curtail still more the historical refer-
ences contained in former editions. At the present day it is not possible
to give even a brief account of the literature of physiology within the
limits of a single volume of convenient size. I have avoided, also, as far
as practicable, discussions of unsettled and disputed questions, as un-
profitable and confusing.

I have adopted the new, chemical nomenclature, which is now almost
universally accepted, but have not attempted to give a full account of the
chemistry of the body. Physiological chemistry has now become a sci-
ence by itself ; and while it has contributed very largely to exact, physio-
logical knowledge, its full consideration is properly confined to special
treatises.

Eecent advances in the knowledge of minute anatomy, due largely to
improved instruments and methods, have had an important share in the
progress of physiology. These have been considered incidentally, and
they now form an essential part of all complete works on anatomy.

One who has long been a student and teacher of physiology can
hardly fail to have an idea, more or less definite, of what a text-book
should be, however imperfectly he may carry out this idea in his own
work. I shall be more than satisfied if I have been able to give concise
and connected statements of well-established facts, in such a form that
they can easily be acquired by students and in language that can not be
misunderstood. Peculiar views and theories, whether of the author or of
others, have no proper place in a text-book, which should represent facts
generally recognized and accepted, and not the ideas of any one individual

PREFACE.

It does not seem to me that the value of a text-book is materially en-
hanced by elaborate descriptions 'of apparatus and methods, except as
they involve principles susceptible of general, physiological application ;
nor does it seem profitable to follow out the details of intricate, mathe-
matical calculations involved in certain studies, such as physiological
optics and acoustics, the results of which are universally accepted. It is
sufficient to teach by text-books the science of physiology. The art of
investigation and the methods employed in physiological research are to
be learned in the laboratory and from special treatises and monographs.

To those who, by early education and common usage, have long been
accustomed to English weights and measures, the metric system frequently
fails to convey a definite idea, without a mental reduction to the familiar
standard ; but the metric system is now very generally used in scientific
works. In the text, the English weights and measures and the Fahren-
heit scale of the thermometer have been retained, and their equivalents in
the metric system are given in parentheses. In microscopic measure-
ments the micromillimetre (ToV(r of a millimetre, or V-^-^Q °^ an incn)?
indicated by the Greek letter p, is frequently employed.

The form and typography of the book have been changed, it is hoped
for the better. One new plate and sixty-one new figures have been intro-
duced. Two plates and sixty-three figures have been discarded. The old
illustrations which remain have been carefully examined and all remedi-
able defects have been corrected. For most of the illustrations that have
been retained, new electrotypes have been taken from the originals, and
thirty cuts have been re-engraved. A few engravings, however, taken
from classical authorities, though defective from an artistic point of view,
have been retained in their original form. It is due to the publishers to
make these statements, and to say that they have spared nothing in the
mechanical execution of the work.

AUSTIN FLINT.

NEW YORK, August, 1888.

I HAVE taken advantage of the opportunity afforded by the printing
of a second impression of this edition, to introduce a new description of
the anatomy of the human ovum, with a lithographic plate, in accord-
ance with the very recent studies of the normal, human ovum, by Nagel
(1888). These observations appeared after the fourth edition had been
completed. I have also introduced three new figures in the text, and
have revised the descriptions of fecundation of the ovum and segmenta-
tion of the vitellus.

A. F.

March, 1889.

CONTENTS

CHAPTER I.

THE BLOOD.

PAGE

Quantity of blood— General characters of the blood— Blood-corpuscles— Development of the blood-
corpuscles — Leucocytes — Development of leucocytes — Blood-plaques — Composition of the red cor-
puscles— Global ine — Haemaglobine — Composition of the blood-plasma — Inorganic Constituents —
Organic saline constituents — Organic non-nitrogenized constituents — Excrementitious constituents
— Organic nitrogenized constituents— Plasmine, fibrin, metalbumen, serine — Peptones — Coloring
matter— Coagulation of the blood— Conditions which modify coagulation— Coagulation of the blood
in the organism — Cause of the coagulation of the blood ...'.. .... 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 the movements of the heart— Force of the heart-
Action of the valves— Sounds of the heart— Causes of the sounds of the heart— Frequency of the
heart's action — Influence of age and sex — Influence of. digestion — Influence of posture and muscu-
lar exertion— Influence of exercise etc. — Influence of temperature — Influence of respiration on the
action of the heart— -Cause of the rhythmical contractions of the heart — Accelerator nerves — Direct
inhibition of the heart— Reflex inhibition of the heart— Summary of certain causes of arrest of the
action of the heart 29

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 on the arterial pressure — Rapidity of the current
of blood in the arteries— Rapidity in different parts of the arterial system— Circulation of the blood
, in the capillaries— Physiological anatomy of the capillaries— Pressure of blood in the capillaries-
Relations of the capillary circulation to respiration — Causes of the capillary circulation — Influence
of temperature on the capillary circulation — Influence of direct irritation on 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— Uses 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— Circulation in the walls of the heart — Passage of
the blood-corpuscles through the walls of the vessels (diapedesis) — Rapidity of the circulation —
Phenomena in the circulatory system after death 60

CHAPTER IV.
RESPIRA TION-RE8PIRA TOR Y MO VEMENTS.

General considerations— Physiological anatomy of the respiratory organs— Movements of respiration-
Inspiration — Muscles of inspiration — Expiration — Muscles of expiration — Types of respiration—

vi CONTENTS.

PAGE

Frequency of the respiratory movements— Relations of inspiration and expiration to each other
—Respiratory sounds— Capacity of the lungs and the quantity of air changed in the respiratory
acts— Residual air— Reserve air— Tidal, or breathing air— Complemental air— Extreme breathing
capacity— Relations in volume of the expired to the inspired air— Diffusion of air in the lungs . . 108

CHAPTER V.

CHANGES WHICH THE AIR AND THE BLOOD UNDERGO IN RESPIRATION.

Composition of the air— Consumption of oxygen — Exhalation of carbon dioxide — Relations between the /
quantity of oxygen consumed and the quantity of carbon dioxide exhaled— Sources of carbon
dioxide in the expired air— Exhalation of watery vapor— Exhalation of ammonia— Exhalation of
organic matter— Exhalation of nitrogen— Changes of the blood in respiration (haematosis)— Difference
in color between arterial and venous blood— Comparison of the gases in venous and arterial blood-
Analysis of the blood for gases— Nitrogen of the blood— Condition of the gases in the blood— Rela-
tions of respiration to nutrition etc.— The respiratory sense— Sense of suffocation— Respiratory
efforts before birth — Cutaneous respiration — Breathing in a confined space — Asphyxia . . . 135

CHAPTER VI.

ALIMENT A TION.

General considerations— Hunger— Seat of the sense of hunger— Thirst— Seat of the sense of thirst-
Duration of life in inanition — Classification of alimentary substances — Nitrogenized alimentary
substances — Non-nitrogenized alimentary substances — Inorganic alimentary substances — Alcohol
—Coffee— Tea -Chocolate— Condiments and flavoring articles— Quantity and variety of food neces-
sary to nutrition — Necessity of a varied diet 164

CHAPTER VII.

DIGESTION— MASTICATION, INSALIVATION AND DEGLUTITION.

Prehension of food— Mastication— Physiological anatomy of the teeth— Anatomy of the maxillary bones
— Temporo-maxillary articulation— Muscles of mastication— Action of the tongue, lips and cheeks
in mastication — 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— Uses of the saliva— Physiological
anatomy of the parts concerned in deglutition— Mechanism of deglutition— First period of degluti-
tion—Second period of deglutition— Protection of the posterior nares during the second period of
deglutition— Protection of the opening of the larynx and uses of the epiglottis in deglutition— Third
period of deglutition— Deglutition of air 188

CHAPTER VIII.

GASTRIC DIGESTION.

Physiological anatomy of the stomach — Glands of the stomach— Closed follicles— Gastric juice-
Gastric fistula in the human subject in the case of St. Martin— Secretion of the gastric juice-
Properties and composition of gastric juice — Action of the gastric juice in digestion — Peptones —
Action of the gastric juice upon fats, sugars and amylaceous substances — Duration of gastric diges-
tion—Conditions which influence gastric digestion— Movements of the stomach 21 1

CHAPTER IX.

INTESTINAL DIGESTION.

Physiological anatomy of the small intestine — Glands of Brunner — Intestinal tubules, or follicles of
Lieberkuhn— Intestinal villi— Solitary glands, or follicles, and patches of Peyer— Intestinal juice-
Action of the intestinal juice in digestion— Pancreatic juice— Action of the pancreatic juice upon
starches and sugars — Action upon nitrogenized substances — Action upon fats — Action of the bile
in digestion— Biliary fistula— Variations in the flow of bile— Movements of the small intestine-
Peristaltic and antiperistaltic movements— Uses of the gases in the small intestine— Physiological
anatomy of the large intestine— Processes of fermentation in the intestinal canal— Contents of the
large intestine— Composition of the fseces— Excretine and excretoleic acid— Stercorine— Indol, skatol,
phenol etc.— Movements of the large intestine— Defeecation— Gases found in the alimentary canal . 233

CONTENTS. vii

PAGE

CHAPTER X.

ABSORPTION— LYMPH AND CHYLE.

Absorption by blood-vessels— Absorption by lacteal and lymphatic vessels— Physiological anatomy of
the lacteal and lymphatic vessels— Lymphatic glands— Absorption by the lacteals— Absorption by
the skin — Absorption by the respiratory surface — Absorption from closed cavities, reservoirs of
glands, etc.— Absorption of fats and insoluble substances— Variations and modifications of ab-
sorption—Mechanism of the passage of liquids through membranes— Lymph arid chyle— Properties
and composition of lymph— Origin and uses of the lymph— Composition of the chyle— Microscopical
characters of the chyle— Movements of the lymph and chyle 272

CHAPTER XI.

SECRETION.

Classification of the secretions — Mechanism of the production of the true secretions — Mechanism of
the production of the excretions — Influence of the composition and pressure of the blood on se-
cretion— Influence of the nervous system on secretion — Anatomical classification of glandular
organs — Classification of the secreted fluids — Synovial membranes and synovia — Mucous mem-
branes and mucus — Physiological anatomy of the sebaceous, ceruminous and Meibomian glands —
Ordinary sebaceous matter— Smegma of the prepuce and of the labia ininora— Vernix caseosa—
Cerumen— Meibomian secretion— Mammary secretion— Physiological anatomy of the mammary
glands— Mechanism of the secretion of milk— Conditions -which modify the lacteal secretion-
Quantity of milk— Properties and composition of milk— Microscopical characters of milk— Composi-
tion of milk— Variations in the composition of milk — Colostrum — Lacteal secretion in the newly-
born— Secretory nerve-centres 306

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 — Physiological anatomy of the hairs — Sudden blanching of the
hair — 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 — Mechanism of the production and discharge of urine — Influence of blood-pressure, the
nervous system etc., upon the secretion of urine— Physiological anatomy of the urinary passages
—Mechanism of the discharge of urine— Properties and composition of the urine— Influence of
ingesta upon the composition of the urine and upon the elimination of nitrogen — Influence of mus-
cular exercise upon the elimination of nitrogen — Water regarded as a product of excretion — Varia-
tions in the composition of the urine . 341

CHAPTER XIII.

USES OF THE LIVER-DUCTLESS GLANDS.

Physiological anatomy of the liver— Distribution of the portal vein, the hepatic artery and the hepatic
duct— 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— Uses of the bile — Properties and composition of the bile — Biliary
salts— Cholesterine— Tests for bile— Excretory action of the liver— Formation of glycogen in the
liver— Change of glycogen into sugar— Conditions which influence the quantity of sugar in the
blood— Summary of the glycogenic action of the liver— Probable office of the ductless glands-
Physiological anatomy of the spleen— Suprarenal capsules— Addison's disease— Thyroid gland—
Myxcedema— Thymus— Pituitary body and pineal gland 392

CHAPTER XIV.

NUTRITION-ANIMAL HEAT AND FORCE.

Nature of the forces involved in nutrition— Life, as represented in development and nutrition — Sub-
stances which pass through the organism — Metabolism— Substances consumed in the organism —
Conditions which influence nutrition— Animal heat and force — Estimated quantity of heat produced
by the body— Limits of variation in the normal temperature in man— Variations with external tem-
perature—Variations in different parts of the body— Variations at different periods of life etc.—

viii CONTENTS.

PAGE

Influence of exercise etc., upon the heat of the body— Influence of the nervous system upon the
production of animal heat (heat-centres) — Mechanism of the production of animal heat — Equaliza-
tion of the animal temperature— Relations of heat to force 426

CHAPTER XV.

MOVEMENTS— VOICE AND SPEECH.

Amorphous contractile substance and amoeboid movements— Ciliary movements— Movements due to
elasticity — Elastic tissue — Muscular movements — Physiological anatomy of the involuntary muscu-
lar tissue — Contraction of the involuntary muscular tissue — Physiological anatomy of the voluntary
muscular tissue— Connective tissue— Connection of the muscles with the tendons— Chemical com-
position of the muscles— Physiological properties of the muscles— Muscular contractility, or excita-
bility— Muscular contraction — Electric phenomena in muscles — Muscular effort — Passive organs of
locomotion— Physiological anatomy of the bones — Physiological anatomy of cartilage — Voice and
speech— Sketch of the physiological anatomy of the vocal organs— Mechanism of the production of
the voice— Laryngeal mechanism of the vocal registers— Mechanism of speech— The phonograph . 460

CHAPTER XVI.

PHYSIOLOGICAL DIVISIONS, STRUCTURE AND GENERAL PROPERTIES OF THE

NERVOUS SYSTEM.

Divisions and structure of the nervous tissue— Medullated nerve-fibres— Simple, or non-mednllated
nerve-fibres — Gelatinous nerve-fibres (fibres of Remak) — Accessory anatomical elements of the
nerves — Termination of the nerves in the muscular tissue — Termination of the nerves in glands —
Modes of termination of the sensory nerves— Corpuscles of Vater, or of Pacini— Tactile corpuscles
—End-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— Degeneration and regeneration of the nerves— Motor and sensory nerves— Mode
of action of the motor nerves— Associated movements— Mode of action of the sensory nerves-
Physiological differences between motor and sensory nerve-fibres — Nervous excitability — Different
means employed for exciting the nerves — Rapidity of nervous conduction — Personal equation —
Action of electricity upon the nerves— Law of contraction— Induced muscular contraction— Electro-
tonus, anelectrotonus and catelectrotonus — Negative variation 50E

CHAPTER XVII.

SPINAL AND CRANIAL NERVES.

Spinal nerves— Cranial nerves— Anatomical classification— Physiological classification— Motor oculi
communis (third nerve)— Physiological anatomy— Properties and uses— Influence upon the move-
ments of the iris — Patheticus, or trochlearis (fourth nerve) — Physiological anatomy — Properties and
uses— Motor oculi externus, or abducens (sixth nerve)— Physiological anatomy— Properties and uses
—Nerve of mastication' (the small, or motor root of the fifth)— Physiological anatomy— Properties
and uses— Facial, or nerve of expression (seventh nerve)— Physiological Anatomy— Intermediary
nerve of Wrisberg — Alternate paralysis — General properties — Uses of the chorda tympani — Influence
of various branches of the facial upon the movements of the palate and uvula — Spinal accessory
(eleventh nerve)— Physiological anatomy— Uses of the internal branch from the spinal accessory to
the pneumogastric— Influence of the spinal accessory upon the heart— Uses of the external, or mus-
cular branch of the spinal accessory — Sublingual, or hypoglossal (twelfth nerve) — Physiological
anatomy— Properties and uses— Trifacial, or trigeminal (fifth nerve)— Physiological anatomy— Prop-
erties and uses— Pneumogastric (tenth nerve)— Physiological anatomy— Properties and uses— Gen-
eral properties of the roots— Properties and uses of the auricular nerves— Properties and uses of the
pharyngeal nerves— Properties and uses of the superior laryngeal nerves — Properties and uses of the
inferior, or recurrent laryngeal nerves— Properties and uses of the cardiac nerves — Depressor nerve
of the circulation— Properties and uses of the pulmonary nerves— Properties and uses of the ceso-
phageal nerves— Properties and uses of the abdominal nerves 53!)

CHAPTER XVIII.

THE SPINAL CORD.

General arrangement of the cerebro-epinal axis— Membranes of the encephalon and spinal cord— Cephalo-
rachidian fluid— Physiological anatomy of the spinal cord— Columns of the cord— Direction of the
nerve-fibres in the cord— General properties of the spinal cord— Motor paths in the cord— Sensory

CONTENTS. ix

PAGB

paths in the cord— Relations of the posterior white columns of the cord to muscular co-ordination-
Nerve-centres in the spinal cord — Reflex action of the spinal cord — Exaggeration of reflex excitability
by decapitation, poisoning with strychnine etc.— Reflex phenomena observed in the human subject 586

CHAPTER XIX.

THE ENCEPHALIC GANGLIA.

Physiological divisions of the encephalon — Weights of the encephalon and of certain of its parts — The
cerebral hemispheres— Cerebral Convolutions— Basal ganglia— Corpora striata, optic thalami and
internal capsule— Tubercular quadrigemina— Pons Varolii— Directions of the fibres in the cerebrum
—Cerebral localization— General uses of the cerebrum— Extirpation of the cerebrum— Facial angle-
Pathological observations — Reaction-time — Centre for the expression of ideas in language — The
cerebellum— Physiological anatomy — Extirpation of the cerebellum — Pathological observations —
Connection of the cerebellum with the generative function — Medulla oblongata (Bulb) — Physiologi-
cal anatomy— Uses of the medulla oblongata— Respiratory nerve-centre— Cardiac centres— Vital
point (so called)— Rolling and turning movements following injury of certain parts of the encephalon 601

CHAPTER XX.

SYMPATHETIC NERVOUS SYSTEM-SLEEP.

General arrangement of the sympathetic system — General properties of the sympathetic ganglia and
nerves — Direct experiments on the sympathetic — Vaso-motor centres and nerves — Reflex vaso-motor
phenomena— Vaso-inhibitory nerves— Trophic centres and nerves (so-called)— Sleep— Condition of
the brain and nervous system during 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— Condition of the organism during sleep . . . . . .635

CHAPTER XXI.

SPECIAL SENSES-TOUCH, OLF ACTION AND GUSTATION.

General characters of the special senses— Muscular sense (so called) — Sense of touch — Variations in
tactile sensibility in different parts (sense of locality of impressions) — Table of variations measured

* by the aesthesiometer — Appreciation of temperature — Tactile centre — Olfaction — Nasal fossae —
Schneiderian and olfactory membranes— Olfactory (first nerve)— Physiological anatomy— Olfactory
bulbs— Olfactory cells and terminations of the olfactory nerve-fibres — Properties and uses of the
olfactory nerves — Mechanism of olfaction — Relations of olfaction to the sense of taste — Reflex acts
through the olfactory nerves — Olfactory centre — Gustation — Savors — Nerves of taste — Chorda tym-
pani — Glosso-pharyngeal (ninth 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— Papillae of the tongue— Taste-beakers— Connections of
the nerves with the organs of taste— Taste-centre . . . . . . . 652

CHAPTER XXII.

VISION.

General considerations— Optic (second nerve)— General properties of the optic nerves— Physiological
anatomy of the eyeball— Sclerotic coat — Cornea — Choroid coat — 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 — Certain laws of refrac-
tion, dispersion etc., bearing upon the physiology of vision— Refraction by lenses— Visual purple
and visual yellow and accommodation of the eye for different degrees of illumination — Formation of
images in the eye — Mechanism of refraction in the eye — Astigmatism — Movements of the iris— Di-
rect 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 for vision at different distances — Changes in
the crystalline lens in accommodation— Changes in the iris in accommodation— Erect impressions
produced by images inverted upon the retina— Field of indirect vision— The perimeter— Binocular
vision — Corresponding points — The horopter — Duration of luminous impressions (after-images) —
Irradiation — Movements of the eyeball — Muscles of the eyeball — Centres for vision — Parts for the
protection of the eyeball— Conjunctival mucous membrane— Lachrymal apparatus— Composition of
the tears . 671

x CONTENTS.

PAGE

CHAPTER XXIII.

A UDITION.

Auditory (eighth nerve)— 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 — Gen-
eral arrangement of the bony labyrinth— Physics of sound— Noise and musical sounds— Pitch of
musical sounds— Musical scale— Quality of musical sounds— Harmonics, or overtones— Resultant
tones — Summation tones — Harmony — Discords — Tones by influence — Uses of different parts of the
auditory apparatus — Structure of the membrana tympani — Uses of the membrana tympani — Mechan-
ism of the ossicles of the ear — Physiological anatomy of the internal ear — General arrangement of
the membranous labyrinth— Liquids of the labyrinth— Distribution of nerves in the labyrinth— Or-
gan of Corti— Uses of different parts of the internal ear— Centres for audition . . . .728

%

CHAPTER XXIV.

ORGANS AND ELEMENTS OF GENERATION.

General considerations — Female organs of generation — General arrangement of the female organs —
The ovaries— Graafian follicles— The parovarium— The uterus— The Fallopian tubes— Structure of
the ovum— Discharge of the ovum— Passage of ova into the Fallopian tubes— Puberty and menstrua-
tion— Changes in the Graafian follicle after its rupture (corpus luteum) — Male organs of genera-
tion—The testicles— Vesiculae seminales— Prostate— Glands of the urethra— Male elements of gen-
eration—Spermatozoids . . . . . . . . ... . . .765

CHAPTER XXV.

FECUNDATION AND DEVELOPMENT OF THE OVUM.

General considerations — Fecundation — Changes in the fecundated ovum— Segmentation of the vitell-
us — Primitive trace — Blastodermic layers — Formation of the membranes— Amniotic fluid — Umbilical
vesicle— Formation of the allantois and the permanent chorion— Umbilical cord— Membranae de-
ciduae— Formation of the placenta— Uses of the placenta— Development of the ovum— Development
of the cavities and layers of the trunk in the chick— Vertebral column— Development of the skele-
ton— Development of the muscles — Development of the skin — Development of the nervous system
— Development of the organs of special sense — Development of the digestive apparatus — Develop-
ment of the respiratory apparatus— Development of the face— Development of the teeth— Develop-
ment of the genito-urinary apparatus— Development of the circulatory apparatus— Description of
the foetal circulation ............ 793

CHAPTER XXVI.

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 intrauterine life— Multiple pregnancy— Cause of the first
contractions of the uterus, in normal parturition— Involution of the uterus— Meconium— Dextral
pre-eminence — Development after birth — Ages — Death — Cadaveric rigidity (rigor mortis) . . 842

LIST OF ILLUSTEATIONS.

Plate I, Fig. 1. Human blood-corpuscles (Stratford) ) .

" 2. Blood of Guinea-pig (Sternberg) . . . ) Fr

Plate II, Fig. 1. Deutoplasm-forming ovum from a Graafian fol-1

licle of a woman twenty-seven years old. . . . I (N n >fad ^
2. Fresh ovum from a Graafian follicle of a woman

thirty years old J

Plate III, Fig. 1. Human embryon at the ninth week. . ) (Erfl) fj. g
" 2. Human embryon at the twelfth week )

FIGURE PAGE

1. Human blood- corpuscles (Sternberg) 6

2. Human red blood-corpuscles arranged in rows (Funke) 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 (Malas-

sez) 9

6. Human blood-corpuscles, showing post-mortem alterations (Funke) 9

6. Human leucocytes, showing amoeboid movements (Landois) 12

7. Human red blood-corpuscles and two leucocytes (Sternbcrg) 14

8. Blood-plaques and their derivatives (Landois) 16

9. Crystallized haemaglobine (Gautier) 18

10. Coagulated fibrin (Robin) 28

11. Heart in situ (Dalton) 32

12. Course of the muscular fibres of the left auricle (Landois) 33

13. Heart, anterior view (Bonamy and Beau) 33

14. Left cavities of the heart (Bonamy and Beau) 34

15. Right cavities of the heart (Bonamy and Beau) 35

16. Muscular fibres of the ventricles (Bonamy and Beau) 36

17. Branched muscular fibres from the heart (Landois) 37

18. Valves of the heart (Bonamy and Beau). 37

19. Diagram showing shortening of the ventricles during systole 40

20. Side view of the heart (Landois) 40

21. Cardiograph (Chauveau and Marey) 41

22. Scheme of the course of the accelerans fibres (Stirling) 65

23. Small artery from the mesentery of the frog (United States Army Medical Museum). . . 63

24. Sphygmograph of Marey 67

25. Sphygmograph applied to the arm (Marey) -. 68

26. Trace of the pulse (Vierordt) 68

27. Portions of four traces taken in different conditions of the pulse (Marey) 68

28. Cardiometer of Magendie (Bernard) 72

29. Compensating instrument of Marey 73

30. Chauvcau's instrument for measuring the rapidity of the flow of blood in the arteries. 76

31. Capillary blood-vessels (Landois) 78

32. Small artery and capillaries (United States Army Medical Museum) 80

33. Web of the frog's foot (Wagner) 81

34. Circulation in the web of the frog's foot (Wagner) 82

xii LIST OF ILLUSTRATIONS.

FIGURE PAGE

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

Museum) 83

36. Portion of the lung of a live triton (Wagner) 84

37. Venous radicles uniting to form a small vein (United States Army Medical Museum). . 88

38. Small blood-vessel of the mesentery of the frog, showing diapedesis of leucocytes

(Landois) , 105

39. Trachea and bronchial tubes (Sappey) 110

40. Lungs, anterior view (Sappey) 112

41. Bronchia and lungs, anterior view (Sappey) 113

42. Mould of a terminal bronchus and a group of air-cells (Robin) 114

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

(Schultze) , 115

44. Thorax, anterior view (Sappey) 116

45. Thorax, posterior view (Sappey) 116

46. Diaphragm (Sappey) 118

47. Action of the diaphragm in inspiration (Hermann) 118

48. Elevation of the ribs in inspiration (Beclard) 120

49. Arrowroot starch-granules (United States Army Medical Museum) 172

50. Crystals of palmitine and palmitic acid (Funke). . . .-. 173

51. Crystals of stearine and stearic acid (Funke) 173

52. Tooth of the cat (\Valdeyer) 190

53. Inferior maxilla (Sappey) 192

54. Salivary glands (Tracy) 195

65. Cavities of the mouth, pharynx etc. (Sappey). 203

56. Muscles of the pharynx, etc. (Sappey) 204

57. Longitudinal fibres of the stomach (Sappey) 212

58. Fibres seen with the stomach everted (Sappey) 213

59. Pits in the mucous membrane of the stomach, and orifices of the glands (Sappey) 213

60. Goblet-cells from the stomach (Landois). 214

61. Glands of the greater pouch of the stomach (Heidenhain) 215

62. Pyloric glands (Ebstein) 215

63. Gastric fistula in the case of St. Martin (Beaumont) 216

64. Dog with a gastric fistula (Beclard) 217

65. Matters taken from the pyloric portion of the stomach (Bernard) 224

66. Stomach, liver, small intestine etc. (Sappey) 234

67. Gland of Brunner (Frey) , . 235

68. Intestinal tubules (Sappey) 236

69. Intestinal villus (Leydig) 238

70. Capillary net-work of an intestinal villus (Frey) 238

71. Epithelium of the small intestine of the rabbit (Funke) 238

72. Patch of Peyer (Sappey) 240

73. Patch of Peyer, seen from its attached surface (Sappey) 240

74. Gall-bladder, ductus choledochus and pancreas (Le Bon) 243

75. Canula fixed in the pancreatic duct (Bernard) 244

76. Pancreatic fistula (Bernard) 245

77. Dog with a biliary fistula 251

78. Stomach, pancreas, large intestine etc. (Sappey) 258

79. Opening of the small intestine into the caecum (Le Bon) 259

80. Micro-organisms of the large intestine (Landois) 264

81. Stercorine from the human faeces 266

82. Origin of lymphatics (Landois) 274

83. Lymphatic plexus, showing endothelium (Bclaieff) 276

84. Superficial lymphatics of the skin of the palmar surface of the finger (Sappey) 277

LIST OF ILLUSTRATIONS. xiii

FIGTTBE

85 Deep lymphatics of the skin of the finger (Sappey) ............................... 277

86. Same finger, lateral view (Sappey) ............................................. 277

87. Superficial lymphatics of the arm (Sappey) ...................................... 278

88. Superficial lymphatics of the leg (Sappey) ...................................... 278

89. Lacteals (Asellius) ......................................................... 280

90. Thoracic duct (Mascagni) ..................................................... 281

91. Valves of the lymphatics (Sappey) ............................ ................ 282

92. Lymphatics and lymphatic glands (Sappey) ..................................... 283

93. Different varieties of lymphatic glands (Sappey) ................................. 284

94. Epithelium of the small intestine of the rabbit (Funke) ........................... 289

95. Epithelium filled with fat, from the duodenum of the rabbit (Funke) ................ 289

96. Villi filled with fat, from the small intestine of an executed criminal (Funke) ........ 289

97. Egg prepared so as to illustrate endosmotic action ............................... 293

98. Chyle from the lacteals and thoracic duct (Funke) ............................... 298

99. Sebaceous glands (Sappey) ................................................... 321

100. Ceruminous glands (Sappey) .................................................. 322

101. Meibomian glands (Sappey) .................................................. 323

102. Mammary gland of -the human female (Lie"geois) ................................. 329

103. Human milk-globules (Funke). . . ............................................. 334

104. Colostrum (Funke) .......................................................... 338

105. Anatomy of the nails (Sappey) ................................................ 346

106. Section of the nail, etc. (Sappey) .............................................. 347

107. Hair and hair-follicle (Sappey) ................................................ 349

108. Root of the hair (Sappey) .................................................... 349

109. Human hair (United States Army Medical Museum) .............................. 351

110. Transverse section of a human hair (United States Army Medical Museum) .......... 351

111. Surface of the palm of the hand (Sappey) ...................................... 354

1 1 2. Sudoriparous glands (Sappey) ................................................ 355

113. Vertical section of the kidney (Sappey) ........................................ 359

114. Longitudinal section of the pyramidal substance of the kidney (Sappey) ............. 360

115. Longitudinal section of the cortical substance of the same kidney (Sappey) .......... 360

116. Structure of the kidney (Landois) .......................... ................... 363

117. Blood-vessels of the kidney (Sappey) ................... ....................... 365

118. Diagram showing the mechanism of micturition (Kiiss) ............. . ............. 372

119. Crystals of urea (Funke) ..................................................... 376

120. Crystals of uric acid (Funke) ................................................. 380

121. Sodium urate (Funke) ...................................................... 380

122. Crystals of hippuric acid (Funke) ............................................. 382

123. Crystals of creatine (Funke) .................................................. 382

1 24. Crystals of crcatinine (Funke) ............................................... „ 382

125. Crystals of calcium oxalate (Funke) .......................................... 383

1 26. Crystals of leucine (Funke) .................................................. 383

127. Crystals of tyrosine (Funke) .................................. . .............. 384

128. Crystals of taurine (Funke). . . .............. ................................. 384

1 29. Crystals of sodium chloride (Funke) ........................................... 385

130. Lobules of the liver, interlobular vessels and intralobular veins (Sappey) ............ 394

131. Transverse section of a single hepatic lobule (Sappey) ............................ 395

132. Liver cells from a human, fatty liver (Funke) ................................... 398

133. Portion of a transverse section of an hepatic lobule of the rabbit (Kolliker) ......... 396

134. Racemose glands attached to the biliary ducts (Sappey) ........................... 397

135. Gall-bladder, hepatic, cystic and common ducts (Sappey) .......................... 398

136. Cholesterine extracted from the bile ........................................... 404

137. Instrument for puncturing the floor of the fourth ventricle (Bernard) ............... 411

xiv LIST OF ILLUSTRATIONS.

FIOTIEB PAGE

138. Operation of puncturing the floor of the fourth ventricle (Bernard) 412

189. Malpighian corpuscle of the spleen of the cat (Cadiat) 415

140. Section of a human, suprarenal capsule (Cadiat) 420

141. Thyroid and thymus glands (Sappey) 424

142. Amoeba diffluens (Longet) 460

143. Ciliated epithelium (Landois) 461

144. Small elastic fibres (Kolliker) 463

145. Larger elastic fibres (Robin) 463

146. Large elastic fibres — fenestrated membrane — (Kolliker) 463

147.*Muscular fibres from the urinary bladder (Sappey) ' 465

148. Muscular fibres from the aorta (Sappey) 465

149. Muscular fibres from the uterus (Sappey) 465

150. Striated muscular fibres (United States Army Medical Museum) 467

151 . Striated muscular fibres (Sappey) 468

152. Fibres of tendon from the human subject (Rollett) 468

153. Net-work of connective tissue (Rollett) 469

154. Frog's leg prepared so as to show the effects of curare (Bernard) 473

155. Diagram of the myograph of Helmholtz (Landois) 479

156. Curve of a single, muscular contraction (Landois) 479

157. Muscular current in the frog (Bernard) 480

158. Longitudinal section of bone (Sappey) 482

159. Longitudinal section of bone (United States Army Medical Museum) 482

160. Transverse section of bone (Sappey) 483

161. Tramsverse section of bone (United States Army Medical Museum) 484

162. Bone-corpuscles (Rollett) 484

163. Section of cartilage (United States Army Medical Museum) 486

164. Section of diarthrodial cartilage (Sappey) 486

165. Section of the cartilage of the ear (Rollett) 487

166. Longitudinal section of the human larynx (Sappey) 488

167. Posterior view of the muscles of the larynx (Sappey) 489

168. Lateral view of the muscles of the larynx (Sappey) 490

169. Glottis seen with the laryngoscope (Le Bon) 492

170. Appearance of the vocal chords in the production of the chest-voice (Grutzner) 497

171. Appearances of the vocal chords in the production of the falsetto-voice (Mills) 498

172. Nerve fibres from the human subject (Kolliker) 508

173. Nodes of Ranvier and lines of Fromann (Ranvier) 509

174. Fibres of Remak (Kolliker) 509

175. Mode of termination of the motor nerves (Rouget) 511

176. Intrafibrillar terminations of a motor nerve in striated muscle (Landois) 512

177. Termination of nerves in non-striated muscle (Cadiat) 512

178. Termination of the nerves in the salivary glands (Pfliiger) , 513

179. Corpuscle of Vater (Sappey) 514

1 80. Papillae of the skin (Sappey) 515

181. End-bulbs, or corpuscles of Krause (Ludden) 516

182. Unipolar cell from the Gasserian ganglion (Schwalbe) 517

183. Unipolar nerve-cell with a spiral fibre (Landois) 518

184. Bipolar nerve-cell (Landois) 518

185. Multipolar nerve-cell (Landois) 518

186. Gray matter of the spinal cord, treated with silver nitrate (Grandry) 519

187. Electric forceps (Liegeois) 535

188. Frog's leg prepared so as to show induced contraction (Liegeois) 535

189. Method of testing the excitability in electrotonus (Landois) 537

190. Cervical portion of the spinal cord (Hirschfeld) 540

LIST OF ILLUSTRATIONS. xv

FIGTTBB PAGE

191. Dorsal portion of the spinal cord (Hirschfeld) 640

192. Inferior portion of the spinal cord, and cauda equina (Ilirschfeld) 540

193. Roots of the cranial nerves (Ilirschfeld) 541

194. Distribution of the motor oculi communis (Ilirschfeld) 542

195. Distribution of the patheticus (Ilirschfeld) 546

196. Distribution of the motor oculi externus (Hirschfeld) 547

197. Distribution of the small root of the fifth nerve (Ilirschfeld) 548

198. Incisors of the rabbit, before and after section of the nerve of mastication (Bernard).. 549

199. Superficial branches of the facial and the fifth (Hirschfeld) 551

200. Chorda tympani nerve (Hirschfeld) 554

201-206. Expressions of the face, produced by contractions of the muscles under electrical

excitation (Le Bon, after Duchenne) 556

207. Spinal accessory nerve (Hirschfeld) 557

208. Sublingual nerve (Sappey) 563

209. Principal branches of the large root of the fifth nerve (Robin) 564

210. Ophthalmic division of the fifth (Hirschfcld) 5KB

211. Superior maxillary division of the fifth (Hirschfcld) 566

212. Inferior maxillary division of the fifth (Hirschfeld) 567

213. Cutaneous distribution of sensory nerves to the face, head and neck (BeclarJ) 668

214. Anastomoses of the pneumogastric (Hirschfeld) 574

215. Distribution of the pneumogastric (Hirschfeld) 575

216. Transverse section of the spinal cord (Gerlach) 690

217. Columns and conducting paths in the spinal corJ 593

218. Frog poisoned with strychnine (Liegeois) 599

219. Structures displayed upon the right side in a median longitudinal section of the brain

semi-diagrammatic 602

220. Vertical section of the third cerebral convolution in man (Meynert) 604

221. Diagram of the external surface of the left cerebral hemisphere 605

222. Diagram of the internal surface of the right cerebral hemisphere 605

223. Horizontal section of the hemispheres at the level of the cerebral ganglia (Dalton). . . 607

224. Diagram of the human brain in a transverse vertical section (Dalton) 608

225. Direction of some of the fibres in the cerebrum (Le Bon) 612

226. Motor cortical zone on the outer surface of the cerebrum (Exner) 613

227. Paracentral lobule (Exner) 614

228. Lateral view of the human brain with certain motor cortical areas 614

229. Inner surface of the right cerebral hemisphere (Scbafer and Horsley) 616

230. Cerebellum and medulla oblongata (Hirschfeld) 623

231. Anterior view of the medulla oblongata (Sappey) 628

232. Floor of the fourth ventrical (Hirschfeld) -. 629

233. Cervical and thoracic portion of the sympathetic (Sappey) 636

234. Lumbar and sacral portions of the sympathetic (Sappey) 637

235. Olfactory ganglion and nerves (Hirschfeld) 659

236. Terminal filaments of the olfactory nerves (Kolliker) 660

237. Glosso-pharyngeal nerve (Sappey) 666

238. Papillae of the tongue (Sappey) 6G8

239. 240. Varieties of papillae of the tongue (Sappey) 669

241. Taste-beakers (Engelmann) 670

242. Optic tracts, commissure and nerves (Hirschfeld) 672

243. Diagram of the decussation at the optic commissure 672

244. Choroid coat of the eye (Sappey) 676

245. Ciliary muscle (Sappey) 678

246. Rods of the retina (Schultze) 682

247. Vertical section of the retina (H. Miiller) 683

xvi LIST OF ILLUSTRATIONS.

FIGTTRE PAGE

248. Connection of the rods and cones of the retina with the nervous elements (Sappey),, . . 683

249. Blood-vessels of the retina (Loring) 685

250. Crystalline lens, anterior view (Babucliin) 686

251. Section of the crystalline lens (Babuchin) 686

252. Zone of Zinn (Sappey) 68*7

253. Section of the human eye 689

254. Refraction by convex lenses 694

255. Achromatic lens 697

256. Section of the lens, etc., showing the mechanism of accommodation (Fick) 710

257. Field of vision (Nettleship, after Landolt) 712

258. Binocular field of vision (Nettleship, after Forster) 714

259. Muscles of the eyeball (Sappey) 718

260. Diagram illustrating the action of the muscles of the eyeball (Fick) 720

261. Lachrymal and Meibomian glands (Sappey) 726

262. Lachrymal canals, lachrymal sac and nasal canal (Sappsy) 727

263. General view of the organ of hearing (Sappey) 732

264. Ossicles of the tympanum (Arnold) 733

265. Ossicles, seen from within (Riidinger) 734

266. Bony labyrinth (Riidinger) 736

267. Resonators of Helmholtz 744

268. Membranatympani (Riidinger) 749

269. Diagram of the labyrinth — vestibule and semicircular canals (Riidinger) 756

270. Otoliths from various animals (Riidinger) 757

271. Section of the first turn of the spiral canal — section of the cochlea (Riidinger) 758

272. Distribution of the cochlear nerve in the spiral canal (Sappey) 760

273. The two pillars of the organ of Corti (Sappey) 761

274. Vertical section of the organ of Corti (Waldcycr) 761

275. Uterus, Fallopian tubes and ovaries (Sappey) 767

276. Section of the ovary (Waldeyer) 770

277. Virgin uterus (Sappey) 771

278. Muscular fibres of the uterus (Sappey) 772

279. Superficial muscular fibres of the uterus (Liegeois) 773

280. Inner layer of muscular fibres of the uterus (Licgeois) 773

281. Blood-vessels of the uterus and ovaries (Rouget) 775

282. Section through the right Fallopian tube (Richard) 776

283. External erectile organs of the female (Liegeois) 777

284. Primordial ovum with two germinal vesicles (Nagel) 778

285. Sections of two corpora lutea (Kolliker) 783

286. Testicle and epididymis (Arnold) 786

287. Vas deferens, vesiculae seminales and ejaculatory ducts (Liegeois) 788

288. Spermatozoids, spermatic crystals, leucocytes etc. (Peyer) 791

289. Human spermatozoids (Landois) , 791

290. Spermatogenesis, semi-diagrammatic (Landois) 792

291. Ovum of the rabbit, showing penetration of spermatozoids and retraction of the vitel-

lus (Hensen) 796

292. Mulatto woman with twins, one white and the other black 798

293. Formation of the blastodermic vesicle (Van Beneden) 800

294. Primitive trace of the embryon (Liegeois) 802

295. Formation of the membranes (Kolliker) 804

296. Villi of the chorion (Haeckel) 808

297. Placenta and deciduse (Liegeois) 811

298-300. Development of the chick (Brticke) 814, 815

301. Development of the notochord (Robin) 816

LIST OF ILLUSTRATIONS. xvii

FIGtTBB PAOB

302. Human embryon one month old (Dalton) 816

303. Development of the nervous system of the chick (Longet, after Wagner) 819

304. Development of the spinal cord and brain of the human subject (Longet, after Tiedc-

mann) 820

305. Foetal pig, showing umbilical hernia (Dalton) 822

306. Development of the bronchial tubes and lungs (Longet, after Rathkc and Miiller) 825

307-309. Development of the face (Coste) 826, 827

310. Temporary and permanent teeth (Sappey) 829

311. Foetal pig, showing the Wolffian bodies (Dalton) 831

312. Diagrammatic representation of the gcnito-urinary apparatus (Henle) 833

313. Area vasculosa (Bischoff) 835

314. Aortic arches, in the mammalia (Von Baer) 837

315. Diagram of the foetal circulation 840

316. Cholesterine extracted from meconium 847

HUMAN PHYSIOLOGY.

CHAPTER I.

TEE BLOOD.

Quantity of blood— General characters of the blood— Blood-corpuscles— Development of the blood-corpus-
cles—Leucocytes— Development of leucocytes— Blood-plaques— Composition of the red corpuscles—
Globuline — Hsemaglobine — Composition of the blood-plasma — Inorganic Constituents — Organic saline
constituents — Organic non-nitrogenized constituents — Excrementitious constituents — Organic nitrogen-
ized constituents— Plasmine, fibrin, metalbumen, serine— Peptones— Coloring matter— Coagulation of
the blood— Conditions which modify coagulation— Coagulation of the blood in the organism— Cause of
the coagulation of the blood.

WITH the progress of knowledge and the accumulation of facts in physi-
ology, the importance of the blood in its relations to the phenomena of ani-
mal life becomes more and more thoroughly understood and appreciated.
The blood is the most abundant and highly organized of the fluids of the
body, providing materials for the regeneration of all parts, without excep-
tion, 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 regeneration of the nutritive constituents of the
blood, and on the other, its constant purification 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 pene-
trated by vessels, are none the less dependent upon the blood, as they imbibe
nutritive material from the blood of adjacent 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 dem-
onstrated by experiments upon the inferior animals. If, in a small dog, a
canula adapted to a syringe be introduced through the right jugular vein
into the right side of the heart, and a great part of the blood be suddenly
withdrawn from the circulation, immediate suspension of all the so-called
vital processes is the result ; and if the blood be then returned to the system,
the animal is as suddenly revived.

Certain conditions, 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 BLOOD.

the f ime-t*orisy 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 made on the inferior ani-
mals, has been applied to the human subject ; and it has been ascertained
that in patients sinking under haemorrhage the introduction of even a few
ounces of fresh blood may restore the functions for a time, and sometimes
permanently.

Quantity of Blood. — The determination of the entire quantity of blood
contained in the body has long engaged the attention of physiologists, with-
out, however, any absolutely definite results. The fact that physiologists
have not succeeded in determining definitely the entire quantity 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 after division of the largest vessels, as after decapi-
tation ; and no perfectly accurate means have been devised for estimating
the quantity which remains. The estimates of experimenters present the
following wide differences : Allen-Moulins, 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, by
mere conjecture. Valentin was the first to attempt to overcome this diffi-
culty by experiment. For this purpose he employed the following process :
He took first a small quantity of blood from an animal for purposes of com-
parison ; then he injected into the vessels a known quantity of a saline solu-
tion, and taking another specimen of blood some time after, he ascertained
by evaporation the proportion of water which it contained, and compared it
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 which had been added 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.

The following process was employed by Lehmann and Weber, and was ap-
plied directly to the human subject in the cases of two decapitated criminals :
These observers estimated the blood remaining in the body after decapita-
tion, by injecting the vessels with water until it came through nearly color-
less. 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 in a definite quantity of blood having been previously ascer-
tained. If it were certain that only the solid matter of the blood was thus
removed, such an estimate would be tolerably accurate.

The process just described gives an idea of the probable quantity of blood
in the body; but the most serious objection to it is the possibility that
certain solid constituents of the tissues are washed out by the water passing
through the vessels, and it is generally thought that the estimate by Leh-
mann and Weber, that the quantity of blood is equal to about one eighth of

GENEEAL CHARACTERS. 3

the weight of the body, is too high. More recent observations have been
made upon the inferior animals, by various methods, which are all more or
less open to objection, and which it is not necessary to describe in detail ;
but the results of nearly all of the experiments made within the last few
years show a less proportion of blood than was estimated by Lehmann, and
Weber. Remembering that all estimates must be regarded as approxi-
mate, it may be assumed that in a person of ordinary adipose and mus-
cular development the proportion of blood to the weight of the body is
about one to ten. The relative quantity of blood is less in the infant than
in the adult and is 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 indi-
cated by the small quantity which can be removed from the body, under this
condition, with impunity; and it has been experimentally demonstrated that
the entire quantity of blood is considerably increased during digestion. Ber-
nard drew from a rabbit weighing -about two and a half pounds (1,134
grammes), during digestion, ten and a half ounces of blood (300 grammes)
without producing death; while he found that the removal of half that
quantity from an animal of the same size, fasting, was fatal. Wrisberg re-
ported a case of a female criminal, very plethoric, from whom nearly twenty-
one and a half pounds of blood (9,745 grammes) flowed after decapitation.
As the relations of the quantity of blood to digestion are so important, it is
unfortunate that the conditions in this respect were not noted in the obser-
vations of Lehmann and Weber. It is evident that the quantity of blood
in the body must be considerably increased during digestion ; but as regards
the extent of this increase, it is not possible to form any very definite idea.
It is shown only that there is a marked difference in the effects of haemor-
rhage 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 homogeneous fluid, but is composed of two distinct elements, a clear plasma
and corpuscles, which are both nearly transparent but which have each a
different refractive power. If both of these elements had the same refrac-
tive 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.

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 ani-
mal 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

4: THE BLOOD.

considerable proportion, three or four parts per thousand, of sodium chloride
in the plasma.

The reaction of the blood is always distinctly alkaline. It is not easy,
however, to demonstrate the alkalinity of the blood, on account of the red
color of the blood-corpuscles; but the difficulty may be avoided by using
certain precautions. The following method, employed by Schafer, is quite
satisfactory : A drop of blood is put upon a piece of glazed, reddened litmus-
paper. After a few seconds the blood is lightly wiped off with a damp cloth,
leaving a spot of a distinctly blue color. According to Zuntz, the alkalinity
diminishes rapidly after the blood is drawn from the vessels. The alkaline
reaction is due to the presence of sodium carbonate and sodium phosphate in
the plasma.

The specific gravity of defibrinated blood is between 1052 and 1057
(Robin), being somewhat less in the female than in the male. The density
varies greatly under different conditions of digestion.

Temperature. — The temperature of the blood is generally given as between
98° and 100° Fahr. (36-67° and 37'78° C.) ; but experiments have shown that
it varies considerably in different parts*of the circulatory system, independ-
ently of exposure to the refrigerating influence of the atmosphere. By the
use of very delicate registering thermometers, Bernard succeeded in estab-
lishing 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.

3. It is generally warmer in the portal vein than in the abdominal aorta,
independently 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 between 101° and 107° Fahr. (38-33° and 41-67° C.). In the aorta,
it ranged between 99° and 105° Fahr. (37'22° and 40-55° C.). It may be
assumed, then, in general terms, that the temperature of the blood in the
deeper vessels is between 100° and 107° Fahr. (37'78° and 41-67° C.).

Color. — 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 some-
times almost black. The color in the veins, however, is not constant. Many
years ago, John Hunter observed, 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 noticed 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 existed only
during the activity of the kidneys ; and when, from any cause, the secretion
of urine was arrested, the blood became dark. He was led, from this obser-
vation, to examine the venous blood from other glands ; and directing his
attention to those which he was able to examine during their activity, par-

ANATOMICAL ELEMENTS. 5

ticularly the salivary glands, he found the blood red in the veins during
secretion, but becoming dark as soon as secretion was arrested. In the sub-
maxillary gland, by Faradization of a certain nerve, called the motor nerve of
the gland, Bernard was able to produce secretion, and by stimulating another
nerve, to arrest it ; in this way changing at will the color of the blood in the
vein. It was 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, produced a red color of the blood in the jugular. He also
found that paralysis of a member by division of the nerve had the same
effect on the blood returning by the veins.

The explanation of these facts is evident in view of the reasons why the
blood is red in the arteries and dark in the veins. Its red color depends upon
the presence of oxygen in the corpuscles ; and as the blood passes through
the lungs it loses carbon dioxide and the corpuscles gain oxygen, changing
from black to red. In its passage through the capillaries of the system, in
the ordinary processes of nutrition, the blood loses oxygen and gains carbon
dioxide, changing from red to black. During the intervals of secretion, the
glands receive just enough blood for their nutrition, and the ordinary inter-
change of gases takes place, with the consequent change of color ; but dur-
ing secretion, the blood is supplied to the glands in greatly increased quan-
tity. Under these conditions, it does not lose oxygen and gain carbon
dioxide 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 blood-vessels 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 supposition,
Even during secretion, a certain quantity of carbon dioxide 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 mus-
cular, 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 IN THE BLOOD.

In 1661, Malpighi, in examining the blood of the hedgehog, with the im-
perfect 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 between forty and 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 Leeuwenhoek is
generally ascribed the honor of the discovery of the blood-corpuscles. About

6

THE BLOOD.

a century later, William Hewson described another kind of corpuscles in the
blood, much less abundant than the red, which are now known under the
name of white globules, or 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 com-
posed of a clear fluid, the plasma, or liquor sanguinis, holding certain corpus-
cles in suspension. These corpuscles are of three kinds :

1. Red 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 proportion of 1 to 750 or 1,000 red corpuscles.

3. Blood-plaques ; varying in size, shape and number.

Red Corpuscles. — These little bodies give to the blood its red color and
its opacity. They are organized structures, containing organic nitrogenized
and inorganic matters molecularly united and a little fatty matter in union
with the organic constituents. They constitute a little less than one-half the

mass of blood, and according to the
observations of all who have investi-
gated this subject, are more abun-
dant in the male than in the female.
The form of the blood-corpuscles
is peculiar. They are flattened, bi-
concave, circular disks, with a thick-
ness of one-fourth to one-third of
their diameter. Their edges are
rounded, and the thin, central por-
tion occupies about one-half of their
diameter. Their consistence is not
much greater than that of the plas-
ma. They are very elastic, and if
deformed by pressure, immediately
resume their original shape when
the pressure is removed. Their spe-
cific gravity is between 1088 and
3105, considerably greater than the specific gravity of the plasma, which is
about 1028.

When the blood has been drawn from the vessels and coagulates slowly,
Ihe greater 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. If
coagulation be prevented by the addition of a small quantity of sodium sul-
phate, 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 characteris-
tic appearance under the microscope. Examined with a magnifying power
of between three hundred and five hundred diameters, those which present
their flat surfaces have a shaded centre when the edges are exactly in focus.

FIG. 1.— Human blood-corpuscles; magnified 1,450

diameters (Sternberg).

This figure also shows a leucocyte containing four
fatty granules.

ANATOMICAL ELEMENTS.

This appearance is an optical effect due to 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 centre is bright, the edges are shaded.

As the blood -corpuscles are examined with the microscope, by transmitted
light, they are nearly transparent and of a pale-amber color. It is only when
they are collected 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. An 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
microscope, the corpuscles are seen
in many different positions, and
this assists in the recognition of
their peculiar form.

It has long been observed that
the blood-corpuscles have a remark-
able tendency to arrange them-
selves in rows like rouleaux of coin.
This appearance is due to the fol-
lowing conditions :

Shortly after removal from the vessels, there exudes from the corpuscles
an adhesive substance which causes them to stick together. Of course the
tendency is to adhere by their flat surfaces (Robin). 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 con-
nection with the normal characters of the blood -corpuscles.

The diameter of the blood-corpuscles has a more than ordinary anatomi-
cal interest; for, varying perhaps less in size than other anatomical ele-
ments, they are often taken as the standard by which an idea is formed of
the size of other microscopic objects. The diameter usually given is ^g^o °f
an inch (7' 17 ft). The exact measurement given by Robin is -^j of an
inch (7'3 /*). Very few corpuscles are to be found which vary from this
measurement. Kolliker, who gives their average diameter as ygVir of an
inch (7 /*), states that "at least ninety-five out of every hundred corpuscles
are of the same size."

Measurements of the blood-corpuscles of different animals are important,
from the fact that it often becomes a 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

FIG. 2. — Human red blood-corpuscles, arranged in
rows (Funke).

8

THE BLOOD.

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; and in all others, they are smaller or of nearly the same
diameter. In some animals, the corpuscles are very much smaller than in
man, and by accurate measurements, their blood can be distinguished 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 the cor-
puscles of the same animal. The
blood of the human subject or of the
mammals generally can be readily dis-
tinguished from the blood of birds,
fishes or reptiles; for in these ani-
mals, the corpuscles are oval and con-
tain 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 muscular activity of the
_ animal. This relation holds good to

FIG. 3. — Blood-corpuscles of the frog ; magnified , ,

370 diameters (from a photograph taken at some extent, while there certamlv ex-

the United States Army Medical Museum).

ists none between the size of the cor-
puscles and the size of the animal. In deer, animals remarkable for
muscular activity, the corpuscles are very small, g0*00 of an inch (5 ft) ;
while in the sloth they are -g-gVir (8*9 /*•)> an(l in the ape, which is com-
paratively inactive -j^^o (7*7 /*)• On the other hand, in the dog, which is
quite active, the corpuscles measure -J-^QT °f an incn CM? /*)> an(i in the ox>
which is certainly not so active, the diameter of the corpuscles is TfVir of an
inch (6/1). Although this relation between the size of the blood-corpuscles
and muscular activity is not invariable, it is certain that, the higher the
animal in the scale, the smaller are the blood-corpuscles ; the largest being
found in the lowest orders of reptiles, and the smallest, in the mammalia.
The blood of the invertebrates, with a few exceptions, contains no colored
corpuscles.

Enumeration of the Blood-Corpuscles. — In most of the quantitative analy-
ses 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 useful to ascertain, if possible, the normal varia-
tions in the proportion of corpuscles, under different conditions of the sys-
tem, particularly as these bodies play so important a part in many of the
functions of the organism. Actual enumerations of the blood-corpuscles
have been made by Vierordt, Weckler, Malassez and others. It is stated by
Malassez that the error in his calculations is not more than two or three per
cent. The process employed by Malassez is the following :

ANATOMICAL ELEMENTS.

9

The blood to be examined is diluted with ninety-nine parts of a liquid com-
posed 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 sodium sulphate and of so-
dium chloride, also of a specific gravity of 1020. The mixture, containing one
part of blood in one hundred, is introduced into a small thermometer-tube
with an elliptical bore, the sides of the tube being ground flat for convenience
of microscopical examination. The
capacity of the tube is to be calcu-
lated by estimating the weight of a
volume of mercury contained in a
given length. The tube is then filled
with the diluted blood, and the num-
ber of corpuscles in a given length of
the tube is counted by means of a mi-
croscope fitted with an eye-piece mi-
crometer. In this way, the number
of corpuscles in a given volume of
blood can be readily estimated. In
man, the number in a cubic millime-

tre of blood — a millimetre = about
-fa of an inch — is estimated to be be-
tween four and a half and five mill-
ions.

FIG. 4. — Artificial capillary, filled with a sanguin-
eous mixture, seen under a quadrilateral mi-
crometer (Malassez).

According to the observations of Malassez, the proportion of corpuscles is
about the same in all parts of the arterial system. In the veins, the cor-
puscles 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 proportion 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 far-
ther observations are necessary to
render this view certain.

Post-mortem Changes in the
Blood- Corpuscles. — In examining
the fresh blood under the micro-
scope, after the specimen has been
under observation a short time, the
corpuscles are observed to assume a
peculiar appearance, from the de-

FIG. 5.— Human blood-corpuscles, showing post-mor-
tem alterations (Funke).

velopment, on their surface, of very
minute, rounded projections, like
the granules of a raspberry. A little later, when they have become partly
desiccated, they present a shrunken appearance and their edges are more or

10 THE BLOOD.

less serrated. Under these conditions, their original form may be restored
by adding to the specimen a liquid of about the density of the serum. When
they have been completely dried, as in blood spilled upon clothing or on a
floor, 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 examinations of old spots supposed to be blood ; and if the manipula-
tions be carefully conducted, the corpuscles may be recognized without diffi-
culty by means of the microscope.

If pure water be added to a specimen of blood under the microscope, the
corpuscles swell up, become spherical and are finally dissolved. The same
effect follows almost instantaneously on the addition of acetic acid.

Structure. — The blood-corpuscles are perfectly homogeneous, presenting,
in their normal condition, no nuclei or granules, and are not provided with
an investing membrane. 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 dis-
tinct 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 homogene-
ous bodies of a definite shape, than that they have a cell- wall with semi-fluid
contents ; especially as the existence of a membrane has been only inferred
and not positively demonstrated.

Development of the Blood- Corpuscles. — Very early in the development of
the ovum, the blood-vessels appear, constituting what is called the area vascu-
losa. 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 embryon is about one-tenth
of an inch (2*5 mm.) in length. From this time until the end of the sixth
or eighth week, they are 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 time, nearly all of them are provided with a nucleus ; but from the
first, there are some in which this is wanting. The nucleus is ^-g^o to -^^
of an inch (3-1 /* to 3*6 /*) 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, a few remain. After this
time, they do not differ anatomically from the blood-corpuscles in the adult.

In many works on physiology and general anatomy, accounts are given of
the development of the red corpuscles from the colorless corpuscles, or leuco-
cytes, which are supposed 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 corpuscles appear before the leu-
cocytes are formed ; and it is mainly the fact that the two varieties co-exist in
the blood-vessels which has given rise to such a theory. It is most reasonable
to consider that the first red corpuscles are formed in the area vasculosa in
the same way that other anatomical elements make their appearance at that
time, the exact process not being understood. In the later periods of devel-

ANATOMICAL ELEMENTS. 11

opment of the foetus and in the adult, it is probable that the red marrow of
the bones and, perhaps, to a certain extent, the spleen have important uses in
connection with the development of the red blood-corpuscles. The observa-
tions of Neumann, of Konigsburg, and of Bizzozero, of Turin, about the
year 1868, have been extended and confirmed by others, and show that there
is a generation of red corpuscles in the red marrow .of the bones, which is
now regarded as the most important of the so-called corpuscle-forming organs.
In the foetus and in the young infant, the marrow of nearly all the bones is
red, or of the kind called lymphoid. In the adult, the marrow of the long
bones is yellow, or fatty, the red marrow being confined to the cancellated
structure of the short and the flat bones. Although the researches with re-
gard to the spleen are less positive and definite in their results, it is proba-
ble that this organ also contributes to the development of the red blood-
corpuscles.

The exact mode of development of the red corpuscles in the marrow and
in the spleen has not been very satisfactorily described and is still a question
concerning which there is much difference of opinion among histologists.
A full discussion of this question would be out of place in this work, which
is intended to embrace only those points in histology that have been defi-
nitely settled.

It is probable that the red corpuscles are, in certain number, destroyed
in the passage of the blood through the liver and perhaps, also, in the spleen,
the coloring matter contributing to the formation of the biliary and the urin-
ary pigmentary matters. If this view be accepted, the spleen is concerned
in both the formation and the disintegration of blood-corpuscles.

In the present state of knowledge, the following seem to be the most
rational views with regard to the development and destination of the red
blood-corpuscles.

1. At the time of their first appearance in the ovum, the blood-corpuscles
are formed by no special organs, for no special organs then exist.

2. In the foetus, after the development of the marrow of the bones and of
the spleen, and in the adult, these parts have important uses in the forma-
tion of the red corpuscles, especially the red marrow of the bones.

3. It is probable that the red blood-corpuscles are constantly undergoing
destruction, and that their coloring matter contributes to the formation of
other pigmentary matters. As the corpuscles are thus destroyed, and as they
are diminished in number in disease or by haemorrhage, they are probably
replaced by new corpuscles formed in greatest part in the red marrow of the
bones.

4. Pathological observations seem to show that in certain cases of anae-
mia, when there is an abnormal destruction of red corpuscles, the activity of
the corpuscle-forming office of the marrow is increased, compensating, to a
certain extent, the conditions which involve the abnormal destruction of the
corpuscles.

Uses of the Red Blood- Corpuscles. — Although the albuminoid constitu-
ents of the plasma of the blood are essential to nutrition, the red corpuscles

12

THE BLOOD.

are the parts most immediately necessary to life. It is well known that life
may be restored to an animal in which the functions have been suspended
by haemorrhage, by the introduction of fresh blood ; and while it is not neces-
sary that this blood should contain the fibrin-factors, it has been shown by
the experiments of Prevost and Dumas and others, that the introduction of
serum, without the corpuscles, has no permanent restorative effect. When all
the arteries leading to a part are tied, the tissues lose their properties of
contractility, sensibility etc., which may be restored, however, by supplying
it again with blood. It will be seen, in treating 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 observa-
tions have shown that blood will absorb ten to thirteen times as much oxygen
as an equal bulk of water ; and this is dependent almost entirely on the pres-
ence of the red corpuscles. As all the tissues are constantly absorbing
oxygen and giving off carbon dioxide, a very important office of the corpus-
cles is to carry oxygen to all parts of the body. In the present state of
knowledge, this is the only well defined use which can be attributed to the
red corpuscles, and it undoubtedly is the principal one. They have an affin-
ity, though not so great, for carbon dioxide which, after the blood has cir-
culated in the capillaries of the system, takes the place of the oxygen. In a
series of experiments on the effects of haemorrhage and the seat of the " sense
of want of air," it was 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 (Flint, 1861).

Leucocytes, or White Corpuscles of the Blood. — In addition to the red cor-
puscles 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,
forming a nucleus of irregular shape.
These have been called by Robin,
leucocytes. This name seems more
appropriate than that of white or
colorless blood-corpuscles, inasmuch

as these bodies 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. The
description which will be given of
the white corpuscles of the blood,

FIG. 6.— Human leucocytes, showing amoeboid move- and the effects of reagents, will an-
ments (Landois).

swer, in the main, for all the cor-
puscular bodies that are grouped together under the name of leucocytes.

Leucocytes are normally found in the blood, lymph, chyle, semen, colos-
trum and vitreous humor. Pathologically, they are found in the secretion

ANATOMICAL ELEMENTS. 13

of mucous membranes, following irritation, and in inflammatory products,
when they are called pus-corpuscles. They are globular, with a smooth sur-
face, 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, the adhesive character of the leucocytes as compared
with the red corpuscles is readily noted. 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 sta-
tionary for a time, 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 2^00 of an inch (10 /n).
It is in pus, where they exist in greatest abundance, that their microscopical
characters may be studied with most advantage. In this fluid, after it is
discharged, the corpuscles sometimes present remarkable changes in form.
They become polygonal in shape, and sometimes ovoid, occasionally present-
ing projections from their surface, which give them a stellate appearance.
These alterations, however, are only temporary ; and after 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 appearance is produced, though more slowly, by
the addition of water. In some corpuscles a nucleus may be seen without the
addition of any reagent.

Leucocytes vary considerably in their external characters in different situ-
ations. Sometimes they are very pale and almost without granulations,
and sometimes 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-cor-
puscles, they generally undergo this change. As the result of inflammatory
action, when they are sometimes called inflammatory or exudation-corpuscles,
leucocytes frequently become much hypertrophied and are filled with fatty
granules.

The deformation of the leucocytes to which allusion has already been
made is sometimes so rapid and changeable as to produce creeping move-
ments, due to the projection and retraction of portions of their substance.
These movements are of the kind called amoeboid and are supposed to be
important in the process of migration of the corpuscles.

The relative number of leucocytes, can only be given approximately. It
has been estimated by counting under the microscope the red corpuscles and
leucocytes contained in a certain space. The average proportion in man is
probably 1 to 750 or 1000. It has been found by Hirt, 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 to 1800 before breakfast ; an hour after breakfast, which was taken at
8 o'clock, 1 to 700 ; between 11 and 1 o'clock, 1 to 1500 ; after dining, at 1
3

THE BLOOD.

FIG. 7. — Human reel blood- corpuscles and two leuco-
cytes (Sternberg).

o'clock, 1 to 400 ; two hours after, 1 to 1475 ; after supper, at 8 P. M.,
1 to 550 ; at 11£ P. H., 1 to 1200. The leucocytes are much lighter than the

red corpuscles, and when the blood
coagulates slowly, they are frequent-
ly found, with a certain quantity of
colorless fibrin, forming a whitish
layer on the surface of the clot.
Their specific gravity is about 1070.
Development of Leucocytes. —
These corpuscles appear in the
blood - vessels very early in foetal
life, before the lymphatics can be
demonstrated. They appear in
lymphatics before these vessels pass
through the lymphatic glands, in
the foetus anterior to the develop-
ment of the spleen, and also on the
surface of mucous membranes; so
that they can not be considered as
produced exclusively by the lymphatic glands, as has been supposed. Al-
though they frequently appear as a result of inflammation, this process is by
no means necessary for their production. Eobin has observed the phenom-
ena of their development in recent wounds. The first exudation consists
of clear fluid, with a few red corpuscles. There appears afterward, a finely
granular blastema. In a quarter of an hour to an hour, pale, transparent
globules, -^Vir to -g-ffW °^ an ^ncn (^ /* to 4 //,) in diameter, make their ap-
pearance, which soon become finely granular and present the ordinary
appearance of leucocytes.

Histological researches show that in the adult, the number of leucocytes
in the lymph is increased during the passage of this fluid through the lym-
phatic glands. The blood, also, in passing through the spleen has been
shown to gain largely in these corpuscles. These facts are important in con-
nection with the pathology of leucocythaemia. This disease, which is char-
acterized by an excess of leucocytes in the blood, is now generally regarded
as having a close relation to certain changes in the spleen, the lymphatic
glands and the marrow of the bones. There is, indeed, a variety of the dis-
ease, known as lymphatico-splenic leucocythasmia, in which the spleen and
certain of the lymphatic glands are enlarged, and another form, called
medullo-lymphatic leucocythaemia, in which changes have been noted in the
lymphatic glands and in the marrow. The anatomical changes which have
been observed in the spleen, lymphatic glands and marrow, in leucocythaemia,
are largely hyperplastic ; that is, the normal structure of these parts is
increased in extent. On the other hand, a disease called pseudo-leucocy-
thaemia, presenting the anatomical characters and general symptoms of leu-
cocythaemia, without d,n increase in the leucocytes of the blood, has been
accurately described. Pathological observations, therefore, are not entirely

ANATOMICAL ELEMENTS. 15

in accord with, the theory that the spleen, lymphatic glands and the bone-
marrow are always directly concerned in the production of leucocytes.

Taking into consideration the histological and pathological observations
bearing on the question, the following seems to be the most reasonable view
with regard to the mode of development of leucocytes :

1. In early foetal life the leucocytes of the blood are developed without
the intervention of any special organs, and perhaps, also, these bodies are
multiplied by division.

2. In adult life the same processes of development probably occur in the
blood and lymph and in other situations.

3. It is probable, though by no means certain, that the spleen, lymphatic
glands and the red marrow of the bones are more or less actively concerned
in the production of leucocytes, both under physiological and pathological
conditions ; but it is certain that these organs and parts are not the exclusive
seat of development of the so-called white blood-corpuscles and lymph-cor-
puscles.

Uses of the Leucocytes. — It is impossible, in the present state of physi-
ological knowledge, to assign any definite use to the leucocytes of the blood
and lymph. These bodies may be concerned to some extent in the develop-
ment of the red blood-corpuscles, but this view, which is held by many physi-
ologists, has no absolutely positive basis in fact. All that can be said is that
the office of the leucocytes has not been ascertained. Their action, however,
is important in the process of coagulation of the blood, lymph and chyle.

Blood- Plaques. — The so-called blood-plaques, described quite elaborately
by Bizzozero and others, have been long known to histologists, under a vari-
ety of names, such as globulins, elementary corpuscles, granular debris, gran-
ule masses, ha^matoblasts etc. Until within a few years these bodies have
not been thought to be of much importance, and even now little is known of
their physiological and pathological relations.

The blood-plaques in human blood may be easily observed, preparing the
blood by the following method (Osier) :

" Upon the thoroughly cleansed finger-pad a single drop of the solution
is placed, and with a sharp needle, or pricker, the skin is pierced through
the drop, so that the blood passes at once into the fluid, which is then received
upon a slide and covered. The withdrawal of the corpuscles into the solu-
tion prevents the plaques from aggregating, and they remain as isolated and
distinct elements. The amount of blood allowed to flow into the drop must
not be large, and should be quickly mixed. In many respects the most suit-
able medium is osmic acid, one-half to one per cent., which has the advantage
that by its use permanent preparations can be obtained."

The plaques are thin, circular discs, homogeneous or very faintly granu-
lar and of a pale, grayish tint. They measure TyJ-g-g- to ro^-Tnr (1*5 to 2-5 p.)
in diameter, about one-sixth of the diameter of the red blood-corpuscles.
They exist in the blood in the proportion of one to about eighteen or twenty
red corpuscles.

In the circulating blood, the plaques are distinct ; but when the blood is

16

THE BLOOD.

drawn from the vessels, they adhere together and are usually collected into
masses. The plaques quickly undergo change out of the body, becoming

FIG. 8. — Blood-plaques and their derivatives, partly after Bizzozero and Laker (Landois).
1, red blood-corpuscles on the flat; 2, from the side; 3, unchanged blood-plaques ; 4, a lymph-corpuscle
surrounded with blood-plaques ; 5. blood-plaques variously altered ; 6, a lymph-corpuscle with two
masses of fused blood -plaques and threads of fibrin; 7, group of blood-plaques fused or run together;
8, a similar small mass of partially dissolved blood-plaques with fibrils of fibrin.

ovoid, elongated or pointed. They sometimes send out processes which give
them a stellate appearance.

Physiologists have no knowledge of the uses of the blood-plaques. The
relations which have been supposed to exist between these bodies and the
development of the other corpuscular elements of the blood, the phenomena
of coagulation, etc., are as yet indefinite and uncertain.

COMPOSITION OF THE BLOOD-CORPUSCLES.

The red corpuscles of the blood contain an organic nitrogenized substance,
called globuline, combined with inorganic salts and a coloring matter.
The composition of the leucocytes has not been accurately determined, and
nothing is known of the composition of the blood-plaques. The inorganic
matters contained in the red corpuscles are in a condition of intimate union
with the other constituents, and can be separated only 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 corpuscles, which latter are par-
ticularly rich in the salts of potassium. Iron exists in the coloring matter of
the corpuscles. In addition, the corpuscles contain cholesterine, lecethine, a
certain quantity of fatty matter and probably some of the organic saline
constituents of the blood.

Globuline. — Rollett, by alternately freezing and thawing blood several
times in succession in a platinum vessel, has succeeded in separating the col-
oring matter from the red corpuscles. 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, entirely decolorized
and floating in a red, semi-transparent serum. Denis extracted the organic

COMPOSITION OF THE BLOOD-PLASMA. IT

constituent of the corpuscles by adding to defibrinated blood about one-half its
volume of a solution of sodium chloride containing one part in ten of water.
Allowing this to stand for 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 have been removed. The whitish, translucid mass which
remains is called globuline. Globuline is readily extracted from the blood of
birds but is obtained with difficulty from the blood of the human subject.

H&maglobine. — This is the coloring matter of the red corpuscles. It has
been called by different writers, haemaglobuline or haematocrystalline ; but
the crystals called haematine and haematosine are derivatives of haemaglobine
and are not normal constituents of the blood. Haemaglobine maybe ex-
tracted from the red corpuscles by adding to them, when congealed, ether,
drop by drop. A jelly-like mass is then formed, which is passed rapidly
through a cloth, crystals soon appearing in the liquid, which may be sepa-
rated by filtration (Gautier).

The crystals of haemaglobine extracted from human blood are in the form
either 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 haemaglobine is precipitated from these
solutions by potassium ferrocyanide, mercuric nitrate, 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 -^ to
|f of the dried corpuscles. A solution of haemaglobine in one thousand
parts, examined with the spectroscope, gives two dark bands between the let-
ters 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 oxyhaemaglobine. There can be no doubt that the oxygen enters
into an intimate, though rather unstable combination with haemaglobine, and
this is an important point to be considered in connection with the absorption
of oxygen by the blood in respiration. A solution of oxyhaemaglobine pre-
sents a different spectrum from that produced by a solution of pure haema-
globine.

COMPOSITION OF THE BLOOD-PLASMA.

Assuming that the blood furnishes matters for the nourishment of all the
tissues and organs, there should be found entering into its composition all
the constituents of the body which undergo no change in nutrition, like
the inorganic salts, and organic matters capable of being converted into the
organic constituents of every tissue. Farthermore, as the products of waste
are all taken up by the blood before their final elimination, these also should
enter into its composition.

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, that the phos-

18

THE BLOOD.

phorized fats are more abundant in the globules, while the fatty acids are
more abundant in the plasma. The salts of potassium exist almost entirely

in the corpuscles, and the sodium salts
are four times more abundant in
the plasma than in the corpuscles
(Schmidt). In addition to the nutri-
tive matters, the blood contains urea,
cholesterine, sodium urate, creatine,
creatinine, and other substances, the
characters of which are not yet fully
determined, belonging to the class of
excrementitious matters. Their con-
sideration comes more appropriately
under the head of excretion.

The following table gives approxi-
mately the quantities of the differ-
ent constituents of the blood-plasma.
These may be divided into the follow-
ing classes : 1. Inorganic constituents ;
2. Organic saline constituents; 3. Or-
ganic non - nitrogenized constituents;
4. Excrementitious constituents ; 5. Or-
ganic nitrogenized constituents. This
table will be taken as a guide for the

FKJ. 9,-Crystallized hcemaglobine (Gautier). study of the individual Constituents
a, 6, crystals from the venous blood of man ; c, nf flip Klnnrl nlflQirm A «j rpcrarrls CTIQPQ

blood of the cat ; d, blood of the Guinea pigi OI tne ci-piasma. AS regai as gases,
e, blood of the marmot;/, blood of the squir- jn addition to carbon dioxide, which

rt?i. (^jrfliitiGr.j

is classed with the excrementitious con-
stituents, the blood contains oxygen, nitrogen and hydrogen. The nitrogen
and hydrogen are not important, and the relations of oxygen will be fully
considered in connection with the physiology of respiration. Most of the
coloring matter of the blood exists in the red corpuscles, which contain a
peculiar substance that has already been 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 has been done in the simplest manner possible.

It is evident, the blood receiving all the products of disassimilation as
well as the nutritive matters resulting from digestion, that there should be
a division of its constituents into nutritive and excrementitious. The ex-
crementitious matters are the 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 explanation of the minute proportion in which
they exist in this fluid.

COMPOSITION OF THE BLOOD-PLASMA. 19

CONSTITUENTS OF THE BLOOD-PLASMA.

Specific gravity, 1028.

Water, 779 parts per 1,000 in the male; 791 parts per 1,000 in the female;
Sodium chloride, 3 to 4 parts per 1,000.
Potassium chloride, 0'359 parts per 1,000.
Ammonium chloride, proportion not determined.
Potassium sulphate, 0'288 parts per 1,000.
Sodium sulphate, proportion not determined.
Potassium carbonate, proportion not determined.
Sodium carbonate (with sodium bicarbonate), 1*200 parts per 1,000.
Magnesium carbonate, proportion not determined.
Calcium phosphate of the bones, and neutral phosphate,
Magnesium phosphate,

Potassium phosphate, }> 1'500 parts per 1,000.

Ferric phosphate (probable),
Basic phosphates and neutral sodium phosphate,
Silica, copper, lead, and magnesia, traces occasionally.

Sodium lactate, proportion not determined.

Calcium lactate (probable), proportion not determined.

Sodium oleate,

" palmitatc,

" stearate,

" valcrate,

« butyrate, M '475 parts

f Oleine,
Palmitine,
Stearine,

g g -I Lecethine, containing nitrogen and called phosphorized fatty matter, 0'400 parts per 1 ,000.
Glucose, 0-002 parts per 1,000.
Glycogen, proportion not determined.
Inosite, proporticn not determined.

f Carbon dioxide in solution.

Urea, 0'177 parts per 1,000, in arterial blood ; 0'088, in the blood of the renal vein.
Sodium urate, proportion not determined.
Potassium urate (probable), proportion not determined.
Calcium urate, " "

Magnesium urate, " " " "

Ammonium urate, " " " "
Sodium sudorates, 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.
f Plasmine, 25 parts (dried) per 1,000. < Metalbumin> M part8 per 1>ooa

^ Serine, 53 parts (dried) per 1,000.

I Peptones, 4 parts (dried) and 28 parts (mcist) per 1,000.
I Coloring matters of the plasma, proportion and characters not determined.

20 THE BLOOD.

Excluding for the present, all consideration of the products of dis-
assimilation, there remain the various constituents of the blood that are
more or less directly concerned in nutrition.

Physiological chemists recognize certain chemical constituents of the
organism, which may be elementary substances, but which are more fre-
quently compounds. Sodium chloride is spoken of as a constituent of
the blood, because, as sodium chloride, it gives to the blood certain proper-
ties. The chemical elements, chlorine and sodium, are not regarded as con-
stituents of the blood, because they do not exist uncombined in the blood.
Still, a chemical constituent may be a chemical element, as in the case of
oxygen, which, as oxygen, has certain important uses in the economy;
although even oxygen probably is loosely combined in the body with other
matters.

A chemical constituent of the blood or of any of the animal tissues or
fluids may be denned as a substance extracted from the body, which can not
be subdivided without chemical decomposition and loss of certain character-
istic properties. This definition will apply to all classes of chemical con-
stituents of the body, organic as well as inorganic. The chemical elements
of which the constituents are composed are properly the ingredients of
the body.

The constituents of the blood, and, indeed, of the entire organism, may
be classified as follows :

1. Inorganic Constituents. — This class is of inorganic origin, definite
chemical composition and crystallizable. The substances included in this
class 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 constituents, and form a part of the organized
fluids or solids. This union is so intimate that they are taken up with the
organic matters, as the latter are worn out and become effete, and are dis-
charged from the body, although themselves unchanged. To supply the place
of the constituents thus thrown off, a fresh quantity is deposited in the pro-
cess of nutrition. They give to the various organs important properties ; and
although identical with substances in the inorganic world, in the interior of
the body they behave as organic substances. They require no special prepara-
tion for absorption, but are soluble and taken in unchanged. They are re-
ceived 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 calcareous in-
crustations and deposits and a considerable increase in the calcareous matter
entering into the composition of the tissues. Water, sodium chloride, the
carbonates, sulphates, phosphates and other inorganic salts may be cited as
examples of this class of constituents.

The uses 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 matters, it constitutes a
medium in which the corpuscles are suspended without solution.

The various salts enumerated in the table exist in solution in water and are

COMPOSITION OF THE BLOOD-PLASMA. 21

more or less intimately combined with the coagulable organic matters. Of
these, the sodium chloride is the most abundant. It undoubtedly has an im-
portant use in giving density to the plasma and in regulating the processes of
endosmosis and exosmosis. In connection with the organic salts and crystal-
lizable excrementitious matters, it may be stated, in general terms, that the
blood contains 14 to 16 parts per 1,000 of matters in actual solution, of which
6 to 8 parts consist of inorganic salts. The presence of these substances in
solution, with the organic coagulable matters, prevents the solution of the
corpuscular elements of the blood. The presence of the chlorides and the
alkaline sulphates assists in dissolving the sulphates, carbonates and the cal-
careous phosphates. The carbonates and phosphates are in part decomposed
in the system and furnish bases for certain of the organic salts, such as the
lactates, urates etc.

2. Organic Saline Constituents. — These substances are in greatest 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, possibly, from a change of a portion of the saccharine matter in
the blood. The physiological relations of these substances are little under-
stood. The salts formed by the union of fatty acids with bases are probably
produced by decomposition of fatty matters, a great part of which is de-
rived from the food.

3. Organic Non-nit rogenized Constituents. — These usually exist in the
blood in small quantity and are derived mainly from the food. Lecethine,
although it contains nitrogen, is included in this class because it presents
many of the properties of the fats. It exists in the blood, bile, nerv-
ous substance and the yelk of egg. Its chemical properties and physio-
logical relations are not well understood. The saccharine matters and glyco-
gen are derived in part from the food and in part from the liver, where
glycogen is formed. They are of organic origin, definite chemical compo-
sition and crystallizable. The fats and sugars are distinguished from other
organic substances by the fact that they are composed of carbon, hydrogen
and oxygen. In the sugars, the hydrogen and oxygen exist in the propor-
tion to form water, which fact has given them the name of carbohydrates.
The constituents of this class play an 'important part in development and
nutrition. One of them, sugar, appears very early in foetal life, formed
first in the placenta and afterward in the liver, its formation by the lat-
ter organ continuing during life. Fat is a necessary constituent 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 ex-
periments and observation have shown that this influence is important.
They will be considered more fully in connection with the physiology of
nutrition.

4. Excrementitious Constituents. — A full consideration of these sub-
stances, 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, be-

22 THE BLOOD.

longs to the physiology of excretion. The relations of carbon dioxide to the
system will be fully considered in connection with the physiology of res-
piration.

5. Organic Nitrogenized Constituents. — This class of constituents is of
organic origin, indefinite chemical composition and non-crystallizable. The
constituents included in this class are apparently the only matters that are en-
dowed 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 different from any
substances 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 transformed 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 without undergoing any change. The analogous
substances which exist in food undergo 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, semi-solids and fluids of the body, never alone, but al-
ways combined with inorganic substances. As a peculiarity of chemical con-
stitution, they all contain nitrogen, which has given them the name of
nitrogenized or azotized matters.

Of the different classes of constituents of the blood, it is at once apparent
that the organic nitrogenized matters are more complex in their constitution,
properties and uses than the other classes. These substances, as they exist in
the blood, possess certain peculiar and characteristic properties.

Plasmine^ Fibrin, Metalbumin, Serine. — The name plasmine was given
by Denis to a substance 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-seventh part of its volume of a concentrated solution of
sodium sulphate, which' prevents coagulation ; in a short time the corpuscles
gravitate to the bottom of the vessel, and the plasma may be separated by
decantation ; to the plasma is added an excess of pulverized sodium chloride,
when a soft, pulpy substance is precipitated, which is plasmine. This sub-
stance, after desiccation, bears a proportion of about twenty-five parts per
thousand of blood. It is soluble in ten to twenty parts of water, when
a portion 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 metalbumin.

According to Denis, plasmine is a proper constituent of the blood, and
after extraction by the process just described, it is decomposed into concrete
fibrin and dissolved fibrin, or metalbumin. Having removed the concrete
fibrin from the solution of plasmine, the metalbumin is coagulated by the
addition of magnesium sulphate, which does not coagulate ordinary albumin.
The proportion of dried metalbumin in the blood is about twenty-two parts

COAGULATION OF THE BLOOD. 23

per thousand. The proportion of dried fibrin is about three parts per
thousand.

After the extraction of plasmine from the blood, another coagulable sub-
stance remains, which is called serine. This is coagulated by heat, the strong
mineral acids or absolute alcohol, but is not coagulated by ether, which
coagulates egg-albumen. Serine bears a close resemblance to ordinary albu-
min but is much more osmotic. Its proportion, desiccated, in the blood is
about fifty-three parts per thousand.

Peptones etc. — A certain quantity of nitrogenized matter, distinct from
the constituents just described, has been extracted from the blood, which is
analogous to peptone. 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 substances are 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 the corpus-
cles be separated as completely as possible, the clear liquid still has a reddish-
amber color. This coloring matter has never been isolated and studied. It
is analogous to the coloring matter of the .red corpuscles, the bile and the
urine.

In addition to the organic nitrogenized constituents which have just been
described, some physiological chemists recognize a substance called para-
globuline, or fibrinoplastic matter, and fibrinogenic matter. These are sup-
posed to be factors of fibrin, which come together in the coagulation of the
blood. They will be considered in connection with the theories of coagula-
tion. The so-called sodium and potassium albuminates have not been posi-
tively established as normal constituents of the blood.

COAGULATION OF THE BLOOD.

The blood retains its fluidity while it remains in the vessels and circula-
tion is not interfered with, and is then composed of a clear plasma holding
corpuscles in suspension. Soon 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, contraction will have taken place, and a clear, straw-colored
fluid expressed, the blood thus separating into a solid portion, the crassa-
mentum, or clot, and a liquid which is called serum. The serum contains
all the constituents of the blood except the corpuscles and fibrin-factors,
which together form the clot. Coagulation takes place in the blood of all
animals, beginning a variable time after its removal from the vessels. In the
human subject, 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 one
minute and forty-five seconds to six minutes ; in 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 seven to sixteen minutes. Contraction

24 THE BLOOD.

then begins, and little drops of clear serum make their appearance on the
surface of the clot. This fluid increases in quantity, and in ten or twelve
hours separation is complete (Nasse). 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. Coagulation is particularly rapid in blood taken
from birds, and sometimes it takes place almost instantaneously. Coagula-
tion is more rapid in arterial than in venous blood. In the former, the pro-
portion of fibrin formed is notably greater and the characters of the fibrin
are somewhat different. A solution of sodium chloride 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
that portion of the serum which is retained between the meshes of the coag-
ulated mass be included in the estimate. As the clot is composed of corpus-
cles 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. Simply taking the
serum which separates spontaneously, there is 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.

On removing the clot, after the separation of the serum is complete, it pre-
sents 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
been rapid, the clot is soft and but slightly contracted. When, on the other
hand, coagulation has been slow, the clot 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 de-
pends merely on the degree of its contraction. It also presents a marked dif-
ference in color at its upper portion. The blood having remained fluid for
some time, the red corpuscles settle, by reason of their greater weight, leaving a
colorless layer on the top. This is the buffy-coat spoken of by some authors.
Examined microscopically, the bufiy-coat presents fibrils of coagulated fibrin
with some of the white corpuscles of the blood. On removing a clot of ve-
nous 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 coagulation have
not been too rapid, the gravitation of the red corpuscles is apparent. If
the clot be cut into small pieces, it will undergo farther contraction and ex-
press 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, nearly all the red cor-
puscles may be removed, leaving the meshes of fibrin.

After coagulation, if the serum be carefully removed, it is found to be a fluid
of a color varying between a light amber and a clear red. This color de-
pends 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 presents all the constituents of the plasma, or
liquor sanguinis, with the exception of the fibrin-factors. It can hardly

COAGULATION OF THE BLOOD. 25

be called a physiological fluid, as it is formed only after coagulation of the
blood.

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 reason of its contractile properties, it soon expresses the
serum, while the red corpuscles are retained. One of the causes which oper-
ate to retain the corpuscles in the clot is the adhesive matter which covers
their surface after they escape from the vessels.

Conditions which modify Coagulation. — 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 instantaneously. In short, it appears that all conditions which favor
evaporation from the blood hasten its coagulation. The blood will coagu-
late more rapidly in a vacuum 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.
(zero and 60° C.), elevation of temperature increases the rapidity of coagula-
tion. Agitation of the blood in closed vessels retards, and in open vessels,
hastens coagulation.

Various chemical substances retard or prevent coagulation. Among them
may be mentioned the following: solutions of potassium or of sodium
hydrate ; sodium carbonate ; ammonium carbonate ; potassium carbonate ;
ammonia; sodium sulphate. In the menstrual flow, the blood is kept
fluid by mixture with the abundant secretions of the vaginal mucous mem-
brane.

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 between
twelve and twenty-four hours after circulation has ceased. Under these
conditions, the blood is found chiefly in the venous system, as the arte-
ries are usually emptied by post-mortem contraction of their muscular
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 already described.
They are frequently covered by a soft, whitish film 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 reported a case of death by lightning, in
which 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

26 THE BLOOD.

coagulum 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 un-
usual during life. In the heart, coagula which bear evidence of having existed
for some time before death are sometimes found. 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 ; and that this becomes larger by
farther depositions, until large, vermicular masses of fibrin are found attached,
in some instances, to the chordae tendineae. Bodies projecting into the caliber
of a blood-vessel soon become coated with a layer of fibrin. , Kough concre-
tions about the orifices of the heart frequently lead to the deposition of little
masses of fibrin, which sometimes become detached and are carried to various
parts of the circulatory system, as the lungs or brain, plugging up one or more
of the smaller vessels. 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.
Coagulation thus takes place in the vessels as the result of stasis or of very-
great retardation of the circulation, and in the tissues or cavities of the body,
whenever it is accidentally effused. In the latter case, it is generally removed
in the course of time by absorption.

The property of the blood under consideration has an 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 haemorrhagic diathesis, or haemophilia; a condition in which
slight wounds are likely to be followed by alarming, and it may be fatal
haemorrhage. This condition of the blood is not characterized by any
peculiar symptoms except the obstinate flow of blood from slight wounds ;
and it may continue for years.

Conditions which accelerate coagulation have a tendency to arrest haemor-
rhage. 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 influ-
ence. A clean cut will bleed more freely than a ragged laceration. In divis-
ion 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 it is well known
that division of an artery of comparatively small size, if it be cut across, would
be fatal if left to itself. Under these conditions, the internal coat is torn in
shreds which retract, their curled ends projecting into the caliber of the ves-
sel 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
can not be permanent, for as soon as the system recovers from the shock,

COAGULATION OF THE BLOOD. 27

the contractions of the heart force out the coagulated blood which has closed
the opening.

From the foregoing considerations, it is evident that coagulation of the
blood has for its chief office the arrest of haemorrhage. 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. — Alex. Schmidt, in 1861, proposed
a theory of coagulation, which involves the coming together of certain mat-
ters called fibrin-factors. This theory, which had been indicated by Buch-
anan, in 1845, has been adopted and more or less modified by Kiihne, Virchow
and others. If blood-plasma, rendered neutral with acetic acid, be diluted
with ten times its volume of water at 32° Fahr. (zero C.), and then be treated
with a current of carbon dioxide, a flocculent precipitate is formed, which
has been called paraglobuline, or fibrinoplastic matter. This substance may
be dissolved in water containing air or oxygen in solution. After this pre-
cipitate has been separated, if the clear liquid be diluted with about twice its
volume of ice-cold water and be treated for two or three hours with a current
of carbon dioxide, a viscid scum is produced, which has been called fibrino-
gen. More recently, a third principle, a ferment, has been described by
Schmidt, which he considers necessary to the formation of fibrin. This
ferment is produced in some way by the leucocytes of the blood, probably
by partial decomposition of these bodies.

In view of the results of recent investigations with regard to the cause of
the coagulation of the blood, which, unfortunately, are not as positive and
definite as could be desired, some physiologists have adopted the following as
a provisional theory of the mechanism of this process :

There exists, probably in small quantity in the circulating blood and in
considerable quantity in blood drawn from the vessels or arrested in its cir-
culation, a peculiar ferment which is produced in some way by changes in
the leucocytes. This ferment may be concerned in the decomposition of
plasmine. It is certainly thrown down with plasmine when plasmine is pre-
cipitated by the action of reagents. The action of this ferment either in-
duces or hastens the separation of plasmine into the, so-called fibrin-factors,
paraglobuline and fibrinogen. Of these two substances, fibrinogen is the
more important in the formation of fibrin, a small quantity of fibrin, only
about three parts per thousand of blood, being formed. A large quantity of
paraglobuline is not used in the formation of fibrin and remains in the serum.
It is possible, indeed, that no part of the paraglobuline is concerned in coagu-
Jation. If the latter be true, paraglobuline may be regarded as identical with
metalbumin, a view which was advanced by Robin many years ago and is
now adopted by some physiologists.

Adopting these views, the mechanism of coagulation may be succinctly
described as follows :

THE BLOOD.

1. As a condition preliminary to coagulation, there is either an increase
in the formation of fibrin-ferment or an appearance of ferment in the blood,
due to changes in certain of the leucocytes. The red corpuscles are probably
not directly concerned in coagulation, and there is nothing definite known of
the action of the blood-plaques in this process.

2. The fibrin-ferment unites with fibrinogen and forms fibrin, which is
the coagulating substance. Paraglobuline (or metalbumin) is little if at all
concerned in this process.

3. The processes described as incident to the coagulation of blood take
place also in the coagulation of lymph and chyle.

In accordance with the views stated in connection with the composition
of blood-plasma, paraglobuline, or metalbumin, fibrinogen and, finally, fibrin
are products of decomposition, are abnormal formations, and are not normal
constituents of the blood.

It is possible that the statement just given of the mechanism of the coagu-
lation of the blood may be modified in the future in accordance with the most
recent views of Schmidt, who claims that all the so-called fibrin-factors result
from decomposition of the leucocytes, a great number of which, it is said,
are dissolved soon after blood is drawn from the vessels. There are, in-
deed, many experimental and pathological facts in support of this view ; but
it can not be adopted without reserve, until the experiments of Schmidt shall
have been supplemented by more extended observations. Schmidt maintains
that in certain classes of animals, dissolved red corpuscles are also concerned
in the production of fibrin-factors.

Leech-drawn blood remains fluid in the body of the animal. 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.

The existence of projections into the caliber of vessels, or the passage of

a fine thread
through an ar-
tery or vein, will
determine the
formation of a
small coagulum
upon the foreign
substance, while
the circulation is
neither inter-
rupted nor re-
tarded. In the
present state of
knowledge, ex-
planation of these facts is difficult if not impossible. The process, under
these conditions, can not be subjected to direct experiment as in the case
of blood coagulating out of the body.

FIG. 10.— Coagulated fibrin (Robin).

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

DISCOVERY OF THE CIRCULATION. 29

During coagulation, fibrin assumes a filamentous form, presenting, under
the microscope, the appearance of rectilinear fibrillae. These fibrillae
gradually increase in number, and as contraction of the clot occurs, they be-
come irregularly crossed. They are always straight, however, and never
assume the wavy appearance characteristic of true fibrous tissue.

The blood of the renal and hepatic veins, capillary blood and the blood
which passes from the capillary system into the veins after death generally
does not coagulate or coagulates very imperfectly ; in other words, these varie-
ties of blood do not readily form fibrin. The reason of this peculiarity is not
known ; but the fact affords a partial explanation 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 losing its coagulability in its pas-
sage 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 coagulation can not take
place while the normal circulation is maintained and while the blood is
undergoing the constant changes incident to general 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 the movements of the heart— Force of the heart— Action
of the valves— Sounds of the heart— Causes of the sounds of the heart— Frequency of the heart's action
—Influence of age and sex— Influence of digestion— Influence of posture and muscular exertion— In-
fluence of exercise etc.— Influence of temperature— Influence of respiration on the action of the heart
— Cause of the rhythmical contractions of the heart — Accelerator nerves — Direct inhibition of the heart
— Reflex inhibition of the heart — Summary of certain causes of arrest of the action of the heart.

HAEVEY "set forth for the first time his discovery of the circulation,"
in his public lectures in 1616, and in 1628 published the " Exercitatio Ana-
tomica de Motu Cordis et Sanguinis in Animalibus." This discovery, from
the isolated facts bearing upon it which were observed by anatomists to its
culmination in the experiments of Harvey, so fully illustrates the gradual
development of most physiological truths, that it does not seem out of place
to begin the study of the circulation with a brief sketch of its history.

The facts bearing upon the circulation developed before the time of
Harvey 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 physi-
ologists 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
4

30 CIRCULATION OF THE BLOOD.

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 ligatures, 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 between 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 passage 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).

A few years later, Colombo, professor of anatomy at Padua, and Cesal-
pinus, 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 ; and 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 priority of observation is almost universally conceded to Fabricius.
As regards this point, only the dates of published memoirs are to be con-
sidered, 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 accurate descriptions and delineations
of the valves, and his first publication is said to have appeared in 1603. He
demonstrated the valves to Harvey, at Padua ; and it is probable that this
was the origin of the first speculations by Harvey on the mechanism of the
circulation.

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 com-
posed contract simultaneously, and "by an admirable 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 passed to the auricles, and showed how these, by their con-
traction, filled 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

DISCOVERY OF THE CIRCULATION. 31

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.

By these simple experiments, the chain of evidence establishing the fact
of the circulation of the blood was completed. Truly it is said that here
began an epoch in the study of physiology; for then scientific observers
began to emancipate themselves from the ideas of the ancients, which had
controlled opinions 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
no 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 sys-
tem 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 circulation in the wing of a bat.
These observations completed the discovery of the circulation.

In man and in the warm-blooded animals, the organism requires blood
that has been oxygenated in the lungs, and to meet this demand fully, the
circulatory system is divided into pulmonic and systemic. The heart is
double, having a right side and a left side, which are entirely distinct from
each other. The right heart receives the blood as it is brought from the gen-
eral system by the veins and sends it to the lungs ; the left heart receives the
blood from the lungs and sends it to the general system. It must be borne in
mind, however, that although the two sides of the heart are distinct from
each other, their action is simultaneous ; and in studying the motions of the
heart, it will be found 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 neces-
sary, therefore, to separate the two circulations in the study of their mechan-
ism ; for the simultaneous action of both sides of the heart renders it possi-
ble to study its action 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 general system ; the capillaries, which distribute
the blood more or less abundantly in different parts of the general system ;
and the veins, which return the blood from the general system to the heart.
The three kinds of blood-vessels present certain anatomical as well as
physiological distinctions, which will be noted in connection with the
description of the vascular system.

32

CIRCULATION OF THE BLOOD.

PHYSIOLOGICAL ANATOMY OF THE HEART.

The heart of the human subject is a pear-shaped, muscular organ, situ-
ated in the thoracic cavity, with its base in the median line and its apex at
the fifth intercostal space, three inches (7'6 centimetres) to the left of the
median line, or one inch (2 -5 centimetres) within the line of the left nipple.

Its weight is eight to
ten ounces (227 to 283
grammes) in the female,
and ten to twelve ounces
(283 to 340 grammes)
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
by the attachment of
the great vessels to the
posterior wall of the
thorax; while the apex
is free and capable of
a certain degree of mo-

Fio. 11.— Heart in situ (Dalton, in Flint, " on the heart"). tion. The whole Organ

a, 6, c etc., ribs ; 1, 2, 3 etc., intercostal spaces ; vertical line, median • i -i • 01

line; triangle, superficial cardiac region ; x on the fourth rib, IS enveloped in a tlbrous

sac called the pericar-
dium. This sac is lined by a serous membrane, which is attached to the
great vessels at the base and reflected over its surface. The membrane is
lubricated by about a drachm (3'7 c. c.) of fluid, so that the movements of
the heart are normally accomplished without any friction. The serous peri-
cardium does not present any differences 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 cavae 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 respectively, 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 cav-
ity are quite thin as compared with the ventricles, measuring about one line
(2-1 mm.). They are composed of muscular fibres arranged in two layers.

PHYSIOLOGICAL ANATOMY OF THE HEART.

33

FIG. 12.— Course of the muscular fibres of the left
auricle (Landois).

one of which, the external, is common to both auricles, and the other, the
internal, is proper to each. These muscular fibres, although involuntary in
their action, belong to the striated 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 auri-
cles; and others are circular, sur-
rounding the auricular appendages
and the openings of the veins, ex-
tending, also, a short distance along
the course of these vessels. One or
two valvular folds are found at the
orifice of the coronary vein, prevent-
ing a reflux of blood, but there are no valves at the orifices of the venae cavae.
The left auricle receives the blood which comes from the lungs by the

pulmonary 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 (3-15 mm.).
It has four openings by
which it receives the
blood from the four pul-
monary veins. These
openings are not provid-
ed With valves. Like the
right auricle, it has a
large opening by which
blood flows into the cor-
responding ventricle. The
arrangement of the mus-
cular fibres is essentially
the same as in the right
auricle. In adult life, the
cavities of the auricles are
entirely distinct from each
other. Before birth, they
communicate by a large
opening, the foramen

FIG. 13.— Heart, anterior view (Bonamy and Beau). OVale, and the Orifice of

1, right ventricle ; 2, left ventricle ; 3, 4, right auricle ; 5, 6, left au- ,1 in-fow^r VOTIQ ™ vn i«

ride ; 7, pulmonary artery; 8, aorta; 9, superior vena caya ; 10, the mleiior Vena Ca\a IS

anterior coronary artery ; 11, branch of the coronary vein ; 12, ^..^.^oH with a

12, 12, lymphatic vessels. plOViaeQ Wltn a

34: CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

16 —

branous 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 disap-
pears.

The ventricles, in the human subject and in warm-blooded animals, con-
stitute the bulk of the heart. They have a capacity somewhat greater than
that of the auricles and are provided with thick, muscular walls. It is by
the powerful action of this portion of the heart that the blood is forced, on

the one hand, to the lungs and
back to the left side of the heart,
and on the other, through the en-
tire system of the greater circula-
tion, to the right side.

The capacity of the cavities on
the right side of the heart is one-
tenth to one-eighth greater than
that of the corresponding cavities
on the left side. The capacity of
the ventricles exceeds that of the
auricles by one-fourth to one- third.
The absolute capacity of the left
ventricle, when distended to its
utmost (Robin and Hiffelsheim),
is 4-8 to 7 ounces (143 to 212 c. c.).
This is much greater than most
estimates, which place the capacity
of each of the various cavities,
moderately distended, at about two
ounces (59*1 c. c.) ; but the ob-
servations of Robin and Hiffel-
sheim, upon the human heart,
were made evidently with the
greatest accuracy, either before

cadaveric rigidity had set in or

left ventricular cavity ; 2, mitral valve ; 8, 4, colum- , , , ?.

no? carneae, ; 5, aorf ic opening ; 6, aorta ; 7, 8, 9, alter it had disappeared.
aortic valves ; 10, right ventricular cavity ; 11, in-
terventricular septum ; 12, pulmonary artery ; 18,
14, pulmonjc valves ; 15, left auricular cavity : 16,
16, right pulmonary veins, with 17, 17, openings of
the veins ; 18, section of the coronary vein.

Notwithstanding the disparity
in the extreme capacity of the va-
rious cavities, the quantity of blood
which enters these cavities is necessarily equal to that which is expelled.
This has been stated to be a little more than two ounces (about 60 c.c.).
There are, however, no means of estimating with exactness the quantity of
blood discharged with each ventricular contraction ; and the question seems
to be rather avoided in many works on physiology. Judging, however, from
observations on the heart during its action, it never seems to contain much
more than half the quantity in all its cavities that it does when fully dis-
tended by injection ; but the right cavities are more dilatable than the left

PHYSIOLOGICAL ANATOMY OF THE HEART.

35

10

and probably the ordinary quantity of blood in the left ventricle is four-
fifths to five-sixths of its extreme capacity, or five to six ounces (120 to
170 c.c.).

The cavities of the ventricles are triangular or conoidal, the right being
broader and shorter than the left, which latter extends to the apex. The
inner surface of both cavities is marked by ridges and papillae, which
are called columnae carneae. Some of these are 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 chordae
tendineae, 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 appearance. This arrangement facilitates
the complete emptying of the ventricles during their contraction.

The walls of the left ventricle are uniformly much thicker than those of
the right side. The average thick-
ness of the right ventricle at the
base is two and a half lines (5*25
mm.), and the thickness of the
left ventricle at the corresponding
part is seven lines (14'7 mm.), or
a little more than half an inch
(Bouillaud).

The arrangement of the mus-
cular fibres constituting the walls
of the ventricles is more regular
than in the auricles, and their
course affords an explanation of
some of the phenomena which
accompany the heart's action.
The direction of the fibres can
not be well made out unless the
heart have been boiled for a num-
ber of hours, when part of the
intermuscular tissue is dissolved
out, and the fibres can be easily
separated and followed. Without
entering into a minute descrip-
tion of their direction, it is suffi-
cient 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 ventri-
cle. 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

FIG. 15.— Right cavities of the heart (Bonamy and Beau).

1, right ventricular cavity ; 2, posterior curtain of the
tricuspid valve ; 3. right auricular cavity ; 4, colum-
nar carnece of the right auricle ; 5, section of the cor-
onary vein ; 6, Eustachian valve ; 7, ring of Vieus-
sens ; 8, fossa ovalis ; 9. superior vena cava ; 10, infe-
rior vena cava \ 11, aorta ; 12, 12, right pulmonary
veins.

36 CIRCULATION OF THE BLOOD— ACTION OF THE HEAET.

the columnae carneae. 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 circu-
lar, 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 ordinary voluntary muscles ; but as already

intimated, it presents certain pe-
culiarities in its minute anatomy.
The fibres are considerably small-
er and more granular than those
of ordinary muscles. They are,
moreover, connected with each
other by short, inosculating
branches. (See Fig. 17.) The
muscular fibres of the heart have
no sarcolemma. These peculiari-
ties, particularly the inosculation
of the fibres, favor the contrac-
tion of the ventricular walls in
every direction and the complete
expulsion 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-termi-
nations in its substance will be
described in connection with the
influence of the nervous system
upon the circulation.

*cular fibres of Me ventricles (Bonamy and Each ventricle hag two ori.

fices; one b

left ventricle*6 °f the heart ' 4' fibres penetrafcills the 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 general
system. All of these openings are provided with valves, which are so ar-
ranged 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 chordae tendineae, some of which arise from the papillae on the inner sur-
face 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 ventri-
cle is completely filled and the fibres contract, they are forced up, their free
edges become applied to each other, and the opening is closed.

MOVEMENTS OF THE HEART.

37

17. — Branched

(Lan'

Pulmomc 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, membranous pouches, with their convex-
ities, 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 regurgi-
tation of blood. At the centre of the free edge of each
valve is a little corpuscle called the corpuscle of 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 prob- FlG
ably aid in the adaptation of the valves to each other and
in the effectual closure of the orifice.

Mitral Valve. — This valve, sometimes called the bicus-
pid, is situated at the left auriculo-ventricular orifice. It is called mitral
from its resemblance, when open, to a bishop's mitre. It is attached to the
edges of the auriculo-ventricular opening, and its free borders are held in

place, when closed, by
the chordae tendineae of
the left side. It presents
no material difference
from the tricuspid valve,
with the exception that it
is divided into two cur-
tains instead of three.

Aortic Valves. — These
valves, also called the sem-
ilunar, or sigmoid valves
of the left side, present
no difference from the
valves at the orifice of

FIG. 18.— Valves of the heart (Bonamy and Beau). the pulmonary artery.

1, right auriculo-ventricular orifice, closed by the tricuspid valve ; rpn •+ , j „ 4/u^

2, fibrinous ring ; 3, left auriculo-ventricular orifice, closed by 1 hey are Situated at tne

the mitral valve ; 4, fibrinous ring ; 5, aortic orifice arid valves ; „„„+• ^fl™
6, pulmonic orifice and valves ; 7, 8, 9, muscular fibres. ^y<

MOVEMENTS OF THE HEART.

The dilatation of the cavities of the heart is called the diastole, and the
contraction 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 and systole,
which are distinct from the action of the ventricles.

A complete revolution of the heart consists in the filling and emptying of
all its cavities, during which they present an alternation of repose and activity.
As these phenomena occupy, in many warm-blooded animals, a period of time

7—-

38 CIECULATION OF THE BLOOD— ACTION OF THE HEART.

less than one second, it will be appreciated that the most careful study is ne-
cessary 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 practically the same as in the human subject ; and
although the exposure of the heart by opening the chest modifies somewhat
the force and frequency of its pulsations, the various phenomena follow each
other in their natural order and present essentially their normal characters.
Having opened the chest, keeping up artificial respiration, the heart, en-
veloped in its pericardium, is observed, 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 v 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 contrac-
tion of the auricles, these cavities are continually receiving blood, on the right
side from the general system, by the venae cavae, and on the left side from the
lungs, by the pulmonary veins. This continues until the cavities of the au-
ricles are completely 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
systole), and force the blood into the ventricles, producing complete diastole
of these cavities. During 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 farthermore, 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 that the systole of the auricles is not immediately neces-
sary to the performance of the circulation ; and the contractility of the auri-
cles may be temporarily exhausted by repeated and prolonged stimulation,
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, there is contrac-
tion of the ventricles. This is the chief active operation performed by the
heart and is generally spoken of as the systole. The contraction of the ven-
tricles is very much more powerful than that of the auricles. By their ac-
tion, the blood is forced from the right side to the lungs, by the pulmonary
artery, and from the left side to the general system, by the aorta. Regurgita-

MOVEMENTS OF THE HEART. 39

tion into the auricles is prevented 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 repose 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, the apex
is sent forward 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 movable. As a consequence of this anatomical ar-
rangement, the heart is moved upward and forward during its systole. 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 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 elastic, and as they receive the charge of blood from the ventricles, they
become enlarged in every 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.

Twisting of the Heart. — The spiral course of the superficial fibres involves
another phenomenon accompanying its contraction ; namely, twisting. By
attentively watching the apex, especially when the action of the heart is
slow, there is observed 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 phenomonen. Like any other
muscle, it is sensibly hardened during contraction.

Shortening of the Ventricles. — The point of the heart is protruded during
the ventricular systole, but this protrusion is not due to elongation of the ven-
tricles. By suddenly cutting the heart out of a warm-blooded animal and
watching the phenomena which accompany the few regular movements which
follow, it is seen that the ventricles invariably shorten as they contract. This
can easily be appreciated by the eye, but more readily if the point of the or-
gan be brought just in contact with a plane surface at a right angle, when, at
each contraction, it is unmistakably observed to recede. During the inter-
vals of contraction, the great vessels, particularly the aorta and pulmonary ar-
tery, which attach the base of the heart to the posterior wall of the thorax,
are filled but not distended with blood ; at each systole, however, these ves-
sels are distended to their utmost capacity ; their elastic coats admit of con-
siderable enlargement, as can be seen in the living animal, and this enlarge-
ment, taking place in every direction, pushes the whole organ forward. It is
for this reason that, in observing the heart in situ, the ventricles seem to elon-

40 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

FIG. 19. — Diagram of the shortening of

the ventricles during systole.
The dotted lines show the position of the
heart during contraction.

gate. It is only when the heart is firmly fixed or is contracting after it has been
removed from the body, that the actual changes which occur in the length of

the ventricles can be appreciated. During
the systole, the ventricles are shortened and
are narrowed in their transverse diameter,
but their antero-posterior diameter is slight-
ly increased.

In addition to the marked changes in
form, position etc., which the heart under-
goes during its action, on careful examina-
tion it is seen that the surface of the ventri-
cles becomes marked with slight, longitudinal
ridges during the systole.

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 right of the perpendicular line of the left
nipple. This 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 there is 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 ar-
terial system. The impulse is due
to the locomotion of the ventricles.
In the words of Harvey, " the heart
is erected, and rises upward to a
point so that at this time it strikes
against the breast and the pulse is
felt externally."

Succession of the Movements of
the Heart. — The main points in the
succession of the movements of the
heart are readily observed in cold-
blooded animals, in which the pul-
sations are very slow. In examining
the heart of the frog, turtle or alii-
gator, the alternations of repose and *• f» $S&2fiS!S ;Lud % S? ftaTf systole'
activity are very strongly marked.

During the intervals of contraction, the whole heart is flaccid and the ven-
tricle is comparatively pale ; the auricles then slowly fill with blood ; when
they have become fully distended, they contract and fill the ventricle, which

FIG. 20.— Side view of the heart (Landois).

MOVEMENTS OF THE HEART.

41

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. These phenomena
may occupy ten to twenty seconds, giving an abundance of time for ob-
servation. 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 just mentioned are followed with more difficulty. In spite
of this rapidity of action, it can be seen that a rapid contraction of the auri-
cles precedes the ventricular systole, and that the latter is synchronous with
the cardiac impulse.

The experiments of 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 jugu-
lar vein. 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 corre-
sponding movements of the levers, which may be registered simultaneously.

FIG. 21.— Cardiograph (Chauveau and Marey).

" The instrument is composed of two principal elements : A E, the registering apparatus, and A S, the
sphygmographic apparatus, that is to say, which receives, transmits, and amplifies the movements
which are to be studied.11 The compression exerted upon the bag c, which is placed over the apex
of, the heart, between the intercostal muscles, is conducted by the tube t c, which is filled with air» to
the first lever. The compression exerted upon the bags o and v, in the double sound, is conducted
by the tubes t o and t v to the two remaining levers. The movements of the levers are registered
simultaneously by the cylinder A E.

To register the impulse of the heart, an incision is made through the skin
and the external intercostal muscle over the point where the apex-beat is felt.

42 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

A little bag, stretched over two metallic buttons separated by a central rod,
is then secured in the cavity thus formed and is 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 communicate with its lever at will.
When the operation is completed and the sound is 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 interfered with. The cylinder which carries the paper destined to receive
the traces is arranged to move by clock-work at a given rate. The paper
may also be ruled in lines, the distances between which represent certain frac-
tions of a second. Fig. 21 represents the apparatus reduced to one-sixth of
its actual size. Two of the levers are connected 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, the move-
ments of the three levers produced traces upon the paper which were inter-
preted as follows :

The auricular systole, marked by the first lever, immediately preceded the
ventricular systole and occupied about two-tenths of a second. The eleva-
tion of the lever indicated that it was much more feeble than the ventricu-
lar systole, and sudden in its character; the contraction, when it had arrived
at the maximum, being immediately followed by relaxation.

The ventricular systole, marked by the second lever, immediately followed
the auricular systole and occupied about four- tenths of a second. The almost
vertical direction of the trace and the degree of elevation showed that it was
sudden and powerful in its character. The abrupt descent of the lever
showed that the relaxation was almost instantaneous.

The impulse of the heart, marked by the third lever, was shown to be ab-
solutely synchronous with the ventricular systole.

Condensing the general results obtained by Marey, which are of course
subject to some variation, and dividing the action of the heart into ten equal
parts, three distinct periods are observed, 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 contraction is powerful and the relaxation is sudden. It is absolutely
synchronous with the impulse of the heart.

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

Force of the Heart. — Hales (1733) was the first to investigate experiment-
ally the question of the force exerted by the heart, 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 pressure in the aorta by the area of the internal surface of the ventricle.
The cardiometer has since undergone various improvements and modifica-

ACTION OF THE VALVES. 43

tions, but the above is the principle made use of at the present day in esti-
mating the pressure of the blood in different parts of the circulatory system.
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 (228-6 centimetres), and gave the area of the left
ventricle as 15 square inches (96-67 square centimetres). From this he cal-
culated the force of the left ventricle as equal to 51-5 pounds (about 23 kilos).
This estimate, however, does not satisfy all the physical conditions, and it
can not be accepted, even as an approximation.

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 pre-
cluding the possibility of introducing a sound into its cavity. By first sub-
jecting the bags to known degrees of pressure, the line of elevation of a
lever may be graduated so as to represent the degrees of the cardiometer. 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 ventricle, only as one to ten.

Action of the Valves. — In man and the warm-blooded animals, there are
no valves at the orifices by which the veins open into the auricles. As has
already been seen, compared with the ventricles, the force of the auricles is
insignificant ; and it has farthermore been shown that the ventricles may bo
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 contraction
of the auricles the openings are considerably narrowed and regurgitation can
not take place to any great extent. The force of the blood flowing into the
auricles likewise offers an obstacle to its return. There is really 110 valvu-
lar apparatus which operates to prevent regurgitation from the heart into
the veins ; for the valvular folds, which are so abundant in the general venous
system and particularly in the veins of the extremities, do not exist in the
venae cavae. The continuous flow of blood from the veins into the auricles,
the feeble character of the auricular contractions, the arrangement of the
fibres around the orifices of the vessels, and the great size of the auriculo-ven-
tricular openings, are conditions which provide sufficiently for the flow of
blood into the ventricles.

Action of the Auricula - Ventricular Valves. — After the ventricles have
become completely distended by the auricular systole, they take on their con-
traction, which is very many times more powerful than the contraction of
the auricles. They force open the valves which close the orifices of the pul-
monary artery and aorta and empty their contents into these vessels. To
accomplish this, at the moment of the ventricular systole, there is a complete
closure of the auriculo-ventricular valves, leaving only the aortic and pul-
monic openings through which the blood can pass. That these valves close at

M CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

the moment of contraction of the ventricles, was demonstrated by the experi-
ments of Chauveau and Faivre, who introduced the finger through an open-
ing 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 produced in part by the closure of the auriculo-
ventricular 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 slightly 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 semi-
lunar 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 adapted that not a drop
passes between them ; but when the pressure is considerable, a certain quan-
tity of fluid passes the tricuspid valve (T. W. King). There is, indeed, a
certain degree of insufficiency of the tricuspid valve, which does not exist on
the opposite side ; but it is very questionable whether there can be sufficient
force exerted by the right ventricle to produce regurgitation of blood at the
right auriculo-ventricular orifice.

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 ven-
tricles. The systole, however, overcomes the resistance of these valves and
forces the contents of the ventricles into the arteries. During this 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 is very great, closes the openings.

The action of the semilunar valves can be studied by cutting away a por-
tion 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. It has been observed that while the aortic semilunar valves oppose
the passage of the liquid so effectually that the aorta may be ruptured before
the valves will give way, a certain degree of insufficiency exists, under a high
pressure, at the orifice of the pulmonary artery (Flint, 1864). A slight in-
sufficiency of the pulmonic valves was observed by John Hunter, in 1794. 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. — The appreciable phenomena which attend the
heart's action are connected with the systole of the ventricles. It is this

. SOUNDS OF THE HEART. 45

which produces the impulse against the walls of the thorax, and as will be
seen farther on, the dilatation of the arterial system, indicated by 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 ; and the sounds,
which are two in number, have been called first and second, with reference to
the ventricular 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 lubb-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.

Both sounds are generally heard with distinctness over the entire praecor-
dial region. The first sound is heard with its maximum of intensity over
the body of the heart, a little below and within the nipple, between the
fourth and fifth ribs, and is propagated with greatest intensity downward,
toward the apex. The second sound is heard with its maximum of intensity
at the base of the heart, between the nipple and the sternum, at about the
third rib, and is propagated upward, along the course of the great vessels. If
the stethoscope be placed between the point of the apex-beat and the left
nipple, the first sound will be heard strongly accentuated, and presenting a
certain quality in its valvular element, due to the closure of the mitral valve.
If the stethoscope be then removed to a point a little to the left of the ensi-
f orm cartilage, the element due to the closure of the tricuspid valve will
predominate, and a slight but distinct difference in quality may frequently
be noted. An analogous difference in the valvular elements of the second
sound may also be observed. When the stethoscope is placed at the base of
the heart, just to the right of the sternum and near the aortic valves, the
character of the second sound is often notably different from the character of
the sound heard with the stethoscope placed just to the left of the sternum,
over the pulmonic valves. In this way the valvular elements of the two
sounds of the heart may be separated, each one into two, one produced by
closure of the valves on the left side, and one by closure of the valves of the
right side. A recognition of these nice distinctions is useful in physical
examinations of the heart in disease.

The rhythm of the sounds bears a definite relation to the rhythm of the
heart's action. Laennec was the first to direct special attention to the rhythm
of the heart-sounds, although the sounds themselves were recognized by Har-
vey, who. compared them to the sounds made by the passage of fluids along
the oesophagus of a horse when drinking. Laennec divided a single revolution
of the heart into four equal parts : the first two parts, occupied by the first
sound ; the third part, by the second sound ; and the fourth part, with no
sound. He regarded the second sound as following immediately after the
first. Some authors have described a " short silence " as occurring after the
5

46 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

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 the mechanism of the production of the two sounds
is considered, it will be seen that if the views on that point be correct, the
first sound should occupy the period of the ventricular systole, or four-tenths
of the heart's action. The second sound occupies about three-tenths, and
the repose, three-tenths.

The first sound is relatively dull, low in pitch, and is made up of two ele-
ments ; one, a valvular element, in which it resembles in character the second
sound, and the other, an element which is directly 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 ele-
ment, which is purely 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 (1832) settled beyond a doubt that it is due to
closure of the aortic and pulmonic semilunar valves. In these experiments,
the second sound was imitated by producing sudden closure of the aortic
valves by a column of water. In the experiments of the British Commission,
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 withdrawn and the valves permitted to resume their action, the normal
sound returned.

The cause of the first sound of the heart has not been so well understood.
It was maintained by Rouanet that this sound was produced by the closure
of the auriculo- ventricular valves ; but the situation of these valves rendered
it difficult to demonstrate this by actual experiment. 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, when the first sound
assumes a purely valvular quality. These observations were made in 1858 by
the late Dr. Austin Flint :

If a folded handkerchief be placed between the stethoscope and in-
tegument, the first sound is divested of some of its most distinctive feat-
ures. It loses the quality of impulsion and presents a well marked valvular
quality.

In many instances, when the stethoscope is applied to the praecordia 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.

When the stethoscope is applied to the chest a little distance from the

SOUNDS OF THE HEART. 47

i

point where the first sound is heard with its maximum of intensity, it pre-
sents only its valvular element.

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 that these valves produce at least one
element of the sound. In farther support of this opinion, is 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 wanting to confirm this view. Chauveau
and Faivre 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 tendinese. In thi& experiment a loud rushing murmur took the place
of the sound. These observations and experiments seem to settle the fact
that the closure of the auriculo-ventricular 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 just mentioned, although they serve to give
it its prolonged and "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 that the muscular murmur is one of the elements
of the first sound ; .and it is this which gives to the sound its prolonged char-
acter 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, its duration must neces-
sarily coincide with that of the ventricular systole.

The impulse of the heart against the walls of the thorax also has a share
in the production of 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 substance between the stethoscope and
the chest, or by auscultating the heart after the sternum has been removed.
Under these conditions, the first sound loses its booming character, retaining,
however, the muscular element when the instrument is applied to the exposed
organ.

The observations showing the valvular character of one of the elements
of the first sound have been so definite and positive in their results that one
can hardly regard them as entirely controverted by the recent experiments
(1885) of Yeo and Barrett, upon the hearts, cut from the body, of cats and
dogs, which show, it is claimed, that "a definite and characteristic tone sim-
ilar in quality to the first sound is produced by the heart-muscle under cir-
cumstances that render it impossible for any tension of the valves to contrib-

48 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

ute to its production." It will be assumed, therefore, that the sounds of the
heart have a mechanism that may be summarized as follows :

The first sound of the heart is a compound sound. It is produced by the
closure of the auriculo- ventricular valves at the beginning of the ventricular
systole, to which are superadded, the muscular sound, due to the contraction
of the muscular fibres of the heart, and the impulsion-sound, due to the
striking of the heart against the walls of the thorax.

The second sound is a simple sound. It is produced by the sudden clos-
ure of the aortic and pulmonic semilunar valves, immediately following the
ventricular systole.

It is of importance, with reference to pathology, to have a clear idea of
the currents of blood through the heart, with their exact relations to the
sounds and intervals. At the beginning of the first sound, the blood is for-
cibly thrown from the ventricles into the pulmonary artery on the right side
and the aorta on the left, and the auriculo-ventricular valves are closed.
During the period occupied by this sound, the blood is flowing through the
arterial orifices, and the auricles are receiving blood slowly from the vense
cavse and the pulmonary veins. When the second sound occurs, the ventri-
cles having become 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's Action. — The number of pulsations of the heart
is not far from seventy per minute in an adult male and is between seventy
and eighty in the 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. Dunglison mentioned a
case which came under his own observation, in which the pulse presented an
average of thirty-six per minute. The same author stated that the pulse of
Sir William Congreve was never less than 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
such instances, the fact may be ascertained by listening to the heart while
the finger is placed upon the artery.

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 pulsations of the heart in the foetus are about
140 per minute. At birth the pulse is 136. It gradually diminishes during
the first year to about 128. The second year, the diminution is quite rapid,
107 being the mean frequency at two years of age. After the second year,

FREQUENCY OF THE HEART'S ACTION. 49

the frequency progressively diminishes until adult life, when it is at its min-
imum, which is about 70 per minute. At the later periods of life the move-
ments of the heart become slightly accelerated, ranging between 75 and 80

During early life there is no marked and constant difference in the rapid-
ity of the pulse in the sexes ; but near the age of puberty, the development
of the peculiarities relating to sex is accompanied with an acceleration of the
heart's action in the female, which continues even into old age.

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 between five and ten beats per minute after each
meal. Prolonged fasting diminishes the frequency of the pulse by about
twelve beats. Alcohol first diminishes and afterward accelerates the pulse.
Coffee is said to accelerate the pulse in a marked degree. It has been ascer-
tained that the pulse is accelerated to a greater degree by animal than by
vegetable food.

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. In the male, there is a difference 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 is,
for the male standing, 81 ; sitting, 71 ; lying, 66 ; — for the female : standing,
01 ; 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 (Guy).

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 making the change of posture. This is answered by the
experiments of Guy, in which the subjects were placed on a revolving board
and the position of the body was changed without any muscular effort. Ths
same results as those cited above were obtained in these experiments, showing
that the difference is due to the position of the body alone. In a single obser-
vation, the pulse, standing, was 89 ; lying, 77 ; difference, 12. With the post-
ure changed without any muscular effort, the results were as follows : stand-
ing, 87; lying, 74; difference, 13. Different explanations of these variations
have been offered by physilogists ; but 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 bearing 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 imperfectly sup-
ported :

50 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

" 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 sup-
ported, 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 ; sup-
ported, 68 ; difference, 18 beats. An average of fifteen experiments of the
same kind on other healthy males gave the following numbers : back unsup-
ported, 80 ; supported, 68 ; a difference of 12 beats."

Influence of Exercise etc. — Muscular exertion increases 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. According to Bryan Robinson
(1734), 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 important influence of the
muscular system on the heart. »

The influence of sleep upon the action of the heart reduces itself almost
entirely to the proposition that during this condition, there is usually en-
tire 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 post-
ure. This fact obtains in the adult male ; but there is a marked difference
in females and young children, the pulse being always slower during sleep
(Quetelet).

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, examinations of the pulse
in disease. In cases which present considerable febrile movement, the pa-
tient is generally in the recumbent posture. The variations induced by vio-
lent exercise are easily recognized, while those dependent upon temperature,
the condition of the digestive system, etc., are so slight that they may prac-
tically be disregarded. It is necessary to bear in mind, however, the varia-
tions which exist in the sexes and at different periods of life, as well as the

INFLUENCE OF RESPIRATION UPON THE HEART. 51

possibility of individual peculiarities, when the action of the heart is extra-
ordinarily rapid or slow.

Influence of Respiration upon the Action of the Heart. — The relations be-
tween the circulation and respiration are very intimate and one process can
not 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. Circulation, also, is impossible if respiration be perma-
nently arrested. When respiration is imperfectly performed, the action of
the heart is slow and labored. The effects of arrest of respiration are marked
in all parts of the circulatory system, arteries, capillaries and veins ; but the
disturbances thus produced all react upon the heart.

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 conditions, res-
piration is entirely under control and the effects of its arrest upon the heart
can easily be studied. If respiration be interrupted, the following changes
in the action of the heart are observed : 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 disten-
tion 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 move-
ments of the mercury will be noted at each contraction of the heart, indi-
cating that the organ is acting with abnormal vigor. If respiration be still
interrupted, the engorgement becomes intense, the heart at each diastole
being distended to its utmost capacity. It now becomes incapable of empty-
ing 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 cease.

The arrest of the action of the heart, under these conditions, is chiefly
mechanical. The unaerated blood passes with difficulty through the capilla-
ries of the system, and as the heart is constantly at work, the arteries be-
come largely distended. This is shown by the great increase in the arterial
pressure while these vessels are full of black blood. If, now, the heart and
great vessels be closely examined, the order in which they become distended
is readily observed. These phenomena show that in asphyxia the obstruction
to the circulation begins, not in the lungs, as is commonly supposed, but in
the capillaries of the system, and is propagated backward to the heart
through the arteries (Dalton). The distention of the heart in asphyxia is
therefore due to the fact that unaerated blood can not circulate freely in the
systemic capillaries. When thus distended, the heart becomes paralyzed, like
any muscle after a severe strain.

52 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

If respiration be resumed before the heart's action has entirely ceased,
the organ in a few moments will resume its contractions. There is observed
first a change from the dusky hue it had 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. The arteries will then be found to contain red
blood. An instrument applied to an artery will show a diminution in ar-
terial pressure and in the force of the heart's action, if the arrest of respi-
ration 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 character 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 ex-
periments upon the warm-blooded animals. In the same way, also, it is pos-
sible 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. Examples
of animation restored by artificial respiration, in drowning etc., are evidence
of this fact. In cases of asphyxia, those measures by which artificial respira-
tion is most effectually maintained have been found most efficient.

CAUSE OF THE RHYTHMICAL CONTRACTIONS OF THE HEAKT.

The question of the actual cause of the rhythmical contractions of the
heart is one of great importance and has long engaged the attention of physi-
ologists. While researches have resulted in much positive information with
regard to influences which regulate or modify this action, there seems to be
little known, even now, concerning the main question, why the fibres of the
heart, unlike the ordinary muscular fibres, seem to contract spontaneously.

The heart in its structure resembles the voluntary muscles ; but it has a
constant office to perform and seems to act without any palpable excitation,
while the latter act only under the influence of a natural stimulus, like the
nervous impulse, or under artificial excitation. The movements of the heart
are not the only examples of what seems to be spontaneous action. The cili-
ated epithelium is in motion from the beginning to the end of life, and will
continue for a certain time, even after the cells are detached from the organ-
ism. This motion can not be explained, unless it be called an explanation to
say that it is dependent upon vital properties ; but if the actual cause of
the rhythmical contraction of the heart be unknown, physiologists are ac-
quainted with certain influences which render its action regular, powerful
and sufficient for the purposes of the economy.

The action of the heart is involuntary. Its pulsations can be neither
arrested, retarded nor accelerated by an effort of the will, excepting, of
course, examples of arrest by stoppage of respiration or acceleration by
violent muscular exercise etc. In this respect the heart differs from cer-
tain muscles, like the muscles of respiration, which act automatically, but
the movements of which may be temporarily arrested or accelerated by a

CAUSE OF THE CONTRACTIONS OF THE HEART. 53

direct voluntary effort. The last-mentioned fact illustrates the difference be-
tween the heart and all other striated muscles. All of them, in order to con-
tract, must receive a stimulus, either natural or artificial. The natural
stimulus comes from the nerve-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 stimula-
tion. Connection with the central 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 body. 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 contractility.

Erichsen, after exposing the heart in a warm-blooded animal and keeping
up artificial respiration, tied 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 twenty-three and a half minutes.
After the pulsations had ceased, they could be restored by removing the liga-
tures and allowing the blood to circulate again in the substance of the heart.

The regular and powerful contractions of the heart are promoted 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 electric current. For a certain time after the
heart has ceased to contract spontaneously, contractions may be produced
in this way. This can easily be demonstrated in the heart of any animal,
warm-blooded or cold-blooded. This excitability, which is manifested, under
these conditions, in 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 stimulation
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 an influence in exciting and keeping
up its contractions. This observation is important, as showing that the
presence of blood is necessary to the natural and regular action of the heart.
Schiff 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. Experiments upon alligators and turtles show that
when the heart is removed from the body and emptied of blood, the pul-
sations are feeble, rapid and irregular; but 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 pulsations were more frequent and not so powerful as
when blood was used (Flint, 1861). 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 its cavities, which may ex,-

54 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

plain its rapid and feeble action in certain cases of anaemia. The heart,
therefore, although capable of independent action, is excited to contraction
by the blood as it passes through its cavities. A glance at the succession 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 con-
tractions are produced. There is first a distention of the auricle, 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 con-
tact 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 simul-
taneously. The successive and 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 insures regular pulsa-
tions, so long as blood is supplied and no disturbing influences are in
operation.

The intermittent contraction and successive action of the fibres of the
heart, when the organ has been removed from the body, are dependent, to a
great extent, upon sympathetic ganglia situated near its base. If the
ventricle of a frog's heart be divided transversely at the upper third, the
lower two-thirds will no longer contract spontaneously, while the auricles
and the upper third of the ventricle continue to pulsate. If a stimulus be
then applied to the lower two-thirds of the ventricle, this is usually followed
by a single contraction, and not by a series of more or less regular pulsations.
It has been observed, also, that small, detached pieces of the auricles will
pulsate regularly for a time.

In the frog there are three ganglia closely connected with the heart ; one
at an expansion of the inferior vena cava just before it enters the auricle,
called the venous sinus (Remak), another between the left auricle and the
ventricle (Bidder), and a third between the two auricles (Ludwig). Accord-
ing to Robert Meade Smith, the first two ganglia communicate the motor
impulse to the muscular fibres of the heart. The third is the inhibitory
ganglion, and this regulates, through its action upon the motor ganglia, the
transmission of motor impulses. " As regards the manner in which these
ganglia produce the rhythmical contraction of the heart, little is known ;
but that they are the prime factors in producing not only the rhythm of
the cardiac revolutions, with its various modifications, but also the starting
point of each individual contraction, is one of the best established facts in
physiology."

In man and in most warm-blooded animals, collections of sympathetic
ganglia are found attached to the nerves at the line of junction of the
auricles with the ventricles.

Nearly all of the experiments just referred to were made upon the hearts
of cold-blooded animals, particularly the frog; but in all animals, under
normal conditions, the contractions of the heart seem to start from the
auricles. The fact, however, that the ventricles will contract regularly in a
living animal, after the excitability of the auricles has been exhausted by

CAUSE OF THE CONTRACTIONS OF THE HEART.

55

MO

repeated stimulations and they have ceased to pulsate, shows that the so-
called pulsating wave coming from the auricles is not absolutely essential to
the contraction of the ventricles.

Finally, in view especially of the results of experiments upon the cold-
blooded animals, it may be stated that the muscular fibres of the auricles
and of the upper third of the ventricles have the property of intermittent
and regular contraction, which is dependent, to a great extent, upon the
influence of the so-called motor ganglia of the heart ; and that the wave of
contraction is transmitted to the lower two-thirds of the ventricles, the fibres
of which do not seem to possess the property of independent contraction.
The muscular tissue of the heart, however, may be thrown into contraction
during diastole by the application of a stimulus, a property which is observed
in all musular fibres. The excitability 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 stimulus in a remarkable
degree and is even capable of restoring excitability after it has become
extinct. The passage of blood through the heart is the natural stimulus ot
the organ and is an important element in the
production of regular pulsations, although it by
no means endows the fibres with their contractile
properties.

Accelerator Nerves. — Experiments on the in-
fluence of the sympathetic nerves upon the heart
have not been entirely satisfactory. It has been
observed that the action of the heart is immedi-
ately arrested by destroying the cardiac plexus;
but with regard to this, the difficulty of making
the operation and the disturbance of the heart
consequent upon the necessary manipulations
must be taken into account. It has been shown,
however, that stimulation of the sympathetic in
the neck has the effect of accelerating the car-
diac movements.

According to Strieker, there exists in the me-
dulla oblongata a centre, stimulation of which in-
creases the rapidity of the heart's action ; and
from this centre, fibres descend in the substance of FIG. 22.— scheme of the course of

,-, -, -, ..-. ., . . the accelerans fibres (Stirling).

the spinal cord, pass out with the communicating p pons . M0 meduiia obionga-

branches of the lower cervical and upper dorsal ta ;>, inhibitory centre tor

nerves to the sympathetic, and go to the cardiac

plexus. In the cat, the accelerator fibres pass

through the first thoracic sympathetic ganglion.

Taking all precautions to eliminate the influence

of variations in the blood pressure, it has been shown that after division of

the pneumogastric, stimulation of the accelerator fibres increases the number

of beats of the heart. This action is direct and not reflex.

VAG.

ta; v,

the heart ; A, accelerans cen-
tre ; VAG., vagus ; SL, supe-
rior, IL, inferior laryngeal ;
sc, superior cardiac ; H,
heart ; c, cerebral impulse ;
s, cervical sympathetic; a, a,
accelerans fibres.

56 CIRCULATION OF THE BLOOD— ACTION OF THE HEAKT.

Direct, Inhibition of the Heart. — Division of the pneumogastric nerves
in the neck increases the frequency and diminishes the force of the contrac-
tions of the heart. To anticipate a little of the history of the pneumogastric
nerves, it may be stated that while they are exclusively sensory at their origin,
they receive, after having emerged from the cranial cavity, a number of fila-
ments from various motor nerves. That they influence certain muscles, is
shown by the paralysis of these muscles after division of the nerves in the
neck, as, for example, the arrest of the movements of the glottis.

A moderate Faradic current passed through both pneumogastrics arrests
the action of the heart in diastole (Ed. Weber). This observation has been
made upon living animals, both with and without exposure of the heart ;
and this kind of action is known as inhibitory, or restraining. Its nervous
mechanism is direct and not reflex ; and the inhibitory influence is conveyed
to the heart through filaments in the pneumogastric which are derived from
the spinal accessory.

It is said that direct stimulation of the medulla oblongata will have the
same effect upon the heart as stimulation of the pneumogastrics ; but it must
be very difficult to limit the stimulation to a particular point in the medulla
and to avoid conditions which would complicate such an experiment. A
sufficiently powerful stimulus applied to one pneumogastric will arrest the
cardiac pulsations, and in some animals the inhibitory action is confined to
the nerve of the right side. It is not known that any such difference between
the two nerves exists in the human subject, and certainly there is no marked
difference in most of the mammalia.

If both pneumogastrics be Faradized for two or three minutes, the con-
tractions of the heart return, even though the stimulation be continued, pro-
vided the current be not too powerful but of sufficient strength to promptly
arrest the pulsations. It is probable that this is due to the fact that the
excitability of the nerve after a time becomes exhausted by the prolonged
excitation, and its inhibitory influence is for the time destroyed.

Stimulation of the pneumogastrics in any part of their course is followed
by the usual inhibitory phenomena, and the same results sometimes follow
stimulation of the thoracic cardiac branches. It has also been observed that
when the heart's action has been arrested and the organ is quiescent in dias-
tole, direct mechanical stimulation of the heart is followed by a single con-
traction, showing that the excitability of the fibres has not been entirely
suspended.

After section of both pneumogastrics in the neck, digitalis fails to diminish
the number of beats of the heart (Traube) ; shoAving that separation of the
heart from its connections with the cerebro-spinal nerves removes the organ
from the characteristic and peculiar effects of the poison.

Feeble stimulation of one or both pneumogastrics, when it produces any
effect, almost always slows the action of the heart. In some animals, how-
ever, the pneumogastrics contain a few accelerator fibres, and feeble excita-
tion sometimes is followed by a slight increase in the rapidity of the cardiac
pulsations, but this is unusual.

INHIBITION OF THE HEAET. 57

Reflex Inhibition of the Heart. — Like most of the direct operations of
nerves that can be imitated by electric stimulation, the inhibitory action of
the pneumogastrics can be produced by reflex action. The action of the heart
may be arrested in the frog by sharply tapping the exposed intestines (Goltz).
The same effect has been produced by stimulation of the splanchnic nerves or
the cervical sympathetic. In some animals, if one pneumogastric be divided
in the neck, the other being left intact, stimulation of the central end of the
divided nerve will produce inhibition of the heart, by an action induced in
the undivided nerve. In all of these instances, the inhibition is reflex.
The stimulation is carried by the afferent fibres of the nerves stimulated, to
the inhibitory centre in the medulla oblongata, and is reflected to the heart
through the efferent fibres of the pneumogastric.

While moderate stimulation of ordinary sensory nerves is sometimes fol-
lowed by inhibition of the heart, very powerful stimulation arrests the cardio-
inhibitory action of the pneumogastrics, as well as certain other reflexes.

The inhibitory fibres of the pneumogastrics undoubtedly have an impor-
tant office in connection with the regulation of the rapidity and force of the
cardiac pulsations. It is important, of course, that the heart should act at
all times with nearly the same force and frequency. It has been seen that
the inherent properties of its fibres and the action, probably, of the cardiac
ganglia are competent to make it contract, and the necessary intermittent
dilatation of its cavities makes these contractions assume a certain regularity ;
but the quantity and density of the blood are subject to very considerable
variations within the limits of health, which, without some regulating influ-
ence, would undoubtedly cause variations in the heart's action, so considerable
as to be injurious. This is shown by the palpitating and irregular action of
the heart when the pneumogastrics have been divided. These nerves convey
to the heart a constant influence, which may be compared to the insensible
tonicity imparted to voluntary muscles by the general motor system. 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, without any effort
of the will, distort the features. An exaggeration of this force may be imitated
by a feeble Faradic current, which renders the pulsations of the heart less
frequent and more powerful, or it may be still farther exaggerated by a
more powerful current, which arrests the action of the heart. Phemonena
are not wanting in the human subject to verify these views. Causes which
operate through the nervous system 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 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 contractions,
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.

58 CIRCULATION OF THE BLOOD— ACTION OF THE HEART.

SUMMAEY OF CERTAIN CAUSES OF ARREST OF THE ACTION OF THE

HEART.

In warm-blooded animals, the heart's action speedily ceases after the organ
is deprived of its natural stimulus, the blood. Proof of this is not derived alone
from experiments on the inferior animals. It is well known that in profuse
haemorrhage in the human subject, the contractions of the heart are progress-
ively 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 asthenia ; and cases are on record
in which life has been prolonged, as in haemorrhage, by transfusion 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 is competent
of itself to arrest contractions of the heart. The experiments of Erichsen,
who paralyzed the heart by tying the coronary arteries, and of Schiff, who
produced a local paralysis by tying the vessel going to the right ventricle,
show that the action of 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 haemorrhage.

The mechanical causes of arrest of the heart's action are of considerable
pathological importance. The heart, in common with other muscles, may
be paralyzed by mechanical 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;
which is due to the fact that the heart is incapable of forcing the unaerated
blood through the systemic capillaries. The heart, in asphyxia, finally be-
comes enormously strained and distended and is consequently paralyzed.
The same result follows the application of a ligature to the aorta. This
effect may be produced also, in the cold-blooded animals, in which, if the
heart be left undisturbed, the pulsations will continue for a long time. The
following experiment illustrating this point was performed upon the heart of
a large alligator :

The animal was poisoned with curare, and twenty-eight hours after death
the 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 com-
parative force, etc., of the pulsations when empty and when filled with blood,
was filled with water, the valves having been destroyed so as to allow free
passage of the fluid through the cavities, and the vessels were tied. The
ventricles, still filled with water confined in their cavity, were then firmly
compressed with the hand. From that time, the heart entirely ceased its
contractions and became hard like a muscle in a state of cadaveric rigidity.

ARREST OF THE HEART'S ACTION. 59

This experiment shows how completely and promptly the heart, even of a
cold-blooded animal, may be arrested in its action by mechanical injury
(Flint, 1861).

Cases of death from engorgement of the heart are not unusual in prac-
tice ; and the form of organic disease* which most frequently leads to sudden
death is that in which the heart is liable to great distention. 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 suffoca-
tion which frequently follows a blow upon the epigastrium ; and a few cases
are on record of instantaneous death following a comparatively slight concus-
sion in this region. Although these cases are rare, they are well recognized,
and "the effects are generally attributed to injury of the solar plexus. The
distress is precisely what would occur from sudden arrest of the heart's ac-
tion. It is the blood charged with oxygen 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 com-
pletely as though the trachea were tied. It is a question whether the ar-
rest 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 it-
self. Present data do not afford a definite answer to this question, but they
sustain, to a certain extent, 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 what is known of the mode of operation of the sym-
pathetic 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 the results of experiments are concerned, the nervous influences
which arrest the action of the heart seem to operate through the pneumogas-
trics and are derived from the spinal accessory nerves. This action can be
closely imitated by electricity. The causes of arrest in this way are many and
varied. Among them may be mentioned, sudden and severe bodily pain and
severe mental emotions. With the exception of arrest of the heart's action
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 examples of the latter, though rare, are sufficiently well authenticated.

In an animal just killed, as the pulsations of the heart become slower and
slower until they are finally arrested, it is constantly observed that the auric-
ular appendage on the right side continues to contract for some time after
the other portions of the heart have ceased their action.

60 CIRCULATION OF THE BLOOD IN THE VESSELS.

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 sys-
tem— Depressor nerve — Influence of respiration on the arterial pressure — Rapidity of the current of blood
in the arteries — Rapidity in different parts of the arterial system — Circulation of the blood in the capil-
laries—Physiological anatomy of the capillaries— Pressure of blood in the capillaries— Relations of the
capillary circulation to respiration — Causes of the capillary circulation — Influence of temperature on the
capillary circulation — Influence of direct irritation on 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 — Uses
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 — Cir-
culation in the walls of the heart — Passage of the blood-corpuscles through the walls of the vessels (dia-
pedesis)— Rapidity of the circulation— Phenomena in the circulatory system after death.

IN" man and in all animals possessed of a double heart, each cardiac con-
traction forces a charge of blood from the right ventricle into the pulmo-
nary artery, and from the left ventricle into the aorta ; and 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 acceleration 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 cause of the arterial cir-
culation. The arteries have the important office of supplying nutritive mat-
ters to all the tissues and 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 spe-
cial functions; and the various physiological processes necessarily demand
considerable modifications in the quantity of arterial blood which is furnished
to parts at different times. The force of the heart, however, varies but little
within the limits of health ; and the conditions necessary to the proper distri-
bution of blood in the economy are regulated almost exclusively by the arte-
rial system. These vessels are endowed with elasticity, by which the circula-
tion is considerably facilitated, and with contractility, by which the supply to
any part may be modified, independently 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.

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 sys-
tem, except in the fact that their coats are somewhat thinner and more dis-
tensible. The aorta, branches and ramifications of which supply all parts of

PHYSIOLOGICAL ANATOMY OF THE ARTERIES. 61

the body, is given off from the left ventricle. Just at its origin, behind the
semilunar valves, the aorta has three sacculated pouches, called the sinuses of
Valsalva. Beyond this point the vessels are cylindrical. The arteries then
branch, divide and subdivide, until they are reduced to microscopic 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 supply with blood ; and while the branches progressively
diminish in size, but few are given off between the great trunk and small ves-
sels which empty into the capillary system. 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 many 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 fora-
men magnum. It has long been remarked that the combined caliber of the
branches of an arterial trunk is greater than that of the main vessel ; so that
the arterial system, as it branches, increases in capacity. A single exception
to this rule is in the instance of the common iliacs, the combined caliber of
which is less than the caliber of the abdominal aorta.

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
possible expenditure of force by the heart. Generally the vessels are so situ-
ated 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 inferior
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
there is 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 fibrous sheaths, of greater or less strength,
as the vessels are situated in parts more or less exposed to disturbing influ-
ences or accidents.

The arteries have three well defined coats. As these vary very consider-
ably 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 ^ to ^ of an inch (1-7 to
2-1 mm.) in diameter.

62 CIRCULATION OF THE BLOOD IN THE VESSELS.

The largest arteries are very strong and elastic. Their external coat is
composed of ordinary fibrous tissue, with a few longitudinal and oblique
fasciculi of non-striated 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 that is vascular.

The middle coat, on which the thickness of the walls of the vessel de-
pends, is composed chiefly of yellow elastic tissue. This tissue is disposed in
a number of layers. Externally there is a thin layer of ramifying elastic
fibres, and then a number of layers of elastic membrane, with oval, longitudi-
nal openings, an arrangement which has given it the name of the " fenes-
trated membrane." Between the different layers of this membrane are found
a few non-striated muscular fibres. These muscular fibres, however, are not
abundant and have but little physiological importance. A small portion of
the aorta and pulmonary artery near the heart is entirely free from mus-
cular fibres. In the largest arteries the fibres are arranged in fasciculi, with
amorphous and fibrous connective tissue running in circular, longitudinal
and oblique directions. The longitudinal and oblique fibres exist chiefly in
the outer coat.

The internal coat of the largest arteries does not differ materially from
the lining membrane of the rest of the arterial system. It is nearly identical
in structure with the endocardium and is continued throughout the vascular
system. It is a thin, homogeneous, elastic membrane, covered with a layer
of elongated cells of endothelium, with oval nuclei, the long diameter of the
cells and nuclei following the direction of the vessel. Between the endo-
thelial cells, is an amorphous cement-substance, which is rendered dark by a
solution of silver nitrate, so that this reagent clearly defines their borders.

The arteries of medium size possess considerable strength, some elasticity
and very great contractility. In the outer and inner coats there is no great
difference between these and the largest arteries, even in thickness. The
essential difference in the anatomy of these vessels is found in the middle
coat. Here there is a continuation of the elastic elements found in the
largest vessels, but relatively diminished in thickness and mingled with the
fusiform, non-striated muscular fibres arranged nearly always 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 primi-
tive iliacs. In arteries of medium size, like the femoral, prof unda femoris,
radial or ulnar, the muscular fibres exist in several layers. There is no dis-
tinct division, as regards the middle coat, between the largest arteries and
those of medium size. As the arteries branch, muscular fibres make their
appearance between the elastic layers, progressively increasing in quantity,
while the elastic elements, are diminished in their relative proportion.

In the smallest arteries, the external coat is thin and disappears just be-
fore the vessels empty into the capillary system ; so that the very smallest
arterioles have only the inner coat and a layer of muscular fibres. Although
most of the muscular fibres in the middle coat of the arteries are arranged

PHYSIOLOGICAL ANATOMY OF THE ARTERIES.

63

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,

FIG. 23.— Small artery from the mesentery of the frog, showing endothelium and circular muscular
fibres; magnified 500 diameters (from a photograph taken at the United States Army Medical
Museum).

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 ad-
mixture of elastic elements. In vessels -^ of an inch (254 p) in diameter,
there are two or three layers of fibres ; but nearer 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 endothelium is rather less distinctly
marked.

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

Nervous filaments accompany the arteries, in all probability, to their re-
motest ramifications. These are not distributed in the walls of the large
vessels, but follow them in their course, their filaments of distribution being

64: CIRCULATION OF THE BLOOD IN THE VESSELS.

found in those vessels in which the muscular element of the middle coat pre-
dominates. The vaso-motor nerves, as they are called, play an important
part in regulating the processes of nutrition.

Course of the Blood in the Arteries. — With every pulsation of the heart,
all the blood contained in the ventricles, excepting perhaps a few drops, is
forced into the great vessels. The valvular arrangement by which the blood,
once forced into these vessels, is prevented from returning into the ventricles
during their diastole, has already been described. The foregoing sketch of the
anatomy of the arteries indicates a complexity of phenomena in the circula-
tion 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 modifi-
cations 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 is particularly marked in the
largest vessels. If the aorta be forcibly distended with water, it may be di-
lated to more than double its ordinary capacity and will resume its original
size and form as soon as the pressure is retaoved, its elasticity being absolutely
perfect. This simple experiment shows 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 has been shown by direct
experiments ; although the immense capacity of the arterial system, as com-
pared with the small charge of blood which enters at each pulsation, renders
the actual distention of the vessels less than would be expected from the force
of the heart's contraction.

Division of an artery in a living animal illustrates one of the important
phenomena due to the elastic and yielding character of its walls. It is ob-
served, even in vessels of considerable size, as the carotid or femoral, that the
flow of blood is not intermittent but remittent. With each ventricular sys-
tole there is a sudden and marked impulse ; but during the intervals of con-
traction, the blood continues to flow with considerable force. In the smaller
vessels, 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 experiment : If the heart be exposed in a living animal, and a
canula be introduced through the walls into one of the ventricles, there is a
powerful jet at each systole, but no blood is discharged during the diastole.
The same absolute intermittency of the current is observed in the aorta near
the heart. The conversion of the intermittent current in the largest vessels
into a nearly constant flow in the smallest arterioles is effected by the physical

CIRCULATION IN THE ARTERIES. 65

property of elasticity ; and the intermittent impulse may be said to be pro-
gressively absorbed by the elastic walls of the vessels. This modification of
the impulse of the heart has great physiological importance ; for it is evi-
dently essential that the current of blood, as it flows into the delicate capil-
lary vessels, should not be alternately intermitted and impelled with the full
power of the ventricle.

The elasticity of the arteries favors the flow of blood toward the capillaries
by a mechanism that 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 the effect of forcing the blood in two directions, were it not for closure
of the valves, which renders regurgitation into the heart impossible. The
influence, then, can be exerted only in the direction of the periphery. It is
evident, therefore, that in vessels removed a sufficient distance from the heart,
the force exerted on the blood by the reaction of the elastic walls is compe-
tent to produce a very considerable current during the intervals of the heart's
action.

Contractility of the, Arteries. — The medium-sized and smallest arteries
contain non-striated muscular fibres ; and it has been shown that as a con-
sequence of the condition of these fibres, the vessels undergo considerable
variations in their caliber. These changes in the size of the arteries can be
produced by stimulation or section of, the vaso-motor nerves. If the sympa-
thetic be divided in the neck of a rabbit, the arteries of the ear on that side
soon become dilated. If the divided extremity of the nerve be stimulated,
the vessels contract and may become smaller than on the opposite side.
These experiments demonstrate the contractile properties of the small arteries
and give an idea how the supply of blood to any particular part may be regu-
lated. The- contractility of the arteries has great physiological importance.
As their office is simply to supply blood to the various tissues and organs, ?t
is evident that when the vessels going to any particular part are dilated, the
supply of blood is necessarily increased. This is particularly well marked in
the glands, which, during the intervals of secretion, receive a comparatively
small quantity of blood. 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 emo-
tions are examples of the same kind of action.

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 erroneous ; and it is hardly necessary to repeat the statement that
the cause of the arterial circulation is the force of the left ventricle. It has
been observed, however, that the arteries in the ear and certain other parts
in the rabbit undergo rhythmical contractions and dilatations, these occur-
ring ten or twelve times per minute (Schiff/ Loven, Vulpian) ; but these
movements are not to be regarded as a contributing force in the production
of the circulation. It is evident, on the othei hand, that the elasticity of the
arteries must actually assist the circulation. The resiliency of the vessels is

66 CIRCULATION OF THE BLOOD IN THE VESSELS.

continually pressing their contents toward the periphery ; the dilatation of
the vessels with each systole of course admits an increased quantity of blood ;
and it has been shown that the same intermittent force exerted on an inelas-
tic tube will discharge a less quantity of liquid from openings of equal
caliber.

Superadded, then, to the direct action of the heart, physiologists now rec-
ognize, as a cause influencing the flow of blood in the arteries, the resiliency of
the vessels, especially of those of large size, this force being derived originally
from the heart. Thus it will be seen that 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 power-
ful contractions of the central organ serve only to keep up an equable current
in the capillaries. The small vessels, by the action of their contractile walls,
regulate the local circulations.

Locomotion of the Arteries and Production of the Pulse, — With each
contraction of the heart, the arteries are increased in length and many of
them undergo a considerable locomotion. 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 observed by
watching attentively the point where an artery bifurcates, as at the division
of the common carotid. It is simply the mechanical effect of sudden disten-
tion, 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 sur-
face experiences 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 cer-
tain degree of obstruction, as in the radial, which can readily be compressed
against the bone. In an artery imbedded in soft parts which yield to press-
ure, 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 after tying
a vessel, the pulsation above the point of ligature is very marked and can be
readily appreciated by the eye. The explanation of this exaggeration of the
movement is the following : Normally, the blood passes freely through the
arteries and produces, in the smaller vessels, very little movement or dilata-
tion ; when, however, the current is obstructed, as by ligation or even com-
pression 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 incom-
pressible from calcareous deposits, the pulse can not be felt. The character
of the pulse indicates, to a certain extent, the condition of the heart and
vessels.

Under ordinary conditions, the pulse may be felt in all arteries that are
exposed 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 impulse given to the blood by the heart, however, is not felt

PRODUCTION OF THE PULSE. 67

in all the vessels at the same instant. Marey registered simultaneously the
impulse of the heart, the pulse of the aorta and the pulse of the femoral
artery, and ascertained 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 confirmed the views of
other physiologists, particularly Weber, who described this progressive retar-
dation of the pulse, 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 is known 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 charac-
ters of the pulse must be subject to great variations. Many of these may be
appreciated simply by the sense of touch. Writers treat of the soft and com-
pressible pulse, the hard pulse, the wiry pulse, the thready pulse etc., as indi-
cating various conditions of the circulatory system. The character of the
pulse, aside from its frequency, has always been regarded as of great impor-
tance in disease.

Form of the Pulse. — It is evident that few of the characters of a pulsa-
tion, 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, instruments for registering the
pulse have been constructed, with the view of analyzing 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,

FIG. 24.—Sphygmograph 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 surface 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.

with one knee over the other, the beating of the popliteal artery will
produce marked movements of the foot. If a lever provided with a mark-
ing-point in contact with a slip of paper moving at a definite rate could be
applied to an artery, the point of the lever would register the movements of

68

CIRCULATION OF THE BLOOD IN THE VESSELS.

the vessel and its changes in caliber. The first physiologist who put this in
practice was Vierordt, who constructed quite a complex instrument, so

FIG. 25.— Sphygmograph of Marey applied to the arm.

arranged that the impulse from an accessible artery, like the radial, was
conveyed to a lever, which marked the movement upon a revolving cylin-
der of paper. This instrument was called a sphygmograph. The traces
made by it were perfectly regular and simply marked the extremes of dilata-
tion — exaggerated, of
course, by the length of
the lever — and the num-
ber of pulsations in a giv-
en time. The latter can
be easily estimated by
more simple means; and
as the former did not con-
vey any very definite physiological idea, the apparatus was regarded rather
as a curiosity than an instrument for accurate research.

The principle on which the instrument of Vierordt was constructed was
correct; and it remained only to devise one which would be easy of ap-

FIG. 26.— Trace of Vierordt.

FIG. 27.— Trace of Marey.
Portions of four traces taken in different conditions of the pulse.

plication and produce a trace representing the shades of dilatation and
contraction of the vessels, in order to lead to important practical results.
These conditions are realized in the sphygmographs now in use, which differ
from each other mainly in the convenience with which they are applied,
the principle of all being substantially that of the sphygmograph of Marey,
which is shown in Figs. 24 and 25. The modern sphygmographs simply
amplify the changes in the caliber of the artery incident to the pulse ; and
although their application is, perhaps, not so easy as to make these instru-
ments generally useful in the practice of medicine, in the hands of Marey
and other physiologists, they have led to a definite knowledge of the
physiological characters of the pulse and its modifications in certain diseases,
information which could hardly be arrived at by other means of investigation.

PRODUCTION OF THE PULSE. 69

In short, their mechanism is so accurate, that when skillfully used, they give
on paper the actual "form of the pulse." The modern instruments,
applied to the radial artery, give traces very different from those obtained
by Vierordt, which were simply series of regular elevations and depressions.
A comparison of these with the traces obtained by Vierordt gives an idea of
the defects which have been remedied by Marey ; for it is evident that the
dilatation and contraction of the arteries can not be so regular and simple
as would be inferred merely from the trace made by the instrument of
Vierordt.

Analyzing the traces taken by Marey, it is seen 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 comparatively 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 degree 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 condition 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 diminishes 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 manifesta-
tion of dicrotism is diminished tension, which is always found co-existing
with a very marked exhibition of this phenomenon.

Marey accurately determined and registered these various phenomena, by

70 CIKCULATION OF THE BLOOD IN THE VESSELS.

observations on the arteries of the human subject and the lower animals ; and
by means of a " schema" representing the arterial system by elastic tubes
and the left ventricle by an elastic bag provided with valves and acting as a
syringe, he established the conditions of tension etc., necessary to their pro-
duction. 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 when the tubes 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 con-
tractions of the heart. This can only occur in a fluid which has a cer-
tain weight and acquires a velocity from the impulse ; for when air was
introduced into the apparatus, dicrotism could not be produced under any
conditions, as the fluid did not possess weight enough to oscillate between
the impulses. Water produced a well marked dicrotic impulse under favor-
able 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 of the arteries, it will be use-
ful to 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 degree of contraction. This contraction
is antagonistic to the distending force of the blood, as is shown by opening
a portion of an artery included between two ligatures in a living animal,
when the contents will be forcibly discharged and the caliber of that
portion of the vessel be 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
to the pulse the characters 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 conditions, 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

PRESSURE OF BLOOD IN THE ARTERIES. 71

more wiry character. As a rule, prolonged contraction of the arteries is fol-
lowed 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.

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 degree of pressure, by which the
blood is continually 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 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 ani-
mal, ascertained the height of the 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 eight to ten feet (243 to 304 centi-
metres).

If a large artery, like the carotid, be exposed in a living animal, and a
metallic point, connected with a vertical tube of smaller caliber and seven or
eight feet (213 or 243 centimetres) long by a bit of elastic tubing, be secured
in the vessel, the blood will rise to the height of about six feet (183 centi-
metres) 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 corre-
sponds with the movements of respiration. The pressure, as indicated by an
elevation of the fluid, is slightly increased during expiration and diminished
during inspiration. In such experiments, it is necessary to fill part of the
tube, or whatever apparatus be used, with a solution of sodium carbonate, in
order to prevent coagulation of the blood as it passes out of the vessels.

The experiment with the long tube gives, perhaps, the best general idea
of the arterial pressure, which will be found to vary between five and a half
and six feet of blood (170 and 183 centimetres), or a few inches more of
water. The oscillations 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 animals 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

CIRCULATION OF THE BLOOD IN THE VESSELS.

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 modifications and
variations of the arterial pressure. It is only since the experiments
performed by Poiseuille with the haemadynamometer, in 1828, that
physiologists have had any reliable data on this latter point. Poi-
seuille'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 is generally considered as possessing great advan-
tages 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 dis-
advantage, 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
e c which -would actually represent the alter-

nation of systole and diastole of the heart.
An important improvement in the
haemadynamometer was made by Magen-
die. This apparatus, the cardiometer, in
which Bernard made some important mod-
ifications, is the one now generally used.
It consists of a small but thick- glass bot-
tle, with a fine, graduated glass tube about
twelve inches (30*5 centimetres) 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 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, some of the inconveniences which are due to the weight of mercury
in the haemadynamometer are avoided, and there is, also, less friction.
This instrument is appropriately called the cardiometer, as it indicates most
accurately, by the extreme elevation of the mercury, the force of the heart ;
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 im-
petus causes the level to fall below the real standard of the constant pressure,
Marey has corrected this difficulty in the " compensating " instrument, which

FIG. 28.— Section of the cardiometer of
Magendie, 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 graudated glass
tube T', which has a caliber of TV to
f of an inch (2'1 to 3'2 mm.). The bottle
is filled with mercury m, until it rises
to n' in the tube, which is marked zero.
The cork is perforated by the tube t,
which is connected by a rubber tube e
with the point C, which is introduced
into the vessel.

PRESSURE OF BLOOD IN THE ARTERIES.

T3

is constructed on the following principle : Instead of a simple glass tube
which communicates with the mercury in the bottle, as in Magendie's
cardiometer, there are 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 its caliber, which
is here reduced to capillary fine-
ness. The latter tube is de-
signed to give the mean arterial
pressure ; the constricted portion
offering such an obstacle to the
rise of the mercury that the in-
termittent action of the heart is
not felt, the mercury rising slow-
ly to a certain level, which is
constant and varies only with
the constant pressure in the ves-
sels.

Physiologists have only an
approximate idea of the arte-
rial pressure in the human sub-
ject, derived from experiments
on the inferior animals. It has
already been stated to be equal
to about six feet (183 centime-
tres) of water or six inches (150
mm.) of mercury.

Pressure in Different Arteries. — The experiments of Hales, Poiseuille,
Bernard and others, seem to show that the constant arterial pressure does
not vary much in arteries of different sizes. These physiologists experi-
mented particularly on the carotid and crural, and found the pressure in
these two vessels about the same. From their experiments they concluded
that the force is equal in all parts of the arterial system. The experiments
of Volkmann, however, have shown that this conclusion is not correct. With
the registering apparatus of Ludwig, he took the pressure in the carotid
and the metatarsal arteries and always found a considerable difference in
favor of the former. In an experiment on a dog, he found the pressure
equal to about seven inches (172 mm.) in the carotid, and 6-6 inches (165
mm.) in the metatarsal. In an experiment on a calf, the pressure was 4-64
inches (116 mm.) in the carotid, and 3-56 inches (89 mm.) in the meta-
tarsal ; and in a rabbit, 3'64 inches (91 mm.) in the carotid, and 3'44 inches
(86 mm.) in the crural. These experiments show that the pressure is not ab-
solutely the same in all parts of the arterial system, that it is greatest in the

FIG. 29.— Compensating instrument of Marey.

74 CIRCULATION OF THE BLOOD IN THE VESSELS.

arteries nearest the heart, and that it gradually diminishes toward the capil-
laries. The difference is very slight, almost inappreciable, except in vessels
of very small size ; but here the pressure is directly influenced by the dis-
charge of blood into the capillaries. The cause of this diminution of press-
ure in the smallest vessels is the proximity of the great outlet of the arteries,
the capillary system ; for, as will be seen farther on, the flow into the capilla-
ries has a constant tendency to diminish the pressure in the arteries.

Influence of Respiration. — It is easy to see in studying the arterial press-
ure, that there is a marked increase with expiration and a diminution with
inspiration. 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 ex-
pelled 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 expi-
ration, in the jet from a divided artery. Under these conditions the ar-
terial pressure is at its maximum. In perfectly tranquil respiration, the
changes due to inspiration and expiration are slight, presenting a difference
of not more than half an inch or an inch (12-7 or 25-4 mm.) in the cardi-
ometer. 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 ar-
terial pressure. This is due, not to causes within the chest, but to obstruction
to the circulation in the capillaries. With an interruption of the respiratory
movements, the non-aerated blood passes into the arteries but can not flow
readily through the capillaries, and as a consequence, the arteries are abnor-
mally distended and the pressure is greatly increased. If respiration be per-
manently arrested, the arterial pressure becomes, after a time, diminished be-
low the normal standard, and is finally abolished on account of the stoppage
of the action of the heart. If respiration be resumed before the action of
the heart has become arrested, the pressure soon returns to its normal
standard.

Influence of Muscular Action etc. — Muscular effort considerably increases
the arterial pressure. This is due to two causes. In the first place, the
chest is generally compressed, and this favors the flow of blood into the great
vessels. In the second place, muscular exertion produces a certain degree of
obstruction to the discharge of blood from the arteries into the capillaries.
Experiments upon the inferior animals show a great increase in pressure in
the struggles which occur during severe operations. It has been shown that
stimulation of the sympathetic in the neck and of certain of the cerebro-spi-
nal nerves increases the arterial pressure, probably from an influence on the

PEESSUEE OF BLOOD IN THE AETEEIES. 75

muscular coats of some of the arteries, causing them to contract and thereby
diminishing the total capacity of the arterial system.

Effects of Haemorrhage etc. — Diminution in the quantity of blood has a
remarkable effect upon the arterial pressure. If, in connecting the instru-
ment with the arteries, even one or two jets of blood be allowed to escape, the
pressure will be found diminished perhaps 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 remarkable how soon the pressure in
the arteries regains its normal standard after it has been lowered by haemor-
rhage. 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 con-
tractions of the heart. In the cardiometer, the mean height of the mercury
indicates the constant, or arterial pressure ; and the oscillations, the disten-
tion 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 in-
dicated by the cardiometer, bears an inverse ratio to the frequency of its pul-
sations.

Depressor Nerve of the Circulation. — Cyon and Ludwig have described
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. In man the
depressor nerve is not isolated, but its fibres are contained in the sheath of
the pneumogastric. This nerve has a reflex action, as was shown by the ex-
periments of Cyon, its Faradization reducing the arterial pressure by one-
third or one-half. This action is known to be reflex, for when the nerve is
divided, stimulation of the central end affects the arterial 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 ner-
vous influence is exerted over the heart. It is thought that the reduction in
the arterial pressure following stimulation of the so-called depressor nerves
is due mainly 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 stimulated. If, after division of the splanchnic nerves and the conse-
quent diminution of the arterial pressure, the depressor nerves be stimulated,
the pressure still undergoes some additional diminution, but this is much less

CIRCULATION OF THE BLOOD IN THE VESSELS.

than the diminution which follows stimulation of the depressor nerves with-
without section of the splanchnics.

Rapidity of the Current of Blood in the Arteries. — The question of the
rapidity of the arterial circulation has long engaged the attention of physiol-
ogists ; but the experiments of Volkmann, with his hsemadrometer, and of
Vierordt, with a peculiar instrument which he devised for the purpose, did
not lead to results that were entirely reliable. The apparatus devised by
Ohauveau, however, is much more satisfactory. This will give, by calcula-
tion, the actual rapidity of the circulation, and it also indicates the 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
(38*1 mm.) in length and of the di-
ameter of the artery (about three-
eighths of an inch, or 9-5 mm.),
which is provided with an oblong,
longitudinal opening, or window,
near the middle, about two lines
(4'2 mm.) long and one line (2*1
mm.) wide. A piece of thin, vul-
canized rubber is wound around
the tube and firmly tied so as to
cover this opening. Through a
transverse slit in the rubber, is in-
troduced a very light, metallic nee-
dle, an inch and a half (38-1 mm.)
in length and flattened at its lower
part. This is made to project about

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 into the carotid of a horse, by making a slit in
the vessel, introducing first one end of the tube directed toward the 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 so 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 withdrawing
the instrument, it is applied to a tube of the size of the artery, in which a
current ol water is made to pass with a rapidity which will produce the same

FIG. 30. — Chauveau's instrument for measuring the
rapidity of the flow of blood in the arteries.

The instrument viewed in face— a, the tube to be fixed half-WaV into the Caliber of
in the vessel ; 6, the dial which marks the extent
of movement of the needle d ; e, a lateral tube for
the attachment of a cardiometer, if desired.

RAPIDITY OF THE FLOW IN THE ARTEEIES. 77

deviations as occurred when the instrument was connected with the blood-
vessel. The rapidity 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 the rapidity of the current
of blood is ascertained. This instrument is made on the same principle as
the one constructed by Vierordt, but in sensitiveness and accuracy it is
much superior.

Rapidity of the Current in the Carotid. — It has been found that three
currents, with different degrees of rapidity, may be distinguished in the ca-
rotid :

1. At each ventricular systole, as the average of the experiments of Chau-
veau, the blood moves in the carotids at the rate of about 20-4 inches (510
mm.) per second. After this, the rapidity quickly diminishes and the needle
returns quite or nearly to zero, which would indicate complete arrest.

2. Immediately succeeding the ventricular systole, a second impulse is
given to the blood, which is synchronous with the closure of the semilunar
valves, the blood moving at the rate of about 8*6 inches (215 mm.) per sec-
ond. This is the dicrotic impulse.

3. After the dicrotic impulse, the rapidity of the current gradually dimin-
ishes until just before the systole of the heart, when the needle is nearly at
zero. The average rate, after the dicrotic impulse, is about 5'9 inches (147*5
mm.) per second.

The experiments of Chauveau correspond 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 present a second, or dicrotic distention, much
less than the first ; and following this, there is a gradual decline in the disten-
tion until the minimum is reached. According to the observations of Chau-
veau, 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, there is a gradual decline in the rapidity, to the time of
the next pulsation.

Rapidity in Different Parts of the Arterial System. — From the fact that
the arterial system progressively increases in capacity, there should be found
a corresponding diminution in the rapidity of the flow of blood. There are,
however, many conditions, aside from simple increase in the capacity of
the vessels, which modify the blood-current and render inexact any calcula-
tions made upon purely physical principles. There 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. Volkmann found a great difference in the
rapidity of the current in the carotid and metatarsal arteries, the averages
being about 10 inches (254 mm.) per second in the carotid, and about 22
inches (56 mm.) in the metatarsal. The same difference, although not quite
7

78

CIRCULATION OF THE BLOOD IN THE VESSELS.

so marked, was found by Chauveau, between the carotid and the facial. The
last-named observer also noted an important modification in the character of
the current in the smaller vessels. As the vessels are farther and farther re-
moved from the heart, the systolic 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 much increased in
rapidity. This fact coincides with the ideas already advanced with regard to
the gradual conversion, by reason of the elasticity of the vessels, of the im-
pulse 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 modifi-
cations due 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 increased. Thus the rapidity bears a relation to
the arterial pressure ; as variations in the pressure depend chiefly on causes
which facilitate or retard the flow of blood into the capillaries. A good ex-
ample 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 a great increase in
the rapidity of the flow in the carotid of a horse during mastication. It must
be remembered that in all parts of the arterial system, the rapidity of the cur-
rent 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, it should be
distinctly stated what is meant by capillary vessels as distinguished from the
smallest arteries and veins. From a strictly physiological point of view, the

capillaries are to be regarded as
beginning at the situation where
the blood is brought near enough
to the tissues to enable them to
separate the matters necessary
for their regeneration and to
give up the products of their
physiological wear ; but at pres-
ent it is impossible to assign
any limit where the vessels cease
to be simple carriers of blood,
and it is not known to what
part of the vascular system the
processes of nutrition are exclu-
sively confined. The divisions
of the blood-vessels must be, to

FIG. 31.— Capillary blood-vessels (L&ndois). . '

The boundaries of the cells (cement-substance between the & Certain extent, arbitrarily de-

endothelium) is blackened with silver nitrate. The nu- n -i mu 4- '™^1^ «™ A

clei of the endothelium are brought out by staining. lined. Ihe most Simple, ana

PHYSIOLOGICAL ANATOMY OF THE CAPILLARIES. 79

what seems to be the most physiological view, is to regard as capillaries those
vessels which have but a single coat ; 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 the vessels 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 dimin-
ishing in size as they branch, and their coats, especially the muscular coat,
becoming thinner and thinner, until at last they present an internal, struct-
ureless coat lined by endothelium 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 bundles of fibrous tis-
sue. These vessels are ^ to -%fo of an inch (62-5 to 125 /*) in diameter.
They become smaller as they branch, and undoubtedly possess the property
of contractility, which is particularly marked in the arterial system. Follow-
ing the course of the vessels, when they are reduced in size to about -g^ of
an inch (31 ft), the external, fibrous coat is lost, and the vessel then presents
only the internal coat and a single layer of muscular fibres. The vessels
become smaller as they branch, finally lose the muscular fibres, and have then
but a single coat. These last will be regarded as the true capillary vessels.

It was formerly thought that the smallest vessels, which are described as
the true capillaries, were composed of a single, homogeneous membrane,
Friinr to ^-§Vo °f an incn (1 to 10 ft) thick, with nuclei embedded in its
substance, but not provided with an endothelial lining; but it has been
shown that the membrane is homogeneous, elastic, perhaps contractile, and,
in some parts at least, provided with fusiform or polygonal endothelium of ex-
cessive tenuity. The borders of the endothelial cells may be seen after stain-
ing the vessels with silver nitrate. 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 in the walls of the vessels
belong to this layer of endothelium. By the same process of staining with
, silver nitrate, irregular, non-nucleated areas are frequently brought into view ;
and it has been supposed by some that these indicate the presence of
stomata, or orifices in the walls of the vessels.

The diameter of the capillaries is generally as small as that of the blood-
corpuscles, or it may be smaller ; so that these bodies always move in a single
line and must become deformed in passing through the smallest vessels,
recovering their normal shape, however, when they pass into vessels of larger
size. The capillaries are smallest in the nervous and muscular tissue, retina
and patches of Peyer, where they have a diameter of -^-$ to ^oW °^ an
inch (4-25 to 6-25 ft). In the papillary layer of the skin and in the mucous
membranes, they are ^gVrr to ^OT of an incn (6 '25 to 10 ft) in diameter.

80

CIRCULATION OF THE BLOOD IN THE VESSELS.

They are largest in the glands and bones, where they are ^oW to
of an inch (8*3 to 12*5 //,) in diameter. These measurements indicate the
size of the vessels and not their caliber. Taking out the thickness of their
walls, it is only the very largest of them that will allow the passage of a
blood-disk without a change in its form. The average length of the capil-
lary vessels is about -fa of an inch (0-5 mm.).

FIG. 32. — Small artery and capillaries from the muscular coats 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 endothelium of the vessels. It is injected with silver nitrate, stained with

carmine and mounted in Canada balsam.

Unlike the arteries, which grow smaller as they branch, and the veins,
which become larger, in following the course of the blood, by union with
each other, the capillaries form a true plexus of vessels of nearly uniform
diameter, branching and inosculating in every direction and distributing
blood to the. parts as their physiological necessities 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. Although
their arrangement presents certain differences in different organs, the capil-
lary vessels have everywhere the same general characteristics, the. most promi-
nent of which are the nearly uniform diameter and an absence of any definite
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 distended with

PHYSIOLOGICAL ANATOMY OF THE CAPILLARIES.

81

blood only during the physiological activity of these parts. In the lungs the
meshes are particularly close. In other parts the vessels are not so abun-
dant, presenting great variations in different tissues. In the muscles and
nerves, in which nutrition is very active, the supply is much more abundant
than in other parts, like fibro-serous membranes, tendons etc. In none of
the tissues do the capillaries penetrate the anatomical elements of the part,
as the ultimate muscular or nervous fibres. Some tissues receive no blood, or
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 capacity of the capillary system is very great. It is necessary only to
consider the great vascularity of the skin, mucous membranes or muscles, to
appreciate this fact. In injections of these parts, it seems, on microscopical
examination, as though they contained nothing but capillaries ; but in prepa-
rations of this kind, the elastic and yielding coats of the capillaries are
distended to their utmost limit. Under some conditions, in health, they
are largely distended with blood, as in the mucous lining of the alimentary
canal during digestion, the whole surface presenting a vivid-red color, indi-
cating the great richness of the capillary plexus. Estimates of the capacity
of the capillary system, as compared with the arterial system, have been
made, but they are simply approximative. The various estimates given are
founded upon calculations from microscopical examinations of the rapidity
of the capillary circulation as compared with the circulation in the arteries.
In this way, it ^mmm^mm^^: b

has been estima-
ted that the ca-
pacity of the
capillary system
is between five
hundred and
eight hundred
times that of the
arterial system.
These estimates,
however, must
be regarded as
mere supposi-
tions based up-
on no very ac-
curate data.

Phenomena of the Capillary Circulation. — The most convenient situation
for observation 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 circulation in the smallest arteries and veins, the variations
in caliber of these vessels, especially the arterioles, by the action of their

FIG. 33.-

- Web of the frog's hind-foot ; magnified (Wagner),
a, a, veins ; 6, 6, &, arteries.

CIRCULATION OF THE BLOOD IN THE VESSELS.

muscular coat, and, indeed, the action of vessels of considerable size. This
has been a 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 any definite idea of the action of these vessels.

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.

In vessels of consid-
erable size as well as in
some capillaries, the cor-
puscles, occupying the
central portion, move
with much greater ra-
pidity than the rest of
the blood, leaving a lay-
er of clear plasma at
the sides, which is near-
ly motionless. This
phenomenon is in obe-
dience to a physical
law regulating the pas-
sage of liquids through
capillary tubes for which they have an attraction, such as exists, for exam-
ple, between the blood and the vessels. In tubes reduced to a diameter ap-
proximating that of the capillaries, the attractive force exerted by their walls
upon a liquid, causing it to enter the tube to a certain distance, 'becomes an
obstacle to the passage of fluid in obedience to pressure. Of course, as the
diameter of the tube is reduced, this force becomes relatively increased, for
a larger proportion of the liquid contents is brought in contact with it. In
the smallest arteries and veins, and still more in the capillaries, the capillary
attraction is sufficient to produce the motionless layer, sometimes called the
" still layer," and the liquid moves only in the central portion. The plasma
occupies the position next the walls of the vessels, for it is this portiSn of the
blood which is capable of " wetting " the tubes. The transparent layer was
observed by Malpighi, Haller and all who have described the capillary circu-
lation. Poiseuille recognized its true relation to the blood-current and ex-
plained the phenomenon of the still layer by physical laws, which had been
previously established with regard to the flow of liquids in tubes of the di-
ameter of one twenty-fifth to one one-eighth of an inch (1 to 3'2 mm.), but
which he had succeeded in applying to tubes of the size of the capillaries.

FIG. 34.— Circulation in the web of the frog's foot (Wagner).
The black spots, some of them star-shaped, are collections of pigme
a, a venous trunk, composed of three principal branches (&, 6,
and covered with a plexus of smaller vessels (c, c).

ent.

CIRCULATION IN THE CAPILLARIES. 83

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,

FIG. 35. — Small artery and capillaries from the lung of a frog ; magnified 500 diameters (from a
photograph taken at the United States Army Medical Museum).

until it is taken up again and carried along with the central current. A few
leucocytes are constantly 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 examining a drop of blood
between glass surfaces, the red corpuscles moving about freely, while the
white corpuscles have a tendency to adhere to the glass.

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 movement 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 thQ
heart. In both the arteries and veins the current is frequently so rapid

84 CIRCULATION OF THE BLOOD IN THE VESSELS.

that the form of the corpuscles can not be distinguished. Only a few of
the white corpuscles occupy the still layer, the others 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 rowT of corpuscles. 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. When
the circulation is normal, the movement in the capillaries is always quite
slow as compared with the movement 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 that are in the field of view.
Certain vessels may not receive a corpuscle for some time, but afterward,
one or two corpuscles become engaged in them and a current is estab-
lished. A corpuscle is sometimes seen caught at the angle where a vessel
divides into two, remaining fixed for a time, distorted and bent by the force
of the current. It soon becomes released, and as it enters the vessel, it
regains its original form. In some of the vessels of smallest size, the cor-
puscles are slightly de-
formed as they pass
through. The scene is
changed with every dif-
ferent part which is ex-
amined. In the tongue,
in addition to the arte-
rioles and venules with
the rich net- work of cap-
illaries, dark - bordered
nerve - fibres, striated
muscular fibres, and epi-
thelium can be distin-
guished. In the lungs
large, polygonal air-cells
are observed, bounded
by capillary vessels, in
which the corpuscles
move with great rapidi-
ty. It has been observed,
also, that the larger ves-
sels in the lungs are
crowded to their utmost

FIG. 36.— Portion of the lung of a live triton, drawn under the mi-
croscope and magnified 150 diameters (Wagner).

capacity with corpuscles, leaving no still layer next the walls, such as is seen
in the circulation in other situations.

Pressure of Blood in the Capillaries. — There is, apparently, no way of
directly estimating the pressure of blood in the capillaries. If, however, a
glass plate be placed upon a part in which the capillary circulation is active

CIRCULATION IN THE CAPILLARIES. 85

and be weighted until the subjacent capillaries are emptied, an approximate
idea of the blood-pressure in the vessels may be obtained. Experiments
made in this way, by Von Kries, show that the pressure in the capillaries of
the hand raised above the head is equal to a little less than one inch (24 mm.)
of mercury ; in the hand hanging down, a little more than two inches (54
mm.) ; and in the ear, about 0'8 of an inch (20 mm).

Rapidity of the Capillary Circulation. — The circulation in the capillaries
of a part is subject to such great variations and the differences in different
situations are so considerable, 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 impracticable to estimate accurately
the capacity of the capillary as compared with the arterial system. In view
of the great uncertainty in the methods employed in the estimation of the
rapidity of the flow of blood in the capillaries, it seems unnecessary to discuss
this question fully. Volkmann calculated the rapidity in the mesentery of
the dog and found it to be about one-thirtieth of an inch (0*85 mm.) 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 ; and by certain calculations, he formed an esti-
mate of its rapidity, putting it at one-fortieth to one-twenty-eighth of an
inch (0-63 and O9 mm.) per second, which estimate may be provisionally
adopted as the probable rate in the human subject.

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 can not 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 the physiology of respiration. It is well known that arrest
of respiration produces arrest of circulation.

The immediate effects of asphyxia upon the circulation are referable to
the general capillary system. In a series of experiments made in 1857, the
medulla oblongata was broken up, and the web of the foot was submitted to
microscopical examination. This operation does not interfere with the cir-
culation, which may be observed for hours without difficulty. The cuta-
neous 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 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 began, but it soon began to de-
cline and in twenty minutes had almost ceased. In another observation, the
coating of collodion was applied without destroying the medulla. The cir-
culation was affected in the same manner as before and ceased in twenty-
five minutes (Flint). These experiments, taken in connection with observa-
tions on the influence of asphyxia upon the arterial pressure, show that non-
aerated blood can not circulate freely in the systemic capillaries. Non-
aerated blood, however, can be forced through them with a syringe, and

86 CIRCULATION OF THE BLOOD IN THE VESSELS.

even in asphyxia, it passes slowly into the veins. 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 ventri-
cle are evidently capable of giving an impulse to the. blood in the smallest
arterioles ; for a marked acceleration of the current accompanying each sys-
tole 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, can not rigidly be applied to the nat-
ural circulation, as the smallest arteries during life are endowed with con-
tractility, which is capable of modifying the blood-current. Sharpey adapted
a syringe, with a hsemadynamometer 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 (89 mm.) of mercury. It spurted out at the vein in a full
jet under a pressure of five inches (127 mm.). 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.

It is thus seen that the pressure in the arteries which forces the blood
toward the capillaries is competent, unless opposed by contraction of the
arterioles, not only to cause the blood to circulate in the capillaries, but to
return it to the heart by the veins ; 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 cir-
culation. A distinct impulse, following each ventricular systole, is observed
in the smallest arteries ; the blood flows from them directly and freely into
the capillaries ; and there is no ground for the supposition that the force is
not propagated to this system of vessels. There is, therefore, a force, the
action of the heart, which is capable of producing the capillary circulation ;
and there is nothing in the phenomena of the circulation in these vessels
which is inconsistent with its full operation. When the heart ceases its
action, movements in the capillaries are sometimes due to the contractions of
the arteries, an action which has already been fully described. Movements
which have been observed in membranes detached from the body were un-
doubtedly due to the mere emptying of the divided vessels or to simple gravi-
tation.

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 defi-
nite 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 cen-
tral organ. Another Example of what is supposed to be circulation without

PHYSIOLOGICAL ANATOMY OF THE VEINS. 87

the intervention of the heart is in cases of acardiac foetuses. Monsters with-
out a heart, which have undergone considerable development and which pre-
sent systems of arteries, capillaries and veins, have been described. All of
these, however, are accompanied by a twin, in which the development of the
circulatory system is quite or nearly perfect.

Influence of Temperature on the Capillary Circulation. — Within moder-
ate limits, a low temperature, produced by local applications, has been found
to diminish the quantity of blood sent to the capillaries and retard the circu-
lation, while a high temperature increases the supply of blood and accelerates
its current. Poiseuille 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. When, on the other hand, the part was covered with
water at 104° Fahr. (40° C.), the rapidity of the current in the capillaries was
so much increased that the form of the corpuscles could with difficulty be
distinguished.

ClKCULATIOX OF TH"E BlOOD IX THE VEINS.

The blood, distributed to the capillaries of all the tissues and organs by
the arteries, is colected from these parts in the veins and carried back to the
heart. In studying the anatomy of the capillaries or in observing the passage
of the blood from the capillaries to larger vessels in parts of the living organ-
ism which can be submitted to microscopical examination, it is seen that
the capillaries, vessels of nearly uniform diameter and anastomosing in every
direction, empty into a system of vessels, which, by union with others, 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 vessels which carry the blood to the heart.

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, other, which is superficial and receives the greatest part of
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 cer-
tain of them, like the brachial or spermatic, have more than two. Added to
these, are the superficial veins which have no corresponding arteries. It is
true that some arteries have no corresponding veins, but examples of this
kind are not sufficient in number to diminish, in any marked degree, the
great preponderance of the veins, both in number and volume. It is impos-
sible to give an accurate estimate of the extreme capacity of the veins as
compared with the arteries, but it must be much greater. Borelli estimated

88

CIRCULATION OF THE BLOOD IN THE VESSELS.

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

FIG. 37.— Venous radicles uniting to form a small vein, from the muscular coat 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 endothelium of the vessels. It is injected with silver nitrate, stained with
carmine and mounted in Canada balsam.

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.

In attempting to compare the quantity of blood normally circulating in
the veins with that contained in the arteries, such variations are found 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
unprofitable to attempt even an approximate comparison, as the variations in
the venous circulation constitute one of its most important physiological
peculiarities, which must be fully appreciated in order to form a just idea of
the uses of the veins. The arteries are always full, and their tension is sub-
ject to comparatively slight variations. Following the blood into the capil-
laries, important modifications in the circulation are observed, with varying
physiological conditions of the parts. As would naturally be expected, the
condition of the veins varies with the changes in the capillaries from which
the blood is received. In addition to this, there are independent variations,

PHYSIOLOGICAL ANATOMY OP THE VEINS. 89

as in the erectile tissues, in the veins of the alimentary canal during absorp-
tion, in veins subject to pressure, 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
"is 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 frequent variations in the quantity 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 essen-
tial to the proper nutrition and action of parts that the quantity and course
of the blood should be regulated exclusively through the arterial system.

Collected by the veins 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
more complex than that of the arteries. Their walls, which are always much
thinner than the walls of the arteries, may be divided into a number of layers ;
but for convenience of physiological description, they may be regarded as
presenting three distinct coats. These have properties which are somewhat
distinctive for each, although not as much so as those of 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, homogene-
ous membrane, somewhat thinner than in the arteries, lined by a delicate
layer of polygonal endothelium, the cells of which are shorter and broader
than the endothelial cells of the arteries.

The middle coat is divided by some anatomists into two layers ; an in-
ternal layer, which is composed 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 con-
tains 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 membrane." In addition, there are inelastic fibres inter-
lacing in every direction and mingled with capillary blood-vessels, and non-
striated muscular fibres. In the human subject, in the veins of the central
portion of the nervous system, the dura mater, the pia mater, the bones, the
retina, the vena cava descendens, the thoracic portion of the vena cava
ascendens, the external and internal jugulars and the subclavian veins, there

90 CIRCULATION OF THE BLOOD IN THE VESSELS.

are no muscular fibres in the middle coat. In the larger veins, such as the
abdominal vena cava, the iliac, crural, popliteal, mesenteric and axillary veins,
there are both longitudinal and circular fibres. In the smaller veins, the
fibres are circular. In the smallest veins, the middle coat is composed of
fine fibres of connective tissue with a very few muscular fibres.

The external coat of the veins is composed of ordinary fibrous tissue, like
that of the corresponding coat of the arteries. In the largest veins, particu-
larly those of the abdominal cavity, this coat contains a layer of longitudinal,
non-striated 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 pulsa-
tion 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
coat. This is most marked in the larger veins, in which the middle coat,
particularly the layer of muscular fibres, is very slightly developed.

The venous sinuses and the veins which pass through bony tissue have
only the internal coat, to which are superadded a few longitudinal fibres, the
whole being closely attached to the surrounding parts. As examples, 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 membrane is adherent to canals formed
by a layer of compact bony tissue. The veins are much more closely adher-
ent to the surrounding tissues than the arteries, particularly when they pass
between layers of aponeurosis.

The peculiarities in the anatomy of the veins indicate considerable dif-
ferences 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 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.

Although with much thinner and apparently weaker walls, the veins, as a
rule, will resist a greater pressure than the arteries. Wintringham (1740)
showed that the inferior vena cava of a sheep, just above the opening of
the renal veins, was ruptured by a pressure of one hundred and seventy-six
pounds (79-8 kilos.), while the aorta, at a corresponding point, yielded to a
pressure of one hundred and fifty-eight pounds (71'7 kilos). 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 habit-
ually subjected in the upright posture. Wintringham noticed a 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

VALVES OF THE VEINS. 91

veins. The splenic vein gave way under a pressure of little more than one
atmosphere, while the artery supported a pressure of more than six atmos-
pheres.

The different influences to which the venous and arterial circulations are
subject serve to indicate the physiological importance of the great difference
in the strength of the two varieties of vessels. It is true that in the arteries
the constant pressure is greater than in the veins ; but it is nearly the same
throughout the arterial system, and the great extent of the outlet at the
periphery 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 mus-
cular fibres of the left ventricle have but a limited power, and when the pressure
in the arteries is sufficient, as it sometimes is in asphyxia, to close the aortic
valves so firmly that the force of the ventricle will not open them, it can not be
increased. At the same time, the pressure is being gradually relieved by the
capillaries, through which the blood slowly filters even when completely un-
ae' rated. 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 valves, which render a general
backward action impossible. Thus, restricted portions of the venous system,
from pressure in the vessels, increase of fluid from absorption, 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
ordinarily to suffei 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 prop-
erty is not so marked as it is in the arteries. If a portion of a vein distended
with blood be included between two ligatures and a small opening be made in
the vessel, the blood will be ejected with some force, and the vessel becomes
much reduced in caliber.

It has been shown by direct experiment that the veins are endowed with
the peculiar contractility characteristic of the action of the non-striated muscu-
lar fibres. On the application of electric or mechanical stimulation, they con-
tract slowly and gradually, the contraction being followed by a correspond-
ingly 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 ex-
ist in the walls of the heart.

Nerves from the vaso-motor system have been demonstrated in the walls
of the larger veins but have not been followed out to the smaller ramifica-
tions of the vessels,

Valves of the Veins. — In all parts of the venous system, except, in general
terms, in the abdominal, thoracic and cerebral cavities, there exist little mem-
branous, semilunar folds, resembling the aortic and pulmonic valves of the
heart. When the valves are closed, their convexities look toward the periph-

92 CIRCULATION OF THE BLOOD IN THE VESSELS.

ery. In the great majority of instances, the valves exist in pairs, but they
are occasionally, although very rarely in the human subject, found in groups
of three. They are seldom if ever found in veins of a less diameter than one
line (2-1 mm.). The valves are formed in part of the lining membrane of
the veins, with fine fibres of connective tissue, elastic fibres and non-striated
muscular fibres. There exists, also, a fibrous ring following the line of
attachment of the valvular curtains to the vein, which renders the vessel
much stronger and less dilatable here than in the intervals between the
valves. The valves are most abundant 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 enters 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. When the vein is thus congested and
knotted, if the finger be pressed along the vessel in the direction of the blood-
current, a portion situated 'between two valves may be emptied of blood ; but
it is impossible to empty any portion of the vessel by pressing the blood in
the opposite direction (Harvey). On slitting open a vein, it is easy to ob-
serve the shape, attachment and extreme delicacy of structure of the valves.
When the vessel is empty or when fluid moves toward the heart, the valves
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. When closed
the application of their free edges form 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 back-
ward, in the sets above and below, the lines run from side to side (Fabricius).
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 the crural
vein is reached ; but occasionally there is a double valve at the origin of tl)e
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 have no valves, except in very
rare instances, when one or two are found in the course of the jugular.

CIECULATION IN THE VEINS. 93

In addition to the double, or more rarely triple yalves 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 mechanism as that by which
the ileo-caecal valve prevents the passage of matters from the large into the
small intestine.

The veins are adapted to the return of blood to the heart in a compara-
tively 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, have established the fact that the ftfrce exerted by the left ven-
tricle is sufficient to account for the venous circulation. The heart must be
regarded as the prime cause of the movement of blood in the veins. Re-
garding 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 influ-
ence of the vessels themselves, the question of the existence of forces which
may assist the vis a tergo from the heart, and conditions which may interfere
with the flow of blood.

As a rule, in the normal circulation, the flow of blood in the veins is con-
tinuous and uniform. The intermittent impulse of the heart, which pro-
gressively diminishes toward the periphery but is still felt even in the small-
est arteries, is lost in the capillaries. Here, for the first time, the blood
moves in a constant current ; and as the pressure in the arteries is continu-
ally 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. Consequently, the venous circulation is
subject to very great variations due to irregularity in 'the supply of blood,
aside from any action of the vessels themselves or any external disturbing
influences.

It often happens that a vein becomes obstructed from some cause which is
entirely physiological, such as the action of muscles. The great number of
veins, as compared with the arteries, and their free communications with each
other, provide that the current, under these conditions, is simply diverted,
passing to the heart by another channel. When any part of "the venous sys-
tem 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.
8

94 CIRCULATION OF THE BLOOD IN THE VESSELS.

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 cardiac impulse may extend to the veins. 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 intermittent jet, as from a divided
artery (Bernard). This is due to the relaxed condition of the arterioles 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
activity.

Pressure of Blood in the Veins. — The pressure in the veins is always
much less than in the arteries. It is very variable in different parts of the
venous system and in the same part at different times. As a rule, it is in
an inverse ratio to the arterial pressure. Whatever favors the passage of blood
from the arteries into the capillaries has a tendency to diminish the arterial
pressure, and as it increases the quantity of blood which passes into the veins,
it must increase the venous pressure. The great capacity of the venous sys-
tem, its frequent anastomoses and the presence of valves which may shut off a
portion from the rest, are conditions which involve considerable variations
in pressure in different vessels. It has been ascertained that as a rule, the
pressure is greatest at the periphery and progressively diminishes in the direc-
tion of the heart. In an observation on the calf, Volkmann found that with
a pressure of about 6'5 inches (165-1 mm.) of mercury in the carotid, the
pressure in the metatarsal vein was 1-1 inch (28 mm.), and but 0-36 (9-1 mm.)
in the jugular. Analogous results were obtained in the more recent experi-
ments by Jacobson. * 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 rela-
tive 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
tying all the veins coming from a part, except one which had the vol-
ume 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 press-

CAUSES OF THE VENOUS CIRCULATION. 95

ure in the vein very much increased, becoming 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 conditions are capable of increasing very con-
siderably the rapidity of the flow in certain veins, and that under certain
conditions, the current in some parts of the venous system is very much re-
tarded. 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. Near the heart, however, the flow becomes more uni-
form 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, estimates of the general rapidity of the venous cir-
culation or of the variations in different vessels must necessarily be very
indefinite.

CAUSES or THE VEKOUS CIKCULATIO^.

In the veins the blood is farthest removed from the influence of the con-
tractions of the left ventricle ; and although these are felt, there are many
other causes which combine to carry on the venous circulation, and many
influences by which it is retarded or obstructed.

The great and uniform force which operates on the circulation in these
vessels is the vis a tergo. Eeference has been made 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. 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 suction force exerted by the action of the thorax in respiration,
operating, however, only on the veins in the immediate neighborhood of the
chest.

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 in-
ferior 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 oblit-
erate the caliber of a vessel, when, from the free communications with other

96 CIRCULATION OF THE BLOOD IN THE VESSELS.

vessels, the current is simply diverted into another channel ; expiratory
efforts ; the contractions, 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 parts of the trunk above the heart.

Influence of Muscular Contraction. — That the action of muscles has con-
siderable influence on the current of blood in the veins situated between
them and in their substance, has long been recognized ; and this action is so
marked, that the parts of the venous system which are situated in the sub-
stance of muscles have been' compared by Chassaignac to a sponge full of
liquid, vigorously pressed by the hand. It must always be remembered, how-
ever, 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 exemplified
in the venous circulation in paralyzed parts.

It has been shown by actual observations with the haemadynamometer, that
muscular action is capable of increasing the pressure in certain veins. Ber-
nard found that the pressure in the jugular of a horse, in repose, was 1-4
inch (31-8 mm.) ; but the action of the muscles in raising the head increased
it to a little more than five inches (127 mm.), or nearly four times. Such ob-
servations show at once the great variations in the current and the impor-
tant influence of muscular contraction on the venous circulation.

In order that contractions of muscles shall assist the venous circulation,
two conditions are necessary :

1. The contraction must be intermittent. This is always the case in the
voluntary muscles. It is a view entertained by many physiologists that each
muscular fibre relaxes immediately after its contraction, which is instantane-
ous, and that a certain period of repose is necessary before it can contract
again. However this may be, it is well known that all active muscular con-
traction, 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 condition is fulfilled by the action of the valves. Anatomical researches
have shown, also, that these valves are most abundant in veins situated in the
substance of or between the muscles, and they do not exist in the veins of
the cavities, which are not subject to the same kind of compression.

Force of Aspiration from the Thorax.— During the act of inspiration, the
enlargement 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 enters by the trachea and expands the lungs so that they follow the move-
ments of the thoracic walls. The flow of blood into the great arteries is
somewhat retarded, as is indicated by a diminution 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 inspi-

CAUSES OF THE VENOUS CIRCULATION. 97

ration. 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 respira-
tion. This can always be observed after exposure of the jugular in the lower
part of the neck in an inferior animal. Direct observations on the jugulars
show conclusively that the influence of inspiration can not 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 flac-
cidity of the walls of the veins will not permit the extended action of any
suction force. In the circulation the veins are moderately distended with
blood by the vis a tergo, and, to a certain extent, they are supported by con-
nections with surrounding tissues, so that the force of aspiration is felt far-
ther than in experiments on vessels removed from the body. The blood,
as it approaches the thorax, impelled by other forces, is considerably accel-
erated in its flow ; but it is evident that beyond a certain point, and that
point very near the chest, ordinary aspiration has no influence, and violent
efforts rather retard than favor the venous current.

In the liver the influence of inspiration becomes a very important ele-
ment 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. 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 must remain
open under all conditions. The thorax can therefore exert a powerful influ-
ence upon the hepatic circulation ; 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 circu-
lates in this organ in the foetus before any movements of the thorax take
place shows that it is not essential.

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 on the
lower part of the neck. When the veins in this situation are kept open by a
tumor or by induration of the surrounding tissues, an inspiratory effort has
occasionally been followed by the entrance of air into the vessels, an acci-
dent which is likely 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
vossels in this particular situation by the flaccidity of their walls.

98 CIRCULATION OF THE BLOOD IN THE VESSELS.

The cause of death from air in the veins is mechanical. The air, finding
its way to the right ventricle, is mixed with the blood in the form of bubbles
and is carried into the pulmonary artery. Once in this vessel, it is impossi-
ble for it to pass through the pulmonary capillaries, and death by suffocation
is the result, if the quantity of air be large, about 7'3 cubic inches (120 c. c.)
in a large dog (Nysten). 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
a short time is absorbed.

Aside from the pressure exerted by the contraction of muscles and the
force of aspiration from the thorax, the influences which assist the venous
circulation are very slight. There is a slight contraction in the venas cavse
in the immediate proximity of the heart, which is much more extended in
many of the lower vertebrate animals 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 elevated 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 rise against the force of gravity.

Some physiologists are of the opinion that the right ventricle exerts an
active suction force during its diastole ; but experiments on anfmals do not
fully sustain this view,' and if such a force be exerted, its effect upon the cir-
culation, even in the veins near the heart, must be very slight. In the great
irregularity in the rapidity of the circulation in different veins, it must fre-
quently 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 neces-
sity, the more rapid current in the large vein exerts a certain suction force
on the fluid in the smaller vessel.

USES or THE VALYES OF THE VEINS.

It is evident that the principal use of the valves of the veins is to present
an obstacle to the reflux of blood toward the capillaries ; and it remains only
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 rise 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

USES OF THE VALVES OF THE VEINS. 99

vessel is temporarily obliterated, they aid in directing the current into anas-
tomosing vessels. It is but rarely, however, that they act thus in opposition
to the force of gravity ; 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 dependent part and
the avenues to the heart become insufficient, the valves divide the columns of
blood, so that the pressure is equally distributed throughout the extent of the
vessels. This is, however, but an occasional action of the valves ; and it is
evident that their influence is only to prevent the weight of the entire col-
umn of blood, in vessels thus obstructed, from operating on the smallest
veins and the capillaries. It can not make the work of the heart, when
the blood is again put in motion, any less than if the column were undi-
vided, as this organ must have sufficient power to open successively each set
of valves.

It is in connection with the intermittent compression of the veins that the
valves have their principal and almost constant use. Their situation alone
would lead to this supposition. They are found in greatest numbers through-
out the muscular system, having been demonstrated in vessels one line (2-1
mm.) in diameter. 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 seconds 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, nevertheless, to oppose regurgitation.

In the action of muscles, the skin is frequently stretched over the part,
and the cutaneous 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 ac-
tion. 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 mus-
cles into the skin, and the valves act to prevent it from taking a retrograde
course.

A full consideration of the venous anastomoses belongs to descriptive
anatomy. It is sufficient to state, in this connection, that they are very
abundant 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 inferior with the superior vena
cava. Even the portal vein has been shown to have its communications with
the general venous system. Thus, in all parts of the organism, temporary
compression of a vein merely diverts the current into some other vessel, and
permanent obliteration of a vein produces enlargement of communicating

100 CIRCULATION OF THE BLOOD IN THE VESSELS.

branches, which soon become sufficient to meet all the requirements of the
circulation.

CONDITIONS WHICH IMPEDE THE VENOUS CIKCULATION.

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 quite marked, these being fol-
lowed by congestion of the veins of the face and neck and a sense of fullness
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 ves-
sels, the obstructive influence of very violent and prolonged 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 a mere reflux from the large trunks of the
thoracic cavity. Were this the case, it would be necessary to assume an insuf-
ficiency 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 regurgitation.
The chief cause of congestion, however, is due, not to regurgitation, but to
accumulation 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 on account of its great size in the human subject, as com-
pared with the other vessels, and the importance and delicacy of the parts
from which it collects the blood. At the opening 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. When the act of expi-
ration arrests the onward flow in the veins near the thorax, these valves are
closed and effectually protect the brain from congestion by regurgitation.
The blood accumulates behind the valves, but the free communication of the
internal jugular with the other veins of the neck relieves the brain from con-
gestion, unless the effort be extraordinarily violent and prolonged.

The above remarks with regard to the influence of expiration are appli-
cable to vocal efforts, violent coughing or sneezing, or any unusual muscular
efforts, such as straining, in which the glottis is closed.

Regurgitant Venous Pulse. — In the inferior animals, such as 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 regurgitation of blood from the thorax

CIRCULATION IN THE CRANIAIj iC^IfY. 101

into the external jugular, and distinct pulsatiohs, s\
ments of respiration, may be produced in this way.

It is evident that there are various other conditions 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 proportion-
ally 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 pass 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 con-
tain 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 abundant 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 produced
by occupations which require constant standing ; but the exercise of walking,
aiding the venous circulation, as it does, by the muscular effort, has no such
tendency.

Circulation in the Cranial Cavity. — In the encephalic cavity there are
certain peculiarities in the anatomy of some of the vessels, with exceptional
conditions of the blood as regards atmospheric pressure, which have been
regarded as capable of essentially modifying the circulation. In the adult
the cranium is a closed, air-tight box, containing the incompressible cerebral
substance, blood, lymph and the cephalo-rachidian fluid ; and the blood is
here under conditions widely different from those presented in other parts of
the system. The venous passages in the brain, 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
semi-solids and liquids which make up the encephalic mass can not increase
in size in congestion and diminish in anaemia. Notwithstanding these con-
ditions, the fact remains, that examinations of the vessels of the brain after
death show great differences in the quantity of blood which 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 ana-
tomical peculiarity which has not yet been considered offers an explanation of
these phenomena. 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 (Magendie). The communication between the
cranial cavity and the spinal canal is very free. It is easy to see one of the

102 RClJA^^ OF THE BLOOD IN THE VESSELS.

tWIiq-uid. When the pressure of blood in the arteries
going 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 takes place when the
supply of blood to the brain is diminished. The physiological action of all
highly organized and vascular parts seems to require certain variations in the
supply of blood ; and there is no good reason to suppose that the brain, in its
varied conditions of activity and repose, is an exception to this general rule.

Physiologists, even before the time of Haller, had noticed alternate move-
ments 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 vio-
lent efforts, is sometimes so considerable as to produce cerebral hernia, and
contraction with inspiration. 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 materially aided, and the brain
is in some degree relieved of this expanding force.

Circulation in Erectile Tissues. — In the organs of generation of both
sexes, there exists a tissue which is subject to increase in volume and rigidity
when in a condition of what is called erection. The parts in which the erect-
ile tissue exists are, in the male, the corpora cavernosa of the penis, the cor-
pus spongiosum and the glans penis ; and in the female, the corpora caver-
nosa of the clitoris, the gland of the clitoris and the bulb of the vestibule.

The vascular arrangement in erectile organs, of which the penis may be
taken as the type, is peculiar and is not found in any other part of the circu-
latory 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 immediately become tortuous
and are distributed in the cavernous and spongy bodies in anastomosing ves-
sels, 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 -fa to ^ of an inch (1 to 1-5 mm.).
The cavernous bodies have an external investment of strong, fibrous tissue
of considerable elasticity, which sends bands, or trabeculae, into the inte-
rior, by which it is divided up into cells. The trabeculae are composed of
fibrous tissue mixed with a large number of non-striated 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 envelops and the trabeculae are more delicate and the cells are smaller.

PULMONARY CIRCULATION. 103

Without going fully into the mechanism of erection, 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 direct 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 capillaries. This peculiarity, which had been noted
by Todd anJ Bowman, Paget and others, has been studied by Sucquet. By
using a black, solidifiable injection, he found that there were certain parts of
the upper and lower extremities and the head which became colored by the
injection, while other parts were not penetrated. Following the vessels by
dissection, he showed that in the upper extremity, the skin of the fingers and
part of the palm of the hand, and the skin over the olecranon are provided
with vessels of considerable size, which allowed the fluid injected by the axil-
lary artery to pass directly into some of the veins, while ki other parts the
veins were entirely empty. Extending his researches to the lower extremity,
he found analogous 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. These observations
have been in the main confirmed by the more recent researches of Hoyer. It
is evident that under certain conditions 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.

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. In
the substance of the lungs, the pulmonary artery is broken up into capilla-
ries, most of them just large enough to allow the passage of the blood-cor-
puscles 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 pul-
monary system as regards capacity. The pulmonary veins in the human
subject are not provided with valves.

104 CIRCULATION OF THE BLOOD IN THE VESSELS.

The blood' in its passage through the lungs does not meet with the resist-
ance which is presented in the systemic circulation ; and the anatomy of the
pulmonary vessels and of the right side of the heart shows that the blood
must circulate in the lungs with comparative facility. 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. The pressure of blood in the pulmonary artery, meas-
ured by connecting a cardiometer with a trocar introduced into the pul-
monary artery of a living horse through one of the intercostal spaces, has
been found to be about one-third as great as the pressure in the aorta,
which corresponds pretty nearly with an estimate of the comparative power
of the two ventricles, judging from the thickness of their muscular walls
(Chauveau and Faivre).

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 pre-
sent 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.

Circulation in the Walls of the Heart. — The circulation in the walls of
the heart does not present any important peculiarities. It has been shown
that the pressure of blood in the coronary arteries in the dog, during the
ventricular systole, is sufficient to supply the arterioles 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-beats
were obtained, it has been found that the coronary and carotid pulses were
practically synchronous (Martin).

Passage of the Blood- Corpuscles through the Walls of the Vessels (Diape-
desis). — In the frog it has been observed that the leucocytes sometimes pass
through the walls of the blood-vessels, either by means of small orifices
(stromata) or by a kind of filtration through the substance which unites the
borders of the endothelial cells. This phenomenon was described by Waller,
in 1841, but has attracted much attention since the more recent researches
of Cohnheim. In this process it is observed that the leucocytes, which first
adhere to the vascular walls, send out little projections which penetrate the
membrane, so that a point appears on the outside of the vessel. This point
becomes larger and larger, until 'the entire mass of the corpuscle has passed
through. The corpuscles then migrate a certain distance by means of the
movements known as amoeboid, which have already been described. It was
supposed by Cohnheim that this was one of the early phenomena of inflam-
mation, the migrating corpuscles afterward multiplying by division, consti-
tuting the so-called pus-corpuscles. Following stasis of blood in the small
vessels, the red corpuscles, it is supposed, pass out in the same way. It is
not certain that diapedesis, even of leucocytes, is a normal process or that it
takes place in the human subject. According to Hering, the red corpuscles

RAPIDITY OF THE CIRCULATION.

105

FIG. 38.— Small blood-vessel of the mesentery of the
frog, showing diapedesis of leucocytes (Landois).

w, w, walls of the vessel ; A, A, still layer ; R, R, red
blood-corpuscles ; L, L, leucocytes in contact with
the wall, c, c, in different stages of diapedesis ;
F, F, leucocytes that have passed out of the vessel.

pass through the walls of the vessels, 'only when the pressure is sufficient

to produce transudation of the

blood-plasma.

RAPIDITY OF THE CIRCULATION.

Several questions of considerable
physiological importance arise in
connection with the general rapidity
of the circulation :

1. What length of time is occu-
pied in the passage of the blood
through both the lesser and the
greater circulations ?

2. What is the time required for
the passage of the entire mass of
blood through the heart ?

3. What influence has the num-
ber 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, Her ing made the
experiment of injecting into the jugular vein of a living animal a solution
of potassium ferrocyanide, noting 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. He drew the blood at inter-
vals of five seconds after beginning the injection, and thus, by repeated ob-
servations, ascertained pretty nearly the rapidity of a circuit of blood in the
animals upon which he experimented. Vierordt (1858) 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 only objection which could be made to these experiments is that a
saline solution, introduced into the circulation, would have a tendency to
diffuse itself throughout the whole mass of blood, it might be, with consider-
able rapidity. This certainly is an element which should be taken into ac-
count ; but from the definite data which have been obtained concerning the
rapidity of the arterial circulation 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 rapidity 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.

106 CIRCULATION OF THE BLOOD IN THE VESSELS.

Hering found that the rapidity of the circulation in different animals
had an inverse ratio to their size and a direct ratio to the rapidity of the
action of the heart.

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 "

Rabbit, " " 6-9 "

Applying these results to the human subject and 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 estimate
is simply approximate ; but the results in the inferior animals may be received
as very nearly 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 circulation. To arrive at any satisfactory result, it is neces-
sary to know the entire quantity of blood in the body and the exact quantity
which passes through the heart at each pulsation. If the whole mass of blood
be divided by the quantity discharged from the heart with each ventricular
systole, the result gives 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, the length of time thus occupied is ascertained. 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, can not 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-tenth the weight of the body, or
fourteen pounds (6-35 kilos.), in a man weighing one hundred and forty
pounds (63-5 kilos.). The quantity discharged at each ventricular systole is
estimated by Valentin at five ounces (141-7 grammes), and by Volkmann, at
six ounces (170-1 grammes). 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 (141-7 grammes), it would require forty-
five 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
thirty-seven and a half seconds.

The relation of the rapidity of the circulation to the frequency of the
heart's action is a question 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 conditions, any increase in the number of
pulsations of the heart would produce a corresponding acceleration of the
general current of blood. This is a proposition, however, which can not be

RAPIDITY OF THE CIRCULATION. 107

taken for granted ; and there are many facts which favor a contrary opinion.
It may be stated as a general rule, that when the acts of the heart increase in
frequency they diminish in force ; and this renders it probable that the ven-
tricle 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 actually increase the rapidity of
the circulation. In observations made on horses, by increasing the frequency
of the pulse, on the one hand, physiologically, by exercise, and on the other
hand, pathologically, by producing inflammatory action, it is shown that when
the pulse is accelerated in inflammation, 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. In the physiological increase in the
rate of the pulse by exercise, there was a considerable increase in the actual
rapidity of the circulation (Hering).

With regard to the relations between the rapidity of the heart's action
and the general 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 exercise, for example, the general circulation is somewhat increased
in rapidity, though not in proportion to the increase in the rapidity of the
pulse.

2. In pathological increase in the rapidity of the heart's action, as in
febrile movement, the rapidity of the general circulation is generally dimin-
ished, 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 diminished, either from lack of complete distention or from
imperfect emptying of the cavities.

Phenomena in the Circulatory System after Death. — 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 belief that the arteries were air-bearing tubes. This is readily explained
by the post-mortem contraction of the muscular coat of the arteries. If the
artery and vein of a limb be exposed in a living animal and all the other ves-
sels be tied, compression 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 (Magendie). The artery, when relieved from the distending force
of the heart, reacts on its contents by virtue of its contractile coat and com-
pletely empties itself of blood. An action similar to this takes place through-
out the arterial system after death. The vessels react on their contents and
gradually force all the blood into and through the capillaries, which are very

108 RESPIRATION— RESPIRATORY MOVEMENTS.

short, to the veins, which are capacious, distensible and but slightly con-
tractile. This begins immediately after death while the contractility 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 can not 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 TORY MO VEMENTS.

General considerations— Physiological anatomy of the respiratory organs— Movements of respiration— Inspi-
ration— Muscles of inspiration — Expiration — Muscles of expiration — Types of respiration — Frequency
of the respiratory movements— Relations of inspiration and expiration to each other — Respiratory
sounds — Capacity of the lungs and the quantity of air changed in the respiratory acts — Residual air
—Reserve air— Tidal, or breathing air— Complemental air— Extreme breathing capacity— Relations 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 differences 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 speci-
men of true capillary blood. In the capillaries, however, the nutritive fluid,
which is identical in all parts of the arterial system, undergoes changes which
render it unfit for nutrition. Thus modified it is known as venous blood ;
and 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 substances it has col-
lected 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 corresponding
variations in the composition of the blood in different veins.

The important substances that 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 the red corpuscles.

A proper supply of oxygen is indispensable to nutrition and even to the
comparatively mechanical process of circulation ; but it is no less necessary
to the nutritive processes that carbon dioxide, which the blood acquires in
the tissues, should be removed.

Respiration may be defined strictly as the process by which the various
tissues and organs receive and appropriate oxygen.

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
carbon dioxide, the respiratory process in the lungs may be said to consist

GENERAL CONSIDERATIONS. 109

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 carbon diox-
ide. Under these conditions they certainly respire ; and it is evident, there-
fore, that in this process, the intervention of the blood is not an absolute
necessity.

The tide of air in the lungs does not strictly constitute respiration.
These organs merely serve to facilitate the introduction of oxygen into the
blood and the exhalation of carbon dioxide. 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 are the ordinary nutritive changes,
it is inseparably connected with and strictly a part of the general process.
As in the nutrition of the tissues the nitrogenized constituents of the blood,
united with inorganic substances, are transformed into the tissue itself,
finally changed into excrementitious products, such as the urinary mat-
ters, and discharged from the body, so the oxygen of the blood is appro-
priated, and carbon dioxide, which is an excrementitious substance, is pro-
duced, 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 in themselves, but as different parts of the general
function of nutrition.

As physiologists are 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 excrementitious substances, it is impos-
sible to say precisely how oxygen is used by the tissues and how carbon dioxide
is produced. It is known only that more or less oxygen is necessary to the
nutrition of all tissues, in all animals, high or low in the scale, and that the
tissues produce a certain quantity of carbon dioxide. The fact that oxygen
is consumed with much greater rapidity than any other nutritive substance
and that the production of carbon dioxide is correspondingly active, as com-
pared with other effete products, points to a connection between the absorp-
tion of the one and the production of the other.

The essential conditions for respiration in animals which have a circulat-
ing nutritive fluid are air and blood separated by a membrane which will
allow the passage of gases. The effete products of respiration contained in
the blood, the most important of which is carbon dioxide, 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 carbon dioxide. The rapidity of
this change is in proportion to the nutritive activity of the animal and the
rapidity of the circulation of the blood.
9

110

RESPIRATION— RESPIRATORY MOVEMENTS.

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 ante-
rior opening, the opening of the larynx, which is the beginning of the pas-
sages concerned exclusively in respiration.

Beginning 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 inspiratory effort. Across its superior opening are the vocal chords,
which are four in number 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 membrane, which is

FIG. 39.— Trachea and bronchial tubes (Sappey).

1, 2, larynx ; 3, 3, trachea ; 4, bifurcation of the trachea ; 5, right bronchus : 6, left bronchus ; 7, bron-
chial 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 bronchia; 13, 13, 13, 13, lungs, represented in contour; 14, 14, summit
of the lungs ; 15, 15, base of the lungs.

quite thick on the superior chords and very thin and delicate on the true
vocal chords. These bands are attached anteriorly to a fixed point between

ANATOMY OF THE RESPIRATORY ORGANS. Ill

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 cri-
coid and attached to the arytenoid cartilages, are capable of separating and
approximating the points to which the vocal chords are attached posteriorly,
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 slightly opened at each inspiration, 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. The expulsio i of air from the lungs in tran-
quil respiration is a passive process and te *ds in itself to separate the vocal
chords ; but inspiration, which is active, 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. The respiratory
movements of the larynx are entirely distinct from those concerned in the
production of the voice.

Attached to the anterior portion of the larynx, is the epiglottis, a little,
leaf-shaped lamella of fibro-cartilage, which, during ordinary respiration, pro-
jects 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 larynx. Physi-
ologists have questioned whether the epiglottis be necessary to the complete
protection of the air-passages ; and it has frequently been removed from the
lower animals without apparently interfering with the proper deglutition of
solids or liquids (Magendie). It is a question, however, whether the results
of this experiment can be absolutely applied to the human subject. In a case
of loss of the 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, and others
of a similar character which are on record, show that the presence of the
epiglottis, in the human subject at least, is necessary to the complete protec-
tion of the air-passages in deglutition.

Passing down the neck from the larynx toward the lungs, is the trachea,
which is four to four and a half inches (10-16 to 11-43 centimetres) in length
and about three-quarters of an inch (19-1 mm.) in diameter. It is provided
with cartilaginous rings, sixteen to twenty in number, which partially sur-
round the tube, leaving about one-third of its posterior portion 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

112

RESPIRATION— RESPIRATORY MOVEMENTS.

lungs, divide and subdivide, until the minute ramifications of the bronchial
tree open directly into the air-cells. After penetrating the lungs, the carti-

FIG. 40. — Lungs, anterior view (Sappey).

1, upper lobe of the left lung ; 2, lower lobe ; 3. fissure ; 4, notch corresponding to the apex of the heart ;
5, pericardium : 6, upper lobe of the right lunq ; 7, middle lobe ; 8, lower lobe ; 9, fissure ; 10, fissure ;
11, diaphragm ; 12, anterior mediastinum ; 13, thyroid gland ; 14, middle cervical aponeurosis ; 15,
process of attachment of the mediastinum to the pericardium ; 16, 16, seventh ribs; 17, 17, transver-
sales muscles : 18, linea alba.

lages 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 (0*5 mm.), they disappear.

The walls of the trachea and bronchial tubes are composed of two distinct
membranes ; an external membrane, between the layers of which the carti-
lages 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 num-
ber of non-striated muscular fibres, which exist in two layers ; a thick, internal
layer, in which the fibres are transverse, and a thinner, longitudinal layer,

ANATOMY OF THE RESPIRATORY ORGANS.

113

which is external. The collection of muscular fibres in the posterior part of
the trachea is sometimes called the trachealis muscle. Throughout the
bronchial tubes,
there are circular
fasciculi of non-
striated muscular
fibres lying just
beneath the mu-
cous membrane,
with a number of
longitudinal elas-
tic fibres. The
character of the
bronchia abruptly
changes in tubes
less than -fa of an
inch (0-5 mm.) in
diameter. They
then lose the car-
tilaginous rings,
and the external
and the mucous
membranes be-
come so closely
united that they

FIG. 41. — Bronchia and lungs, posterior view (Sappey).

1,1, summit of the lungs ; 2, 2, base of the lungs ; 3, trachea ; 4, right bronchus;
5, division to the upper lobe of the lung ; 6, division to the lower lobe ; 7,
left bronchus ; 8, division to the upper lobe ; 9, division to the lower lobe ;

,

10, left branch of the pulmonary artery; 11, right branch; 12, left auricle
of the heart ; 13, left superior pulmonary vein ; 14, left inferior pulmonary
vein ; 15, right superior pulmonary vein ; 16, right inferior pulmonary
vein ; 17, inferior vena cava ; 18, left ventricle of the heart ; 19, right ven-
tricle.

can no longer be
separated by dis-
section. The cir-
cular muscular fibres continue as far as the air-cells. The mucous mem-
brane is smooth, covered by ciliated epithelium, the movements of the cilia
being always from within outward, and it is provided with mucous glands.
These glands are of the racemose variety and in the larynx they are of con-
siderable size. In the trachea and bronchia, racemose glands exist in the
membrane on the posterior surface of the tubes ; but anteriorly are small fol-
licles, terminating in a single, and sometimes a double, blind extremity.
These follicles are lost in tubes measuring less than fa of an inch (0-5 mm.)
in diameter.

When moderately inflated, the lungs have the appearance of irregular
cones, with rounded apices, and concave bases resting upon the diaphragm.
They fill that part of the cavity of the thorax which is not occupied by the
heart and great vessels, and are completely separated from each other by the
mediastinum. The lungs are in contact with the thoracic walls, each lung
being covered by a reflection of the serous membrane which lines the cavity
of the corresponding side. Thus they necessarily follow 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 di-

114

RESPIRATION— RESPIRATORY MOVEMENTS.

vided into irregularly polygonal spaces, £ of an inch to an inch (6-4 to 25*4
mm.) in diameter, which mark what are sometimes called the pulmonary
lobules ; although this term is incorrect, 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
(0-5 mm.), the smallest, which are Tfg- to ^ Of an inch (0*21 to 0-33 mm.)
in diameter, open into a collection of oblong vesicles, which are the air-
cells. Each collection of vesicles constitutes one of the true pulmonary
lobules and is -^ to ^ of an inch (0-5 to 2-1 mm.) in diameter. After
entering the lobule, the tube forms a tortuous central canal, sending off
branches which terminate in groups of eight to fifteen 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 cir-
cular constrictions, or rugae. In
the healthy lung of the adult, after
death, they measure -g-^-g- to TJ7 or
TV of an inch (0-125 to 0-21 or
0-36 mm.) 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 sur-
face. There are considerable vari-
ations 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 very
abundant small, elastic fibres,
which do not form distinct bun-
dles for each air-cell, but anasto-
mose 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 important part in ex-
pelling 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 cells of flattened epithelium,

FIG. 42.— Mould of a terminal bronchus and a group of
air-cells moderately distended by injection, from
the human subject (Robin).

INSPIRATION.

115

g-^-g- of an inch (10 to 12*5 /*), in diameter, which are applied directly to the
walls of the blood-vessels. The epithelium here does not seem to be regular-
ly desquamated as in other situations. Examination 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 pul-
monary 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 nourishment of these parts. It is possible that
the tissue of the lungs may receive some nourishment from the blood of
the pulmonary artery ; but as this vessel does not send any branches to the

FIG. 43.— 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.

bronchial tubes, the bronchial arteries supply the matters for their nutrition
and for the secretion of the mucous glands.

The foregoing anatomical sketch shows the 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 gases. It is also evident, from the great number of air-cells,
that the respiratory surface must be very large, although it is impossible to
form an accurate estimate of its extent.

MOVEMENTS OF RESPIRATION.

In man and in the warm-blooded animals generally, inspiration takes
place as a consequence of enlargement of the thoracic cavity and the en-
trance of a quantity of air through the respiratory passages, corresponding

116

RESPIRATION— RESPIRATORY MOVEMENTS.

FIG. 44.— 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, sec-
ondrib; 8, 8, last five sternal ribs; 9 up-

to the increased capacity of the lungs. In the mammalia, the chest is en-
larged by the action of muscles ; and in ordinary respiration, inspiration is

an active process, while ordinary expira-
tion is passive.

A glance at the physiological anato-
my of the thorax in the human subject
makes it evident that the action of cer-
tain muscles will considerably increase its
capacity. In the first place, the dia-
phragm 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 diameter of the
thorax is increased. The walls of the
thorax are formed by the dorsal vertebrae
and ribs posteriorly, by the upper ten
ribs laterally, and by the sternum and
costal cartilages anteriorly. The direc-
tion 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 move-
ments, the antero-posterior and trans-
verse diameters of the chest may be considerably 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
part of the chest. They are articulated
with the bodies of the vertebras, so as to
allow of considerable motion. The up-
per seven ribs are attached by the costal
cartilages to the sternum, these cartilages
running upward and inward. The car-
tilages of the eighth, ninth and tenth
ribs are joined to the cartilage of the sev-
enth. The eleventh and twelfth are
floating ribs and are attached only to the
vertebrae.

It may be stated in general terms that
inspiration is effected by descent of the
diaphragm and elevation of the ribs ; and
expiration, by elevation of the diaphragm
and descent of the ribs.

Arising severally from the lower bor- „, „, mMgmo ,

der of each rib and attached to the up- BSJETO^^ *

FIG. 45.— Thorax, posterior view (Sappey).

MUSCLES OF INSPIRATION. 117

per 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 borders 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 certain 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 be-
come the movable points. Some of them are called into action during ordi-
nary respiration ; others act as auxiliaries when respiration is a little exag-
gerated, as after exercise, and are called ordinary auxiliaries ; while others,
which ordinarily have different uses, act only when respiration is difficult,
and are called extraordinary 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 cervical 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 cer-
vical vertebrae outer surface of second rib.

External intercostals Outer borders of the ribs.

Sternal portion of internal intercostals. .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 cer-
vical and upper two or three dorsal vertebrae

upper borders of second, third, fourth and fifth
ribs, just beyond the angles.

Sterno-mastoideus Upper part of sternum mastoid process of tem-
poral bone.

Extraordinary Auxiliaries.

Levator anguli scapulae Transverse processes of upper three or four cer-
vical vertebrae posterior border of superior

angle of scapula.

Trapezius (superior portion) Ligamentum nuchae and seventh cervical verte-
bra upper border of spine of scapula.

Pectoralis minor Coracoid process of scapula anterior surface

and upper margins of third, fourth and fifth
ribs, near the cartilages.

Pectoralis major (inferior portion) Bicipital groove of humerus costal cartilages

and lower part of sternum.

Serratus magnus Inner margin of posterior border of scapula

external surface and upper border of upper
eight ribs.

118

RESPIRATION— RESPIRATORY MOVEMENTS.

1!

19

FIG. 46.— Diaphragm (Sappey).

1, 2. 3, central tendon ; 4, right pillar ; 5, left pillar ; 6, 7, processes between the pillars ; 8, 8, openings
for the splanchnic nerves ; 9, fibrous arch passing over the psoas magnus ; 10, fibrous arch passing
over the quadratus lumborum ; 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 oesophagus ; 16, opening for the aorta ; 17, 17, part of the transver-
salis muscle ; 18, 18, aponeurosis ; 19, 19, quadratus lumborum ; 20, 20, psoas magnus ; 21, fourth
lumbar vertebra.

Action of the Diaphragm. — The descriptive and general anatomy of the
diaphragm gives a pretty correct idea of its uses in respiration. It arises

from the border of the lower circumfer-
ence of the thorax and 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
something like the club on a playing-
card, with middle, right and left leaflets.
The remainder of the organ is composed
of radiating fibres of striated muscular
tissue. The oesophagus, aorta and infe-
rior vena cava pass through the dia-
phragm from the thoracic to the abdom-
inal cavity, by three openings.

The opening for the oesophagus is sur-
rounded by muscular fibres, by which it

FIG. 47.— Action of the diaphragm in inspira- is partially closed when the diaphragm
tion (Hermann). • ,. ,1 n-i

Vertical section through the second rib on the contracts in inspiration, as the fibres

lines simply surround the tube and none are
attached to its walls.

MUSCLES OF INSPIRATION. 119

The orifice for the aorta is bounded by the bone and aponeurosis posteri-
orly, and in front, by a fibrous band to which the muscular fibres are attached,
so that their contraction 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 struct-
ure, and contraction of the diaphragm, although it might render the form of
the orifice more nearly circular, can have no effect upon its size.

In ordinary respiration, the descent of the diaphragm and its approxima-
tion to a plane are the chief phenomena observed ; but as there is some re-
sistance to the depression of the central tendon, it is probable that there is
also a slight elevation of the inferior ribs.

The phenomena referable to the abdomen which coincide with the de-
scent of the diaphragm can easily be observed in the human subject. As the
diaphragm is depressed, it necessarily pushes the viscera before it, and inspi-
ration is therefore accompanied by protrusion of the abdomen. This may
be rendered very marked by a forced or deep inspiration.

The effects of the action of the diaphragm upon the size of its orifices
are limited chiefly to the cesophageal opening. The anatomy of the parts is
such that contraction of the muscular fibres has a tendency to close this
orifice. The contraction of the diaphragm is auxiliary to the action of the
muscular walls of the oesophagus itself, by which the cardiac opening of the
stomach is regularly closed during inspiration. This may become impor-
tant 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
exclusively, by the phrenic nerve ; a nerve which, having the office of sup-
plying the most important respiratory muscle, derives its filaments from a
number of sources. It arises from the third and fourth cervical nerves, re-
ceiving a branch from the fifth and sometimes from the sixth. It then passes
through the chest, penetrates the diaphragm, and is distributed to its under
surface. Stimulation of this nerve produces convulsive contractions of the
diaphragm, and its section paralyzes the muscle almost completely.

From the great increase in the capacity of the chest produced by the ac-
tion 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 diaphragm, particularly hiccough and sobbing, which are produced by
spasmodic contractions of this muscle, generally not under the control of the
will.

Action of the Muscles which elevate the Ribs. — Scalene Muscles. — In ordi-
nary respiration, 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 vertebrae and the first and second ribs. These muscles, which
act particularly upon the first rib, must elevate with it, in inspiration, the

120 RESPIKATION— RESPIRATORY MOVEMENTS.

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 and an-
tero-posterior diameters of the thorax, on account of 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
muscles there is considerable difference of opinion among physiologists ; so
much, indeed, that the question is still left in some uncertainty. The most
extended researches on this point are those of Beau and Maissiat (1843), and
Sibson (1846). The latter seem to settle the question of the mode of action
of the intercostals and explain satisfactorily certain points which even now
are not generally appreciated. Onimus, and more recently, Laborde, have
shown, by experiments upon decapitated criminals, that the external inter-
costals raise and .the internal intercostals depress the ribs, thus confirming
the views of Sibson.

In the dorsal region, the spinal column forms an arch with its concavity
looking toward the chest, and the ribs increase in length progressively, from
above downward, to the deepest portion of the arch, where they are longest,
and then become progressively shorter. " During inspiration the ribs ap-
proach to or recede from each other according to the part of the arch with
which they articulate ; the four superior ribs approach 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 mod-
erate, the diaphragmatic set (four inferior), to a great extent. The upper
edge of each of these ribs glides toward the vertebrae in relation to the lower

edge of the rib above, with the exception of the
lowest rib which is stationary" (Sibson). These
movements increase the antero-posterior and trans-
verse diameters of the thorax. As the ribs are ele-
vated and become more nearly horizontal, they
must push forward the lower portion of the ster-
num. Their configuration and mode of articula-
tion with the vertebrae are such that they can not
be elevated without undergoing a considerable ro-
tation, by which the concavity looking directly to-
ward the lungs is increased, and with it the lateral
diameter of the chest. All the intercostal spaces
. 48.-E^iol 'o7the nbs in posteriorly are widened in inspiration.
inspiration (Beciard). The ribs are elevated by the action of the ex-

The dark lines represent the ribs, J n . , , , . „ , , . ,

sternum and costal cartilages ternal intercostals, the sternal portion oi the inter-
nal intercostals and the levatores costarum. The

external intercostals are situated 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

MUSCLES OF INSPIKATION. 121

movable, the direction of the fibres of the intercostals from above downward
and forward renders elevation of the ribs a necessity of their contraction, if
it can be assumed that the first rib is fixed or at least does not move down-
ward. The scalene muscles elevate the first rib in ordinary inspiration ; and
in deep inspiration, this takes place to such an extent as to palpably carry
with it the sternum and the lower ribs. Theoretically, then, the external in-
tercostals can do nothing but render the ribs more nearly horizontal.

If the external intercostals be exposed in the dog — in which the costal
type of respiration is very marked — close observation can hardly fail to show
that these muscles enter into action in inspiration. 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 back-
ward, it is equally evident that they enter into action with inspiration. By
artificially inflating the lungs after death, it is seen that when the lungs are
filled with air, the fibres of these muscles are shortened (Sibson). In inspira-
tion the ribs are all separated 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 up-
per three, are widened in inspiration. Sibson has shown by inflation of the
chest, that although the ribs are separated from each other, the attachments
of the intercostals a*re approximated. The ribs, from an oblique position, are
rendered nearly horizontal ; and consequently the inferior attachments of the
intercostals are brought nearer the spinal column, while the superior attach-
ments to the upper borders of the ribs are slightly removed from it. Thus
these muscles are shortened. If, by separating and elevating the ribs, the
muscles be shortened, it follows that shortening of the muscles will necessa-
rily elevate and separate the ribs. In the three superior interspaces, the con-
stant direction of the ribs is nearly horizontal, and the course of the inter-
costal 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 others are widened in inspiration.

Levatores Costarum. — The action of these muscles can not 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.

Auxiliary Muscles of Inspiration. — The muscles which have just been
considered are competent to increase the capacity of the thorax sufficiently in
ordinary respiration ; but there are certain muscles attached to the chest and
the upper part of the spinal column or the upper extremities, which may act
in inspiration, although ordinarily 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

122 RESPIRATION— RESPIRATORY MOVEMENTS.

slight and is physiological, as after exercise, certain of the ordinary auxilia-
ries 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
difficult from any cause, threatening suffocation, all the muscles which can
by any possibility raise the chest are brought into action. These are put down
in the table under the head of extraordinary auxiliaries. Most of these mus-
cles can voluntarily be brought into play to raise the chest, and the mechan-
ism of their action can in this way be demonstrated.

8erratus Posticus Superior. — This muscle, by reversing its ordinary
action, 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 acting as a muscle of inspiration. It does not act in ordinary
respiration, but its contractions 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 very difficult or labored :

Levator Anguli Scapulce and Superior Portion of the Trapezius. — Move-
ments of the scapula have often been observed in labored respiration. Its
elevation during inspiration is effected chiefly by the levator anguli scapulse
and the upper portion of the trapezius.

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 efficient. With the coracoid process as the fixed point,
this muscle is capable of powerfully assisting 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 insertion into
the bicipital groove of the humerus, when the shoulders are fixed, in concert
with the pectoralis minor.

Serratus Magnus. — Acting from the scapula as the fixed point, this mus-
cle is capable of assisting the pectorals in raising the ribs and becomes a pow-
erful auxiliary in difficult inspiration.

The uses of the principal inspiratory muscles have been considered with-
out 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 es-
sential to life as are the respiratory movements of the larynx. In man, as
a rule the nares undergo no movements unless respiration be somewhat ex-
aggerated. In very difficult respiration the mouth is opened at each inspira-
tory act.

The division into muscles of ordinary inspiration, ordinary auxiliaries and
extraordinary auxiliaries, must not be taken as absolute. In the male, in
ordinary respiration, the diaphragm, intercostals and levatores costarum are
the principal inspiratory muscles, and the action of the scaleni, with the con-
sequent elevation of the sternum, is commonly very slight or it may be want-
ing. In the female the movements of the upper parts of the chest are more

EXPIRATION. 123

marked, and the scaleni, the serratus posticus superior, and sometimes the
sterno-mastoid, are brought into action in ordinary respiration. In the
different types of respiration, the action of the muscles engaged in ordinary
respiration necessarily presents considerable variations.

Expiration. — The air is expelled from the lungs, in ordinary expiration,
by a simple and comparatively passive process. The lungs contain a large
number of elastic fibres surrounding the air-cells and the smallest ramifica-
tions of the bronchial tubes, which give them great elasticity. 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 tonicity of the muscles which have been put on
the stretch restore the chest to what may be called 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 respira-
tion, are antagonistic to those which elevate the ribs. Aside from this, many
operations, such as speaking, blowing, singing etc., require powerful, pro-
longed or complicated acts of expiration, in which many muscles are brought
into play.

Expiration may be considered as depending upon two causes :

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 ster-
num, or the vertical diameter, by pressing up the abdominal viscera against
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 pul-
monary structure in expiration. From the collapse of the lungs when open-
ings are made in the chest, it is seen that even after the most complete expi-
ration, these organs have a tendency to expel part of their gaseous contents,
which can not be fully satisfied until the chest is opened. They remain par-
tially distended, on account of 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 tho-
racic cavities. In inspiration and in expiration, then, the relations between
the lungs and diaphragm are reversed. In inspiration, the descending dia-
phragm exerts a suction force on the lungs, drawing them downward ; in
expiration, the elastic lungs exert a suction force upon the diaphragm, draw-
ing it upward. This antagonism is one of the causes of the great power and
importance of the diaphragm as an inspiratory muscle.

The elasticity of the lungs operates chiefly upon the diaphragm in reduc-
ing the capacity of the chest ; for the walls of the thorax, by reason of their
own elasticity, have a reaction which succeeds the movements produced by
the inspiratory muscles. . Although this is the main action of the lungs

124 RESPIRATION— RESPIRATORY MOVEMENTS.

themselves in expiration, their relations to the walls of the thorax are impor-
tant. By virtue of their elasticity, they assist the passive collapse of the
chest. When they lose this property to any considerable extent, as in vesic-
ular emphysema, they offer a notable resistance to the contraction of the
thorax ; so much indeed, that in old cases of this disease the thoracic move-
ments are restricted, and the chest presents a characteristic rounded and dis-
tended appearance.

Little more need be said concerning the passive movements of the tho-
racic 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 mus-
cles concerned in expiration :

MUSCLES OF EXPIRATION".
Ordinary Respiration.

MUSCLE. ATTACHMENTS.

Osseous portion of internal intercostals . . 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 carti-
lages 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, Poupart'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, pectineal line.

Transversalis Outer third of Poupart's ligament, anterior two-
thirds of the crest of the ileum, lumbar verte-
brae, 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 uses in
different parts of the thorax. They are attached to the inner borders of the
ribs and costal cartilages. 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 action of that portion of
the internal intercostals situated between the costal cartilages has already
been noted. They assist the external 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, par-
ticularly in that portion of the thorax where the obliquity of the ribs is

MUSCLES OF EXPIRATION. 125

greatest. They are elongated when the chest is distended, and are shortened
when the chest is collapsed (Sibson). This fact, taken in connection with
experiments on living animals, shows that they are muscles of expiration.
Their contraction tends1 to depress the ribs and consequently to diminish the
capacity of the chest.

I nfraco stales. — These muscles, situated at the posterior part of the tho-
rax,' are variable 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 intercostals, 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 action of the triangularis sterni. From its origin, the ensiform
cartilage, lower borders of the sternum, and lower three or four costal carti-
lages, 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.

The above-mentioned muscles are called into action in ordinary, tranquil
respiration, and their sole office 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 formation of the walls of the abdomen, and
their general action in expiration is to press the abdominal viscera and dia-
phragm 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 extent of the expiratory act is
regulated. They are also attached to the ribs or costal cartilages, and while
they press the diaphragm upward, they depress the ribs and thus dimin-
ish 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 force of the ex-
piratory act.

In labored respiration in disease and in the hurried respiration which fol-
lows violent exercise, the auxiliary muscles of expiration, as well as of inspi-
ration, are called into action to a considerable extent.

Obliquus Externus. — This muscle, in connection with the obliquus in-
ternus and transversalis, is efficient in forced or labored expiration, by press-
ing the abdominal viscera against the diaphragm. Acting from its attach-
ments to the linea alba, the crest of the ileum and Poupart's ligament, by its
attachment to the eight inferior ribs, it draws the ribs downward.

Obliquus Internus. — This muscle also acts in forced expiration, by com-
pressing the abdominal 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 carti-
lages of the four inferior ribs, it draws them downward. The direction of the
10

126 RESPIRATION— RESPIRATORY MOVEMENTS.

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.

Transver sails. — The expiratory action of this muscle is mainly in com-
pressing the abdominal 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 downward, acting as an antagonist to the
lower levatores costarum.

There are some other muscles which may be used in forced expiration,
assisting in the depression of the ribs, such as the serratus posticus inferior,
the superior fibres of the serratus magnus and the inferior portion of the
trapezius, but their action in respiration is unimportant.

Types of Respiration. — In the movements of expansion of the chest, al-
though all the muscles which have been classed as ordinary inspiratory mus-
cles 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. Three 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 less than three years of
age, irrespective of sex, respiration being carried on almost exclusively by the
diaphragm.

At a variable period after birth, a difference in the types of respiration in
the sexes is observed. 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 predom-
inates. Without discussing the question as to the exact age when this differ-
ence in the • sexes first makes its appearance, it may be stated in general
terms, that a short time before the age of puberty in the female, the superior
costal type becomes more marked and soon predominates. In the male,
respiration continues to be carried on mainly by the diaphragm and the
lower part of the chest.

The cause of the pronounced movements of the upper part of the chest in
the female has been the subject of considerable discussion. It is probably due,
in a great measure, to the mode of dress now so general in civilized countries,
which confines the lower part of the chest and renders movements of expan-
sion somewhat difficult. In a series of observations by Thomas J. Mays
(1887), upon eighty-two chests of Indian girls at the Lincoln Institution in

FREQUENCY OF THE RESPIRATORY MOVEMENTS. 127

Philadelphia, between ten and twenty years of age, who had never worn tight
clothing, the abdominal type of respiration was found to predominate, the
respiratory tracings hardly differing from the tracings in the male. These
observations seem to show, in opposition to the views of Hutchinson and
others, that the predominance of the superior costal type in the female is
confined to civilized races ; but it is certain that females accommodate them-
selves more readily than the male to the superior costal type ; and this is
probably a provision against the physiological enlargement of the uterus in
pregnancy, which nearly arrests all respiratory movements except those of the
upper part of the chest. In pathology it is observed that females are able to
carry, without great inconvenience, a large quantity of water in the abdominal
cavity ; while a much smaller quantity, in the male, produces great distress
from difficulty of breathing.

Frequency of the Respiratory Movements. — In counting the respiratory
acts, it is desirable that the subject be unconscious of the observation, other-
wise their normal rhythm is likely to be disturbed. Of all who have written
on this subject, Hutchinson has presented the largest and most reliable col-
lection of facts. This observer ascertained the number of respiratory acts
per minute, in the sitting posture, in 1,897 males. The results of his ob-
servations, with reference to frequency, are given in the following table :

RESPIRATIONS PER MINUTE. NUMBER OP CASES.

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 (1,731) breathed 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 four pulsations of the heart.
The same proportion generally obtains when the pulse is accelerated in dis-
ease, except when the pulmonary organs are involved.

Age has an 'influence on the frequency of the respiratory acts, correspond-
ing with what has already been noted with regard to the pulsations of the
heart.

The following are the results of observations on 300 males (Quetelet) :

44 respirations per minute, soon after birth ;

128 RESPIRATION— RESPIRATORY MOVEMENTS.

26, at the age of five years ;

20, between fifteen and twenty years ;

19, between twenty and twenty-five years ;

16, about the thirtieth year ;

18, between thirty and fifty years.

The influence of sex is not marked in very young children. There is 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 num-
ber of respiratory acts is diminished by about twenty per cent. (Quetelet).
Muscular effort accelerates the respiratory movements pari passu with the
movements of the heart.

Relations of Inspiration and Expiration to each other — Respiratory
Sounds. — In ordinary respiration, inspiration is produced by the action of
muscles, and expiration, by the passive reaction of the lungs and of the elas-
tic walls of the thorax, The inspiratory and expiratory acts do not immedi-
ately follow each other. Beginning with inspiration, it is found that this
act maintains about the same intensity throughout. There is then a very
brief interval, when expiration follows, which has its maximum of intensity
at the beginning of the act and gradually dies away. Between the acts of
expiration and inspiration is an interval, which is somewhat longer than the
interval between inspiration and expiration.

The duration of expiration is generally somewhat longer than that of
inspiration, although the two acts may be nearly, or in some instances, quite
equal. After five to eight ordinary respiratory acts, an effort generally occurs
which is rather more profound than usual, by which the air in the lungs is
more thoroughly changed. The temporary arrest of the acts of respiration
in violent muscular efforts, in straining, in parturition etc., is sufficiently
familiar.

Ordinarily respiration is not accompanied by any sound which can be
heard without applying the ear directly, or by the intervention of a stetho-
scope, to the chest, except when the mouth is closed and breathing is carried
on exclusively through the nasal passages, when a soft, breezy sound accom-
panies both acts. If the mouth be opened sufficiently to admit the free pas-
sage of air, no sound is to be heard in health. In sleep the respirations are
more profound; and if the mouth be closed the sound is rather more
intense.

Snoring, 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 in many individuals,
although those who do not snore habitually may do so when the system is
unusually exhausted and relaxed. It occurs only when the mouth is open,
and the sound is produced by vibration and a sort of flapping of the velum

RESPIRATORY SOUNDS. 129

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 respira-
tion. In inspiration, according to the late Dr. Austin Flint, " it attains its
maximum of intensity quickly after the development of the sound and main-
tains 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 expiration fol-
lows. This is also tubular in quality. It soon attains its maximum of inten-
sity, but unlike the sound of inspiration, it gradually dies away and is lost im-
perceptibly. 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 character 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 tracheal sound. It is continuous and
rather increases in intensity from its beginning to its termination, ending
abruptly, like the tracheal inspirator^ sound. The sound is produced in part
by the movement of air in the small bronchial tubes, but chiefly by the expan-
sion of the air-cells of the lungs. It is followed, without an interval, by the
sound of expiration, which is shorter — one-fifth or one-fourth as long — lower
in pitch and much less intense. A sound is not always heard in expiration.

The variations in the intensity of the respiratory sounds in different indi-
viduals are very considerable. As a rule they are more intense in young per-
sons ; 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 unnecessary to make the attempt, when they can be so easily studied in the
living subject.

Coughing, Sneezing, Sighing, Yawning, Laughing, Sobbing and Hic-
cough.— These peculiar acts demand a few words of explanation. Coughing
and sneezing are generally involuntary acts, produced by irritation in the air-
tubes or nasal passages, although coughing is often voluntary. In both of
these acts, there is first a deep inspiration followed by a convulsive action of
the expiratory muscles, by which the air is violently expelled with a charac-
teristic 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 bronchial mucous mem-
brane, the accumulated mucus is carried by the act of coughing either to the
mouth or well into the larynx, when it may be expelled by the act of exspui-

130 RESPIRATION— RESPIRATORY MOVEMENTS.

tion. When either of these acts is the result of irritation from a foreign
substance or from secretions, it may be modified or partly smothered by the
will, but is not completely under control. The sensibility of the mucous
membrane at the summit of the air-passages usually protects them from the
entrance of foreign matters, both liquid and solid; for the slightest im-
pression received by the membrane gives rise to a violent and involuntary
cough, by which the offending substance is removed. The glottis, also, is
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 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 efficiently per-
formed. Yawning is an analogous process, but it differs from sighing in the
fact that it is involuntary and can not be produced by an effort of the will.
It is characterized 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 contagion. When not the result of imitation,
it has the same exciting cause as sighing — 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.

Laughing and sobbing, although expressing opposite conditions, are
produced by very nearly the same action. The characteristic sounds accom-
panying these acts are the result of short, rapid and convulsive movements
of the diaphragm, attended with contractions 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 invol-
untary. 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 con-
striction of the glottis. The contraction of the diaphragm is more extensive
than in laughing and sobbing and occurs only once every four or five respir-
atory acts.

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 hun-
dred cubic inches (3,277 c.c.) ; but it is evident, from the simple experiment of
opening the chest, when the elastic lungs collapse and expel a certain quan-
tity of air which can not 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

CAPACITY OF THE LUNGS. 131

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, and a nearly equal quantity is expelled by the succeeding expira-
tion. By the extreme action of all the inspiratory muscles in a forced inspi-
ration, 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 of description, physiologists have adopted the following names,
which are applied to these various volumes of air :

1. Residual Air ; that which is not and can not be expelled by a forced
expiration.

2. Reserve Air ; that which remains after an ordinary expiration, deduct-
ing the residual air.

3. Tidal, or Ordinary Breathing Air ; that which is changed by the
ordinary acts of inspiration and expiration.

4. Complemented Air ; the excess over the ordinary breathing air, which
may be introduced by a forcible inspiration.

In measuring the air changed in ordinary breathing, it has been found
that the acts of respiration are so easily influenced 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 and of
Hutchinson. Those of the last-named observer are very elaborate and
were made on a large number of subjects of both sexes and of all ages and
occupations. They are generally accepted by physiologists, as the most ex-
tended and accurate.

Residual Air. — Perhaps there is not one of the questions under consider-
ation 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 in health are always 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 vol-
ume which thus remains has been variously estimated. The residual volume
has been estimated at about one hundred cubic inches (1,639 c.c.), but the
quantity varies very considerably in different individuals (Hutchinson).
Taking everything into consideration, it may be assumed that this estimate
is as nearly correct as any.

Reserve Air. — This name is given to the volume of air which may be ex-
pelled 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, accord-
ing to Hutchinson, is one hundred cubic inches (1,639 c.c.).

132 RESPIRATION— RESPIRATORY MOVEMENTS.

More or less of the reserve air is changed whenever there is 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 once in every five to eight acts. It is used in certain prolonged vocal
efforts, in blowing etc. Added to the residual air, it constitutes the mini-
mum capacity of the lungs in ordinary respiration. As it is continually re-
ceiving watery vapor and carbon dioxide, 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, 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 sus-
pend the respiratory acts for two or three minutes without inconvenience.
The introduction of fresh air with each inspiration, and the constant
diffusion which is going on arid 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 certain physiological varia-
tions ; and the respiratory movements, as regards their extent, are so easily
influenced, that great care is necessary to avoid error in estimating the vol-
ume of ordinary breathing air. As a mean of the results obtained by
Herbst and by Hutchinson, the average volume of breathing air, in a man of
ordinary stature, is twenty cubic inches (327'7 c.c.). According to Hutchin-
son, in perfect repose, when the respiratory movements are hardly perceptible,
not more than seven to twelve cubic inches (114*7 to 196-6 c.c.) are changed ;
while, under excitement, the volume may be increased to seventy-seven cubic
inches (1,261-8 c.c.). The breathing volume progressively increases in pro-
portion to the stature of the individual, and bears no definite relation to the
apparent capacity of the chest (Herbst).

Complemental Air. — The thorax may be so enlarged by an extreme vol-
untary inspiratory effort as to contain a quantity of air much larger than
after an ordinary inspiration. 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 (1,802-9 c. c.).

The complemental air is drawn upon whenever an effort is made which
requires a temporary arrest of respiration. Brief and violent muscular exer-
tion is generally preceded by a profound inspiration. In sleep, as the vol-
ume of breathing air is somewhat increased, the complemental air is en-
croached upon. A part or the whole of the complemental air is also used in
certain vocal efforts, in blowing, in yawning, in the deep inspiration which
precedes sneezing, in straining etc.

CAPACITY OF THE LUNGS. 133

Extreme Breathing Capacity. — By the extreme breathing capacity is
meant the volume of air which can be expelled from the lungs by the most
forcible expiration after the most profound inspiration. This has been
called by Hutchinson, the vital capacity, 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 it
represents the extreme capacity of the chest, less the residual air. Its
physiological importance is due to the fact that it can readily be determined
by an appropriate 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 Hutchinson amounts in all to a little
less than 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 begins with the proposition that in a man of medium height
(five feet eight inches, or 170-2 centimetres), it is equal to two hundred and
thirty cubic inches (3,768-6 c. c.).

The most striking result of the experiments of 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 by 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. He ascertained that for every inch
(2-5 centimetres) in height, between five and six feet (152-4 and 182-9 centi-
metres), the extreme breathing capacity is increased by eight cubic inches
(131-1 c. c.).

Age has an influence, though less marked than stature, upon the extreme
breathing capacity. As the result of 4,800 observations on males, it was ascer-
tained that the volume increases with age up to the thirtieth year, and pro-
gressively decreases, with tolerable regularity, from the thirtieth to the six-
tieth year. These figures, though necessarily subject to certain individual
variations, may be taken as a basis for examinations of the extreme breath-
ing capacity in disease.

Relations in Volume of the Expired to the Inspired Air. — A certain pro-
portion 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. The
loss was put by Davy at fa and by Cuvier at -g^ of the volume of air intro-
duced. Observations on this point, to be exact, must include a considerable
number of respiratory acts ; and from the difficulty of continuing respiration
in a perfectly regular and normal manner when the attention is directed to
the respiratory movements, 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 2,990 cubic inches
(49,000 c. c.) of air, and ascertained that the volume had diminished by
sixty-one cubic inches (1,000 c. c.), or a little more than one-fiftieth. Adopt-
ing the approximations of Davy and Cuvier, applied to the human subject, as

134 RESPIRATION— RESPIRATORY MOVEMENTS.

nearly correct, it may be assumed that in the lungs, ^ to -g^ of the inspired
air is lost.

Diffusion of Air in the Lungs. — When it is remembered that with each
inspiration, but about twenty cubic inches (327*7 c. c.) of fresh air are intro-
duced, sufficient only to fill the trachea and larger bronchial tubes, it is evi-
dent 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 interchange between the fresh air in the upper portions of the respira-
tory apparatus and the air in the deeper parts of the lungs is constantly going
on by simple diffusion aided by the active currents or impulses produced by
the alternate movements of the chest. In the respiratory apparatus, at the
end of an 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 heavier, as it con-
tains a certain quantity of carbon dioxide. 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 carbon dioxide 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 inversely proportionate to the square root of their densities, the
penetration of atmospheric 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 carbon dioxide ; so that eighty-one parts of carbon dioxide
should be replaced by ninety-five parts of oxygen. It is found, indeed, that
the volume of carbon dioxide exhaled is always less than the volume of
oxygen absorbed. This diffusion is constantly going on, so that the air in
the pulmonary vesicles, where the interchange of gases with the blood takes
place, maintains a nearly uniform composition. The process of aeration of
the blood, therefore, has little of that intermittent character which attends
the muscular movements of respiration, which would occur if the entire
gaseous contents of the lungs were changed with each respiratory act.

COMPOSITION OF THE AIR. 135

CHAPTER V.

CHANGES WHICH THE AIR AND THE BLOOD UNDERGO IN RESPIRATION.

Composition of the air— Consumption of oxygen— Exhalation of carbon dioxide— Relations between the
quantity of oxygen consumed and the quantity of carbon dioxide exhaled — Sources of carbon dioxide
in the expired air— Exhalation of watery vapor— Exhalation of ammonia — Exhalation of organic matter
—Exhalation of nitrogen— Changes of the blood in respiration (haematosis)— Difference in color between
arterial and venous blood— Comparison of the gases in venous and arterial blood— Analysis of the blood
for gases— Nitrogen of the blood— Condition of the gases in the blood— Relations of respiration to nutri-
tion etc.— The respiratory sense— Sense of suffocation— Respiratory efforts before birth — Cutaneous
respiration— Breathing in a confined space— Asphyxia.

FROM the allusions already made to the general process of respiration, it
is apparent that before the discovery of the nature of the gases which com-
pose 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 also evident that no definite knowledge of the processes of
respiration could exist prior to the discovery of the circulation of the blood.

The discovery of the properties of oxygen and carbon dioxide 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 La-
voisier, whose observations mark the beginning of an accurate knowledge of
the physiology of respiration. With the balance, Lavoisier showed the nature
of the oxides of the metals ; he discovered that carbon dioxide is formed by a
union of carbon and oxygen ; and noting the consumption of oxygen and the
production of carbon dioxide in respiration, he advanced, for the first time,
the view that the one was concerned in the production of the other. Although,
as would naturally be expected, the doctrines of Lavoisier have been modified
with the advances in science, he developed facts which have served as the
starting-point of definite knowledge on this subject.

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 Boussin-
gault). It contains, in addition, a very small quantity of carbon dioxide,
about one part in two thousand. 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. Floating in the atmosphere, are large numbers of minute
organic bodies ; and various odorous and other gaseous matters sometimes are
present as accidental constituents.

In considering the processes 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 regular performance of respiration, 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 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

136 CHANGES OF AIR AND BLOOD IN RESPIRATION.

surface and the reduced atmospheric pressure diminishes the capacity of the
blood for retaining gases.

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 carbon
dioxide and water exhaled, as fast as they were produced, died of asphyxia
when the quantity of oxygen became reduced to between three and five per
cent.

A few experiments are on record in which the human subject and the
lower animals have been made to respire for a time pure oxygen. Allen and
Pepys confined animals for twenty-four hours in an atmosphere of pure oxy-
gen without any notable results ; but these experiments do not show that it
would be possible to respire unmixed oxygen indefinitely without incon-
venience. As it exists in the air, oxygen is undoubtedly in the best condi-
tion for the permanent maintenance of the respiratory function. The blood
seems to have a certain capacity for the absorption of oxygen, which is not
materially increased when the pure gas is respired.

The only other gas which has the power of maintaining respiration, even
for a time, is nitrogen monoxide. This is appropriated by the blood-cor-
puscles with great avidity, and for a time it produces an exaggeration of the
vital processes, with delirium etc., which has given it the common name of
the laughing gas ; but this condition is followed by ansesthesia, and finally
by asphyxia, probably because the gas has so strong an affinity for the blood-
corpuscles as to remain to a certain extent fixed, interfering with the inter-
change of gases which is essential to life. Notwithstanding this, experiment-
ers have confined with impunity rabbits and other animals in an atmosphere
of nitrogen monoxide for a number of hours. In all cases they became
asphyxiated, but in some instances they were restored on being brought again
into the ordinary atmosphere.

Other gases which may be introduced into the lungs either produce as-
phyxia, negatively, from the fact that they are incapable of carrying on respi-
ration, like hydrogen or nitrogen, or positively, by a poisonous effect on the
system. The most important of the gases which act as poisons are carbon
monoxide, hydrogen monosulphide and arsenious hydride. Carbon mo-
noxide unites with the coloring matter of the red corpuscles, forming carbon-
monoxide-haemaglobine. This union is so stable that it paralyzes the cor-
puscles as oxygen-carriers and produces death by asphyxia. It is probable
that carbon dioxide is not in itself poisonous. Regnault and Reiset exposed
animals (dogs and rabbits) for many hours, to an atmosphere containing
twenty-three per cent, of carbon dioxide artificially introduced, with between
thirty and forty per cent, of oxygen, without any ill effects.

Consumption of Oxygen. — The determination of the quantity of oxygen
which is removed from the air by the process of respiration is important ; and
on this point, there is an accumulated mass of observations which are com-
paratively unimportant from the fact that they were made before the means
of analysis of the gases were as accurate as they now are. In the observations

CONSUMPTION OF OXYGEN. 137

of Regnault and Reiset, animals were placed in a receiver filled with air, a
measured quantity of oxygen was introduced as fast as it was consumed by
respiration, and the carbon dioxide was constantly removed and carefully esti-
mated. 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 wa$ 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 carbon dioxide and other matters must interfere more or
less with the proper performance of the respiratory function. As employed
by Regnault and Reiset, it is adapted only to experiments on animals of small
size. These give but an approximate idea, however, of the processes as they
take place in the human subject. Pettenkofer constructed a chamber large
enough to admit a man and allow perfect freedom of motion, eating, sleep-
ing etc., into which air could be constantly introduced in definite quantity,
and from which the products of respiration were constantly removed and
estimated. This method had been adapted to the human subject on a small
scale in 1843, by Scharling, but there was no arrangement for estimating the
quantity of oxygen consumed.

Estimates of the absolute quantities of oxygen consumed or of carbon
dioxide exhaled, based on analyses of the inspired and expired air, calcula-
tions 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, Where there is so
much multiplication and calculation, a very slight inaccuracy in the estimates
of the quantities consumed or produced in a single respiration will make a
large error in the estimate for a day or even for an hour. Bearing in mind
all these sources of error, from the experiments of Valentin and Brunner, Du-
mas, Regnault and Reiset and others, a sufficiently accurate approximate esti-
mate of the proportion of oxygen consumed by the human subject may be
made. 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 useful to extend this estimate as far as pos-
sible 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 build-
ings, hospitals etc., is a question of great practical importance. Assuming
that the average respirations per minute are eighteen, and that with each act,
twenty cubic inches (327*7 c. c.) of air are changed, fifteen cubic feet (424-8
litres) of oxygen are consumed in the twenty-four hours, which represent
three hundred cubic feet (8*5 cubic metres) of pure air. This is the mini-
mum quantity of air which is actually used, making no allowance for any in-
crease in the activity of the respiratory processes, which is liable to occur
from various causes. To meet all the respiratory exigencies of the system, in
hospitals, prisons etc., it has been found necessary to allow at least eight

138 CHANGES OF AIR AND BLOOD IN RESPIRATION.

hundred cubic feet (22-65 cubic metres) of air for each person, unless the con-
ditions be such that the air is changed with unusual frequency ; for in ad-
dition to the actual loss of oxygen in the respired air, emanations from both
the pulmonary and cutaneous surfaces are constantly taking place, which
should be removed. In some institutions as much as twenty-five hundred
cubic feet (70*79 cubic metres) of air are allowed for each person.

The quantity of oxygen consumed is subject to great variations, depend-
ing upon temperature, the condition of the digestive system, muscular activ-
ity etc. The following conclusions, the results of the observations of La-
voisier and Seguin, give at a glance the variations from the above-mentioned
causes :

" 1. A man, in repose and fasting, with an external temperature of about
90° Fahr. (32*5° C.), consumes 1,465 cubic inches (24 litres) of oxygen per
hour.

" 2. The same man, in repose and fasting, with an external temperature
of 59° Fahr. (15° C.), consumes 1,627 cubic inches (26-66 litres) of oxygen
per hour.

"3. The same man, during digestion, consumes 2,300 cubic inches (37'69
litres) of oxygen per hour.

" 4. The same man, fasting, accomplishing the labor necessary to raise, in
fifteen minutes, a weight of about 16 Ib. 3 oz. (7*343 kilos.) to the height of
656 feet (200 metres) consumes 3,874 cubic inches (63*48 litres) of oxygen per
hour.

" 5. The same man, during digestion, accomplishing the labor necessary
to raise, in fifteen minutes, a weight of about 16 Ib. 3 oz. (7'343 kilos.) to the
height of 692 feet (211*146 metres), consumes 5,568 cubic inches (91*24 litres)
of oxygen per hour."

All who have experimented on the influence of temperature upon the con-
sumption of oxygen, in the warm-blooded animals and in the human subject,
have noted a marked increase 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 longer under water ; and cases are
on record in which life has been restored in newborn 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 is near-
ly that of a cold-blooded animal. The lungs are relatively very small, and it
is some time before they fully assume their office. The muscular movements
are hardly more than are necessary to take the small quantity 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 a low temperature. Although accu-
rate 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 difference in color is not so marked as it is after pulmonary respira-
tion has become established. The direct researches of W. F. Edwards have
shown that the absolute consumption of oxygen by very young animals is

CONSUMPTION OF OXYGEN. 139

quite small ; and the observations of Legallois, on rabbits, made every five
• days during the first month of life, show a rapidly increasing demand for
oxygen.

The consumption of oxygen is greater in lean than in very fat animals,
provided they be in perfect health. The consumption is greater, also, in car-
nivorous than in herbivorous animals ; and in animals 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 (Regnault and Reiset).

During sleep the quantity of oxygen consumed is considerably dimin-
ished ; and in hibernation it is so small, that Spallanzani could not detect
any difference in the composition of the air in which a marmot, in a state of
torpor, had remained for three hours. In experiments on a marmot in hiber-
nation, Regnault and Reiset observed a reduction in the oxygen consumed to
about -fa of the ordinary quantity.

It has been shown by experiments, that the consumption of oxygen bears
a nearly constant ratio to the production of carbon dioxide; and as the
observations upon the influence of sex, the number of respiratory acts etc., on
the activity of the respiratory processes have been made chiefly with reference
to the carbon dioxide exhaled, these influences will be considered in connec-
tion 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 remarkable.
When hydrogen is thus substituted for the nitrogen of the air, the consump-
tion of oxygen is largely increased. Regnault and Reiset attributed this to
the superior refrigerating power of the hydrogen ; but a more rational expla-
nation would seem to be in its greater 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 carbon dioxide, is undoubt-
edly 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 nitro-
xge<nof the air plays an important part in the phenomena of respiration, by
jr 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 ap-
proximately, the average quantity consumed per hour. The estimate arrived
at by Longet, from a comparison of the results obtained by different reliable
observers, is perhaps as near the truth as possible. This estimate puts the
hourly consumption at 1,220 to 1,525 cubic inches (20 to 25 litres), " in an

140 CHANGES OF AIR AND BLOOD IN RESPIRATION.

adult male, during repose and in normal conditions of health and tem-
perature."

In passing through the lungs, the air, in addition to losing a certain pro-
portion of its oxygen, undergoes the following changes :

1. Elevation in temperature.

2. Gain of carbon dioxide.

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 studied by Grehant. He found that with an external tem-
perature of 72° Fahr. (22-22° C.), 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 external influences, marked
a temperature of 95-4° Fahr. (35'22° C.). Taking in the air by the mouth,
the temperature of the expired air was 93° Fahr. (33'89° C.). At the begin-
ning of the expiration, Grehant noted a temperature of 94° Fahr. (34'44° C.).
After a prolonged expiration, the temperature was 96° Fahr. (35-55° C.). In
these observations the temperature taken beneath the tongue was 98° Fahr.
(36-67° C.)

Exhalation of Carbon Dioxide. — On account of the variations in the quan-
tities of carbon dioxide exhaled at different times of the day, and particularly
the great influence of the rapidity of the respiratory movements, it is 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 form-
ing an estimate of the proportion of this gas consumed. As it was 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 carbon dioxide 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 carbon dioxide is equal to the
volume of the carbon dioxide, it is seen that a certain quantity of oxygen
disappears in respiration and is not represented in the carbon dioxide ex-
haled.

There are great differences in the proportion of carbon dioxide in the
expired air, depending upon the time during which the air has remained in
the lungs. This point was 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 carbon dioxide
expelled at each expiration is much less than in a slow expiration ; but the
quantity of carbon dioxide produced during a given time by frequent respira-
tions is greater than that which is thrown off by slow expirations."

EXHALATION OF CARBON DIOXIDE. 141

The air which escapes during the first part of an expiration is less rich
in carbon dioxide than that which is last expelled and comes directly from
the deeper portions of the lungs. Dividing, as nearly as possible, the expira-
tion into two equal parts, Vierordt found, as the mean of twenty-one experi-
ments, 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 has a marked influence
in increasing the proportion of carbon dioxide 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 carbon dioxide 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 carbon dioxide in
the expired air was increased 1-73 above the normal standard; but the abso-
lute quantity exhaled was diminished by 2-642 cubic inches (43-3 c. c.) After
taking the deepest possible inspiration and holding the breath for one hun-
dred seconds, the percentage was increased 3*08 above the normal standard ;
but the absolute quantity was diminished more than fourteen cubic inches
(229-4 c. c.). Allen and Pepys noted that air which had passed nine or ten
times through the lungs contained 9*5 per cent, of carbon dioxide.

Vierordt has given the following formula as representing the influence of
the frequency of the respirations on the production of carbon dioxide :
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 carbon dioxide exhaled in a given time is a more
important subject of inquiry than the proportion contained in the expired
air ; for the latter varies 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 carbon dioxide
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 Edward Smith. The
observations of Lavoisier and Seguin, Prout, Davy,' Dumas, Allen and Pepys,
Scharling and others, do not seem to have fulfilled the necessary experimental
conditions so completely. The observations of Andral and Gavarret were
made on sixty-two persons of both sexes and different ages, and under identi-
cal conditions as regards digestion, time of the day, barometric pressure and
temperature ; and the observations on males between the ages of sixteen and
thirty, between 1 and 2 P. M., under identical conditions of the digestive and
muscular systems, each experiment lasting eight to thirteen minutes, showed
an exhalation of about 1,220 cubic inches (20 litres) of carbon dioxide per
hour.

Edward Smith employed the following method for the estimation of
the carbon dioxide exhaled : He used a mask, fitting closely to the face, which
covered only the air-passages. The air was admitted after having been meas-
11

142 CHANGES OF AIR AND BLOOD IN RESPIRATION.

ured by an ordinary, dry gas-meter. The expired air was passed through a
drying apparatus, and the carbon dioxide was absorbed by a solution of
potassium hydrate, arranged in a number of layers so as to present a surface
of about seven hundred square inches (45 square decimetres), and was care-
fully weighed. This apparatus was capable of collecting all the carbon dioxide
exhaled in an hour. The estimates were made for eighteen waking hours
and six hours of sleep. The observations occupied ten minutes each and
were made every hour and half -hour for eighteen hours. The average for
the eighteen hours gave 20,082 cubic inches (329 litres) of carbon dioxide for
the whole period. Observations during the six hours of sleep showed a total
exhalation of 4,126 cubic inches (7*145 litres). 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, or
336-145 litres), containing 7-144 oz. (202-47 grammes) of carbon. In view
of the great variations in the exhalation of carbon dioxide, this estimate can
be nothing more than an approximation.

One of the important modifying influences is muscular exertion, by which
the production of carbon dioxide 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 has given the following approxi-
mate estimates of these differences :

In quietude 7*144 oz. (202*47 grammes) of carbon.

Non- laborious class 8*68 " (246*04 grammes) "

Laborious class 11*7 " (331-61 grammes) " •

In studying the variations in the exhalation of carbon dioxide, important
imformation 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 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 ; kind of diet ; sleep ; muscu-
lar 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 extraiiterine existence, the demand for oxy-
gen on the part of the system is very small. At this period there is a corre-
spondingly feeble exhalation of carbon dioxide. It is well known that during
the first hours and days after birth, the new being has little power of generat-
ing heat, needs constant protection from changes in temperature, 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 ani-
mal functions are so imperfectly developed and until the alimentation be-
comes more abundant and the child begins to increase rapidly in weight, the
quantity of carbon dioxide exhaled is very small.

After the respiratory function has become fully established, it is probable.

EXHALATION OF CARBON DIOXIDE. 143

from the greater number of respiratory movements in early life, that the pro-
duction of carbon dioxide, 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 exhala-
tion of carbon dioxide in the male, between the ages of twelve and 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. Taking into con-
sideration 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, and there
can be no doubt that there is a rapid diminution in the relative quantity of
carbon dioxide produced in old age. Scharling, in a series of observations
on a boy nine years of age, an adult of twenty-eight, and one of thirty-five
years, showed that the respiratory activity in the child was nearly twice as
great, in proportion to his weight, as the average in the .adults.

Influence of Sex. — All observers have found a marked difference between
the sexes, in favor of the male, in the proportion of carbon dioxide exhaled.
Andral and Gavarret noted an absolute difference of about forty-five cubic
inches (737'4 c. c.) per hour, but did not take into consideration the differ-
ences 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 muscular activity in the sexes is sufficient to account for
the greater elimination of carbon dioxide in the male, for this substance
is exhaled in proportion to the muscular development of the individual;
but there is an important difference connected with the variations with
age, which depends upon the condition of the generative system of the
female. The absolute increase in the exhalation of carbon dioxide with age,
in the female, is arrested at the time of puberty and remains stationary until
the cessation of the menses, provided the menstrual flow occur with regular-
ity (Andral and Gavarret). During this time the average exhalation per
hour is 714 cubic inches (11-69 litres). After the cessation of the menses
the quantity gradually increases, until, at the age of sixty, it amounts to 915
cubic inches (15 litres) per hour. From the age of sixty to eighty- two the
quantity diminishes to 793 (13 litres), and finally to 670 cubic inches (about
11 litres). When the menses are suppressed, there is an increase in the
exhalation of carbon dioxide, which continues until the flow becomes reestab-
lished. In a case of pregnancy observed by Scharling the exhalation was
increased to about 885 cubic inches (14-5 litres).

Influence of Digestion. — Almost all observers agree that the exhalation of
carbon dioxide is largely increased during digestion. Lavoisier and Seguin
found that in repose and fasting, the quantity exhaled per hour was 1,210
cubic inches (19-82 litres), which was raised to 1,800 and 1,900 (29-5 and
31-14 litres) during digestion. A series of observations on this point was
made by Vierordt upon his own person. Taking his dinner between 12*30

144 CHANGES OF AIR AND BLOOD IN RESPIRATION.

and 1 P. M., having noted the frequency of the pulse and respirations and the
exhalation of carbon dioxide at 12 M., he found at 2 p. M., the pulse and res-
pirations increased in frequency, the volume of expired air augmented, and
the carbon dioxide exhaled increased from 15*77 to 18-22 cubic inches
(258-43 to 298-6 c. c.) 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 carbon dioxide exhaled.

The effect of inanition is to gradually diminish the exhalation of carbon
dioxide. Bidder and Schmidt noted the daily production 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. Edward Smith noted in his own
person the influence of a fast of twenty-seven hours. There was a marked
dimunition 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 exhala-
tion of carbon dioxide was diminished one-fourth. An important point in
this observation was that the quantity was as small four and a half hours
after eating as at the end of the twenty-seven hours.

Influence of Diet. — The most extended series of investigations on the in-
fluence of diet upon the absolute quantity of carbon dioxide exhaled are those
of Edward Smith. This observer made a large number of experiments 011
the influence of various kinds of food, and extended his inquiries into the
influence of certain beverages, such as tea, coffee, cocoa, malt liquors and fer-
mented liquors. He divided food into two classes : one which increases the
exhalation of carbon dioxide, which he called respiratory excitants, and the
other, which diminishes the exhalation, he called non-exciters. The follow-
ing are the results of a large number of observations upon four persons :

" 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 vola-
tile elements of wines and spirits, and^ coffee-leaves.

u 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 propor-
tion to their quantity. Compound aliments, as the cereals, containing sev-
eral of these substances, have an action greater than that of any of their ele-
ments.

" 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 substance containing a large amount of carbon
evolves more than a small portion of that carbon in the temporary action

EXHALATION OF CARBON DIOXIDE. 145

occurring above the basis-line, and hence a large portion remains unaccounted
for by these experiments."

The comparative observations 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 idiosyncra-
sies and the tastes of different individuals.

The following are the results of observations upon the effects of different
alcoholic beverages taken during the intervals of digestion :

" Brandy, whiskey, and gin, and particularly the latter, almost always less-
ened the respiratory changes recorded, while rum 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 de-
cided 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."

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 exhala-
tion of carbon dioxide. This effect is almost instantaneous, when the articles
are taken into the stomach fasting ; and when taken with the meals, the
increase in carbon dioxide, which habitually accompanies the process of
digestion, is materially lessened. Rum, which was found to be a respiratory
excitant, is an exception to this rule. Malt liquors seem to increase the ex-
halation of carbon dioxide. " The action of pure alcohol was much more to
increase than to lessen the respiratory changes, and sometimes the former
effect was well pronounced."

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 carbon dioxide. According to Edward Smith, the quantity
during the night is to the quantity during the day, in complete repose, as ten
to eighteen.

It has already been stated that there is great diminution in the quantity
of oxygen consumed in hibernating animals while in a torpid condition.
Regnault and Reiset found that a marmot in hibernation consumed only -fa
of the oxygen ordinarily appropriated in the active condition. In the same
animal they noted an exhalation of carbon dioxide equal to but little more
than half the weight of oxygen absorbed.

Influence of Muscular Activity. — Vierordt, in a number of observations
on the human subject, ascertained that moderate exercise increased the average
quantity of air respired per minute by nearly nineteen cubic inches (311-4
c. c.), and that there was an increase of 1-197 cubic inch (19-63 c. c.) per
minute in the absolute quantity of carbon dioxide exhaled.

146 CHANGES OF AIR AND BLOOD IN RESPIRATION.

The results of the experiments of Dr. Edward Smith on the influence of
exercise are as follows :

In walking at the rate of two miles (3-22 kilometres) per hour, the exhala-
tion of carbon dioxide during one hour was equal to the quantity produced
during 1£ hour of repose with food or 2£ hours of repose without food.

Walking at the rate of three miles (4-828 kilometres) per hour, one hour
was equal to 2f hours with food or 3£ hours without food.

One hour's labor at the tread-wheel, while actually working the wheel,
was equal to 4J hours of rest with food or 6 hours without food.

It has been observed, however, that when muscular exertion is carried so
far as to produce great fatigue and exhaustion, the exhalation of carbon
dioxide is notably diminished.

Influence of Moisture and Temperature. — It has been shown that the ex-
halation of carbon dioxide is greater in a moist than in a dry atmosphere
(Lehmann). It has also been ascertained that the exhalation is much greater
at low than at high temperatures, within the limits of heat and cold that are
easily endured, amounting, according to the experiments of Vierordt on
the human subject, to an increase of about one-sixth, under the influence of
a moderate diminution in temperature. It was found, also, that the quantity
of air taken into the lungs was slightly increased at low temperatures.

Influence of the Season of the Year, etc. — It has been shown by the re-
searches of Edward 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.

Observations on the influence of barometric pressure have not been suf-
ficiently definite in their results to warrant any exact conclusions.

Some physiologists have attempted to fix certain hours of the day when
the exhalation of carbon dioxide is at its maximum and 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 CARBON DIOXIDE EXHALED.

Oxygen unites with carbon in a certain proportion to form carbon dioxide,
the volume of which is equal to the volume of the oxygen which enters into
its composition. It is possible, therefore, to study the relations of the vol-
umes of these gases in respiration, by simply comparing 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 regards nitrogen and
all gases except oxygen and carbon dioxide, are insignificant, it must be ad-
mitted that a certain quantity of the oxygen consumed by the economy is
unaccounted for by the oxygen which enters into the composition of the

EXHALATION OF CARBON DIOXIDE. 147

carbon dioxide exhaled. It has already been stated that -^ to -fo (T4 to 2 per
cent.) of the inspired air is lost in the lungs ; or it may be said in general
terms, that the oxygen absorbed is equal to about five per cent, of -the volume
of air inspired, and the carbon dioxide exhaled, only about four per cent. A
part of the deficiency in volume of the expired air is to be accounted for,
then, by a deficiency in the exhalation of carbon dioxide.

The experiments of Regnault and Reiset have an important bearing on
the question under consideration. As these observers were able to accurately
measure the entire quantities of oxygen consumed and carbon dioxide pro-
duced 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 carbon dioxide. In six experiments on rabbits, the mean was
919 for every 1,000 parts of oxygen.

In animals fed on grains, the proportion of carbon dioxide exhaled was
greatest, sometimes 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 can not 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 Reiset was that the
" relation between the oxygen contained in the carbon dioxide and the total
oxygen consumed, varies, in the same animal, between 0-62 and 1-04, accord-
ing to the regimen to which it is subjected." These observations on animals
have been confirmed in the human subject by Doyere, who found a great
variation in the relations of the two gases in respiration ; the volume of
carbon dioxide exhaled varying between 0-862 and 1-087 for 1 part of oxygen
consumed.

As regards the destination of the oxygen which is not represented in the
carbon dioxide exhaled, it is certain that a part of it, at least, unites with
hydrogen to form water, this contributing to the production of animal heaty
a question that will be fully discussed in another connection.

The variations in the relative volumes of oxygen consumed and carbon
dioxide produced in respiration are not favorable to the hypothesis that the
carbon dioxide is always a result of the direct action of oxygen upon the car-
bohydrates and fats. Such a definite relation between these two gases can
not be assumed to exist, in view of the fact that carbon dioxide may be given
off by the tissues in the absence of oxygen.

Many of the points that have been considered with relation to the varia-

148 CHANGES OF AIR AND BLOOD IN RESPIRATION.

tions in the exhalation of carbon dioxide have been investigated in Petten-
kofer's chamber, and the results very nearly correspond with the observations
quoted from Scharling, Edward Smith and others.

Sources of Carbon Dioxide in the Expired Air. — All the carbon dioxide
in the expired air comes from the venous blood, where it exists in two forms ;
in a condition either of simple solution or of association with certain of the
constituents of the plasma, and in union with bases, forming the carbonates
and bicarbonates. The fact that carbon dioxide, as regards the quantity
absorbed by the blood, does not obey, in all regards, the laws which regulate
the absorption of gases by liquids under different conditions of pressure, has
led some physiologists to regard all of this gas as existing in the blood in
chemical combination ; the greater part being very loosely united with cer-
tain other substances, and a small quantity of that which is thrown off in
the expired air being in a condition of union much more stable.

The greater part of the carbon dioxide exhaled comes from the plasma,
where it is in a condition of what is known as association. Another and a
smaller part is probably set free by the action of the oxyhaemaglobine, which
is distinctly acid. It has been shown that more carbon dioxide can be
extracted by means of a vacuum from the entire blood than from the serum ;
and this gas is more readily extracted from arterial than from venous blood.
The mechanism by which the carbon dioxide is discharged from the venous
blood is probably the following :

Carbon dioxide is carried from the tissues to the lungs, in the venous
blood. Here it exists mainly in the plasma, a small quantity, only, existing
in the corpuscles. As the venous blood passes through the lungs, the greater
part of the carbon dioxide of the plasma either simply diffuses from the blood
into the air-cells or passes out by a process known to chemists as dissociation
(Deville). It is certain that the oxyhaemaglobine, which is constantly form-
ing in the lungs, assists materially in this process.

There can be no doubt with regard to the existence of an acid of some
kind in the lungs, which possibly decomposes a portion of the bicarbonates
of the blood, in ordinary respiration. When sodium bicarbonate 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 carbon dioxide 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 (Bernard).

Exhalation of Watery Vapor. — From a large number of observations on his
own person and upon eight others, collecting the water by sulphuric acid,
Valentin made the following estimates of the quantities of water exhaled
from the lungs in twenty-four hours :

In his own person the exhalation in twenty-four hours was 5,934 grains
(384-48 grammes).

In a young man of small size the quantity was 5,401 grains (350
grammes).

EXHALATION OF WATERY VAPOR ETC. 149

In a student rather above the ordinary height the quantity was 11,929
grains (773 grammes).

The mean of his observations gave a daily exhalation of 8,333 grains (540
grammes), or about a pound and a half.

The extent of respiratory surface has a 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, as in advanced life 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 over which
the air passes in respiration, and not exclusively from the air-cells. The air
which passes into the lungs derives a certain quantity of moisture from
the mouth, nares and trachea. The great vascularity of the mucous mem-
branes 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 surfaces
constantly moist. This is important, for only moist membranes allow the
free passage of gases, which is of course essential to the process of respira-
tion.

Exhalation of Ammonia, Organic Matter etc. — A small quantity of am-
monia is exhaled by the lungs in health, and this is increased in certain dis-
eases, particularly in uraemia. Its characters in the expired air are frequently
so marked, that patients who are entirely unacquainted with the pathology
of uraemia sometimes recognize 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 for analysis, but its presence
may be demonstrated by the fact that a sponge completely 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 but occasionally found
in the blood may be eliminated by the lungs. Certain odorous matters in
the breath are constant in those who take liquors habitually in considerable
quantity. The odor of garlics, onions, turpentine and of many other articles
taken into the stomach, may be recognized in the expired air.

The lungs eliminate 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. Hydrogen monosulphide, 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 eliminated by
the lungs with great promptness and rapidity (Bernard). The lungs, while
they present an immense and rapidly absorbing surface for volatile poisonous

150 CHANGES OF AIR AND BLOOD IN RESPIRATION,

substances, are capable of relieving the system of some of these by exhalation
when they find their way into the veins.

Exhalation of Nitrogen. — The most accurate direct experiments, particu-
larly those of Regnault and Reiset, show that the exhalation of a small quan-
tity of nitrogen is a nearly constant respiratory phenomenon. As the result
of a large number of experiments, 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 y^j- or -^ 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, 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.
Notwithstanding the conflicting testimony of physiologists, there can be little
doubt that under ordinary physiological conditions, there is an exhalation of
a small quantity of nitrogen by the lungs.

CHANGES or THE BLOOD IN RESPIRATION (H^MATOSIS).

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
wear of the tissues, connected with the lymphatic system, and exposed to the
action of the air in the lungs, should present important differences in compo-
sition 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 pas-
sage through the lungs. The blood which goes to the lungs is collected from
all parts of the body and presents great differences in its composition in dif-
ferent veins. In some veins it is almost black, and in some it is nearly as red
as in the arteries. In the hepatic vein it contains sugar, and its nitrogenized
constituents and the corpuscles are diminished ; in the portal vein, during di-
gestion, it contains matters absorbed from the alimentary canal ; and finally,
there is every reason to suppose that parts which require different substances
for their nutrition and produce different excrementitious matters exert differ-
ent 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. The change, therefore, 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 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 carbon dioxide, the other phenomena being com-
paratively unimportant. As the blood is capable of absorbing gases, the.

CHANGES OF THE BLOOD IN RESPIRATION. 151

essential changes which this fluid undergoes in respiration are to be looked
for in connection with the proportions of oxygen and carbon dioxide before
and after it has passed through the lungs.

The change of color in the blood from dark-blue to red, in its passage
through the lungs, was recognized by Lower, Goodwyn and others, as due
to the action of the air, long before the discovery of oxygen. 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 car-
bon dioxide ; while all these gases, by displacing oxygen, will change the
arterial blood from red to black. Carbon monoxide, although it is not a
respirable gas and does not properly arterialize the blood, changes it from
black to red.

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 that the volume of oxygen fixed by the
corpuscles is about twenty-five times that which is dissolved in the plasma
(Fernet, Lothar Meyer).

Comparison of the Gases in Venous and Arterial Blood. — The demon-
stration of the fact that oxygen and carbon dioxide exist in the blood, with a
knowledge of the relative proportion of these gases in the blood before and
after its passage through the lungs, are points hardly second in importance to
the relative composition of the air before and after respiration. The idea enun-
ciated 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 was not named or its other properties described,
expresses what is now regarded as 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 described the evolution of gas from blood placed in a
vacuum. Many observers have since succeeded in extracting gases from
the blood by various processes ; but notwithstanding this, before the experi-
ments of Magnus, in 1837, many denied the existence of free gases in the
blood.

Analysis of the Blood for Gases.— 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, carbon dioxide and nitro-
gen 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 ; but a careful study of his
essay shows another element of inaccuracy which is even more important.
The relative quantities of oxygen and carbon dioxide in any single 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 difficult 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

152 CHANGES OP AIR AND BLOOD IN RESPIRATION.

displacement is employed, and the bubbling of the gas when extracted by the
air-pump, the objection is very serious. It is necessary to wait until the froth
has subsided before attempting to make an accurate estimate of the volume
of gas given off. This fact is illustrated by one of the published observations
of Magnus upon three different specimens of human blood. In this observa-
tion the specimens of blood were thoroughly mixed with hydrogen. The
excess of carbon dioxide found twenty-four hours after, over the quantity
found six hours after, in two specimens, was a little more than fifty per cent.,
while in one specimen it is very nearly one hundred per cent. In these analyses
the proportion of oxygen was not given. The question naturally arises as to
the source of the carbon dioxide which was evolved during the last eighteen
hours of the observation. The question is readily solved by certain experi-
ments, which are by no means of recent date, although the results of these
observations have been confirmed by modern investigations. A number of
years ago, Spallanzani demonstrated that in common with other parts of the
body, fresh blood has, of itself, the property of consuming oxygen ; and W. F.
Edwards has shown that the blood will exhale carbon dioxide. In 1856, Har-
ley found that blood, kept in contact with air in a closed vessel for twenty-
four hours, consumed oxygen and gave off carbon dioxide. 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 carbon dioxide. If
all the carbon dioxide 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 the blood 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 carbon
dioxide 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 is allowed to remain in contact with oxygen for
a number of hours, can be accurate. The only process which can give a
rigorous estimate of the relative quantities of oxygen and carbon dioxide
in the blood is one in which the gases can be estimated without allowing
the blood to stand, or in which the formation of carbon dioxide, at the ex-
pense of the oxygen in the specimen, is prevented. All others will give a
less quantity of oxygen and a greater quantity of carbon dioxide than exists
in the blood circulating in the vessels or immediately after it is drawn from
the body.

Carbon monoxide, one of the most active of the poisonous gases, has a re-
markable affinity for the blood-corpuscles. When taken into the lungs, it is
absorbed by and becomes fixed in the corpuscles, preventing the consumption
of oxygen and the production of carbon dioxide, which normally take place
in the capillary system and which are indispensable conditions 01 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
action as oxygen-carriers. As it is the -continuance of this transformation
of oxygen into carbon dioxide, after the blood is drawn from the vessels,

CHANGES OF THE BLOOD IN EESPIRATION. 153

which interferes with the ordinary analysis of the blood for gases, it would
seem possible to extract all the oxygen by immediately saturating the blood
with carbon monoxide. The experiments of Bernard on this point are con-
clusive. He ascertained that by mixing carbon monoxide in sufficient quan-
tity 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
carbon monoxide after two hours and leaving it in contact with the blood for
an hour, a quantity of oxygen was removed so small that it might be disre-
garded. A third experiment on the same blood failed to disengage any oxy-
gen or carbon dioxide.

The view entertained by Bernard of the action of carbon monoxide in
displacing the oxygen of the blood is that the former gas has a remark-
able affinity for the blood-corpuscles, in which nearly all the oxygen is
contained, and when brought in contact with them unites with the hsema-
globine, setting free the oxygen, in the same way that an 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 cor-
rect, as carbon monoxide is much less soluble than oxygen and as it has
the property of disengaging this gas only from the blood, leaving the other
gases still in solution. In drawing the blood for analysis, Bernard took
the fluid directly from the vessels by a syringe and passed it under mer-
cury into a tube, in such a way that it did not come in contact with the
air. In this tube, which was graduated, the blood was brought in contact
with carbon monoxide, which displaced the oxygen from the corpuscles
and prevented the formation of carbon dioxide at the expense of a portion
of the oxygen.

As carbon monoxide displaces the oxygen alone, it is necessary to resort
to some other process to disengage the other gases contained in the blood.
Modern experimenters, Ludwig, Lothar Meyer and others, have made use of
the mercurial gas-pumps, either of Ludwig or of Pniiger, in which all the
gases of the blood are disengaged by removing the atmospheric pressure.
By means of a "froth-chamber," the gases can be collected and analyzed,
with but little loss of time ; but it is probable that there is always a slight
error in estimates, made in this way, of the relative proportions of oxygen
and carbon dioxide, the proportion of oxygen being too small, and of carbon
dioxide, too large. Nevertheless, the results obtained by this method corre-
spond pretty closely with what is known of the nature of the respiratory
process ; and analyses of the blood taken at different periods show variations
in the quantities of oxygen in the arterial blood and of carbon dioxide in the
venous blood, corresponding with some of the variations which have been
noted in the loss of oxygen and gain of carbon dioxide in the air in respira-
tion. Nearly all the gases contained in the blood may be disengaged by
means of the gas-pump, but according to most observers, a small quantity of
carbon dioxide remains in the blood in combination. This may be removed
by the introduction into the apparatus of a small quantity of tartaric acid.
It was justly remarked by Bert, that as the apparatus for the exhaustion of

154 CHANGES OF AIR AND BLOOD IN RESPIRATION.

air has been made more and more nearly perfect, the quantity of carbon
dioxide in combination has seemed less and less. By far the greatest
quantity of the excrementitious carbon dioxide in the blood is extracted
by the removal of atmospheric pressure in the most carefully perfected
apparatus.

According to Bernard, arterial blood, while an animal is fasting, contains
nine to eleven parts per hundred in volume 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 carbon dioxide is even more
variable than the quantity of oxygen. During digestion there are five to six
parts per hundred of carbon dioxide in the arterial blood. During the inter-
vals of digestion this quantity is reduced to almost nothing ; and after fasting
for twenty-four hours, frequently not a trace is to be discovered.

The quantity of carbon dioxide 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 secretion. In the venous blood from the submaxillary
gland of a dog, Bernard found 18-07 per cent, of carbon dioxide 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 carbon dioxide.
The quantity of carbon dioxide is increased in the venous blood during diges-
tion ; and it is owing to this that the gas then exists in quantity in the arte-
rial blood. Bearing in mind the fact that the proportion of gases in the
arterial and venous blood varies considerably under different conditions of
the system and that it is variable in the blood of different veins, the following
general statement, taken from Bert (1870), may be accepted as representing the
average results obtained up to that time. The most recent results, particularly
those obtained by German observers, present no important variations from
this average :

Carbon dioxide Carbon dioxide Total gas

disengaged in combi- Carbon dioxide, in volume

Oxygen, by a vacuum. nation. total. Nitrogen. per 100.

"Arterial blood. 15-03 27-99 1-15 29-14 1-60 45-77

Venous blood.. 8-17 31-27 2-38 33-65 1-37 43-19

" If the blood coming from different parts of the body be now examined,
it is found that the blood of the hepatic veins is poorer in oxygen and
richer in carbon dioxide than the general venous blood ; 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.

" In comparing the venous blood of the right side of the heart with the
arterial blood of the left side, it is found that the latter is richer in oxygen
and poorer in carbon dioxide. In examining this more closely, it is seen that

CHANGES OF THE BLOOD IN RESPIRATION. 155

the difference in the oxygen is greater than in the carbon dioxide ; this being
in accordance with the well known fact that animals absorb more oxygen
than is eouivalent to the carbon dioxide exhaled."

These facts coincide with the views which are now held regarding the
essential processes of respiration. The blood going to the lungs contains
carbon dioxide and but a small proportion of oxygen. In the lungs carbon
dioxide is given off, appearing in the expired air, and the oxygen which dis-
appears from the air is carried away by the arterial blood.

Nitrogen of the Blood. — As far as is known, nitrogen has no important
office connected with 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 large 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 is supplied by the food.
There is no evidence that nitrogen enters into combination with the blood-
corpuscles. It exists simply in solution in the blood, which is capable of ab-
sorbing about ten times as much as can be absorbed by 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 generally admitted that
the oxygen of the blood exists, not in simple solution, but in a condition of
association with the haemaglobine of the blood-corpuscles. In studying the
composition of the corpuscles, it has been seen that when air is admitted to
venous blood, oxygen unites with the haemaglobine, forming oxyhaemaglobine.
Carbon monoxide, which has a great affinity for the corpuscles, displaces
almost immediately all the oxygen which the blood contains. When the
corpuscles are destroyed, as they may be readily by receiving fresh blood into
a quantity of pure water, the red color is instantly changed to black.

The condition under which carbon dioxide exists in the blood has already
been considered in connection with the mechanism of its passage from the
venous blood into the air-cells. This gas is contained chiefly in the plasma ;
a small quantity, however, probably exists in the red blood-corpuscles. The
greatest part of the carbon dioxide of the plasma is either in solution or in
association with other matters, a condition in which the union does not take
place in definite proportions as in true chemical combination. It has been
ascertained that the blood-serum will absorb much more carbon dioxide than
is absorbed under similar conditions by pure water. It has been shown, also,
that neutral sodium phosphate increases to a remarkable degree the quantity
of carbon dioxide that can be absorbed by any liquid. It is probable that a
small part of the carbon dioxide of the plasma, which passes into the expired
air, is in combination with sodium in the form of sodium bicarbonate.

General Differences in the Composition of Arterial and Venous Blood. —
All observers agree that there are certain marked differences in the composi-

156 CHANGES OF AIR AND BLOOD IN RESPIRATION.

tion of arterial and venous blood, aside from the proportion of gases. The
arterial blood contains less water and is richer in organic and in most inor-
ganic constituents than the venous blood. It also contains a larger propor-
tion of corpuscles. It is more coagulable and offers a larger and firmer clot
than the clot of venous blood. The only constituents which are constantly
more abundant in venous blood are water and the alkaline carbonates. Ac-
cording to Longet, 10,000 parts of venous blood contained 12'3 parts of car-
bon dioxide 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 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 dif-
ferent organs. Arterial blood is capable of carrying on the processes of
nutrition, while venous blood is not, and it can not even circulate freely in
the systemic 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 appropriating oxygen and exhaling carbon dioxide, in-
dependently of the presence of blood; and that the arterial blood carries
oxygen from the lungs to the tissues, there gives it up, and receives carbon
dioxide, which is carried by the venous blood to the lungs, to be exhaled.
This fact alone shows 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.

Oxygen taken from the air is immediately absorbed by the blood and en-
ters into the composition of the red corpuscles. Part of the oxygen disap-
pears in the red corpuscles themselves, and carbon dioxide is given oft. 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 carbon dioxide, which belongs
. 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
it occurs in the tissues. The theory has been proposed that the respiratory
change takes place in the blood as it circulates ; but the avidity of the tissues
for oxygen and the readiness with which they exhale carbon dioxide leave no
room for doubt that much of this change is eifected in their substance.

Oxygen, carried by the blood to the tissues, is appropriated and consumed
in their substance, together with the nutritive materials contained in the cir-
culating fluid. Physiologists are acquainted with some of the laws which
regulate its consumption, but have not been able to ascertain the exact nature
of the changes which take place. All that can be said definitely on this point
is that oxygen unites with the organic constituents of the body, 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 its absorp-
tion, oxygen is lost in the processes of nutrition. There is no evidence in

THE RESPIRATORY SENSE.

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 carbon dioxide.

That carbon dioxide makes its appearance in the blood itself, produced
in the red corpuscles, has been abundantly proved 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 wear of the tissues,
is absorbed by the blood circulating in the capillaries and is conveyed by the
veins to the right side of the heart. It has been shown 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 reason-
able to consider the carbon dioxide thus formed as a product of excretion.
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. It may be possible at some future time to
produce artificially all the excremetitious principles, as has already been done
in the case of urea ; but it can not be assumed that the mode of formation
of carbon dioxide, as one of the phenomena of nutrition, is precisely the same
as when it is made by chemical manipulations.

THE RESPIRATORY SENSE.

It is generally admitted that there exists in the system what may be re-
garded as a respiratory sense, which operates upon -the respiratory nerve-
centre and gives rise to the involuntary movements of respiration ; and that
this sense is exaggerated by anything which interferes with respiration, and
is then conveyed to the brain, where it is appreciated as dyspnoea and finally
as the sense of suffocation. An exaggeration of the respiratory sense consti-
tutes a sense of oppression, which is referred to the lungs ; but it can not be
assumed, from sensations only, that the sense of want of air is really situated
in the lungs.

At the present day it is hardly necessary to discuss the views of those
who attributed the sense of -want of air, at least in its exaggerated form,
to an accumulation of carbon dioxide in the lungs (Marshall Hall), distention
of the right cavities of the heart (Berard), or to impressions conveyed to the
medulla oblongata, exclusively by the pneumogastric nerves. These theories
have long since been disproved and are now merely of historical interest.
Volkmann, in 1841, advanced the view that this sense is dependent upon a
deficiency of oxygen in the tissues, producing an impression which is con-
veyed to the medulla oblongata by the nerves of general sensibility. By a
series of experiments, this observer disproved the view that the respiratory
sense always originates in the lungs and is transmitted by the pneumogastric
nerves ; and by exclusion, he located it in the general system. In a series of
experiments (Flint, 1861) the following facts, some of which had been previ-
ously noted, were observed :

The chest was opened in a living animal, artificial respiration was care-
fully performed, inflating the lungs sufficiently but cautiously and taking
12

158 CHANGES OF AIR AND BLOOD IN RESPIRATION.

care to change the air in the bellows every few moments. So long as this
was continued, the animal made no respiratory effort ; showing 'that for the
time the respiratory sense was abolished. This was little more than a
repetition of the classical experiment of Robert Hook, an account of which
was published in 1664.

When the artificial respiration was interrupted, the respiratory muscles
were thrown into contraction, and the animal made regular, and at last vio-
lent efforts. An artery was then opened and the color of the blood was
noted. It was observed that the respiratory efforts began only when the blood
in the vessel became dark. When artificial respiration was resumed, the re-
spiratory efforts ceased only when the blood became red in the arteries.

While artificial respiration was being regularly performed, a large artery
was opened and the system was drained of blood. When the haemorrhage
had proceeded to a certain extent, the animal made respiratory efforts, which
became more and more violent, until they terminated, just before death, in
general convulsions.

These facts, which may be successively observed in a single experiment,
remained precisely the same when both pneumogastric nerves had been
divided in the neck.

The conclusion which may legitimately be drawn from the above-men-
tioned facts is that the respiratory sense does not always and necessarily
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.

A similar conclusion was arrived at by Rosenthal (1862) and by Pfliiger
(1868). Pfliiger produced asphyxia in dogs by causing them to respire pure
nitrogen. In his experiments, he analyzed the blood after thirty seconds
and after one minute of inhalation of nitrogen. He found a great diminu-
tion in oxygen with very slight increase in carbon dioxide at the end of
thirty seconds. After one minute the oxygen was reduced from 14-35 per
cent, in volume to 0-2 per cent., and the carbon dioxide from 36-9 to 29-9.
As a conclusion he stated that " no one, therefore, can be of the opinion that
dyspnoea and asphyxia in breathing indifferent gases are connected with the
accumulation of carbon dioxide."

In 1877 the experiments made in 1861 were repeated and extended (Flint).
The later experiments were made upon dogs, in the following way : The ani-
mals 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 separately constricted at will. In a number of experiments
upon different animals, the innominate artery and the left subclavian were
constricted, and the animal began to make respiratory efforts about two min-
utes after, although artificial respiration was kept up constantly and effi-
ciently. 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 ex-
tremities. In the experiments in which the vessels going to the head and

THE RESPIRATORY SENSE. 159

upper extremities were constricted, the respiratory efforts always ceased when
the vessels were freed.

The object of these experiments was to study the effects of cutting off the
supply of oxygenated blood from different parts. It may be assumed that
the respiratory nervous centre is in the medulla oblongata, and an attempt
was made to devise some means of cutting off the arterial supply from
this part. Animals respire when all of the encephalic centres have been de-
stroyed except 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 were efficiently maintained. Blood may
be supplied to the medulla oblongata by the internal carotids, which are con-
nected with the circle of Willis, by the vertebral arteries, which unite to form
the basilar artery, and perhaps by 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, 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 respiratory efforts in two minutes and five seconds.

In a third experiment, both subclavian arteries and both carotids were
constricted, 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 subclavians 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 respiration, either the innominate artery and the left
subclavian artery, or both subclavians, both carotids and both vertebral arte-
ries, must be tied. In other words, according to the view taken of the cause
of these respiratory efforts, the supply of blood to the medulla oblongata can
not be cut off completely except by tying all the vessels given off from the
arch of the aorta.

These observations, taken in connection with the experiments of 1861,
lead to the conclusion that the sense of want of air, under certain conditions,
is due to a want of circulation of oxygenated blood in the medulla oblongata.
This view has been advanced by some writers, but it has lacked the positive
experimental proof afforded by the experiments of 1877.

If the sense of want of air be regarded as due, under certain conditions,
to a deficiency of oxygen in the medulla oblongata — which can hardly be
doubted — it becomes an important question to determine whether the normal
respiratory movements be actually reflex in their character or whether they
be due to direct excitation of the nerve-cells in the respiratory centre.

It is difficult to account for the phenomena observed in experiments in
which the pneumogastrics are divided or stimulated, without assuming that

160 CHANGES OF AIR AND BLOOD IN RESPIRATION.

these nerves sometimes — and possibly always, in tranquil respiration — convey
an impression to the respiratory nervous centre, which gives rise to the ordi-
nary automatic and periodical action of the muscles of inspiration. If such
an impression be conveyed from the lungs by the afferent fibres of the pneu-
mogastrics, it could not operate when both pneumogastrics are divided in the
neck. This operation, as is well known, profoundly affects the respiratory
movements. After division of both nerves, the respirations become slow and
unusually deep, without, as a rule, any evidence of respiratory distress. In
dogs, the number of respirations often falls to four or five per minute, and
their nervous mechanism seems to be modified. Any respiratory distress that
occurs is due to the arrest of the respiratory movements of the larynx, and
not to an exaggeration of the sense of want of air. When a feeble Faradic
current is passed through the nerves, the respiratory movements are increased
in frequency, but the movements are arrested by a relatively powerful current.
This action is reflex.

In view of all the experimental facts bearing upon the question, it is proba-
ble that the respiratory movements are sometimes reflex and sometimes due
to direct excitation of the cells of the respiratory centre by the absence of
oxygen.

In perfectly normal and tranquil respiration, an impression is probably
conveyed from the lungs to the respiratory centre by the pneumogastrics,
which stimulates this centre to excite movements of inspiration. This is
probably due to a gradual and progressive change in the character of the con-
tents of the air-cells, although experiments are wanting to show the exact
mechanism of this process.

When this reflex action is abolished, as by section of both pneumogastrics
in the neck, the respiratory centre is stimulated only when the deficiency in
the supply of oxygen becomes considerable. This excitation of the respira-
tory centre is direct. It requires a certain time for its operation, and this
accounts for the slow respirations in animals after the pneumogastrics have
been divided. Under certain physiological conditions, this direct stimulation
may be added to the impression conveyed by the pneumogastrics, and it is
probable that this always occurs in dyspnoea.

Sense of Suffocation. — The respiratory sense must not be confounded
with the sense of distress from want of air, and its extreme degree, the sense
of suffocation. 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. Once in every seven or eight respirations, or when the respiratory
movements are 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 degree of interference with the mechanical process of respira-
tion during violent muscular exercise put one " out of breath," and for a time
the respiratory movements are exaggerated. This is perhaps the first physio-
logical way in which the want of air is appreciated by the senses. A defi-

RESPIRATORY EFFORTS BEFORE BIRTH. 161

ciency in haematosis, either from a vitiated atmosphere, mechanical obstruc-
tion 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 haematosis 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.

RESPIRATORY EFFORTS BEFORE BIRTH.

It is generally admitted that one of the most important uses of the pla-
centa, and the one which is most immediately connected with the life of the
foetus, is a respiratory interchange of gases, analogous to that which takes
place in the gills of aquatic animals. The placental villi are bathed in the
blood of the uterine sinuses, and this is the only way in which the foetal blood
can receive oxygen. Legallois 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 oxyhaemaglobine 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 sys-
tem, the foetus is in a condition similar to that of the animals in which arti-
ficial 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 defi-
ciency 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 enter only during efforts at respiration. 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 mother, they
make vigorous efforts at respiration. After the death of the mother, the
foetus always makes a certain number of distinct and unmistakable respiratory
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 oxy-
gen is the cause of respiratory 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 pla-
centa, the impression due to want of oxygen is made upon the medulla oblon-
gata, and efforts at respiration are the result.

CUTANEOUS RESPIRATION.

Respiration by the skin, although very important in many of the lower
forms of animals, is inconsiderable in the human subject and is even more
insignificant in animals covered with hair or feathers ; still, an appreciable

162 CHANGES OF AIR AND BLOOD IN RESPIRATION.

quantity of oxygen is absorbed by the skin of the human subject, and a quan-
tity of carbon dioxide, which is relatively larger, is exhaled. Exhalation of
carbon dioxide, which is connected with the uses of the skin as a general
eliminating organ and is by no means an essential part of the respiratory
process, will be more fully considered in connection with the physiology of
excretion. Carbon dioxide is given off with the general emanations from the
surface, being found, also, in solution in the urine and in most of the secre-
tions. It is well known that death follows the application of an imperme-
able coating to the entire cutaneous surface ; but this is by no means due to a
suppression of its respiratory office alone. The skin has other uses, particu-
larly in connection with regulation of the animal temperature, which are
much 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 carbon dioxide exhaled in the twenty-four hours. According to this ob-
server, the skin performs fa to ^V of the respiratory office. It is difficult to
collect all the carbon dioxide given off by the skin under perfectly normal
' conditions. In the observations by Aubert, 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 in treat-
ing of the influence of respiration upon the circulation. It will be remem-
bered that in asphyxia the unaerated blood passes with so much difficulty
through the systemic capillaries as finally to arrest the action of the heart.
It is the experience of experimenters on living animals, that the movements
of the heart, once arrested in this way, can not be restored ; but that while
the slightest regular movements continue, the heart's action will gradually
return if air be re-admitted to the lungs.

A remarkable power of resisting asphyxia exists in newborn animals
that have never breathed. This was noticed by Haller and others and has
been the subject of many experiments. 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 species. 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 for more than seven minutes. The explanation of this is that
in most warm-blooded animals, during the very first periods of extraiiterine
life, the demands on the part of the system for oxygen are comparatively
slight. At this time, there is very little activity in the general processes of
nutrition and in the consumption of oxygen and the exhalation of carbon
dioxide. The actual difference between the consumption of oxygen imme-

ASPHYXIA. 163

diately after birth and at the age of a few days is sufficient to explain the
remarkable power of resisting asphyxia just after birth.

Breathing in a Confined Space. — An important (Question connected with
the physiology of asphyxia, is the effect on the system, of air vitiated by breath-
ing in a confined space. There are here several points which present them-
selves for consideration. The effect of respiration on the air is to take away a
certain proportion of oxygen and to add certain matters which are regarded
as deleterious. The emanation which has been generally regarded as hav-
ing the most decided influence upon the system is carbon dioxide ; but this
influence has been much over-estimated. In death from charcoal-fumes,
it is ganorally carbon monoxide which is the poisonous agent. Regnault and
Reiset exposed dogs and rabbits for many hours to an atmosphere contain-
ing twenty-three parts per hundred of carbon dioxide artificially introduced,
and between thirty and forty parts of oxygen, without any ill effects. They
took care, however, to keep up a free supply of oxygen.

These experiments are at variance with the result obtained by others, but
Regnault and Reiset explained this difference by the supposition that the
gases in other observations were probably impure, containing a little chlorine
or carbon monoxide. This view is sustained by the experiments of Bernard
with carbon monoxide. 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.

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 presence of carbon dioxide. When the latter gas is re-
moved as fast as it is produced, the effects of diminution in the proportion of
oxygen are soon very marked, and they progressively increase until death oc-
curs. The influence of emanations from the lungs and general surface is
undoubtedly very considerable ; and this fact, which almost all have experi-
enced more or less, has been fully illustrated in several instances of large
numbers of persons 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 disease prevalent in large cities, that
are almost unknown in the rural districts and that can be alleviated only by
proper sanitary regulations, which, unfortunately, it is often difficult to en-
force.

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 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 ( 5-486 metres ) 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

164: ALIMENTATION.

of the eight hours. Many of those who immediately survived died afterward
of putrid fever ("Annual Eegister," 1758). The incident of the "Black
Hole of Calcutta " 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.

The condition of the system has a marked and important influence on
the rapidity with which the effects of vitiated atmosphere are manifested.
As a rule, the immediate effects of confined air are not developed so soon 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 has been restored
some time after life had become extinct in the male. This is probably owing
to the greater demand for oxygen on the part of the male.

When poisoning by confined air is gradual, the system becomes accus-
tomed to the toxic influence, the temperature of the body is lowered, and an
animal will live in an atmosphere which will produce instantaneous death in
one that is fresh and vigorous. Bernard has made a number of experiments
on this point. In one of them, a sparrow was confined under a bell-glass for
an 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.

CHAPTER VI.

ALIMENTATION.

General considerations— Hunger— Seat of the sense of hunger— Thirst— Seat of the sense of thirst— Dura-
tion of life in inanition— Classification of alimentary substances— Nitrogenized alimentary substances—
Non-nitrogenized alimentary substances— Inorganic alimentary substances— Alcohol— Coffee— Tea-
Chocolate— Condiments and flavoring articles— Quantity and variety of food necessary to nutrition-
Necessity of a varied diet.

Itf the organism of animals, every part is continually undergoing what
may be called physiological wear ; the nitrogenized constituents of the body
are being constantly transformed into effete matter ; and as these constitu-
ents never exist without inorganic matters, with which they are closely and
inseparably united, it is found that the products of their disassimilation
are always discharged from the body in combination with inorganic sub-
stances. This process of molecular change is a necessary condition of life.
Its activity may be increased or retarded by various means, but it can not be
arrested. The excrementitious matters which are thus formed are produced
constantly by the . tissues and must be continually removed from the or-
ganism.

HUNGER AND THIRST. 165

It is evident, from the amount of matter that is daily discharged from
the body, that the process of disassimilation 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 al-
ways ready to perform their offices in the economy. The blood contains
all the materials necessary for the regeneration of the organism. Its inor-
ganic constituents are found generally in the form in which they exist in
the substance of the tissues ; but the organic constituents of the parts are
formed in the substance of the tissues themselves, by a transformation of
matters furnished by the blood. The physiological wear of the organism is,
therefore, being constantly repaired by the blood ; but in order to keep the
great nutritive fluid from becoming impoverished, the matters which it is
constantly losing must be supplied from some source out of the body, and
this necessitates the ingestion of articles 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 of thirst, when it relates to water.

HUNGER AND THIRST.

The term hunger may be applied to all degrees of that peculiar want felt
by the system, which leads to the ingestion of nutritive substances. Its
first manifestations are, perhaps, best expressed by the term appetite ; a sen-
sation 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 refer-
able 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 digestive 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.

It has been observed that children and old persons do not endure depri-
vation of food so well as adults. This was noted 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 ; and the children, the 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 agreeable at that time, and the quantity of nutri-
ment which is demanded by the system is then considerably increased, iu.

166 ALIMENTATION.

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 exhaustion, increase the desire for food and undoubtedly facili-
tate digestion. Certain articles, especially the vegetable bitters, taken into
the stomach immediately before the time when food is habitually taken, fre-
quently 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.

If food be not taken in obedience to the demands of the system as ex-
pressed by the appetite, the sensation of hunger becomes most distressing.
It is then manifested by a peculiar and indescribable sensation in the stom-
ach, which soon becomes developed into actual pain. This is generally accom-
panied with 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. Furious delirium frequently super-
venes after a few days of complete abstinence; and this is generally the
immediate precursor of death. It is unnecessary to cite the many instances
in which murder and cannibalism have been 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.

The question of the seat of the sense of hunger is one of considerable
physiological interest. Saying that it is instinctively referred to the stomach,
is simply expressing the fact that the sensation is of a nature to demand
the introduction of food in the usual way. When the system is suffering
from defective nutrition, as after prolonged abstinence or during recovery
from diseases which have been accompanied by a 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 nutri-
tion be active and sufficient, the stomach is frequently entirely empty for a
considerable time without the development of the sense of hunger. The
appetite is preserved and hunger is felt by persons who suffer from extensive
organic disease of the stomach, and the sensation has been occasionally
relieved by nutritious enernata or by injections into the veins. It is certain
that the appetite and the sense of hunger are expressions of a want on the
part of the organism, referred by the sensations to the stomach, but really
existing in the general system. This can be completely satisfied only by the
absorption of digested alimentary matters by the blood and their 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 convey this

HUNGER AND THIRST. 167

impression to the encephalon. The nerve which would naturally be sup-
posed to have this office is the pneumogastric ; but notwithstanding certain
observations to the contrary, it has been shown 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 undoubt-
edly the sympathetic system of nerves which presides specially over nutrition ;
and hunger, which depends upon deficiency of nutrition, is certainly not con-
veyed to the brain by any of the cerebro-spinal nerves.

Thirst is the peculiar sensation which leads to the ingestion of water.
In its moderate development, this is usually an indefinite feeling, accom-
panied by 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
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 conditions 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 is 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 characterized 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 second only to the demand for oxygen.
Animals will live much longer when 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 processes of nutrition, and acts, moreover, as a solvent in
removing from the system the products of disassimilation.

After deprivation of water for a considerable time, the intense thirst be-
comes most distressing. The dryness and heat of the throat and fauces are
increased and accompanied with a sense of constriction. A general febrile
condition supervenes, the blood is diminished in quantity and becomes thick-
ened, 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

168 ALIMENTATION.

demonstrated, by the following experiment, that water must be absorbed
before the demands of the system can be satisfied : He made an 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 ani-
mal 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 continued to drink without being satis-
fied, until the fistula was closed and the water could be absorbed.

In a case reported by Gairdner (1820), 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 of water were taken in the day ; but on injecting water, mixed with
a little spirit, into the stomach, the sensation was soon relieved.

Although the sensation of thirst is referred to special parts, it is an ex-
pression of the want of liquids in the system and is to be effectually relieved
only by their absorption by the blood. There are no nerves belonging to the
cerebro-spinal system which have the office of conveying 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.

The duration of life after complete deprivation of food and drink is
very variable. The influence of age has already been referred to. Tak-
ing no account of certain remarkable individual instances of starvation in
the human subject which have been reported, it may be stated, in general
terms, that death occurs within five to eight days after total deprivation
of food. In the instance of the one hundred and fifty persons, wrecked on
the frigate Medusa, in 1816, who were exposed on a raft in the open sea for
thirteen days, only fifteen were found alive. Savigny, one of the survivors,
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.

Berard quoted 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 has also quoted, from
various authors, instances of deprivation of food for periods varying between
four months and sixteen years ; but these accounts are not properly authen-
ticated and are discredited by physiologists. They generally occurred in
hysterical females, and their consideration belongs to psychology rather than

HUNGER AND THIRST. 169

to physiology. 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.

Thirty to thirty-five days may be taken as the average duration of life in
dogs deprived entirely of food and drink. It is important to bear in mind
this fact in connection 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 substances in a form which en-
ables them to be used for the nourishment of the body, either by being them-
selves appropriated by the organism, by influencing favorably the process of
nutrition, or by retarding disassimilation. Those substances which are them-
selves 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. In 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 commonly called drinks.

In the various articles used as food, nutritious substances are frequently
combined with each other and with indigestible and innutritions matters.
The constituents of the food which are directly used in nutrition are the true
alimentary substances, embracing, thus, only those which are capable of
absorption and assimilation. The ordinary food of the warm-blooded ani-
mals contains alimentary matters 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 matter forms so small a part of the ingesta that the digestive
apparatus is even more complicated than in the human subject. This is
specially 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 ali-
mentary substances, food has many constituents which exert an important
influence on nutrition, which have never been isolated and analyzed, but
which render it agreeable. Many of these are developed in the process of
cooking.

Alimentary substances belong to the inorganic, vegetable, and animal
kingdoms. They are generally divided into the following classes :

1. Organic iiitrogenized substances (albumin, fibrin, caseine, myosine
etc.), belonging to the animal kingdom, and vegetable nitrogenized substances,
such as gluten and legumine.

2. Organic non-nitrogenized substances (sugars, starch and fats).

3. Inorganic substances.

Nitrogenized Alimentary Substances. — In the nutrition of certain classes
of animals, these substances are derived exclusively from the animal king-
dom, and in others, exclusively from the vegetable kingdom ; but in man,

170 ALIMENTATION.

both animals and vegetables contribute nitrogenized matters. In both ani-
mal and vegetable food, nitrogenized substances are always found combined
with inorganic matters (water, sodium chloride, the phosphates, sulphates etc.),
and frequently with non-nitrogenized matters, especially the carbohydrates.

The most important nitrogenized alimentary constituents of food are con-
tained in the muscular substance, eggs, milk, the juices of vegetables, cereal
grains etc. Many of these substances have been isolated and studied by
chemists. Among the most important are myosine, the chief organic con-
stituent of muscle, the various albumins found in eggs and in animal fluids,
analogous substances existing in vegetables, caseine in milk, a substance
sometimes called vegetable caseine, vitelline in yelk of egg, fibrin, gelatine,
and gluten, an important alimentary substance found in the cereal grains,
etc. A distinctive character of these substances is that they all contain nitro-
gen, being composed of carbon, oxygen, hydrogen and nitrogen, with prob-
ably a small quantity of sulphur. They are all either liquid or semi-solid in
consistence, not crystallizable, and are coagulable by various reagents. The
type of substances of this class is albumin, which has the provisional formula,
C^Hj^OggNigS (Lieberkuhn) ; and they are sometimes called albuminoids.
Certain of these are called proteids, after a hypothetical substance described
by Mulder, under the name of proteine.

The nitrogenized substances are found in animal bodies, as has already
been stated. They originate in vegetables by a union of nitrogen, derived
from saline matters, with the carbohydrates, the carbohydrates in vegetables
being produced from carbon dioxide and water. No part of the nitrogen
used by vegetables in the formation of the albuminoids is derived from the
atmosphere (Hoppe-Seyler).

A distinctive character of substances of this class is that under favorable
conditions of heat and moisture they undergo a peculiar form of decomposi-
tion, called putrefaction. In the process of digestion, these substances are
changed into peptones, and afterward, it is thought, into leucine, tyrosine
and some other substances not well defined. An analogous decomposition is
said to take place under the influence of dilute hydrochloric acid, at a tem-
perature of 104° Fahr. (40° C.), and of dilute sulphuric acid, at a tempera-
ture of 212° Fahr. (100° 0.). The chemical history of these substances
would require for its comprehension an elaborate description such as proper-
ly belongs only to special works on physiological chemistry.

Non- Nitrogenized Alimentary Substances. — The important non-nitro-
genized alimentary substances are sugars, starch and fats. They are all com-
posed of carbon, hydrogen and oxygen. In sugars and starch, the hydrogen
and oxygen exist in the proportion to form water, and these matters are there-
fore called carbohydrates. The 'non-nitrogenized constituents of food are of
organic origin, definite chemical composition and crystallizable.

Sugars. — Many varieties of sugar occur in food, and this substance
may be derived from both the animal and the vegetable kingdoms. 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 '

NON-NITROGENIZED ALIMENTARY SUBSTANCES. 171

used as food. The sugars derived from the vegetable kingdom are cane-
sugar, under which head may be classed all varieties of sugar except that ob-
tained from fruits, and grape-sugar, which comprises all the varieties existing
in fruits. The following are the formulae for the different varieties of sugar
in a crystalline formj

Cane-Sugar (Saccharose), C^H^On

Milk-Sugar (Lactose), C^H^Ojg

Grape-Sugar (Glucose, Dextrose), C6H1206

All varieties of sugar have a peculiar, sweet taste ; they are all soluble in
water, glucose being more soluble than cane-sugar or lactose; glucose is
sparingly soluble in alcohol, which dissolves small quantities, only, of cane-
sugar or lactose ; glucose ferments readily and is changed into alcohol and
carbon dioxide ; cane-sugar and lactose are said to be incapable of fermenta-
tion, but cane-sugar may easily be converted into fermentable glucose, and
lactose, into a fermentable sugar called galactose, by boiling with dilute
mineral acids ; they are capable of being converted into lactic acid in the
presence of decomposing nitrogenized matters ; they are inflammable, leav-
ing an abundant carbonaceous residue and giving off a peculiar odor of cara-
mel ; they undergo other modifications when treated with the mineral acids
or with alkalies, which are interesting more in a chemical than a physiolog-
ical point of view. Of all the varieties of sugar, that made from the sugar-
cane is the most soluble, the sweetest and the most agreeable. Beet-root
sugar is identical with cane-sugar.

Much of the sugar used in the nutrition of the organism is formed in the
body by the digestion of starch. This transformation of starch may be
effected artificially. The sugar thus formed, called glucose, 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 substance, closely resembling sugar in its
ultimate composition (C6H1005), is contained in abundance in a great num-
bor 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 legumi-
nous 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
(arrowroot), in the sago-plant and in the bulbs of orchis. In the cereals,
after desiccation, the proportion of starch is usually between sixty and sev-
enty per cent. It is most abundant in rice, which contains, after desiccation,
88-65 per cent.

When extracted in a pure state, starch is in the form of granules, varying
in size between Io^00 and -yfa of an inch (2'5 and 62*5 //,), and presenting, in
most varieties, certain peculiarities of form. The granule frequently is
marked by a little conical excavation called the hilum, and the starch-
substance is arranged in the form of concentric laminaa, the outlines of
which are often quite distinct. When starch is rubbed between the
fingers, these little, hard bodies give it rather a gritty feel and produce a

172

ALIMENTATION.

Fio. 49. — Arrowroot starch-granules ; magnified
370 diameters (from a photograph taken at the
United States Army Medical Museum).

crackling sound. The different varieties of starch may be recognized micro-
scopically by the peculiar appearance of the granules.

Starch is insoluble in cold water ; but when boiled with several times its
volume of water, the granules swell up, become transparent, and finally fuse

together, mingling with the water
and giving it a mucilaginous con-
sistence. The mixture on cooling
forms a jelly-like mass of greater or
less consistence. This change in
starch is called hydration and is im-
portant as one of the transforma-
tions which take place in the process
of digestion, when starch is taken
uncooked. This change is generally
effected more or less completely,
however, in the process of cooking.
The most important properties
of starch are connected with its
transformation, first into dextrine,
and finally into glucose. This al-
ways takes place in digestion, before
starch can be absorbed. In the digestive apparatus, the change into sugar is
almost instantaneous, and the intermediate substance, dextrine, is not easily
recognized. By boiling starch for a number of hours with dilute sulphuric
acid, it is transformed, without any change in chemical composition, into
dextrine, which is soluble. If the action be continued, it appropriates one
atom of water and is converted into glucose. The change of starch into
dextrine may be effected by a dry heat of about 400° Fahr. (204° C.), a pro-
cess which is commonly employed in commerce.

Vegetable Substances 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 great im-
portance as alimentary matters and demand only a passing mention. These
are inuline, lichenine, cellulose, pectose, mannite, mucilages and gums. Inu-
line is found in certain roots. It is convertible into sugar but does not, pass
through the intermediate stage of dextrine. It differs from starch in being
very soluble in hot water. Lichenine is found in many kinds of edible mosses
and lichens. It differs from starch only in its solubility. Mannite is a
sweetish substance found in manna, mushrooms, celery, onions and asparagus.
It is perhaps more analogous to sugar than to starch, but it is not fermentable
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 matters. 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 roots

NON-NITROGENIZED ALIMENTARY SUBSTANCES.

173

and leaves. Both gums and mucilages mix readily with water, giving it a
consistence called mucilaginous. The composition of gum is C20H10010.
Experiments have shown that gum passes unchanged through the alimentary
canal and has no nutritive properties. Gum is mentioned in this con-
nection from the fact that it is frequently used in the treatment of disease
and is thought by many to be nutritious.

The carbohydrates, although important articles of food and especially use-
ful in the processes involved in the production of animal heat, are not in
themselves capable of sustaining life.

Fats. — Fatty matters, derived from both the animal and the vegetable
kingdoms, are important articles of food. As a constituent of the organism,
fat is found in all parts of the body,
with the exception of the bones, teeth
and fibrous tissues. It necessarily con-
stitutes 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, palmitine and stearine, in va-
rious proportions, and possesses a con-
sistence which depends upon the relative
quantities of these substances.

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.

In the vegetable kingdom, fat is
particularly abundant in seeds and
grains, but it exists in quantity in some
fruits, as in the olive. Here it is gen-
erally called oil. It exists in consider-
able proportion in nuts and in certain
quantity in the cereals, particularly In-
dian corn.

Fat, both animal and vegetable,
may be either liquid or solid. It has a
peculiar oily feel, a neutral reaction,
and is insoluble in water and soluble in
alcohol — particularly hot alcohol — chlo-
roform, ether, benzine and solutions of soaps- The solid varieties are exceed-
13

FIG. 50. — Crystals of palmitine and palmitic
acid (Funke). a, a, a, palmitine ; 6, pal-
mitic acid.

FIG. 51.— Crystal* of stearine and stearir, acid
(Funke). a, a, a, stearine ; 6, stearic acid.

174: ALIMENTATION.

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 acids uniting with the bases to form soaps. 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 three varieties of fats usually recognized are stearine and palmitine,
which are solid at the temperature of the body, and oleine, which is liquid.
The formulae for these varieties are the following :

Stearine (Tristearine), C57H11006

Palmitine (Tripalmitine), C51H9806

Oleine (Trioleine), C57H10406

It is noticeable that in the composition of fats, the hydrogen and oxygen
do not exist in the proportions to form water, as they do in the carbohy-
drates, and that they are relatively poor in oxygen. One variety of fat can
not be converted into another by chemical manipulation.

As alimentary substances, fats are undoubtedly of great importance.
They are supposed by many to be particularly concerned in the production
of animal heat. It has been proved by repeated experiments that fat, as a
single article of diet, is insufficient for the purposes of nutrition.

Inorganic Alimentary Substances. — It has been shown that all the or-
gans, tissues and fluids of the body contain inorganic matter in greater or
less abundance. The same is true of vegetable products. All the organic
nitrogenized matters contain mineral substances which can not be separated
without incineration. When new organic matter is appropriated by the tis-
sues to supply the place of that which has become effete, the mineral sub-
stances are deposited with them ; and the organic matters, as they are trans-
formed into excrementitious substances and discharged from the body, are
always thrown off in connection with the mineral substances which enter into
their composition. This constant discharge of inorganic matters, forming,
as they do, an essential part of the organism, necessitates their introduction
with the food, in order to maintain the normal constitution of the parts.
As these matters are necessary to the proper constitution of the body, they
must be regarded as alimentary substances.

Water. — This is one of the most important of the constituents of the
organism, is found in every tissue and part without exception, is introduced
with all kinds of food and is the basis of almost 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 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 driven off by boiling or by removing the atmos-
pheric pressure. The demand on the part of the system for water is regu-
lated, 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.

INORGANIC ALIMENTARY SUBSTANCES. 175

Sodium Chloride. — Of all saline substances, sodium chloride is the one
most widely distributed in the animal and the vegetable kingdoms. It exists
in all varieties of food ; but the quantity which is taken in combination with
other matters is usually insufficient for the purposes of the economy, and
common salt is generally added to certain articles of food, as a condiment,
when it improves their flavor, promotes the secretion of certain of the digest-
ive fluids and meets a nutritive demand on the part of the system. Experi-
ments and observations have shown that a deficiency of sodium chloride in the
food has an unfavorable influence on the general processes of nutrition.

Calcium Phosphate. — This is almost as common a constituent of vegetable
and animal food as sodium chloride. It is seldom taken except in combina-
tion, particularly with nitrogenized alimentary matters. Its importance in
alimentation has been experimentally demonstrated, it having been shown
that in animals deprived as completely as possible of this salt, the nutrition
of the body, particularly in parts which contain it in considerable quantity,
as the bones, is seriously affected.

Iron. — Haemaglobine, the coloring matter of the blood, contains, inti-
mately united with organic matter, a certain proportion of iron. Examples
of simple anaemia, which are frequently met with in practice and are almost
always relieved in a short time by the administration of iron, are proof of
the importance of this substance in alimentation. The quantity of iron
which is discharged from the body is very slight, only a trace being discov-
erable in the urine. A small quantity of iron is frequently introduced 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 normal processes of nutrition, to administer it in some
form, until its proportion in the organism shall have reached the proper
standard.

It is hardly necessary even to enumerate the other inorganic alimentary
substances, as nearly all are in a state of such intimate combination with
nitrogenized matters that they may be regarded as part of their substance.
Suffice it to say, that all the inorganic matters which exist as constituents of
the organism are found in the food. That these are essential to nutrition,
can not be doubted ; but it is evident that by themselves they are incapable
of supporting life, as they can not be converted into either nitrogenized or
non-nitrogenized organic matters.

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 excessive use are so serious, the influence of alco-
hol upon the organism has become one of the most important questions con-
nected with alimentation. Some alcoholic beverages influence the functions
solely through the alcohol which they contain ; while others, as beer and por-
ter, with a comparatively small proportion of alcohol, contain a considerable
quantity of solid matter.

Alcohol (C9H60), from its composition, is to be classed with the non-nitro-
genized substances. It has already been stated that sugar and fat are essen-

176 ALIMENTATION.

tial to proper nutrition and that they undergo important changes in the or-
ganism. Alcohol is absorbed and taken into the blood ; and it becomes a
question of importance to determine whether it be consumed in the economy
or whether it be discharged unchanged 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 th'e earlier ob-
servations with regard to its elimination in its original form, and have shown
that after it has been taken in quantity, it exists in the blood and all the tis-
sues and organs, particularly the liver and nervous system. Lallemaiid, Per-
rin and Duroy have stated, also, that there is a considerable elimination of al-
cohol by the lungs, skin and kidneys ; but the accuracy of the experiments
by which these results were arrived at has been questioned. The observa-
tions of Anstie and of Dupre have, indeed, thrown great doubt upon the
chromic-acid test for alcohol, which was employed by the French observers
above mentioned. Nevertheless, when alcohol has been taken in narcotic
doses, there is some alcoholic elimination in the urine, as was shown long ago
by Percy.

As the result of the final experiments of Anstie, it is 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 quantity is
thrown off, either in the urine, the faeces, the breath or the cutaneous tran-
spiration. This question is of 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 degree of
nervous exaltation which gradually passes off. In some individuals the men-
tal 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 phenom-
ena of intoxication^ delirum, more or less anaesthesia, coma, and sometimes,
if the quantity be excessive, death. As a rule, the mental exaltation pro-
duced by alcohol is followed by reaction and depression, except in debilitated
or exhausted conditions of the system, when the alcohol seerns to supply a de-
cided want.

The views of physiologists concerning the influence of a moderate quanti-
ty 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, can not be doubted ; but this effect is not produced in all individuals.
The constant use of alcohol may create an apparent necessity for it, produc-
ing 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 diminishes the exhalation
of carbon dioxide and the discharge of other excrementitious matters, par-
ticularly urea. These facts have long since been experimentally demonstrat-
ed. Proper mental and physical exercise, tranquillity of the nervous system,

ALCOHOL. 177

and all conditions which favor the vigorous nutrition and development of
the organism physiologically increase, rather than diminish, the quantity of
the excretions, correspondingly increase the demand for food, and if contin-
ued, 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 become so weakened that the proper quantity of food can not
be appropriated, and alcohol is craved to supply a self-engendered want.
The organism may, in many instances, be restored to its physiological condi-
tion by discontinuing the use of alcohol ; but it is generally 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 other assimi-
lable matters. These effects are too well known to the physician, particularly
in hospital-practice, to need farther comment. Notwithstanding these un-
doubted 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 question 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, can not 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 absolutely 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 certain warmth when the system is suffering
from excessive cold, it is not proved that it enables men to endure a very low
temperature for a great length of time. This end can be effectually attained
only by an increased quantity of food. The testimony of Dr. Hayes, the Arc-
tic explorer, is very strong upon this point. He says : " W^hile fresh animal
food, and especially fat, is absolutely essential to the inhabitants and travellers
in Arctic countries, alcohol is, in almost any shape, not only completely use-
less but positively injurious .... Circumstances may occur under which its
administration seems necessary ; such, for instance, as great prostration 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

178 ALIMENTATION.

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 injudi-
cious use of whiskey for the purpose of temporary stimulation, and have also
known strong able-bodied men to have become utterly incapable of resisting
cold in consequence of the long-continued use of alcoholic drinks." In a recent
paper by General Greely (1887), is the following, which confirms the results
of the experience of Hayes : " It seems to me to follow from these Arctic ex-
periences that the regular use of spirits, even in moderation, under conditions
of great physical hardship, continued and exhausting labor, or exposure to
severe cold can not be too strongly deprecated, and that when used as a men-
tal stimulus or as a physical luxury they should be taken in moderation.
When habit or inclination induces the use of alcohol in the field, under con-
ditions noted above, it should be taken only after the day's work is done, as
a momentary stimulus while waiting for the preferable hot tea and food ; or
better, after the food, when going to bed, for then it may quickly induce
sleep and its reaction pass unfelt."

It is not demonstrated that alcohol increases the capacity to endure severe
and protracted bodily exertion. Its influence as a therapeutic agent, in pro-
moting assimilation in certain conditions of defective nutrition, in relieving
shock and nervous exhaustion, in sustaining the powers of life in acute dis-
eases characterized by rapid emaciation and abnormally active disassimilation,
etc., can hardly be doubted ; 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 in-
dispensable, enabling men on moderate rations to perform an amount of labor
which would otherwise be impossible. After exhausting efforts of any kind,
there is no article which relieves the overpowering sense of fatigue so com-
pletely 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. 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 work, by producing wakefulness and
clearness of intellect. From these facts, the importance of coffee, either as
an alimentary substance or as taking the place, to a certain extent, of ali-
ment, 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 tranquillity 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 unaccus-

COFFEE, TEA ETC. 1Y9

tomed to its use, particularly when taken at night, it produces persistent wake-
fulness. These effects are so well known that it is often taken for the pur-
pose of preventing sleep.

Experimental researches have shown that the use of coffee permits a
reduction in the quantity of food, in workingmen especially, much below the
standard which would otherwise be necessary to maintain the organism in
proper condition. In the observations of De Gasparin upon the regimen 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 where this article was not
used. Experiments have shown, also, that coffee diminishes the absolute quan-
tity 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 it may reasonably
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 analyses by Payen :

Cellulose 34-000

Water (hygroscopic) 12-000

Fatty substances 10 to 13-000

Glucose, dextrine, indeterminate vegetable acid 15-500

Legumine, caseine etc 10*000

Potassium chlorolignate and caffeine 3-5 to 5-000

Nitrogenized organic matter 3-000

Free caffeine 0-800

Concrete, insoluble essential oil 0-001

Aromatic essence, of agreeable odor, soluble in water 0-002

Mineral substances ; potash, magnesia, lime, phosphoric, silicic, and sul-
phuric 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 roasting before an infusion is made.
During this process, the grains are considerably swollen, but they lose sixteen
or seventeen per cent, in weight. A peculiar aromatic substance is also
developed by roasting. If the torrefaction be pushed too far, much of the
agreeable flavor of coffee is lost, and an acrid, empyreumatic substance is
produced.

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
large 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 they are generally not so marked. Ordinary tea, taken in moderate
quantity, like coffee, relieves fatigue and increases mental activity, but does
not usually produce such persistent wakefulness.

180

ALIMENTATION.

It is unnecessary to describe all the varieties of tea in common use
There are, however, certain varieties, called green teas, which present impor-
tant differences, as regards composition and physiological effects, from the
black teas, which latter are more commonly used. The following is a com-
parative analysis of these two varieties by Mulder :

CONSTITUENTS.

CHINES

E TEA.

JAVANK

-K TEA.

Green.

Black.

. Green.

Black.

Volatile oil

0-79

0-60

0-98

0-65

2-22

1-84

3-24

1-28

0-28

0-32

Resin . . • .

2-22

3-64

1-64

2-44

Gum ....

8-56

7-28

12-20

11-08

Tannin

17-80

12-88

17-56

14-80

Theine . . ...

0-43

0-46

0-60

0-65

Extractive

22-80

19-88

21-68

18-64

Apotheme

1-48

1-64

Extract obtained by hydrochloric acid

23-60
3-00

19-12

2-80

20-36
3-64

18-24
1-28

17-08

28-32

18-20

27-00

Salts included in the above . .

98-78
5-56

98-30
5-24

100-42
4-76

97-70
5-36

Both tea and coffee contain peculiar organic substances. The active prin-
ciple of tea is called theine, and the active principle of coffee, caffeine. As
they are supposed to be particularly efficient 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. Analyses more recent than the one quoted from Mulder (Stenhouse,
Peligot) have shown that theine, or caffeine (C8H10N402 + H20), exists in
greater proportion in tea than in coffee ; but as a rule, a greater quantity of
soluble matter is extracted in the preparation of coffee, which may account
for its more marked effects upon the system. Some analyses have given as
much as six per cent, as the proportion of theine in tea (Landois).

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 powder, 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
substance, theobromine (C7H8N402), 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. Torrefaction has the effect of developing the pecul-
iar aromatic principle, and of moderating the bitterness, which is always more
or less marked :

NECESSAEY QUANTITY AND VARIETY OF FOOD. 181

Fatty matter (cocoa-butter) 48 to 50

Albumin, 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 mixt-
ure. Its influence as a stimulant, supplying the place of matter which is
directly assimilated, and retarding disassirnilation, is dependent, if it exist at
all, upon the theobromine ; but its stimulating properties are slight as com-
pared with those of coifee and tea.

Condiments and Flavoring Articles. — The refinements of cookery involve
the use of many articles which can not be classed as alimentary substances.
Pepper, capsicum, vinegar, mustard, spices and other articles of this class,
which are so commonly used in various sauces, have no decided influence
on nutrition, except in so far as they promote the secretion of the digestive
fluids. Common salt, however, is very important, and this has been consid-
ered in connection with inorganic alimentary substances. The various flavor-
ing 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 modified 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 indicate when to
change the form in which nutriment is taken ; and that a sufficient quantity
has been taken is manifested by a sense, not exactly of satiety, but of evi-
dent satisfaction 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 assimi-
lation of matter 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 excre-
tions. An illustration of this is the influence of food upon the exhalation
of carbon dioxide ; and this is but an example of what takes place with re-

182 ALIMENTATION.

gard to other excretions. The quantity of the excretions is even more strik-
ingly 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 con-
servative provision, 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 excretions ; and in the same way, the forces are retained
after complete deprivation of food much longer than if disassimilation pro-
ceeded 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 by
idiosyncrasies.

The daily loss of substance which must be supplied by matters introduced
from without is very great. A large portion of this discharge takes place by
the lungs, and a consideration of the mode of introduction of gases to supply
part of this waste belongs 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 condition. The entire quantity
of water daily removed from the system has been estimated at about four and
a half pounds (2,041 grammes), and it is probable that about the same quan-
tity is introduced 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. Dalton estimates the daily quantity necessary for a full-grown,
healthy male, at fifty-four fluid ounces'(l,530 grammes), or 3'38 pounds.

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 correspond 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 physiology. Ac-
cording to this observer, the following are the daily losses of the organism :

Carbon (or its] Respiration, 8-825 oz. (250 grammes) ) ^ >1Q.941 QZ (310 grammes)i

equivalent). ( Excretions, 2*116 oz. ( 60 grammes) )
Nitrogenized substances (containing 308-64 grains,

or 20 grammes of nitrogen) 4-586 oz. (130 grammes).

15-527 oz. (440 grammes).

From this he estimates that the normal ration, supposing the food to
consist of lean meat and bread, is as follows :

NECESSARY QUANTITY AND VARIETY OF FOOD. 183

Bread 35-300 oz. (1,000 grammes).

Meat (without bones) 10-088 oz. (286 grammes).

45-388 oz. (1,286 grammes).

Nitrogenized substances. Carbon.

Bread contains 2/-469 oz. (70-00 grammes) and 10-582 oz. (300-00 grammes).

Meat contains .... 2-125 oz. (60-26 grammes) and 1-109 oz. (31-46 grammes).

4-594 oz. (130-26 grammes) and 11-691 oz. (331-46 grammes).

This daily ration, which is purely theoretical, is shown by actual observa-
tion to be nearly correct. Dalton says : " According to our own observa-
tions, a man in full health, taking active exercise in the open air, and re-
stricted to a diet of bread, fresh meat, and butter, with water and coffee for
drink, consumes the following quantities per day :

Meat 453 grammes, or about 16 oz.

Bread 540 " " 19 oz.

Butter or fat 100 " " 3'5 oz.

Water 1,530 " " 54 oz.

Bearing in mind the great variations in the nutritive demands of the sys-
tem in different persons, it may be stated, in general terms, that in an adult
male, ten to twelve ounces (282 to 340 grammes) of carbon and four to five
ounces (113 to 142 grammes) of nitrogenized matter, estimated dry, are dis-
charged from the organism and must be replaced by the ingesta ; and this
demands a daily consumption of between two and three pounds (907 and
1,361 grammes) of solid food, the quantity of food depending, of course,
greatly on its proportion of solid, nutritive constituents.

It is undoubtedly true that the daily ration has frequently been dimin-
ished considerably 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 without 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 per-
form severe labor, the question of food is of great importance, and the men
collectively are like a powerful machine in which a certain quantity of ma-
terial must be furnished in order to produce the required amount of force.
This important physiological fact is 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
comparison of the amount of work accomplished by English and French
laborers, in 1841, on a railway from Paris to Rouen. The French laborers
engaged on this work were 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 regimen, they
were able to accomplish r.n equal amount of work. In all observations of

184 ALIMENTATION.

this kind, it has been shown than 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 considerable difference in the appetite at
different seasons of the year. Travelers' accounts of the quantity of food
taken by the inhabitants of the frigid zone are almost incredible. They speak
of men consuming more than a hundred pounds (45-36 kilos.) of meat in a
day ; and a Russian admiral, Saritcheff, gave an instance o£ a man who, in
his presence, ate at a single meal a mess of boiled rice and butter weighing
twenty-eight pounds (12 -7 kilos.). 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.
Hayes stated, from his personal observation, that the daily ration of the Es-
quimaux is twelve to fifteen pounds (5-443 to 6-804 kilos.), of meat, about
one-third of which is fat. On one occasion he saw an Esquimau consume
ten pounds (4-536 kilos.) 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 thermom-
eter ranging from— 60° to— 70° Fahr. (—51° to — 57° C.), there was a persist-
ent 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 substances, the fact that no single one of them is capable
of supplying all the material for the regeneration of the organism has fre-
quently been mentioned. The normal appetite, which is the best guide as
regards the quantity and the selection of food, indicates that a varied diet is
necessary to proper nutrition. This fact is 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 chem-
istry fails to show why this change in alimentation 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 effecting the changes necessary to proper nutrition. This fact
is particularly well marked when the diet consists in great part of salted
meats, although it sometimes occurs when a single kind of fresh meat is con-
stantly used. After long confinement to a diet restricted as regards variety,
a supply of other matters, such as fresh vegetables, the organic acids, and
articles which are called generally antiscorbutics, becomes indispensable;
otherwise, the modifications in nutrition and in the constitution of the blood
incident to the scorbutic condition are almost always developed.

It is thus apparent that adequate quantity and proper quality of food are

MEATS, BREAD ETC. 185

not all that is required in alimentation ; and those who have the responsi-
bility of regulating the diet of a large number of persons must bear in mind
the fact that the organism demands 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 craving for
particular articles, and these, if possible, should be supplied. This was fre-
quently exemplified in the civil war. At times when the diet was necessarily
somewhat monotonous, there was an almost universal craving for onions and
raw potatoes, which were found by army surgeons to be excellent antiscor-
butics.

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, particu-
larly 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 quan-
tity of food as a matter of education or habit.

A full consideration of the varieties of food and of the different methods
employed in its preparation belongs properly to special works on dietetics.
Among the ordinary articles of diet, the most important are meats, bread,
potatoes, milk, butter and eggs ; and it is necessary only to treat of these
very briefly.

Meats. — Among the various kinds of muscular tissue, beef has been found
to possess the greatest nutritive value. Other varieties of flesh, even that of
birds, fishes and animals in a wild state, do not present an appreciable differ-
ence, 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 eat animal as well as vegetable food, such as
pigs or ducks, acquire a disagreeable flavor when they are not fed on vege-
tables. Soups, broths, and most of the liquid extracts of meat really pos-
sess but little nutritive value and they can not replace the ordinary cooked
meats. The following is the composition of roasted meat, no dripping be-
ing lost, according to the analysis of Ranke, quoted by Pavy :

Nitrogenous matters 27-60

Fat 15-45

Saline matters 2-95

Water 54-00

100-00

Bread. — Bread presents a considerable variety of alimentary constituents
and is a very important article of diet. The constituents of flour undergo
peculiar changes in panification, which give to good bread its character-
istic flavor. Bread, especially coarse, brown bread, as a single article of
food, is capable of sustaining life for a long time. It contains a large pro-
portion of starch, but its important nitrogenized constituent is gluten, which
is not a simple substance but contains vegetable fibrin, vegetable albumin, a

186 ALIMENTATION.

peculiar substance soluble in alcohol, called glutine, with fatty and inorganic
matters. The following is the composition of bread, according to Letheby :

Nitrogenized matters 8'1

Carbohydrates (chiefly starch) 51-0

Fatty matters 1-6

Saline matters 2-3

Water 37'0

100-0

Potatoes. — Potatoes are very useful as an article of diet, especially on
account of the agreeable form in which starchy matter is presented ; for they
contain but a small proportion of nitrogenized matter and do not possess as
much nutritive value as exists in bread. They are selected for description
from the vegetable foods for the reason that they are almost universally used
in civilized countries throughout the year. They are usually cooked thor-
oughly, but the raw potato is a valuable antiscorbutic. The following is the
composition of potato, according to Letheby :

Nitrogenized matter 2'1

Starchy matters 18'8

Sugar 3-2

Fat 0-2

Saline matters 0-7

• Water . . 75-0

100-0

Milk. — Milk, and articles prepared from milk, such as butter, cheese etc.,
are important articles of food. In the treatment of disease, milk is frequently
used as a single article of diet. On account of the great variety of aliment-
ary matters which it contains, including a great number of inorganic salts
and even a small quantity of iron, milk will meet all the nutritive demands
of the system, probably for an indefinite time. It is largely used in the prep-
aration of other articles of food by cooking. Pure butter, which represents
the fatty constituents of milk, contains, in 100 parts, 30 parts of oleine, 68
parts of palmitine, and 2 parts of other fats peculiar to milk (Bromeis).
The following is the composition of cow's milk, according to Letheby :

Nitrogenized matters 4*1

Fatty matters 3-9

Sugar 5-2

Inorganic matters 0*8

Water . . 86-0

100-0

In connection with the composition of human milk, to be given farther
on, the great variety of its constituents will be more fully considered.

Eggs. — As regards nutrition, the analogy between eggs and butter is evi-
dent when it is remembered that the constituents of eggs furnish materials
for the growth of the chick, to which must be added certain saline matters

MEATS, BREAD ETC. 1ST

absorbed from the shell during the process of incubation. Among the inor-
ganic constituents of eggs, there is always a small quantity of iron. The
following is the composition of the entire contents of the egg, quoted from
Pavy :

Nitrogenized matters 14-0

Fatty matters 10-5

Inorganic matters 1-5

Water 74-0

1000

A number of different nitrogenized and fatty matters, a small quantity of
saccharine matter, as well as a great variety of inorganic salts, exist in eggs.

The physiological effects of a diet restricted to a single constituent of food
or to a few articles have been closely studied both in the human subject and
in the inferior animals. Animals subjected to a diet composed exclusively
of non-nitrogenized matters die in a short time with all the symptoms of
inanition. The same result follows when dogs are confined to white bread
and water ; but these animals live very well on the military brown bread, as
this contains a greater variety of alimentary matters (Magendie). Facts of
this nature were multiplied by the " gelatine commission," and the experi-
ments were extended to nitrogenized substances and articles containing a
considerable variety of alimentary matters. In these experiments, it was
shown that dogs could not live 011 a diet of pure myosine, the appetite en-
tirely failing at the forty-third to the fifty-fifth day. They were nourished
perfectly well by gluten, which is composed of a number of different ali-
mentary substances. Among the conclusions arrived at by this commission,
which bear particularly on the questions under consideration, were the fol-
lowing :

" Gelatine, albumin, fibrin, taken separately, do not nourish animals ex-
cept for a very limited period and in a very incomplete manner. In general,
these substances soon excite an insurmountable disgust, to the point that ani-
mals prefer to die of hunger rather than touch them.

" The same substances artificially combined and rendered agreeably sapid
by seasoning 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.

" Muscular flesh, in which gelatine, albumin and fibrin are united accord-
ing 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 com-
plete and prolonged nutrition."

In Burdach's treatise on physiology, is an account of some interesting
experiments by Ernest Burdach on rabbits, showing the influence of a re-
stricted diet upon nutrition. Three young rabbits from the same litter were
experimented upon. One was fed with potato alone and died on the thir-

188 ALIMENTATION.

teenth 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 animal increased in size and
was perfectly well nourished.

In 1769, long before any of the above-mentioned experiments were per-
formed, Dr. Stark, a young English physiologist, fell a victim at an early age
to 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.

CHAPTEE VII.

DIGESTION— MASTICATION, INSALIVATION AND DEGLUTITION.

Prehension of food — Mastication — Physiological anatomy of the teeth — Anatomy of the maxillary bones —
Temporo-maxillary articulation — Muscles of mastication — Action of the tongue, lips and cheeks in
mastication— 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 — Uses of the saliva — Physiological anatomy of the parts
concerned in deglutition — Mechanism of deglutition — First period of deglutition — Second period of deg-
lutition — Protection of the posterior nares during the second period of deglutition — Protection of the
opening of the larynx and uses of the epiglottis in deglutition — Third period of deglutition — Deglutition
of air.

alimentary substances 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 organic nitrogenized substances 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 are taken up by the blood. The non-nitrogenized
matters also undergo changes in constitution or in form preparatory to ab-
sorption.

'Prehension of Food. — Prehension of food in the adult is a process so
simple and well known that it demands little 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 virtual
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 anything to do with the condition of the thoracic walls. The mechan-
ism of drinking from a vessel is essentially the same. The vessel is inclined

MASTICATION. 189

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.

MASTICATION.

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 as to be readily
acted upon by the gastric juice ; otherwise, gastric digestion is prolonged and
difficult. Non-observance of this physiological law is a frequent cause of
what is generally called dyspepsia.

Physiological Anatomy of the Organs of Mastication. — In the adult, each
jaw is provided with sixteen teeth, all of which are about equally developed.
The canines, so largely developed in the carnivora but which are rudimentary
in the herbivora, and the incisors and molars, so fully developed in the her-
bivora, are, in man, of nearly the same length. Each tooth presents for ana-
tomical 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 the neck is
the portion, sometimes slightly constricted, situated between the crown and
the root and covered by the edge of the gum. Each tooth presents, on sec-
tion, 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. 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, ter-
minating just beneath the cuticle of the teeth.

The exposed surfaces of the teeth are still farther protected by a
membrane, -jyj-^ to 15i0o of an inch (O8 to 1-7 ft) in thickness, closely
adherent to the enamel, called the cuticle of the enamel (Nasmyth's mem-
brane). The cuticle presents a strong resistance to reagents and is 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 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 central 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 a large number of canals radiating from
14

190 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

the pulp-cavity toward the exterior. These are called the dentinal tubules or
canals. They are ^&loo to Tronr °^ an inch (1 to 2 /x) in diameter, with
walls of a thickness a little less than their caliber. Their course is slightly
wavy or spiral. Beginning at the pulp-cavity, into which these canals open,
they are found to branch and occasionally anastomose, their communications
and branches becoming more frequent as they approach the external surface
of the tooth. The canals of largest diameter are found next the pulp-cavity,
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 intertubular substance of the dentine ; but in

some portions of the tooth, the tu-
bules are so abundant that their
walls touch each other, and there
is, therefore, no intertubular sub-
stance. Near the 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. Sometimes these cavities form
regular zones near the peripheral
termination of the tubules. The
dentine is sometimes marked by
concentric lines, indicating a lam-
ellated arrangement. In the nat-
ural condition, the dentinal tubules
are filled with a clear liquid, which
penetrates from the vascular struct-
ures 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 at the deeper
portions of the root, where it is
sometimes lamellated, and it be-
comes thinner near the neck. It

— 3

FIG. 52.— Tooth of the cat, in situ (Waldeyer).

finally becomes continuous with

1, enamel ; 2, dentine ; 3, cement ; 4, periosteum of the the enamel of the Crown, SO that
alveolar cavity ; 5, lower jaw ; 6, pulp-cavity. ,

the dentine is everywhere com-
pletely covered. The cement 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 minute

MASTICATION. 191

blood-vessels and nervous filaments, held together by longitudinal fibres of
connective tissue. This is the only portion of the tooth endowed with sensi-
bility. The blood-vessels and nerves penetrate by a little orifice at the ex-
tremity of each root.

The dentine and enamel of the teeth must be regarded as perfected struct-
ures ; for when the second, or permanent teeth are lost, they are never re-
produced, and when these parts are invaded by wear or by decay, they are
not restored.

The thirty-two permanent teeth are classified 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, flattened antero-posteriorly, and bevelled
at the expense of the posterior face, giving them a sharp, cutting edge, which
is sometimes perfectly straight but is generally more or less rounded. Each
incisor has a single root. The special use of the incisor teeth is to divide the
food as it is taken into the mouth. The permanent incisors make their ap-
pearance between the seventh and the eighth years.

The canines are more conical and pointed ^han the incisors, and have
longer and larger roots, especially those in the upper jaw. Their roots are
single. They are used, with the incisors, in dividing the food. The perma-
nent canines make their appearance between the eleventh and the twelfth
years.

The bicuspid teeth are shorter and thicker than the canines. Their op-
posed surfaces are rather broad and are marked by two eminences. The
upper bicuspids are larger than the lower. The roots are single, but in the
upper jaw they are slightly bifurcated at their extremities. They are used,
with the true molars, in triturating the food. The permanent bicuspids
make their appearance between the ninth and the tenth years.

The molar teeth, called respectively — counting from before backward —
the first, second and third molars, are the largest of all and are, par excel-
lence, 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 resem-
ble 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 use-
ful in mastication. The first molars are the first of the permanent teeth,
making their appearance between the sixth and the seventh years. The sec-
ond molars appear between the twelfth and the thirteenth years; and the

192 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

third molars, between the seventeenth and the twenty-first years, and some-
times even much later. In some instances the third molars are never de-
veloped.

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 cor-
responding teeth in the upper jaw and generally make their appearance a
little earlier.

The physiological anatomy of the maxillary bones and of the temporo-
maxillary articulation necessarily precedes the study of the muscles of masti-
cation 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 mastication.
Their inferior borders, with the upper teeth embedded in the alveolar cavi-
ties, 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 horse-
shoe shape, and in the alveolar cavities in its superior border, are 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.

Temporo- Maxillary A rticulation. — In
man the articulation of the lower jaw with
the temporal bone is such as to allow an
antero-posterior sliding movement and a
lateral movement, in addition to the move-
ments of elevation and depression. The
condyloid process is convex, with an ovoid
surface, the general direction of its long
FIG. ^.-inferior maxilla (Sappey) diameter being transverse, and slightly ob-

1, body ; 2. ramus ; 3, symphysis ; 4, incisive J

fossa ; 5, mental foramen ; 6 attachment lique from without in ward and from before

of the digastric muscle : 7, depression at

the site of the facial artery : 8, angle ; 9, backward. This prOCCSS IS received into a

attachment of the superior constrictor x .

of the pharynx ; 10, coronoid process ; cavitv 01 corresponding; shape in the tem-

11, condyle ; 12, sigmoid notch ; 13, open- / ° A . .

ing of the inferior dental canal ; 14, poral bone, the glenOld lOSSa, WlllCn IS
groove for the mylo-hyoid muscle ; 15, ~ • •> •> -i i •

alveolar border ; i, incisor teeth ; c, ca- bounded anteriorly by a rounded eminence,

nine teeth ; b, bicuspid teeth ; m, molars. « 3 , i ' ,• i- i •

called the emmentia articulans.

Between the condyle of the lower jaw and the glenoid fossa, is an oblong,
interarticular disk of fibro-cartilage. This disk is thicker at the edges than
in the centre. It is pliable and is so situated that when the lower jaw is pro-
jected forward, making the lower teeth project beyond the upper, it is ap-
plied to the convex surface of the eminentia articularis and presents a con-
cave surface for articulation with the condyle. One of the uses of this
cartilage is to constantly present a proper articulating surface upon the
articular eminence and thus permit the antero-posterior sliding movement

MASTICATION. 193

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 for-
ward, 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.

MUSCLE. ATTACHMENTS.

Digastric Mastoid process of the temporal bone — Lower

border of the inferior maxilla near the symphy-
sis, with its central tendon held to the side of
the body of the hyoid bone.

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 infe-
rior border.

Muscles which 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, tuberosity of the palate and the
superior maxillary bone — Inner surface of the
neck of the condyle of the inferior maxilla and
the interarticular fibro-cartilage.

Action of the Muscles which depress the Lower Jaw. — The most impor-
tant of these muscles have for their fixed point of action, the hyoid bone,
which is fixed by the muscles extending 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. In ordinary mastication the upper jaw undergoes a
slight movement of elevation, and this becomes somewhat exaggerated when
the mouth is opened to the fullest possible extent.

194: DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

Action of the Muscles ivhich elevate the Lower Jaw and move it laterally
and antero-posteriorly. — The temporal, masseter and internal pterygoid
muscles are chiefly concerned in the simple act of closing the jaws. Their
anatomy alone gives a sufficiently clear idea of their mode of action ; and
their great power is explained by the number of their fibres, by the attach-
ments of many of these fibres to the strong aponeuroses by which they are
covered, and by 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 alternate 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-maxil-
lary articulation. The articulation of the lower jaw is of such a kind that
in its lateral movements the condyles themselves can not be sufficiently dis-
placed 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 above explanation of the lateral movements of the jaw presupposes
the possibility 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 an-
terior 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 shown the importance of the tongue and
cheeks in mastication. Section of the facial nerves is a common physiologi-
cal experiment. Operations 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 incon-
venience.

The varied1 and complex movements of the tongue during mastication
are not 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 uses of the tongue as an organ of taste, its sur-
face is endowed with peculiar sensibility as regards the consistence, size and
form of different articles ; and this is undoubtedly important in determining
when mastication is completed, although the thoroughness with which mas-
tication is accomplished is 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 office, however, is performed mainly by the buccina-

SALIVA.

195

tor ; 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 ali-
mentary bolus so as to subject new portions to trituration.

The process of mastication is regulated to a very great extent by the
sensibility 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 the
presence and the consistence of the smallest substance between the teeth are
recognized, to show the importance of this tactile sense in mastication.

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 sputation, is composed of the secretions
of a considerable number and variety of glands. The most important of these
are the parotid, submaxillary and sublingual, which are usually called the
salivary glands. The labial and buc-
cal glands, the glands of the tongue
and general mucous surface and cer-
tain glandular structures in the mu-
cous membrane of the pharynx also
contribute to the production of the
saliva. The liquid which becomes
more or less incorporated with the
food before it descends to the stom-
ach, and which must be regarded as
the digestive fluid of the mouth, is
known as the mixed saliva ; but the
study of the composition and prop-
erties of this fluid as a whole should
be prefaced by a consideration of
the different secretions of which it
is composed. The salivary glands
belong to the variety of glands
called racemose. They resemble the other glands belonging to this class,
and their structure will be more fully considered in connection with the
physiology of secretion.

Parotid Saliva. — The parotid is the largest of the three salivary glands.
It is situated 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.

The organic matter of the parotid saliva is coagulable by heat (212° Fahr.,
or 100° C.), alcohol or the strong mineral acids. A compound of sulpho-
cyanogen is now generally acknowledged to be a constant constituent of the
parotid saliva. This can not be recognized by the ordinary tests in the fresh
saliva taken from the duct of Steno, but in the clear, filtered fluid which

FIG. 54.— Salivary glands (Tracy).

196 DIGESTION-MASTICATION, INSALIVATION, DEGLUTITION.

passes after the precipitation of the organic matter, there is always a distinct,
red color on the addition of ferric sulphate. As this reaction is more marked
in the mixed saliva, the methods by which the presence of a sulphocyanide
is to be recognized 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 ; but the entire quantity in the twenty-four hours has
not been directly estimated.

In the horse, ass and ox, it has been found that when mastication is per-
formed on one side of the mouth, the flow from the gland on that side is
greatly increased, exceeding by several times the quantity produced upon the
opposite side (Colin). This fact has been confirmed by Dalton in the human
subject.

The flow of saliva from the parotid takes place with greatly increased
activity during the process of mastication. The orifioe of the parotid duct is
so situated that the fluid is poured directly upon the mass of food as it is un-
dergoing 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 office 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 quan-
tity is regulated somewhat by the character of the food, being much greater
when the articles taken into the mouth are dry than when they contain con-
siderable moisture. In the human subject, the stimulus produced by sapid
substances will sometimes cause a great increase in the flow of the parotid
saliva. Mitscherlich and Eberle observed this in persons suffering from sali-
vary fistula and noted, farthermore, that the mere sight or odor of food pro-
duced the same effect. The supposition that the flow from the parotid is
dependent upon the mechanical pressure of the muscles or of the condyle of
the lower ja.w during mastication has no foundation in fact. 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 (Bernard).

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 — evidently has an important mechanical office. It is discharged in
large quantity during the act of mastication and is poured into the mouth
in such a manner as to become of necessity thoroughly incorporated with the
food. Its use is chiefly, although not exclusively, connected with mastication
and indirectly, with deglutition; for it is only by becoming incorporated
with this saliva, that dry, pulverulent substances can be swallowed.

Submaxillary Saliva. — In the human subject, the submaxiliary is the sec-
ond of the salivary glands in point of size. Its minute structure is nearly
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, the duct of Wharton,

SALIVA. 197

is about two inches (5 centimetres) in length and passes from the gland, be-
neath the tongue, to open by a small papilla by the side of the f renum.

The pure submaxillary saliva presents many important points of difference
from the secretion of the parotid. It may be obtained by exposing the duct
and introducing a fine silver tube, when, on the introduction of any sapid
substance into the mouth, the secretion will flow in large, pearly drops. This
variety of saliva is much more viscid than the parotid secretion. It is per-
fectly clear, and on cooling, it frequently becomes of a gelatinous consist-
ence. Its organic matter is not coagulable by heat. It contains a sulpho-
cyanide, but in very small quantity.

The submaxillary gland pours out its secretion in greatest abundance when
sapid substances are introduced into the mouth ; but unlike the parotid saliva,
the secretion does not alternate on the two sides with alternation in mas-
tication. Although sapid articles excite an abundant secretion from the
submaxillary glands, they also increase 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
quantity of fluid during the intervals of digestion. The viscid consistence
of the submaxillary saliva renders it less capable than the parotid secretion
of penetrating the alimentary mass during mastication.

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, 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 opening in the mouth.

The secretion of the sublingual glands is more viscid, even, than the sub-
maxillary saliva, but it differs in the fact that it does not gelantinize on cooling.
It is so glutinous that it adheres strongly to any vessel and flows with diffi-
culty from a tube introduced into the duct. Like the secretion from the
other salivary glands, its reaction is distinctly alkaline. Its organic matter is
not coagulable by heat, acids or the metallic salts.

It has been shown 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 viscid-
ity of the sublingual saliva renders it less easily mixed with the alimentary
bolus than the secretions 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 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 mem-
brane of the posterior half of the hard palate ; but the glands on the under

198 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

surface of the soft palate are larger and here form a continuous layer. The
glands of the tongue are situated beneath the mucous membrane, mainly on
the posterior third of the dorsum ; but a few are found at the edges and the
tip, and there is a gland of considerable size on either side of the frenum,
near 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 simple and
compound follicular glands, which extend over its entire surface, but are
most abundant at the posterior portion, behind the circumvallate papillae.
The most important of the glands of the tongue will be described in connec-
tion with the physiology of gustation.

In the pharynx and the posterior portion of the buccal cavity, are the
pharyngeal glands and the tonsils. In the pharynx, particularly the upper
portion, racemose glands, like those found in the mouth, exist in large num-
bers. The mucous membrane .is provided, also, with simple and compound
mucous follicles. The tonsils, situated on either side of the fauces between
the pillars of the soft palate, consist of an aggregation of compound follicular
glands. The number of glands entering into the composition of each tonsil
is ten to twenty.

The secretion from the glands and follicles above enumerated can not be
obtained, in the human subject, unmixed with the fluids from the true sali-
vary glands. It has been collected in small quantity, however, from the in-
ferior 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 opaline character to
the mixed saliva, as the secretions of the salivary glands are all perfectly
transparent. The fluid from these glands in the mouth is mixed with the
salivary secretions ; and that from the posterior part of the tongue, the ton-
sils, and the pharyngeal glands passes down to the stomach with the aliment-
ary bolus. This secretion, consequently, forms a constant and essential part
of the mixed saliva.

Mixed Saliva. — Although the study of the distinct secretions discharged
into the mouth possesses considerable physiological 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 condition for phonation. A little reflec-
tion 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.
The discharge of the 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 parotid, the secreting action of which is most powerfully
influenced by the act of mastication and the impression of sapid substances.

Upon the introduction of food the quantity of saliva is greatly increased ;
and the influence of the sight, odor, and occasionally even the thought of

SALIVA. 199

agreeable articles has already been mentioned. The experiments of Frerichs
on dogs with gastric fistulae, and the observations of Gardner on a patient
with a wound in the oesophagus, 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 absorbed by the various
articles of food. Estimates of this kind can be approximate only, and those
made by Dalton are apparently the most satisfactory. The following repre-
sents, according to Dalton, the quantities of saliva secreted during mastica-
tion and during the intervals of meals :

Saliva required for mastication ^ 17-32 oz. (491 grammes).

Saliva secreted in intervals of meals 27'93 oz. (792 grammes).

Total quantity per day 45-25 oz. (1,283 grammes).

The total daily quantity of saliva, therefore, is a little more than two and
three-fourths pounds.

Eemembering that the quantity of saliva must necessarily be subject to
great variations, this estimate may be taken as giving a sufficiently close ap-
proximation of the quantity of saliva ordinarily secreted. It must be borne
in mind, however, with reference to this and the other digestive secretions,
that this large 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 dis-
charged from the organism.

General Properties and Composition of the 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, com-
posed mainly of desquamated epithelial scales with a few leucocytes, leaving
the supernatant fluid tolerably clear. Its specific gravity is variable, ranging
between 1004 or 1006 and 1008. Its reaction is almost constantly alkaline ;
although, under certain abnormal conditions of the system, it has occasion-
ally been observed to be neutral, and sometimes, though rarely, acid. The
saliva becomes slightly opalescent by boiling or on the addition of strong
acids. The addition of absolute alcohol produces an abundant, whitish, floc-
culent 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 sulphocyanide either of potassium or of sodium.

A number of analyses of the human mixed saliva have been made by dif-
ferent chemists, presenting, however, few differences, except in the relative
proportions of water and solid ingredients, which are probably quite variable.
The following is an analysis by Bidder and Schmidt :

200 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

COMPOSITION OF HUMAN SALIVA.

Water 995-16

Epithelium 1-62

Soluble organic matter 1-34

Potassium sulphocyanide 0'06

Sodium, calcium and magnesium phosphates 0*98

Potassium chloride )
Sodium chloride } '

1,000-00

The organic matter of the mixed saliva, called by Berzelius, ptyaline, 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 substance
has been 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 has no direct influence upon the nitrogenized alimentary matters, but
when brought in contact with 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 potassium sulphocyanide in the
mixed saliva can be demonstrated by the addition of a per-salt of iron. That
this is a constant and normal ingredient of the human saliva, can not be
doubted.

Very little need be said concerning the other 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 action of the saliva as a digest-
ive fluid.

USES OF THE SALIVA.

In 1831, Leuchs discovered that hydrated starch, mixed with fresh saliva
and warmed, became liquid and was converted into sugar. This fact has
since been repeatedly confirmed ; and it is now a matter of common observa-
tion 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 experiment of taking a little cooked
starch into the mouth, mixing it well with the saliva, and testing in the ordi-
nary way for sugar. This can hardly be done so rapidly that the reaction
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 un-
cooked starch, the transformation takes place much more slowly.

It has been shown that all the varieties of human saliva have the same
effect on starch as the mixed fluids of the mouth. Dalton found no differ-
ence between the pure parotid saliva and the mixed saliva of the human
subject, as regards the power of transforming starch into sugar. Bernard

SALIVA. 201

obtained the pure secretions from the parotid and from the submaxillary
glands in the human subject, by drawing the fluids out of the ducts as they
open into the mouth, by means of 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 sub-
lingual glands has the same property.

Several carbohydrates are formed as intermediate products between the
hydrated starch and glucose, which latter is the final result of the action of
the salivary ferment. After passing through one or two conditions slightly
different from that of pure dextrine, the starch is converted into dextrine,
which is changed into maltose (C^H^On), and the maltose is finally con-
verted into glucose (C6H1206). This action is due entirely to the presence of
ptyaline, although its intensity is increased in moderately alkaline solutions
or by the addition of certain salts, especially sodium chloride. Feeble acids
diminish the activity of this change, and it is arrested by strong mineral
acids ; although direct experiments have shown that the action of the saliva
is slowly and feebly continued in the stomach. The temperature at which the
action of the salivary ferment is most vigorous is about 100° Fahr. (38° C.) ;
and any considerable variation from this temperature arrests the process.

In early infancy the action of the saliva upon starch is not so vigorous as
in the adult, and it is said that immediately after birth the parotid secretion
is the only one of the salivary fluids which contains ptyaline. In a few
months, however, ptyaline appears in the submaxillary and sublingual secre-
tions.

It is evident that the saliva, in addition to its mechanical action, trans-
forms a considerable portion of the cooked starch, which is the common
form in which starch is taken by the human subject, into sugar; but it
is by no means the only fluid engaged in its digestion, similar properties
belonging to the pancreatic and the intestinal juices. The last-named fluids
are probably more active, even, than the saliva. The saliva acts slowly and
imperfectly on raw starch, which becomes hydrated in the stomach and is
digested mainly by 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 action to the saliva draw their conclusions entirely
from experiments on the lower animals, particularly the carnivora ; and such
observations can not properly be applied to the human subject.

In treating of the various fluids which are combined to form the mixed
saliva, their mechanical uses have necessarily been touched upon. To sum
up this part of the subject, however, it may be stated that the fluids of the
mouth and pharynx 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 diges-
tion of starch. It is a matter of common experience that the rapid deglu-
tition of very dry articles is impossible. 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

202 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION. '

is very large. It seems impossible that the fluid thus incorporated with the
food should not have an important influence on the changes which take
place in the stomach, although it must be confessed that 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 coherent mass. The secre-
tions 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 secretion, penetrate the alimentary bolus less easily and form a
glairy coating on its exterior, agglutinating the particles near the surface
with peculiar tenacity.

When the processes of mastication and insalivation have been completed,
and the food has passed 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 engages bubbles of air in the ali-
mentary mass. In mastication, a considerable quantity of air is mixed with
the food, and this facilitates the penetration of the gastric juice. It is well
known that moist, heavy bread, and articles that can not 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 passed from
the mouth into the stomach. The process involves first, the passage, by an
automatic 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 ; and finally, a peristaltic
action of the muscular walls of the oesophagus, extending from its opening at
the pharynx to the stomach.

Physiological Anatomy of the Parts concerned in Deglutition. — The parts
concerned in this process are the tongue, the muscular walls of the pharynx
and the oesophagus. In the passage of food and drink through the pharynx,
it is necessary to completely protect from the entrance of foreign matters a
number of openings which are exclusively for the passage of air. These are
the posterior nares and the Eustachian tubes above, and the opening of the
larynx below.

The tongue — a muscular organ capable of a great variety of movements
— is the chief agent in the first processes of deglutition. A study of the
muscles which are brought into action in deglutition would involve an ana-
tomical description so elaborate as to be out of place in this work. The
movements of the tongue, however, will be described in connection with the
mechanism of deglutition.

The pharynx, in which the most complex of the movements of deglutition
take place, is an irregular, funnel-shaped cavity, its longest diameter being

DEGLUTITION.

203

transverse and opposite the cornua of the hyoid bone, with its smallest por-
tion at the opening into the oesophagus. Its length is about four and a half
inches (11-43 cen-
timetres). It is
connected superi-
orly and posterior-
ly with the basilar
process of the oc-
cipital bone and
with the upper cer-
vical vertebras. It
is incompletely sep-
arated from the
cavity of the mouth
by the velum pen-
dulum palati, a
movable, musculo-
membranous fold
continuous with
the roof of the
mouth and marked
by a line in the
centre, which in-
dicates its original
development by
two lateral halves.
This, which is
called the soft
palate, when re-
laxed, presents a
concave surface
looking toward
the mouth, a free,
arched border, and a
the uvula. On either
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 mem-
brane 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 membrane 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 membrane of the palate and pharynx, are small glands, which have
already been described.

FIG. 55.— 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 mouth in its relations to the nasal fossae, the phar-
ynx and the larynx : 1. sphenoidal sinuses ; 2, internal orifice of the Eu-
stachian tube ; 3, 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. laryrigeal portion of the cavity of the pharynx;
12, cavity of the larynx.

conical
side of

process hanging from the centre, called
the soft palate, are two curved pillars, or

204: DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION,

In Fig. 55, are shown the cavities of the mouth and pharynx with their
relations to the nares and the larynx.

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 pillars of the palate and the tonsils ; and below, by

the base of the
tongue.

The openings
into the pharynx
above are the pos-
terior nares and
the orifices of the
Eustachian tubes.
Below, are the
openings of the
oesophagus and of
the larynx.

The muscles of
the pharynx are
the superior con-
strictor, the stylo-
pharyngeus, the
middle constrictor
and the inferior
constrictor ; and
it is easy to see,
from the situation
of these muscles,
which is shown in
Fig. 56, how, by
their successive
action from above
downward, the

middle constrictor ; 9, 10, 11, 12, in- fnnrl ic r»acapr1 irtfn
ferior constrictor ; 13, 13, stylo-pharyngeus ; 14, stylo-hyoid muscle ; 15, ]

16, hyo-glossus ; 17, mylo-hyoi
19, tensor palati ; 20, levator palati.

FIG. 56. — Muscles of the pharynx, etc. (Sappey).
1, 2, 3, 4, 4, superior constrictor ; 5, 6, 7,

ryngeus ; 14, stylo-hyoid muscle ; 15, J

oesophagus.
The muscles

which form the fleshy portions of the soft palate are likewise important in
deglutition. These are the levator palati, the tensor palati, the palato-glossus
and the palato-pharyngeus. The azygos uvulae, which forms the fleshy por-
tion of the uvula, has no marked or important action in deglutition.

The mucous membrane of the pharynx, aside from the various glands sit-
uated beneath it and in its substance, which have already been described, pre-
sents some peculiarities, which are interesting more from an anatomical than
a physiological point of view. In the superior portion, which forms a cuboid-
al 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 pro-

DEGLUTITION. 205

vided with ciliated, columnar epithelium, like that which covers the mem-
brane of the posterior nares. Laterally, below 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 flattened cells, similar to those which cover the mucous
membrane of the oesophagus. The membrane is also paler and less vascular.
It is provided with papillae, some of which are simple, conical elevations, while
others present two to six conical processes with a single base. These papillae
are rather thinly distributed over all of that portion of the mucous surface
which is covered with flattened epithelium.

The contractions of the muscular walls of the pharynx force the aliment-
ary bolus into the oesophagus, a tube possessed of thick, muscular walls, ex-
tending to the stomach. The oesophagus is about nine inches (23 centi-
metres) in length. It is cylindrical and is slightly constricted at its superior
and inferior extremities. Its upper extremity is in the median line, behind
the lower border of the cricoid cartilage and opposite the fifth cervical verte-
bra. At first, as it descends, it passes a little to the left of the cervical
vertebrae. 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 there be included,
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 inter-
nal 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 froni the posterior 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 ex-
ternal 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 -fa to ^ of an inch (0*5 to 2*1 mm.) 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 cir-
cular layer. These latter fibres become gradually more abundant, 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
gradually becomes paler in the inferior portion. The mucous membrane is
ordinarily thrown into longitudinal folds, which are obliterated when the

15

206 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

tube is distended. Its epithelium is thick, of the squamous 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. 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 generally 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 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. At the beginning
of this period, 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 see, 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 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 case of a young girl,
reported by De Jussieu (1718), 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 por-
tion of its base generally remains, which is sufficient to press against the
palate and thus act in the first period of deglutition.

The movements in the first period of deglutition are under the control of
the will but are generally automatic. When the food has been thoroughly
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 imper-

DEGLUTITION. 20T

ative necessity of air in the system must, in a short time, overcome any vol-
untary 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 succession 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 called
reflex. After the alimentary mass has passed beyond the isthmus of the
fauces, it is easy to observe a sudden and peculiar movement of elevation of
the larynx, by the action of muscles which 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 di-
gastric (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 elevation of the larynx, there is necessarily an elevation of the ante-
rior 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
simultaneously 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 acting from the median raphe, draw up 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 returned to their
original position.

Protection of the Posterior Nares during the Second Period of Degluti-
tion.— 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 embrace,
during their contraction, not only the alimentary mass, but the velum pend-
ulum 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 oper-
ations, and its mechanism has also been observed in the human subject, by
Bidder and by Kobelt.

While the food is passing through the pharynx, the palato-pharyngeal
muscles, which form the posterior pillars of the soft palate, are in a con-
dition of contraction by which the edges of the pillars are nearly approxi-
mated, 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 fossae.

208 DIGESTION— MASTICATION, INSALIVATION, DEGLUTITION.

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 a violent cough. This accident is of not
infrequent occurrence, especially when an act of inspiration is inadvert-
entty performed while solids or liquids are in the pharynx. During inspi-
ration, the glottis is opened, and at that time only can a substance of any
considerable size find its way into the respiratory passages. Respiration is in-
terrupted, however, during each and every act of deglutition ; and there can,
therefore, be hardly any tendency at that time to the entrance of foreign sub-
stances into the larynx. During a regular act of swallowing, nothing can find
its way into the respiratory passages, so complete is the protection of the larynx
during the period when the food passes through the pharynx into the oesophagus.

It is evident, from the anatomy of the parts and the necessary results of
the contractions 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, the natural movements of the tongue and larynx
can be imitated, and it is seen that they must be sufficient to protect the
larynx from the entrance of solid or semi-solid particles of food, particu-
larly when it is remembered how the alimentary particles are agglutinated
by the saliva and how easy their passage becomes over the membrane coated
with mucus. It is impossible, also, for the muscles of the pharynx to con-
tract 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 move-
ments of respiration are arrested during deglutition, the lips of the glottis
fall together, as they always do except in inspiration. In addition to this
passive and incomplete approximation of the vocal chords, it has repeatedly
been observed that the lips of the glottis are accurately and firmly closed
during each act of deglutition.

Longet justly attached great importance to the acute 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 after 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.

With reference to the action of the epiglottis in contributing to the pro-
tection of the larynx during the second period of deglutition, observations on
the human subject only are to be relied upon. Such observations, in cases of
loss of the epiglottis especially, show that this part is necessary to the com-
plete protection of the larynx. While loss of the epiglottis may not inter-
fere always with the perfect deglutition of solids, and even of liquids, parti-
cles of food and liquids frequently find their way into the larynx, and
deglutition is often effected with difficulty, showing that complete protection
of the larynx at all times, does not exist unless the epiglottis be intact.

To appreciate the mechanism by which the opening of the larynx is pro-

DEGLUTITION. 209

tected during the deglutition of solids and liquids, one has only to carefully
follow the articles as they pass 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 the intrinsic muscles. If the food be tolerably con-
sistent and in the form of a single bolus, it slips easily from the back of the
tongue along the membrane covering the anterior and inferior part of the
pharynx ; but if it be liquid or of soft consistence, a portion takes this
course, while another portion passes over the epiglottis, being directed by it
into the two grooves by the side of the larynx. It is by these means,
together with those by whicft the posterior nares are protected, that all solids
and liquids are passed into the oesophagus, and the second period of degluti-
tion is safely accomplished.

The third period of deglutition is the most simple of all. It merely
involves contractions of the muscular walls of the oesophagus, by which the
food is passed into the stomach. 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 peristaltic contraction from
above downward, propel the food into the stomach. In experiments on the
lower animals, it has been observed that while the peristaltic contractions of
the upper two-thirds of the tube is immediately followed by a relaxation,
which continues till the next act of deglutition, the lower third remains con-
tracted generally for about thirty seconds after the passage of the food into
the stomach. During its contraction, this part of the oesophagus is hard,
like a cord firmly stretched. This is followed by relaxation; and alter-
nate contraction and relaxation continue, even when the stomach is empty,
although, during digestion, the contractions are frequent in proportion to the
quantity of food in the stomach. The contraction is always increased by
pressing the stomach and attempting to pass some of its contents into the
oesophagus (Magendie). This provision is important in preventing regurgi-
tation of the contents of the stomach, especially when the organ is exposed
to pressure, as in urination or defecation.

An approximate estimate of the duration of the acts of deglutition is
given in the following quotation from Landois :

" According to Meltzer and Kronecker, the duration of deglutition in the
mouth is 0*3 sec. ; then the constrictors of the pharynx contract O9 sec. ;
afterward, the upper part of the oesophagus ; then after 1/8 sec. the middle ;
and after another 3 sec. the lower constrictor. The closure of the cardia,
after the entrance of the bolus into the stomach, is the final act in the total
series of movements."

210 DIGESTION— MASTICATION, INSAIIVATION, DEGLUTITION.

The entire process of deglutition, therefore, occupies about six seconds.

The muscular movements which take place during all the periods of deg-
lutition are peculiar. The first act is generally automatic, but it is under
the control of the will. The second act is involuntary when once begun,
but it 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 unless there be some 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 move-
ments ; but a little attention will show that with each act a small quantity of
saliva is swallowed. When the efforts have been frequently repeated, the
movements become impossible, until time enough has elapsed between them
for the saliva to collect.

All the movements of deglutition, except those of the first period, must
be regarded as reflex, depending upon an impression made upon the afferent
nerves distributed to the mucous membrane of the pharynx and oesophagus.

The position of the body has little to do with the facility with which deg-
lutition is effected. Liquids or solids may be swallowed indifferently in all
postures. Berard saw a juggler pass an entire bottle of wine from the mouth
to the stomach, while standing on his head. The same feat was accom-
plished with apparent ease, by a juggler who drank three glasses of beer
.while standing on his hands in the inverted posture (Flint).

Deglutition of Air. — In his essay on the mechanism of vomiting, Ma-
gendie stated that as soon as nausea occurred the stomach began to fill
with air, so that before vomiting occurred, the organ became tripled in size.
Magendie showed, fathermore, that the air entered the stomach by the oesoph-
agus, for the distention occurred when the pylorus was ligated. In a sub-
sequent memoir, the question of the deglutition of air, aside from the small
quantity which is incorporated with the food during mastication and insali-
vation, was farther investigated. It was found that some persons had the
faculty of swallowing air, and by practice, Magendie himself was able to ac-
quire 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 the
habit of swallowing air, in order to relieve uncomfortable sensations in the
stomach ; and when confirmed, it occasions persistent disorder in digestion.
Quite a number of cases of this kind were reported by Magendie, and in sev-
eral it was carried to such an extent as to produce great distention of the
abdomen. A curious case of habitual air-swallowing was observed by the late
Dr. Austin Flint and is reported in his work on the Practice of Medicine.

PHYSIOLOGICAL ANATOMY OF THE STOMACH. 211

CHAPTER VIII.

GASTRIC DIGESTION.

Physiological anatomy of the stomach— Glands of the stomach— Closed follicles— Gastric jnice— Gastric
fistula in the human subject in the case of St. Martin— Secretion of the gastric juice— Properties and
composition of gastric juice— Action of the gastric juice in digestion— Peptones— Action of the gastric
juice upon fats, sugars and amylaceous substances — Duration of gastric digestion — Conditions which in-
fluence gastric digestion— Movements of the stomach.

PHYSIOLOGICAL ANATOMY OF THE STOMACH.

THE stomach 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 ossophagus. Its form is not easily de-
scribed. It has been compared to a bagpipe, which it resembles somewhat,
when moderately distended. When empty, it is flattened, and in many parts
its opposite walls are in contact. When moderately distended, its length is
thirteen to fifteen inches (33 to 38 centimetres), its greatest diameter, about
five inches (12'7 centimetres), and its capacity, one hundred and seventy-five
cubic inches (2,868 c. c.), or about five pints. The parts usually noted in
anatomical descriptions are the following : a greater and a lesser curvature ;
a greater and a lesser pouch; a cardiac, or oesophageal opening; 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 anatomists 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 layer of peritoneum, similar in struct-
ure to the membrane which covers the other abdominal viscera. It is a re-
flection of the membrane which lines the general abdominal cavity, which,
on the viscera, is somewhat thinner than it is on the walls of the cavity.
Over the stomach the peritoneum is -3^-5- to ^J-g- of an inch (83 to 125 ft)
in thickness. It is a serous membrane and consists of ordinary fibrous
tissue 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 regularly polygonal cells of pavement endothelium, closely adherent to
each other and presenting a perfectly smooth surface which is moistened
with a small quantity of liquid. An important office of this membrane is to
present a smooth surface covering the abdominal parietes and viscera, so as
to allow free movements of the organs over each other and against the walls
of the abdomen.

Muscular Coat. — Throughout the alimentary canal, from the cardiac
opening of the stomach to the anus, the muscular fibres forming the middle
coat are of the non-striated variety. These fibres, called sometimes muscu-

212 GASTRIC DIGESTION.

lar fibre-cells, are very pale, with faint outlines, fusiform or spindle-shaped,
and contain each an oval, longitudinal nucleus. They are closely adher-
ent 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 f undus. Its average thickness is about -fa of
an inch (1 mm.). In the pylorus its thickness is -fa to T^ of an inch (1*6 to
2*1 mm.), and in the fundus, ^5- to fa of an inch (O5 to 0*7 mm.).

The musculaT fibres exist in the stomach in two principal layers ; an ex-
ternal longitudinal 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 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 with the organ everted and the mucous membrane care-
fully removed. The circular layer is not very distinct to the left of the car-
diac opening, over the great pouch. Toward the pylorus, the layers of fibres
are thicker, 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
the 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

10

FIG. 57.— Longitudinal fibres of the stomach (Sappey).

1, lesser curvature ; 2, 2, greater curvature : 3, greater pouch ; 4. lesser pouch ; 5, 6, 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 longitudinal fibres over the anterior surface of the
stomach ; 11, circular fibres seen through the thin layer of longitudinal fibres.

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

PHYSIOLOGICAL ANATOMY OF THE STOMACH.

213

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. At about the line where the oblique layer of fibres ceases
the stomach becomes constricted during the movements which are incident
to digestion, dividing the organ into tolerably distinct compartments.

The blood-vessels of the muscular coat are quite abundant and are arranged
in a peculiar, rectangular net-work, which they always present in the non-

Fio. 58.— Fibres seen with the stomach everted (Sappey).

1, 1, oesophagus ; 2, circular fibres at the oesophageal opening ; 3, 3, circular fibres at the lesser curva-
ture ; 4, 4, circular fibres at the pylorus ; 5, 5, 6, 7, 8, oblique fibres ; 9, 10, fibres of this layer cover-
ing the greater pouch ; 11, portion of the stomach from which these fibres have been removed to
show the subjacent circular fibres.

striated muscular tissue. The nerves come from the pneumogastrics and the
sympathetic system and are demonstrated with difficulty.

Mucous Coat. — The mucous mem-
brane of the stomach is soft and vel-
vety in appearance and of a reddish-
gray color. It is loosely attached to
the submucous muscular tissue and is
thrown into large, longitudinal folds,
which become effaced as the organ is
distended. If the mucous membrane
be stretched or if the stomach be
everted and distended and the mucus
be gently removed under a stream of
water, the membrane will be found
marked with polygonal pits or de-
pressions, enclosed by ridges, which, FIG. 59.-Pits in the mucous membrane of the
J stomach, and orifices of the glands ; magnified

in some parts of the organ, are quite 20 diameters (Sappey).

T m, i Xi.1. 1, 1, 1, 2, 2, 2, 3, pits of different sizes ; 4, 5, orifices

regular. These are best seen with ' of the gastric glands.

214 GASTRIC DIGESTION.

the aid of a simple lens, as many of them are quite small. The diameter of
the pits is very variable, but the average is about ^-J-g- of an inch (0-125 mm.).
This appearance is not distinct toward the pylorus ; the membrane here pre-
senting irregular, conical projections and well marked villi resembling those
found in the small intestine. The surface of the mucous membrane is cov-
ered with columnar or prismoidal epithelium, the cells being tolerably regular
in shape, each with a clear nucleus and a distinct nucleolus. According to
Landois, these cells, which he calls " mucus-secreting gob-
let-cells," have a clear portion occupying their outer half,
which is open and discharges a viscid secretion.

The thickness of the mucous membrane of the stom-
ach varies in different parts. Usually it is thinnest near
the oesophagus and thickest near the pylorus. Its thin-
nest portion measures T*g- to -jfo of an inch (0*34 to O5
FIG. w.-Gobtet- ceils mnL) 5 its thickest portion, -^ to TV of an inch (1-6 to
2'1 mm.), and the intermediate portion, about -fa of an
inch (1 mm.).

Glands of the Stomach. — Extending from the bottoms of the pits in the
mucous membrane of the stomach to the submucous connective tissue, are
large numbers of glands. These generally are arranged in tolerably dis-
tinct groups, surrounded 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 differences in the anatomy of the glands
in different parts of the stomach, which are supposed to correspond with
differences in the uses of various parts of the mucous membrane. There are,
indeed, two distinct varieties of glands; the peptic glands, which secrete
pepsine, or an organic substance that is readily changed into pepsine, and the
acid-glands, which are supposed to secrete free hydrochloric acid. The pep-
tic glands are most abundant in the pyloric portion of the stomach and
around the cardiac opening. The so-called acid-glands are found through-
out the mucous membrane, especially in the greater pouch. The secretion
in the pyloric portion of the stomach is not acid at any time, while the se-
cretion in the greater pouch, during digestion, is always strongly acid. The
difference in the action of these two kinds of glands is supposed to depend
upon differences in the secreting cells.

The pyloric glands are lined by cells which may be called peptic cells (the
chief-cells of German writers), conoidal or cuboidal in form, and relatively
clear, especially during the intervals of digestion. Similar cells are found, in
connection with the so-called acid-cells (parietal cells) in the secreting por-
tion of the glands of the greater pouch.

The acid-glands are found throughout the stomach, except near the pylo-
rus. The secreting portion of these glands contains peptic cells, but near
the tubular membrane are rounded cells, larger than the peptic cells, darker
and more granular, which are the acid, or parietal cells. These are strongly
stained when treated with osmic acid (Nussbaum). It is probable that the
so-called acid-glands secrete pepsine as well as an acid, while the pyloric

PHYSIOLOGICAL ANATOMY OF THE STOMACH.

215

glands secrete pepsine but no acid. According to the views just stated, in
the glands of the greater pouch, the acid is secreted by the rounded acid-cells
while the pepsine is secreted by cells (peptic cells) similar to those which line
the secreting portion of the pyloric glands. During the intervals of diges-
tion, pepsine is in process of formation by the peptic cells, and no acid is
produced ; but acid begins to be secreted soon after food is received into the
stomach. It is now thought that the peptic cells do not produce pepsine
directly, but a substance sometimes called zymogen, but more properly pro-
pepsine or pepsinogen, which is changed into true pepsine by the action of
hydrochloric acid.

There is some confusion among writers with regard to the names of the
different kinds of secreting cells of the stomach, the acid -cells being fre-
quently described as " peptic cells." It seems proper, however, to call the

FIG. 61. — Glands of the greater pouch of
the stomach (Heidenhain).

FIG. 62.— Pyloric glands (Ebstein).

cells which produce pepsine, peptic cells, and the cells that are supposed to
produce acid, acid-cells.

The glands of the stomach have an excretory portion and a secreting
portion, the latter presenting several branches. The excretory portion is
lined by cells like those found on the surface of the mucous membrane.

216

GASTEIC DIGESTION.

The secreting portion is lined by the peptic and the acid-cells already
described. In Fig. 61 the darker cells are the acid-cells, and the lighter
cells, the peptic cells. In Fig. 62 the secreting portion contains peptic cells
only.

Closed Follicles. — In the substance of the mucous membrane, between the
tubes and near their cascal extremities, are occasionally found closed follicles,
like the solitary glands 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 curvature, though they may be
found in other situations. In their anatomy they are identical with the closed
follicles of the intestines, and they do not demand special consideration in
this connection.

.Gastric Juice. — The observations of Beaumont upon Alexis St. Martin,
the Canadian who had a large fistulous opening into the stomach, gave the
first definite knowledge of the most important of the physiological properties
of the gastric juice. St. Martin, .the subject of these observations, received a
gunshot wound in the left side, at the age of eighteen years, being at the time
of good constitution and in perfect health. He slowly recovered from the
injury, and after three years, having regained his health, was made the sub-
ject of a great number and variety of experiments. Although the general
health had been restored, there remained a perforation into the stomach,
irregularly circular in form and nearly an inch (2-5 centimetres) in diameter.

This opening was closed
by a protrusion of the
mucous membrane in the
form of a valve, which
could readily be de-
pressed by the finger so
as to expose the interior
of the stomach.

From May, 1825, un-
til August of the same
year, St. Martin was un-
der the observation of
Beaumont. At the end
of that time he was lost
sight of for four years.
He then came again un-
der the observation of
Beaumont and continued

opening into the stomach ; c, left nipple ; . . . ...

D, chest ; E, cicatrices from the wound made for the removal of in hlS SCl'VlCe, doing the
a piece of cartilage ; F, F, F, cicatrices of the original wound. , _ . .,

work oi a servant, until

March, 1831. After this he was under observation from time to time until
1836, always enjoying perfect health, with good digestion. The last pub-
lished observations made upon this case were in 1856.

•The following was the method employed by Beaumont in extracting the

FIG. 63. — Gastric fistula in the case of St. Martin (Beaumont).
A, A, B, borders of the opening into the stomach ; c, left nipple

GASTEIC JUICE.

217

gastric juice : The subject was placed on the right side in the recumbent
posture, the valve was depressed 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
to six inches (12 to 15 centimetres). 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.

Since the publication of Beaumont's experiments, many observations
have been made upon animals in which a permanent gastric fistula had been
established. In these experiments the dog is most frequently used, as in this
animal the operation usually is successful. The animals operated upon by
Basso w, who was the first to establish a gastric fistula (1842), were merely
objects of curiosity ; but Blondlot (1843) and others fixed a tube in the
stomach, collected the juice and made important observations with regard to
its action in digestion. Most experimenters follow the method employed by
Blondlot and Bernard, making the opening in the abdomen in the median
line, a little below the ensiform cartilage.

Having established a permanent fisfula into the stomach, after the wound
has cicatrized around the canula, the animal suffers no inconvenience and
may serve indefinitely for experiments on the
gastric juice. In some experiments, the flow of
gastric juice has been excited by the introduc-
tion into the stomach, of pieces of tendon or
hard, indigestible articles, on the ground that
the fluid taken from the fistula, under these con-
ditions, is unmixed with the products of gastric
digestion ; but it has been shown that the
quantity and character of the secretion are in-
fluenced by the nature of the stimulus, and it is
proper, therefore, to excite the action of the
stomach by articles 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 some-
what hardened. The cork is then removed from
the tube, which is freed from mucus etc., when
the gastric juice will begin to flow, sometimes
immediately and sometimes in four or five min-
utes 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 diges-
tion. At the end of this time it is generally accompanied with grumous
matter, and the experiment should be concluded if it be desired simply to
obtain the pure secretion. In fifteen minutes, two to three ounces (60 to
90 c.c.) of fluid may be obtained from a good-sized dog, which, when filtered,
is perfectly clear ; and this operation may be repeated three or four times a

FIG. 64.— Dog with a gastric fistula
(Beclard).

218 GASTEIC DIGESTION.

week without interfering with the character of the secretion or injuring the
health of the animal.

Although instances of gastric fistula in the human subject had been re-
ported before the case of St. Martin and have been observed since that time,
the remarkably healthy condition of the subject and the extended experi-
ments of Beaumont have rendered this case memorable in the history of
physiology. This is the only instance on record,, in which pure, normal gas-
tric juice has been obtained from the human subject ; and it has served as
the standard for comparison for subsequent experiments on the inferior
animals.

Artificial gastric juice, prepared by extracting the active principle from
the mucous membrane of the stomach of different animals and adding hydro-
chloric acid, is useful in observations with regard to the chemistry of the
peculiar ferment, but fluids prepared in this way are not absolutely identical
with the natural secretion. Extracts of the mucous membrane were made
by Eberle (1834), Von Wittich, Briicke and many others.

Secretion of the Gastric Juice. — According to Beaumont, during the in-
tervals of digestion, the mucous membrane is comparatively pale, " and is
constantly covered with a very thin, transparent, viscid mucus, lining the
whole interior of the organ." On the application of any irritation, or better,
on the introduction of food, the membrane changes its appearance. It
becomes red and turgid with blood ; small pellucid points begin to appear
in various parts, which are drops of gastric juice ; and these gradually in-
crease 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 secretion generally is abnormal. It is but slightly acid and
does not possess the characteristic properties 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 degluti-
tion. The stimulation of the mucous membrane is then general, and secre-
tion 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 compara-
tively 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.

GASTRIC JUICE. 219

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 into the stomach of a dog by a fistula, pro-
duced 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
the saliva and passed it in by the fistula, when the same difference was
observed. In some animals, particularly when they are very hungry, the
sight and odor of food will excite secretion of gastric juice.

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, vitiate, diminish and sometimes entirely suppress secretion by the stom-
ach. At some times, under these conditions, the mucous membrane becomes
red and dry, and at others it is pale and moist. In the morbid conditions,
drinks are immediately absorbed, but food remains undigested in the stomach
for twenty-four to forty-eight hours (Beaumont).

After the food has been in part liquefied and absorbed and in part reduced
to a pultaceous consistence, the secretion of gastric juice ceases ; the move-
ments 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 in-
testines out at the pylorus. The stomach is thus entirely emptied, the mucous
membrane becomes pale, and its reaction loses its marked, acid character,
becoming neutral or faintly alkaline.

Quantity of Gastric Juice. — The data for determining the quantity of
gastric juice secreted in the twenty-four hours are so uncertain that it seems
impossible to fix upon any estimate that can be accepted even as an approxi-
mation. Still, the quantity must be considerable, in view of the large quan-
tity of alimentary matter which is acted upon in gastric digestion. It is
probably not less than six pounds (2- 72 kilos.) or more than fourteen pounds
(6-35 kilos.). After this fluid has performed its office in digestion, it is im-
mediately reabsorbed, and but a small quantity of the secretion exists in the
stomach at any one time.

Properties and Composition of 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 inter-
vals of digestion as well as when the stomach is active. By adopting certain
precautions, however, the fluid may be obtained nearly free from impurities,
except the admixture 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 normal gastric juice.

The specific gravity of the gastric juice in the case of St. Martin, accord-

220 GASTRIC DIGESTION.

ing to the observations of Beaumont and Silliman, was 1005 ; but later, 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 nor-
mal, and 1005 to 1009 may be taken as the range of the specific gravity of the
gastric juice in the human subject.

The gastric juice is described by Beaumont as inodorous, when taken
directly from the stomach ; but it has rather an aromatic and a not disagree-
able odor when it has been kept for some time. It is a little saltish, and its
taste is similar to that of " thin, mucilaginous water slightly acidulated with
muriatic acid."

It has been found by Beaumont, in the human subject, and by those who
have experimented 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 period. The only change which it undergoes is
the formation of a pellicle, consisting of a vegetable, confervoid growth, upon
the surface, some of which breaks up and falls to the bottom of the vessel,
forming a whitish, flocculent sediment. In addition to this remarkable fac-
ulty of resisting putrefaction, putrefactive changes are arrested in decompos-
ing 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 se-
cretion 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 more than 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 pepsine, and
various inorganic salts.

The following analysis by Bidder and Schmidt gives the mean of nine
observations upon dogs :

COMPOSITION OF THE GASTRIC JUICE OF THE DOG (BIDDER AND SCHMIDT).

Water 973-062

Ferment (pepsine) 17-127

Free hydrochloric acid 3'050

Potassium chloride 1*125

Sodium chloride 2-507

Calcium chloride 0-624

Ammonium chloride 0*468

Calcium phosphate 1-729

Magnesium phosphate 0-226

Ferric phosphate 0-082

1,000-000

In another series of three observations, in which the saliva was allowed to
pass into the stomach, the proportion of free acid was 2-337, and the propor-
tion of organic matter was somewhat increased.

GASTRIC JUICE. 221

Organic Constituent of the Gastric Juice. — Pepsine is an organic nitro-
genized substance, which is peculiar to the gastric juice and 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 Blondlot, an organic matter was spoken of as one of its constituents.

Experiments on artificial digestive fluids, by Eberle, Schwann and Miil-
ler, Wasmann and others, have demonstrated that acidulated extracts of the
mucous membrane of the stomach 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, described 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 insoluble in absolute alcohol. A
solution of it is rendered somewhat turbid by a temperature of 212° Fahr.
(100° 0.), but it is not coagulated, although it loses its digestive properties.
It is not affected by acids but is precipitated by tannin, creosote and a great
number of metallic salts. This substance dissolved in water slightly acidu-
lated possesses, in a very marked degree, the solvent properties of the gastric
juice ; but it has been found by Payen and Mialhe not to be so active as the
substance 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, between six and
ten pints (2 -8 and 4-7 litres) of gastric juice ; and from this he extracted the
pure pepsine by the process recommended by Payen, which consists merely in
one or two precipitations by alcohol. This substance he found to be identical
with the substance obtained by Payen from the gastric juice of the dog. Its
action upon albuminoid matters was precisely the same as that of pepsine
extracted from artificial gastric juice, except that it was more powerful.

Free Acid of the Gastric Juice.. — The character of the free acid of the
gastric juice has long been a question of uncertainty and dispute. In former
editions of this work, the different views of chemists with regard to the nature
of this acid were fully discussed. It may now be stated that almost all physi-
ologists adopt the view that the gastric juice contains free hydrochloric acid,
with possibly a very small quantity of lactic acid. It is admitted, however,
that the degree of acidity of the gastric juice is variable, and that the normal
acid may be replaced, without loss of the digestive properties of the fluid, by
lactic, oxalic, acetic, formic, succinic, tartaric, citric, phosphoric, nitric or
sulphuric acid.

Saline Constituents of the Gastric Juice. — It has been shown that
artificial fluids containing the organic matter 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.
16

222 GASTRIC DIGESTION.

Boudault and Oorvisart evaporated 6-76 oz. (200 c. c.) of the gastric juice of
the dog to dryness and added to the residue, 1-69 oz. (50 c. c.) of water. They
found that the fluid thus prepared, containing four times the normal propor-
tion of saline constituents, 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 saline constituents of the gas-
tric juice, except sodium chloride, Avhich is thought to be concerned in the
production of hydrochloric acid.

Action of the Gastric Juice in Digestion. — Certain of the substances most
readily attacked by the gastric juice are acted upon by weak, acid solutions
containing no organic matter ; but it is now well established that the presence
of a peculiar organic matter is a condition indispensable to actual diges-
tion. It has also been shown that fluids containing the organic constituent
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 substances are dissolved by them it is simply
accidental.

The presence of any one particular acid does not seem essential to the
digestive properties of the gastric juice, so long as the proper degree of acidity
is preserved, and it is undoubtedly important that the normal acid can be re-
placed by other acids ; for in case any salt were introduced into the stomach
which would be decomposed by the 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 disturbances might occur from this
cause, were the existence of any one acid indispensable to the digestive prop-
erties of the gastric juice ; while if only a certain degree of acidity were re-
quired, this condition might be produced by any acid, either derived from the
food or secreted by the stomach.

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 ensemble, rather than as a process consisting
of several successive and distinct operations, in which different classes of ali-
mentary matters 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.

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, contain-
ing the muscular substance enveloped in its sarcolemma, blood-vessels, nerves,
ordinary fibrous tissue holding the muscular fibres together, interstitial fat,
and a small quantity of albuminoids and corpuscles from the blood, all com-
bined with a considerable quantity of inorganic salts ; albumin, sometimes
unchanged, but generally in a more or less perfectly coagulated condition ;

ACTION OF THE GASTRIC JUICE. 223

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
matters, in cheese ; vegetable nitrogenized matters, of which gluten may be
taken as the type ; vegetable fats and oils ; sugars, both from the animal and
vegetable kingdoms, but chiefly from vegetables ; the different varieties of
amylaceous substances ; and finally, organic acids and salts, derived chiefly
from vegetables. These matters, particularly those from the vegetable king-
dom, are united with more or less innutritions matter, such as cellulose.
They are also seasoned with aromatic substances, condiments etc., which are
not directly used in nutrition.

The various articles described as drinks are taken without any consid-
erable admixture with the saliva. They embrace water and the various
nutritious or stimulant infusions (including alcoholic beverages) with a small
proportion of inorganic salts in solution.

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 prop-
erly prepared acidulated extracts of the mucous membrane of the stomach,
which have been shown to have many of the properties of the gastric juice,
differing mainly 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 complete. The parts of the muscular structure most easily attacked
are the fibrous tissue which holds the muscular fibres together, and the sar-
colemma, 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 about 100° Fahr. (37*78° C.), agitating the
vessel occasionally so as to subject, as far as possible, every particle of the
tmeat 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 cer-
tain 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 ordinary fibrous tissue ; and the fibres of muscular tissue,
although presenting the well marked and characteristic striae, are broken into
short pieces and possess very little tenacity. It 'is evidently only the muscu-
lar substance which remains ; the connective tissue and the sarcolemma hav-
ing been dissolved. These facts have been repeatedly noted, and even on
adding fresh juice to the undigested matter, it is not dissolved to any con-
siderable extent, the residue not being sensibly diminished in quantity, and

224:

GASTEIC DIGESTION.

the muscular substance always presenting its characteristic striae, on micro-
scopical examination. Bernard, in experiments with the gastric juice of
different animals, found the fluid from the stomach of the rabbit or the horse
° g much inferior, as re-

• ^ji"'-i'Vi" / gards the activity of its

^w?»*-jV-'«. *£.•*•.. action upon meat, to

FIG. 65.— Matters taken from the pyloric portion of the stomach of a
dog during digestion of mixed food (Bernard).

a, disintegrated muscular fibres, the striae having disappeared ; 6, c,
muscular fibres in which the striae have partly disappeared ; d, eZ, d,
globules of fat ; e, e, e, starch ; g, molecular granul

Whether the gas-
tric juice be entirely
incapable of acting
upon the muscular
substance or not, the
above-mentioned facts
clearly show that mus-
cular tissue usually is
not completely digest-
ed in the stomach.
The action in this or-
gan is to dissolve the
intermuscular fibrous
tissue and the sarco-
lemma, or sheath of
the muscular fibres,
setting the true muscular substance free and breaking it up into small par-
ticles. The mass of tissue is thus reduced to the condition of a thin, pulta-
ceous fluid, which passes into the small intestine, where the process of diges-
tion is completed.

The constituents of the blood, albuminoids, corpuscles etc., which may
be introduced in small quantity in connection with muscular tissue, probably
are completely dissolved in the stomach.

Action upon Albumin, Fibrin, Caseine and Gelatine. — 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 albumin
is contained. It also acts upon the albumin itself, forming a new fluid sub-
stance, called albumin-peptone, which, unlike albumin, 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 albumin
takes place with considerable rapidity in the stomach ; and the digestion of
albumin in this form is more rapid than when it has been completely coagu-
lated by heat. It is a matter of common as well as of scientific observation,
that eggs when hard-boiled are less easily digested than when they are soft-
boiled or uncooked. The products of the digestion of raw or of coagulated
albumin, albumin-peptone, are essentially the same. It is probable that the
entire process of digestion and absorption of albumin takes place in the
stomach ; and if any albumin pass out of the pylorus, the quantity is very small.

ACTION OF THE GASTRIC JUICE.

Fibrin, as distinguished from the so-called fibrin of the muscular tissue,
or myosine, is not a very important article of food. The action of the gas-
tric juice upon it is more rapid and complete than upon albumin. 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 con-
stituent in the gastric juice necessary to the digestion of this substance;
but 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 nitrogen-
ized alimentary substances. The action of water containing a small propor-
tion of acid is to render fibrin soft and transparent, frequently 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 pepsine 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 fibrin-peptone, resembles albumin-
peptone, but nevertheless has certain distinctive characters.

Liquid caseine is immediately coagulated by the gastric juice, by the
action 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. The caseine of human
milk, which coagulates only into a sort of jelly, is more easily digested than
caseine. from cow's milk (Eliisser). The product of the digestion of caseine
is a soluble substance, not coagulable by heat or the acids, called caseine-
peptone.

Gelatine is rapidly dissolved in the gastric juice, when it loses the char-
acters 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 products of its digestion in the gastric
juice resemble the substances resulting from the digestion of the albumi-
noids generally.

Action on Vegetable Nitrogenized Substances. — These substances, of which
gluten may be taken as the type, undoubtedly are digested chiefly in the
stomach. Raw gluten is acted upon very much in the same way as fibrin,
and cooked gluten behaves like coagulated albumin. Vegetable articles of
food generally contain gluten in greater or less quantity, or substances resem-
bling it, as well as various non-nitrogenized matters, and cellulose. The fact
that these articles are not easily attacked in any portion 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 faeces. When properly pre-
pared by mastication and insalivation, the action of the gastric juice is to
disintegrate them, dissolving out the nitrogenized matters, freeing the starch
and other matters so that they may be more easily acted upon in the intes-
tines, and leaving the hard, indigestible matters, such as cellulose, to pass

226 GASTRIC DIGESTION.

away in the faeces. The iiitrogenized constituents of bread are probably acted
upon in the stomach in the same way and to the same extent as albumen,
fibrin and caseine.

Peptones. — It has been shown that gastric digestion is not merely a solu-
tion of certain alimentary matters, but that these substances undergo very
marked changes and lose the properties by which they are generally recog-
nized. That the different products of this transformation resemble each
other very closely is also undoubted ; but there are certain differences in the
chemical composition of the products of digestion of the different constitu-
ents of food, as well as differences, which have lately been noted, as regards
their behavior with reagents.

The peptones in solution form colorless liquids, having a feeble odor re-
sembling that of meat. They are not coagulable by heat or by most acids, a
property which distinguishes them from almost all of the nitrogenized con-
stituents of food. They are coagulated, however, by many of the metallic
salts, by chlorine, and by tannin, in slightly acidulated solutions. On evapo-
rating peptones 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 is entirely insoluble in alcohol.

It is evident that the gastric juice, aside from its action in preparing cer-
tain articles for digestion by the intestinal fluids, does not simply liquefy
certain of the alimentary matters, but changes them in such a way as to ren-
der them osmotic and provides against the coagulation which is so readily
induced in ordinary nitrogenized bodies. Peptones pass through membranes
with great facility.

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. Pure albumin
and gelatine, when injected into the blood, are not assimilable and are
rejected by the kidneys ; but albumin and gelatine which have been digested
in gastric juice are assimilated in the same way as though they had pene-
trated by the natural process of absorption from the alimentary canal (Ber-
nard and Barreswil). The same is true of caseine and fibrin. These facts,
showing that something more is necessary in gastric digestion than mere
solution, point to pepsine as the important agent in producing the peculiar
modifications so necessary to proper assimilation of nitrogenized alimentary
substances. The action of pepsine is essential to the changes which occur in
the albuminoid alimentary matters, resulting in the formation of what are
known as peptones ; and the change into peptones takes place in all nitro-
genized substances that are dissolved in the stomach. This may occur even
when the albuminoid matters are somewhat advanced in putrefaction ; and
the gastric juice possesses antiseptic properties, which fact accounts for the
frequent innocuousness of animal substances in various stages of decomposi-
tion when taken into the stomach.

The change of the albuminoids into peptones in the stomach is not direct.
The intermediate processes probably are the following : The albuminoids are

ACTION OF THE GASTRIC JUICE. 227

first changed by the gastric juice into an acid-albumin or albuminate ; this is
farther changed into propeptone, or as it is called by Kuhne, hemialbumose ;
and the final action is a change into the true peptones. These intermediate
processes have been studied in artificial digestion, and the acid-albumin and
propeptone differ, in some of their chemical properties which it is not neces-
sary to describe in detail, from both albumin and peptone. A temperature
near that of the body is necessary to the various changes just mentioned.

Action of the Gastric Juice on Fats, Sugars and Amylaceous Substances.
—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 vesicles in
which the fatty matters are contained are dissolved, the fat is set free, is
melted and floats in the form of drops of oil on the alimentary mass. The
action of the stomach, then, seems to be to prepare the fats, chiefly by dis-
solving the adipose vesicles, for the complete digestion which takes place in
the small intestine.

The varieties of sugar of which glucose is the type undergo little if any
change in digestion and are probably in greatest 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 sys-
tem 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 gas-
tric juice, it no longer behaves as a foreign substance and does not appear in
the urine. Experiments have shown that cane-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 a dilute mixture of hydrochloric acid had an equally marked
effect. Experiments in artificial 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 pro-
cess of digestion, this action may take place to a certain extent ; but it is not
shown to be constant or important.

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 vegetable 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 stoniach, 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.

Cooked or hydrated starch, the form in which it exists in bread, fari-
naceous preparations 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 entirely prevent a con-
tinuance of the action of the saliva ; and experiments have shown that gastric

228 GASTRIC DIGESTION.

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.

The changes which vegetable acids and salts, the various inorganic con-
stituents of food and the liquids which are classed as drinks undergo in the
stomach are very slight. Most of these substances can hardly be said to be
digested ; for they are either liquid or in solution in water and are capable
of direct absorption and assimilation. 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 substances. In the latter case, they
become intimately combined with the organic matters resulting from gastric
digestion. It has been noted that the various peptones contain the same
inorganic salts which existed in the nitrogenized substances from which they
were formed.

Some discussion has arisen with regard to the action of the fluids of the
stomach upon calcium phosphate and calcium carbonate, salts which are con-
sidered nearly if not entirely insoluble. Observations on 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 faeces. In the nat-
ural process of digestion, the solution of the calcareous constituents of bone
is more rapid than in artificial digestion, from the fact that the juice is being
continually absorbed and secreted anew by the mucous membrane of the
stomach.

Duration of Gastric Digestion. — Inasmuch as comparatively few articles,
and these belonging exclusively to the class of organic nitrogenized sub-
stances, 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 represent the
absolute digestibility of different articles. It is, nevertheless, an impor-
tant question to ascertain, as nearly as possible, the duration of gastric diges-
tion.

There has certainly never been presented so favorable an opportunity for
determining the duration of gastric 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 conclusion 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 observations of F. G. Smith, made
upon St. Martin many years later, gave two hours as the longest time that
aliments remained in the stomach. In a case of intestinal fistula reported
by Busch, 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 gastric digestion varies in different individ-
uals and is greatly dependent upon the kind and quantity of food taken, con-
ditions of the nervous system, exercise etc. As a mere approximation, the

ACTION OF THE GASTRIC JUICE. 229

average time that food remains in the stomach after an ordinary meal may
be stated to be between two and four hours.

Milk is one of the articles digested in the stomach with greatest ease.
Its highly nutritive properties and the variety of its nutritious constituents
render it very valuable as an article of diet, particularly when the digest-
ive 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 eggs. " 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, venison, lamb, beef and mut-
ton are easily digested, while veal and fat roast-pork are digested with diffi-
culty. Soups are generally very easily digested. The animal substances
which are digested most rapidly, however, are tripe, pigs' feet and brains.
Vegetable articles are 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 diges-
tion of the ordinary meats (Beaumont).

Conditions which influence Gastric Digestion. — The various conditions
which influence gastric 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 that temperature has
any influence, for the temperature of the stomach in health does not present
variations sufficient to have any marked effect upon digestion.

As a rule, gentle exercise, with repose or agreeable and tranquil occupa-
tion, of the mind, is more favorable to digestion than absolute rest. Violent
exercise or severe mental or physical exertion is always undesirable immedi-
ately after the ingestion of a large quantity of food, and as a matter of com-
mon experience, has been found to retard digestion.

The effects of sudden and considerable loss of blood upon gastric di-
gestion are very marked. After a full meal, the whole alimentary tract
is deeply congested, and this condition is undoubtedly necessary to the
secretion, in proper quantity, of the various digestive fluids. When the
entire quantity of blood in the economy is greatly diminished from any
cause, there is difficulty in supplying the amount of gastric juice neces-
sary for a full meal, and disorders of digestion are likely to occur, es-
pecially 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 con-
dition, although the system constantly craves nourishment and the ap-
petite frequently is 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 ordinarily in old age digestion is carried on with more vigor

230 GASTRIC DIGESTION.

and regularity than the other vegetative processes, such as general assimila-
tion, circulation and respiration.

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 pneumogastric has been the
more carefully studied, experiments upon the sympathetic being more diffi-
cult. Although the complete history of the influence of the pneumogastrics
upon digestion belongs to the physiology of the nervous system, it will be
useful 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.

The experiments of Bernard and others have shown that the vascular
mechanism of the mucous membrane is to a great extent under the influence
of the pneumogastrics. If these nerves be divided while gastric digestion is at
its height, the mucous membrane immediately becomes pale, and the secre-
tion of gastric juice is nearly if not quite arrested. It has been found, how-
ever, that gastric juice may be secreted in small quantity under the stimulus
of food, even when both pneumogastrics and the sympathetic nerves going
to the stomach have been divided (Heidenhain).

Section of both pneumogastrics, while it does not entirely paralyze the
muscular coat of the stomach, renders its contractions irregular and feeble.
It is stated that section of these nerves is followed by " a short temporary
contraction of the cardiac aperture " (Stirling).

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 longitu-
dinal folds. As the organ is distended, these folds are effaced, the stomach
itself becoming more rounded, and as the two ends, with the lesser curva-
ture 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 hypo-
chondriac region ; the greater curvature presents anteriorly and comes in con-
tact with the abdominal walls. Aside from these changes, which are merely
due to the distention, the stomach undergoes 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. By the rhythmical contractions of the
lower extremity of the oesophagus, 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 indefinitely, for indigestible articles

MOVEMENTS OF THE STOMACH. 231

of considerable size, such as stones, have been passed by the anus after having
been introduced into the stomach ; but observations have 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 more or less disintegrated.

The contractions oi the walls of the stomach are of the kind character-
istic 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
of the organ. The movements during digestion present certain differences
in different, animals ; but there can be no doubt that the phenomenon is
universal. 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 Bowman, 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 intestines, for which, in-
deed, they were mistaken, as the nature of the case was not recognized during
life. No argument, therefore, seems necessary to show that during digestion,
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 the 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 contraction above mentioned, the movements are more frequent,
vigorous and expulsive.

As the result chiefly of the observations of Beaumont, the following may
be stated as a summary 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 mem-
brane becomes congested and the secretion of gastric juice begins, contrac-
tions of the muscular coat occur, which are at first slow and irregular, but
become more vigorous and regular as the process of digestion 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
pyloric division, they are intermittent and more expulsive. The effect of the

233 GASTRIC DIGESTION.

contractions of the stomach upon the food contained in its cavity is to sub-
ject it to a tolerably uniform pressure in the cardiac portion, the general
tendency of the movement being toward the pylorus, along the 'greater curva-
ture, 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 obstruction to the passage oi the food until it has
been sufficiently acted upon by the secretions in the cardiac division to have
become reduced to a pultaceous consistence. The alimentary 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.

The revolutions of the alimentary mass, thus accomplished, take place
slowly, by gentle and persistent contractions of the muscular coat ; the food
occupying two or 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 ab-
sorption of digested matter by the stomach itself, but chiefly by the gradual
passage of the softened and disintegrated mass into the small intestine. This
process continues until the stomach is emptied, lasting between two and four
hours ; after which, the movements of the stomach cease until food is again
introduced.

Regurgitation of food by contractions of the muscular coats of the stom-
ach, eructation, or the expulsion of gas, and vomiting are not physiological
acts. It has been shown that vomiting is produced by contractions of the
abdominal muscles and the diaphragm, compressing the stomach, which is
passive, except that the pyloric opening is firmly closed, the cardiac opening
being relaxed. Eructation, although usually involuntary, is sometimes 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 frequently becomes a habit, which in many persons
is so developed by practice that the act may be performed voluntarily at any
time. The gaseous contents of the stomach during digestion are composed
of oxygen, carbon dioxide, hydrogen and nitrogen, in proportions that are
very variable.

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 233
CHAPTER IX.

INTESTINAL DIGESTION.

Physiological anatomy of the small intestine— Glands of Brunner— Intestinal tubules, or follicles of Lieber-
kuhn— Intestinal villi— Solitary glands, or follicles, and patches of Peyer— Intestinal juice— Action of
the intestinal juice in digestion — Pancreatic juice — Action of the pancreatic juice upon starches and
sugars— Action upon nitrogenized substances— Action upon fats— Action of the bile in digestion— Bil-
iary fistula— Variations in the flow of bile— Movements of the small intestine— Peristaltic and antiperi-
Ptaltic movements— Uses of the gases in the small intestine— Physiological anatomy of the large intes-
tine—Processes of fermentation in the intestinal canal— Contents of the large intestine— Composition of
the fseces— Excretine and excretoleic acid — Stercorinc — Indol, skatol, phenol etc. — Movements of the
large intestine— Defsecation— Gases found in the alimentary canal.

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE.

THE small intestine, extending from the pyloric extremity of the stomach
to the ileo-caecal valve, is loosely held to the spinal column by a double fold of
serous membrane, called the mesentery. 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, it divides 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 three to four inches (7'62 to 10-16 centi-
metres) ; but at the beginning and at 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 it allows a certain degree 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,
according to Gray, is about twenty feet (6-1 metres) ; but the canal is very
distensible, and its dimensions are subject to frequent variations. Its average
diameter is about an inch and a quarter (3-18 centimetres).

The small intestine has been divided into three portions, which present
anatomical and physiological peculiarities, more or less marked. These are
the duodenum, the jejunum 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 eight to ten inches (20-32 to 25-4
centimetres). This portion of the intestine is considerably wider than the
constricted pyloric end of the stomach, with which it is continuous, and is
also much wider than the jejunum.

The coats of the duodenum, like those of the other divisions of the
intestinal tube, are three in number. The external is the serous, or peri-
toneal coat, which has already been described. The middle, or muscular
coat is composed of non-striated 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 out easily only at the outer portions
of the tube, opposite the attachment of the mesentery. Near the mesenteric
border the outlines of the fibres are very faint. This is true throughout the

234

INTESTINAL DIGESTION.

whole of the small intestine ; although the fibres are most abundant in the
duodenum. The internal layer of fibres is considerably thicker than the

longitudinal layer. These
fibres encircle the tube,
running generally at right
angles to the external layer,
but some of them having
rather an oblique direction.
The circular layer is thick-
est in the duodenum, di-
minishing gradually in
thickness to the middle of
the jejunum, but afterward
maintaining a nearly uni-
form thickness throughout
the canal, to the ileo-csecal
valve.

The jejunum, the sec-
ond division of the small
intestine, is continuous
with the duodenum. It
presents no well marked
line of separation from the
third division, but is gen-
erally considered as in-
cluding the upper two-
fifths of the small intes-
tine, the lower three-fifths
being called the ileum. It
has received the name je-

FIG. 66.— Stomach, liver, small intestine etc. (Sappey).
1, inferior surface of the liver ; 2, round ligament of the liver ; 3,

gall-bladder ; 4, superior surface of the right lobe of the liver ; lunum f rom the fact that

5, diaphragm ; 6, lower portion of the oesophagus ; 7, stomach ; .

8. gastro-hepatic omentum ; 9, spleen ; 10, gastro-splenic omen- it is almost always f OUnd

turn; 11, duodenum; 12, 12, small intestine; 13, ccecum; 14,

appendix vermiformis ; 15, 15, transverse colon ; 16, sigmoid emptv after death.

flexure of the colon ; 17, urinary bladder. __,,

The ileum is some-
what narrower and thinner than the jejunum, otherwise possessing no
marked peculiarities except in its mucous membrane. This division of the
intestine opens into the colon.

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 duodenum and gradually becomes thinner toward the
ileum. It is highly vascular, presenting, like the mucous membrane of the
stomach, a great increase in the quantity of blood during 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 : 1, folds of the membrane, called valvulse
conniventes ; 2, duodenal racemose glands, or glands of Brunner ; 3, intestinal

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 235

tubules, or follicles of Lieberkulm ; 4, intestinal villi ; 5, solitary glands, or
follicles ; 6, agminated glands, or patches of Peyer.

The valvulse 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 mam-
mals, 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. Be-
ginning at about the middle of the duodenum, they extend, with no diminu-
tion in number, throughout the jejunum. In the ileum they progressively
diminish in number, until they are lost at about its lower third. There are
about six hundred of these folds in the first half of the small intestine and
two hundred to two hundred and fifty in the lower half (Sappey). In those
portions of intestine where they are most abundant, they increase the length
of the mucous membrane 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 one-third to one-half of the circumfer-
ence of the tube, although a few may extend entirely around it. The great-
est width of each fold is at its centre, where it measures a quarter to half an
inch (6-4 to 12'7 mm.). From this point 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 valvulae conniventes are such that
they move freely in both directions and may be applied to the inner surface
of the intestine either above or
below their lines of attachment.
It is evident that the food, as it
passes along in obedience to the
peristaltic movements, must, by
insinuating itself beneath the
folds and 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.

Thickly set beneath the mu-
cous 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 Brun-
ner. These are not found in other parts of the intestinal canal. In their
structure they closely resemble the racemose glands of the oesophagus. On

FIG. 67. — Gland of Brunner, from the human subject
(Frey).

236

INTESTINAL DIGESTION.

dissecting the muscular coat from the mucous membrane, they may be seen
with the naked eye, in the areolar tissue, in the form of little, rounded bod-
ies, about one- tenth of an inch (2-5 mm.) in diameter. Examined micro-
scopically, these bodies are found to consist of a large number of rounded
follicles held together by a few fibres of connective tissue. They have blood-
vessels ramifying on their exterior and are lined with glandular epithelium.
They communicate with an excretory duct which penetrates the mucous mem-
brane 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 secre-
tion has never been obtained in quantity sufficient to admit of the determi-
nation of its chemical or physiological properties. Its quantity must be very
small, compared with the secretion produced by the follicles of Lieberkuhn.

The intestinal tubules, or follicles of Lieberkuhn, the most important
glandular structures in the intestinal mucous membrane, are found through-

FIG. 68.— Intestinal tubules ," magnified 100 diameters (Sappey).

A. From the dog. 1, excretory canal ; 2. 2, primary branches ; 3, 3, secondary branches ; 4, 4, terminal

culs-de-sac.

B. From the ox. 1, excretory canal ; 2, principal branch dividing into two ; 3, branch undivided ; 4, 4,

terminal culs-de-sac.

C. From the sheep. 1, trunk ; 2, 2, branches.

D. Single tube, from the pig.

E. From the rabbit and hare. 1, simple gland ; 2, 3, 4, bifid glands ; 5, compound gland from the

duodenum.

out the whole of the small and large intestines. In examining a thin section
of the mucous membrane, these little tubes are seen closely packed together,

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 237

occupying nearly the whole of its structure. Between the tubules, are blood-
vessels, embedded in a dense stroma of fibrous tissue with non-striated mus-
cular fibres. In vertical sections of the mucous membrane, the only situa-
tions where the tubules are not seen are in that portion of the duodenum
occupied by the ducts of the glands of Brunner 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. 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 usually are simple, though sometimes bifurcated, are com-
posed externally of a structureless basement-membrane, and are lined with a
layer of cylindrical epithelium like the cells which cover the villi, the only
difference being that in the tubes the cells are shorter. These cells never
contain fatty granules, even during the digestion 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 constitu-
ent of the intestinal juice. The length of the tubules is equal to the thick-
ness of the mucous membrane and is about ^ of an inch (0-33 mm.). Their
diameter is about ^¥ °t an incn (0'07 mm.). In man they are cylindrical,
terminating in a single, rounded, blind extremity, which frequently is a little
larger than the rest of the tube. These tubules are the chief agents concerned
in the production of the fl,uid known as the intestinal juice.

The intestinal villi, though chiefly concerned in absorption, are most con-
veniently considered in this connection. These exist throughout the whole
of the small intestine, but are not found beyond the ileo-caecal 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 char-
acteristic velvety appearance. They are found on the valvulae conniventes as
well as on the general surface of the mucous membrane. They are most
abundant in the duodenum and jejunum. Sappey estimated, as an average,
about 6,450 fo the square inch (1,000 in a square centimetre) and more than
ten millions (10,125,000) throughout the whole of the small intestine. In
the human subject the villi are flattened cylinders or cones. In the duode-
num, where they resemble somewhat the elevations found in the pyloric por-
tion 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 cylin-
drical form predominates in the lower portion of the intestine. In the jeju-
num they attain their greatest length, measuring here -fa to -fo of an inch
(0-83 to 1-25 mm.) in length by ^ to y^ of an inch (0-36 to 0'21 mm.)
in breadth at their base.

The structure of the villi shows them to be simple elevations of the
mucous membrane, provided with blood-vessels and with lacteals, or intestinal
lymphatics. Externally is found a single layer of long, cylindrical epithelial
17

238

INTESTINAL DIGESTION.

FIG. 69.— Intestinal villus (Ley-
dig).

a, a,'a, epithelial covering ; 6, 6,
capillary net- work ; c, c, longi-
tudinal muscular fibres ; d,
lacteal.

FIG. 70.— Capillary net-work
of an intestinal villus

(Frey).

cells, resting on a structureless basement-membrane. These cells, though
closely adherent to the subjacent 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 diffi-
culty in microscopical prep-
arations. The borders of
the free surfaces of these
cells are thickened and fine-
ly striated, forming, as it
were, a special membrane
covering the villus and ex-
ternal to the cells. Between
the cylindrical cells are a
few of the so-called goblet-
cells similar to those found
on the mucous membrane of
the stomach (see Fig. 60,
page 214).

The substance of the
villus is composed of amor-
phous matter, in which are
embedded nuclei and a few fibres, fibro-plastic cells and non-striated mus-
cular fibres. The blood-vessels are very abundant ; four or five, and some-
times as many as twelve or fifteen arterioles entering at the base, rami-
fying through the substance of the vil-
lus, but not branching or anastomosing
or even diminishing in caliber until, by
a slightly wavy turn or loop, they com-
municate with the venous 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 long axis of the villus.

The muscular fibres of the villi are
longitudinal, forming a thin layer sur-
rounding the villus, about half-way be-
tween the periphery and the centre,
and continuous with the muscular coat
of the intestine.

In the central portion of each villus, is a small lacteal, one of the vessels of
origin of the lacteal system, with an extremely delicate wall composed of
endothelial cells with frequent stomata, or small openings, between their

a, venous trunk ;
trunk,

6, arterial

FlO. 71.— Epithelium of the small intestine of
the rabbit (Funke).

PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 239

borders. This vessel is probably in the form of a single tube, either simple
or presenting a few short, rounded diverticula.

The stomata of the lacteal vessel are thought to communicate with
lymph-spaces or canals in the substance of the villus. Owing to the ex-
cessive tenuity of the walls of the lacteals in the villi, it has been found
impossible to fill these vessels with an artificial injection, although the
lymphatics subjacent to them may be easily distended and studied in this
way.

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.

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 scattered singly in very variable numbers throughout the
small and large intestine, while the agminated glands consist of these folli-
cles collected into patches of different sizes. These patches are generally
found in the ileum. The number of the solitary glands is very variable, and
they are sometimes absent. The patches of Peyer are always situated in
that portion of the intestine opposite the attachment of the mesentery.
They are likewise variable in number and are irregular in size. They usu-
ally are irregularly oval in form, and measure half an inch to an inch and
a half (12-7 to 38'1 mm.), in length by three-fourths of an inch (19-1 mm.)
in breadth. Sometimes they are three to four inches (7*6 to 10-1 centi-
metres) 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 abundant — 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 described by anatomists.
In one of these varieties, the patch is quite prominent, its surface being
slightly raised above the general mucous surface ; in the other, the surface is
smooth, and the patch is distinguished at first with some difficulty. The
more prominent patches are covered with mucous membrane arranged in
folds something like the convolutions on the surface of the brain. The
valvulae conniventes cease 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 frequently overlooked. The
latter are covered with a smooth, thin, and closely adherent mucous mem-
brane. Their follicles are small and abundant. The borders of these patches
are much less strongly marked than in 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
wanting. They are usually in less number than the first variety.

The villi are very large and prominent on the mucous membrane cover-
ing 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 mu-

240

INTESTINAL DIGESTION.

cous membrane, except that they are placed more irregularly and are not so

abundant.

The follicles which form the patches of Peyer are completely closed and

are somewhat pear-shaped, with their pointed projections directed toward

the cavity of the intestine. Just above the fol-
licle, there generally is a small opening in the
mucous membrane, surrounded by a ring of in-
testinal tubules, and leading to a cavity, the base
of which is convex and is formed by the coni-
cal projection of the follicle. The diameter of
the follicles is -fa fo -fa or fa of an inch (0-34 to
1 or 2 mm.) The small follicles generally are
covered by mucous membrane and have no open-
ing leading to them. Each follicle consists of
a rather strong capsule composed of an almost
homogeneous or slightly fibrous membrane, en-
closing a semi-fluid, grayish substance, cells,
blood-vessels and possibly lymphatics. The
semi-fluid matter is of an albuminoid character

The cells *™ TCI7 small> ™unded, and mingled
; s, 3, grooves with small, free nuclei. The blood-vessels have

; 4, 4, fossettes

between some of the folds ; 5, 5, rather a peculiar arrangement. In the nrst place

5, 5, 5, 5, 5, 5, valvulae conniven-

tes ; 6, e, 6, 6. solitary glands ; 7, they are distributed between the lollicles, so as

7, 7, 7. smaller solitary glands ; . , . ,

8, 8, solitary glands upon the vai- to form a rich net-work surrounding each one.

Capillary branches are sent from these vessels

into the interior of the follicle, returning in the form of loops. Lymphatic
vessels have not been distinctly shown within the investing membrane.
They have been demonstrated surrounding the follicles, but it is still doubt-
ful whether they exist in their interior. 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 containing a
milky fluid are never seen within the follicles.
The description of the follicles which com-
pose the patches of Peyer answers, in general
terms, for the solitary glands, except that the
latter are found in both the small and large
intestines.

seen on the surface

between the folds

INTESTINAL JUICE.

»l

Of the three fluids with which the food is

brought in contact in the intestinal canal, FlG-

namely, the bile, the pancreatic juice and the i, i, serous coat of the intestine ; 2, 2 2,

2, serous coat removed to show the
patch ; 3, 3, fibrous coat of the in-
testine ; 4, 4, patch ; 5, 5, 5, 5, 5, 5, 5,

*'

intestinal juice, the last, the secretion of the
mucous membrane of the small intestine, pre-

5, valvulas conniventes.

INTESTINAL JUICE.

sents the greatest difficulties in the investigation of its properties and uses.
If it be admissible to reason from the known mechanism of secretion in other
parts, it is fair to suppose that the normal secretion of the glands in the
mucous membrane of the small intestine can take place only under the
stimulus of food. The same cause excites the secretion of the pancreatic
juice and increases the flow of bile ; and the food, as it passes from the
stomach into the duodenum, is to a great extent disintegrated and is min-
gled with the secretions from both the mouth and the stomach. Under these
circumstances, it is evidently impossible to collect the intestinal juice under
perfectly physiological conditions, in a state of purity sufficient to admit of
extended experiments regarding its composition, properties, and action in
digestion.

The experiments of Bidder and Schmidt, Thiry, Colin, Meade Smith and
others have given but little positive information with regard to the general prop-
erties, even, of the intestinal juice, to say nothing of its digestive action. It may
be stated in general terms, that the physiologists just mentioned have attempted
to obtain the pure secretion of the follicles of Lieberkiihn by isolating portions
of the intestine and either taking the secretion as it formed spontaneously or
exciting the action of the glands by various means. When it is remembered
how different the secretion of the stomach, under the natural stimulus of food,
is from the fluid produced during the intervals of digestion, it is evident that
little reliance is to be placed upon the experiments that have thus far been
made upon the lower animals. Nearly all observers agree, however, that the
intestinal juice which they have been able to collect is yellow, thin and
strongly alkaline. Some have found it thin and opalescent, while others
state that it is viscid and clear. According to Colin the closed follicles of the
intestine produce a viscid fluid, which probably exudes through their walls.
Colin came to this conclusion from observations upon a large, ribbon-shaped
agminate gland, about six feet (183 centimetres) in length, which exists in
the small intestine of the pig. In a case of fistula into the upper third of
the intestine in the human subject, produced by a penetrating wound of the
abdomen — which will be referred to again — Busch found a fluid that was
white or of a pale rose-color, rather viscid and always strongly alkaline. The
maximum proportion of solid matter which it contained was 7*4 and the
minimum, 3.87 per cent. The secretion apparently could not be obtained in
sufficient quantity for ultimate analysis. No better opportunity than this
has been 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 perfectly normal fluid.

From what has been ascertained by experiments upon the lower animals
and observations 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 ex-
amined is small ; but when the extent of the canal is considered, it is evident

242 INTESTINAL DIGESTION.

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 generally is either colorless or of a faint rose-tint, and its re-
action 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 five and a half 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 structures which secrete the fluid known as the intestinal juice are
the follicles of Lieberkuhn, the glands of Brunner and possibly the solitary
follicles and patches of Peyer. The secretion, however, is produced chiefly
by the follicles of Lieberkuhn. Although the other structures mentioned do
not contribute much to the secretion, they produce a certain quanity of
fluid ; and the intestinal juice must be regarded as a compound fluid, like
the saliva, and not as the product of a single glandular organ, like the pan-
creatic juice.

Action of tJie Intestinal Juice in Digestion. — The physiological action of
the intestinal juice has been studied in the inferior animals by Frerichs, Bid-
der and Schmidt and many others ; but their experiments have been some-
what contradictory. All are agreed, however, that this fluid is more or less
active in transforming starch into sugar. The observations of Busch, on
the case of intestinal fistula in the human subject, have given the most
satisfactory and definite information on this point. In many regards these
observations simply confirm those which have been made upon the infe-
rior animals, but they are of great value, as they establish many important
facts relating to the physiological action of the intestinal juice in the human
subject.

The case reported by Busch was that of a woman, thirty-one years of age,
who, in the sixth month of her fourth pregnancy, was injured in the abdo-
men by being tossed by a bull. The wound was between the umbilicus and
the pubes, presenting two contiguous openings 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 observation, 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 discharge of alimentary matters from the fistula.
Having been treated, however, by the introduction of cooked food into the
opening connected with the lower end of the intestine, she soon improved in
her nutrition and was then made the subject of extended observations upon
intestinal digestion.

In this case, starch, both raw and hydrated, when introduced into the
lower opening, where it came in contact only with the intestinal juice, was

PANCREATIC JUICE.

243

invariably changed into glucose. Cane-sugar was not transformed into glu-
cose but appeared in the faeces as cane-sugar ; and 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 absorbed in quantity by the in-
testinal mucous membrane.

Coagulated albumin and cooked meats were always more or less digested
by the intestinal juice. This fact coincides with the observations of Bidder
and Schmidt in their experiments upon dogs and cats.

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 faeces unchanged. When, however,
fatty 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 having a peculiar action upon any distinct
class or classes of alimentary substances. It undoubtedly assists in complet-
ing the digestion of the albuminoids 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 aliment-
ary substances, the in-
testinal juice should
be studied as it acts
upon the food in con-
nection with the other
fluids found in the
small intestine.

PANCREATIC JUICE.

The pancreas is sit-
uated transversely in
the upper part of the
abdominal cavity and
is closely applied to
its posterior wall. Its
form is elongated, pre-
senting an enlarged,
thick portion, called
the head, which is at-
tached to the duodenum, a body, and a pointed extremity, which latter is in
close relation to the hilum of the spleen. Its average weight is four to five
ounces (114-4 to 141-7 grammes) ; its length is about seven inches (17*78
centimetres) ; its greatest breadth, about an inch and a half (3*81 centime-

FIG. 74.— Gall-bladder, ductus choledochus and pancreas (Le Bon),
a, gall-bladder ; 6, hepatic duct ; c, opening of the second duct of the
pancreas ; cZ, opening of the main pancreatic duct and the bile-duct ;
e, e, duodenum ; /, ductus choledochus ; p, pancreas.

244

INTESTINAL DIGESTION.

tres) ; and its thickness, three-quarters of an inch (1-91 centimetre). It lies
behind the peritoneum, which covers only its anterior surface.

There are nearly always, in the human subject, two pancreatic ducts
opening into the duodenum ; one which opens in common with the ductus
communis choledochus, and one which opens about an inch (25-4 mm.) above
the main duct. The main duct is about an eighth of an inch (3'2 mm.) in
diameter and extends along the body of the gland, becoming larger as it
approaches the opening. The second duct is smaller and becomes dimin-
ished in caliber as it passes to the duodenum. In general appearance and in
minute structure, the pancreas resembles the parotid and submaxillary glands.
The normal pancreatic juice may be obtained by establishing a temporary
fistula in the main pancreatic duct of a living animal (Bernard). This may
be done in the dog, the pancreas being exposed by an incision in the right
hypochondrium, and a canula of proper size being introduced through a slit
made in the duct, and secured by a ligature. The external wound is then

closed and the
end of the tube
is allowed to pro-
ject from the ab-
domen. The fluid
as it is dis-
charged from the
tube may be col-
lected in a test-
tube, or a thin
gum-elastic bag,
may be attached.
Like the other
digestive fluids,
the pancreatic
juice is secreted
in abundance on-
ly during diges-
tion. It is there-
fore necessary to
feed the animal

moderately about an hour before the operation, so that the pancreas may be
in full activity. When the gland 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.

The secretion of normal pancreatic juice is entirely suspended during the
intervals of digestion. This fact can be observed by opening animals in
digestion and while fasting. During digestion the pancreatic duct is always
found full of normal secretion; and during the intervals it generally is
empty. The secretion begins to flow into the duodenum during the first
periods of gastric digestion, before alimentary matters have begun to pass in

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.

PANCREATIC JUICE. 245

quantity into the intestine (Bernard). The secretion is readily modified by
irritation and inflammation following the operation of making the fistula.
The normal pancreatic juice is strongly alkaline, viscid and coagulable by

FIG. 76.— Pancreatic fistula (Bernard).

Full-grown shepherd-dog (female), in which a pancreatic fistula has been established. A, silver tube to
which a bladder has been attached ; B, bladder ; c, stop-cock for the purpose of collecting the juice
which accumulates in the bladder.

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 pecul-
iar ; and its secretion is sometimes abnormal 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 nor-
mal 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 coagulable by heat. This excessive
sensitiveness of the pancreas rendered fruitless all the attempts to establish a
permanent pancreatic fistula from which the normal juice could be collected
(Bernard). The fluid collected from a permanent fistula does not represent
the normal secretion.

General Properties and Composition of the Pancreatic Juice. — In all the
inferior animals from which the pancreatic secretion has been obtained in a
normal condition, the fluid has been found to present certain uniform char-
acters. It is viscid, slightly opaline and has a distinctly alkaline reaction.
Bernard found the specific gravity of the fluid from the dog to be 1040. The
normal fluid from a temporary fistula in a dog has been observed with a spe-

246 INTESTINAL DIGESTION.

cific gravity of 1019 (Flint). The quantity of organic matters in the normal
secretion is very great, so that the fluid is completely solidified by heat. Thi^
coagulability is one of the properties by which the normal fluid may be dis-
tinguished from that which has undergone alteration.

COMPOSITION" OF THE PANCREATIC JUICE OF THE DOG (BERNARD),

Water 900 to 920

Organic matters, precipi table by alcohol and containing always a

little lime (amylopsine, trypsine, steapsine etc.) 90 to 73*60

Sodium carbonate ....

Sodium chloride

Potassium chloride. ... f '.

Calcium phosphate. . .

1,000 1,000

The properties of the organic constituents of the pancreatic juice are dis-
tinctive. Although, like albumen, these substances are coagulable by heat,
the strong mineral acids and absolute alcohol, they differ from albumen in the
fact that their dried alcoholic precipitate can be redissolved in water, giving
to the solution the physiological properties of the normal pancreatic secre-
tion. Bernard has also found that they are coagulable by an excess of mag-
nesium sulphate, which will coagulate caseine but has no effect upon albu-
men. It is important to recognize this distinction between the organic
constituents of the pancreatic juice and other nitrogenized substances, espe-
cially albumen, from the fact that the last-named substance has the property
of forming an imcomplete emulsion with fats. The name pancreatine, given
to the organic matter of the pancreatic juice, is inappropriate, as this sub-
stance is now known to be composed of several distinct constituents.

A ferment, almost if not quite identical with ptyaline, may be extracted
from the normal juice by nearly the same processes as those employed in the
isolation of the active principle of the saliva. On account of its vigorous
action upon starch, this substance has been called amylopsine.

Trypsine is a ferment capable of acting upon the albuminoids, changing
them into peptones. According to Heidenhain, there exists in the secreting
cells of the gland a substance called zymogen or more properly, trypsinogen,
which, before the secretion is discharged, becomes oxygenated and is changed
into trypsine. The action of trypsine on the albuminoids is increased by the
addition of small quantities of sodium chloride, sodium glycocholate or sodi-
um carbonate and is diminished by acids.

A substance called steapsine, capable of decomposing fats into fatty
acids and glycerine, has been described as one of the organic constituents of
the pancreatic juice. This action upon fats, which was described by
Bernard, though slight, probably assists in their emulsification.

The inorganic constituents of the pancreatic juice, beyond giving the
fluid an alkaline reaction, do not possess any great physiological interest.
inasmuch as they do not seem to be essential to its peculiar digestive proper-
ties. It has been shown that the organic constituents alone, extracted from

PANCREATIC JUICE. 247

the pancreatic juice and dissolved in water, are capable of imparting to the
fluid the characters of the normal secretion (Bernard).

The entire quantity of pancreatic juice secreted in the twenty-four hours
has been variously estimated by different observers. After what has been
said concerning the variations to which the secretion is subject, it is not sur-
prising that these estimates should present great differences. Bernard was
able to collect from a dog of medium size eighty to one hundred grains (5'2
to 6*5 grammes) in an hour ; but it must be remembered that only one of
the ducts was operated upon, and that the gland is very susceptible to irri-
tation. There is no accurate basis for an estimate of the quantity of pan-
creatic fluid secreted in the twenty-four hours in the human subject or of the
quantity necessary for the digestion of a definite quantity of food.

Unlike the gastric juice, the pancreatic juice, 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 tempera-
ture of 50° to 70° Fahr. (10° to 21° C.), the fluid decomposes gradually in
two or three days. As it thus undergoes decomposition, the fluid acquires a
very offensive, putrefactive odor, and its coagubility 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 car-
bon dioxide.

Action of the Pancreatic Juice upon Starches and Sugars. — The action of
the pancreatic juice in transforming starch into sugar was first observed, in
1844, by Valentin, who experimented with an artificial fluid made by infus-
ing pieces of the pancreas in water. Bouchardat and Sandras first noted this
property in the normal pancreatic secretion. Amylopsine is undoubtedly the
substance concerned in the action of this fluid upon starch.

The property of converting starch into sugar is possessed by several of
the digestive fluids. The starchy constituents of food are acted upon by the
saliva, and this action is not necessarily arrested as the food, mixed with the
saliva, passes into the stomach. The intestinal juice is also capable of effect-
ing 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 substances.

Bernard placed the pancreatic juice at the head of the list of the digestive
fluids which act upon starch. This view is correct, although he was in
error in claiming that starch is digested almost exclusively by the pancreas.
Bernard's experiments, however, were made chiefly on dogs, and these ani-
mals do not naturally take starch as food. In man, some of the starchy
constituents of the food are acted upon by the saliva, but most of the starch
taken as food is digested in the small intestine. Although the intestinal
juice is capable of effecting the transformation of starch into sugar, the ex-
perimental evidence is conclusive that in this it is subordinate to the pancre-
atic juice, which latter effects this transformation, at the temperature of the
body, with great activity. It is possible that the bile assists in this process
to a slight extent. In the transformation of starch into sugar in the small

218 INTESTINAL DIGESTION.

intestine, the same intermediate processes are observed as occur in the action
of the saliva ; but the change in the intestine into glucose is very rapid. It
is stated that amylopsine is not present in the pancreas of the new-born
infant (Korowin) and that in early infancy — before the second or third
month — the pancreatic extract will not digest starch.

As cane-sugar passes from the stomach into the duodenum, it is almost
instantly transformed into glucose. This fact, which has been observed in
the lower animals, has received confirmation in the case of intestinal fistula
in the human subject, 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 has of itself but little direct action upon any of the alimentary mat-
ters. This point was settled by the experiments of Busch upon 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 exposed thus to the action of the intestinal juice was not
converted into glucose, but a large portion of it passed unchanged in the
fasces.

Out of the body, the pancreatic juice is capable, if kept but for a short
time in contact 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-sugar are readily
changed into glucose and are absorbed without undergoing farther trans-
formation.

Action of the Pancreatic Juice upon Nitrogenized Substances. — Reference
has already been made to the great relative importance of intestinal diges-
tion ; and it has been apparent that the process of disintegration of food in
the stomach is not final, even as regards many of the nitrogenized substances,
but is rather preparatory to the complete liquefaction of these matters,
which takes place in the small intestine. In experiments in which the pan-
creas has been partially destroyed in dogs, there was rapid emaciation, with
great voracity, and the passage, not only of unchanged fats and starch, but
of undigested nitrogenized matter in the dejections (Bernard). The vora-
cious appetite, progressive emaciation and the passage of all classes of ali-
mentary substances in the fasces, after this operation, indicate the great im-
portance of the pancreatic juice in digestion ; but the precise mode of action
of this fluid upon the albuminoids is a question of some obscurity. If the
bile be shut off from the intestine and discharged externally by a fistulous

PANCREATIC JUICE. 249

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 very decided digestive action. Farthermore, the pancreatic juice is
evidently adapted to act upon alimentary matters after they have been sub-
jected to the action of the stomach, a preparation which is 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. It
remains to study, therefore, the special action of the pancreatic secretion
upon the albuminoids, as far as this influence can be isolated, and its action
in conjunction with the other intestinal fluids and in the presence of other
alimentary matters in process of digestion. Nitrogenized alimentary sub-
stances, when exposed to the action of the pancreatic juice out of the body,
become rapidly softened and dissolved in some of their parts, but soon un-
dergo putrefaction (Bernard). Analogous changes take place in starchy and
fatty matters when they are exposed to the action of the pancreatic juice out
of the body, and they pass through the various stages of transformation re-
spectively into lactic acid and the fatty acids. Putrefactive action, however,
does not readily 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 concluded that the fats have
an important influence in the intestinal digestion of nitrogenized substances.
Experiments made since the observations of Bernard have shown that the
ferment of the pancreatic juice concerned in the digestion of albuminoids is
trypsine.

Trypsine, in an alkaline medium, changes the albuminoids into their
respective peptones, in much the same way and involving nearly the same
intermediate conditions as in the digestion of these substances by the gastric
juice ; but if the action be prolonged, out of the body, the changes continue,
and substances are formed which yield leucine, tyrosine and other analogous
products. The final putrefactive changes, which result in indol, skatol,
phenol etc., some of which have a distinctly faecal odor, are probably due to
the influence of micro-organisms.

Taking into consideration what has been ascertained concerning the
action of the pancreatic juice upon the albuminoids, there can be no doubt
with regard to the importance of its office in the digestion of these sub-
stances after they have been exposed to the action of the gastric juice. Ex-
periments upon the digestion of the albuminoids, 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 un-
doubtedly necessary to the easy digestion, in the small intestine, of that por-
tion which is not dissolved by the gastric juice. This fact has been shown
by experiments on intestinal digestion in the inferior animals and by the
observations of Busch in the case of intestinal fistula in the human subject.

250 INTESTINAL DIGESTION.

Action of the Pancreatic Juice upon Fats. — 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
arid 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. The emulsion resulting from the action
of pancreatic juice upon fats persists when diluted with water and will pass
through a moistened filter, like milk. This does not take place in the imper-
fect 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
indispensable condition as regards its peculiar action upon fats; for the
emulsion is none the less complete when the fluid has been previously neu-
tralized with gastric juice. These facts with regard to the action of the
pancreatic juice upon fats were first ascertained by Bernard, in 1848.

A substance called steapsine, extracted from the fresh pancreas, has the
property of decomposing fats into the fatty acids and glycerine, but the
fatty acids do not appear in the chyle. The emulsification of the fats by the
pancreatic juice is to a great extent a mechanical process dependent upon
the general physical characters of the fluid ; but although the fat which is
contained in the lacteal vessels is always neutral, it is thought that steapsine
assists in rendering the emulsion fine and permanent.

The cases of fatty diarrhoea connected with disorganization of the pan-
creas, which were reported by Richard Bright, in 1832, apparently did not
direct the attention of physiologists to the uses of this organ. These cases,
with others of a similar character which have been reported from time to
time, are now brought forward as evidence of the action of the pancreas in
the digestion of fats. Many of them presented a train of symptoms anal-
ogous to those observed in animals after partial destruction of the gland.
The presence of fat in the alvine dejections was marked ; and as is now well
known, this could be nothing but the undigested fatty constituents of the food.
In the three cases observed by Bright, the pancreas was found so disorga-
nized that its secreting action must have been almost if not entirely abol-
ished. In the case reported by Lloyd, the condition was the same ; and in
the case reported by Elliotson, " the pancreatic duct and the larger lateral
branches were filled with white calculi." Another case of disease of the
pancreas was described in the catalogue of the Anatomical Museum of the
Boston Society for Medical Improvement, in 1847. In this case it was ob-
served 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 cases of this character have been

ACTION OF THE BILE IN DIGESTION. 251

quoted by Bernard and others, and they confirm the observations and experi-
ments made upon the lower animals. They all seem to show that the action
of the pancreas in digestion is essential to life, but that one of the chief
disorders incident to the destruction of this gland relates to the digestion of
fats.

Taking into consideration all the facts bearing upon this subject, it is
evident 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 condition in which it can be absorbed. How far the bile may
assist in this process, is a question which will come up for consideration farther
on ; but the facts with regard to the pancreatic juice are conclusive.

ACTION OF THE BILE IN DIGESTION.

The physiological anatomy of the liver and the general properties and
composition of the bile will be fully considered in connection with the

FIG. 77.— Dog with a biliary fistula.

From a rousrh sketch made the fourteenth day after the operation. A small glass vessel is tied around
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.

physiology of secretion and excretion ; and here it will be necessary only to
study the action of the bile in digestion.

The question whether the bile be a purely excrementilious fluid or one
concerned in digestion was formerly the subject of much discussion ; but it
is now admitted by all physiologists that the action of the bile in digestion
and absorption, whatever the office of the bile may be as an excretion, is
essential to life. The experiments of Swann, Nasse, Bidder and Schmidt,
Bernard and others, who have discharged all the bile by a fistula into the
gall-bladder, communication between the bile-duct and the duodenum having
been cut off, show that dogs operated on in this way have a voracious appetite

252

INTESTINAL DIGESTION.

but die of inanition after having lost four-tenths of the body- weight. The
following is an example of experiments of this kind (Flint, 1861) : A fistula
was made into the gall-bladder of a dog, after excising nearly the whole of
the common bile-duct. The animal suffered no immediate effects from the
operation, but died at the end of thirty-eight days, having lost 37£ per
cent, in weight. He had a voracious appetite, was fed as much as he would
eat, was protected from cold and was carefully prevented from licking the
bile. During the progress of the experiment, various observations were
made on the flow of bile. During the last five or six days, the animal was
ravenous but was not allowed to eat all that he would at one time. At that
time he was fed twice a day, but he would not eat fat, even when very hun-
gry. During the last day, when too weak to stand, he attempted to eat while
lying down.

Human bile is a moderately viscid fluid, of a dark, golden-brown color, an
alkaline reaction and a specific gravity of about 1028. Among other con-
stituents, which will be described in connection with the physiology of secre-
tion, it contains sodium united with two acids peculiar to the bile, called
glycocholic and taurocholic acids. Sodium taurocholate is much more abun-
dant than the glycocholate. The viscidity of the bile is due to mucus de-
rived in part from the lining membrane of the gall-bladder and in part,
probably, from little, racemose glands attached to the larger bile-ducts in the
substance of the liver. The so-called biliary salts, sodium taurocholate and
sodium glycocholate, are probably the constituents of the bile which are con-
cerned in digestion.

Although the bile is constantly discharged in certain quantity into the
duodenum, its flow presents marked variations corresponding with certain
stages of the digestive process. In fasting animals, the gall-bladder is dis-
tended with bile ; but in animals opened soon after feeding, it is nearly always
found empty. The actual secretion of bile by the liver is also influenced by
digestion. The following table gives the variations observed in the dog with
a biliary fistula :

TABLE OF VARIATIONS IN THE FLOW OF BILE WITH DIGESTION.

(At each observation the bile was drawn for thirty minutes.)

Time after feeding.

Fresh bile.

Dried bile.

Percentage of
dry residue.

Immediately

Grains. Grammes.
8-103 0-525

Grains. Grammes.
0-370 0-024

4-566

One hour . . <

20-527 1-330

0-586 0-038

2-854

Two hours

35-760 2-317

1-080 0-070

3-023

Four hours ...

38-939 2-523

1-404 0-091

3-605

Six hours

22-209 1-439

0-987 0-051

4-450

Eight hours.

36-577 2-370

1-327 0-086

3-628

Ten hours ...

24-447 1-584

0-833 0-054

3-407

Twelve hours

5-710 0-370

0-247 0-016

4-325

Fourteen hours . ....

5-000 0-324

0-170 0-011

3-400

Sixteen hours

8-643 0-560

0-309 0-020

3-575

Eighteen hours . .

9-970 0-646

0-277 0-018

2-778

Twenty hours

4-769 0-309

0-170 0-011

3-565

Twenty-two hours

7-578 0-491

0-293 0-019

3-866

ACTION OF THE BILE IN DIGESTION. 253

Disregarding slight variations in this table, which may be accidental, it
may be stated, in general terms, that the bile begins 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 its minimum.

One of the uses which has been ascribed to the bile is that of regulating
the peristaltic movements of the small intestine and of preventing putrefac-
tive changes in the intestinal contents and the abnormal development of gas ;
but observations on this point have been somewhat conflicting. During the
first few days of the experiment just described, the dejections were very rare ;
but they afterward became regular, and at one time there was even a tend-
ency to diarrhoea. There can be little 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 with biliary fistula 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 intestinal fistula in the
human subject (Busch), 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.

It has been shown that the bile of itself has little action upon any of the
different classes of alimentary substances. 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. This was observed in the
faeces of a patient suffering under jaundice apparently due to temporary ob-
struction of the bile-duct (Flint). The fact was also 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 absorption of fats. Bidder and Schmidt noted, in ani-
mals 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 pro-
portion of fat was 1-90 parts to 1,000 parts of chyle ; while in an animal
with the biliary passages intact, the proportion was 32-79 parts per 1,000.
In animals operated upon in this way there is frequently a great distaste for
fatty articles of food. In the observation made in 1861 the dog refused fat
meat, even when very hungry and when lean meat was taken with avidity.

Experiments on animals, with regard to the influence of the bile upon
the absorption of fats, have resulted in hardly anything definite. It is
known, however, that when the bile is diverted from the intestine, the
quantity of fat in the chyle is greatly reduced and a large proportion of

18

254 INTESTINAL DIGESTION.

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
non-striated muscular fibres, is 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 emptying the lacteals of the villi. The ques-
tion, however, of the absorption of fats is difficult of investigation. Not-
withstanding the obscurity in which this subject is involved, it is certain that
the progressive emaciation, loss of strength, and final death of animals de-
prived of the action of the bile in the intestine, are due to defective digestion
and assimilation. Notwithstanding 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 necessary 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 process and are absorbed in a modi-
fied form with the food.

The observations of Bidder and Schmidt show that the characteristic con-
stituents of the bile are absorbed in their passage down the alimentary canaL
Having arrived at an estimate of the quantity of bile daily produced in dogs,
they collected and analyzed all the faecal matter passed by a dog in five days.
Of the dry residue of the faeces, the proportion which could by any possibil-
ity 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 sulphur contained in the faeces and found that the entire
quantity was hardly one-eighth of that which was discharged into the intes-
tine 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 experiment
showed that nearly all the sulphur contained in the sodium taurocholate had
been taken up again by the blood. These observations show that the greater
part of the bile, with the biliary salts, is absorbed by the intestinal mucous
membrane. Dal ton attempted to follow the constituents of the bile into the
blood of the portal system, but was unable to detect the biliary salts. Like
the peculiar constituents of other secretions which are reabsorbed in the ali-
mentary canal, these substances become changed and are not to be recognized
by the ordinary tests, after they are taken into the blood.

While 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 show great disturbance in
the digestion and absorption of other constituents 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.

Although it has been demonstrated that the presence of the bile in the

MOVEMENTS OF THE SMALL INTESTINE. 255

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 estab-
lished, physiologists have but little definite information concerning the exact
mode of action of the bile in intestinal digestion and absorption. Nearly all
that can be said on this subject is that the action of the bile 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 ali-
mentary mass is made to pass along the canal, sometimes in one direction and
sometimes in another, the general tendency, however, being toward the cae-
cum ; and the partially digested matters which pass out at the pylorus are pre-
vented from returning to the stomach by the peculiar arrangement of the
fibres which constitute the pyloric muscle. Once in the intestine, the food is
propelled along the canal by peculiar movements which have been called peri-
staltic, when the direction is toward the large intestine, and antiperistaltic,
when the direction is reversed. These movements are of the character pecul-
iar to the non-striated muscular fibres ; viz., slow and 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
participate in these movements.

Although the mechanism of the peristaltic movements of the intestine
may be studied in living animals after opening the abdomen or in animals
just killed, the movements thus observed do not entirely correspond with
those which take place under natural conditions. In vivisections no move-
ments 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 diges-
tion 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 intervals of repose. In Busch's case of intestinal fistula, there existed
a large ventral hernia, the coverings of which were so thin that the peristal-
tic 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. It was
also observed that the movements, as indicated by flow of matters from the
upper end of the intestine, were intermitted with considerable regularity dur-
ing part of the night. Antiperistaltic movements, producing discharge of
matters which had been introduced into the lower portion 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 alimentary matters 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

256 INTESTINAL DIGESTION.

action being reversed for a time, until the indigestible residue, mixed with a
certain quantity of intestinal secretion, more or less modified, is discharged
into the caput coli. These movements are apparently not continuous, and
they depend in some degree upon the quantity of matter contained in different
parts of the intestinal tract. Judging from the movements in the inferior
animals after the abdomen has been opened, the intestines are always chang-
ing their position, mainly by the action of their longitudinal muscular fibres,
so that the force of gravity does not oppose the onward passage of their con-
tents 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 found in the intestine have an important mechanical
office. They are useful, in the first place, in keeping the canal constantly
distended to the proper degree, thus avoiding the liability to disturbances in
the circulation and facilitating the passage of the alimentary mass in obedience
to the peristaltic contractions. They also support the walls of the intestine
and protect these parts against concussions, 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 be exerted in straining
and in expiration.

There can be hardly any question that the normal movements of the in-
testine are due principally to the impression made upon the mucous mem-
brane 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 nor-
mal 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 portion of
the canal, there was at first an abundant evacuation every twenty-four hours ;
but subsequently it became necessary to use enemata. As there was no com-
munication between the lower and the upper portions of the intestine, this
fact is an evidence that the peristaltic movements can take place without the
action 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 lowering 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 the thin, abdominal walls, even
while the cavity is unopened. According to Schiff, the cause of these exag-
gerated movements is diminution or arrest of the circulation. By compress-
ing the abdominal aorta in a living animal, he was able to excite 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 sym-

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 257

pathetic and from branches of the pneumogastric, which latter come from
the nerve of the right side and are distributed to the whole of the intestinal
tract, from the pylorus to the ileo-caecal valve. The intestine receives no
filaments from the left pneumogastric. Throughout the intestinal tract, is a
plexus of non-medullated nerve-fibres with groups of nerve-cells, lying be-
tween the longitudinal and circular layers of the muscular coat. This is
known as Auerbach's plexus. From this plexus, very fine, non-medullated
filaments are given off, which form a wider plexus, also with ganglionic cells,
situated just beneath the mucous membrane. This is called the plexus of
Meissner.

The experiments of Brachet, by which he attempted to prove that the
movements of the intestines were under the control of the pneumogastrics
and nerves given off from the spinal cord, have not been verified by other
observers. The experiments of Mtiller, however, render it certain that the
peristaltic movements are to some extent under the influence of the sympa-
thetic system. In these experiments, movements of the intestine were pro-
duced by stimulation of filaments of the sympathetic distributed to its mus-
cular coat, after the ordinary post-mortem movements had ceased. The
same results followed the application of potassium hydrate to the semilunar
ganglia, the movements reappearing when the agent was applied, " with ex-
traordinary 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.

The fact that movements occur in portions of intestine cut out of the
body and separated, of course, from the nervous system, has led to the view
that the peristaltic action is automatic, like the action of the excised heart,
and these automatic movements have been attributed to the influence of the
ganglia found in the intestinal walls. An analogy between such intestinal
movements and the movements of the excised heart seems probable ; and a
reasonable explanation of this action is afforded by the existence of ganglia
in the plexuses of Auerbach and of Meissner.

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE.

The entire length of the large intestine is about five feet (1-5 metre.) Its
diameter is greatest at the caecum, where it measures, when moderately dis-
tended, two and a half to three and a half inches (6*35 to 8'89 cen-
.timetres). According to the observations of Brinton, the average diameter
of the tube beyond the caecum is one and two-thirds to two and two-thirds
inches (4-23 to 6'77 centimetres). Passing from the caecum, the canal
diminishes in caliber, gradually and very slightly, to where the sigmoid flex-
ure 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

258

INTESTINAL DIGESTION.

right iliac fossa, to the left iliac fossa, thus encircling the convoluted mass
formed by the small intestine, in the form of a horseshoe. From the caecum

to the rectum, the canal is
known as the colon. The
first division of the colon,
called the ascending colon,
passes almost directly up-
^ ward to the under surface
of the liver ; the canal here
turns at nearly a right an-
gle, passes across the upper
part of the abdomen and
is called the transverse co-
lon ; it then passes down-
ward at nearly a right an-
gle, forming the descend-
ing colon. The last divis-
ion 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 curvatures,
as follows : it passes first
in an oblique direction
from the left sacro-iliac
symphysis to the median

FIG. 78.— Stomach, pancreas, large intestine etc. (Sappey). , . , .

1, anterior surface of the liver ; 2, gall-bladder ; 3, 3, section of lme Opposite the third

the diaphragm ; 4, posterior surface of the stomach ; 5, lobus -ninnn ~4? +!-»« cio^^n™ . if

Spigelii of the liver ; 6, cceliac axis ; 7, coronary artery of the Pi^Ce OI tne Sacrum , It

stomach ; 8, splenic artery ; 9, spleen : 10, pancreas ; 11, supe- f npT1 r^oQpa rlnwnwarrl in

rior mesenteric vessels ; 12, duodenum ; 13, upper extremity tnen PaSS6S downward in

of the small intestine ; 14, lower end of the ileum ; 15, 15, mes- fnp mprlian linp fnllnwino-

entery ; 16, ccecum ; 17, appendix vermiformis ; 18, ascending l Lie' 1V lia&

colon ; 19, 19, transverse colon ; 20, descending colon ; 21, sig- fV,p ponpnvitv of thp saoriim

moid flexure of the colon ; 22, rectum ; 23, urinary bladder. Heavily O.

and coccyx ; and the lower

portion, which is about an inch (2*54 centimetres) in length, turns backward
to terminate in the anus.

The caecum, or caput coli, presents a rounded, dilated cavity continuous
with the colon above and communicating by a transverse slit with the ileum.
At its lower portion is a small, cylindrical tube, opening below and a little
posterior to the opening of the ileum, called the vermiform appendix. This
is covered with peritoneum and has a muscular and a mucous coat. It is
sometimes entirely free and is sometimes provided with a short fold of mes-
entery for a part of its length. The coats of the appendix are very thick.
The muscular coat consists of longitudinal fibres only. The mucous mem-

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 259

brane is provided with tubules and closed follicles, the latter frequently
being very abundant. This little tube generally contains a quantity of clear,
viscid mucus. The uses of the vermiform appendix are unknown.

Ileo-ccecal Valve. — The opening by which the small intestine commu-
nicates with the caecum is provided with a valve, known as the ileo-caecal
valve, situated at the inner and posterior portion of the caecum. The small
intestine, at its termination, presents a 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 covered with a mucous mem-
brane provided with villi and in all respects resembling the general mucous
lining of the small intestine. Viewed from the caecum, a convexity is
observed corresponding to the concavity upon the other side. The caecal
surface of the valve is covered with a mucous membrane identical with the
general mucous lining of the large intestine. It is evident, from an exami-
nation of these parts, that pressure from the ileum would open the slit and
allow the easy passage of the semi-fluid contents of the intestine ; but press-
ure from the caecal side approximates the lips of the valve, and the greater
the pressure the more firmly is the opening closed. The valve itself is com-
posed of folds formed of the fibrous tissue of
the intestine, 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 extremity of the slit
and are prolonged on the inner surface of the
caecum, forming two raised bands, or bridles ;
and these become gradually effaced and are thus
continuous with the general lining of the canal.
The posterior bridle is a little longer and more
prominent than the anterior. These assist some-
what in enabling the valve to resist pressure from
the caecal side. The longitudinal layer of mus-
cular 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,

,. -n ja -, IT i

gentle traction Will SUmCe to draw OUt and Obllt-

, , „ , i , , , , ,

erate the folds, leaving a simple and unprotected

,. i , JIT -i,i -n

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 caecum is covered by this mem-
brane only anteriorly and laterally. It usually is bound down closely to the
subjacent parts, and its posterior surface is without a serous investment;
although sometimes it is completely covered, and there may be even a short
mesocaecum. The ascending colon is likewise covered with peritoneum only
in front, and is closely attached to the subjacent parts. The same arrange-

.^.-opening of the ^aiiint
tine into the C(Kcum &* Eon^

small intestine; 2, ileo - csecal
valve ; 3, caecum ; 4, opening of
the appendix vermiformis ; 5,

mucous fold at the opening o^

the appendix ; 6, large intestine ;

7, 7, folds of the mucous mem-

260 INTESTINAL DIGESTION.

merit is found in the descending colon. The transverse colon is almost com-
pletely 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 epiploicae. The sigmoid flexure
of the colon is covered by peritoneum, except at the attachment of the iliac
mesocolon. This division of the intestine is quite movable. The upper por-
tion of the rectum is almost completely covered by peritoneum and is but
loosely held in place. The middle portion is closely bound down, and is
covered by peritoneum only anteriorly and laterally. The lowest portion of
the rectum has no peritoneal covering.

Muscular Coat. — 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 begin in the caecum at the vermi-
form appendix. Passing along the ascending colon, one of the bands is sit-
uated anteriorly, and the others, latero-posteriorly. In the transverse colon
the anterior band becomes inferior and the two latero-posterior bands
become respectively postero-superior and postero-inferior. In the descend-
ing 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 surface. Thus the three bands here become two.
These two bands as they pass downward, though remaining distinct, become
much wider ; and longitudinal muscular fibres beginning 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 nearly uniform layer.

Mucous Coat. — The mucous lining of the large intestine presents several
important points of difference from the corresponding membrane in the small
intestine. It is paler, somewhat thicker and firmer, and is more closely ad-
herent 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 smooth and free from villi.

Throughout the entire mucous membrane, from the ileo-caecal valve to
the anus, are orifices which lead to simple follicular glands. These struct-
ures 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 rather more abundant. Among these small follicular openings
are found, scattered irregularly throughout the 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 exist throughout the intes-

PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 261

tine, together with the closed follicles, except in the rectum. In the caecum
and colon, isolated closed follicles are generally found, which are identical
in structure with the solitary glands of the small intestine. These are very
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 vascular ity, the veins, espe-
cially, being very abundant.

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 passage of the faeces, by the powerful external sphincter. This
muscle is composed entirely of 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 substances is completed either in the stomach or in the small in-
testine, and that the mucous membrane of the large intestine does not secrete
a fluid endowed with any well marked digestive properties. The simple fol-
licles, the closed follicles, and the utricular glands, produce a glairy mucus,
which, as far as is known, serves merely to lubricate the canal. This has
never been obtained in sufficient quantity to admit of any accurate investiga-
tion into its properties.

In studying the changes which the alimentary mass undergoes in its pas-
sage through the small intestine, it has been 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 muscular fibre, oil-globules, and
other matters in a state of partial disintegration, may be detected in the
faeces ; but generally this is either the result of the ingestion of an excessive
quantity of these substances or it depends upon some derangement of the
digestive apparatus. When intestinal digestion takes place with regularity,
the transformation of the alimentary residue into faecal matter is slow and
gradual. As the contents of the stomach are passed little by little into the
duodenum, the mass becomes of a bright-yellow color, and its fluidity is in-
creased, from the admixture of bile and pancreatic fluid. In passing along
the canal, the consistence of the mass gradually diminishes on account of
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 caecum, the
greatest part of those substances recognized as alimentary has become

262 INTESTINAL DIGESTION.

changed and absorbed. The various forms of starchy and saccharine matters,
unless they have been taken in excessive quantity, soon disappear from the
intestine ; and the glucose, which is the result of their digestion, may be rec-
ognized in the portal blood. 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 the muscular substance, as recognized by its microscopical characters,
becomes gradually disintegrated 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 succes-
sive and combined action of the different digestive secretions are derived
chiefly from the vegetable kingdom. Hard, vegetable seeds, the cortex of
the cereals, spiral vessels, and, indeed, all parts which are composed largely
of cellulose, pass through the intestinal canal without 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 matters be taken in a concen-
trated and readily assimilable form, leaves very little undigested matter to
pass into the large intestine, and gives to the faeces a character quite different
from that which is observed in herbivorous animals or in man when subjected
to an exclusively vegetable diet. The characters of the residue of the diges-
tion of albuminoid substances are not very distinct. As a rule, none of the
albuminoids are to be recognized in the healthy fasces by the ordinary tests.

Absorption of various articles of food in a liquid form may take place
with great activity in the large intestine, although it has not been shown that
the secretions in this part of the alimentary canal have any distinct digestive
properties ; still, as is shown in rectal alimentation, eggs, milk and meat-ex-
tracts may be taken up by the mucous membrane, and they enter the circu-
lation in such a form that they contribute to the nutrition of the body.

Processes of Fermentation in the Intestinal Canal. — The processes of
fermentation in the intestines are not properly digestive and are to a great
extent due to the action of micro-organisms, which exist here in great num-
bers and variety. It is possible, however, that future researches may show
that micro-organisms play an important part in actual digestion, as is fore-
shadowed in a recent article by Pasteur (August, 1887). Pasteur has isolated
seventeen different micro-organisms of the mouth. Some of these dissolved
albumen, gluten and caseine, and some transformed starch into glucose. The
micro-organisms described were not destroyed by the action of the gastric
juice. These observations are very suggestive, and they seem to open a new
field of inquiry as regards certain of the processes of digestion. Most of the
fermentations in the small intestine are either putrefactive or of a nature
analogous to fermentation, and the processes are continued with increased
activity in the large intestine.

Some of the substances resulting from intestinal fermentations have
.already been described. Indol, skatol, phenol etc., seem to be produced by

CONTENTS OF THE LARGE INTESTINE. 263

the action of micro-organisms ; but the effect of these products is to kill the
micro-organisms and thus to limit the putrefactive processes. The produc-
tion of indol, skatol and phenol is arrested by the action of certain drugs,
;such as calomel, salicylic acid and other so-called antiseptics. The fermenta-
tive changes in the intestines involve the production of certain gases, which
will be described at the close of this chapter.

CONTENTS OF THE LARGE INTESTINE.

When the contents of the small intestine have passed the ileo-caecal valve,
they become 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 notable changes relate to consistence, color and odor. The odor,
especially, of normal faecal matter is characteristic.

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
faeces 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 yellowish-brown characteristic of the
faeces. Although the bile-pigment can not usually be recognized by the ordi-
nary 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 duode-
num. In a specimen of healthy human faeces, which had been dried, ex-
tracted with alcohol, the alcoholic extract precipitated with ether and the
precipitate dissolved in distilled water, it was impossible to detect the biliary
salts by Pettenkofer's test. In a watery extract of the same faeces, the addi-
tion of nitric acid failed to show the reaction of the coloring matter of the
bile (Flint, 1862). The color of the faeces, however, varies considerably
under different forms of diet. With a mixed diet the color is yellowish-
brown ; with an exclusively flesh-diet it is much darker ; and with a milk-
diet it is more yellow (Wehsarg).

The odor of the faeces, which is characteristic and quite different from
that of the contents of the ileum, is variable and is due in part to the pecul-
iar decomposition 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 faeces in the twenty-four hours, according to Weh-
sarg, is about 4*6 ounces (128 grammes). This was the mean of seventeen
observations ; the largest quantity being 1O8 ounces (306 grammes), and the
smallest, 2-4 ounces (68 grammes).

The reaction of the faeces is variable, depending chiefly upon the char-
acter of the food. Marcet found the human excrements always alkaline.
Wehsarg, on the other hand, found the reaction generally acid, but very fre-
quently it was alkaline or neutral.

The proportions of water and solid matter in the faeces are variable. Ber-

264 INTESTINAL DIGESTION.

zelius found in the healthy human faeces, 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 observations of Wehsarg, the mean quantity of
solid matter discharged in the fasces in the twenty-four hours was 463 grains
(30 grammes), the extremes being 882-8 grains (57'2 grammes), and 251-6
grains (16-28 grammes). The proportion 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
(3-4 grammes). This was found, however, to be very variable ; the largest
quantity being 126-5 grains (8-2 grammes), and the smallest, 12-5 grains (0-81
gramme).

Microscopical examination of the faeces reveals various vegetable and ani-
mal structures which have escaped the action of the digestive fluids. Weh-
sarg also found a " finely divided faecal matter " of indefinite structure, but
containing partly disintegrated intestinal epithelium. Crystals of cholester-
ine were never observed. Whenever the matter is neutral or alkaline, crys-
tals of ammonio-magnesian phosphate are found. Mucus is also found
in variable quantity in the faeces, with desquamated epithelium and a few
leucocytes. In addition, recent microscopical researches have shown the
presence of spores of yeast and a great variety of bacteria, which latter exist
in the faeces in great abundance. These organisms probably excite many
of the so-called putrefactive changes in the intestinal contents, which result
in the formation of indol, phenol, skatol, cresol etc. According to Senator,

L\ t'o^ thesePutrefac-

* <= J 9

' \W *&) W ^5 ^^

XA

do not occur in

the meconium.
^e quantity

of ^organic

salts in the

FIG. SO.— Micro-organisms of the large intestine (Landois). f 33068 IS not
1, bacterium coli commune ; 2, bacterium lactis aerogenes ; 3, 4, the large bacilli

of Bienstock, with partial endogenous spore-formation ; 5, the various stages of great. In ad-

the development of the bacillus which causes the fermentation of albumen. ° . .

dition to the

ammonio-magnesian phosphate, magnesium phosphate, calcium phosphate
and a small quantity of iron have been found. The chlorides are either ab-
sent or are present only in small quantity.

Marcet has pretty generally found in the human f asces a substance pos-
sessing the characters of margaric acid, and volatile fatty acids ; the latter
free, however, from butyric acid. He also found a coloring matter, which is
probably a modification of bile-pigment. Cystine is mentioned as an occa-
sional constituent of the faeces.

In addition to the matters just enumerated, the following substances have
been extracted from the normal faeces :

Excretine and Excretoleic Acid. — Excretine was obtained from the nor-
mal faeces, by Marcet, in 1854. This substance crystalizes from an ethereal
solution in two or three days, in the form of long, silky crystals. Examined

CONTENTS OF THE LARGE INTESTINE. 265

with the microscope, these are found to consist of acicular, four-sided prisms
of variable size. Excretine is insoluble in water, slightly soluble in cold alco-
hol, but very soluble in ether and in hot alcohol. Its alcoholic solutions are
faintly though distinctly alkaline. Its fusing-point is between 203° and 205°
Fahr. (95° and 96° C.). It may be boiled with potassium hydrate for hours
without undergoing saponification. The quantity of excretine contained in
the faeces is not large. Only 12-6 grains (0-810 gramme) were obtained by
Marcet from nine evacuations.

There exists very little definite information concerning the production
of excretine. Marcet examined on one occasion the contents of the small
intestine of a man who had died of disease of the heart, without finding any
excretine. It is probable that this substance 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 properties. 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 between 77° and 79° Fahr. (25° and 26-11° C.).

Stercorine. — This substance, discovered in the faeces in 1862 (Flint), was
described by Boudet in 1833, as existing in minute quantity in the serum of
the blood, and was called seroline. As it is one of the most abundant and
characteristic constituents of the stercoraceous matter, it may properly be
called stercorine, particularly as observations have led to the opinion that
it really does not exist in the serum, but is formed from cholesterine by the
processes employed for its extraction from the blood (Flint).

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 entirely decolorize 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 potassium hydrate
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 washed until the fluid which
passes through is neutral and perfectly clear. The filter is then 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 pure stercorine.

When first obtained, stercorine is a clear, slightly amber, oily substance, of
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, from seven and a half ounces (202-5 grammes) of normal
human faeces (the entire quantity for the twenty-four hours), 10-417 grains
(0-675 gramme) of stercorine were obtained, the extract consisting entirely

INTESTINAL DIGESTION.

of 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 (72*58 kilos.). In the absence of other inves-
tigations, the daily quantity of this substance excreted may be assumed to be
not far from ten grains (0-648 gramme).

In many regards stercorine bears a close resemblance to cholesterine. It
is neutral, inodorous, and insoluble in water and in a solution of potassium
hydrate. 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 sul-
phuric acid. It may be easily distinguished from cholesterine, however, by
the form of its crystals. It fuses at a low temperature, 96'8° Fahr. (36° C.),,
while cholesterine fuses at 293° Fahr. (145° C.).

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 consid-
erable size, the borders near their ex-
tremities are split longitudinally for a
short distance. The crystals are fre-
quently arranged in bundles. They
are not to be confounded with excre-
tine, which crystallizes in the form
of 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 Verdiel.

There can be no doubt with regard
to the origin of the stercorine which
exists in the faeces. Whenever the bile
is not discharged into the duodenum,,
as is probably the case for a time in

FIG. 81.— Stercorine from the human fceces.

icterus accompanied with clay-colored evacuations, stercorine is not to be dis-
covered in the dejections. In one case of this kind, in which the fa3ces were
subjected to examination, the matters extracted with hot alcohol were entirely
dissolved by boiling for fifteen minutes with a solution of potassium hydrate,
showing the 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 stercorine. Both
of these substances are crystallizable, non-saponifiable, are extracted by the
same chemical manipulations, and behave in the same way when treated with
sulphuric acid. Stercorine must be regarded as a modification of cholesterine,
which is the excrementitious constituent of the bile.

The change of cholesterine into stercorine is directly connected with the
process of intestinal digestion. If an animal be kept for some days without

MOVEMENTS OF THE LARGE INTESTINE. 267

food, cholesterine will be found in the faeces, although, for a few days, ster-
corine is also present. It is a fact generally recognized by those who have
analyzed the faeces, that cholesterine does not exist in the normal evacu-
ations; but whenever digestion is arrested, the bile being constantly dis-
charged into the duodenum, cholesterine is found in large quantity. 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 me-
conium always containing a large quantity of cholesterine, which disappears
from the evacuations when the digestive function becomes established. Ster-
corine has not been subjected to ultimate analysis. Its physiological relations
will be considered in connection with the excretory office of the liver.

Indol, Skatol, Phenol etc. — The so-called putrefactive processes, which
begin in the small intestine, are more marked in the large intestine and give
rise to certain products which have the characteristic faecal odor. Certain of
these substances may be produced by the prolonged action, out of the body,
of the pancreatic juice upon albuminoids. The pancreatic juice, in an alka-
line medium, changes the trypsine-peptones into leucine, tyrosine, hypoxan-
thine and asparaginic acid. By still farther prolonging this action, indol
(C8H71S"), skatol (C9H9N) and phenol (C6H60), with some other analogous
substances and volatile fatty acids, are formed, and there is an evolution of
certain gases. It is probable that these products are formed in abnormal
quantities in the small intestine in certain cases of intestinal dyspepsia.
The relations of the substances just mentioned to the general process of nu-
trition are not understood.

Movements of the Large Intestine. — Movements of the general character
noted in the small intestine occur in the large intestine, although the pecul-
iarities in the arrangement of the muscular fibres and the more solid consist-
ence of the contents render these movements in the large intestine 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 vig-
orous 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 electric stimulation ; and they are
then more circumscribed and much less marked than in any other part of
the alimentary canal. That the faeces remain 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 caecum, the pressure of matters received from the ileum forces the
mass onward into the ascending eolon, and the contractions of its muscular
fibres are probably 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 relax-
ing above — are capable of passing the faecal mass slowly onward. Although

268 INTESTINAL DIGESTION.

the transverse fibres are thin and apparently of little power, their contraction
is undoubtedly sufficient to empty the sacculi, when assisted by the move-
ments 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 pas-
sage of the fasces through the ascending, transverse and descending colon is
undoubtedly variable in different persons, as great variations are observed in
the intervals between the acts of defascation. During their passage along
the colon, the contents of the canal assume more and more of the normal
f ascal consistence and odor and become slightly coated with the mucous secre-
tion of the parts.

The accumulation of fasces generally takes place in the sigmoid flexure of
the colon ; and under normal conditions, the rectum is found empty and
contracted. This part of the colon is much more movable than other por-
tions of the large intestine. At certain tolerably regular intervals, the fascal
matter is passed into the rectum and is then almost immediately discharged
from the body.

Defcecation. — In health, expulsion of fascal matters takes place with regu-
larity 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 health. At the time when
defascation 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 impossible. It is probable
that the fasces are then passed out of the rectum by antiperistaltic action.

The condition which immediately precedes the desire for defascation is
probably the descent of the contents of the sigmoid flexure of the colon into
the rectum. It was formerly thought that the fasces constantly accumulated
in the dilated portion of the rectum, where they remained until an evacua-
tion took place ; but the arguments of O'Beirne against such a view are
conclusive. He demonstrated, by explorations in the human subject, that
under ordinary conditions, the rectum is contracted and contains neither
fasces 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 physi-
cal examinations, and that paralysis or section of the muscles which close
the anus by no means involves, necessarily, a constant passage of fascal mat-
ter. O'Beirne not only found the rectum empty and presenting a certain
degree of resistance to the passage of injected fluids, but on passing a stom-
ach-tube into the bowel, after penetrating six to eight inches (15 to 20 cen-
timetres), 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 fasces, or of
both, through the tube. In some instances in which nothing escaped through
the tube, the instrument conveyed to the hand an impression of having en-
tered a solid mass ; and on being withdrawn it contained solid fasces in its

DEFECATION. 269

upper portion. 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, upper portion of the rectum. This constriction,
situated at the most superior portion of the rectum, is sometimes called the
sphincter of O'Beirne.

The above is the mechanism of the descent of faecal matter into the rec-
tum in defaecation, as the act is usually performed ; but under certain condi-
tions, faeces must accumulate in the dilated portion of the rectum. Ordina-
rily, the discharge of fasces takes place only after the efforts have been con-
tinued 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 ; but in
cases in which the faeces are very fluid, or when the call for an evacuation
has not been regarded and has become imperative, the immediate discharge
of matters when the sphincter is relaxed shows that the rectum has been
more or less distended.

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 opening of the rectum into its dilated portion below.
The faecal matter, however, is not allowed 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 abdominal muscles and the
diaphragm. The circular fibres of the rectum undergo the ordinary peri-
staltic contraction ; and the action of the longitudinal fibres is to render the
rectum shorter and more nearly straight. The internal and the external
sphincters present a certain resistance to the discharge of the faeces, particu-
larly the external 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 contraction, 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
ramus 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 median 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 rec-
tum, and by its contractions, favors the relaxation of the sphincter and
draws the anus forward.

The diaphragm and the abdominal muscles merely compress the abdom-
inal organs, and consequently those contained in the pelvis, and assist in the
expulsion of the contents of the rectum. The diaphragm is the most im-
portant of the voluntary muscles concerned in this process ; and during the
act of straining, the lungs are moderately filled and respiration is inter-
rupted. 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. Although more or less

1Q

270 INTESTINAL DIGESTION.

straining generally takes place, the contractions of the muscular coats of the
rectum frequently are competent of themselves to expel the faeces, especially
when they are soft.

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 contraction 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, notwithstanding
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 rec-
tum has been emptied.

Very little need be said concerning the influence of the nervous system
on the movements concerned in defaecation. The non-striated muscular
fibres which form the muscular 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 spinal nerves. These nerves bring the
sphincter in a certain degree under the control of the will, and impart like-
wise the property of tonic contraction, by which the anus is kept constantly
closed. The nerve-centre for defaecation in the dog, or the ano-spinal
centre, is in the spinal cord, at the site of the fifth lumbar vertebra (Budge),

GASES FOUND IN THE ALIMENTARY CANAL.

The gases in the stomach appear to have no definite office. They gener-
ally exist in very small quantity and they are sometimes absent. The oxy-
gen and nitrogen are derived from the little bubbles of air which are incor-
porated with the alimentary bolus during 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 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 as-
certained that it had the following composition :

GASES CONTAINED IN THE STOMACH.
Oxygen
Carbon dioxide

Pure hydrogen 3'55

Nitrogen • 71-45

100-00

Magendie and Chevreul found three different gases in the small intes-
tine. Their examinations were made upon three criminals soon after execu-
tion. The first was twenty-four years of age, and two hours before execu-
tion, he 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

GASES FOUND IN THE ALIMENTAEY CANAL.

271

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.

Carbon dioxide . ....

24-39

40-00

25-00

Pure hydrogen

55-53

51-15

8-40

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 pro-
parti on is not at all definite. Reference has already been made to the
mechanical office 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 rec-
tum of the third, were found traces of hydrogen monosulphide. The follow-
ing 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.

Carbon dioxide

43-50

70-00

Caecum.
12-50

Rectum.
42-86

Carburetted hydrogen and traces
of hydrogen monosulphide

5-47

Pure hydrogen and Carburetted
hydrogen

11-60

11-18

Pure hvdrogen ....

7-50

Carburetted hydrogen

12-50

N itrogen

51-03

18-40

67-50

45-96

100-00

100-00

100-00

100-00

Origin of the Intestinal Gases. — 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 decomposi-
tion. 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 vege-
tables, generate 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 certain of the articles of food. Gases do not exist in the
alimentary canal of the foetus.

272 ABSORPTION-LYMPH AND CHYLE.

CHAPTER X.

ABSORPTION— LYMPH AND CHYLE.

Absorption by blood-vessels— Absorption by lacteal and lymphatic vessels— Physiological anatomy of the
lacteal and lymphatic vessels— Lymphatic glands— Absorption by the lacteals— Absorption by the
skin — Absorption by the respiratory surface — Absorption from closed cavities, reservoirs of glands,
etc.— Absorption of fats and insoluble substances— Variations and modifications of absorption-
Mechanism of the passage of liquids through membranes —Lymph and chyle — Properties and composi-
tion of lymph — Origin and uses of the lymph — Composition of the chyle — Microscopical characters of
the chyle — Movements of the lymph and chyle.

DIGESTION has two great objects : one is to liquefy the different aliment-
ary substances; and the other, to b3gin the series of transformations by
which these are rendered capable of nourishing the organism. The matters
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 nutritive fluid, supplying the loss which the constant
regeneration of the tissues from matters furnished by the blood necessarily
involves. The only constituents of food which possibly do not obey this
general law, as regards their absorption, are the fats. Although a small por-
tion of the fat taken as food may pass 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 what-
ever way fat enters the blood, it is not dissolved but is reduced to the condi-
tion of a fine emulsion.

ABSORPTION BY BLOOD-VESSELS.

That substances in solution can pass through the walls of the capillaries
and of the 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 substances 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 ; and it has been shown that during absorption, the blood
of the portal vein is rich in albuminoids, sugar and other matters resulting
from digestion.

In the mouth and oesophagus, the sojourn of alimentary matters is so
brief and the changes which they undergo are so slight, that no considerable
absorption can take place. It is evident, however, that the mucous mem-
brane of the mouth is capable of absorbing certain soluble matters, from the
effects which are constantly observed when the smoke or the juice of tobac-
co is retained in the mouth, even for a short time. In the stomach, how-
ever, absorption takes place with great activity. A large proportion of the
ingested liquids and of those constituents of food which are dissolved by the
gastric juice and converted into peptones is taken up directly by the blood-
vessels of the stomach. It may, indeed, be assumed, as a general law, that
alimentary matters are in great part absorbed as soon as their digestive
transformations in the alimentary canal have been completed.

ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS. 2Y3

In the passage of the food along the intestinal canal, as the digestion of
the albuminoids is completed, these matters are absorbed, and their passage
into the mass of blood is indicated by an increase in its proportion of albu-
minoid constituents. The greatest part of the food is absorbed by the intes-
tinal mucous membrane, and with the alimentary substances proper, a large
quantity of secreted fluid is reabsorbed. This fact is particularly marked as
regards the bile. The biliary salts disappear as the alimentary mass passes
down the intestine, and undoubtedly are absorbed, although they are so
changed that they can not be detected in the blood by the ordinary tests.
In this portion of the alimentary canal, it will be remembered, an immense
absorbing surface is provided by the arrangement of the mucous membrane
in folds, forming the valvulae conniventes, and by the presence of villi, which
are found throughout the small intestine. A certain portion of the gaseous
contents of the intestines is also taken up, although it is not easily ascer-
tained what particular gases are thus absorbed.

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 description of the thoracic duct in the middle of the six-
teenth century, by Eustachius, and finally to the discovery of the lacteals by
Asellius, in 1622, is more interesting in an anatomical than in a physiologi-
cal point of view. The history of the anatomy of the absorbent system dates
from the discovery of the thoracic duct ; but from the discovery of the lac-
teals, 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
thoracic duct, by which it is finally conveyed into the venous system. In
1650-'51, the anatomical history of the absorbent 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. Rudbeck demonstrated the ana-
tomical identity of these vessels with the lacteals. They were afterward
studied by Bartholinus, who gave them the name of lymphatics.

The idea, which dates from the discoveries of Asellius and Pecquet, that
the lacteals absorb all the products of digestion, was disproven by the exper-
iments of Magendie and of those who experimented after him upon vascu-
lar absorption. It is now known that fats in the form of a very fine emul-
sion are absorbed by the lacteals, and that these are the only constituents of
food taken up in great quantity by this system of vessels. It becomes an
important question to determine, however, whether the lacteals be not con-
cerned, to some extent, in the absorption of drinks, the albuminoids, saline
and saccharine matters, etc. This question will be taken up after a consid-
eration of certain points in the anatomy of the lymphatic system.

Physiological Anatomy of the Lacteal and Lymphatic Vessels. — The
lacteals are the intestinal lymphatics ; and during the intervals of intestinal

274

ABSORPTION— LYMPH AND CHYLE.

absorption they carry a liquid which is identical with the contents of other
lymphatic vessels. In their structure, also, the lacteals are identical with
the general lymphatics.

Owing to the exceeding tenuity of the walls of the small lymphatics and
the existence of great numbers of valves which prevent injection from the
large trunks, the anatomy of these vessels is studied with some difficulty ;
and still greater difficulty is presented in the study of the vessels of origin of
the lymphatic system in different tissues and organs. The origin of the
lymphatics in the intestinal villi has already been considered, and it remains
to study the origin of these vessels in other parts.

Comparatively recent investigations, particularly those of Yon Reckling-
hausen and his followers, have entirely changed the views of anatomists
with regard to the mode of origin of the lymphatics of various parts; but
the results of these investigations are so definite and positive and have been
so fully confirmed, that they are now almost universally adopted. Accord-
ing to these results, the lymphatics have several modes of origin.

In the connective tissues, which are so widely distributed in the body,
there are always found, irregularly shaped, stellate spaces, which communicate

FIG. 82. — Origin of lymphatics (Landois).

I. From the central tendon of the diaphragm of the rabbit (semi-diagrammatic) ; s, lymph-canals com-

municating by x with the lymphatic vessel L ; A, origin of the lymphatic by a union of lymph-
canals ; E, E, endothelium.

II. Perivascular canal.

with each other by branching canals, that can properly be called lymph-
spaces, or " juice-canals." These spaces contain a liquid and large numbers
of leucocytes. The leucocytes in these spaces may be called lymph-corpus-
cles, as they eventually find their way into the true lymphatic vessels ; but
they are thought to be white blood-corpuscles which have passed through the
stomata of the capillary blood-vessels. The connective-tissue lymph-spaces,
by certain of their branches, finally communicate with the so-called lymph-

ANATOMY OF THE LACTEAL AND LYMPHATIC VESSELS. 2T5

capillaries, through what have been regarded as the stomata of these vessels.
These anatomical data have led to the following view with regard to the re-
lations between the blood, the lymph and the tissues.

Nutrient matters are supplied to the parts by transudation through the
walls of the capillary blood-vessels; and the effete matters pass from the
lymph-spaces into the true lymphatic vessels, to be finally carried to the
venous system. In certain tissues and organs, however, such as the cornea
and fibrous membranes, the lymph -spaces or canals supply the nutrient
fluid ; and in the glands they probably supply part of the material used in
the formation of the secretions.

In the serous membranes and in other analogous structures, there are
large numbers of openings into the cavities ; and the peritoneum, pleura,
pericardium, tunica vaginalis testis, chambers of the eye, labyrinth of the in-
ternal ear and subarachnoid space are to be regarded as great lymph-sacs, the
contained fluids being lymph, without, however, presenting the so-called
lymph-corpuscles.

The relations between the blood-vessels and the smallest lymphatics are
very close in certain parts. In the cerebro-spinal centres, Eobin and His
have demonstrated a system of canals which surround the small blood-ves-
sels and are connected with the lymphatic-trunks or reservoirs described by
Fohmann and found under the pia mater. The capillary blood-vessels
thus float in surrounding vessels filled with liquid. These vessels surround-
ing the blood-vessels are called peri vascular canals, and the contained liquid
is true lymph, containing leucocytes, or lymph-corpuscles. They exceed the
blood-vessels in diameter by -3-^-5- to -^-$ of an inch (20 to 62/x). Since the
perivascular canals of the nerve-centres have been described, similar vessels
have been found in the retina and in the liver.

The true capillary lymphatics have been studied in various parts by
means of mercurial injections, but the presence of valves in the small trunks
renders it necessary to make these injections from the periphery. The ves-
sels have been injected in certain situations with mercury, by simply punct-
uring with a fine-pointed canula the parts in which the plexus is supposed
to exist, and allowing the liquid to gently diffuse itself. Following the
course of the vessels, the injection passes into the larger trunks and thence
to the lymphatic glands. The regularity of the plexus through which the
liquid is first diffused and the passage of the injection through the larger
vessels to the glands are proof that the lymphatics have been penetrated and
that the appearances observed are not the result of mere infiltration in the
tissue. It does not appear that the vessels composing this plexus vary much
in size. They are quite elastic, and after distention by injection, they return
to a very small diameter when the fluid is allowed to escape,

By the method above indicated, it is possible to inject the superficial
lymphatics of the skin, the 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 anatomical characters as the general lymphatics,

276

ABSORPTION— LYMPH AND CHYLE.

and the vessels are filled with colorless lymph during the intervals of diges-
tion. In many situations the lymphatics present in their course little, solid
structures, called lymphatic glands, although, as regards structure and office,
they are not true glandular organs. The smallest capillary lymphatics have
a diameter of about ^-J-g- of an inch (83 /*). This may be taken as their aver-
age 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

FIG. 8&.—Lyni£h:itic plexus, showing the endothelium (Belaieff).

are thinner and their diameter is greater. The vessels are lined by endo-
thelial cells, the borders of which are brought into view by the action of sil-
ver nitrate, as is shown in Fig. 83.

The smallest lymphatic vessels are by far the most abundant. 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 between two plexuses of capil-
lary lymphatics. A plexus analogous to the superficial plexus of the skin is
found just beneath the surface of the mucous membranes. These may, in-
deed, be classed with the superficial lymphatics. The deep lymphatics are
much larger and less abundant, and their origin is less easily made out.
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, con-
tain valves in great numbers. These valves, being so closely set in the ves-
sels, give to them, when filled with injection, a peculiar and characteristic
beaded appearance.

ANATOMY OF THE LACTEAL AND LYMPHATIC VESSELS. 277

The course of the lymphatics is generally direct. As they pass toward
the great trunks by which they communicate with the venous system, they

FIG 84 — Superficial lym- Fia. So.— Deep lymphatics of the skin of the FlG 86 _ game finger, lat-

phaiics of the skin of finger (Sappey). erai view, showing lym-

the palmar surface of 1, 1, deep net-work of cutaneous lymphatics ; phatic trunks connected

the finger (Sappey). 2, 2, 2, 2, lymphatic trunks connected with with the superficial net-

this net-work. * work (Sappey).

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 ves-
sels on either side. These anastomoses are quite frequent, and they generally
occur between vessels of equal size. In their course, the vessels pass through
the so-called lymphatic glands.

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 pro-
gressively enlarge as they pass on to the great lymphatic trunks. The largest
vessels that pass from the skin are -fa to -fa of an inch (1 to 2 mm.) in diame-
ter, and the larger vessels, in their course, have a diameter of ^ to -J of an
inch (2 to 3 mm.). As in the case of the smallest lymphatics of the primi-
tive plexuses, the elasticity of the walls of the vessels renders their diame-
ter greatly dependent upon the pressure of fluid in their interior. Many
anatomists have noticed that vessels which are hardly perceptible while emp-
ty are capable of being dilated to the diameter of half a line (about 1 mm.)

278

ABSOKPTION— LYMPH AND CHYLE.

or more, returning to their original size as soon as the distending fluid is

removed.

In the lymphatics of the skin, the only important peculiarity which has

not yet been mentioned is
that the vessels appear to
be very unequally distrib-
uted in different parts of
the surface. According to
Sappey, they are particularly
abundant in the scalp over
the biparietal suture, the
soles of the feet and the
palms of the hand, the fin-
gers 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 extremities, the skin
over the mammae, and around
the orifices of the mucous
passages. Sappey has in-
jected lymphatic vessels in
the anterior portion of the
forearm, the thigh and the
leg, and in the middle por-

tion of the face> altho»gh

they are demonstrated with
difficulty in these situations. If they exist at all in other portions of the cu-
taneous surface, they are not abundant.

In the mucous membranes the lymphatics are very abundant. Here are
found, as in the skin, two distinct layers which enclose between them the
entire 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. The superficial
plexus is very 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, lymphatics have been demon-

FIG. 87. — Superficial lymphatics
of the arm (Sappey).

ANATOMY 0F THE LACTEAL AND LYMPHATIC VESSELS. 279

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 difficult.

Lymphatics are found coming from the lungs in great 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 at 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 lymphatic vessels are, as a rule, more abundant than in any other parts
of the body. They are especially abundant in the testicles, the ovaries, the
liver and the kidneys.

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 lym-
phaticus dexter, which empties into the venous system at the junction of
the right subclavian with the internal jugular. This vessel is about an inch
(25'4 mm.) in length and one-twelfth to one-eighth of an inch (2 to 3 mm.)
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, the abdominal organs generally and the left half
of the body above the abdomen empty 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. Two to six vessels, called the
vasa afferentia, penetrate each gland, having first broken up into a number
of smaller vessels just before they enter. 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 afferentia. The vessels which thus emerge from the
glands are called vasa efferentia.

The lymphatics of the small intestine, called lacteals, pass from the intes-
tine between the folds of the mesentery to empty, sometimes by one and
sometimes by four or five 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 most of the lymphatic vessels empty, is a
vessel with very delicate walls and about the size of a goose-quill. It begins
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 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.

280

ABSORPTION— LYMPH AND CHYLR

It diminishes in size from the receptaculum to its middle portion and be-
comes larger again near its termination. It occasionally bifurcates near the
middle of the thorax, but the branches become reunited 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, how-
ever, a pair of semilunar valves in the duct, three-quarters of an inch to an

FIG. 89. — Stomach, intestine and mrs'intery, with the. mesenteric bloo'l-vessels mid lacteals (copied und
slightly reduced from a figure in the original work of Asellius, published in 1628).

A, A. A. A, A, mesenteric arteries and veins ; B, B, B, B, B, B, B, B, B, B, lacteals ; C, C, C, C, mesen-
tery ; D, D, stomach ; E, pyloric portion of the stomach ; F, duodenum ; G, G, G, jejunum ; H, H,
H, H, H, ileum ; I, artery and vein on the fundus of the stomach ; K, portion of the omentum.

ANATOMY OF THE LACTEAL AND LYMPHATIC VESSELS. 281

inch (19 to 25 mm.) from its termination, which effectually prevent the
entrance of blood from the venous system.

The foregoing sketch of the descriptive anatomy o£ what has been called
the absorbent system of vessels shows that they may collect fluids, not only
from the intestinal canal during digestion, but from nearly every tissue and
organ in the body, and that these fluids are finally 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 the
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 not been very satisfactory. It is
supposed, however, that the
vessels here consist of a single
coat, resembling, in this re-
gard, the capillary blood-ves-
sels. Belaieff has described in
the capillary lymphatics of the
penis a lining of endothelial
cells arranged in a single layer.
These cells are oval, polygonal,
fusiform or dentated, with
their long diameter in the di-
rection of the axis of the ves-
sels.

In all but the capillary lym-
phatics, although the walls are
very thin, three distinct coats
can be distinguished. The in-
ternal coat consists of an elas-
tic membrane lined with ob-
long, endothelial cells. This
coat readily gives way when
the vessels are forcibly dis-
tended. The middle coat is
composed of longitudinal fibres
of connective tissue, with deli-
cate elastic fibres, and non-
striated muscular fibres ar-
ranged transversely. The external coat is composed of the same structures
as the middle coat, but most of the fibres are arranged longitudinally. In
this coat the muscular fibres do not form a continuous sheet, but are col-
lected into separate fasciculi, which have a direction either longitudinal or

FIG. 90.— 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.

282

ABSORPTION— LYMPH AND CHYLE.

oblique. The fibres of connective tissue are very abundant and unite the
vessels to the surrounding parts. The internal and the middle coats 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 lym-
phatics, and the existence of vaso-motor nerves is probable.

The walls of the lymphatic vessels are very closely adherent to the sur-
rounding tissues ; so closely, indeed, that even a small portion of a vessel is
detached with great difficulty, and the vessels, even those of large size, can
not be followed out and isolated for any considerable distance.

In all the lymphatic vessels, beginning a short distance from their plexus
of origin, are semilunar valves, generally arranged in pairs, with their con-
cavities looking toward the larger trunks. These folds are formed of the
middle and inner coats ; but the fold formed from 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 directly to the vessel. The valves are
most abundant in the superficial vessels. The distance between the valves is
one-twelfth to one-eighth of an inch (2 to 3 mm.), near the origin of the ves-
sels, and one-quarter to one-third of an inch (6 to 8 mm.), in their course.
In the lymphatics situated between the muscles the valves are less abun-
dant. 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 abundant 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 tho reflux
of fluids when the vessels are subjected to pressure.

The lymphatics are very elastic; and it is generally
admitted that the larger vessels and those of medium size
are contractile, although the action of their muscular fibres,
like that of all fibres of the non-striated variety, is slow
and gradual.

One of the most important points in connection with
the physiological anatomy of the lymphatic vessels is the
question of the existence of orifices in their walls, which
might allow the passage of solid particles or of emulsions.
Anatomical observations have indicated the existence of
stomata, of variable size and irregular shape, in the small-
est vessels ; and a strong argument in favor of the existence of these orifices
has been the fact of the actual passage, through the walls of the vessels, of
fatty particles, the entrance of which can not be explained by the well known
laws of endosmosis. The anatomical evidence of the existence of openings
is derived mainly from preparations stained with silver nitrate, It is assumed

FIG. 91.— Valves of
the lymphatics
(Sappey).

ANATOMY OF THE LACTEAL AND LYMPHATIC VESSELS. 283

that silver nitrate stains the solid parts of tissues and the borders of the en-
dothelial cells, and that non-nucleated areas which do not present any stain-
ing are necessarily open. In preparations of the lymphatics, the solution of
silver is seen staining the tissues and the borders of the cells lining the ves-
sels ; but there are areas between these cells where no staining is observed
and in which no nuclei are brought out by staining with carmine.

Lymphatic Glands. — In the course of the lymphatic vessels, are small,
lenticular bodies, called lymphatic glands. The number of these is very
great, although it is estimated with difficulty, from the fact that many of
them are very small and are
consequently liable to escape
observation. It may be stated
as an approximation that there
are six or seven hundred lym-
phatic glands in the body.
Their size and form are also
very variable within the lim-
its of health. They generally
are flattened and lenticular,
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 and corresponding
with the superficial lymphatic
vessels, and a deep set, corre-
sponding with the deep ves-
sels. The superficial glands
are most abundant 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 abundant 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 empty into the great lymphatic trunks, and most
of them pass through several glands in their course.

The perfect, healthy glands are of a grayish-white or reddish color, of
about the consistence of the liver, presenting a hilum where the larger blood-
vessels enter and the efferent vessels emerge, and are covered, except at the
hilum, with a delicate membrane composed of inelastic fibres, a few elastic
fibres and non-striated muscular fibres. Their exterior is somewhat tuber-

FIG. ^.—Lymphatics and lymphatic glands (Sappey).
1, 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
lymphatic glands are seen in the course of the vessels.

284

ABSORPTION— LYMPH AND CHYLE.

culated, from the projections of the follicles just beneath the investing mem-
brane. 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 one-
sixth to one-fourth of an inch (4 to 6 mm.) in thickness in the largest
glands. The medullary portion, which comes to the surface at the hilum, is
lighter colored and coarser than the cortical substance. Throughout the
gland, are found delicate fasciculi of fibrous tissue connected with the in-
vesting 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 -gfa of an
inch (100 ft.) in diameter, filled with a fluid and with cells like those con-
tained in the solitary glands of the intestines and the patches of Peyer. These
follicles do not seem to occupy the medullary portion of the glands, which,
according to Kolliker, is composed chiefly of a net- work of lymphatic capil-
laries, mixed with rather coarse bands of fibrous tissue. The follicular struct-
ures in the lymphatic glands resemble the closed follicles in the mucous mem-
brane of the intestinal canal and the Malpighian bodies of the spleen.

According to Von Recklinghausen, there exist in the substance of the
lymphatic glands great numbers of lymph-spaces or canals, which are proba-
bly lined with endothelium ;
and these spaces communicate
with the efferent vessels, by
the stomata. The afferent
vessels, two to six in number,
penetrate the gland, and prob-
ably empty their contents into
the lymph-spaces. The lymph
is then collected from the
lymph - spaces, by the vasa
efferentia, one to three in
number, which are always
larger than the afferent ves-
sels.

•The lymphatic glands are
supplied with blood, some-
times by one but generally by
several small arteries, which
penetrate at the hilum. These
vessels pass directly to the
medullary portion and there
break up into several coarse
branches to be distributed to the cortical substance, where they ramify in a
delicate, capillary net- work with rather wide meshes, in the closed follicles
found in this portion of the gland. This capillary plexus also receives
branches from small arterial twigs which penetrate the capsule of the gland

FIG. 93.— Different varieties of lymphatic glands (Sappey).

ABSORPTION BY THE LACTEALS. 285

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.

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 uses of the lymphatic glands are somewhat obscure. They are sup-
posed, however, to have an important office in the elaboration of the corpus-
cular 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 corpuscles, while the large trunks and the efferent vessels contain
them in large numbers.

Absorption of Albuminoids by the Lacteals. — Comparative analyses of the
lymph and chyle always show in the latter fluid an excess of albuminoid
matters ; and it is natural to infer that the excess of nitrogenized matters in
the chyle is due to absorption of albuminoids from the intestinal canal.
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 Rees, who found that the chyle
contained about three times as much albumin and fibrin as the lymph.
While by far the greatest 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 regarding the absorption of albuminoids applies 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 determined
by Colin. While the products of the digestion of saccharine and amylaceous
matters are taken up mainly by the blood-vessels, a small quantity is also ab-
sorbed by the lacteals. In the comparative analyses of the chyle and lymph by
Rees, the proportion of inorganic salts was found to be considerably greater in
the chyle. The great excess in the quantity of blood coming from the intes-
tine, and the rapidity of its circulation, as compared with the chyle, will ex-
plain the more rapid penetration by endosmosis of the soluble products of di-
gestion.

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 proved by experiments of a most positive character. When an ani-
mal has taken solid food only and is killed during digestion, the thoracic duct
contains a very small quantity of chyle ; but when the animal has taken liq-

20

286 ABSORPTION— LYMPH AND CHYLE.

uids with the food, the thoracic duct and the lacteals are very much distended
(Leuret and Lassaigne). In an experiment by Ernest Burdach, a dog was de-
prived of food and drink for twenty-four hours, after which he was allowed to
drink water, and in addition, half a pound(227 c. c.) was injected into the
stomach. The animal was killed a half-hour after, and the thoracic duct
was found engorged with watery lymph, which contained a very few lymph-
corpuscles.

Aside from the entrance of gases into the blood from the pulmonary sur-
face, physiological absorption is almost entirely confined to the mucous mem-
brane of the alimentary canal. It is true that liquids may find their way in-
to the circulation through the skin, the lining membrane 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 occasional or accidental and is not connected with the gen-
eral 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 disassimilation are taken up
by what is called interstitial absorption, and are carried by the blood to the
proper organs, to be excreted. It seems probable that the vessels of these
parts would also be capable of absorbing soluble foreign substances ; 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 vascular
parts are permeable.

Absorption by the Skin. — It is universally admitted that absorption can
take place from the general surface, although at one time this was a question
much discussed by physiologists. The proofs, however, of the entrance of
certain 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.
The question which is of most importance in this connection relates to the
normal action 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, nevertheless, facts which render it certain that water may be absorbed
by the skin. In a series of experiments by Collard de Martigny, in 1821, it
was shown 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 hermetically 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 disappeared. In a series of
observations upon the absorption of water and soluble substances, by Wille-

ABSORPTION BY THE SKIN ETC. 287

min (1863), it was shown 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.

It has been frequently remarked that the sensation of thirst is always least
pressing in a moist atmosphere, and that it may be allayed 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 pro-
portion of fluids in the body with a less amount of drink than ordinary ; but
one could hardly account for an actual alleviation of thirst by immersion of
the body in water, unless it were 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
he 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 can not 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 circumstance, 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 nour-
ishment."

Absorption by the Respiratory Surface. — Animal and vegetable emana-
tions may be taken into the blood by the lungs and produce certain well
marked pathological conditions. Many contagious diseases are propagated
in this way, as well as some fevers and other general diseases which are not
contagious. With regard to certain poisonous gases and volatile matters,
the effects of their absorption by the lungs are even more striking. Carbon
monoxide and arsenious hydride produce death almost 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 in-
halation of their vapors ; and the serious effects produced by the emanations
from lead or mercury, in persons who work in these articles, are well known.
Not only have vapors introduced in this way been recognized in the blood,
but many of the matters thus absorbed are excreted by the kidneys and may
be detected 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 ad-
ministered in this way manifest their peculiar effects with great promptness.
Experimenters on this subject have shown the facility with which liquids
may be absorbed from the lungs and the air-passages, but it must be remem-
bered that the natural conditions are never such as to admit of this action.
The normal office of the lungs is to absorb oxygen and sometimes a little ni-

288 ABSORPTION— LYMPH AND CHYLE.

trogen 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, showing absorption from closed cavities, the areolar tissue, the
muscular and nervous tissues, the conjunctiva and other parts, are sufficient-
ly well known. In cases of eifusion of serum into the pleural, peritoneal, per-
icardial 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 tis-
sue are generally removed by absorption. . In cases of penetration of air into
the pleura or the general areolar tissue, absorption likewise takes place ; show-
ing 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 tis-
sue may become entirely or in part absorbed. It is true that these are path-
ological conditions, but in the closed cavities, 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 hy-
podermatic method is a familiar evidence of the facility with which soluble
substances are taken into the blood, when introduced beneath the skin.

Under some conditions, 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 secretion is not interrupted. Cer-
tainly, when the duct is in any way obstructed, absorption of a portion of the
bile takes place, as is shown 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, also, that some of the watery por-
tions 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
reabsorption is ordinarily very slight. Absorption may take place from the
ducts and the parenchyma of glands, although this occurs chiefly when for-
eign 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 considerable 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 fats are taken up by the lacteals and
may be absorbed in small quantity by the blood-vessels.

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. During the digestion of fat,
these cells become filled with fatty granules (Goodsir). Funke, in his atlas of
physiological chemistry, figures the appearances of the intestinal epithelium

ABSORPTION OF FATS AND INSOLUBLE SUBSTANCES. 289

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 has not been demonstrated exactly how the fatty particles penetrate the
epithelium of the villi, but the fact of such penetration is undoubted. From
the epithelium, the particles of emulsion
pass into the substance of the villi —
probably into the lymph-spaces and ca-
nals— and from these they readily find
their way into the lymphatic capillaries.
It has been shown that fatty emulsion
will pass more easily through porous
septa that have been moistened with
bile; and it is probably in this way
mainly that the bile aids in the passage
of the fine particles of fat into the lac-
teals.

As a general law, insoluble substan-
ces, with the exception of the fats, are
never regularly absorbed, no matter how
finely they may be divided. The appar-
ent exceptions to this are mercury in a state of minute subdivision like
an emulsion, and carbonaceous particles. As regards mercury, it is well
known that minute particles in the form of unguents may be introduced into
the system by prolonged frictions ; but this can not be taken 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

FIG. 94.— Epithelium of the small intestine of
the rabbit (Funke).

FIG. 95.— Epithelium from the duodenum of a
rabbit, two hours after having been fed
with melted butter (Funke).

FIG. 96.— Villi filled with fat, from the small
intestine of an executed criminal, one hour
after death (Funke).

into the alimentary canal ; but the experiments of Mialhe with pulverized
charcoal, and particularly those of Berard, Robin and Bernard with lamp.

290 ABSORPTION— LYMPH AND CHYLE.

black introduced into the intestinal canal of 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 dis-
covered 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.

VARIATIONS AND MODIFICATIONS OF ABSORPTION.

Very little is known concerning the variations in lacteal or lymphatic ab-
sorption ; 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 con-
ditions 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 densi-
ties 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 potassium nitrate and of sodium sul-
phate, 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 curare poison and most of the venoms are remark-
able exceptions to this rule. In a series of experiments upon the absorption
of curare, Bernard has shown that this poison, which is absorbed so readily
from wounds or when injected 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 curare is introduced into the stomach of a fasting animal. This pecul-
iarity in the absorption of many of the animal poisons has long been ob-
served ; and it is well known that the flesh of animals poisoned with curare
may be eaten with impunity. It is curious, however, to see an animal carry-
ing in the stomach without danger a fluid which would produce death if in-
troduced under the skin ; and the explanation of this is not readily apparent.
The poison is not neutralized by the digestive fluids, for curare digested for
a long time in gastric juice, or taken from the stomach of a dog, is found to
possess all its toxic properties. This may be shown by poisoning a pigeon
with curare drawn by a fistula from the stomach of a living dog (Bernard).
If the absorption of this poison be recognized simply by its effects upon the
system, it must be assumed that during digestion, it can not be absorbed by
the mucous membrane of the stomach and small intestine, notwithstanding
its solubility.

VARIATIONS AND MODIFICATIONS OF ABSORPTION. 291

It has been shown that liquids which immediately disorganize the tissues,
such as concentrated nitric or sulphuric acid, can not be absorbed. Another
important peculiarity in absorption is that solutions which readily coagulate
the albumen of the circulating fluids are absorbed very slowly (Miahle).
This is explained by the supposition that there is a coagulation of the albu-
minous fluids with which the absorbing membrane is permeated, which in-
terferes with the passage of liquids. These substancs are nevertheless taken
up by the blood-vessels, though rather slowly.

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 generally 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 produce their more
speedy action upon the system.

The rapidity of the circulation has an important influence in facilitating
absorption, and this process is generally active in proportion to the vascu-
larity of different parts. During intestinal absorption, the increase in the
activity of the circulation in the mucous membrane is very marked and un-
doubtedly has an influence upon the rapidity with which the products of di-
gestion are taken up by the blood.

Influence of the Nervous System on Absorption. — It is certain that ab-
sorption, especially in the stomach, is subject to certain variations, which can
hardly be dependent upon anything but nervous action. "Water and other
liquids, which usually are readily absorbed 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 experiments of Bernard and others upon the vaso-motor nerves,
by the action of which the supply of blood in different parts is regulated,
point out a line of experimentation which would probably throw much light
upon some of the important variations in absorption. When it is remem-
bered that the small arteries may become so contracted under the influence
of the vaso-motor nerves that their caliber is almost obliterated, of course re-
tarding in a corresponding degree the capillary and venous circulation in the
parts, and again, that the same vessels may be so dilated as to admit to a par-
ticular part many times more blood than it ordinarily receives, it becomes
apparent that absorption may be profoundly affected through this system of
nerves. It has been ascertained that while a section of some of the nerves
distributed to the alimentary canal will slightly retard the absorption of the
poisonous substances, the process is never entirely arrested.

IMBIBITION AND ENDOSMOSIS.

If liquids pass through the substance of an animal membrane, it is evident
that the membrane itself must be capable of taking up a certain portion by
imbibition ; and this must be considered as the starting-point in absorption.

202 ABSORPTION-LYMPH AND CHYLE.

Imbibition is, indeed, a property common to all animal tissues. It is a well
known fact, however, that the tissues do not imbibe all solutions with the
same degree of activity. Distilled water is the liquid which is always taken
up in greatest quantity, and saline solutions enter the substance of the tissues
in an inverse ratio to their density. This is also the fact with regard to
mixtares of alcohol and water, imbibition always being in an inverse propor-
tion to the quantity of alcohol present in the liquid. Among the other con-
ditions which have a marked influence upon imbibition, is temperature. It
is a familiar fact that dried animal membranes 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 a considerable in-
crease at a moderately elevated temperature. While nearly all the structures
of the body, after desiccation, will imbibe liquids, the membranes through
which the processes of absorption are most active are, as a rule, most easily
permeated ; and 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.

Mechanism of the Passage of Liquids through Membranes. — The passage
of liquids through membranes is called osmosis. In the case of two liquids
passing in opposite directions, the stronger current is called endosmotic and
the weaker current is called exosmotic. In the passage of liquids into the
vessels, in physiological absorption, the process is generally called endosmosis.
The attention of physiologists was first directed to these phenomena by the
researches of Dutrochet, published in 1826.

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 takes place in
only one direction.

2. That the liquids be miscible with each other and be differently consti-
tuted. Although it is found that the currents are most active when the
liquids are of different densities, this condition is not indispensable ; for cur-
rents 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 when-
ever 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 absorbed, and in this condition, they
are capable of " wetting " the walls of the blood-vessels. All the liquids ab-
sorbed are capable, also, of mixing with the plasma of the blood. What
makes this application still more complete, is the behavior of albumin in
endosmotic experiments. In physiological absorption, there is always a great
predominance of the endosmotic current, and there is very little transudation,

IMBIBITION AND ENDOSMOSIS.

or exosmosis, of the albuminoid constituents of the blood. On the other
hand, there is a constant absorption of peptones, which are destined to be
converted into the albuminoid constituents of the blood.

Recognizing the fact that albumin is capable of inducing a more power-
ful 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 peptones, or albumin
mixed with gastric juice, pass through animal membranes with great facility.
The experiments by which these facts are demonstrated 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 is rendered evident by the projection of the distended mem-
branes ; but although the surrounding liquid becomes alkaline and the appro-
priate tests reveal the presence of some of the inorganic constituents of the
egg, the presence of albumin can not be detected. When the contents of the
egg are replaced by the serum of the blood, the same result follows. " After
six or eight hours of immersion, the serum had yielded to the water in the ves-
sel all its saline elements, chlorides, sulphates, phosphates, which were easily
recognized by their peculiar reactions, but not a trace of albumin " (Dutrochet).

A very simple apparatus for illustrating endosmotic action can be con-
structed in the following way : Remove carefully a circular portion, about
an inch (25-4 mm.) 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 small, glass tube is then
introduced through an opening in the shell and mem-
branes of the other end of the egg, and is secured in a
vertical position by wax or plaster of Paris, the tube
penetrating the yelk. The egg is then placed in a wine-
glass partly filled with water. In the course of a few
minutes the water will have penetrated the exposed
membrane, and the yelk will rise in the tube.

The force with which liquids pass through mem-
branes, called endosmotic or osmotic force, is to a great
degree dependent upon the influence of the membranes
themselves. This influence is always purely physical, in
experiments made out of the body ; and physiological ab-
sorption can be explained, to a certain extent, by the same
laws. It must be remembered, however, that the prop-
erties of organic structures, which are manifested only in
living bodies, are capable of modifying these physical phe-
nomena in a remarkable degree. For example, all living
tissues are capable of selecting and appropriating from
the nutritive fluids the materials necessary for their regeneration ; and the
secreting structures of glands also select from the blood certain constituents
which are used in the formation of their secretions. These phenomena and

294 ABSORPTION -LYMPH AND CHYLE.

their modifications through the nervous system can not be fully explained.
This is true, also, of many of the phenomena of absorption and their modi-
fications, which are probably dependent upon the same kind of action.

It js not necessary to assume the existence of infinitely small 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 ani-
mal membrane, the mechanism of the endosmotic 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 surface 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.

In no experiments performed out of the body, can the conditions favor-
able to the passage of liquids through membranes in accordance with purely
physical laws be realized as they exist in the living organism. The great ex-
tent of the absorbing surfaces ; the delicacy and permeability of the mem-
branes ; the rapidity with which substances are carried on by the torrent of
the circulation, as soon as they pass through these membranes ; the uniform-
ity of the pressure, notwithstanding the penetration of liquids ; all these
favor the physical phenomena of absorption in a way which can not be imi-
tated in artificially constructed apparatus. Within the blood-vessels, the
albuminoid matters exist in a form which does not permit them to pass
through membranes, while the peptones are highly osmotic. The sugars,
also, pass through the walls of the vessels with facility, as well as various
salts and medicinal substances in solution. The fats, as has been stated, pass
mainly into the lacteals, by a process which has already been described and
which can not be fully explained by the laws of endosmosis.

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 great quan-
tity of this liquid which is continually passing into the blood are of com-
paratively recent date.

The first successful experiments in which the lymph and chyle were
obtained in quantity 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 junction 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 ruminants, were

PROPERTIES AND COMPOSITION OF LYMPH. 295

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, 105-3
Ibs. (47,963 grammes) ; and he stated that a very much greater quantity can
be obtained by operating upon ruminants of larger size.

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 produced in the twenty-four hours in a man weighing one
hundred and forty- three pounds (65 kilos.) is about 6' 6 pounds (3,000
grammes). And again, reasoning from experiments made upon dogs thir-
teen 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 about 4-4 pounds (2,000 grammes). These estimates can be accepted
only as approximate, 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 physi-
ological variations in the quantity of lymph. Collard de Martigny found
the lymphatics always distended with fluid in dogs killed after two days of
total deprivation of food. This condition continued during the first week
of starvation ; but after that time, the quantity in the vessels 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 lymphat-
ics 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 transpar-
ent and colorless or of a slightly yellowish 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. Microscopical examination
shows that this reddish color is dependent upon the presence of a few red
blood-corpuscles, which are entangled in the clot as the lymph coagulates,
thus accounting for the deepening of the color when the fluid has been
allowed to stand.

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. According to Robin, the specific gravity of the defibrinated serum of
lymph is 1009. In analyses by Dahnhardt, of the lymph taken from dilated
vessels in the leg, in the human subject, the specific gravity was 1007.

A few minutes after discharge from the vessels, both the lymph and
chyle undergo coagulation. This process, as regards the chemical changes

296 ABSORPTION— LYMPH AND CHYLE.

involved, is identical with the coagulation of the blood, in which the leuco-
cytes play an important part. 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. The clot is tolerably consistent, but
there is never any spontaneous separation of serum (Colin). This may be
the fact with regard to the lymph and the chyle of the large ruminants,
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, pre-
cisely like coagulated blood, expressing a considerable quantity of serum. In
one instance, in the dog, the volume of serum, after twenty-four hours of re-
pose, was about twice that of the contracted clot.

Although many analyses have been made of lymph from the human sub-
ject, the conditions under which the fluid has been obtained render it proba-
ble that in the majority of instances it was not entirely normal. It will be
necessary, therefore, to compare these analyses with observations made upon
the lymph of the inferior animals ; as in the latter, this fluid has been col-
lected under conditions which leave no doubt as to its normal character. In
the experiments of Colin especially, the fluids taken from the thoracic duct
during the intervals of digestion undoubtedly represented the normal, mixed
lymph collected from nearly all parts of the body ; and the operative proced-
ure in the large ruminants is so simple as to produce little if any general dis-
turbance. The following 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

Albumin 28'0

Fatty matter 0'4

Sodium chloride 5*0

Sodiuni carbonate, sodium phosphate and sodium sulphate 1*2

Calcium phosphate 0-5

1,000-0

The proportions given in the table are by no means invariable, the differ-
ences in coagulability indicating differences in the proportion of fibrin-fac-
tors, and the degree of lactescence showing great variations in the quantity
of fatty matters. The table may be taken, however, as an approximation of
the average composition of the lymph of these animals, during the intervals
of digestion.

The analysis of human lymph which seams 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 dilatation 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 considerable quantity.

PROPERTIES AND COMPOSITION OF LYMPH. 297

When an opening existed, the discharge of fluid could be arrested at will by
flexing the trunk upon the thigh. Gubler and Quevenne made 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., or 39° C) 3-82 9-20

Hydro-alcoholic extract (containing sugar, and leaving,
after incineration, sodium chloride, with sodium phos-
phate and sodium carbonate) 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, however, from a
comparison of the two analyses by Gubler and Quevenne, that the composi-
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 albuminous matter mentioned by other chemists.

The distinctive characters of the different constituents of the lymph do
not demand 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 that of the blood, the great excess of solid
constituents in the latter fluid is at once apparent.

In nearly all analyses the organic nitrogenized constituents have been
found to be very much less in the lymph than in the blood. This is gener-
ally most marked with regard to the fibrin-factors ; but as before stated,
the proportion of all these substances is quite variable. On account of this
deficiency, lymph is much inferior to the blood in coagulability, and the
coagulum, when it is formed, is soft and friable. There does not appear,
however, to be any actual difference between the coagulating constituents of
the lymph and of the blood.

Fatty matters have generally been found to be more abundant in the
lymph than in the blood ; but their proportion is even more variable than
that of the albuminoid constituents.

Very little remains to be said concerning the ordinary inorganic constitu-
ents 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 a small proportion of iron is given in the
analyses by Gubler and Quevenne.

298

ABSORPTION— LYMPH AND CHYLE.

These facts indicate a remarkable correspondence in composition between
the lymph and the blood. All of the constituents of the blood, except the
red corpuscles, 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.

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 excrementi-
tious substance is taken up from the tissues. Although urea always exists in
the blood, its quantity is less than in the lymph.

According to Ludwig and Hammersten, the lymph of the dog contains
about forty parts per hundred in volume of carbon dioxide, of which seven-
teen parts may be extracted by the air-pump and twenty-three parts, by acids.

In addition, the lymph contains a trace
of oxygen and one or two parts of ni-
trogen.

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 cor-
puscular elements known as lymph-cor-
puscles. These exist, not only in the
clear lymph, but in the opaque fluid
contained in the lacteals during absorp-
tion. They are now regarded as identi-
cal with the white blood-corpuscles, or
leucocytes. Eight thousand two hun-
dred leucocytes have been counted in
0-061 cubic inch (1 c. c.) of lymph from
a dog (Ritter).

The leucocytes found in the lymph and chyle are rather less uniform in
size and general appearance than the white corpuscles of the blood. Their
average diameter is about -g-^r of an inch (10 /u,.) ; but some are larger, and
others are as small as -g-gVo °* an ^ncn (5 /*•)• Some of these corpuscles are
quite clear and 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 as in the blood, and
frequently they are found collected in masses in different parts of the lym-
phatic system. In all other regards, these bodies present the same charac-
ters as the leucocytes of the blood, and they need not, therefore, be farther
described.

In addition to the ordinary leucocytes and a certain number of fatty gran-
ules, a few small, clear globules or granules, about y^r of an inch (3-3 p.)

FIG. 98.— Chyle taken from the lacteals and
thoracic duct of a criminal executed dur-
ing digestion (Funke).

This figure shows the leucocytes and excessive-
ly fine granules of fatty emulsion.

ORIGIN AND USES OF THE LYMPH. 299

/

in diameter, called sometimes globulins, are almost constantly present in the
lymph. These are insoluble in ether and acetic acid but are dissolved by
ammonia. They were regarded by Robin as a variety of leucocytes and
described by him as free nuclei.

Origin and Uses of the Lymph. — There can hardly be any doubt concern-
ing the source of most of the liquid portions of the lymph, for they can bo
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 anatomical reason why the water, mixed
with albuminoid matters and holding salts in solution, should not pass from
the blood into the lymphatics ; and this is rendered nearly certain by the fact
that the lymphatics surround many of the blood-vessels. In comparing the
composition of the lymph with that of the plasma of the blood, it is seen that
the constituents of these fluids are nearly if not quite identical ; the only
variations being in their relative proportions. This is another 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 can not be derived from the blood, for its proportion is greater in the
lymph, notwithstanding the fact 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 office of the lymph are not very many. From the composition of
this fluid, its mode of circulation, and the fact that it is being constantly dis-
charged into the blood, it would not seem to have an important use in the
active processes of nutrition. The experiments of Collard de Martigny sus-
tain this view, inasmuch as the quantity and the proportion of solid constitu-
ents 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 disassimilation, is undoubt-
edly taken up by the lymph and conveyed in this fluid to the blood. It
remains for future investigations to determine whether other excrementitious
matters may not be taken up from the tissues in the same way — a question
of importance in its relations to the mechanism of excretion.

What is positively known with regard to the uses 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 to nutrition are not under-
stood. The same may be said of sugar, which is a constant constituent of
the lymph. Urea and perhaps other excrementitious matters are taken up
from the tissues by the lymph, and are discharged into the blood, to be re-
moved from the system by the appropriate organs.

Properties and Composition of Chyle. — During the intervals of digestion,
the intestinal lymphatics and the thoracic duct carry ordinary lymph ; but

300 ABSORPTION-LYMPH AND CHYLE.

as soon as absorption of alimentary matters begins, certain nutritive matters
are taken up in quantity by these vessels, and their contents are known under
the name of chyle.

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 con-
centrated acid, the process employed by Barreul to develop the characteristic
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 reaction of the chyle is either alkaline or neutral. Dalton noted an
alkaline reaction 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 Lassaigne 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, arid 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 food. Colin found the chyle milky in the carnivora, espe-
cially after fats had been taken in quantity ; while in dogs that were nour-
ished with articles containing but little fat, its appearance was hardly lac-
tescent. Tiedemann and Gmelin found the chyle almost transparent in
herbivora fed with hay or straw. They also observed that the chyle was
nearly transparent in dogs fed with liquid albumen, fibrin, gelatine, starch
and gluten ; while it was white in the same animals fed with milk, meat,
bones etc.

It is impossible to give an accurate 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 large 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. No attempt will be made, therefore, 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, undergoes
coagulation. Different specimens of the fluid vary very much as regards the
rapidity with which coagulation takes place. The chyle from the thoracic

PROPERTIES AND COMPOSITION OF CHYLE. 301

duct generally coagulates in a few minutes. The first portion of the fluid
collected from the human subject by Rees — the chyle was collected in this
case in two portions — coagulated in an hour. Received into an ordinary
glass vessel, the chyle generally separates more or less completely after coagu-
lation, into clot and serum. The serum 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
contains, also, a number of leucocytes and organic granules.

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 defi-
nite results that can be applied to the human subject. It is usual to find the
chyle fluid in the lacteals and in the thoracic duct for many hours after
death ; but it soon coagulates after exposure 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 opportunity of taking the fluid
from the thoracic duct in cases of sudden death during digestion ; 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 analy-
sis. In operating upon the ox, however, Colin has succeeded in collecting
pure chyle in considerable quantity.

In the analysis by Rees, 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 to the moment of his death.
The evening before, he ate two ounces (56-7 grammes) of bread and four
ounces (113-4 grammes) of meat. At seven 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 (22-2 c. c.)
of milky chyle were collected. The fluid was neutral and had a specific
gravity of 1024. The following was its approximate composition :

COMPOSITION OF HUMAN CHYLE FROM THE THORACIC DUCT.

Water 904-8

Albumin, 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 phos-
phates and oxides of iron 4'4

Fatty matters 9-2

1,000-0
21

302 ABSORPTION— LYMPH AND CHYLE.

Of the constituents of the chyle not given in the ordinary analyses, the
most important are the urea, which in all probability is derived exclusively
from the lymph, and sugar, coming from the saccharine and amylaceous arti-
cles of food during digestion.

The difference in chemical composition between the unmixed lymph and
the chyle is illustrated in a comparative examination of these two fluids taken
from a donkey. The fluids were collected by 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 Rees :

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 i- ( Alkaline chlorides, sulphates and carbonates, with ) nii
oaits, •( i_ . i. j • i « • r •"*

( traces of alkaline phosphates and oxide of iron.

1,000-00 1,000-00

The above analyses show a very marked difference in the proportion of
solid constituents in the two fluids. The chyle contains about three times as
much albumen and fibrin as the lymph, with a 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 admixt-
ure 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 con-
stituents as the plasma of the blood.

The presence of sugar in the chyle was first mentioned by Brande, who
described it, however, rather indefinitely. Glucose was first distinctly recog-
nized 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 contrasted with the lymph is due to the presence of a large number
of very 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 di-

MOVEMENTS OF THE LYMPH AND CHYLE. 303

minishes progressively from the smaller to the larger vessels, on account
of the constant admixture of lymph. The size of the granules is pretty
uniformly ^fg-g- to ysiur o* an *nch (1 to 2 /*). 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 composed of
the different varieties of fat which are taken as food, mixed with each
other in various proportions. The ordinary corpuscular elements of the
lymph, leucocytes and globulins, are also found in variable quantity in the
chyle.

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 evidently due to a variety of causes. As regards those constitu-
ents which are derived directly from the blood, the lymph may be said to un-
dergo 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 by the communications of the lymphatic system with the
great veins. The constituents of the lymph, however, are not derived entirely
from the blood, a considerable portion resulting from interstitial absorption
in the general lymphatic system ; and the chyle contains certain nutritive
matters absorbed by the lacteal vessels. These are, physiologically, the most
important constituents of the lymph and chyle ; and they are taken up sim-
ply 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 movements of these fluids in the lymphatic vessels, there is no difference
between the imbibition of new matters 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 can not 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 very
great and is independent of the action of the heart, being due entirely to the
processes 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 con-
tain 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 momentary 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 intermit-
tent. 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

304 ABSORPTION-LYMPH AND CHYLE.

act of expiration ; and an impulse synchronous with the pulsations of the
heart has frequently been observed.

The fact that the lymphatic system is never distended, and the existence
of the valves, by which different portions may become isolated, render it im-
possible 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 degree of distention of the thoracic duct is very variable,
its capacity not infrequently being many times increased during active ab-
sorption. 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 penetrate these vessels is very great. This is illustrated by the ex-
periment of tying the thoracic duct ; for after this operation, unless com-
municating vessels exist by which the fluids can be discharged into the
venous system, their accumulation is frequently sufficient to rupture the
vessel.

The general rapidity of the current in the lymphatic vessels has never
been accurately estimated. As a natural consequence of the variations in the
distention of these vessels, the rapidity of the circulation must be subject to
constant modifications. Beclard, making his calculation from the experi-
ments of Colin, who noted the quantity of fluid discharged in a given time
from fistulous openings into the thoracic duct, estimated that the rapidity of
the flow in this vessel was about one inch (25-4 mm.) per second. This esti-
mate, however, can be only approximate ; 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.

Various influences combine to produce the movements of fluids in the
lymphatic system, some being constant in their operation, and others, inter-
mittent or occasional. These will be considered, as nearly as possible, in the
order of their relative importance.

The forces of endosmosis and transudation are undoubtedly the main
causes of the lymphatic circulation, more or less modified, however, by influ-
ences 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 operation, as is seen in cases of ligation of the
thoracic duct, a procedure which must finally abolish all other forces which
aid in producing the lymphatic circulation. When the receptaculum chyli
is ruptured 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.

The situations in which the endosmotic force originates are at the periph-
ery, where the single wall of the vessels is very thin, and where the extent of
absorbing surface is large. If liquids can penetrate with such rapidity and

MOVEMENTS OF THE LYMPH AND CHYLE. 305

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
valves in the lymphatic system effectually prevent any backward current.

In describing the anatomy of the lymphatic system, it has already been
stated that the large vessels and those of medium size are provided with
non-striated muscular fibres and are endowed with contractility. This fact
has been demonstrated by physiological as well as anatomical investigations.
Beclard stated that he often produced contractions of the thoracic duct
by the application of the two poles of an inductive apparatus. It is not un-
common 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 contractions in the lymphatic system, it
is probable that the vessels contract upon their contents, when they are un-
usually distended, and thus assist the circulation, the action of the valves
opposing a regurgitating current. This action, however, can not have any
considerable and regular influence upon the general current.

Contractions of the ordinary voluntary muscles, compression of the
abdominal organs by contraction of the abdominal muscles, peristaltic move-
ments of the intestines and pulsations of large arteries situated against the
lymphatic trunks, particularly the thoracic aorta, are all capable of increas-
ing 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 there is nothing to be added regarding this action to what has
already been said on this subject in connection with the description of the
venous circulation.

Increase in the flow of chyle in the thoracic duct, as the result of com-
pression of the abdominal organs or of kneading the abdomen with the
hands, was observed by Magendie, 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 exper-
iments on the thoracic duct, and he described 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.

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

306 SECRETION.

Haller there is a full discussion of the influence of the diaphragm and of the
movements of the thorax upon the circulation of chyle. Colin always found
marked impulses in the flow of chyle from a fistula into the thoracic duct,
Avhich were synchronous with the movements of respiration. With each act
of expiration the fluid was forcibly ejected, and with inspiration 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 impulses were sometimes so decided, that the pulsations were
repeated in a long elastic tube attached to the canula for the purpose of col-
lecting the fluid.

From all these considerations, it is evident that although there are many
conditions capable of modifying the currents in the lymphatic system, the
regular flow of the lymph and chyle depends chiefly upon the vis a teryo ;
but the vessels themselves sometimes undergo contraction, and they are sub-
ject to occasional compression from surrounding parts, which, from the exist-
ence of valves in the vessels, must favor the current toward the venous sys-
tem. The alternate dilatation and compression of the thoracic duct with
the acts of respiration likewise aid the circulation, and they are more effi-
cient than any other force, except the vis a tergo. The action of the valves
is precisely the same in the lymphatic as in the venous system.

CHAPTER XL

SECRETION.

Classification of the secretions— Mechanism of the production of the true secretions— Mechanism of the
production of the excretions — Influence of the composition and pressure of the blood on secretion —
Influence of the nervous system on secretion — Anatomical classification of glandular organs— Classifi-
cation of the secreted fluids — Synovial membranes and synovia — Mucous membranes and mucus —
Physiological 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-
Mammary secretion— Physiological anatomy of the mammary glands— Mechanism of the secretion of
milk— Conditions which modify the lacteal secretion — Quantity of milk— Properties and composition of
milk — Microscopical characters of milk— Composition of milk — Variations in the composition of milk —
Colostrum — Lacteal secretion in the newly-born — Secretory nerve-centres.

THE processes of secretion are intimately connected with general nutri-
tion. In the sense in which the term secretion is usually received, it em-
braces most of the processes in which there is a separation of matters from
the blood by glandular organs or a formation of a new fluid out of materials
furnished by the blood. The blood itself, the lymph and the chyle, are in
no sense to be regarded as secretions. These fluids, like the tissues, are per-
manent parts of the organism, undergoing those changes only that are neces-
sary to their proper regeneration. They are likewise characterized by the
presence of certain formed anatomical elements, which themselves undergo
processes of molecular destruction and regeneration. These characters are

CLASSIFICATION OF THE SECRETIONS. 307

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 secre-
tions are either discharged from the body, when they are called excretions,
or after having performed their proper office as secretions, are absorbed in a
more or less modified form by the blood.

Physiologists now regard secretion as the act by which fluids, holding
certain substances in solution, and sometimes containing peculiar ferments
but not necessarily possessing formed anatomical elements, are separated
from the blood or are formed by special organs out of materials furnished by
the blood. These organs may be membranes, follicles or collections of folli-
cles, or tubes. In the latter instances they are called glands. The liquids
thus formed are called secretions; and they may be destined to perform
some office connected with nutrition or may be simply discharged from the
organism.

It is not strictly correct to speak of formed anatomical elements as prod-
ucts of secretion, except in the instance 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 anatomi-
cal elements developed in the way in which such structures are ordinarily
formed. For example, leucocytes, or pus-corpuscles, may be developed with-
out the intervention of any special secreting organ ; and spermatozoids and
ova are generated in the testicles and the ovaries, by a process entirely differ-
ent from ordinary secretion. It is important to recognize these facts in
studying the mechanism by which the secretions are produced.

Classification of the Secretions. — Certain secretions are formed by special
organs and have important uses which do not involve their discharge from
the body. These may be classed as the true secretions ; and the most strik-
ing 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
office ; and they are never produced by any other part. It is the gland which
produces the characteristic constituent or constituents of the true secretions,
out of materials furnished by the blood ; and the matters thus formed never
pre-exist in the circulating fluid. The office which these fluids have to per-
form is generally not continuous ; 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 secretions are destroyed, as is some-
times done in experiments upon living animals, the characteristic constituents
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, with the disturbances consequent upon the loss of
its physiological action.

Certain other of the fluids are composed of water, holding one or more
characteristic constituents in solution, which result from the physiological
wear of the tissues. These matters have no office to perform in the animal
economy and are simply separated from the blood to be discharged from the

308 SECRETION.

body. These may be classed as excretions, the urine being the type of fluids
of this kind. The characteristic constituents of the excrementitious fluids
are formed in the tissues, as one of the results of the constant changes going
on in all organized, living structures. They always pre-exist in the circulating
fluid and may be eliminated, 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 constantly separated from the blood
by the proper eliminating organs. When the glands which thus eliminate
these substances are destroyed or when their action is seriously impaired, the
excrementitious matters may accumulate in the blood and give rise to certain
toxic phenomena. These effects, however, are often retarded by the vicarious
action of other organs.

There are some fluids, as the bile, which have important uses as secre-
tions, 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, in the substance of mus-
cles and in some other situations, fluids are found which simply moisten the
parts and which contain very little organic matter, with but a small propor-
tion 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 phe-
nomena of secretion ; particularly as experiments upon dialysis have shown
that simple, osmotic membranes are capable of separating complex solutions,
allowing certain constituents to pass much more freely than others. This
fact explains why the transuded fluids do not contain all the soluble con-
stituents of the blood in the proportions 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 constituents 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
from the glands, particularly during their intervals of so-called repose. This
fact has been repeatedly demonstrated with regard to many of the digestive
fluids, as the saliva, the gastric juice and the pancreatic juice ; and artificial
fluids, possessing certain of the physiological properties of the natural secre-
tions, have been prepared by simply extracting the glandular tissue with water.
There can be no doubt, therefore, that during the periods when the secre-
tions are not discharged, the glands are taking from the blood matters which
are to be transformed into the characteristic constituents of the individual
secretions, and that this process is constant, bearing 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 materials from the
blood and causing them to undergo peculiar transformations ; in the same
way that the muscular tissue takes from the nutritive fluid albuminoid mat-

PRODUCTION OF THE SECRETIONS. 309

ters and transforms them into its own substance. The exact nature of this
property is unexplained.

In all of the secreting organs, epithelium is found which seems to possess
the power of forming the peculiar constituents of the different secretions.
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 generally in the economy ; and these cells alone contain the
constituents of the secretions. It has been found, for example, that the
liver-cells contain the glycogen 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 this principle to the glands generally, both secre-
tory 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 constituents of the
urine.

With regard to the origin of the characteristic constituents to the .true
secretions, it is impossible to entertain any other view than that they are pro-
duced in the epithelial structures of the glands. While the secretions con-
tain inorganic salts in solution transuded from the blood, the organic con-
stituents, such as ptyaline, pepsine, trypsine etc., are readily distinguished
from all other albuminoid substances, by their peculiar physiological proper-
ties.

It may be stated, then, as a general proposition, that the characteristic
constituents of the true secretions, as contradistinguished from the excre-
tion:-, are formed by the epithelial structures of the glands, out of materials
furnished mainly by the blood. Their formation is by no means confined to
what is usually termed the period of 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, indeed, that the formation
of the peculiar and characteristic constituents of the secretions takes place
with 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 intervals of repose and are capable of discharging their
secretions for a limited time only.

When a secreting organ is called into activity — like the gastric mucous
membrane or the pancreas, upon the introduction of food into the aliment-
ary 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 constituents of the secretion. This difference in the quan-
tity of blood in the glands during their activity is very marked when the
organs are exposed in a living animal, and is one of the important facts bear-
ing upon the mechanism of secretion.

In all the secretions proper, there are intervals, either of complete re-
pose, as is the case with the gastric juice or the pancreatic juice, or periods

310 SECRETION.

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 action of the
secreting glands ; forming a marked contrast with the constant action of
organs of excretion. It is well known, for example, that digestion is seri-
ously disturbed when the act is too prolonged on account of the habitual in-
gestion of an excessive quantity of food.

From the considerations already mentioned, it is evident that the charac-
teristic constituents of the true secretions are formed by the epithelial
structures of the glands. While the mechanism of this process is not under-
stood in all its details as regards all of the secretions, in some of the glands
the processes have been studied with tolerably definite results. In some of
the salivary glands, in the peptic cells and in the cells of the pancreas, it
has been shown that the so-called ferments are not formed directly.
The secreting cells are apparently divided into two portions, or zones ; an
outer zone, which is next the tubular membrane, and an inner zone, next
the lumen of the tube or follicle. In the inner zone, during the intervals
of actual secretion, there appears a substance, which at the time when the
secretion is formed and is poured out, is changed into the true ferment,
or active principle of the secretion ; so that there is probably a zymogenic,
or ferment-forming substance, first produced by the cells. The substance,
if such a substance exists, out of which ptyaline is formed, has not been
described ; but in the viscid forms of saliva, there appears to be first formed
a substance called mucinogen, afterward changed into mucine, upon which
the viscidity of the fluid depends.

In the salivary glands which produce viscid secretions, the submaxillary
and sublingual, the parenchyma presents two kinds of acini, serous and
mucous. The so-called serous acini are the more abundant and are thought
to produce the true saliva, while the mucous acini secrete the viscid con-
stituents of the saliva.

In the production of pepsine, the inner zone of the peptic cells first
forms pepsinogen, which is changed into pepsine as it is discharged from
the glands. In the pancreas, trypsinogen is formed in the inner zone of the
cells, and this is changed into trypsine. The general name zymogen has
been given to the substances which are changed into the digestive ferments ;
although, as is evident, this substance is not identical in the different glands.
The formation of the .ferments of the true secretions is analogous in its na-
ture to certain of the nutritive processes.

The theory that the discharge of the secretions is due simply to mechan-
ical causes and is attributable solely to the increase in the pressure of blood
can not be sustained. Pressure undoubtedly has considerable influence upon
the activity of secretion ; but the flow will not always take place in obedi-
ence to simple pressure, and secretion may be excited for a limited time
without any increase in the quantity of blood circulating in the gland.

The glands possess a peculiar excitability, 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

PRODUCTION OF THE EXCRETIONS. 311

secretion may be excited without any modification of the circulation. This
excitability will disappear when the artery supplying the part with blood is
tied for a number of hours ; and secretion can not then 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 excitability is soon restored ; but it may
be permanently destroyed by depriving the part of blood for a long time.
These facts show a certain similarity between glandular and muscular excita-
bility, although these properties are manifested in very different ways.

Mechanism of the Production of the Excretions. — Certain of the glands
separate from the blood excrementitious matters which are of no use in the
economy and are simply discharged from the body. 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 constituents of the secretions.
The formation of excrementitious matters 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 products already formed. The action
of the excreting organs is constant, and 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 kid-
neys is nearly as red as arterial blood, showing that the quantity of blood
which these organs receive 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 secre-
tion of urine is interrupted, the blood of the renal veins becomes dark like
the blood in the general venous system.

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 excre-
mentitious 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. —
IJnder normal conditions, the composition of the blood has little to do with
the action of the secreting organs, as it simply furnishes the materials out of
which the characteristic constituents of the secretions 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 and potassium fer-
rocyanide 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 discharge of secretions is almost always accompanied with an in-
crease 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

312 SECRETION.

activity of secretion. The experiments of Bernard on this point show the
influence of pressure upon the salivary and renal secretions, 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 abstraction of blood, which
was followed by a corresponding diminution in the quantity of urine. The
same phenomena were observed in analogous experiments upon the submax-
illary secretion. These facts, however, do not demonstrate that secretion is
due simply to an increase in the pressure of blood in the glands, although
this undoubtedly 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 may completely arrest 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 excite the secretion.

Influence of the Nervous System on Secretion. — The fact that the secre-
tions are generally intermittent in their flow, being discharged in obedi-
ence to impressions which are made only when there is a demand for their
physiological action, 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 modifying and regulat-
ing local circulations. The same facts apply, to a certain extent, to the
excretions, which are also subject to considerable modifications.

It is evident that the nervous system has an important influence in the
production of the secretions ; and this is exerted largely through modifica-
tions in the activity of the circulation in the glands. This takes place in
greatest part through vaso-motor nerves distributed to the muscular coats of
the arteries of supply. When these nerves are divided, the circulation is in-
creased here, as in other situations, and secretion is the result ; and if the
extremity of the nerve connected with the gland be stimulated, contraction
of the vessels follows, and the secretion is arrested.

With regard to many of the glands, it has been shown that the influence
of the vaso-motor nerves is antagonized by certain other nerves, which latter
are called the motor nerves of the glands. The motor nerve of the submax-
illary is the chorda tympani ; and as both this nerve and the sympathetic,
which latter contains the vaso-motor filaments, together with the excretory
duct of the gland, can be easily exposed and operated upon in a living animal,
many experiments 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
stimulated alternately, it will be found that stimulation of the sympathetic

INFLUENCE OF THE NERVOUS SYSTEM ON SECRETION. 313

produces contraction of the vessels of the gland and arrests secretion, while a
stimulus applied to the chorda tympani increases the circulation and excites
secretion (Bernard). Enough is known of the nervous influences which
modify secretion, to admit of the inference that all the glands are supplied
with nerves through which certain reflex phenomena, affecting their secre-
tions, take place.

As. reflex phenomena involve the action of nerve-centres, it becomes a
question to determine whether any particular parts <5f the central nervous
system preside over the various secretions. Experiments showing the exist-
ence of such centres are not wanting, but it will be more convenient to treat
of these in connection with the physiology of the individual secretions.

Mental emotions, pain, and various conditions, the influence of which
upon secretion has long been observed, operate through the nervous system.
Many familiar instances of this kind are mentioned 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.

Paralytic Secretion by Glands. — The effects of destruction of the nerves
distributed to the parenchyma of some of the glandular organs are very re-
markable. M tiller 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 renal tissue became softened and broken down. Ber-
nard found that animals operated upon in this way died, and that the tissue
of the kidney was broken down into a fetid, semi-fluid 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 nerves were paralyzed by
introducing a few drops of a solution of curare at the origin of the little
artery which is distributed to the submaxillary gland. It is possible that
other glands have so-called motor-nerves, stimulation of which excites secre-
tion, but such nerves have been most satisfactorily isolated and studied in
connection with the salivary secretions. When the motor-nerves of the sali-
vary glands are divided, in the course of a day or two, the secretion becomes
abundant and watery, losing its normal characters. After about eight days,
the secretion begins to diminish and the glands undergo atrophy. The in-
creased secretion first observed has been called "paralytic." The watery
secretion discharged from a permanent pancreatic fistula is thought to be
paralytic ; and certainly it does not present the physiological properties of
normal pancreatic juice.

Anatomical- Classification of Glandular Organs. — The organs which
produce the different secretions are susceptible of a classification according
to their anatomical peculiarities, which greatly facilitates their study. They
may be divided as follows :

1. Secreting membranes. — Examples of these are the synovial mem-
branes.

314 SECRETION.

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 suprarenal capsules and the spleen.

The liver is a glandular organ which can not be placed in any one of the
above divisions. The lymphatic glands and other parts connected with the
lymphatic and the lacteal system are not true glandular organs ; and these
are sometimes called conglobate glands.

The general structure of secreting membranes and of the follicular
glands is very simple. The secreting parts consist of a membrane, gen-
erally homogeneous, covered on the secreting surface with epithelial cells.
Beneath this membrane, ramify the blood-vessels which furnish materials
for the secretions. The follicular glands are simply digital inversions of
this structure, with rounded, blind extremities, the epithelium lining the fol-
licles.

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 contain connective tissue, blood-vessels, nerves and
lymphatics. •

The compound racemose glands are composed of branching ducts, around
the extremities 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, lymphatics, non-striated
muscular fibres, and nerves. In the simple racemose glands the excretory
duct does not branch.

The ductless glands contain blood-vessels, lymphatics, nerves, sometimes
non-striated muscular fibres, and a peculiar structure called pulp, which is
composed 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
office is to develop certain anatomical elements, the spermatozoids and the
ova. The physiology of these organs will be considered in connection with
the physiology of generation.

Classification of the Secreted Fluids! — The products of the various glands
may be divided, according to their uses, into secretions proper and excretions.
Some of the true secretions have certain mechanical uses, and some, like
mucus, are thrown off in small quantity without being actually excremen-

SYNOVIAL MEMBRANES AND SYNOVIA. 315

titious ; while others, like most of the digestive fluids, are produced at certain
intervals and are taken up again by the blood.

TABULAB VIEW OF THE SECRETED FLUIDS.
Secretions Proper.

Synovia.

Mucus, in many varieties.

Sebaceous matter.

Cerumen, the waxy secretion of the external

auditory meatus.
Meibomian fluid.
Milk and colostrum.
Tears.

Saliva.

Gastric juice.
Pancreatic juice.

Secretion of the glands of B runner.
Secretion of the follicles of Lieberkiihn.
Secretion of the follicles of the large intes-
tine.
Bile (also an excretion).

Excretions.
Perspiration and the secretion of the axillary j Urine.

glands. I Bile (also a secretion).

Fluids containing Formed Anatomical Elements.
Seminal fluid, containing, in addition to spermatozoids, the secretions of a number of

glandular structures.
Fluid of the Graafian follicles.

The serous cavities are now regarded as sacs connected with the lym-
phatic system, and the liquids of these cavities are not classed with the secre-
tions.

Synovial Membranes and Synovia. — 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 mem-
branes both in structure and in their office. Every movable joint is envel-
oped in a capsule, which is closely adherent to the edges of the articular
cartilage and is even reflected upon its surface for a short distance ; but it is
now the general opinion that the cartilage which incrusts the articulating
extremities of the bones, though bathed in synovial fluid, is not itself cov-
ered by a distinct membrane.

The fibrous portion of the synovial membranes is dense and resisting. It
is composed of ordinary fibrous tissue, with a few elastic fibres, and blood-
vessels. The internal surface is lined with small cells of flattened endothe-
lium with rather large, rounded nuclei. These cells exist in one, two, three
or sometimes four layers.

In most of the joints, especially those of large size, as the knee and the
hip, the synovial membrane is thrown into folds which contain adipose tis-
sue. In nearly all the joints, the membrane presents fringed, vascular pro-
cesses, called synovial fringes. These are composed of looped vessels of con-
siderable size ; and when injected they bear a certain resemblance to the
choroid plexus. The edges of these fringes present a number of leaf-like,
membranous appendages, of a great variety of curious forms. They are gen-
erally situated near the attachment of the membrane to the cartilage.

The arrangement of the synovial bursae is very simple. Wherever a ten-
don plays over a bony surface, there is a delicate membrane in the form of

316 SECRETION.

an irregularly shaped, closed sac, one layer of which is attached to the ten-
don, and the other, to the bone. These sacs are lined with an endothelium
like that found in the synovial cavities, and they secrete a true synovial fluid.
Bursaa are also found beneath the skin, especially in parts where the integu-
ment moves over bony prominences, as the olecranon, the patella and the
tuberosities of the ischium. These sacs, sometimes called bursas mucosas, are
much more common in man than in the inferior animals, and they have essen-
tially the same uses as the deep-seated bursas. The form of both the super-
ficial and deep-seated bursaa 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 bursas, and present two layers, one of
which lines the canal, while the other is reflected over the tendon. The vas-
cular folds, described in connection with the articular synovial membranes,
are found in many of the bursas and the synovial sheaths.

The quantity of synovia 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 1-6 fluidrachm (6 c. c.) in
the shoulder-joint; 1-9 drachm (7 c. c.) in the elbow-joint; 1-6 drachm (6
c. c.) in the coxo-femoral articulation ; 2 '2 drachms (8 c. c.) in the femoro-
tibial articulation; and 1-9 drachm (7 c. c.) 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 ves-
sel into another. This peculiar character is due to the presence of an organic
substance called synovine. When this organic matter has been extracted
and mixed with water, it gives to the fluid the peculiar viscidity of the syno-
vial secretion. The reaction of the fluid is faintly alkaline, on account of the
presence of a small proportion of sodium carbonate. The fluid, especially
when the joints have been much used, usually contains in suspension pale
endothelial cells and a few leucocytes. According to Robin, the synovia of
the human subject contains about sixty-four parts per thousand of organic
matter, with sodium chloride, sodium carbonate, calcium phosphate and am-
monio-magnesian phosphate.

The synovial secretion is produced by the general surface of the mem-
brane and not by any special organs. The folds and fringes which have been
described 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.

Mucous Membranes and Mucus. — A distinct anatomical division of the
mucous membranes may be made into two classes ; first, those provided with
squamous epithelium, and second, those provided with columnar or conoidal
epithelium. All of the mucous membranes line cavities or tubes communica-
ting with the exterior by the different openings in the body.

The following are the principal situations in which the first variety
of mucous membranes, covered with squamous epithelium, is found: the
mouth, the lower part of the pharynx, the oesophagus, the conjunctiva, the

MUCOUS MEMBRANES AND MUCUS. 317

female urethra and the vagina. In these situations the membrane is com-
posed of a chorion made up of inelastic and elastic fibrous tissue, with capil-
laries, lymphatics and nerves. The elastic fibres are small and quite abun-
dant. The membrane itself is loosely united to the subjacent parts. The
chorion is provided with vascular papillae, more or less marked ; but in all
situations, except in the pharynx, the epithelial covering 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-mem-
brane. The mucous glands open upon the surface of the membrane by their
ducts, but the glandular structure is situated in the submucous tissue. Certain
of these glands have been described in connection with the anatomy of the
mucous membrane of the mouth, pharynx and oesophagus. They generally
are simple racemose glands, presenting a collection of follicles arranged around
the extremity of a single excretory duct, and lined or filled with rounded,
nucleated epithelium. The squamous 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 ^-gVo" *° ¥o~o °f an incn (1® to 83 //,). The cells are pale and
slightly granular, each with a small, ovoid nucleus and one or two nucleoli.

The second variety of mucous membranes, covered with columnar epi-
thelium, 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 bronchia, the Eustachian tubes and the male urethra. In certain situ-
ations 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, beginning about three-
quarters of an inch (19*1 mm.) within the nose ; in the upper part of the
pharynx ; the posterior surface of the soft palate ; the Eustachian tube ; the
tympanic cavity ; the larynx, trachea, and bronchial tubes, until they become
less than -^ of an inch (O5 mm.) in diameter ; the neck and body of the
uterus; the Fallopian tubes; the internal surface of the eyelids; and the
ventricles of the brain. Mucous membranes of this variety are formed of a
chorion, a basement-membrane and epithelium. The chorion is composed of
inelastic and elastic fibres, a few non-striated muscular fibres, amorphous mat-
ter, blood-vessels, nerves and lymphatics. It is less dense and less elastic
than the chorion of the first variety and generally is 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 fol-
licular 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 race-
mose glands, the ducts passing through the membrane, and the glandular

22

318 SECRETION.

structure being situated in the submucous areolar tissue. The columnar epi-
thelium covering these membranes rests upon an amorphous structure called
basement-membrane. The epithelium 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 at-
tached. The cells of the lower strata are shorter and more rounded than
those in the superficial layer. The cells are pale and very closely adherent
to each other by their sides, each with a moderate-sized, oval nucleus and one
or two nucleoli. The length of the cells is -g-^ to -g-J-g: of an inch (30 to 40 /*),
and their diameter, 7oW to YF<FO °f an incn (8 to 10 /x). 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 squamous epithelium.

The mucous membrane of the urinary bladder, of the ureters and of the
pelvis of the kidneys can not be classed in either of the above divisions. In
these situations the membrane is covered with mixed epithelium, presenting
all varieties of form between the squamous 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 many
fluids known under the name of mucus is composed of the products of sev-
eral different glandular structures. Certain membranes which do not possess
glands, as the mucous lining of the ureters and of a great portion of the
urinary bladder, are capable of secreting mucus. The mucous membrane of
the stomach produces an alkaline, viscid secretion, during the intervals of di-
gestion, when the gastric glands do not act ; and the gastric glands, during
digestion, secrete a fluid of an entirely different character. The fluid pro-
duced by the follicles of the small intestine likewise has peculiar digestive
properties. These considerations and the fact that the entire extent of the
mucous membranes is covered with more or less secretion show that the gen-
eral 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, a special fluid can be recognized by certain distinctive
physiological properties.

In the membranes covered with columnar epithelium, which are usually
provided with simple follicles, the secretion is produced mainly by these fol-
licles, but in part by the epithelium covering the general surface. The
membranes covered with squamous epithelium usually contain but few folli-
cles and are provided with simple racemose glands situated in the submucous
structure, which are to be regarded as appendages to the membrane. The
secretion is here produced by the epithelium on the free surface and 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 secre-

COMPOSITION AND VARIETIES OF MUCUS. 319

tion of mucus in addition to what has already been stated in connection with
the general mechanism of secretion. All the mucous membranes are quite
vascular, and the cells covering the membrane and lining the follicles and
glands attached to it have the property of taking from the blood the materi-
als necessary for the formation of the secretion. These matters pass out of
the cells upon the surface of the membrane, in connection with water and
inorganic salts in variable proportions. Many of the cells themselves are
thrown off and are found in the secretion, together with a few leucocytes,
which latter are produced upon mucous surfaces with great facility.

Composition and Varieties of Mucus. — All the varieties of mucus are more
or less viscid ; but this character is very variable in the secretions from differ-
ent membranes, in some of them the secretion being quite fluid, and in others,
almost semi-solid. The different kinds of mucus vary considerably in gen-
eral appearance. Some of them are perfectly clear and colorless ; but the
secretion is generally grayish and semi-transparent. Examined by the mi-
croscope, in addition to the mixture of epithelium and the occasional leuco-
cytes, which give to the fluid its serni-opaque character, the mass of the secre-
tion presents a very finely striated appearance, as though it were composed
of thin layers of nearly transparent substance with many folds. These deli-
cate striae do not usually interlace with each other, and they are rendered
more distinct by the action of acetic acid. This appearance, with the pecul-
iar 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 coagulated 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 difficult to get an exact idea of the composition of normal 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, however, contain a peculiar organic matter, called mucine, which
gives to the fluid its peculiar viscidity. They likewise present a consid-
erable variety of inorganic salts, as sodium chloride, potassium chloride,
alkaline lactates, sodium carbonate, calcium phosphate, a small propor-
tion of the sulphates, and in some varieties, traces of iron and of silica. Of
all these constituents, mucine is the most important, as it gives to the
secretion its characteristic properties. Like all other organic nitrogenized
substances, mucine is coagulable by various reagents. It is imperfectly coag-
ulated by heat ; and after desiccation 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 alcohol,
forming a fibrinous clot soluble in hot and cold water. Mucine 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

320 SECRETION.

been dried, be exposed to water, it assumes the viscid consistence peculiar to
mucine. This property serves to distinguish it from albumin and other or-
ganic nitrogenized matters.

General Uses 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. Aside
from these mechanical uses, it has been shown that mucus, 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 secretions 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 reasonable
to suppose that the mucous membranes are capable of resisting their absorp-
tion. This fact is illustrated by the following experiment :

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 mem-
brane be exposed to a solution containing some venomous fluid. The liquid
will mount in the interior of the apparatus, but the poison will not pene-
trate 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 (Robin).

These facts show that mucus is an important secretion. It not only has
a useful mechanical office, 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.

Physiological Anatomy of the Sebaceous, Ceruminous and Meibomian
Glands. — The true sebaceous glands are found in all parts of the skin that
are provided with hair ; and as nearly every part of the general surface pre-
sents 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 connected with small, downy hairs.

Nearly all of the sebaceous glands are either simple racemose glands, that
is, presenting a number of follicles connected with a single excretory duct, or
compound racemose glands, presenting several ducts, with their follicles,
opening by a common tube. Although there is this variation in the size and

SEBACEOUS GLANDS.

321

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

B n . D

FIG. 99.— Sebaceous glands (Sappey).

A, a gland in its most rudimentary form : 1, rudimentary hair-follicle ; 2, downy hair ; 3, simple seba-

ceous 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 : 3, follicle imperfectly divided.

D, a compound gland : 1, hair-follicle ; 2, lobule with three follicles ; 3, lobule with four follicles.

E, a gland 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 ; 3, second lobule ; 4, third lobule ; 5, fourth

lobule ; 6, excretory duct.

largest glands are connected 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 geni-
tal organs and with the coarse, short hairs, and those connected with the
fine, downy hairs.

The glands connected with the larger hair-follicles are of the simple race-
mose variety and are -^ to ^ of an inch (0-21 to 0-64 mm.) in diameter.
Two to five of these glands are generally found arranged around each hair-
follicle. They discharge their secretion at about the junction of the upper

322

SECRETION.

third with the lower two-thirds of the hair-follicle. The follicles of the long
hairs of the scalp are generally provided each with a pair of sebaceous glands,
measuring TJ7 to -^ of an inch (0-21 to 0-34 mm.) in diameter. Encircling
the hairs of the beard, the chest, axilla and genital organs, are large glands,
some of them ^ of an inch (0-64 mm.) in diameter, arranged in groups of
four to eight.

The glands connected with the follicles of the small, downy hairs are so
large, as compared with the hair-follicles, that the latter seem rather as ap-
pendages 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 curuncula lachrymalis, the penis
and the areola of the nipple, where they measure -gV to -fa of an inch (O51
to 2-1 mm.). The glands connected with the downy hairs of other parts
usually are smaller. The glands of Tyson, situated upon the corona and
cervix of the glans penis, are sebaceous glands of the compound racemose
variety.

The minute structure of the sebaceous glands is very simple. The folli-
cles 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, with an external layer of inelastic and small
elastic fibres, and are lined by cells. Next the membrane, the cells are poly-
hedric, pale and granular, most of them presenting a nucleus and a nucle-
, olus; but the follicle

I I *' i I itself contains fatty

granules and the other
constituents of the
sebaceous matter, with
cells filled with fatty
particles. These cells
abound in the seba-
ceous matter as it is
discharged from the
duct. The great quan-
tity of fatty granules
and globules found
in the ducts and fol-
licles of the sebaceous
glands renders them
dark and opaque when

FIG. m.-Ceruminous glands (Sappey). examined with the
Vertical section of the skin of the external auditory meatus : 1, 1, epi-
dermis ; 2, 2, derma : 3, 3, series of hair-follicles lodged in the sub- microscope by trans-
stance of the skin : 4, 4, series of sebaceous glands attached to these , , .
follicles ; 5. 5, subcutaneous areolar layer ; 6. 6, ceruminous glands ; milted llgnt, and tlieir
7, 7, ceruminous glands with the ducts divided ; 8, 8, adipose vesicles. . . ,

appearance is quite

distinctive. The larger glands are surrounded with capillary blood-vessels.

The ceruminous glands produce a secretion resembling the sebaceous

matter in many regards, but in their anatomy they are almost identical with

MEIBOMIAN GLANDS.

the sudoriparous glands. They belong to the variety of glands called tubu-
lar, 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 auditory meatus,
where they exist in great numbers.

The ducts of the ceruminous glands are short and nearly straight, sim-
ply penetrating the different layers of the skin, and are ^^ to yj-g- of an
inch (36 to 50 ft) in diameter. Their openings are rounded and about
-gfa of an inch (93 p) in diameter. They sometimes terminate in the upper
part of one of the hair-follicles. They present an external coat of fibrous
tissue and are lined with several layers of small, pale, nucleated epithelial
cells.

The glandular coil is an ovoid or rounded, brownish mass, r|T to -fa or ^
of an inch (0-21 to 0'51 or 1-6 mm.) in diameter. It is simply a convoluted
tube,' continuous with the excretory duct and terminating in a somewhat
dilated, rounded extremity. It occasionally presents small, lateral protru-

sions. The diameter of the tube is
has a fibrous coat, with a longitudinal
layer of non-striated muscular fibres, and
externally a few elastic fibres. It is
lined by a single layer of irregularly
polygonal cells, which are 20i00 to T^^
of an inch (12 to 20 ft) in diameter.
These cells contain a number of brown-
ish or yellowish pigmentary granules.
The tube forming the gland contains a
clear fluid mixed with a granular sub-
stance containing cells.

In addition to the ceruminous glands,
sebaceous follicles are found connected
with the hair-follicles. The arrange-
ment of the ordinary sebaceous glands
and the ceruminous glands, which are
situated in different planes in the subcu-
taneous structure, is shown in Fig. 100.

The Meibomian glands have essen-
tially the same structure as the ordinary
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 part-
ly in the substance of the tarsal carti-
lages, between their posterior surfaces
and the conjunctival mucous membrane.

to

of an inch (83 to 100 //,). It

FIG. 101.— Meibomian glands of the upper lid ;
magnified 7 diameters (Sappey).

of the lid ; 2, 2, anterior lip
y the eyelashes ; 3, 3, posteri-
or lip, with the openings of the Meibomian
glands ; 4, a gland passing obliquely at the
summit ; 5, another gland bent upon itself ;
6, 6, two glands in the form of racemose
glands at their origin ; 7, a very small gland;
8, a medium-sized gland.

They are placed at right angles to

the free border of the eyelids, opening upon the inner edge and occupying

324: SECRETION.

the entire width of the cartilages. Twenty-five to thirty glands are found in
the upper lid, and twenty to twenty-five, in the lower lid.

Each Meibomian gland consists of a nearly straight excretory duct, 7fg- to
-%\-Q of an inch (83 to 100 //,) in diameter, communicating laterally with com°
pound racemose acini, or collections of follicles, measuring -g^-g- to T|T of an
inch (83 to 200 /x). Fifteen or 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 ordinary sebaceous
glands. They are lined with cells ^rVo to y^Vu~ of an inch (10 to 20 /A) in
diameter. The cells contain fatty globules, but these do not coalesce into
large drops, such as are often seen in the ordinary sebaceous cells. The folli-
cles and ducts are filled with the whitish, oleaginous matter which consti-
tutes the Meibomian secretion, or the sebum palpebrale.

In addition to the Meibomian secretion, the edges of the palpebral orifice
receive a small quantity of secretion from ordinary sebaceous glands of the
compound racemose variety (ciliary 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 surface, that
the amount of sebaceous matter must be considerable, it has been impossible
to collect the normal fluid in quantity sufficient for ultimate analysis. In
some parts, as the skin of the nose, where the glands are particularly abun-
dant, a certain quantity 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 may be col-
lected 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 abundant 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 number. 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.

The chemical constituents of the sebaceous matter are largely fatty. In
an analysis made by Lutz, in a case of general hypertrophy of the seba-
ceous system, the proportion of water was only 357 parts per 1000. The
solid matters consisted of oleine, 270 parts, palmitine, 135 parts, caseous
matter, 129 parts, gelatine, 87 parts, a little albumin, butyric acid and so-
dium butyrate, with sodium phosphate, sodium chloride, sodium sulphate
and traces of calcium phosphate. Cholesterine, which is present so fre-

SEBACEOUS MATTER. 325

quently in the contents of sebaceous cysts, does not exist in the normal se-
cretion.

During the later 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 oily globules and granules. Fre-
quently 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 Ldbia Minora. — 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 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 pre-
puce has really little analogy with the ordinary sebaceous secretion. Exami-
nation with the microscope shows that it is composed almost entirely of
irregular scales of epithelium, which do not present the fatty granules and
globules usually observed in the cells derived from the> sebaceous glands.
The production of this substance is probably 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 seba-
ceous glands found in these parts.

Vernix Caseosa. — The surface of the foetus at birth and near the end of
utero-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 is observed only on close inspection. There are few analy-
ses which give accurately the chemical composition of this substance ; and
the best idea of its constitution and mode of formation can be formed 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 examination, to consist of a large number of epi-
thelial cells with a very few small, fatty granules. These cells, after desicca-
tion, constitute about ten per cent, of the entire mass. The fatty granula-
tions are very few and do not seem to be necessary constituents of the vernix,
as they are of the sebaceous matter. In fact, the vernix caseosa must be re-
garded as the residue of the secretion of the sebaceous glands, rather than
an accumulation of true sebaceous matter.

The office of the vernix caseosa is undoubtedly protective. In making a
microscopical preparation of the cells with water, it becomes evident that
the coating is penetrated by the liquid with very great difficulty, even when
mixed with it as thoroughly as possible. The protecting coat of vernix cas-
eosa allows the skin to perform its office in utero, and at birth, when this

326 SECRETION.

coating is removed, the surface is found in a condition perfectly adapted to
extraiiterine existence. It is not probable that the vernix caseosa is necessa-
ry to facilitate the passage 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 auditory meatus, under the
name of ceruminous glands, mixed 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.
According to Robin, the waxy portion of the secretion is produced entirely by
the sebaceous glands, and the convoluted glands, commonly known as the ce-
ruminous glands, produce a secretion like the perspiration. This view is to
a certain extent reasonable ; for the sebaceous matter is not removed from
the meatus by friction, as in other situations, and would have a natural ten-
dency to accumulate; but the contents of the ducts of the ceruminous
glands differ materially from the fluid found in the ducts of the ordinary
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 sudoripa-
rous glands, the fluid which they produce is peculiar. The perspiratory
glands of the axilla and of some other parts also produce secretions differing
somewhat from ordinary perspiration. As far as can be ascertained, the cer-
umen 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
fluidity, but containing a certain quantity of granular and fatty matter.

The consistence and general appearance of cerumen are quite variable
within the limits of health. When first secreted, it is of a yellowish color
and 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 semi-solid,
dark granulations of an irregularly polyhedric shape, with epithelium from the
sebaceous glands, and epidermic scales, both isolated and in layers. Some-
times, also, a few crystals of cholesterine are found.

Chemical examination shows that the cerumen is composed of oily mat-
ters fusible at a low temperature, a peculiar organic matter resembling
mucine, with sodium salts and a certain quantity of calcium phosphate.
The yellow coloring matter is soluble in alcohol ; and the residue after evap-
oration of the alcohol is very soluble in water and may be precipitated from
its watery solution by neutral lead acetate or tin chloride. This extract has
a very bitter taste.

The cerumen lubricates the external meatus, accumulating in the canal
around the hairs. Its peculiar bitter taste is supposed to be useful in prevent-
ing the entrance of insects.

Meibomian Secretion. — Very little is known concerning any special prop-

ANATOMY OF THE MAMMAEY GLANDS. 327

erties of the Meibomian fluid, except that it mixes in the form of an emulsion
with water more readily than the other sebaceous secretions. It is produced
in small quantity, mixed with mucus and the secretion from the ordinary se-
baceous glands attached to the eyelashes 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 the excess of fluid passes into
the nasal duct.

MAMMARY SECRETION.

The mammary glands are among the most remarkable organs in the econ-
omy ; not only on account of 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.. Rudi-
mentary in early life and in the male at all periods of life, these organs are
fully developed in the adult female only in the later months of pregnancy'
and during lactation. In the female, after puberty, the mammary glands
undergo a marked and rapid increase in size ; but even then they are not ful-
ly developed.

Physiological Anatomy of the Mammary Glands. — The form, size and
situation of the mammae in the adult female are too well known to de-
mand 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 muscles. In women who have never borne children, they gener-
ally are firm and nearly hemispherical, with the nipple at the most promi-
nent point. In women who have borne children, the glands during the
intervals of lactation usually are larger, are held more loosely to the sub-
jacent parts and are often flabby and pendulous. The areola of the nipple,
also, is 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 des-
tined 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 (8'5 mm,) in di-
ameter. At this time there are twelve to fifteen lobes in each gland, and each
lobe is penetrated by a duct, with but few branches, composed of fibrous tis-
sue and lined with cylindrical epithelium. The ends of these ducts are fre-
quently somewhat dilated ; but what have been called the gland- vesicles do
not make their appearance before puberty. In the adult male the glands
are half an inch to two inches (12- 7 to 50-8 mm.) broad, and ^ to £ of an
inch (2-1 to 6-4 mm.) in thickness. In their structure, however, they pre-
sent little if any difference from the rudimentary glands of the infant.

As the time of puberty approaches in the female, the rudimentary ducts
of the different lobes become more and more ramified. Instead of each duct
having but two or three branches, the different lobes, as the gland enlarges,

328 SECEETION.

are penetrated by innumerable ramifications which have gradually been devel-
oped as processes from the main duct. It is important to remember, how-
ever, that these branches are never so abundant or so long during the inter-
vals of lactation as they are when the gland is in full activity.

Between the fourth and fifth months of utero-gestation the mammary
glands of the mother 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 devel-
oped, and the areola becomes larger, darker and thicker. The glandular
structure of the breasts during the latter half of pregnancy becomes so far de-
veloped, that if the child be born at the seventh month, the lacteal secretion
may be established at the usual time after parturition. Even when parturi-
tion 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 pa-
pillae, 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 nipples is composed of inelastic and
elastic fibres, containing a large number of sebaceous glands, but no hair-fol-
licles or sudoriparous glands. These glands are always of the racemose va-
riety, and they never exist in the form of simple follicles (Sappey). The
nipple contains the lactiferous ducts, fibres of inelastic and elastic tissue,
with a large number of non-striated muscular fibres. The muscular fibres
have no definite direction, but are so abundant that when they are contracted
the nipple becomes very firm and hard.

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 gland-
ular 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 concentric rings around the nipple. These fibres are supposed to
be useful in compressing the ducts during the discharge of milk. The
areola presents the following structures ; papillae, considerably smaller than
those upon the nipple ; hair-follicles, containing small, rudimentary hairs ;
sudoriparous glands ; and sebaceous glands connected with the hair-follicles.
The sebaceous glands are very large, and their situation is indicated by little
prominences on the surface of the areola, which are especially marked dur-
ing pregnancy.

The mammary gland itself is of the compound racemose variety. It is

ANATOMY OF THE MAMMARY GLANDS.

329

covered in front by a subcutaneous layer of fat, and posteriorly it is envel-
oped in a fibrous membrane loosely attached to the pectoralis major muscle.
A considerable quantity 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, fifteen to twenty-four in number. These 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 identical in structure.

The canals which discharge the milk at the nipple are called lactiferous
or galactophorous ducts. They are ten to fourteen in number. The open-
ings of the ducts at the nipple are very small, measuring only -fa to ^ of an
inch (0-42 to 0-64 mm.). As each duct passes downward, it enlarges in the
nipple to -fa or ^ of an inch (1 or 2 mm.) in diameter, and beneath the are-
ola it presents an elon-
gated dilatation, $ to J
of an inch (4-2 to 8-5
mm.) in diameter, called
the sinus of the duct.
During lactation a con-
siderable quantity of milk
collects in these sinuses,
which serve as reservoirs.
Beyond the sinuses, the
caliber of the ducts meas-
ures ^ to -J- of an inch
(2-1 to 4-2 mm.). The
ducts penetrate the dif-
ferent lobes, branching
and subdividing, to ter-
minate finally in the col-
lections of culs -de- sac
which form the acini.
There is no anastomosis
between the different lac-
tiferous ducts, and each
one is distributed inde-
pendently to one or more
lobes.

The lactiferous ducts have 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 lon-

FIG. 102.— Mammary gland of the human female (Ltegeois).
a, nipple, the central portion of which is retracted; &, areola ; c, c.
c, c, c, lobules of the gland: 1. sinus, or dilated portion of one of
the lactiferous ducts ; 2, extremities of the lactiferous ducts.

330 SECRETION.

gitudinally and existing throughout the duct, from its opening at the nipple
to the secreting culs-de-sac. The internal coat is an amorphous membrane,
lined with flat, polygonal cells during the intervals of lactation and even dur-
ing pregnancy, the cells being cylindrical in form and frequently presenting
multiple nuclei, when milk is secreted.

The acini of the gland, which are very abundant, are visible to the naked
eye, in the form of small, rounded granules of a reddish-yellow color. Be-
tween these acini, there exists a certain quantity of the ordinary white fibrous
tissue, with quite a number of adipose 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 twenty to
forty secreting vesicles. These vesicles are irregular in form, often varicose,
and sometimes they are enlarged and imperfectly bifurcated at their termi-
nal extremities. During lactation their diameter is -^ to -^ of an inch
(60 to 80/t).

During the intervals of lactation, as the lactiferous ducts become re-
tracted, the glandular culs-de-sac disappear ; and in pregnancy, as the gland
takes on its full development, the ducts branch and extend themselves, and
the vesicles are gradually developed around their extremities.

Mechanism of the Secretion of Milk. — With the exception of water and
inorganic matters, 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 separating .from the blood a great variety of
inorganic salts ; and the milk furnishes all the inorganic matter necessary
for the nutrition of the infant, even containing a small quantity of iron.

The lactose, or sugar of milk, the caseine, and the fatty particles, are all
produced 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, in-
jected 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.

Caseine is produced in the mammary glands, probably by a peculiar
transformation of the albuminoid constituents of the blood. The fatty par-
ticles 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
somewhat obscure. The particles are produced in the cells, probably by a
process analogous to that which takes place in the formation of the fatty
particles found in the sebaceous matter.

As regards the mechanism of the formation of the peculiar and character-
istic constituents of the milk, the mammary glands are to be classed among
the organs of secretion and not with those of elimination or excretion ; for
none of these elements pre-exist 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

SECRETION OF MILK. 331

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 during lactation, it diminishes and modifies,
and it may arrest the secretion of milk. The secreting action of the mam-
mary glands is nearly continuous. When the secretion of milk has become
fully established, while there may be certain times when it is formed in
greater quantity than at others, there is no actual intermission in its pro-
duction.

General 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 requirements 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 lactation.
It is evident that as the development of the child advances, a constant in-
crease of nourishment is demanded ; and as a rule, the mother is capable of
supplying all the nutritive requirements of the infant for 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 influ-
enced by the character 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 delicate ali-
mentation, and the milk of females in the lower walks of life, when the gen-
eral 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 ali-
mentation 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. It is very common, however, for women
to become quite fat during lactation ; which shows that the fatty cbnstituents
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 situations in which
it is ordinarily 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. Dur-
ing lactation there is always an increased demand for water and for liq-
uids 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 fully established by observations 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

332 SECRETION.

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 se-
cretion, and sometimes they produce a certain eifect upon the child ; but di-
rect 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, particularly in assisting
the mother to sustain the unusual drain upon the system. There are, how-
ever, few instances of normal lactation in which their use is absolutely ne-
cessary.

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 many
instances of modification or arrest of the secretion from this cause, which are
quoted by authors. Vernois and Becquerel reported a case, in which a
hospital wet-nurse, who lost her only child from pneumonic fever, became
violently aifected with grief and presented, as a consequence, an immediate
diminution in the quantity of her milk, with a great reduction in the propor-
tion of salts, sugar and butter. In this case the proportion of caseine was
increased. Astley Cooper reported two cases in which the secretion of milk
was instantaneously and permanently arrested by terror. These cases are
types of many others, which have been cited by writers, of the effects of
mental emotions upon secretion.

Direct observations 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 quantity of the secretion. It is difficult, however, to operate upon all
the nerves distributed to these organs. There are no observations indicating
the situation of a nerve-centre presiding over the secretion of milk, although
such a centre may exist.

Quantity of Milk. — It is difficult to form a reliable estimate of the aver-
age quantity of milk secreted by the human female in the twenty-four hours.
The quantity undoubtedly varies very much in different persons ; some women
being able to nourish two children, while others, though apparently in per-
fect health, furnish hardly enough food for one. Astley Cooper, as the result
of direct observation, stated that the quantity that can be drawn from a full
breast is usually about two fluidounces (60 grammes). 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 Lamperierre, who found, as the result of sixty-seven experi-
ments, that between 1/7 and 2 ounces (50 and 60 grammes) of milk were
secreted in two hours, estimated that the average quantity discharged in
twenty-four hours, is about 44-5 fluidounces (1,320 grammes). Taking into

PROPERTIES AND COMPOSITION OF MILK. 333

consideration the variations in the quantity of milk secreted by different
women, it may be assumed that the daily production is between two and three
pints (950 and 1,420 grammes).

Certain conditions of the female are capable of materially influencing the
quantity of milk secreted. It is evident that the secretion is usually some-
what increased within the first few months of lactation, when the progressive
development of the child demands an increase in the quantity of nourish-
ment. If the menstrual function become re-established during lactation, the
milk usually is diminished in quantity during the periods, but sometimes it
is not affected, either in its quantity or composition. Should the female
become pregnant, there generally is a great diminution in the quantity of
milk, and that which 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.
No marked and constant variations have been observed in the quantity of
milk in females of different ages.

Properties and Composition of Milk. — The general appearance and char-
acters of ordinary cow's milk are sufficiently familiar. Human milk is nei-
ther so white nor so opaque as cow's milk, having ordinarily a slightly
bluish tinge. After the secretion has become fully established, the fluid
possesses no viscidity and is nearly opaque. It is almost inodorous, of a
peculiar soft and sweetish taste, and when perfectly fresh it has a decidedly
alkaline reaction. The taste of human milk is sweeter than xthat 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 is 1032 ; although this is
subject to considerable variation, the minimum of eighty-nine observations
being 1025, and the maximum, 1046 (Vernois and Becquerel). The observa-
tions 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 com-
bined action of heat and the atmosphere upon the caseine. Although a
small quantity of albumin 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 a vacuum or in an atmosphere of carbon dioxide or of
hydrogen.

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 sooner in warm than in
cold weather. It is a curious fact that fresh milk frequently is coagulated
during a thunder-storm, a phenomenon which has never been satisfactorily
explained.

23

334

SECRETION.

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 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. The spe-
cific 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. — Milk contains an immense num-
ber of minute, spherical globules, of highly refractive power, held in sus-
pension in a clear fluid. These are known under the name of milk-glob-
ules and are composed of palmitine, oleine, and fatty matters peculiar to
milk.

The human milk-globules are -g-^-J-oT to T^g~o °^ an inc^ (1 to 20 ft) in
diameter. They usually are distinct from each other, but they may occasion-
ally become collected into groups, without indicating any thing abnormal.
In a perfectly normal condition of the glands, when the lacteal secretion has

become fully established, the milk con-
tains nothing but a clear fluid with
these globules in suspension. The pro-
portion of fatty matters in the milk is
twenty -five to thirty- eight parts per
thousand ; and this gives an idea of the
proportion of globules which are seen
on microscopical examination.

In some regards milk does not pre-
sent the characters of a simple emulsion.
If it be shaken with ether, the mixture
remains opaque ; but the fatty matters
are dissolved on the addition of potassi-
um hydrate. Dilute acetic acid added
to milk causes the globules to run to-
gether. These reactions have led to the
view that the milk-globules have a membrane which is dissolved by potassi-
um hydrate and by acetic acid. It is probable that the butter in normal
milk does not exist precisely in the form of a simple emulsion, but that the
globules have a very thin, caseous coating. In view of the action of reagents
upon the globules, the only alternative, if the existence of a caseous coating
be denied, is the opinion that the addition of potassium hydrate or of acetic
acid renders the caseine incapable of holding the fat in the condition of an
emulsion. There is actually little more than a verbal difference between
these two opinions.

Composition of the Milk. — The following table, compiled by Robin
from the analyses of various chemists, gives the constituents of human
milk :

FIG. 103. — Human milk-globules, from a healthy
ing-in
unke).

lying-in woman, eight days 'after delivery
(Fi '

PROPERTIES AND COMPOSITION OF MILK. 335

COMPOSITION OF HUMAN MILK.

Water 902-717 to 863-149

Caseine (desiccated) 29-000 " 39-000

Lactoproteine I'OOO " 2-770

Albumin traces " 0-880

f Palmitine 17-000 " 25-840

Butter, 25 to 38 ) Oleine 7-500 " 11-400

( Butyrine, caprine, caprome, caprilene etc. 0-500 " 0'760

Sugar of milk (lactose) 37-000 " 49-000

Sodium lactate (?) 0-420 " 0-450

Sodium chloride 0-240 " 0-340

Potassium chloride 1-440 " 1-830

Sodium carbonate ! . . 0-053 " 0-056

Calcium carbonate 0-069 " 0-070

Calcium phosphate 2-310 " 3-440

Magnesium phosphate 0-420 " 0-640

Sodium phosphate 0-225 " 0*230

Ferric phosphate (?) 0-032 " 0-070

Sodium sulphate 0*074 " 0-075

Potassium sulphate traces.

1,000-000 1,000-000

( Oxygen 1-29 }

Gases in solution < Nitrogen 12-17 £ 30 parts per 1,000 in volume. (Hoppe.)

' Carbon dioxide. 16*54 )

The proportion of water in milk is subject to certain changes, but these
are not so considerable as might be expected from the great variations in
the entire quantity of the secretion. As regards the quantity of milk in the
twenty-four hours, the influence of drinks, even when nothing but pure water
is taken, is very marked ; and although the activity of the secretion is much
increased by fluid irigesta, the quality of the milk usually is not affected, and
the proportion of water to the solid matters remains about the same.

Nitrogenized Constituents of Milk. — Very little remains to be said con-
cerning the nitrogenized constituents of human milk, after what has been
stated in connection with alimentation. The different constituents of this
class undoubtedly have the same nutritive office and they appear to be iden-
tical in all varieties of milk, the only difference being in their relative pro-
portions. 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 natural food of the child. A comparison of the composi-
tion of human milk and of cow's milk shows that the former is poorer in nitro-
genized matters and richer in butter and sugar ; and consequently, the upper
strata of cow's milk, properly sweetened and diluted with water, very nearly
represents the ordinary breast-milk.

Caseine is by far the most important of the nitrogenized constituents of
milk, and it supplies nearly all of this kind of nutritive matter demanded by
the child. Lactoproteine, described by Millon and Commaille, is not so well
defined, and albumin exists in the milk in very small quantity.

336 SECRETION.

The coagulation of milk depends upon the reduction of caseine from a
liquid to a semi-solid condition. When milk is allowed to coagulate spon-
taneously, 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. If fresh milk be slightly raised in temperature and be treated with
an infusion of the gastric mucous membrane of the calf, coagulation will
take place in five or ten minutes, the clear liquid still retaining its alkaline
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-nitrogeiiized matters exist
in abundance in the milk. The liquid caseine and the water hold the fats
in the condition of a fine and permanent emulsion. This fat may easily be
separated from the milk, 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, particularly the cow; but it is composed of essentially the same
constituents, although in different proportions. In different animals, there
are developed, even after the discharge of the milk, certain odorous matters,
which are more or less characteristic of the animal from which the butter is
taken.

The greatest part of the butter consists of palmitine. Butter contains
in addition, oleine, and a small proportion of peculiar fats, which have not
been very well determined, called butyrine, caprine, caproi'ne, capriline, with
some other analogous substances. Palmitine and oleine are 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 decomposition give the peculiar odor and flavor to rancid butter.

Sugar of milk, or lactose, is the most abundant of the solid constituents
of the mammary secretion. It is this 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 that
it takes on alcoholic fermentation slowly and with difficulty. In the fer-
mentation of milk, the lactose is changed first into galactose, and then into
alcohol and carbon dioxide. In some parts of the world, alcoholic beverages
made from milk are in common use.

Inorganic Constituents of Milk. — It is probable that many inorganic salts
exist in the milk, which are not given in the table ; and the separation of
these from their combinations with organic matters is one of the most diffi-
cult problems in physiological chemistry. This must be the case, for during
the first months of extrauterine 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 pres-
ence of the alkaline carbonates, and these are important in preserving the

VARIATIONS IN THE COMPOSITION OF MILK. 337

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 impor-
tant inorganic matters found in the latter fluid exist also in the milk.

Hoppe has indicated the presence of carbon dioxide, nitrogen and oxygen,
in solution in milk. Of these gases, carbon dioxide 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 carbon dioxide increases very materially
their solvent properties. Aside from these considerations, the uses of the
gaseous constituents of the milk are not apparent.

In addition to the constituents given in the table of composition, the
milk contains small quantities of peptone, nucleine, dextrine, urea, lecithine,
hypoxanthine, fluorine and silica.

A study of the composition of the milk fully confirms the fact 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 Milk. — 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 an-
other name. It is then known as colostrum, the peculiar properties of which
will be considered more fully 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 in its proportion of water and of sugar,
while there is a progressive increase in the proportion of most of the other
constituents ; viz., butter, caseine and the inorganic salts. The milk, there-
fore, as far as one 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 impor-
tance 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
between the milk of primiparse and multipart are slight and unimportant.
As a rule, however, the milk of primiparae approaches more nearly the normal
standard.

In normal lactation, there is no marked and constant difference in com-
position between milk that has been secreted in great abundance and milk
which is produced in comparatively small quantity ; and the difference be-
tween the fluid first drawn from the breast and that taken when the ducts
are nearly empty, which is observed in the milk of the cow, has not been
noted in human milk.

338

SECRETION.

COLOSTRUM.

Near the end of utero-gestation, during a period which varies considera-
bly in different women and has not been accurately determined, a small
quantity of a thickish, stringy fluid may frequently be drawn from the mam-
mary glands. This bears little resemblance to perfectly formed milk. It is
small in quantity and is usually more abundant in multipart than in primi-
parae. This fluid, as well as that secreted for the first few days after delivery,
is called colostrum. It is yellowish, semi-opaque, of a distinctly alkaline re-
action and is somewhat mucilaginous in its consistence. Its specific gravity
is considerably above that of the ordinary milk, being between 1040 and 1060.
As lactation progresses, the character of the secretion rapidly changes, until
the fluid becomes filled 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 differ-
ent corpuscular 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, supposed to be characteristic of

the colostrum, always exist in this fluid.
These are known as colostrum-corpus-
cles. They are spherical, varying in
size between ^oo- an(i TOT °^ an incn
(10 and 50 /x,.), are sometimes pale, but
more frequently quite granular, and
they contain very often a large number
of fatty particles. They behave in all
respects like leucocytes and are de-
scribed as a variety of these bodies.
Many of them are precisely like the
leucocytes found in the blood, lymph
or pus. In addition to these corpuscu-
lar elements, a small quantity of mucine
may frequently be observed in the co-
lostrum on microscopical examination.
On the addition of ether to a speci-
men 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 gelatinous consistence.

In its 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

FIG. 104.— Colostrum, from a healthy lying-in
woman, twelve hours after delivery (Funke).

The smaller globules are globules of milk. The
larger globules, a, a, filled with granula-
tions, are colostrum-corpuscles. As lacta-
tion advances, the colostrum - corpuscles
gradually disappear, and the milk-globules
become more abundant, smaller and more
nearly uniform in size.

COLOSTRUM. 339

colostrum contains a large proportion of serum-albumin ; and as the charac-
ter of the secretion changes in the process of lactation, the albumin 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

Albumin, 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 putrefactive changes very rapidly. If it be allowed to stand for twelve
to twenty-four hours, it separates into a thick, opaque, yellowish cream and
a serous fluid. In an observation by Astley Cooper, nine measures of colos-
trum, taken soon after parturition, 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 deliv-
ery, in assisting to relieve the infant of the accumulation of meconium.

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 important question to determine
whether this secretion have any relation to the quantity of milk that may be
expected after delivery. This question has been studied by Donne, who ar-
rived at the following conclusions :

In women in whom the secretion of colostrum is almost absent, the fluid
being in exceedingly small quantity, viscid, and containing hardly any cor-
puscular elements, there is hardly any milk produced after delivery.

In women who, before delivery, present a moderate quantity of colostrum,
containing 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 after delivery is always abundant and of good quality.

From these observations, it would seem that the production of colostrum
is an indication 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 shall have become fully established.

The secretion of the mammary glands preserves the characters of colos-
trum until toward the end of the so-called milk-fever, when the colostrum-

340 SECRETION.

corpuscles rapidly disappear, and the milk-globules become more abundant,
regular and uniform in size. It may be stated, in general terms, that the
secretion of milk becomes fully established and all the characters of the
colostrum disappear between the eighth and the tenth day after delivery. A
few colostrum-corpuscles and masses of agglutinated milk-globules may
sometimes be discovered after the tenth day, but they are rare. After the
fifteenth day, the milk does not sensibly change in its microscopical or its
chemical characters.

LACTEAL SECRETION IN THE NEWLY-BORN.

In infants of both sexes there is generally a certain amount of secretion
from the mammary glands, beginning at birth or two or three days after,
and continuing sometimes for two or three weeks. The quantity of fluid
that may be pressed out at the hippies at this time is very variable. Some-
times only a few drops can be obtained, but occasionally the fluid amounts
to one or two drachms (3-7 or 7 '4 grammes.) 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
physiologists, 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 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 894-00

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

This fluid does not differ much in its composition from ordinary milk.
The proportion of butter is much less, but the proportion of sugar is greater,
and the quantity of caseine 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 described in connection with the physiology of digestion. The physi-
ology of the lachrymal secretion will be taken up in connection with the eye,
and the bile will be treated of fully under the head of excretion.

Secretory Nerve- Centres. — It remains now to consider the influence of
nerve-centres upon certain secretions. Cerebro-spinal centres presiding over
secretion have not been determined for all of the glands, although they may
exist. No cerebro-spinal centres have been described for the secretions of

DIFFERENCES BETWEEN SECRETIONS AND EXCRETIONS. 341

mucous membranes, the gastric juice, the intestinal juice, the sebaceous
fluids, the milk or the lachrymal fluid.

The centres for the salivary secretions are in the medulla oblongata, near
the points of origin of the facial and glosso-pharyngeal nerves. The centre
for the pancreatic secretion is also in the medulla oblongata. The centres
which act upon the liver and upon certain excretions will be treated of in
connection with the physiology of the liver, kidneys and skin.

CHAPTER XII.

EXCRETION BY THE SKIN AND KIDNEYS.

Differences between the secretions proper and the excretions— Physiological anatomy of the skin— Physio-
logical anatomy of the nails — Physiological anatomy of the hairs — Sudden blanching of the hair — Per-
spiration— 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 — Mechan-
ism of the production and discharge of urine — Influence of blood-pressure, the nervous system etc.,
upon the secretion of urine— Physiological anatomy of the urinary passages— Mechanism of the dis-
charge of urine— Properties and composition of the urine— Influence of ingesta upon the composition
of the urine and upon the elimination of nitrogen— Influence of muscular exercise upon the elimination
of nitrogen— Water regarded as a product of excretion— Variations in the composition of the urine.

IN entering upon the study of the elimination of effete matters, it is ne-
cessary to appreciate fully the distinctions between the secretions proper and
the excretions, in their composition, the mechanism of their production, and
their destination. The urine may be taken as the type of the excrementi-
tious fluids. None of its normal constituents belong to the class of non-crys-
tallizable, organic nitrogenized matters, but it is composed entirely of crys-
tallizable matters, simply held in solution in water. The solid constituents
of the urine represent the ultimate physiological changes of certain parts of
the 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 in-
organic matters are found in the excrementitious fluids, are discharged with
the products of excretion, and are thus associated with the organic constitu-
ents of the body in their physiological changes as well as in their deposition
in the tissues. Coagulable organic matters, or albuminoids, never exist in
the excrementitious fluids under normal conditions ; except as the products
of other glands may become accidentally or constantly mixed with the ex-
crementitious fluids proper. The same remark applies to the non-nitrogen-
ized matters, sugars and fats, which, whether formed in the organism or
taken as food, are consumed in the organism. The production of the excre-
tions is constant, being subject only to certain modifications in activity,
which are dependent upon varying conditions of the system. All of the
elements of excretion pre-exist in the blood, either in the condition in
which they are discharged or in some slightly modified form.

The urine is a purely excrementitious fluid. The perspiration and the

34:2 EXCEETION BY THE SKIN AND KIDNEYS.

secretion of the axillary glands are excrementitious fluids, but they contain a
certain quantity of the secretion of the sebaceous glands. Certain excre-
mentitious matters are found in the bile, but at the same time, this fluid con-
tains substances that are formed in the liver, and it has an important office
as a secretion, in connection with the processes of digestion.

PHYSIOLOGICAL ANATOMY OF THE SKIN,

The skin is one of the most complex and important structures in the
body, and it has a variety of uses. In the first place, it forms a protect-
ive 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 sensibility, the skin
has important uses, being abundantly supplied with sensory nerves, some of
which present an arrangement peculiarly adapted to the nice appreciation of
tactile impressions. The skin assists in preserving the external forms of the
muscles. It also relieves the abrupt projections and depressions of the gen-
eral surface and gives roundness and grace to the contours of the body. In
some parts it is very closely attached to the subjacent structures, 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, the
evaporation of water from the general surface is always considerable and is
subject to such modifications as may become necessary from the varied con-
ditions of the animal temperature. Thus, while the skin protects the body
from external influences, its office is important in regulating the heat pro-
duced as one of the phenomena attendant upon the general process of nu-
trition.

As the skin presents such a variety of uses, its physiological anatomy is
most conveniently considered in connection with different divisions of the
subject of physiology. For example, under the head of secretion, the struct-
ure of the different varieties of sebaceous glands has already been described ;
and the anatomy of the skin as an organ of touch will be most appropriately
considered in connection with the physiology of the nervous system. In
connection with the excreting organs found in the skin, it will be convenient
to describe 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 Skin. — Sappey has made a number of obser-
vations upon the extent of the surface of the skin. Without detailing the
measurements 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 lit-
tle more than sixteen square feet (15,000 square centimetres) ; and in men of

PHYSIOLOGICAL ANATOMY OF THE SKIN. 343

more than ordinary size, it may extend to twenty-one or twenty-two square
feet (2 square metres). In women of medium size, as the mean result of
threa observations, the surface was found to equal about twelve and a half
square feet (11,500 square centimetres).

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 pressure and friction to which the surface is
habitually subjected. The true skin is TV to -J- of an inch (2-1 to 3-2 mm.)
in thickness ; but in certain parts, particularly in the external auditory mea-
tus, the lips and the glans penis, it frequently measures not more than y^- of
an inch (0-254 mm.).

Layers of the Skin. — The skin is naturally divided into two principal lay-
ers, 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 more or less closely attached to the subjacent
structures by a fibrous structure called the subcutaneous areolar tissue, in the
meshes of which there is usually a certain quantity of adipose tissue. This
layer is sometimes described under the name of the panniculus adiposus. 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. Be-
neath 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 T^- of an inch (2-1
mm.) in thickness. In other parts it usually measures -J- to \ of an inch (4-2
to 12'7 mm.). In very fat persons it may measure an inch (25-4 mm.) or
more. Upon the head and the neck, in the human subject, are muscles at-
tached 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
subcutaneous areolar tissue ; and the under surface of the skin is always ir-
regular, from the presence of fibres which are necessarily divided in detach-
ing it from the subjacent structures. The fibres which enter into the com-
position of the skin become looser in their arrangement near its under surface,
the change taking place rather abruptly, until they present large alveoli, which
generally contain a certain quantity 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 epi-
dermis 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 Skin. — The reticulated and the papillary layers of
the true skin are quite distinct. The lower stratum, the reticulated layer, is

344 EXCEETION BY THE SKIN AND KIDNEYS.

much thicker than the papillary layer and is dense, resisting, quite elastic
and slightly contractile. It is composed of bundles of fibrous tissue, inter-
lacing with each other in every direction, generally at acute angles. Distrib-
uted throughout this layer, are found anastomosing elastic fibres of the small
variety, and with them a number of non-striated muscular fibres. This por-
tion 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 con-
nected 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 particularly 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 arrangement 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 man-
ner in which the " goose-flesh " is produced. (See Fig. 107, page 349.) Con-
traction of the skin, under the stimulus of electricity, has been repeatedly
demonstrated, both in the living subject and in executed criminals immedi-
ately after death.

The papillary layer of the skin passes insensibly into the subjacent struct-
ure without any marked line of division. It is composed chiefly of amor-
phous matter like that which exists in the reticulated layer. The papilla?
themselves appear to be simple elevations of this amorphous matter, although
they contain a few fibres, connective-tissue nuclei and little corpuscular
bodies called cytoblastions (Robin).

As regards their form, the papillae 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 distrib-
uted on the general surface. The smallest are T^ to ^-g- of an inch (36 to
62 /A) 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
^io- to -gfa of an inch (100 to 125 ft). 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, particu-
larly the palmar surfaces of the last phalanges, are formed by double rows of
compound papillae, which present two, three or four elevations attached to a
single base. In the centre of each of these double rows of papillae, is a fine
and shallow groove, in which are found the orifices of the sudoriferous ducts.

The papillae are abundantly supplied with blood-vessels terminating in
looped capillary 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 abundant in the skin,
has already been indicated in the general description of the lymphatic system.

The Epidermis and its Appendages. — The epidermis, or external layer of
the skin, is composed of cells. It has neither blood-vessels, nerves nor lym-

PHYSIOLOGICAL ANATOMY OF THE NAILS. 345

phatics. Its external surface is marked by shallow grooves, which correspond
to the deep furrows between the papillae 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 Mal-
pighian layer, and the external is called the horny layer. These two layers
present certain important distinctive characters.

The Malpighian layer is composed of a single stratum of prismoidal, nu-
cleated cells, containing pigmentary matter, 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-transparent and nearly colorless ; and it is the pigment-
ary layer chiefly which gives to the skin its characteristic color and the pe-
culiarities in the complexion of different races and of different individuals.
All the epidermic cells are somewhat colored in the dark races, but the upper
layers contain no pigmentary granules. The thickness of the rete mucosum
is -J-J00- to T^J of an inch (15 to 333 ft).

The horny layer is composed of a number of strata of hard, flattened cells,
irregularly polygonal in shape and generally without nuclei. The deeper
colls are thicker and more rounded than those of the superficial layers.

The epidermis serves as a protection to the more delicate structure of the
true skin, and its thickness is in proportion to the exposure of the different
parts. It is consequently 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 and eyelids, and in the external auditory pas-
sages, the epidermis is most delicate. The variations in thickness depend
entirely upon the development of the horny layer. The thickness of the
rete mucosum, although it varies in different parts, is rather more uniform.

There is constantly more or less desquamation of the epidermis, particu-
larly of the horny layer, and the cells are regenerated from the subjacent
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, flattened scales of the horny layer.

Physiological Anatomy of the Nails. — The nails are situated on the dor-
sal 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 prehen-
sion. The general appearance of the nails is sufficiently familiar. In their
description, anatomists have distinguished a root, a body and a free border.

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, ex-
tending around the nail to its free edge. The length of the root varies with
the size of the nail, but it is generally 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

316

EXCRETION BY THE SKIN AND KIDNEYS.

2 7 3 il

to the free border. This portion of the nail, with the root, is closely adher-
ent by its under surface to the true skin. It is marked by fine but distinct

longitudinal stria}
and very faint
transverse lines.
It usually is red-
dish in color on ac-
count of the great
vascularity of the
subjacent struct-
ure. At the pos-
terior part, is a
whitish portion, of

FIG. 105 — Anatomy of the nails (Sappey).

A, nail in situ : 1, cutaneous fold covering 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.

C, longitudinal section of the nail : 1, 2, epidermis ; 3, superficial layer of

the nail ; 4, epidermis of the pulp of the finger ; 5, 6, true skin : 7, 11, r»pnranr>p
bed of the nail ; 8, Malpighian layer of the pulp of the finger ; 9, 10, true r ec
skin on the dorsal surface of the finger ; 12, true skin of the pulp of the
finger ; 13, last phalanx of the finger.

„ ,

a Semilunar shape,

™liinVi Via a
WHICH lias

ap-

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 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 an inch and a half to two inches (40 to 50 mm.).

On examining the nail in a longitudinal section, the horny layer, which is
usually regarded as the true nail, is found to increase progressively in thick-
ness 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 nail be-
comes 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 layers of the epidermis, although
they are much more 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 com-
posed of a number of strata of elongated, prismoidal, nucleated cells, arranged
perpendicularly to the matrix.

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 strata of flattened cells which can not be isolated without

PHYSIOLOGICAL ANATOMY OF THE NAILS.

34T

the use of reagents. If the different strata of this portion of the nail be
studied after boiling in a dilute solution of sodium or potassium hydrate,
it becomes evident that here, as

in the horny layer of the epider- IMH^^^Hi^S^B^M 4
mis, the lower cells are rounded,
while those nearer the surface
are flattened. These cells are
nearly all nucleated. The thick-
ness of this layer varies in differ-
ent portions of the nail, while
that of the Malpighian layer is
nearly uniform. This layer is'
constantly growing, and it con-
stitutes 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 rela-
tions of these structures to the
epidermis itself are somewhat
peculiar. Before the fourth
month of foetal life, the epider-
mis covering the dorsal surfaces
of the last phalanges of the fin-
gers and toes does not present
any marked peculiarities ; but at
about the fourth month, the pe-
culiar hard cells of the horny

laver Of the nails make their ap- 6, 6, dark line between the two layers.

J B, cells of the superficial layer, lateral view,

pearance between the Malpighi- C, cells of the superficial layer, flat view.

to D, cells of the deep layer.

an 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 thickened
and the cells assume a more 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 nails are therefore to be regarded as
modifications of the horny layer of the epidermis, possessing certain anatom-
ical and chemical peculiarities. The Malpighian layer of the nails is con-
tinuous with the same layer of the epidermis, but the horny layers are dis-
tinct.

One of the most striking peculiarities of the nails is their mode of

348 EXCRETION BY THE SKIN AND KIDNEYS.

growth. The Malpighian layer is stationary, but the horny layer is con-
stantly 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 dimin-
ished.

Physiological Anatomy of the Hairs. — Hairs, varying greatly in size,
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 surfaces of the fingers and toes, the dorsal surfaces 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.

The second variety, the short, stiff hairs, is found just within the nostrils,
upon the edges of the eyelids and upon the eyebrows.

The third variety, the short, soft, downy hairs, is found on parts of the
general surface not occupied by the long hairs, and in the caruncula lachry-
malis. In early life, and ordinarily in the female at all ages, the trunk and
extremities are covered with downy hairs ; but in the adult male, these fre-
quently become developed into long, soft hairs.

The hairs are usually set obliquely in the skin and take a definite direc-
tion 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
directions in different persons.

The diameter and length of the hairs are variable in different persons, es-
pecially in the long, soft hairs of the head and beard. It may be stated in
general terms that the long hairs attain the length of twenty inches to
three feet (500 to 900 mm.) in women, and considerably less in men. 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 J to \ of an inch (6-4 to 12'7 mm.) in length. The
soft, downy hairs measure ordinarily TV to \ of an inch (2-1 to 12-7 mm.) in
length.

Of the long hairs, the finest are upon the head, where they average about
-fa of an inch (64 p] in diameter. The hair ordinarily is 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

PHYSIOLOGICAL ANATOMY OF THE HAIRS.

349

head. The average number of hairs upon a square inch of the scalp is about
1,000 (155 in a square centimetre) and the number upon the entire head,
about 120,000 (Wilson).

When the hairs are in a perfectly normal condition, they are very elastic
and may be stretched to one-fifth or one-third more than their original

FIG. 107.— Hair and hair-follicle (Sappey).
root of the hair ; 2, bulb of the hair ; 3, internal root-
sheath ; 4, external root-sheath ; 5, membrane of
the hair-follicle (the internal, amorphous mem-
brane of the follicle is very delicate and is not rep-
resented in the figure) ; 6, external membrane of
the follicle ; 7, 7, muscular bands attached to the
follicle ; 8, 8, extremities of these bands passing to
the skin ; 9, compound sebaceous gland, with its
duct (10) opening into the upper third of the fol-
licle ; 11. simple sebaceous gland ; 12, opening of
the hair-follicle.

FIG. 108.— Root of the hair (Sappey).
1, root of the hair ; 2, hair-bulb : 3, papilla of
the follicle ; 4, opening of the follicle ; 5,
5, internal root-sheath ; 6, external root-
sheath ; 7, 7, sebaceous glands ; 8, 8, ex-
cretory ducte of the sebaceous glands.

length. Their strength varies with their thickness, but an ordinary hair from
the head will bear a weight of six to seven ounces (170 to 200 grammes). A
well known property of the hair is that of becoming strongly electric by

350 EXCEETION BY THE SKIN AND KIDNEYS.

friction ; and this is particularly 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 ist 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 hygrometers.

Roots of the Hairs, and Hair-follicles. — The roots of the hairs are em-
bedded in follicular openings in the skin, which differ in the different vari-
eties 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 becomes enlarged into a rounded bulb at the bottom of the follicle, and rests
upon a fungiform papilla, constricted at its base, to which the hair is closely
attached.

The hair-follicles are tubular inversions of the structures that compose the
corium, and their walls present three membranes. Their length is ^ to ^ of
an inch (2*1 to 6*4 mm.). The membrane that forms the external coat of the
follicles is composed of inelastic fibres, generally arranged longitudinally. It
is provided with blood-vessels, a few nerves and some connective-tissue ele-
ments, but no elastic tissue. This is 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 re-
semble non-striated muscular fibres. The internal membrane is structureless
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 con-
nected 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 rec-
ognizable, it is evident that the hair-sac is nothing more than an inversion of
the corium, with certain 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 pecul-
iar 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 papillae 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 ex-
actly with the Malpighian layer of the epidermis. This sheath is continu-
ous with the bulb of the hair. The internal root-sheath is a transparent

PHYSIOLOGICAL ANATOMY OF THE HAIRS.

351

membrane, composed of flattened cells, generally 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 certain
peculiarities in their anatomy, but all of them are composed of a fibrous
structure forming the greater part of their substance, covered by a thin layer

FIG. 109. — Human hair from the head of a white
child ; magnified 370 diameters (from a pho-
tograph taken at the United States Army Med-
ical Museum).

This figure shows the imbricated arrangement of
the epidermis of the hair.

FIG. 110. — Transverse section of a human hair
from the beard of a ivhite adult ; magnified
370 diameters (from a photograph taken at the
United States Army Medical Museum).

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.

The fibrous substance of the hairs is composed of hard, elongated, longi-
tudinal fibres, which can not be isolated without the aid of reagents. They
may be separated, however, by maceration in warm sulphuric acid, when
they present themselves in the form of dark, irregular, spindle-shaped plates.
These contain pigmentary matter of various shades of color, occasional cavi-
ties filled with air, and a few nuclei. The pigment may be of any shade,
between a light yellow and 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 very thin and is composed of flattened,
quadrangular plates, overlying each other from below upward. These scales,
or plates, are without 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,
tne cells are thicker, softer, are frequently nucleated, and they exist in two
layers.

The medulla is found in the short, stiff hairs, and it is often very distinct

352 EXCRETION BY THE SKIN AND KIDNEYS.

in the long, white hairs of the head. It occupies one-fourth to one-third of
the diameter of the hair. The medulla can be traced, under favorable con-
ditions, from just above the bulb to near the pointed extremity of the hair.
It is composed of small, rounded, nucleated cells, which frequently contain
dark granules of pigmentary matter. Mixed with these cells are air-glob-
ules ; and frequently the cells are interrupted for a short distance and the
space is filled with air. The medulla likewise contains a glutinous fluid be-
tween the cells and surrounding the air-globules.

Groivth of the Hairs. — Although not provided with blood and devoid
of sensibility, the hairs are connected with vascular parts and are nourished
by imbibition from the papillae. Each hair is first developed in a closed
sac, and at about the sixth month of intrauterine life, its pointed extremity
perforates the epidermis. These first-formed hairs are afterward shed, like
the milk-teeth, being pushed out by new hairs from below, which latter arise
from a second and a more deeply seated papilla. This shedding of the hairs
usually takes place between the second and the eighth month 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 be-
comes white or gray from a blanching of the cortex and medulla.

Sudden Blanching of the Hair. — There are a few instances on record 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 important in connection
with the rep'orted instances which have not been subjected to proper investi-
gation. One of these cases has been reported by Landois. In this instance
the blanching of the hair occurred in a hospital in a single night, while the
patient, who had an acute attack of delirium tremens, was under the daily
observation of the visiting physician.

The microscopical examinations by Landois and others leave no doubt as
to the cause of the white color of the hair in cases of sudden blanching ; and
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 gradually become gray 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 under-
stand ; 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 con-
nected with intense grief or terror. The terror was very marked in the case
reported by Landois. In the great majority of recorded observations, the
sudden blanching of the hair has been apparently connected with intense

PERSPIRATION. 353

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 Hair. — The hairs serve an important purpose in the protec-
tion 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
quantity 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, which is very important in per-
sons exposed to dust in long journeys or in their daily work ; and the short,
stiff hairs at the openings of the ears and nose protect 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
action of the skin as an excreting organ and includes the exhalation of carbon
dioxide as well as of watery vapor and organic matters. The office of the
skin as an eliminator is undoubtedly very important ; but the quantity of
excrementitious matters with the properties of which physiologists are well
acquainted, such as carbon dioxide and urea, thrown off from the general
surface, is small as compared with what is 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 difficult to explain. All that can be said upon this point
is that death takes place when the heat of the body has been reduced to about
70° Fahr. (21° C.), and that suppression of the action of the skin in this way
is always followed by a depression of the animal temperature. Warm-blooded
animals die usually when more than one-half of the general surface has been
varnished. Rabbits die when one-fourth of the surface has 'been covered
with an impermeable coating (Laschkewitsch). Valentin and Laschkewitsch
found that when the temperature was kept at about the normal standard by
artificial means, no morbid symptoms were developed. The cause of death
in these experiments has never been satisfactorily explained ; and it is not
easy to understand why coating the surface should be followed by such a
rapid diminution in the general temperature. The experimental facts, how-
ever, indicate that the skin probably possesses important uses with which
physiologists are unacquainted. Urea and some other effete products have
been detected in the perspiration, but it is probable that some volatile mat-
ters are eliminated by the general surface, which have thus far escaped ob-
servation.

Sudoriparous Glands. — With few exceptions, every portion of the skin
is provided with sudoriparous glands. They are not found, however, in tne

354

EXCRETION BY THE SKIN AND KIDNEYS.

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 re-
garded as sudoriparous organs, in the external auditory meatus.

On examining the surface of the skin with a low magnifying power, espe-
cially on the palms of the hands and the soles of the feet, the orifices of the

sudoriferous ducts may be seen in the mid-
dle of the papillary ridges, forming a regu-
lar line in the shallow groove between the
two rows of papillae. The tubes always
open upon the surface obliquely. In a thin
section of the skin, the ducts are seen pass-
ing through the different layers and ter-
minating in rounded, convoluted coils in
the subcutaneous structure. These little,
rounded or ovoid bodies, which are the su-
doriparous, or sweat-producing structures,
FIG. in.— Surface of the palm of the hand, maybe seen attached to the under surface

a portion of the skin about one half an »,n , . -, .,T -, -,/.

inch (is-? mm.) square ; magnified 4 di- of the skin when it has been removed from

i,i,Monsothe sudoriferous ducte; the subjacent parts by maceration. A per-
of'thlskifr°ovesbetween the papillae spiratory gland consists, indeed, of a simple

tube, presenting a coiled mass, the sudorip-
arous portion, beneath the skin, and a tube of greater or less length, in pro-
portion to the thickness of the cutaneous layers, which is the excretory duct,
or the sudoriferous portion.

The glandular coils are yj^ to ^ of an inch (O2 to 1 mm.) in diameter ;
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 perineum. Very large glands are
found mixed with smaller ones in the axilla, and these produce a peculiar
secretion. The coiled portion of the tube is about -^ of an inch (0-07 mm.)
in diameter, and presents six to twelve turns. It consists of a sharply defined,
strong, external membrane, which is very transparent, uniformly granular and
sometimes indistinctly striated. The tube 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 matter, usually not
segmented into cells, and is provided with small, oval nuclei. The glandular
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 delicate 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 papillae 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. Six to ten are found in the palms of the
hands and twelve to fifteen in the soles of the feet (Sappey). As it emerges
from the glandular coil, the excretory duct is somewhat narrower than the

MECHANISM OF THE SECRETION OF SWEAT.

355

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.

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

< . I- I 1 ?-:

generally are situated at different planes be-
neath the skin, as is indicated in Fig. 112.

Sudoriparous glands in the axilla have been
described which do not differ so much from
the glands in other parts in their anatomy as
in the character of their secretion. The coil
in these glands is much larger than in other
parts, measuring -fa to ^ of an inch (1 to 2
mm.) ; the walls of the tube are thicker, and
they present an investment of fibrous tissue
with an internal layer of longitudinal, non-
striated muscular fibres ; and finally, the tubes
of the coil itself are lined with cells of epithe-
lium. These glands are very abundant in the
axilla, forming a continuous layer beneath the
skin. Mixed with these, are a few glands of
the ordinary variety.

Estimates have been made of the number
of sudoriparous glands in the body and the
probable extent of the exhalant surface of the

skin, but they are to be taken as merely approx- FIG. 112.— sudoriparous glands ;

nified 20 diameters (Sappey).
, epidermis ; 2, 2, mucous layer ;
3, 3, papillae ; 4, 4, derma ; 5, 5, sub-
cutaneous areolar tissue ; 6, 6, 6, 6,
sudoriparous glands ; 7, 7, adipose
vesicles ; 8, 8, excretory ducts in
the derma ; 9, 9, excretory ducts
divided.

-*r £ j , j-ry, • j_i

imate. Krause found great differences in the

number of perspiratory openings in different

portions of the skin; but taking an average

for the entire surface, it was estimated that

the entire number of perspiratory glands is

2,381,248 ; and assuming that each coil when unravelled measures about ^

of an inch (1*8 mm.), the entire length of the secreting tubes is about 2J-

miles (3f kilometres). 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 glandu-
lar 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 separation 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, which becomes vaporous
as it is discharged upon the surface.

The influence of the nervous system upon the secretion of sweat is impor-

356 EXCRETION BY THE SKIN AND KIDNEYS.

tant. It is well known, for example, that an abundant production of per-
spiration is frequently the result of mental emotions. Bernard has shown
that the nervous influence may be exerted through the sympathetic system.
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 stimu-
lating the divided extremity of the nerve, the secretion of sweat was arrested.
The local secretion of sweat after division of the sympathetic in the neck of
the horse was first observed by Dupuy, in 1816.

The stimulation as well as the division of certain nerves induces local
secretion of sweat, but this is nearly always associated with dilatation of the
blood-vessels of the part ; still, sweat is frequently secreted when the surface
is pale and bloodless, showing that dilatation of the blood-vessels is not an
indispensable condition. The action of the so-called vaso-dilator nerves will
be treated of in connection with the physiology of the nervous system. In
experiments upon the cat, excito-secretory fibres have been found to exist in
the cerebro-spinal nerves going to the anterior extremities. The fibres for
the posterior extremities are in the sheath of the sciatic nerve. In all in-
stances the action of these nerves is direct and not reflex. Experiments upon
the cat have been very satisfactory, as this animal sweats only on the soles of
the feet, and the secretion can be readily observed.

The so-called sweat-centres are in the lower part of the dorsal region of
the spinal cord, for the posterior extremities, and in the lower part of the
cervical region of the cord, for the anterior extremities. According to Adam-
kiewicz, both of these centres are subordinate to the principal sweat-centre,
which is situated in the medulla oblongata. Ott has collected a number of
cases of disease of the cord in the human subject, which go far to confirm
the results of experiments on the inferior animals, with regard to the action
of excito-secretory nerves and sweat-centres.

When the skin is in a normal condition, after exercise 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 quantity of cutaneous exhala-
tion 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 action of the skin in regulating the tempera-
ture of the body ; and it is probable that the elimination of excrementitious
matters by the skin is not subject, under normal conditions, to the same
modifications, although positive experiments upon this point are wanting.
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 pos-
sible only to give approximate estimates of the quantity of sweat secreted

PROPERTIES AND COMPOSITION OF THE SWEAT. 357

and exhaled in the twenty-four hours. Seguin and Lavoisier (1790) esti-
mated the daily quantity of cutaneous transpiration at one pound and four-
teen ounces (850 grammes), and the results of their observations have been
fully confirmed by recent investigations. It may be assumed that the aver-
age quantity is nearly two pounds, or about 900 grammes.

Under violent and prolonged exercise, the loss of weight by exhalation
from the skin and lungs may become very considerable. It is stated by
Maclaren, the author of a work on training, that in one hour's energetic
fencing, the loss by perspiration and respiration, taking the average of six
consecutive days, was forty ounces (1,130 grammes), with a range of variation
of eight ounces (227 grammes).

When the body is exposed to a high temperature, the exhalation from the
surface is largely increased ; and it is by this rapid evaporation that persons
have been able to endure for several minutes a dry heat considerably exceed-
ing that of boiling water. Southwood Smith made a series of 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 was two to four pounds (907 to 1,814 grammes), this being chiefly by
exhalation of watery vapor from the skin. In such instances the loss of water
by transpiration is compensated by the ingestion of large quantities of liquid.

Properties and Composition of the Sweat. — An analysis of the sweat was
made by Favre, in 1853. After taking every precaution to obtain the secre-
tion in a perfectly pure state, he collected a very large quantity, nearly thirty
pints (14 litres), the result of six transpirations from one person, which he
assumed to represent about the average in composition. The liquid was per-
fectly 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 be-
comes alkaline on being subjected to evaporation, showing that it contains
some of the volatile acids. Favre 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, it was con-
stantly alkaline. The specific gravity of the sweat is 1003 to 1004. The fol-
lowing 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 1-562

Sodium chloride,
Potassium chloride,
Alkaline sulphates,
Alkaline phosphates,
Alkaline albuminates,

Alkaline earthy phosphates (soluble in acidulated water) a trace

Epidermic debris (insoluble; a trace

2-230

0-244

soluble in water 0-012

a trace

0-005

1,000-000

358 EXCRETION BY THE SKIN AND KIDNEYS.

The sweat is exhaled usually in the form of 'vapor, when it is known as
insensible perspiration. When from any cause it collects on the surface, in
the form of a liquid, it is called sensible perspiration.

The peculiar constituents of the sweat have been more carefully and suc-
cessfully studied since the analyses of Favre. The neutral fats are probably
derived in great part from the sebaceous glands, although certain fats, palmi-
tine and stearine, have been found in the secretion of the palms of the hands,
which contain no sebaceous glands. The volatile fatty acids are formic,
butyric, caproic, capric, acetic etc., some of which exist also in milk. These
give to the sweat its peculiar odor. Urea is always present in small quan-
tity, and its proportion may be largely increased when there is a deficiency of
elimination by the kidneys. It is a matter, also, of common as well as of
scientific observation that the sweat is more abundant when the kidneys are
comparatively inactive, and vice versa. Generally, however, conditions oper-
ate to increase the quantity of sweat, and the quantity of urine is proportion-
ally diminished. The skin is undoubtedly an important organ of excretion,
and it may eliminate excrementitious matters of a character as yet unknown.
The action of the skin as a respiratory organ has already been considered.
With regard to the inorganic constituents of the sweat, there is no great inter-
est attached to any but the sodium chloride, which exists in a proportion
many times greater than that of all the other inorganic salts 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 alka-
line ; 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. Sometimes
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.

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS.

The kidneys are symmetrical organs, situated in the lumbar region, be-
neath the peritoneum, invested by a proper fibrous coat, and always sur-
rounded 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
appropriately compared to a bean ; and the concavity, the deep, central por-
tion of which is called the hilum, looks inward toward the spinal column.
The weight of each kidney is four to six ounces (113 to 170 grammes), usu-
ally about half announce (14 grammes) less in the female than in the mala
The left kidney is nearly always a little heavier than the right.

Outside of the proper coat of the kidney, is a certain quantity of adipose
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 ordinary

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS.

359

fibrous tissue, interlaced with small elastic fibres. 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.

The kidney in a vertical section presents a cavity at the hilum, which is
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 re-
ceive two or three. The calices unite into three short, funnel-shaped tubes,
called infundibula, corresponding respectively to the superior, middle and
inferior portions of the kidney. These finally open into the common cavity,
or pelvis. The substance of the kid-
ney is composed of two distinctly
marked portions, called the cortical
substance, and the medullary, or py-
ramidal substance.

The cortical substance is reddish
and granular, rather softer than the
pyramidal substance, and is about one-
sixth of an inch (4*2 mm.) in thick-
ness. This occupies the exterior of
the kidney and sends little prolonga-
tions, called the columns of Bertin, be-
tween the pyramids. The surface of
the kidney is marked by little, poly-
gonal divisions, giving it a lobulated
appearance. This, however, is mainly
due to the arrangement of the super-
ficial blood-vessels. The medullary
substance is arranged in the form of
pyramids, sometimes called the pyra-
mids of Malpighi, twelve, fifteen or
eighteen in number, their bases pre-

3 *

sen ting toward the cortical substance, i, i, 2, 2, 3, 3, 3, 4, 4, 4, 4, pyramids of

and their apices being received into

the calices, at the pelvis. Ferrein sub-

divided the pyramids of Malpighi into

smaller pyramids, called the pyramids of Ferrein, 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 pass into the cor-

tical substance, forming corresponding pyramids of convoluted tubes, thus

dividing this portion of the kidney into lobules, more or less distinct.

The medullary substance is firm, of a darker red color than the cortical
substance, and is marked by tolerably distinct striae, which take a nearly

FIG. 113.— Vertical section of the kidney (Sappey).

8' upper extremi'

360

EXCRETION BY THE SKIN AND KIDNEYS.

straight course from the bases to the apices of the pyramids. As these strise
indicate the direction of the little tubes that constitute the 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, these
organs 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 constituents of this fluid 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, presents ten to twenty-five little openings, -^ to -^ of an inch (85
to 425 p) in diameter. The tubes leading from the pelvis immediately

FIG. 111.— Longitudinal section of the py-
ramidal substance of the kidney of the
foetus (Sappey).

1, trunk of a large uriniferous 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. 115. — Longitudinal section of the cortical sub
stance of the same kidney (Sappey).

1,1, limit of the cortical substance and base of the pyr-
amids ; 2, 2, 2, tubes passing toward the surface of
the kidney ; 3, 3. 3, 8, 8, 8, convoluted tubes ; 4, 4, 4,
4, 5, Malpighian bodies ; 6, 6, artery, with its branch-
es (7, 7, 7) ; 9, 9, fibrous covering of the kidney.

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. 361

divide at very acute angles, generally dichotomously, until a bundle of tubes
arises, as it were, from each opening. These bundles constitute the pyra-
mids of Ferrein. In their course the tubes are slightly wavy and are nearly
parallel to 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 blood-vessels,
which latter generally pass beyond the pyramids, to be finally distributed in
the cortical substance. Small tubes, continuous with the convoluted tubes
of the cortical substance, dip down into the pyramids, returning to the corti-
cal substance in the form of loops. This arrangement will be fully described
in connection with the cortical substance.

The tubes of the pyramidal substance are composed of a strong, struct-
ureless basement-membrane, lined with granular, nucleated cells. Accord-
ing to Bowman, the tubes measure ^-j-g- to -gfa of an inch (85 to 127 /*), in
diameter at the apices, and near the bases of the pyramids their diameter is
about -g^- of an inch (42 /*).

The cells lining the straight tubes exist in a single layer applied to the
basement-membrane. They are thick and irregularly polygonal in shape, with
abundant albuminoid granules. They present one, and occasionally, though
rarely, two granular nuclei, with one or two nucleoli. They readily undergo
alteration and are seen in their normal condition only in a perfectly fresh,
healthy kidney. Their diameter is about J-^Q of an inch (17 /A). The cali-
ber of the tubes is reduced by the thickness of their lining epithelium to ?fa
or -5^0 of an inch (28 or 30 ft).

Cortical Substance. — In the cortical portion of the kidney, are found
tubes, differing somewhat from the tubes of the pyramidal portion in their
size and in the character of their epithelial lining, but presenting the most
marked difference in their direction. These tubes are rather larger than the
tubes of the pyramidal substance, and are very much convoluted, interlacing
with each other 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 Malphigian bodies. These
are simply flask-like, terminal dilatations of the tubes themselves.

The cortical portion of the kidney presents a delicate, fibrous matrix,
which forms a support for the secreting portion and its blood-vessels. The
tubes of the cortical substance present considerable variations in size, and
three well defined varieties can be distinguished :

1. The ordinary convoluted tubes, directly connected with the Malpig-
hian 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. Communicating tubes, forming a plexus connecting the different
varieties of tubes with each other and finally with the straight tubes of the
pyramidal portion.

In tracing out the course of the tubes, it will be found most convenient
to begin with a description of the Malpighian bodies and to follow the tubes

362 EXCEETION BY THE SKIN AND KIDNEYS.

from these bodies to their connections with the straight tubes of the pyram
idal substance.

Malpighian Bodies. — These are ovoid or rounded, terminal dilatations of
the convoluted tubes, and are ^ to ^ of an inch (100 to 250 /A), in diam-
eter. They are composed of a membrane, which is continuous with the ex-
ternal membrane of the convoluted tubes, and is of the same homogeneous
character, but somewhat thicker. This sac, called the capsule of Miiller or
of Bowman, encloses a mass of convoluted blood-vessels and is lined with a
layer of nucleated epithelial cells. In addition to the cells lining the cap-
sule, there are other cells which are applied to the blood-vessels.

The cells attached to the capsule of Miiller are smaller and more trans-
parent 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 T^F to y^Vo °f an incn (16 to 25 /*), in diameter, by about -g-gVo- °f
an inch (10 //,) in thickness.

Tubes of the Cortical Substance. — Passing from the Malpighian bodies,
the tubes present first a short, constricted portion, called the neck of the
capsule, which soon dilates to the diameter of about -^ of an inch (50 /A),
when their course becomes quite 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 is
lined throughout with a single layer of epithelial cells, y^ to y^Vo of an
inch (16 to 25 p) in diameter, somewhat larger, consequently, than the cells
lining the straight tubes. The cells lining the convoluted tubes present two
tolerably distinct portions. The inner portion or zone, which is next the
lumen of the tube, is finely granular, with sometimes a few small oil-glob-
ules. The outer zone presents little fibrils or rods, which are perpendicular
to the tubular membrane. These are called " rodded " cells, and a similar
appearance is presented by some of the cells of the pancreas and of the sali-
vary glands. The nucleus is usually situated between the granular and the
rodded zones.

The researches of Heidenhain and others have shown that the greatest
part 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 and a certain portion of the inorganic salts
of the urine transude through the blood-vessels in the Malpighian bodies.
This view was first advanced by Bowman, in 1842.

Narrow Tubes of Henle. — The convoluted tubes above described, after a
tortuous course in the cortical substance, become continuous, near the pyra-
mids, with the 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

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS.

363

present enlargements at irregular intervals in their course. The narrow por-
tions are about j-^ of an inch (12 p) in diameter, and the wide portions,

FIG. 116.— Structure of the kidney (Landois).

I, blood-vessels and tubes (semi-diagrammatic). A, capillaries of the cortical substance ; B, capillaries

of the medullary substance ; 1. artery penetrating a Malpighian body ; 2, vein emerging from a

Malpighian body ; R, arteriolae rectae ; c, venae rectae ; v, v, interlobular veins ; s, stellate veins ;

I, i, capsules of Miiller ; x, x, convoluted tubes ; T, T, T. tubes of Henle ; N, N, N, N, communicating

tubes ; o, o, straight tubes ; O, opening into the pelvis of the kidney.

IT, Malpighian body. A, artery ; E, vein ; c, capillaries ; K, epithelium of the capsule ; H, beginning of
a convoluted tube.

III, rodded cells from a convoluted tube. 1, view from the surface ; 2, side view (o, granular zone).

IV, cells lining the tubes of Henle.

V, cells lining the communicating tubes.

VI, section of a straight tube.

about twice this size. The narrow portion is lined by small, clear cells
with very prominent nuclei. The wider portions are lined by larger, gran-

364 EXCRETION BY THE SKIN AND KIDNEYS.

ular cells. Near the bases of the pyramids the wide portion sometimes
forms the loop, but near the apices the loop is always narrow. The differ-
ence 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 Bel-
lini.

Intermediate Tubes. — After the narrow tubes of Henle have returned to
the cortical substance, they communicate with a system of flattened, ribbon-
shaped, anastomosing canals, y^- to -^^ of an inch (21 to 25 /x) in diam-
eter, with very thin walls, lined by rodded 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 es-
tablishing 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.

The tubes into which the intermediate canals open join with others gen-
erally two by two, and then pass in a nearly straight direction into the pyra-
mids, where they continue to unite. with each other in their course, becoming,
consequently, reduced in number until they open at the apices of the pyra-
mids, into the infundibula and the pelvis of the kidney.

Distribution of Blood-vessels in the Kidney. — The renal artery, which is
quite voluminous in proportion to the size of the kidney, enters at the hilum
and divides into four branches. A number of smaller branches penetrate
between the pyramids and ramify in the columns of cortical substance which
occupy the spaces between the pyramids (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,
the arterial arcade, situated between the rounded base of the pyramid and
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 direc-
tions. From its concavity, small branches, measuring at first T^ o- to -?%-$ of
an inch (21 to 34 ft) in diameter, pass downward toward the papillae, giving
off small ramifications at very acute angles, and becoming reduced in size to
about ^g-g- of an inch (10 /u,). These vessels, called sometimes the arteri-
olge rectse, surround the straight tubes, and pass into capillaries in the sub-
stance of the pyramids and at their apices.

From the convex surface of the arterial arcade, branches are given off at
nearly right angles. These pass into the cortical substance, breaking up into
a large number of little arterial twigs, Tfjnf to -^ of an inch (17 to 40 /A) in
diameter, each one of which penetrates a Malpighian body at a point oppo-

PHYSIOLOGICAL ANATOMY OF THE KIDNEYS.

365

site the neck of the capsule. Once within the capsule, the arteriole breaks
up into five to eight branches, which then divide dichotomously into vessels
measuring -^^ to y^r of an incn (8 to ^ f1) in diameter, arranged in the
form of coils and loops, constituting a dense, rounded mass (the Malpighian
coil, or glomerulus), filling the capsule.
These vessels break up into capillaries
without anastomoses.

The blood is collected from the vessels
of the Malpighian bodies by veins, some-
times one and frequently three or four,
which pass out of the capsule and form
a second capillary plexus surrounding the
convoluted tubes. When there is but one
vein, it generally emerges from the cap-
sule near the point of penetration of the
arteriole.

The efferent vessels, immediately after
their emergence from the capsule, break
up into a very fine and delicate plexus of
capillaries, closely surrounding the con-
voluted tubes. These form a true plexus,
the branches anastomosing freely in every
direction ; and the distribution of vessels
in this part resembles essentially the vas-
cular arrangement in most of the glands.
Bowman has called the branches which
connect together the vessels of the Mal-
pighian tuft and the capillary plexus sur-
rounding the tubes, the portal system of
the kidney. These intermediate vessels
form a coarse plexus surrounding the pro-
longations of the pyramids of Ferrein into
the cortical substance.

The renal, or emulgent vein takes its
origin in part from the capillary plexus FIG. 117.— Blood-vessels of the

.. . r bodies and convoluted tubes of the kidney

surrounding the convoluted tubes and in (Sappey).

T^QT«f -Fr^m +>io imooalo rJiQ+Tn'Vvnforl in +V,rv ^ 1> Malpighian bodies surrounded by the cap-
part irom trie vessels aistrioutea 111 tne

pyramidal substance. A few branches
come from vessels in the envelopes of the
kidney, but these are comparatively un-
important. The plexus surrounding the
convoluted tubes empties into venous rad-
icles which pass to the surface of the kidney, and these present a number of
little radiating groups, each converging toward a central vessel. This arrange-
ment gives to the vessels of the fibrous envelope of the kidney a peculiar, stel-
late appearance, forming what are sometimes called the stars of Verheyn. The

25

sules of Muller : 2, 2. 2, convoluted tubes
connected with the Malpighian bodies ; 3,
artery branching 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 bod-
ies : 8, vessel, the branches of which (9)
pass to the capillary plexus (10).

366 EXCRETION BY THE SKIN AND KIDNEYS.

large trunks which form the centres of these stars then pass through the corti-
cal substance to the rounded bases of the pyramids, where they form a vaulted,
venous plexus corresponding to the arterial plexus already described. The
vessels distributed upon the straight tubes of the pyramidal substance form a
loose plexus around these tubes, except at the papillae, where the network 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 axis of the inter-
pyramidal substance, enveloped in the same sheath with the arteries. Passing
thus to the pelvis of the kidney, the veins converge into three or 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 volu-
minous than the arteries.

The capsule of the kidney has a lymphatic plexus connected with lymph-
spaces below ; and lymph-spaces, in the form of large slits, exist between and
around the convoluted tubes.

The nerves are quite abundant and are derived from the solar plexus, their
filaments following the renal artery in its distribution in the interior of the
organ, and ramifying upon the walls of the vessels.

MECHANISM OF THE PRODUCTION AND DISCHARGE OF URINE.

The most important constituent of the urine is urea — CO(NH2)2 — , a crys-
tallizable, nitrogenized substance, which is discharged by the skin as well as
by the kidneys. This has long been recognized as an excrementitious sub-
stance ; but the first observations that gave any definite 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 developed. For the first two or
three days after the operation there were no symptoms of blood-poisoning ; but
finally stupor and other marked evidences of nervous disturbance supervened,
when the presence of urea in the blood could be easily determined. These ob-
servations were confirmed and extended by Segalas and Vauquelin, in 1822.
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 quan-
tity in the normal blood. Picard (1856) estimated and compared the propor-
tions 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 in the lymph and chyle, in
larger quantity, even, than in the blood(Wurtz).

Bernard and Barreswil (1847) found that animals from which both kid-
neys 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 time the blood never con-
tained an abnormal quantity of urea ; but the contents of the stomach and

MECHANISM OF THE PRODUCTION OF URINE. 367

intestine were found to be highly ammoniacal, and the secretions from these
parts, particularly the stomach, became continuous as well as increased in
quantity. Animals operated upon in this way usually live for four or five
days, and they then die in coma following convulsions. Toward the end of
life, the secretion of gastric and intestinal fluids becomes arrested, probably
from the irritating eifects of ammoniacal decomposition of their contents,
and then, and then only, urea is found to accumulate in the blood.

The results obtained by other experimenters have generally corresponded
with those of Bernard and Barreswil. It has also been ascertained, as was
shown by Segalas and Vauquelin, that urea is an active diuretic when inject-
ed 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.
When urea is injected into the vascular system of a nephrotomized animal,
it produces death in a very short time, with the characteristic symptoms of
uraemic poisoning.

Experiments which were supposed to show that urea and the urates are
formed in the kidneys have been made with the view of comparing the effects
of removal of both kidneys with those produced by tying the ureters. Ac-
cording to these observations, the blood contains much more urea after the
ureters are tied than after removal of the kidneys. These experiments,
which are directly opposed in their results to the observations of Prevost and
Dumas, Bernard and Barreswil, Segalas, and many others, can not be accepted
unless it be certain that all the necessary physiological conditions were fulfilled.
In the first place, it was demonstrated, as early as 1847, that urea does not
accumulate 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 large quan-
tity. In the second place, it is well known that the operation of tying the
ureters is followed by a greatly increased 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 nervous sys-
tem upon the secretions has been closely studied, it is evident that the pain
and disturbance consequent upon the accumulation of urine above the ligat-
ed ureters must have an important reflex action upon the secretions ; and
this would probably interfere with the vicarious elimination of urea and of
other excrementitious substances by the stomach and intestines. It is well
known 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 uraemic symptoms are frequently relieved by the administration of
remedies that act promptly and powerfully upon the intestinal canal. '

From a careful review of the important facts bearing upon the question
under consideration, there does not seem to be any valid ground for a change
in the ideas of physiologists concerning the mode of elimination of urea and
the other important excrementitious constituents of the urine. There is every
reason to suppose that these substances are produced in 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.

368 EXCKETION BY THE SKIN AND KIDNEYS.

Extirpation of one kidney from a living animal is not necessarily fatal.
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 elimination of urine for an indefinite period. In a large number of ex-
periments, the animals killed long after the wound had healed never pre-
sented any marked symptoms of retention of excrementitious matters in the
blood, except in one or two instances. It is a noticeable fact, however, that
in many instances they showed a marked change in disposition, and the ap-
petite became voracious and unnatural. These animals would sometimes eat
faeces, the flesh of dogs, etc., and, in short, presented certain of the phenom-
ena so frequently observed after extirpation of the spleen (Flint). After
extirpation of one kidney, it has been observed that the remaining kidney
increases in weight, although investigations have shown that this is due
mainly to an increase in the quantity of blood, lymph and urinary matters,
and not to a new development of renal tissue. The following is an excep-
tional experiment in which the animal died after extirpation of one kidney :
One kidney was removed 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.
Forty-three days after the operation, the dog appeared to be uneasy, cried
frequently, and went into convulsions, which continued for about three
hours, when he died (Flint, 1864). In one other instance, in which a dog
was kept for more than a year after extirpation of one kidney, it was occa-
sionally observed that the animal was rather quiet and indisposed to move
for a day or two, but this always passed off, and when he was killed he was
as well as before the operation.

Influence of Blood-pressure, the Nervous System etc., upon the Secre-
tion 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., which must operate 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, vaso-motor nerves are distrib-
uted to the walls of the blood-vessels, and they are capable of modifying the
quantity and the pressure of blood in these organs.

It may be stated as a general proposition, ths-t 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
will in a measure account for the increase in the flow of urine during diges-
tion ; but it can not serve to explain all of the modifications that may take
place in the action of the kidneys. Bernard measured the pressure of blood
in the carotid artery of a dog and noted the quantity of urine discharged in
the course of a minute from one of the ureters. Afterward, by tying the

PHYSIOLOGICAL ANATOMY OF THE URINARY PASSAGES. 369

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 min-
ute was immediately increased by a little more than fifty per cent. In
another animal, he diminished the pressure by taking blood from the jugu-
lar vein, and the quantity of urine was immediately reduced about one-half.
He also showed that the increase in the quantity of urine produced by ex-
aggerated pressure of blood in the kidneys could be modified through the
nervous system. The nerves going to one kidney were divided, which pro-
duced an increase in the arterial pressure and a consequent exaggeration 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.

When irritation is applied to the floor of the fourth ventricle, in the median
line, exactly in the middle of the space between the origin of the pneumo-
gastrics and the auditory nerves, the urine is increased in quantity and be-
comes strongly saccharine. When the irritation is applied a little above
this point, the urine is simply increased in quantity, but it contains no sugar ;
and when a puncture is made a little below, sugar appears in the urine,
without any increase in the quantity of the secretion (Bernard). It has also
been observed that section of the spinal cord in the upper part of the dor-
sal region arrests, for a time, the secretion of urine.

Other physiological conditions that affect the urinary excretion influence
the composition of the urine and the quantity of excrementitious matters sep-
arated by the kidneys. These will be fully considered in another place. 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 quantity of urine usually is increased. This is particularly marked when
a large quantity of liquid has been taken.

Inasmuch as the excrementitious matters eliminated by the kidneys are
being constantly produced 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 distin-
guished from the excretions. It was noted by Erichsen, in a case of extro-
version 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. Bernard exposed the ureters in a living animal and fixed a small, silver
tube in each, so that the secretion from either kidney could be readily ob-
served ; and he noted that a large quantity of fluid was discharged from one
side for fifteen to thirty minutes, while the flow from the other side was slight
and in some instances was arrested. The flow then began with activity upon
the other side, while the discharge from the opposite ureter was diminished
or arrested.

Physiological Anatomy of the Urinary Passages. — The excretory ducts
of the kidneys, the ureters, begin each by a funnel-shaped portion, which is

370 EXCRETION BY THE SKIN AND KIDNEYS.

applied to the kidney at the hilum. The ureters themselves are membranous
tubes of about the diameter of a goose-quill, becoming much reduced in cali-
ber as they penetrate the coats of the bladder. They are sixteen to eighteen
inches (40 to 46 centimetres) in length, and pass from the kidneys to the
bladder, behind the peritoneum. They have three distinct coats : an external
coat, composed of ordinary fibrous tissue, with small elastic fibres ; a middle
coat, composed 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.

The fibres of the muscular coat, in the greatest part of the length of the
ureters, interlace with each other in every direction and are not arranged in
distinct layers ; but near the bladder, is an internal layer, in which the direc-
tion of the fibres is longitudinal.

The mucous lining is thin, smooth and without any follicular glands. It
is thrown into narrow, longitudinal folds, when the tube is flaccid, which are
easily effaced by distention. The epithelium exists in several layers and is
remarkable for the irregular shape of the cells. These present, usually, 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, pene-
trate the coats of this organ obliquely, their course in its walls being a little
less than an inch (25 mm.) 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 rela-
tions to the pelvic and abdominal organs as it is empty or more or less
distended. When empty, it lies deeply in the pelvic cavity and is then a
small sac, of an irregularly triangular form. As it becomes filled, it assumes
a globular or ovoid form, rises up in the pelvic cavity, and when excessively
distended, it may extend partly into the abdomen. When the urine is voided
at normal intervals, the bladder, when filled, contains about a pint (nearly
500 c. c.) of liquid ; but under pathological conditions it may become dis-
tended so as to contain ten or twelve pints (about 4 or 5 litres), and in some
instances of obstruction it has been found to contain even more. The blad-
der is usually more capacious in the female than in the male.

The coats of the bladder are three in number. The external coat is sim-
ply a reflection of the peritoneum, 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.

The middle or muscular coat consists of non-striated fibres, 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 vertical diam-
eter. The fibres of the external layer are of a pinkish hue, being much more

MECHANISM OF THE DISCHARGE OF URINE. 371

highly colored than the other layers. The middle layer is formed of circular
fibres, arranged, on the anterior surface 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 layer is composed
of pale fibres arranged in longitudinal fasciculi, the anterior and lateral bun-
dles anastomosing with each other, as they descend toward the neck of the
bladder, by oblique bands of communication, and the posterior bundles inter-
lacing in every direction, forming an irregular plexus. Here they are not to
be distinguished from the fibres of the middle layer. This is sometimes called
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 vesicse is a band of non-striated fibres, about half an inch
(12- 7 mm.) in breadth and one-eighth of an inch (3-2 mm.) 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.

The mucous membrane of the bladder is smooth, rather pale, thick, and
loosely adherent to the submucous tissue, except over the corpus trigonum.
The epithelium is stratified 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 columnar 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 ordinary 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 vesicae. 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 membrane. They are not very abundant except at the fundus, where
the mucous membrane is quite vascular. Lymphatics have been described as
existing in the walls of the bladder, but Sappey has failed to demonstrate
them in this situation. The nerves of the bladder are derived from the hypo-
gastric 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 physiology of generation. In the female the epithelium of the ure-
thra 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 the human subject the urine

372

EXCRETION BY THE SKIN AND KIDNEYS.

is discharged into the pelves of the kidneys and the ureters by pressure due
to the act of separation of 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. M tiller
has found that the ureters can be made to undergo a powerful local contrac-
tion by the application of a Faradic current ; and Bernard has shown that
this may be produced by stimulation of the anterior roots of the eleventh
dorsal nerves.

When the urine has accumulated to a certain extent in the bladder, a pe-
culiar sensation is felt which leads to the act for its expulsion. The intervals
at which it is experienced are very 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, how-
ever, depends very much upon habit, upon the quantity of liquids ingested
and upon the degree of activity of the skin.

Evacuation of the bladder is accomplished by the muscular walls of the
organ itself, aided by contractions of the diaphragm and the abdominal mus-
cles with certain muscles which oper-
ate upon the urethra, and it is accom-
panied by relaxation of the sphincter
vesicae. This act is at first voluntary,
but once begun, it may be continued
by the involuntary contraction of the
bladder alone. During the first part
of the process, the distended bladder
is compressed by contraction of the di-
aphraghm and the abdominal mus-
cles ; and this after a time excites the
action of the bladder itself. A cer-
tain time usually elapses then before
the urine begins to flow. When the
bladder contracts, aided by the mus-
cles of the abdomen and the dia-
phragm, the resistance of the sphinc-
ter is overcome, and a jet of urine
flows from the urethra. All voluntary

ripfinr, tYiav tVipn ppasp for a limp anrl
^CtlOn may tnen Ctase I H6, ail

nearer the base without the aid of the abdom- +V,P "hlarlrlpv will nparlv pmntv it<?plf •
inal muscles, which, by a voluntary effort, bring tlie Dlaaaei wm nearly empty 1IS61I ,

the summit to the position indicated by the but the f orce of the jet may be con-
siderably increased by voluntary effort.

Toward the end of the expulsive act, when the quantity of liquid remain-
ing 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 remains. At this time the impulse from the
bladder, and, indeed, the influence of the abdominal muscles and diaphragm,
are very slight, and the flow of urine along the urethra is aided by the con-

FIG. 118.— Diagram showing the mechanism of mic-
turition (Ktiss.).

1, bladder distended with liquid ; by the contrac-
tion of its walls it assumes successively the po-
sitions 2, 3, 4, 5 ; but the walls can not approach

PROPERTIES AND COMPOSITION OF THE URINE. 373

tractions of its muscular walls and the action of some of the perineal mus-
cles, the most efficient being the accelerator urinse ; but with all this muscu-
lar action, a few drops of urine generally remain in the male urethra after the
act of urination has been 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 direction and length of the
urethra.

According to Budge, the influence of the nervous system on the bladder
operates through the sympathetic ; and he has described a centre in the spinal
cord, which presides over the contractions of the lower part of the intestinal
canal, the bladder and the vasa deferentia. This is called the genito-spinal
centre, and it has been located, 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 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 yellowish or
amber, with more or less of a reddish tint. The fluid is perfectly transpar-
ent, 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 decomposition. The color and odor of
the urine usually are modified by the same physiological conditions. When
the fluid contains a large proportion 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 is pale and the
odor is faint. The first urine passed in the morning, immediately after
rising, usually is more intense in color than that passed during the day, and
contains a relatively larger proportion of solids in solution.

The temperature of the urine at the moment of its emission, under physio-
logical conditions, varies but a very small fraction of a degree from 100°
Fahr. (37'78° C.). This estimate is the result of an extended series of obser-
vations, by Byasson, in 1868.

In estimating the total quantity of urine discharged in the twenty-four
hours, it is important to take into consideration the specific gravity, as an
indication of the amount of solid matter excreted by the kidneys. Variations
in quantity constantly occur in health, depending upon the proportion of
water ; but the quantity of solid matters excreted is usually more nearly uni-
form. It must also be taken into account that differences in climate, habits
of life, etc., in different countries, have an important influence upon the daily
quantity of urine. Parkes collected the results of twenty-six series of observa-
tions made in America, England, France and Germany, and found the aver-
age daily quantity of urine in healthy male adults, between twenty and forty

374: EXCRETION BY THE SKIN AND KIDNEYS.

years of age, to be fifty-two and a half fluidounces (1,552-6 c. c.), the average
quantity per hour being two and one-tenth fluidounces (62 c. c.). The
extremes were thirty-five ounces and eighty-one ounces (1,035 and 2,395
c. c.). The average quantity may be assumed to be about fifty-one fluid-
ounces (1,500 c. c.). The normal range of variation is between thirty and
sixty ounces (about 900 and 1,775 c. c.). The conditions which lead to a
diminution in the quantity of urine usually are more efficient in their opera-
tion than those which tend to an increase ; and the range below the normal
standard is rather wider than it is above. More urine usually is secreted
during the day than at night. 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 quantity of solid
constituents is relatively and absolutely less (Becquerel).

The specific gravity of the urine should be estimated in connection with
the absolute quantity in the twenty-four hours. Those who assume that the
daily quantity is about fifty-one ounces (1,500 c. c.), give the ordinary specific
gravity of the mixed urine of the twenty-four hours as about 1020. The
specific gravity is liable to the same variations as the proportion of water, and
the density is increased as the 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 usually is acid at the moment of its
discharge from the bladder ; although at certain times 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 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 ex-
pressed by calling it equivalent to so many grains of crystallized oxalic
acid.

As the result of a large number of 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 between thirty and sixty grains (2 and 4
grammes) of oxalic acid. The hourly quantity in these observations was
equal, in round numbers, to between one and a half and three grains (0-1 and
0-2 gramme) of acid. The proportion of acid was found to be very variable
in the same person at different times of the day. The urine contains no free
acid, but its acidity under an animal or a mixed diet depends upon the pres-
ence of acid salts, of which the principal one is acid sodium phosphate, with
possibly a little acid calcium phosphate.

Composition of the Urine. — Regarding the excrementitious constituents
of the urine as a measure, to a certain extent, of the general process of dis-
similation, it is more important to recognize the quantities of these products
discharged in a definite time than to learn simply their proportions in the
urine ; and in the following table of composition of the urine, the absolute

PROPERTIES AND COMPOSITION OF THE URINE. 375

quantities of its different constituents, excreted in twenty-four hours, have
been given when practicable.

COMPOSITION OF THE HUMAN URINE.

Water (in 24 hours, 27 to 50 fluidounces, 800 to 1,480 c. c.— Becquerel) . . 967-47 to 940-36

Urea (in 24 hours, 355 to 463 grains, 23 to 30 grammes— Robin) 15-00 " 23-00

Uric acid, accidental, or traces '.

Sodium urate, neutral and acid ~] (In 24 hours. 6 to 9 grs., 0-39

Ammonium urate, neutral and acid (in

small quantity) t.

Potassium urate

Calcium urate . . ,

to 0-58 gramme, of uric acid
— Becquerel — or 9 to 14 grs.,
0-58 to 0-9 gramme, of urates,
estimated as neutral urate of

Magnesium urate ..................... J soda) ..................... I'OO " 1-60

Sodium hippurate. . . } (In 34 hours,about 7«5 grs., 0-486 gramme,

Potassium hippurate ...... I of hlPPuric acid-Thudichum-equivalent

Calcium hippurate ....... to about 8'7 «"" °'566 Sramme' °* sodium

J hippurate) ............................ 1-00 " 1-40

Sodium lactate ......... 1

Potassium lactate ........ I (Daily quantity not estimated) ......... 1-50 " 2-60

Calcium lactate .......... J

Creatine ................ ) (In 24 hours, about 11-5 grains, 0-745

Creatinine ............... ) gramme, of both— Thudichum) ......... 1-60 " 3-00

Calcium oxalate (daily quantity not estimated) ....................... traces " 1*10

Xanthine ...................... ................................. not estimated.

Margarine, oleine and other fatty matters ........... . ................ 0*10 to 0-20

Sodium chloride (in 24 hours, about 154 grains, 10 grammes— Robin) . . . 3-00 " 8-00

Potassium chloride ................................................ traces.

Ammonium chloride .......... . .................................... 1-50 to 2*20

"j (In 24 hours, 23 to 38 grains, 1-5 to 2-5

grammes, of sulphuric acid — Thudichum.
Sodium sulphate ......... I Abouf. ^^ parts Qf ^.^ gulphate and

Potassium sulphate ...... > potassium sulphate-Robin-equivalent to

Calcium sulphate (traces).. ^ to 3?.5 ^.^ 1>45 to ^ grammes

J of each) ............................... 3-00 " 7-00

Sodium phosphate, neutral ) (Daily . not estimated) ......... 2.50 „ 4.30

Sodium phosphate, acid . . )

Magnesium phosphate (in 24 hours, 7*7 to 11*8 grains, 0*5 to 0*768

gramme — Neubauer) .............................. . ........... 0'50 " 1*00

Calcium phosphate, acid . . ) (In 24 hours, 4*7 to 5'7 grains, 0-307 to

Calcium phosphate, basic.. ) 0-372 gramme — Neubauer) ............... 0-20 " 1*30

Ammonio-magnesian phosphate (daily quantity not estimated) ......... 1-50 " 2-40

(Daily excretion of phosphoric acid, about 56 grains, 3-629 grammes —

Thudichum.)
Silicic acid ..................................................... ... 0-03 " 0-04

Urochrome .............. ) 0.10 „

Mucus from the bladder . . )

1,000-00 1,000-00
Proportion of solid constituents, 32*63 to 59'89 parts per 1,000.

Gases of the Urine. (Parts per 1,000, in. volume.)

Oxygen in solution ........... • ...................................... 0-90 to 1-00

Nitrogen in solution .............................................. 7-00 " 10-00

Carbon dioxide in solution . . -45 " 50-00

376

EXCRETION BY THE SKIN AND KIDNEYS.

Urea. — As regards quantity, and probably as a measure of the activity
of the general process of disassimilation, urea — CO(NH8)g — is the most im-
portant of the urinary constituents. Regarding the daily excretion of urea
as a measure of the physiological wear of certain tissues, its consideration
would come properly under the head of nutrition, in connection with other
substances known to be the results of disassimilation ; but it is 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 composition of the urine.

The formula for urea, showing the presence of a large proportion of
nitrogen, would lead to the supposition that this substance is one of the prod-
ucts of the wear of the nitrogenized constituents of the body. It is found,
under normal conditions, in the urine, the lymph and chyle, the blood, the
sweat, the vitreous humor, and a trace in the saliva. Its presence has been
demonstrated, also, in the substance of the healthy liver in both carnivorous
and herbivorous animals ; and it has been shown that it exists in minute
quantity in the muscular juice (Zalesky). Under pathological conditions,
urea finds its way into various other fluids, such as the secretion from the
stomach, the serous fluids etc.

Urea is one of the few organic substances that have been produced artifi-
cially. In 1828, Wohler obtained urea by adding ammonium sulphate to a
solution of potassium cyanate. The products of this combination are potas-
sium sulphate, with cyanic acid and am-
monium in a form to constitute urea.
Ammonium cyanate is isomeric with
urea, and the change is effected by a
re-arrangement of its elements. It has
long been known that urea is readily
convertible into ammonium carbonate ;
and ammonium carbonate, when heated
in sealed tubes to the temperature at
which urea begins to decompose, is con-
verted into urea (Kolbe).

Urea may readily be extracted from
the urine, by processes fully described in
works upon physiological chemistry;
and its proportion may now easily be
estimated by the various methods of
volumetric analysis. It is not so easy, however, to separate it from the blood
or from the substance of any of the tissues, on account of the difficulty in
getting rid of other organic matters and the readiness with which it under-
goes decomposition.

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
alcohol, but they are entirely insoluble in ether. In its behavior with reagents,

FIG. 119. — Urea crystallized from an aqueous
solution (Funke).

ORIGIN OF UREA. 377

urea acts as a base, combining readily with certain acids, particularly nitric
and oxalic. It also forms combinations with certain salts, such as mercuric
oxide, sodium chloride etc. It exists in the economy in a state of watery
solution, with perhaps a small portion modified by the presence of sodium
chloride.

Origin of Urea. — It is now universally admitted by physiologists that
urea is not formed in the kidneys but pre-exists in the blood. It finds its way
into the blood, in part directly from the tissues, and in part from the lymph,
which contains a greater proportion of urea than is found in the blood itself.
The quantity of urea in the blood is kept down by the eliminating action of
the kidneys. Although a great part of the lymph is probably derived from
the blood, it is not probable that the blood gives to the lymph all of the urea
contained in the latter fluid ; and it must be assumed that a part of the urea
of the lymph passes from the tissues into the lymph-spaces and canals,
although a certain quantity may be produced by the lymphatic glands.

As an outcome of many contradictory experiments and opinions on the
subject, it must now be considered as proved that the liver produces urea in
large quantity. If defibrinated blood be passed several times through a per-
fectly fresh liver, it gains urea. This observation, which was first made by
Cyon, in 1870, has been repeatedly confirmed. In certain cases of struct-
ural disease of the liver, the excretion of urea is much diminished, and this
substance may disappear from the urine. A number of cases illustrating
this fact has been reported by Brouardel.

Assuming that urea is the most abundant and important of the nitrogen-
ized excrementitious products — which is fully justified by physiological facts —
it is difficult to avoid the conclusion that this substance represents, to a great
extent, the disassimilation of the nitrogenized parts of the tissues, and neces-
sarily the physiological wear of the. muscular substance. The fact that urea
exists in very minute quantity in the muscles — and some chemists state that
it is absent — is probably due to its constant removal by the blood and lymph.

Uric acid, creatine, creatinine, xanthine, hypoxanthine, leucine, tyrosine
and some other analogous substances are to be regarded as formations ante-
cedent to urea, urea being the final and perfect excrementitious product.

It is convenient, in this connection, to consider the principal conditions
which influence the formation and elimination of area, or in order to com-
pare this substance with certain constituents of food, the elimination of
excrementitious nitrogen from the body.

Influence of Ingesta upon the Composition of the Urine and upon the
Elimination of Nitrogen. — Water and other liquid ingesta usually increase
the proportion of water in the urine and diminish its 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 physiologists as the
urina potus ; but when an excess of water has been taken for purposes of ex-
periment, the diet being carefully regulated, the absolute quantity of solid
matters excreted is considerably increased. This is particularly marked as
regards urea, but it is noticeable in the sulphates and phosphates, though not

378 EXCRETION BY THE SKIN AND KIDNEYS.

to any great extent in the chlorides. The results of experiments upon this
point seem to show that water taken in excess increases the activity of disas-
similation.

The ordinary meals increase the solid constituents of the urine, the most
constant and uniform increase being in the proportion of urea. This, how-
ever, 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 maxi-
mum at the third or fourth hour. The inorganic matters are increased as
well as the excremehtitious substances 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 tis-
sues, which is called the urina sanguinis.

It is an 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 a
number of observations upon this point, and his results have been confirmed
by many other physiologists. Without discussing fully all of these observa-
tions, it is sufficient to state that the ingestion of an excess of nitrogenized
food always produced 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
general results of the experiments of Lehmann are embodied in the following
quotation :

" My experiments show that the amount of urea which is excreted is ex-
tremely dependent on the nature of the food which has been previously taken.
On a purely animal 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."

The influence of food is not absolutely confined to the period when any
particular kind of food is taken, but is continued for many hours after a re-
turn to the ordinary diet.

With regard to the influence of food upon the inorganic constituents of
the urine, it may be stated in general terms that the ingestion of mineral
substances increases their proportion in the excretions.

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 quantity 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, alcohol 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 upon the Elimination of Nitrogen. — In

ELIMINATION OF NITROGEN. 379

all observations with regard to the influence of muscular exercise upon the
elimination of nitrogen, account should be taken of the influence of diet ; and
those observations are most valuable which have given the proportion of nitro-
gen eliminated to the nitrogen of food. The observations of Fick and Wisli-
cenus (1866) showed a diminution in the elimination of nitrogen during work ;
but during the time of the muscular work, no nitrogenized food was taken.
The same conditions obtained in certain of the observations of Parkes. In
a series of observations made in 1870 (Flint), on a person who walked 317£
miles (about 510 kilometres) in five consecutive days, the diet was normal,
and the proportionate quantity of nitrogen was calculated for three periods of
five days each, with the following results :

For the five days before the walk, with an average exercise of about eight
miles (13 kilometres) 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 work ;
and the excess of nitrogen eliminated, over the nitrogen of food, almost ex-
actly corresponded with a calculation of the nitrogen of the muscular tissue
consumed, as estimated from the loss of weight of the body. In 1876, a similar
series of observations was made upon the same person by Pavy. In these ob-
servations, the subject of the experiment walked 450 miles (724'21 kilometres)
in six consecutive days. During this period, the proportionate elimination of
nitrogen was increased, but not to the extent observed in 1870. Similar re-
sults, although the experiments were made on a less extended scale, were ob-
tained by North, in 1878. These results are opposed to the views of many
physiologists, since the experiments of Fick and Wislicenus, who regard the
elimination of nitrogen under ordinary conditions as dependent mainly upon
the diet and not upon the muscular work performed. The observations of
Voit, indeed, are favorable to this view.

Notwithstanding the results obtained by Fick and Wislicenus, Frankland,
Haughton, Voit and others, the fact remains that excessively severe and
prolonged muscular work increases the elimination of nitrogen over and
above the quantity to be accounted for by the nitrogenized food taken. Ac-
tual observations (Flint, Pavy and others) are conclusive as regards this
simple fact ; but it is well known that muscular exercise largely increases
the elimination of carbon dioxide and the consumption of oxygen. In exer-
cise so violent as to produce dyspnoea, the distress in breathing is probably
due to the impossibility of supplying by the lungs sufficient oxygen to meet
the increased demand on the part of the muscular system, and the possible
amount of muscular work is thereby limited.

The observations and conclusions of Oppenheim (1880) go far to harmon-
ize the results obtained by different experimenters. Oppenheim concludes
that muscular work, when not carried to the extent of producing shortness of
breath or when moderate and extending over a considerable length of time,

380

EXCRETION BY THE SKIN AND KIDNEYS.

does not increase the elimination of urea ; but that even less work, when vio-
lent and attended with shortness of breath, increases the discharge of urea.
According to this view, moderate work draws upon the oxygen supplied to
the body and at once largely increases the elimination of carbon dioxide ; but
the less active processes which result in the production of urea are not so
promptly affected. Violent muscular work, however, or work which is ex-
cessively prolonged, consumes those parts of the tissues the destruction of
which is represented by the discharge of urea. This view, if accepted, har-
monizes the apparently contradictory experiments upon the influence of
muscular work on the elimination of nitrogen.

The daily quantity of urea excreted is subject to very great. variations.
It is given in the table as 355 to 463 grains (23 to 30 grammes). This is
less than the estimates frequently given ; but when the quantity has been
very large, it has generally depended upon an unusual amount of nitrogen-
ized food, or the weight of the body has been above the average. Parkes
has given the results of twenty-five different series of observations upon this
point. The lowest estimate was 286-1 grains (18-24 grammes), and the
highest, 688-4 grains (44-61 grammes).

Uric Acid and its Compounds. — Uric acid (CgH^N^Os) seldom if ever
exists in a free state in normal urine. It is very insoluble, requiring four-
teen to fifteen thousand times its volume of cold water or eighteen to nine-
teen hundred parts of boiling water for its solution Its presence uncom-
bined in the urine must be regarded as a pathological condition.

In normal urine, uric acid is combined with sodium, ammonium, potas-
sium, calcium and magnesium. Of these combinations, the sodium urate

FIG. 120.— Crystals of uric acid, obtained partly
by the solution and subsequent precipita-
tion of chemically pure acid, and partly by
decomposition of the urates by nitric or
acetic acid (Funke).

FIG. 121.— Sodium urate (Funke).

and ammonium urate are by far the most important, and they constitute the
great proportion of the urates, potassium, calcium and magnesium urates
existing only in minute traces. Sodium urate is very much more abundant
than ammonium urate. The union of uric acid with the bases is very feeble.

HIPPURIC ACID, HIPPURATES AND LACTATES. 381

If from any cause the urine become excessively acid after its emission, a
deposit of uric acid is likely 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 (1858), and his observations have
been confirmed by recent authorities. The urates also exist in the blood in
very small quantity and pass ready-formed into the urine. The fact that
the urates exist in the liver has led to the opinion that this organ is the prin-
cipal seat of the formation of uric acid (Meissner). However this may be, uric
acid certainly is not formed in the kidneys, but is simply separated by these or-
gans from the blood. Meissner did not succeed in finding uric acid in the mus-
cular tissue, although the specimens were taken from animals in which he had
found large quantities in the liver. The urates, particularly sodium urate,
are products of disassimilation of the nitrogenized constituents of the body.

The daily excretion of uric acid, given in the table, is six to nine grains
(0-39 to 0-58 gramme), the equivalent of nine to fourteen grains (O58 to 0'9
gramme) of urates estimated as neutral sodium urate. Like urea, the pro-
portion of the urates in the urine is subject to certain physiological varia-
tions.

Hippuric Acid, Hippurates and Lactates. — The compounds of hippuric
acid (C9H9N03), which are so abundant in the urine of the herbivora, are
now known to be constant constituents 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 detected 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. As to the exact mode of origin
of the hippurates, there is even less information than with regard to the
origin of the other urinary constituents 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 proba-
bly it also exists during fasting. The daily excretion of hippuric acid is
about 7'5 grains (0-486 gramme), which is equivalent to about 8- 7 grains
(0-566 gramme) of sodium hippurate.

Hippuric acid itself, unlike uric acid, is soluble in water and in a mixture
of 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.

Sodium, potassium and calcium lactates exist in considerable quantity 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 readily be detected. Physiologists have little
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 transforma-
26

EXCRETION BY THE SKIN AND KIDNEYS.

tion of glucose. The lactic acid contained in the lactates extracted from the
muscular substance is not identical with the acid resulting from the trans-
formation of the sugars. The former
have been called sarcolactates, and they
contain one equivalent of water less
than the ordinary lactates. The com-
pounds of lactic acid in the urine are in
the form of sarcolactates (Robin).

Creatine and Creatinine. — Creatine
(C4H9N302) and creatinine (C4H7N30)
are probably 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 rea-
son to suppose that in the organism,
they are the products of physiological
These substances have been found in the
urine, blood, muscular tissue and brain. Scherer has demonstrated the pres-
ence of creatine in the amniotic fluid. By certain chemical manipulations,
both creatine and creatinine may be converted into urea. Verdeil and Mar-
cet have found both creatine and creatinine in the blood ; and these sub-
stances are now regarded as excrementitious matters, taken from the tissues
by the blood, to be eliminated by the kidneys.

Creatine has a bitter taste, is quite soluble in cold water (one part in sev-
enty-five), and is much more soluble in hot water, >from which it separates in

FIG. 122.— Crystals of hippuric acid (Funke).

wear of the same tissue or tissues.

FIG. 123.— Creatine, extracted from the muscu-
lar tissue, and crystallized from a hot, wa-
tery solution (Funke).

FIG. 124.— Creatinine, formed from creatine by
digestion with hydrochloric acid, and crys-
tallized from a hot, watery solution (Funke).

a crystalline form on cooling. It is slightly soluble in alcohol and is insolu-
ble 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, nitric, hydrochloric and

CALCIUM OXALATE.

383

sulphuric. When boiled for a long time with barium hydrate, it is changed
into urea and sarcosine. When boiled with the strong acids, creatine loses
an atom of water and is converted into creatinine. This change takes place
very readily in decomposing urine, which contains neither urea nor creatine,
but a large quantity of creatinine, when far advanced in putrefaction.

Creatinine is more soluble than creatine, and its watery solution has a
strongly alkajine 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 one of the most
powerful of the organic bases, readily forming crystalline combinations with
a number of acids. According to Thudichum, creatine is the original excre-
mentitious substance 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." The fact that creatine has been found in the brain would lead to
the supposition that it is also one of the products of disassimilation of the
nervous tissue.

The average daily excretion of creatine and creatinine was estimated by
Thudichum at about 11*5 grains (0*745 gramme). Of this he estimated that
4-5 grains (0-292 gramme) consisted of creatine, and 7 grains (0-453 gramme)
of creatinine.

Calcium Oxalate. — Calcium oxalate (oxalic acid, C2H204) is not constantly
present in normal human urine, although it may exist in certain quantity

Fio. 125: — Crystals of calcium oxalate, depos-
ited from the normal human urine, on the
addition of ammonium oxalate to the urine
(Funke).

FIG. 126.— Crystals of leucine (Funke).

without indicating any pathological condition. 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 Neubauer, a small
quantity may be retained in solution by the acid sodium phosphate in the
urine. Calcium oxalate may find its way out of the system by the kidneys,

384

EXCRETION BY THE SKIN AND KIDNEYS.

after it has been taken with vegetable food or with certain medicinal sub-
stances. The ordinary rhubarb, or pie-plant, contains a large quantity of cal-
cium oxalate, which, when th'is article is taken, will pass into the urine. It
is probable, however, that a certain quantity may be formed in the organism.

Inasmuch as pathological facts have shown pretty conclusively that oxalic
acid may appear in the system without having been introduced with the food,
some physiologists have endeavored to show how it may originate from a
change in certain other substances from which it can be produced artifi-
cially out of the body. One of the substances from which oxalic acid can be
thus formed is uric acid. Woehler and Frerichs injected into the jugular
vein of a dog a solution containing about twenty-three grains (1*5 gramme)
of ammonium urate. In the urine taken a short time after, there was no
deposit of uric acid, but there appeared a large number of crystals of calcium
oxalate. The same result followed in the human subject, on the adminis-
tration of sixty-seven grains (4-34 grammes) of ammonium urate by the
mouth. These questions have more pathological than physiological impor-
tance ; for the quantity of calcium oxalate in the normal urine is insig-
nificant, and this salt does not seem to be connected with any of the well
known processes of disassimilation.

Xanthine, Hypoxantliine, Leucine, Tyrosine and Taurine. — Traces of
xanthine (CsH^N^Og) have been found in the normal human urine, but its pro-

Fio. 127.— Crystals of tyrosine (Funke).

FIG. 128.— Crystals of taurine (Funke).

portion has not been estimated, and observers are as yet but imperfectly
acquainted with its physiological relations. It has been found in the liver,
spleen, thymus, pancreas, muscles and brain. It is insoluble in water but is
soluble in both acid and alkaline fluids. Hypoxanthine (05H4N40) has never
been found in normal urine, although it exists in the muscles, liver, spleen and
thymus. Leucine (C6H13N02) exists in the pancreas, salivary glands, thyroid,
thymus, suprarenal capsules, lymphatic glands, liver, lungs, kidneys and the
gray substance of the brain. It has never been detected in the normal urine.
The same remarks apply to tyrosine (CaHnNOs), although it is not so exten-
sively distributed in the economy, to taurine (C2H7N03S) and to cystine

INORGANIC CONSTITUENTS OF THE URINE.

385

(C3H7N"S02). The last two, however, contain sulphur, and they may have
peculiar physiological and pathological relations that are not at present un-
derstood.

These various substances are mentioned, although some of them have not
been found 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 them may
not be actual constituents of the urine, but substances produced by the pro-
cesses employed for their extraction, some, which have thus far been discov-
ered only under pathological conditions, may yet be found in health, and
they represent, perhaps, important physiological processes.

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 salts are discharged from the
organism ; and it is probable that even now physiological chemists are not
acquainted with the exact proportion and condition of all the constituents
of this class found in the urine. In all the processes of nutrition, it is
found that the inorganic constituents of the blood and tissues accompany
the organic matters in their various transformations, although they are them-
selves unchanged. Indeed, the condition of union of inorganic with organic
matters is so intimate, that they can not be completely separated without in-
cineration. In view of these facts, it is evident that a certain proportion, 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 eliminate from the blood foreign matters taken
into the system, and are capable sometimes of throwing off an excess of the
normal constituents, which may be in-
troduced into the circulation, it can
readily be understood how a large pro-
portion of some of the inorganic con-
stituents of the urine may be derived
from the food.

Chlorides. — Almost all of the chlo-
rine in the urine is in the form of so-
dium chloride, the quantity of potassi-
um chloride being insignificant and not
of any special physiological importance.
By reference to the table of the compo-
sition of the urine, it is seen that the
proportion of sodium chloride is subject
to very great variations, the range being
between three and eight parts per thou-
sand. This at once suggests the idea that the quantity excreted is dependent
to a considerable extent upon the quantity taken in with the food ; and, in-

FIG. 129.— Crystals of sodium chloride (Funke)-

386 EXCRETION BY THE SKIN AND KIDNEYS.

deed, it has been shown by direct observations that this is the fact. The pro-
portion of sodium chloride in the blood seems to be tolerably constant ; and
any excess that may be introduced is thrown off, chiefly by the kidneys. As
the chlorides are deposited with the organic matters in all the acts of nutri-
tion, they are found to be eliminated constantly with the products of dis-
assimilation of the nitrogenized parts, and their absence from the food does
not completely arrest their discharge in the urine. According to Robin, by
suppressing salt in the food, its daily excretion may be reduced to between
thirty and forty-five grains (1-9 and 2-9 grammes). This quantity is less
than that ordinarily contained in the ingesta, and under these conditions
there is a gradual diminution in the general nutritive activity. In nearly all
acute febrile disorders the chlorine in the urine rapidly diminishes and is
frequently reduced to one-hundredth of the normal proportion. The quan-
tity rapidly increases to the normal standard during convalescence. Most of
the chlorides of the urine are in simple watery solution ; but a certain pro -
portion of sodium chloride exists in combination with urea.

The daily elimination of sodium chloride is about one hundred and fifty-
four grains (10 grammes.) The great variations in its proportion in the
urine, under different conditions of alimentation, etc., will explain the differ-
ences in the estimates given by various authorities.

Sulphates. — There is very little to be said regarding the sulphates, in
addition to the general statements already made concerning the inorganic
constituents of the urine. The proportion of these salts in the urine is very
much greater than in the blood, in which there exist only about 0-28 of a,
'part per thousand. Inasmuch as the proportion in the urine is three to
seven parts per thousand, it seems probable that the kidneys eliminate these
salts as fast as they find their way into the circulating fluid either from the
food or from the tissues. Like other constituents derived in great part from
the food, the normal variations in the proportion of sulphates in the urine
are very great. It is unnecessary to consider in detail the variations in the
quantity of sulphates discharged in the urine, depending upon the ingestion
of different salts or upon diet, for all recorded observations have given the
same results, and they show that the ingestion of sulphates in quantity is
followed by a corresponding increase in the proportion eliminated.

Thudichum estimated the daily excretion of sulphuric acid at 23 to 38
grains (1-5 to 2-5 grammes). Assuming that the sulphates consist of about
equal parts of potassium sulphate and sodium sulphate with traces of calcium
sulphate, the quantity of salts would be 22'5 to 37'5 grains (1-46 to 2-23
grammes) of potassium sulphate, with an equal quantity of sodium sul-
phate.

Phosphates. — The urine contains phosphates in a variety of forms ; but
inasmuch as it is not known that any one of the different combinations pos-
sesses peculiar relations to the processes of disassimilation, as distinguished
from the other phosphates, the phosphatic salts may be considered together.

The phosphates exist constantly in the urine and are derived in part from
the food and in part from the tissues. Like other inorganic matters, they are

INORGANIC CONSTITUENTS OF THE URINE. 387

united with the nitrogenized constituents of the organism, and when these
are changed into excrementitious substances and are separated from the blood
by the kidneys, they pass with them and are discharged from the body.

It is a question of some importance to consider how far the phosphates
are derived from the tissues and what proportion comes directly from the
food. 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 phos-
phates 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. Deprivation of food
diminishes the quantity of phosphates in the urine, but a certain proportion
is discharged, which is derived exclusively from the tissues.

In connection with the fact that phosphorus exists in the nervous mat-
ter, it has been assumed that mental exertion is always attended with an in-
crease in the elimination of phosphates ; and this has been advanced to sup-
port 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 by mental work, but urea, the chlorides, sulphates
and inorganic matters generally; and in point of fact, any physiological
conditions which increase the proportion of nitrogenized excrementitious
matters increase as well the elimination of inorganic salts. It can not be
assumed, therefore, that the discharge of phosphates is specially connected
with the activity of the brain. Little has been learned upon this point from
pathology, for although many observations have been made upon the excre-
tion of phosphoric acid in disease — Vogel having made about one thou-
sand different analyses in various affections — no definite results have been
obtained. From these facts it is seen that there is no physiological reason
why the elimination of the phosphates should be specially connected 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 phosphoric acid at different times of the day ; but these do not appear to
bear any definite 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 sodium. These exist in the form
of the neutral and acid phosphates. The acid salt 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. The proportion of the sodium phos-
phates in the urine is larger than that of any of the other phosphatic salts,
but the daily quantity excreted has not been estimated. 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 crys-
talline deposit. The daily excretion of the phosphates is subject to great

388 EXCRETION BY THE SKIN AND KIDNEYS.

variations, but the average quantity of phosphoric acid excreted daily may
be estimated at about fifty-six grains (3*629 grammes).

The urine contains, in addition to the inorganic salts that have been
mentioned, a small quantity of silicic acid ; but as far as is known, this has
no physiological importance.

Coloring Matter and Mucus. — The peculiar color of the urine is due to
the presence of a nitrogenized substance called urochrome. This is also called
urohgematine, uroxanthine and purpurine. There is no accurate account of
its composition, and all that is known is that it contains carbon, oxygen,
hydrogen and nitrogen, and probably iron. Although its exact chemical
composition is not absolutely determined, its elements are supposed to be
nearly the same as those of the coloring matter of the blood, the proportion
of oxygen being much greater. These facts point to the probability of the
formation of urochrome from haemaglobine.

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 substance first makes its appearance in the urine and is probably
formed in the kidneys. So little is known of its physiological or pathologi-
cal 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 re-
agents.

The normal urine always contains a small quantity of mucus, with more
or less epithelium 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 different 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 putrefactive changes.

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 observations on
this subject have been made by Morin (1864), in which the proportions of
the free gases in solution have been accurately estimated. 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. He ascertained, however, that a certain quantity of gas
remained in the urine and could not be extracted by the ordinary process.
This was about one-fifth of the whole volume of gas. Adding this to the
quantity of gas extracted, he obtained the following proportions to one litre
of urine, in cubic centimetres (one part per thousand in volume) :

Oxygen 0-824

Nitrogen 9-589

Carbon dioxide . . . 19-620

WATER REGARDED AS A PRODUCT OF EXCRETION. 389

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 O824 to 1'024), and the carbon dioxide was diminished more than one-
half. The most important variations, however, were in connection with
muscular exercise. After walking a long distance, the exercise being taken
both before and after eating, the quantity of carbon dioxide 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 ; but
the variations of these gases were insignificant.

It is not probable that the kidneys are very important as eliminators of
carbon dioxide, 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.

Water regarded as a Product of Excretion. — It has been shown by indi-
rect observations that a large proportion of the hydrogen introduced as an
ingredient of food, about eighty-five per cent., is not accounted for by the
hydrogen of the excreta. Direct observations have shown, also, that under
certain conditions, an excess of water over that introduced with food and
drink is discharged from the body. One of these conditions is abstinence
from food (Flint, 1878). The elimination of water is very much increased
by muscular work (Pettenkofer and Voit, 1868 ; Flint, 1879). These facts
point to the actual production of water in the body by a union of oxygen
with hydrogen.

While it is not certain that water is constantly produced in the body,
there can be no doubt with regard to its formation under some conditions,
and the oxidation of hydrogen is important as one of the factors in the pro-
duction of animal heat. If a certain proportion of the water discharged by
the lungs, skin and kidneys be regarded as a product of oxidation within the
body, the relations which it bears to nutrition are probably the same as those
of some of the excretions, especially carbon dioxide,1 and are subject to nearly
the same laws. It has not been shown, however, that water is produced
constantly, like those substances universally regarded as true excretions ; and
it gives rise to no direct toxic phenomena when retained in the system or
when its production is diminished pathologically. Water also has important
physiological uses, particularly as a solvent. Still, carbon dioxide, with
which water may be compared as regards its mode of production, is not in
itself poisonous, its retention in the blood simply interfering with the absorp-
tion of oxygen ; and carbon dioxide probably is useful in increasing the solvent
properties of the liquids of the organism. The relations of the formation of
water in the body to the production of animal heat will be fully considered
in connection with the physiology of nutrition and calorification.

Variations in the Composition of the Urine. — The urine not only repre-
sents, in its varied constituents, a great part of the physiological disintegra-

390 EXCRETION BY THE SKIN AND KIDNEYS.

tion of the organism, but it contains matters evidently derived from the
food. Its constitution is varying with every different condition of nutrition,
with exercise, bodily and mental, with sleep, age, sex, diet, respiratory
activity, the quantity of cutaneous exhalation, and, indeed, with every con-
dition that affects any part of the system. There is no fluid in the body
that presents such a variety of constituents as a constant condition, but in
which the proportion of these constituents is so variable. It is for this
reason that in the table of the composition of the urine, the ordinary limits
of variation of its different constituents have been given ; and it has been
found necessary, in treating of the individual excrementitious products, to
refer to some of the variations in their proportion in the urine.

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 variations, 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 has been stated that urea does not exist in the urine of the foetus ; but
in a specimen of urine taken from a still-born child delivered with forceps,
examined by Elliot and Isaacs, the presence of urea was determined. Beale
found urea in a specimen taken at the seventh month. Observations upon
children between the ages of three and seven have shown that at this period
of life, the urea excreted in proportion to the weight of the body is about
double the quantity excreted in the adult. The chlorine in the urine of chil-
dren is about three times the quantity in the adult ; and the quantities of
other solid matters are also greater. The quantity 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. Between the ages of eight
and eighteen years, the urinary excretion gradually approximates the 'stand-
ard in the adult. It has been observed that crystals of calcium oxalate 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 diminution, at this time, in the excretion of urea, and that
the absolute quantity of urine is somewhat less. ^

The absolute quantity of the urinary excretion in women is less than in
men, and the same is true of the quantity 'in proportion to the weight of the
body ; still, the differences are not very marked, and the proportion of the
urinary constituents being subject to modifications from the same causes as
in men, the small deficiency, in the few direct observations on 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 IN THE COMPOSITION OF THE URINE. 391

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 conditions of digestion, temperature, sleep, exercise
etc., have long been recognized by physiologists ; but it is difficult so to sepa-
rate 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. Under
strictly physiological conditions, the modifying influence of digestion 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 physiological modifications in the various processes and conditions of
life.

At different seasons of the year and in different climates, the urine pre-
sents 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 temperature or the hygrometric condition of
the atmosphere is favorable to the action or the skin, as in a warm, dry cli-
mate, 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.

At different times of the day, the urine presents certain important varia-
tions. It is evident that the specific gravity must be constantly varying
with the relative proportions of water and of 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 certain variations, which
have already been mentioned.

Influence of Mental Exertion. — Although the influence of mental exer-
tion upon the composition of the urine has not been very closely studied, the
results of the investigations 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 emotions, sometimes pro-
duce a sudden and copious secretion of urine containing a large proportion of
water, and this is often observed in cases of hysteria. Intense mental exer-
tion will occasionally produce the same result. In studying the influence
of cerebral activity upon the composition of the urine, Byasson found that
by mental exertion the quantity of urine was increased ; the 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.

The products of spontaneous decomposition of the urine have a certain
chemical interest but are of no physiological importance.

392 USES OF THE LIVER— DUCTLESS GLANDS.

CHAPTER XIII.

USES OF THE LIVER-DUCTLESS GLANDS.

Physiological anatomy of the liver— Distribution of the portal vein, the hepatic artery and the hepatic duct-
Structure of a lobule of the liver— Arrangement of the bile-ducts in the lobules— Anatomy of the excre-
tory biliary passages — Nerves and lymphatics of the liver — Mechanism of the secretion and discharge of
bile — Quantity of bile — Uses of the bile — Properties and composition of the bile — Biliary salts— Choles-
terine — Tests for bile — Excretory action of the liver — Formation of glycogen in the liver— Change of
glycogen into sugar — Conditions which influence the quantity of sugar in the blood — Summary of the
glycogenic action of the liver — Probable office of the ductless glands — Physiological anatomy of the
spleen— Suprarenal capsules— Addison's disease— Thyroid gland— Myxoedema— Thymus— Pituitary body
and pineal gland.

PHYSIOLOGICAL ANATOMY OF THE LIVER.

THE liver has several uses in the economy, which are more or less dis-
tinct from each other. It secretes bile, a fluid concerned in digestion and
containing at least one excrementitious product. Another office is the for-
mation of glycogen, in which it acts as a ductless gland.

It is unnecessary, in this connection, to dwell upon the ordinary descrip-
tive anatomy of the liver. It is sufficient to state that it is situated just be-
low 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 (2 kilos.). Its weight is somewhat variable, but in a per-
son 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 (Sappey).

The liver is covered externally by peritoneum, folds or duplicatures of
this membrane 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 is a thin but dense and resisting fibrous
membrane, adherent to the substance 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, investing the vessels, and branching with
them. This membrane, as it ramifies in the substance of the liver, is called
the capsule of Glisson. It will be more fully described in connection with
the arrangement and distribution of the hepatic vessels.

The substance of the liver is made up of lobules, of an irregularly ovoid
or rounded form, and about -g-% of an inch (1 mm.) in diameter. The space
which separates these lobules is about one-quarter of the diameter of the
lobule and is occupied by the blood-vessels, nerves and ramifications of the
hepatic duct. In certain animals, 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 mammalia, the lobules are not so distinct, although
their arrangement is essentially the same. The lobules are intimately con-

PHYSIOLOGICAL ANATOMY OF THE LIVER. 393

nected with each other, and branches going to a number of different lobules
are given off from the same interlobular vessels ; but they are sufficiently
distinct to represent, each one, the general anatomy of the secreting portion
of the liver.

At the transverse fissure, the portal vein, collecting the blood from the
abdominal organs, and the hepatic artery, which is a branch of the cceliac
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 cap-
sule of Glisson. The portal vein is by far the larger of the two blood-vessels,
and its caliber may be roughly estimated as 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 collapsed when not filled with blood ;
presenting a striking contrast to the hepatic veins, which are closely adher-
ent 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 follows 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 ves-
sels are distributed between the lobules.

The vessels distributed in the liver are the following :

The portal vein, the hepatic artery and the hepatic duct, passing in at
the transverse 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.

The hepatic veins ; vessels that originate in the lobules, and collect the
blood distributed 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, forming
the so-called 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 anas-
tomose 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 hepatic artery 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

394

USES OF THE LIVEK-DUCTLESS GLANDS.

FIG. 130. — 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.

branches of the artery itself, to the walls of the hepatic veins, and a very rich
net- work of branches to the hepatic duct. In its course, the hepatic artery

also sends branches
to the capsule of
Glisson (capsular
branches), which,
with branches of
the portal vein,
go to form the so-
called vaginal plex-
us. From these ves-
sels, a few arterial
branches are given
off, which pass be-
tween the lobules.
The hepatic artery
can not be followed
beyond the inter-
lobular vessels. 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.

Interlobular Vesseh. — Branches of the portal vein, coming from the ter-
minal ramifications of the vessel 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 between -j^Vo an(i TITO °f an incn
(17 and 34 //,). In this distribution, the blood-vessels are followed by branches
of the duct, which are much fewer and smaller, measuring only -^-^ of an
inch (10 /u,), and some, even, have been measured that are not more than
so*00 of an inch (8 /x) in diameter.

Lobular Vessels. — From the interlobular veins, eight or ten branches are
given off which 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 into the lobules, the vessels
immediately break up into an elongated net- work of capillaries, -^oW ^° 2 Ao
of an inch (8 to 11 /«,) in diameter, which occupy the lobules with a true
plexus. These vessels are very abundant. The blood, having been distrib-
uted in the lobules by this lobular plexus, is collected by three or four venous
radicles into a single central vessel situated in the long axis of the lobule,

PHYSIOLOGICAL ANATOMY OF THE LIVER.

395

•«*?1*''";r<f-\ -* . " •

FIG. 131. — Transverse section of a single hepatic lobule (Sappey).
1, intralobular vein, cut across ; 2, 2, 2, 2, afferent branches of the intra-
lobular vein ; 3, 3. 3, 3, 3, 3, 3, 3, 3, interlobular branches of the portal
vein, with its capillary branches, forming the lobular plexus, ex-
tending to the radicles of the intralobular vein.

called the intralobular vein. A single lobule, surrounded by an interlobular
vessel, showing the lobular capillary plexus, and the central vein (the intra-
lobular vein) cut across,
is represented in Fig.
131.

Intralobular Veins.
—The capillaries of
the lobules converge
into three or four ve-
nous radicles (2, 2, 2, 2,
in Fig. 131), which
empty into a central
vessel. This is the in-
tralobular vein. If a
liver be carefully in- 3<11^^fp^
jected from the he- % ^^^R^'

patic veins, and if sec-
tions be made in vari-
ous directions, it will
be seen that the intra-
lobular 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 called the base of the lobules.
These latter are 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.

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 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 non-striated 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 dia-
phragm and from the anterior abdominal walls. These vessels penetrate at
different points on the surface of the liver, and they may serve as deriva-
tives, when the circulation through the portal vein is obstructed.

Structure of a Lobule of the Liver. — Each hepatic lobule, bounded and
more or less distinctly separated from the others by the interlobular 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 injection, the space occupied by the
blood-vessels is exaggerated by excessive distention, and the difficulties in

396

USES OF THE LIVER— DUCTLESS GLANDS.

FIG. 132.— Liver-cells from a human, fatty liver
(Funke).

the study of the relations of the ducts and the liver-cells are thereby much
increased.

Hepatic Cells. — If a scraping from the cut surface of a fresh liver be ex-
amined with a moderately high magnifying power, the field of view will be
found filled with rounded, ovoid or irregularly polygonal cells, measuring
to roW °f an illch (16 to 25 /x) 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
occasionally two nuclei, sometimes with
and sometimes without nucleoli. The
presence of small, pigmentary granules
gives to the cells a peculiar and char-
acteristic appearance ; and in addition,
nearly all of them contain a few gran-
ules or small globules of fat. Some-
times the fatty and pigmentary gran-
ules are so abundant as to obscure the
nuclei. The addition of acetic acid
renders the cells pale and the nuclei
become more distinct. The cells also
contain more or less glycogen in the form of granules surrounding the nu-
clei.

Arrangement of the Bile-ducts in the Lobules. — In the substance of the
lobules is a fine and regular net-work of vessels of nearly uniform size, about
10Soo of an inch (2 or 3 /*) in diame-
ter, which surround the liver-cells, each
cell lying in a space bounded by inos-
culating branches of these canals. This
plexus is entirely independent of the
blood-vessels, and it seems to enclose
in its meshes each individual cell, ex-
tending from the periphery of the lob-
ule to the intralobular vein.

The reticulated bile-ducts were dis-
covered in the substance of the lobules,
near their borders, by Gerlach, in 1848.
It is evident, from an examination of
his figures and description, that he
succeeded in filling with injection that

portion of the lobular net-WOrk near FIG. 133.— Portion of a transverse sect ion of an
i-i -i 3 -C-Lii-ui j i 3 hepatic lobule of the rabbit ,' magnified 400

the borders 01 the lobules, and he dem- diameters (Koiiiker).

onstrated the continuity of these ves- 6' 6' 6- cap£fer_5u^

sels with the interlobular ducts ; but he

did not recognize the vessels nearer the centre of the lobule. It is now

ANATOMY OF THE EXCRETORY BILIARY PASSAGES. 397

known 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, however, whether these passages be simple spaces between
the cells or true vessels lined with a membrane.

Anatomy of the Excretory Biliary Passages. — Between the lobules the
ducts are very small, the smallest measuring about yj-g- of an inch (8 ft) in
diameter. They are composed of a delicate membrane lined with epithe-
lium. The ducts larger than T^nr °f an incn (about 20 ft) 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 extent of the biliary passages, from the interlobular canals
to the ductus choledochus, are little utricular or racemose glands, varying in
size in different portions of the liver. These are situated, at short intervals,
by the sides of the canals. The glands connected with the smallest ducts are
simple follicles, -g-j-g- to ^j-g- of an inch (31 to 62 ft) long. The larger glands
are formed of groups of these follicles, and they measure -^^ or y-J-g- of an
inch (100 or 250 ft) in diameter. The glands are only found connected with
the ducts ramify-
ing in the sab-
stance of the liver,
and they do not ex-
ist in the hepatic,
cystic and common
ducts. They are
composed of a ho-
mogeneous mem-
brane, lined with
small, pale cells of
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 race-
mose gland, except
that the acini are
relatively small and scattered. This appearance is represented in Fig. 134.

The excretory biliary ducts, from the interlobular vessels to the point of
emergence of the hepatic duct, present frequent anastomoses with each other
in their course.
27

FIG. 134.— Racemose glands attached to the biliary ducts of the pig ; mag-
nified 18 diameters (Sappey).

1,1, branch of an hepatic duct, with the surface almost entirely covered
with racemose glands opening into its cavity ; 2, branch in which the
glands are smaller and less abundant : 3, 3, 3, branches of the duct with
still simpler glands ; 4, 4, 4, 4, biliary ducts with simple follicles at-
tached ; 5, 5, 5, 5, the same, with fewer follicles ; 6, 6, 6, 6, 6, anasto-
moses in arches ; 7, 7, 7, angular anastomoses ; 8, 8, 8, 8, anastomoses
by transverse branches.

398

USES OF THE LIVER— DUCTLESS GLANDS.

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 biliary ducts, which have been called vasa aberrantia.
These are never found in the foetus or in children. They are 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 atrophied.

Gall-bladder, Hepatic, C'ystic and Common Ducts. — The hepatic duct is
formed by 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 (38 mm.) in length
and joins at an acute angle with the cystic duct, to form the ductus coin-
munis choledochus. The common duct is about three inches (76 mm.) 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 in-
testine, and opens into its cavity, in connection with the principal pancreatic

20 12 19

FIG. 135. — 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, (jail-blad-
der ; 15, hepatic duct ; 16, cystic duct ; 17, common duct ; 18, portal vein ; 19, branch from the coeliac
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.

duct. The cystic duct is about an inch (25 mm.) in length, and is the
smallest of the three canals.

The structure of these ducts is essentially the same. They have a proper
coat formed of ordinary fibrous tissue, a few elastic fibres and non-striated
muscular fibres. The muscular tissue is not sufficiently distinct to form a
separate coat. The mucous membrane is always found tinged yellow with

NERVES AND LYMPHATICS OF THE LIVER. 399

the bile, even in living animals. It is marked by a large number of minute
excavations and is covered with cells of columnar epithelium. This mem-
brane contains a large number of mucous glands.

The gall-bladder is an ovoid or pear-shaped sac, about four inches (10
centimetres) in length, one inch (25 mm.) in breadth at its widest portion,
and capable of holding an ounce to an ounce and a half (30 to 45 c. c.) of
fluid. Its f undus 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 ordinary 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 sub-
ject. The mucous coat is of a yellowish color, with very»small, interlacing
folds which are very vascular. The mucous membrane of the gall-bladder
has a general lining of columnar epithelium with a few goblet-cells. In the
gall-bladder are found small, racemose glands, formed of four to eight folli-
cles lodged in the submucous structure. These are essentially the same as
the glands opening into the ducts in the substance of the liver, and they
secrete a mucus which is mixed with the bile.

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 pene-
trate at the transverse fissure and follow the blood-vessels in their distribu-
tion. They have not been traced farther than the final ramifications of the
capsule of Glisson, and their exact mode of termination is unknown.

The lymphatics of the liver are very abundant. They are divided into
two layers ; the superficial layer, situated just beneath the serous membrane,
and the deep layer. 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.

The mode of origin of the lymphatics is peculiar. The superficial lym-
phatics are subperitoneal and are connected with spaces or canals in the
general connective tissue of the liver. The deep lymphatics are supposed to
originate by perivascular canals surrounding the blood-vessels of the lobules,
which are connected with vessels in the walls of small branches of the hepatic
and portal veins, afterward surrounding the larger vessels.

Mechanism of the Secretion and Discharge of Bile. — In its anatomy the
liver differs greatly from other glandular organs, both secretory and excretory.
The liver-cells are not enclosed in ducts, but are surrounded by a plexus of
exceedingly small vessels which undoubtedly receive the bile as it is formed.
The liver, also, is supplied with both venous and arterial blood, the venous
blood largely predominating. In addition it is now recognized that the bile

400 USES OF THE LIVER— DUCTLESS GLANDS.

is necessary to intestinal digestion, that it contains excrementitious matters
and that the cells constantly produce glycogen. The liver produces urea,
which is excreted, however, chiefly by the kidneys. It may also effect certain
changes in digested and foreign matters that are absorbed from the aliment-
ary canal. As regards its varied uses, therefore, as well as in its anatomy, it
has no analogue in the glandular system, and the mechanism of its action is
necessarily complex.

As regards the secretion of bile, the only view that is consistent with
actual knowledge is that this fluid is produced by the liver-cells and is taken
up by the plexus of bile-ducts which surrounds these cells. The little gland-
ular organs that are attached to the larger branches of the duct secrete mucus
which gives the viscidity observed in the bile of some animals. The bile,
indeed, is viscid in different animals in proportion to the development of
these mucous glands ; and in the rabbit, in which the glands do not exist, the
bile has no viscidity (Sappey). The passage of excrementitious substances
from the blood into the bile will be discussed in connection with the action
of the liver as an organ of excretion, and the formation of glycogen will be
considered in its proper place.

Of course the circulation of blood in the liver is a condition necessary to
the secretion of bile. As regards the question of the production of bile from
venous or arterial blood, it has been shown that the materials out of which
the bile is formed may be supplied by either the hepatic artery or the portal
vein. Bile is secreted after the hepatic artery has been tied, and also after
the portal vein has been gradually obliterated, the hepatic artery being intact
(Ore). Bile is produced in the liver from the blood distributed in its sub-
stance by the portal vein and the hepatic artery, and not from the blood of
either of these vessels exclusively ; and bile may continue to be secreted, if
either one of these vessels be obliterated, provided the supply of blood be
sufficient.

Some of the variations in the discharge of bile have been described in
connection with the physiology of digestion; but although the bile is
poured out much more abundantly during intestinal digestion than at other
times, its production and discharge are constant. 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 on the secretion of bile has been
very little studied, and the question is one of great difficulty and obscurity.
The liver is supplied very abundantly with nerves, both cerebro-spinal and
sympathetic, and some observations have been made upon the influence of
the nerves upon its glycogenic action ; but with regard to the secretion of
bile, there is little to be said beyond what has already been stated concerning
the influence of the nervous system on other secretions.

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 communis, in part by contractions of its walls, and in

PROPERTIES AND COMPOSITION OF THE BILE. 401

part, probably, by compression exerted by the distended and congested diges-
tive organs adjacent to it. It seems that this fluid, which is necessarily pro-
duced by the liver without intermission, separating from the blood certain
excrementitious matters, is retained in the gall-bladder for use during diges-
tion.

Quantity of Bile. — The estimates of the daily quantity of bile in the
human subject must be merely approximate ; and the ideas of physiologists
on this point are derived chiefly from experiments 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 quan-
tity in the carnivora 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 (63-5 kilos.) would be about two and a half pounds (1,134 grammes).

USES OF THE BILE.

The uses of the bile in digestion have already been fully described ; but
before considering its characters as an excretion, it will be necessary to study
its general properties and composition.

Properties and Composition 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 by 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
semi-transparent, except -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 human bile from the gall-bladder is 1026 to 1032
(Landois). When perfectly fresh it is almost inodorous, but it readily un-
dergoes putrefactive changes. It has a 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 alkaline. This is true of the fluid
discharged 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 observations
on human bile that show that the fluid is not alkaline in all of the biliary
passages.

The epithelium of the biliary passages is strongly tinged with yellow, even
in living animals. . This is due to the facility with which the coloring mat-

402 USES OF THE LIVER— DUCTLESS GLANDS.

ter of the bile stains the animal tissues. This is very well illustrated 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 quantity of mucus, the characters of which have already been de-
scribed. 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 HUMAN BILE. (ROBIN.)

Water 916-00 to 819-00

Sodium taurocholate 56-50 " 106*00

Sodium glycocholate traces.

Cholesterine 0-62 to 2-66

Bilirubin 14-00 " 30-00

Lecithene I, 3.30 « 3J.QO

Palmitine, oleine and traces of soaps. . )

Choline traces.

Sodium chloride 2'77 to 3-50

Sodium phosphate 1-60 " 2-50

Potassium phosphate 0*75 *• 1-50

Calcium phosphate 0-50 " 1-35

Magnesium phosphate „ 0-45 " 0-80

Salts of iron 0-15 "• 0-30

Salts of manganese traces " 0-12

Silicic acid 0-03 " 0-06

Mucine traces.

Loss 3-43 to 1-21

1,000-00 1,000-00

There are no peculiarities in the composition of the bile, in respect to its
inorganic constituents, which demand more than a passing mention. It con-
tains no coagulable organic matters except mucine, and all of its constitu-
ents are simply solids in solution. The quantity of solid matter is very large,
and the proportion of water is relatively small. Among the inorganic salts,
sodium chloride exists in considerable quantity, with a large proportion of
phosphates. There exist, also, salts of iron and of manganese, with a small
quantity of silicic acid.

The fatty and saponaceous constituents demand hardly any more extended
consideration. A small quantity of palmitine and oleine are held in solu-
tion, partly by the soaps, but chiefly by the sodium taurocholate. The fats
sometimes exist in larger quantity, when they may be discovered in the form of
globules. The proportion of soaps is very small. Lecithene (C44H90NPOg)
is a neutral, fatty substance extracted from the bile, and may be decomposed
into phosphoric acid and glycerine. Choline (C5H15N02) is an alkaloid
found in the bile in exceedingly minute quantity.

Biliary Salts. — In human bile the characteristic biliary salt is a combi-
nation of taurocholic acid (C26H45NS07) with sodium. A very small quantity
of sodium exists in combination with glycocholic acid (C^6H43N06). These

COMPOSITION OF THE BILE. 403

two salts were discovered in the bile of the ox, by Strecker, in 1848. Sodi-
um glycocholate exists in quantity in ox-gall. Both of these salts may be
precipitated from an alcoholic extract of bile by an excess of ether. The
taurocholate is precipitated in the form of dark, resinous drops which crys-
tallize with difficulty. The glycocholate is readily crystallizable. The bil-
iary salts are very soluble in water and in alcohol. Their reaction is neutral.

There can be no doubt that the biliary salts are products of secretion and
are formed in the substance of the liver. In no instance have they ever
been discovered in the blood in health ; and although they present certain
points of resemblance with some of the constituents of the urine, they have
never been found in the excreta. In experiments made by Miiller, Kunde,
Lehmann and Moleschott, on frogs, in which the liver was removed and
the animal survived several days — and in the observations of Moleschott, be-
tween two and three weeks — it was found impossible to determine the pres-
ence of the biliary salts in the blood. There is no reason, therefore, for sup-
posing that these salts are products of disassimilation. Once discharged
into the intestine, they undergo certain changes and can no longer be recog-
nized by the usual tests ; but experiments have shown that, changed OP un-
changed, they are absorbed with the products of digestion. They are prob-
ably concerned in the digestive action of the bile.

Cholesterine. — Cholesterine ^eH^O) is 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 faecal
matter. It is to be found in all these situations, with the exception of the
faeces, where it does not exist normally, being transformed into stercorine in
its passage down the intestinal canal.

In the fluids of the body Cholesterine exists in solution ; but by virtue of
what constituents it is held in this condition, is a question that is not en-
tirely settled. It is stated that the biliary salts have the power of holding
cholesterine in solution in the bile, and that the small quantity of fatty acids
contained in the blood holds it in solution in that fluid ; but direct experi-
ments on this point are wanting. In the nervous tissue and in the crys-
talline lens, it is united with the other substances which go to make up
these parts. 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 certain 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 an alcohol, having many of the prop-
erties of the fats, but not that of saponification with the alkalies. It is neu-
tral, inodorous, crystallizable, insoluble in water, soluble in ether and very
soluble in hot alcohol, though sparingly soluble in cold alcohol. It is in-
flammable and burns with a bright flame. It is not attacked by the alkalies
even after prolonged boiling. When treated with strong sulphuric acid it
strikes a peculiar red color.

Cholesterine may easily and certainly be recognized under the microscope

404

USES OF THE LIVER-DUCTLESS GLANDS.

by the form of its crystals. They are rectangular or rhomboidal, very thin
and transparent, of variable size, with distinct and generally regular borders,
and frequently arranged in layers, with the borders of the lower strata show-
ing through those which are super-
imposed. The plates of cholesterine
are often marked by a cleavage at
one corner, the lines running par-
allel to the borders. Frequently the
plates are rectangular, and some-
times they are almost lozenge-shaped.
Crystals of cholesterine melt at 293°
Fahr. (145° C.), but they are formed
again when the temperature falls be-
low that point.

The proportion of cholesterine in
the bile is not very large. In the
table, it is estimated at 0-62 to 2-66

^.m.-Cholesterine extracted from the bile. partg per thousand< In a gingle ex_

amination of the human bile, the proportion was 0-618 of a part per thou-
sand (Flint).

The origin and destination of cholesterine involve an office of the liver
which has not been generally recognized by physiologists ; and these questions
will be considered specially, under the head of the excretory action of the
liver.

BiliruUn. — The coloring matter of the bile, bilirubin (C32H36N406),
bears a certain resemblance to the coloring matter of the blood and is sup-
posed to be formed from it in the liver. It gives to the bile its peculiar tint
and has the property of coloring the tissues with which it comes in contact.
Whenever the flow of bile is obstructed for any considerable time, the color-
ing matter is absorbed by the blood and can be readily detected in the serum
and in the urine. It also colors the skin and the conjunctiva. It is soluble
in chloroform, by which it is distinguished from biliverdine, and forms sol-
uble combinations with alkalies, in which form it is thought to exist in the
bile. It probably is formed in the liver from the haemoglobine of the red
blood-corpuscles. When exposed to the air or to the influence of certain ox-
idizing agents, it assumes a greenish color and is changed into biliverdine.
It is unnecessary to follow the various other changes produced by spontane-
ous decomposition or by the action of reagents.

Tests for Bile. — A simple test for bile-pigment is the following : A thin
stratum of the liquid to be tested is placed upon a white surface, as a porce-
lain plate, and to this is added a drop of nitroso-nitric acid. If the coloring
matter of the bile be present, a play of colors will be observed surrounding
the drop of acid. The color will rapidly change from green to blue, red,
orange, purple and finally to yellow. This test is applicable only to the col
oring matter and does not detect the biliary salts.

A very delicate test for the biliary salts in a clear solution not contain^

EXCKETORY ACTION OF THE LIVER. 405

ing albumen is what is known as Pettenkofer's test : To the suspected
liquid are added a few drops of a strong solution of cane-sugar. 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 dark lake or purple. If the biliary matters exist in very small pro-
portion,'" it may be several minutes before a red color makes its appearance,
and the change to a purple is correspondingly slow, the whole process occu-
pying fifteen to twenty minutes.

EXCRETORY ACTION OF THE LITER.

Although the liver produces a greater or less quantity of urea, this sub-
stance is discharged from the body chiefly in the urine and mere traces exist
in the bile. The excretory action of the liver will be considered, in this con-
nection, with reference to the bile itself. At the present day it is generally
admitted that the bile is an excretion as well as a secretion ; and this ques-
tion has been fully discussed in connection with the physiology of digestion.
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 excre-
tion. It will be useful, as bearing upon the probable office of the bile as an
excretion, to apply to this fluid the general law of the distinctions between
secretions and excretions.

Cells of glandular epithelium are constantly forming, out of materials
furnished by the blood, the characteristic constituents of the true secre-
ions ; but these do not pre-exist in the blood, they appear first in the secret-
ting organ, and they never accumulate in the system when the action of the
secreting organ is disturbed. Again, the true secretions are not discharged
from the body, but they have an office to perform in the economy, and are
poured out by the glands intermittently, at the times when this office is called
into action. As far as the biliary salts, sodium taurocholate and sodium
glycocholate, are concerned, the bile corresponds entirely to the true secre-
tions. These salts are formed in the liver, they do not pre-exist in the blood,
and they do not accumulate in the blood when their formation in the liver is
disturbed. The researches of Bidder and Schmidt and others have shown
that although the biliary salts can not be detected in the blood or chyle
coming from the intestine, they are not discharged in the faeces. These facts
point to an important office of the bile as a secretion. It is true that the
bile 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 forming the materi-
als of secretion, which are washed out, as it were, in the great afflux of blood
which takes place during what has been called the activity of the gland.

4:06 USES OF THE LIVER— DUCTLESS GLANDS.

The constant and invariable presence of cholesterine in the bile assimi-
lates 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.
Physiologists know of no office which it has to perform in the economy, any
more than urea or any other of the excrementitious constituents of the urine.
It accumulates in the blood in certain cases of organic disease of the liver
and gives rise to symptoms of blood-poisoning.

Origin bf Cholesterine. — Cholesterine exists in largest quantity in the sub-
stance 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 exceptions, it is found only in the nervous tissue and
blood. 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.

In a series of experiments made in 1862, it was invariably found that the
proportion of cholesterine in the blood of the internal jugular vein and the
femoral vein was greater than in the arterial blood. In experiments made
on dogs not etherized, the blood of the jugular vein contained, in one in-
stance 23 '3 and in another 59'8 per cent, more cholesterine than the arterial
blood of the same animals. The blood of the femoral vein contained about
6'3 per cent, more cholesterine than arterial blood. In three cases of hemi-
plegia, cholesterine was found in normal quantity in blood taken from the
arm of the sound side, while blood from the paralyzed side contained no
cholesterine (Flint).

These observations point to the production of cholesterine in the tissues ;
and the fact of its existence, under normal conditions, in the nervous tissue
renders it probable that the chief seat of its production is the substance of
the nerve-centres and nerves. The question of its formation in the spleen is
one that has not been investigated.

In another series of experiments, it was shown that the blood lost cho-
lesterine in passing through the liver. In one observation it was found that
the arterial blood lost a little more than 23 per cent, and the portal blood,
about 44 per cent., in passing through the liver (Flint).

The portal blood, as it goes into the liver, contains but a small percent-
age of cholesterine over the blood of the hepatic vein, while the percentage
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 goes to the liver, it contains a quantity of this sub-
stance 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 predomi-
nates and is necessary to other important actions of this organ, such as the
production of glycogen ; but soon after the portal vein enters the liver, its

EXCRETORY ACTION OF THE LIVER. 407

blood becomes mixed with that from the hepatic artery, and from this mixt-
ure the cholesterine is separated. It is necessary only that blood, contain-
ing 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 proved 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.

In treating of the composition of the faeces, the changes which the choles-
terine of the bile undergoes in its passages down the intestinal canal have
been so fully considered that it is not necessary to refer to this portion of
the subject again. But one examination only was made of the quantity of
stercorine contained in the daily faecal evacuation ; and assuming that
the quantity of cholesterine excreted by the liver is equal to the stercorine
found in the evacuations, the quantity in twenty-four hours is about ten and
a half grains (0'68 gramme). This corresponds with the estimates of the
daily quantity of cholesterine excreted, calculated from its proportion in the
bile and the estimated daily quantity of bile produced by the liver.

To complete the chain of the evidence leading 'to the conclusion that
cholesterine is an excrementitious product which is formed in certain of the
tissues and eliminated by the liver, it is necessary only to show that it may
accumulate in the blood when the eliminating action of the liver is inter-
rupted.

In a case of simple jaundice from duodenitis, in which there was no
great disturbance of the system, a specimen of blood taken from the arm
presented undoubted evidences 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 proportion of saponfiable fat, but no
cholesterine or stercorine.

In a case of cirrhosis with jaundice, there was ascites, with great general
prostration. This patient died a few days after the blood and faeces 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 1-85 of a part of cholesterine per thousand, more than double the
largest quantity found in health. The faeces contained a small quantity of
stercorine.

Inasmuch as cases frequently present themselves in which there are evi-
dences of cirrhosis of the liver with little if any constitutional disturbance,
while others are attended with grave nervous symptoms, it seemed an inter-
esting question to determine whether it be possible for cholesterine to accu-
mulate in the blood without the ordinary evidence of jaundice. An oppor-
tunity occurred 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 the general health was little impaired. In this

408 USES OF THE LIVER— DUCTLESS GLANDS.

case the proportion of cholesterine in the blood was only 0-246 of a part per
thousand, considerably below the quantity ordinarily 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 found in health. A few other
pathological observations of this kind are on record. Picot, in 1872, re-
ported a fatal case of " grave jaundice," in which he determined a great in-
crease in the quantity of cholesterine in the blood, the proportion being
1-804 per 1000.

It is probable that organic disease of the liver, accompanied with grave
symptoms generally affecting the nervous system, does not differ in its pathol-
ogy 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 and its consequent accumula-
tion in the system. Like the accumulation of urea in structural disease of
the kidney, this produces blood-poisoning ; and this condition may be char-
acterized by the name Cholesteraamia, a term expressing a pathological con-
dition, but at the same time indicating the physiological relations of choles-
terine.

Koloman Miiller, in 1873, succeeded in injecting cholesterine into the
blood-vessels without producing any effects due to mechanical obstruction of
the circulation. He made a preparation by rubbing cholesterine with glyc-
erine and mixing the mass with soap and water. He injected into the veins of
dogs, 2-16 fluidounces (about 64 c. c.) of this solution, containing about
69 grains (4-5 grammes) of cholesterine. In five experiments of this kind, he
produced a complete representation of the phenomena of " grave jaundice."

In view of all these facts, an excretory action of the liver, involving the
separation. of cholesterine from the blood and its discharge in the faeces in
the form of stercorine, must be regarded as established, as well as the exist-
ence of cholesteraemia as a definite pathological condition.

FORMATION OF GLYCOGEF IN THE LIVER.

In addition to the uses of the liver already described, this organ con-
stantly produces in health a substance resembling starch, called glycogen,
which is converted into glucose and is carried into the circulation by the
hepatic veins. In this way the liver acts as a ductless gland, glycogen being
formed by the liver-cells in precisely the manner that the various constitu-
ents of the secretions are produced by other glands. The discovery of this,
which was first called the sugar-producing office of the liver, was made by
Bernard, in 1848. During the present century there have been few dis-
coveries which have attracted so much attention, and Bernard's experiments
have been repeated and extended by physiologists in different parts of the
world. In 1857, Bernard discovered glycogen in the liver and showed that
the production of this substance precedes the formation of sugar. In study-
ing, then, the mechanism of sugar-production in animals, it will be necessary
to begin with the physiological history of glycogen.

FORMATION OF GLYCOGEN IN THE LIVER. 409

Glycogen (C6H1005) belongs to the class of carbohydrates and is iso-
meric with starch. It is readily converted into glucose (C6H1206). In nearly
all regards it has the properties of starch, but it gives a deep red color with
iodine instead of a blue. In the liver-cells it exists in the form of amor-
phous granules surrounding the nuclei. It may be extracted from a decoc-
tion of the liver-substance, by precipitating the albuminoids by adding alter-
nately dilute hydrochloric acid and potassio-mercuric iodide, filtering and
treating the filtrate with an excess of alcohol. The alcoholic precipitate,
washed with alcohol and dried rapidly, is in the form of a white powder,
which will keep indefinitely. In the adult, glycogen is most abundant in
the liver ; but it has been found in small quantity in the muscular substance,
in cartilage and in certain cells in process of development. In the early
months of foetal life it exists in nearly all the tissues. It is found, also, in
cells attached to the villi of the placenta.

The most important of the conditions which influence the quantity of
glycogen in the liver relate to alimentation and digestion. The liver always
contains more glycogen during digestion than in fasting animals. After a
few days of starvation, glycogen may almost or quite disappear from the
liver. This also occurs in animals fed for a time exclusively with fats, and
the quantity is diminished by a purely albuminous diet as contrasted with a
mixed diet. Still, as was shown by Bernard, glycogen is invariably present
in the livers of healthy carnivorous animals that have always been fed with
meat alone.

A very great increase in the quantity of glycogen in the liver is produced
by feeding animals largely with carbohydrates. Not only are the starches
apparently stored up for a time in the form of glycogen in the liver, but
sugars seem to undergo a change into glycogen which accumulates in the
liver. This is to be expected, as the starches are changed into sugar before
they are absorbed, and all the carbohydrates behave in the same way as
regards general nutrition. Very abundant alimentation with carbohydrates
sometimes produces a temporary diabetes, the quantity of sugar in the blood
increasing to such an extent that sugar is discharged in the urine. This is
due either to the passage of a certain quantity of sugar unchanged through
the liver or to an excessive formation of glycogen, which is more actively
changed into sugar than under normal conditions.

As far as regards the influence of alimentation upon the formation of
glycogen, it seems probable that in the herbivora and in man the chief source
of hepatic glycogen is the class of alimentary substances called carbohydrates ;
but the fact that glycogen exists in the livers of the carnivora, and probably
in man, under a nitrogenized diet, shows that the liver is capable of forming
glycogen from the albuminoids.

Change of Glycogen into Sugar. — It is almost certain that the liver does
not contain sugar during life. Many years ago (1858) this fact was recog-
nized by Pavy, and it has since been confirmed by other physiologists. Pavy,
however, assumed that there was no such thing as sugar-formation by the
liver, under absolutely normal conditions. He regarded the sugar found in

410 USES OF THE LIVER— DUCTLESS GLANDS.

the substance of the liver and in the blood of the hepatic veins as due to post-
mortem action, and his observations seemed to be directly opposed to those
of Bernard. The views of these two observers and their followers seemed to
be harmonized by a series of experiments made in 1868. If the abdomen of
a dog, perfectly quiet and not under the influence of an anaesthetic, be opened,
and a portion of the liver be excised, rinsed in cold water and rapidly cut up
into boiling water, the extract will show no reaction with Fehling's test for
sugar. In one experiment, in which twenty-eight seconds elapsed between
the time of opening the abdomen and the action of the boiling water, the
reaction with Fehling's test was doubtful. In an experiment in which the
time was only ten seconds, there was no trace of sugar in the extract from
the liver (Flint). Dalton, however, in 1871, found small quantities of sugar
in extracts of portions of liver taken from an animal in an average time of
6 J seconds ; but it is possible that the sugar may have been in blood retained
in the liver. All observers, however, are now agreed that sugar is formed in
the liver very rapidly after death.

If the view be correct, that the glycogen of the liver is being constantly
transformed into sugar during life, and that this sugar is carried away
in the blood-current, as fast as it is formed, sugar would not necessarily be
contained in the liver under normal conditions ; and there is no actual antag-
onism between the results obtained by Bernard and the fact that sugar itself
is not a normal constituent of the liver, as is asserted by Pavy, McDonnell,
Meissner, Eitter and others.

If the liver be washed by a stream of water passed through its vessels
until it is free from sugar, and if it be kept at the temperature of the body
for a few hours, sugar will appear in abundance (Bernard, 1855). This is
due to a conversion of the glycogen of the liver into sugar by a ferment, which
has been extracted and isolated by Bernard and others by a process analogous
to that by which similar ferments have been extracted from the saliva and
the pancreatic juice. This ferment probably exists originally in the liver
and does not appear first in the blood.

The question of the transformation of glycogen into sugar during life
depends upon the comparative quantities of sugar in the blood going to and
coming from the liver. Bernard always found sugar in quantity in the blood
of the hepatic veins taken immediately after death, and it exists in blood
drawn during life by a catheter introduced into the right cavities of the
heart ; while in the carnivora, under a purely animal diet, no sugar is con-
tained in the blood of the portal system. The normal blood contains, per-
haps, a small quantity of sugar — 0-5 to 1 part per 1,000 — but the proportion
is always greater in the blood of the hepatic veins.

The characters of animal sugar do not materially differ from those of glu-
cose, except that it ferments more readily and is destroyed in the system
with great facility. This property of the sugar which results from the gly-
cogen formed in the liver is probably of great importance. The sugar which
results from digestion is all carried to the liver. Here it is changed into
glycogen ; and it is probable that without this change into glycogen and its

FORMATION OF GLYCOGEN IN THE LIVER. 411

subsequent transformation into what is called liver-sugar, it is not perfectly
adapted to the purposes of nutrition. In many cases of diabetes, a possible
explanation of the glycosuria is that the carbohydrates pass unchanged into
the vena cava and do not undergo the changes which take place normally
in the liver, at the same time being received into the general circulation sud-
denly and in large quantity, instead of gradually, as when they are changed
into glycogen and afterward into liver-sugar. When an excess of sugar finds
its way into the blood, it is probable that the liver, under normal conditions,
retains it for a time in the form of glycogen.

The sugar which is discharged into the venous system by the hepatic
veins is usually lost in the passage of the blood through the lungs. The ques-
tion of the final destination of sugar will be taken up again in connection
with the physiology of nutrition.

Conditions which influence the Quantity of Sugar in the Blood. — It is
probable that disturbances of the circulation in the liver are the most impor-
tant conditions influencing the discharge of sugar by the
hepatic veins, and these operate mainly through the nervous
system.

The most remarkable experiment upon the influence of
the nervous system on the liver is the one in which artificial
diabetes is produced by irritation of the floor of the fourth
ventricle (Bernard). This operation is not difficult. The
instrument used is a delicate stilet, with a flat, cutting ex-
tremity, and a small, projecting point about ^ of an inch
(1 mm.) long. In performing 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 within
the cranium, the instrument is passed obliquely downward
and forward, so as to cross an imaginary line drawn be-
tween the two auditory canals, until its point reaches the
basilar process of the occipital bone. The point then pene-
trates the medulla oblongata, between the roots of the audi-
tory nerves and the pneumogastrics, and by its projection
it serves to protect the nervous centre from more serious
injury from the cutting edge. The instrument is then care-
fully withdrawn and the operation is completed. This ex-
periment is almost painless, and it is not desirable to ad-
minister an anaesthetic, as this, in itself, would disturb the
glycogenic process. The urine may be drawn before the op- Fio 137
eration, by pressing the lower part of the abdomen, taking care

not to allow the bladder to pass up above the point of press- fourth ventricle
ure, 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 readily with any of the copper-tests. When this opera-

412

USES OF THE LIVER-DUCTLESS GLANDS.

tion is performed without injuring the adjacent organs, the presence of sugar
in the urine is temporary, and the next day the secretion will have returned
to its normal condition. The production of diabetes in this way, in animals,
is important in its relations to certain cases of the disease in the human
subject, in which the affection is traumatic and directly attributable to injury
near the medulla. Its mechanism is difficult to explain. The irritation is
not propagated through the pneumogastric nerves, for the experiment suc-
ceeds after both of these nerves have been divided ; nevertheless, the pneumo-
gastrics have an important influence upon glycogenesis. 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 action has been
arrested. After division of the nerves in the neck, stimulation of their periph-
eral ends does not affect the production of sugar ; but stimulation of the cen-
tral ends produces an impression which is conveyed to the nervous centre, is
reflected to the liver and gives rise to an increased production of sugar.

"With regard to
the influence of the
sympathetic nerves
upon glycogenic
action, there have
been few if any ex-
periments which
lead to conclusions
of any great value.
It has been ob-
served that the in-
halation of anaes-
thetics and irrita-
ting vapors pro-
duces temporary
diabetes ; and this
has been attributed
to an irritation con-
veyed by the

FIG. 138.— Section of the head of a rabbit, showing the operation of punct

uring the floor of the fourth ventricle (Bernard).
a, cerebellum : b, origin of the seventh pair of nerves ; c, spinal cord ;

, , ,

prigin of the pneumogastric ; e, opening of entrance of the instrument .

into the cranial cavity ; /, instrument ; g, fifth pair of nerves ; h, audi- mOSfastricS to the
tory canal ; /, extremity of the instrument upon the spinal cord, after it
has penetrated the cerebellum ; k, occipital venous sinus ; Z, tubercula
quadrigemina ; m, cerebrum ; n, section of the atlas.

nerve-centre, and
reflected, in the

form of a stimulus, to the liver. It is for this reason that the administration of
anaesthetics should be avoided in all accurate experiments on glycogenic action.

The following summary expresses what is known with regard to the pro-
duction of glycogen by the liver and its conversion into sugar :

A substance exists in the healthy liver, which is readily convertible into
sugar; and inasmuch as this is changed into sugar during life, the sugar
being washed away by the blood passing through the liver, it is proper to
call it glycogen, or sugar-forming matter.

PHYSIOLOGICAL ANATOMY OF THE SPLEEN. 413

The liver has a glycogenic action, which consists in the constant forma-
tion of sugar out of the glycogen, the sugar 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 to a certain extent in-
dependent of the kind of food taken.

During life the liver contains glycogen only and no sugar, because the
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 glycogen into sugar continues. The sugar is not
removed under these conditions, and it can then be detected in the substance
of the liver.

The liver serves as a receptacle for the carbohydrates, which, under nor-
mal conditions of alimentation and nutrition, are all converted into glycogen.
The glycogen is then converted into sugar, which is supplied to the system
as the nutritive requirements demand.

In addition to the varied uses of the liver which have been described, it is
thought that this organ either arrests or in some way influences the condition
of certain foreign and poisonous substances which may be absorbed from the
alimentary canal ; but a study of this action does not properly belong to
physiology.

DUCTLESS GLANDS.

Certain 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 speculation ; and the most extravagant notions concerning their
uses have prevailed in the early history of physiology. The discovery of the
action of the liver, which consists in modifications in the composition of the
blood passing through its substance, has foreshadowed the probable mode of
action of the ductless glands ; for as far as the production of glycogen is con-
cerned, the liver belongs to this class. Indeed, the supposition that the
ductless glands effect certain changes in the blood is now regarded by physi-
ologists as the most reasonable of the many theories that have been entertained
concerning their uses in the economy. Under this idea, these organs have
been called blood-glands or vascular glands. Under the head of ductless
glands, are classed the spleen, the suprarenal capsules, the thyroid gland, the
thymus, and sometimes the pituitary body and the pineal gland.

PHYSIOLOGICAL ANATOMY OF THE SPLEEN.

The spleen is situated in the left hypochondriac region, next the cardiac
extremity of the stomach. Its color is a dark bluish-red and its consistence
is rather soft and friable. It is shaped somewhat like the tongue of a dog,
presenting above, a rather thickened extremity, which is in relation with
the diaphragm, and below, a pointed extremity, in relation with the trans-
verse colon. Its external surface is convex. Its internal surface is concave,
presenting a vertical fissure, the hilum, which gives passage to the vessels and

28

414 USES OF THE LIVER— DUCTLESS GLANDS.

nerves. It is connected with the stomach by the gastro-splenic omentum and
is still farther fixed by a fold of peritoneum passing to the diaphragm. It is
about five inches (127mm.) in length, three to four inches (75 to 100mm.) in
breadth, and a little more than an inch (25*4 mm.) in thickness. Its weight is
six to seven ounces (170 to 198 grammes). In the adult it attains its maxi-
mum 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 ad-
herent to the subjacent fibrous structure. The proper coat is dense and resist-
ing, but in the human subject it is quite thin and somewhat translucent. It
is composed of ordinary fibrous tissue mixed with abundant small fibres of
elastic tissue and a few non-striated muscular fibres.

At the hilum the fibrous coat penetrates the substance of the spleen in
the form of sheaths for the vessels and nerves. The 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 ramifi-
cations to the smallest branches and are lost in the spleen-pulp. Between
the sheath and the outer coat, are bands, or trabeculse, presenting the same
structure as the fibrous coat. The presence of elastic fibres in the trabeculse
can be easily demonstrated, and this kind of tissue is very abundant in the her-
bivora. In the carnivora the muscular tissue is particularly abundant and
can be readily demonstrated ; but in man this is not so easy, and the fibres
are less abundant. These peculiarities in the fibrous structure are important
in their relations to certain physiological changes in the size of the spleen.
Its contractility may be easily demonstrated in the dog, by the application of
a Faradic current to the nerves as they enter at the hilum. This is followed
by a prompt and enegetic contraction of the organ. Contractions may be pro-
duced, 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 with the fingers or even washed away
by a stream of water. Aside from the vessels and nerves, it presents for
study: 1, an arrangement of fibrous bands, or trabeculae, by which it is
divided into communicating spaces ; 2, closed vesicles, called Malpighian
bodies, attached to the walls of the blood-vessels ; 3, a soft, reddish substance,
containing large numbers of 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 ves-
sels (capsule of Malpighi), are bands, or trabeculse, which, by their interlace-
ment, divide the substance of the organ into irregularly shaped, communi-
cating cavities. These bands are ^ to ^ of an inch (1 to 1-7 mm.) broad, and
are composed, like the proper coat, of ordinary fibrous tissue with elastic
fibres and probably a few non-striated muscular fibres. They pass off from

PHYSIOLOGICAL ANATOMY OF THE SPLEEN.

415

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 ^Ju-'to -fa of an inch (0*1 to 0*42 mm.). This fibrous net- work
serves as a support for the softer and more delicate parts.

Malpighian Bodies. — These bodies are sometimes called the splenic cor-
puscles or glands. They are rounded or slightly ovoid, about -fa of an inch
(O5 mm.) in diameter, and are filled with what are thought to be lymph-
corpuscles, and free nuclei. The Malpighian bodies have no investing mem-
brane. With this difference, they resemble in structure the solitary glands
of the intestine. 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, capil-
lary plexus — and by what is thought
to be a lymphatic space or sinus.

The number of the Malpighian
corpuscles in a spleen of ordinary
size has been estimated at about ten
thousand (Sappey). They are readi-
ly made out in the ox and sheep
but are frequently not to be discov-
ered in the human subject. The
occasional absence of these bodies
constitutes another point of resem-
blance to the solitary glands of the
small intestine.

The Malpighian bodies are at-
tached to arteries measuring -fa to
-fa of an inch (O32 to 0-42 mm.) or
less in diameter (Sappey). They are often found in the notch formed by
the branching of an artery, but they usually lie by the sides of the vessel.

Spleen-pulp. — The spleen-pulp is a dark, reddish, semi-fluid 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 trabeculae, and it contains itself microscopic bands of fibres arranged
in the same way. It surrounds the Malpighian bodies and contains the termi-
nal branches of the blood-vessels, nerves and lymphatics. Upon microscopi-
cal examination, it presents free nuclei and cells like those described in the Mal-
pighian bodies ; but the nuclei are here relatively much more abundant. In
addition are found, red blood-corpuscles, some natural in form and size and
others more or less altered, with pigmentary granules, both free and en-
closed in cells.

Blood-vessels, Nerves and Lymphatics of the Spleen. — The quantity of blood
which the spleen receives is very large in proportion to the size of the organ

FIG. 139. — Malpighian corpuscle of the spleen of the

caffcadiat).

A, artery around which the corpuscle is placed ; B,
meshes of the pulp, injected ; c, the artery of the
corpuscle ramifying in the lymphatic tissue.
The clear space around the corpuscle is the lymphat-
ic sinus

416 USES OF THE LIVER— DUCTLESS GLANDS.

The splenic artery is the largest branch of the cceliac axis. It is a vessel of con-
siderable length and is remarkable for its tortuous course. In an observation
by Sappey, in a man between forty and fifty years of age, the vessel measured
about five inches (12 centimetres), without taking account of its deflections;
and a thread placed on the vessel so as to follow exactly all its windings meas-
ured a little more than eight inches (21 centimetres). The large caliber of
this vessel and its tortuous course are important points in connection with
the great variations in the size of the spleen under various conditions 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 six to ten vessels. These penetrate the sub-
stance of the spleen, with the veins, nerves and lymphatics, enveloped in
fibrous sheaths. 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 -fa or -fa of an inch (0'32 or 0-42 mm.) 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 arteries passing
in at the hilum have no inosculations with each other in the substance of the
spleen, so that the organ is divided up into six to ten vascular compartments.

The veins join the small 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 as
about twice that of the arteries (Sappey). The estimates which have put
the caliber of the veins at four or five times that of the arteries are probably
much exaggerated. The number of veins emerging from the spleen is equal
to the number of arteries of supply.

By most anatomists two sets of lymphatic vessels have been recognized,
the superficial and the deep. The superficial lymphatics are in the investing
membrane of the spleen and probably are connected with the deep lym-
phatics. The origin of the deep vessels is somewhat obscure. Lymphatic
spaces or sinuses surround the Malpighian bodies, and there is probably a
perivascular canal-system, the exact origin of which is unknown. At the
hilum the deep lymphatics are joined by vessels from the surface. The ves-
sels, numbering five or six, then pass into small lymphatic glands and empty
into the thoracic duct opposite the eleventh or twelfth dorsal vertebra. No
lymphatic vessels have been observed going to the spleen.

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. When these nerves are
stimulated, 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 uses of the spleen from analyses of
its substance ; and it would therefore be out of place to discuss its chemical

VAKIATIONS IN THE VOLUME OF THE SPLEEN. 417

constitution very fully. 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, lactic acid, acetic acid, butyric acid,
inosite, amyloid matter and some indefinite fatty matters.

Variations in the Volume of the Spleen. — One of the theories with regard
to the uses of the spleen, which merits some consideration, is that it serves
as a diver tic ulum 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 four or 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 succeed-
ing twelve hours ; but it is not apparent how far these changes are important
or essential to normal digestion and absorption. Experiments have shown
that animals may live, digest, and absorb alimentary matters after the spleen
has been removed, and this has been observed even in the human subject.
In view of these facts, it can not be assumed that the office of the spleen,
as a diverticulum for the blood, is essential to the proper action of the other
abdominal organs.

Changes in the volume of the spleen may be produced by operating on
the nervous system, chiefly through the vaso-motor nerves. Section of the
nerves at the hilum increases the size of the spleen by increasing the quantity
of blood which it receives ; and stimulation of these nerves produces contrac-
tion of the spleen. It is stated that stimulation of the medulla oblongata
diminishes the size of the spleen, and that the same result can be produced
by reflex action, stimulating the central ends of the pneumogastrics or of
various sensory nerves, provided that the splanchnic nerves be intact. Start-
ing from the medulla oblongata, the nerve-fibres which influence the size of
the spleen pass down the spinal cord to the lower dorsal region, enter the
semilunar ganglion by the left splanchnic, and are distributed to the spleen
through the splenic plexus.

Extirpation of the Spleen. — There is one experimental fact that has pre-
sented itself in opposition to nearly every theory advanced with regard to
the uses of the spleen, which is that the organ may be removed from a liv-
ing animal and yet all the processes of life go on apparently as before. The
spleen is certainly not necessary to life, nor, as far as is known, is it essential
to any of the important general functions. It has been removed 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 diver-
ticulum, this is not essential to normal digestion and absorption ; and if its
office be the destruction or the formation of the blood-corpuscles, the forma-
tion of leucocytes, of uric acid, cholesterine or of any excrementitious matter,
there are other organs which may perform these acts. Extirpation of the
spleen is an old and a very common experiment. In the works of Malpighi,
published in 1687, is an account of an experiment on a dog, in which the

418 "USES OF THE LIVER-DUCTLESS GLANDS.

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 authori-
ties upon the subject. There are many 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. One of the phenomena following extirpation of the
spleen is a modification of the appetite. Great voracity in animals after
removal of the spleen was noted by the earlier observers. Later experiment-
ers have observed this change in the appetite and have noted that digestion
and assimilation do not appear to be disturbed, the animals becoming unusu-
ally fat. Dalton has also observed that the animals, particularly dogs, some-
times present a remarkable change in their disposition, becoming unnaturally
ferocious and aggressive.

In the following observation these phenomena were very well marked :

The spleen was removed from a young dog weighing twenty-two pounds
(about 10 kilos.). 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 voracious. The dog became so irrita-
ble and ferocious that it was dangerous to approach him, and it became neces-
sary to separate him from the other animals in the laboratory. He would
eat refuse from the dissecting-room, the flesh of dogs, faeces etc. About six
weeks after the operation, having been well fed twenty-four hours before, the
dog ate at one time a little more than four pounds (1,814 grammes) of beef-
heart, nearly one-fifth of his weight. This he digested well, and the appetite
was undiminished on the following day. This dog had a remarkably sleek
and well nourished appearance (Flint, 1861).

The above is a striking example of the change in the appetite and dis-
position of animals after extirpation of the spleen ; but these results are by
no means invariable. In many instances of removal of the spleen from dogs,
the animals we,re kept for several months and nothing unusual was observed.
On the other hand, the change in disposition and the development of an
unnatural appetite were observed 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 accounted for 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 are not so readily explained.

Cases are on record of congenital absence of the spleen in the human sub-
ject, in which no special phenomena had been observed during life.

Aside from certain uses which are connected with changes in its volume,
it is certain that the spleen has some relation to the formation of the blood-
corpuscles, both white and red. In certain cases of leucocythaemia, the spleen
is in a condition of hyperplastic enlargement. The blood coming from the
spleen is peculiarly rich in leucocytes, but the proportion of its red corpuscles
is diminished. It may be that the spleen destroys a certain number of red

SUPRARENAL CAPSULES. 419

corpuscles, the coloring matter being changed into other pigmentary matters,
and that it also produces new red corpuscles. After removal of the spleen,
the red blood-corpuscles are diminished in number, and the proportion of
leucocytes is increased. This condition continues for about six months, but
after that time, in dogs, the marrow of the long bones, which normally is
yellow, becomes red, assuming the character of the marrow concerned in the
formation of red corpuscles. Temporary diminution of red corpuscles and
increase of leucocytes have been observed in the blood in cases of extirpation
of the spleen in the human subject.

Whatever uses the spleen has in connection with the development of red
and of white blood-corpuscles it shares with the red marrow of the bones
and the so-called lymphatic glands.

The above expresses about all that is known with regard to the physiology
of the spleen.

SUPRARENAL CAPSULES.

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 semi-
lunar in form, the right being more nearly triangular. Their size and
weight are very variable in different individuals. It may be stated, as an
average, that each capsule weighs about one hundred grains (6*5 grammes).
The capsules are about an inch and a half (38 mm.) in length, a little less in
width, and a little less than one-fourth of an inch (6-4 mm.) in thickness.

The weight of the capsules, in proportion to the weight of the kidneys,
presents great variations at different periods of life. They are relatively much
larger in the foetus than after birth. 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 (Meckel). In the foetus at term the
proportion is as one to three, and in the adult, as one to twenty-three.

The color of the capsules is whitish-yellow. They are completely cov-
ered by a thin, fibrous coat, which penetrates their interior, in the form of
trabeculae. Upon section they present a cortical and a medullary substance.
The cortex is yellowish and ^ to -^ of an inch (1 to 2 mm.) in thickness. It
surrounds the capsule completely and constitutes about two-thirds of its sub-
stance. The medullary substance is whitish, very vascular, and is remark-
ably prone to decomposition, so that it is desirable to study the anatomy of
these bodies in specimens that are perfectly fresh.

Cortical Substance. — The cortical substance is divided into two layers.
The external layer is pale-yellow and is composed of closed vesicles, rounded
or ovoid in form, containing an albuminoid fluid, cells, nuclei and fatty glob-
ules. This layer is very thin. The greater part of the cortical substance is of
a reddish-brown color and is composed either of closed tubes containing

420

USES OF THE LIVER— DUCTLESS GLANDS.

cells or of columns of cells surrounded by delicate, fibrous trabeculae. On
making thin sections through the cortical substance previously hardened in
chromic acid and rendered clear by glycerine, rows of cells are seen, arranged
with great regularity, and extending, apparently, from the investing mem-
brane to the medullary substance. The cells appear to be enclosed in tubes
measuring y^^ to g-J-g- of an inch (25 to 80 /u,) in diameter. They are gran-
ular, with a distinct nucleus and nucleolus and a variable number of oil-
globules. They measure ^^ to ToVo- °f an incn (14 to 35 /A) in diameter.
Between the rows of cells of the cortical substance, are bands of fibrous tissue
connected with the investing membrane of the capsule.

Medullary Substance. — The medullary substance is much paler and more
transparent than the cortex. In its centre are openings which mark
the passage of its venous sinuses. It is penetrated in every direction by very
delicate bands of fibrous tissue, which enclose blood-vessels, nerves, and elon-
gated, closed vesicles containing cells, nuclei and granular matter, These
vesicles, which are ¥V of an inch (0-32 mm.) long and about ¥-J^ of an inch
(64 /A) broad, have been demonstrated in the ox and in the human subject.
The cells in the human subject are i^00 to 1^00 of an inch (15 to 20 /x) in
diameter. They are isolated with difficulty and are very irregular in their

form. The nuclei measure about ^rVo °f
an inch (10 /A). The medullary substance is
peculiarly rich in vessels and nerves.

Vessels and Nerves. — The blood-vessels
going to the suprarenal capsules are very
abundant and are derived from the aorta,
the phrenic artery, the ccsliac axis and the
renal artery. Sometimes as many as twenty
distinct vessels penetrate each capsule. In
the cortical substance the capillaries are ar-
ranged in elongated meshes, anastomosing
freely and surrounding the tubes but never
penetrating them. In the medullary sub-
stance 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 abundant and are
derived from the semilunar ganglia, the re-
nal plexus, the pneumogastric and the phren-
ic. Kolliker counted in the human subject

tjitm thirty-three nervous trunks entering the

right suprarenal capsule. The nerves prob-
ably pass directly to the medullary substance, but here their mode of distri-

FIG. 140. — Section of a human suprarenal
capsule (Cadiat).

A, fibrous coat; B, cells of the cortical sub-
stance, arranged in rows; c, vesicles of
the medullary substance ; D, blood- ves-

THYROID GLAND. 421

bution is unknown. In the medullary substance, however, there are two
ganglia situated close to the central vein.

Nothing is known of lymphatics in the suprarenal capsules, and the exist-
ence of such vessels is doubtful.

Chemical Reactions of the Suprarenal Capsules. — Vulpian has described
(1856), in the medullary portion of the suprarenal capsules, a peculiar sub-
stance, 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 Cloez, he discovered hippuric and taurocholic
acid in the capsules of some of the herbivora. These bodies contain in
addition, leucine, hypoxanthine, taurine, fats and inorganic salts, the latter
chiefly phosphates and salts of potassium.

The suprarenal capsules are not essential to life. If care be taken to
avoid injury of the semilunar ganglia, they may be removed from animals
and the operation apparently has no remote effects. In Addison's disease, a
disorder attended with bronzing of the skin and serious and finally fatal dis-
order of nutrition, there usually is disorganization of the suprarenal capsules,
but this is not invariable. It is not established that disorganization of the
capsules stands in a causative relation to the discoloration of the skin or to
the constitutional disturbance. Investigations into these diseased conditions
have developed little -or nothing of importance concerning the physiology of
the suprarenal capsules.

THYROID GLAKD.

The thyroid gland is attached to the lower part of the larynx and follows
it in its 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 presents two lateral
lobes, each with a rounded, thickened base below, and a long, pointed extrem-
ity extending upward, the lobes being connected by an isthmus (see Fig. 141,
page 424). Each of these lobes is about two inches (50 mm.) in length,
three-quarters of an inch (19 mm.) in breadth, and about the same in thick-
ness at its thickest portion. The isthmus connects the lower portion of the
lateral lobes, covers the second and third tracheal rings, and is about half an
inch (12 mm.) wide and one-third of an inch (8'5 mm.) thick. From the
left side of the isthmus, and sometimes from the left lobe, is a portion pro-
jecting upward, called the pyramid. The weight of the thyroid gland,
according to Sappey, is three hundred and fifty to three hundred and eighty
grains (22 to 24 grammes). It is usually stated by anatomical writers that
it is relatively larger in the foetus and in early life than in the adult ; but
according to Sappey, 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 of the Thyroid Gland. — The thyroid gland is covered with a
thin but resisting coat of ordinary fibrous tissue, which is loosely connected

422 USES OF THE LIVER— DUCTLESS GLANDS.

with the surrounding parts. From the internal surface of this membrane,
are fibrous bands, or trabeculae, giving off, as they pass through the gland,
secondary trabeculae, and then subdividing until they become of microscopic
size. By this arrangement the gland is divided up into small, communicat-
ing cells. The trabeculae contain many small, elastic fibres. Throughout
the substance of the gland, lodged in the meshes of the trabeculag, are
rounded or ovoid, closed vesicles, measuring -^ to -^ of an inch (40 to
100 fji). These are formed of a structureless membrane and are lined by
a single layer of pale, granular, nucleated cells, -5^0- to ^Air °^ an incn
(8 to 12 //,) in diameter. The layer of cells sometimes lines the vesicle com-
pletely, sometimes it is incomplete, and sometimes it is wanting. The con-
tents of the vesicles are a clear, yellowish, slightly viscid, albuminoid fluid,
with a few granules, pale cells, and nuclei. The vesicles are arranged in the
form of lobules, and between them are the great veins.

Vessels and Nerves. — The blood-vessels of the thyroid gland are very
abundant, this organ being supplied by the superior and inferior thyroid
arteries and sometimes by a branch from the innominata. The arteries
break up into a close, capillary plexus, surrounding 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 pneumogastrics and from the cervical sympathetic gan-
glia. The lymphatics are abundant but are difficult to inject. The exact
distribution of the nerves and the origin of the lymphatics are not well un-
derstood.

What little is known with regard to the chemical constitution of the
thyroid gland is embodied in the statement that it contains leucine, xanthine,
lactic acid, succinic acid and some volatile fatty acids. The blood of the
thyroid veins has been analyzed, but the changes in its composition in pass-
ing through the gland are slight and indefinite. It has been asserted that
one of the uses of the thyroid gland is to regulate the blood- circulation in the
brain, but the observations in support of this view are not very satisfactory.

Myxmdema. — Important facts have lately been developed showing a con-
nection between the thyroid gland and a disease characterized by infiltration
of the connective tissues with a gelatinous substance containing mucine.
This disease has been described by Ord, under the name of myxcedema. It
is attended with marked impairment of the mental faculties, and a condition
like cretinism. This is usually associated with disease of the thyroid' gland.

Complete excision of the thyroid gland in the human subject has been
followed by the peculiar mental condition characteristic of cretinism. In
the lower animals the operation of complete extirpation is fatal. The ex-
periments of Horsley, upon dogs and monkeys, show great differences in the
results, depending upon age. In young animals- death usually occurs in a
few days, while old animals survive the operation four, five, or six months.

THYMUS GLAND. 423

As far as could be ascertained from these experiments upon the lower ani-
mals— dogs and monkeys — the conditions, including the mental phenomena,
resembled those observed in cases of myxoedema in the human subject, The
animals operated upon were found to be exceedingly sensitive to cold. If put
in a hot-air bath at a temperature of 105° Fahr. (40-5° C.) after the general
symptoms made their appearance, the animals could be kept alive for several
months. Horsley described the symptoms in monkeys, after three to seven
weeks, as " commencing hebetude and mucinoid degeneration of the connect-
ive tissues," and after five to eight weeks, " complete imbecility and atrophy
of all tissues,"especially muscles."

It is difficult to draw, from these observations, absolutely definite conclu-
sions with regard to the physiological relations of the thyroid gland. This
organ seems essential to life, and its removal profoundly affects the general
processes of nutrition. It influences the quantity of mucine in the body, but
precisely in what way, it is difficult to determine.

THYMUS GLAND.

In its anatomy the thymus resembles the ductless glands, but its office,
whatever this 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 uses of this organ, the existence of which is
confined to the first two or three years of life, it seems necessary only to give
a brief sketch of its structure.

The thymus appears at about the third month of foetal life and 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 situ-
ated partly in the thorax and partly in the neck. The thoracic portion is in
the anterior mediastinum, resting upon the pericardium, 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
(50-8 mm.) in length, an inch and a half (38 mm.) broad at its lower por-
tion, and about one-quarter of an inch (6'4 mm.) 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 a number of lobules held together by con-
nective 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. Portions of
the gland may be, as it were, unravelled, by loosening the interstitial fibrous
tissue. In this way it is found to be composed of little lobular masses at-
tached to a continuous cord. This arrangement is more distinct in the in-
ferior animals of large size than in man. The lobules are composed of
rounded vesicles, ten to fifteen in number, and T£j to ^ of an inch (20ft
to 600 //,) in diameter. The walls of these vesicles are thin, finely granular

USES OF THE LIVER— DUCTLESS GLANDS.

and very fragile. The vesicles contain a small quantity of an albuminoid
fluid, with cells and free nuclei. The cells are small and transparent, and

FIG. 141. — Thyroid and thymus glands (Sappey).

A. 1, right lobe of the thymus ; 2, left lobe ; 3, groove between the two lobes ; 4, lungs, the anterior bor-
ders raised to show the thymus : 5, terminal branch of the internal mammary vein ; 6, thyroid
gland ; 7, median inferior thyroid veins; 8, lateral inferior thyroid veins; 9, common carotid artery;
10, internal jugular vein ; 11, pneumogastric nerve.

B. Right lobe of the thymus with the investing membrane removed. 1, upper extremity of the lobe ; 2,

lower extremity ; 3, external border : 4, internal border.

C. Arrangement of the lobules of the same lobe, around the central cord. 1, upper extremity of the

lobe ; 2, lower extremity ; 3, 3, 3, lobules ; 4, 4, central cord.

the nuclei are spherical, relatively large, and contain one to three nucleoli.
The free nuclei are also rounded and contain several distinct nucleoli. These
vesicles are easily ruptured, when their contents exude in the form of an
opalescent fluid, which is 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 Astley Cooper, that the cord has a central canal connected with cavities
in the lobules ; while others believe that the cavities thus described are pro-
duced artificially by the processes employed in anatomical investigation.
The latter opinion is probably correct.

The blood-vessels of the thymus are abundant, but their caliber is small
and the gland is not very vascular. They are derived chiefly from the in-
ternal mammary artery, a few coming from the inferior thyroid, with occa-

PITUITARY BODY AND PINEAL GLAND. 425

sional branches from the superior diaphragmatic or the pericardia!. 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 abun-
dant but they do not follow the course of the arteries. The principal vein
emerges at about the centre of the gland posteriorly and 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 surround the principal thymic artery and penetrate the gland.
Their ultimate distribution is uncertain. The lymphatics are very abundant.

As regards its chemical constitution, it may be stated in general terms
that the thymus contains matters of about the same character as those found
in the other ductless glands.

Inasmuch as the thymus is peculiar to early life, one of the most impor-
tant points in its anatomical history relates to its mode of development.
This, however, does not present any great physiological interest 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 definite idea of their
uses.

The pituitary body is of an ovoid form, a reddish-gray color, weighs five
to ten grains (0-324 to 0-648 grammes), 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 fcetal life it has a cavity communicating with the third ventricle. This
little body has been studied by Grandry, in connection with the suprarenal
capsules. He regarded it as essentially composed of closed vesicles, with
fibres of connective tissue and blood-vessels. The vesicles are formed of a
transparent membrane, containing irregularly polygonal, nucleated cells and
free nuclei. The nuclei are distinct, with a well marked nucleolus. Capillary
vessels surround these vesicles without penetrating them. Grandry did not
observe either nerve-cells or fibres between the vesicles.

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 (8-5 mm.) 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 composed
of calcium phosphate, calcium carbonate, ammonio-magnesian phosphate
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
Grandry, it has been found to present a cortical substance, analogous in its
structure to the pituitary body, and a central portion composed of the ordi-
nary nervous elements found in the gray matter of the brain. Its structure

426 NUTRITION— ANIMAL HEAT AND FORCE.

is very like that of the medullary portion of the suprarenal capsules
(Grandry).

It is difficult to classify organs, of the uses of which physiologists are en-
tirely ignorant; but in structure, the little bodies just described certainly
resemble the ductless glands.

CHAPTER XIV.

NUTRITION— ANIMAL HEAT AND FORCE.

Nature of the forces involved in nutrition— Life, as represented in development and nutrition— Substances
which pass through the organism— Metabolism— Substances consumed in the organism — Conditions
which influence nutrition — Animal heat and force — Estimated quantity of heat produced by the body
— Limits of variation in the normal temperature in man — Variations with external temperature — Varia-
tions in different parts of the body— Variations at different periods of life etc.— Influence of exercise
etc., upon the heat of the body— Influence of the nervous system upon the production of animal heat
(heat-centres) — Mechanism of the production of animal heat — Equalization of the animal temperature —
Relations of heat to force.

NUTRITION proper, in the light in which it is proposed to consider it in
this chapter, is the process by which the physiological wear of the tissues and
fluids of the body is compensated by the appropriation of new matter. All
of the physiological operations that have thus far been described, including
the circulation of the blood, respiration, alimentation, digestion, absorption
and secretion, are to be regarded as means directed to a single end ; and the
great end, to which all of the functions enumerated 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 gen-
eral process, however, have been carefully studied, and certain important
positive results have been attained ; but there is really no more satisfactory
explanation of the nature of the causative force of nutrition to be found in
the doctrines of to-day than in the speculative theories of the past.

The blood contains all the matters that enter into the composition of the
tissues and secretions, either identical with them in form and composition,
as is the case in most of the inorganic matters, or in a condition .which
admits of their transformation into the characteristic constituents of the tis-
sues, as in the organic substances proper. These matters are supplied to the
tissues, in the required quantity, through the circulatory apparatus ; and oxy-
gen, which is immediately indispensable to all the operations of life, is intro-
duced by respiration. The great nutritive fluid,, being constantly drawn upon
by the tissues for materials for their regeneration, is kept at the proper stand-
ard by the introduction of new matter into the system in alimentation, its
elaborate preparation by digestion, and its appropriation by the fluids by
absorption. Many of these processes require the action of certain secretions

GENERAL PROCESSES OF NUTRITION. 427

The introduction of new matter, so essential to the continuance of the phe-
nomena of life, is demanded, on account of the change of the substance of
the tissues into what is called effete matter ; and this is discharged from the
animal organism, to be appropriated by vegetables and thus maintain the
equilibrium between the animal and the vegetable kingdoms.

It is a well established fact that nearly all of the tissues undergo disassimi-
lation, or conversion into effete matter, during their physiological wear in the
living organism, while 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 nutri-
tive property or force resolves itself into vitality. Life is always attended
with what are known as the phenomena of nutrition, and nutrition does not
exist except in living organisms. 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 — re-
garding life as the sum of the phenomena peculiar to living organisms — that
are not open to grave objections.

If life be regarded as a principle, it stands in the relation of a cause to
the vital phenomena; if it be regarded as the totality of these phenomena, it
is an effect.

In the study of the development of a fecundated ovum, life seems to be
a principle, giving the property of appropriating matter from without, until
the germ becomes changed, from a globule of microscopic size and compara-
tively 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. It may be said that an organism dies physiologically
because the vital principle, if such a principle be admitted, has a limited
term of existence ; but on the other hand, the fully developed living organ-
ism, called an animal, presents many distinct parts, each endowed with
an independent property called vital, that property recognized by Haller
in various tissues, under the name of irritability ; and it is the co-ordinated
association of these vitalities that constitutes the perfect being. These are
more or less distinct ; and a sudden and simultaneous arrest of the physio-
logical properties in all the tissues, in what is called death, is not often ob-
served. For example, the nerves may die before the muscles, or the muscles,
before the nerves. It is found, also, that physiological properties, apparently
lost or destroyed, may be made to return ; as in resuscitation after asphyxia
or in the restoration of muscular or nervous excitability by injection of blood.

The life of a fecundated ovum is the property which enables it to undergo
development when placed under favorable conditions ; and by the surround-
ing conditions, its development may be arrested, suspended or modified.
The life of a non-fecundated 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

428 NUTRITION— ANIMAL HEAT AND FORCE.

and performs certain denned offices, as far as its organization will permit.
This can also be destroyed, suspended or modified by surrounding conditions.

The life of a perfected anatomical element or tissue is the property which
enables it to regenerate itself and perform it offices, subject, also, to modifica-
tions from surrounding 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 physiological properties 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 with-
out consciousness or with organs paralyzed ; but certain functions, such as
respiration and circulation, are indispensable to the nutrition of all parts, the
properties of the different tissues are 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 phe-
nomena of which constitutes the science of physiology.

The general process of nutrition begins with the introduction of matter
from without, called food. It is carried on by the appropriation of this mat-
ter by the organism. It is attended with the production of excrementitious
matters and the development of certain phenomena that remain to be studied,
the most important of which is the production of heat.

The term metabolism, now used by many English writers, seems destined
to become generally adopted. It was employed by Schwann to designate a
kind of action by cells, resulting in a change in the character of substances
brought in contact with them. Modern writers use it as a translation of the
German word Stoffwechsel. The literal signification of the Greek word
H€Ta(3o\7} is change. As applied to nutritive changes, metabolism is equiva-
lent to assimilation ; and as applied to the changes which result in the pro-
duction of effete matters, it is equivalent to disassimilation, a term much
used by the French, and one which well expresses changes that are exactly
the opposite of assimilation. The signification of the term metabolism seems
likely to be extended so as to include the acts of cells in the production of
the constituents of the secretions, a process which it is difficult to express in
a single word.

The behavior of various substances in nutrition has already been treated
of, to some extent, in connection with alimentation ; but certain general rela-
tions of nutritive substances to assimilation remain to be considered. It is
convenient, as before, to divide these substances into the following classes :
1, Inorganic; 2, organic non-nitrogenized ; 3, organic nitrogenized. The
excrementitious products constitute a distinct class by themselves.

SUBSTANCES WHICH PASS THROUGH THE ORGANISM.

All of the inorganic matters taken in with the food pass out of the organ-
ism, generally in the form in which they enter, in the fseces, urine and per-
spiration ; but it must not be inferred from this fact that they are not useful
as constituent parts of the body. Some of these, such as water and the chlo-

SUBSTANCES WHICH PASS THROUGH THE ORGANISM. 429

rides, have important uses of a purely physical character. It is necessary, for
example, that the blood should contain a certain proportion of sodium chlo-
ride, this substance modifying and regulating the processes of absorption and
probably of assimilation. In addition, however, the chlorides exist as con-
stituent parts of every tissue and organ of the body, and they are so closely
united with the nitrogenized matters that they can hot be completely sepa-
rated without incineration. Those inorganic matters, the uses of which are
so important in their passage through the body, are found largely as con-
stituents of the fluids and are less abundant in the solids. They are con-
tained in large proportion, also, in the liquid excretions ; and any excess over
the quantity actually required by the system is thrown off in this way. Other
inorganic matters are specially important as constituent parts of the tissues,
and they are more abundant in the solids than in the fluids. Examples of
substances of this class are the calcium salts, particularly the phosphates.
These are also in a condition of intimate union with organic matters.

If certain simple chemical changes be excepted, such as the decomposi-
tion of the bicarbonates, the inorganic constituents of food do not necessarily
undergo any modification in digestion. They are generally introduced already
in combination with organic matters, and they accompany them in the
changes which they pass through in digestion, assimilation by the blood,
deposition in the tissues, and the final transformations that result in the
various excrementitious products ; so that the inorganic salts are found united
with the organic matter of the food as it enters the body, and what seem to
be the same substances, in connection with the organic excrementitious mat-
ters. Between these two conditions, however, are the various operations of
assimilation and disassimilation, or metabolism, from which inorganic matters
are never absent.

Inorganic Constituents of the Body. — The number of inorganic substances
now well established as existing in the human body is about twenty-one ; but
some are found in small quantities, are not always present and apparently
have no very important uses. 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.

Gases. — The gases (oxygen, hydrogen, nitrogen, carburetted hydrogen
and hydrogen monosulphide) 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 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 inanition,
when the blood absorbs a little from the inspired air. It exists in greatest
quantity in the intestinal canal. Carburetted hydrogen and hydrogen mono-
sulphide, with pure hydrogen, are found in minute quantities in the expired
air and exist in a gaseous state in the alimentary canal. From the offensive
nature of the contents of the large intestine, one would suspect the presence
of hydrogen monosulphide in considerable quantity ; but actual analysis has
shown that the gas contained in the stomach and in the small and large in-
29

430 NUTEITION— ANIMAL HEAT AND FOECE.

testines 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 hydrogen monosulphide. With the exception, then, of oxy-
gen and carbon dioxide, the latter being an excretion, the gases do not hold
an important place among the constituents of the organism. At all events,
their uses, whether they be important or not, are but little understood.

Water. — Water 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 semi-solids it does not exist as water, but it enters into their composition,
assuming the consistence by which the tissues are characterized.

The quantity of water which each organic substance contains is impor-
tant ; and it is provided that this quantity, though indefinite, shall not ex-
ceed or fall below certain limits. All organs and tissues must contain a tol-
erably definite quantity of water to give them proper consistence. The
effects of too great a proportion of water in the system are well known to
physicians. General muscular debility, loss of appetite, dropsies and various
other indications of imperfect nutrition are among the results of such a con-
dition ; while a deficiency of water is immediately made known by the sensa-
tion of thirst, which leads to its introduction from without.

The fact that water never exists in any of the fluids, semi-solids or solids,
without being combined with inorganic salts, especially sodium chloride, is
one reason why its proportion in various situations is nearly constant. The
presence of these salts influences, in the semi-solids at least, the quantity of
water entering into their composition, and consequently it regulates their
consistence. 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 on the addition of a strong solution
of salt, they lose water and become shrunken and corrugated. Their nat-
ural 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
a necessary part of all tissues and is especially important to the proper con-
stitution of organic nitrogenized substances ; that it enters into the constitu-
tion of these substances, not as pure water, but always in connection with
certain inorganic salts ; that its proportion is confined within certain lim-
its ; and that the quantity in which it exists, in organic nitrogenized sub-
stances 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 tempera-
ture (212° Fahr., or 100° 0.), from the different fluids and tissues of the
body, vary of course very considerably according to the consistence of the
parts. The following is a list of the quantities in the most important fluids
and solids (Robin and Verdeil) :

SUBSTANCES WHICH PASS THROUGH THE ORGANISM. 431

TABLE OF QUANTITIES OF WATER.

Parts per 1,000.

f In the enamel of the teeth 2

In epithelial desquamation 37

In teeth 100

In bones , 130

In tendons (Burdach) 500

In articular cartilages 550

In skin (Weinholt) 575

In liver (Frommherz and Gugert) 618

In muscles of man (Bibra) 725

In ligaments (Chevreul) 768

In the blood of man (Becquerel and Rodier) 780

In milk of the human female (Simon) 887

In chyle of man (Rees) 904

In bile 905

In urine 933

In human lymph (Tiedemann and Gmelin) 960

In human saliva (Mitscherlich) 983

In gastric juice 984

In perspiration 986

In tears 990

Uses of Water. — After what has been stated with regard to the condition
in which water exists in the body, there remains but little to. say concerning
its uses. As a constituent of organized tissues, it gives to cartilage its elas-
ticity, and to tendons their pliability and toughness ; it is necessary to the
power of resistance of the bones, and it is essential to the proper consistence
of all parts of the body. It also has other important uses, as a solvent.
Soluble articles of food are introduced in solution in water. The excremen-
titious products, which generally are soluble in water, are dissolved by it in
the blood, are carried to the organs of excretion, and are discharged in a
watery solution from the body.

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 ; but water is also formed in the
body by a direct union of oxygen and hydrogen. The evidences of forma-
tion of water in the body have already been given, in connection with the
question of water considered as a product of excretion, and will be again dis-
cussed in treating of the relations of water to the processes of calorification.
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 dis-
charge a large quantity of water ; and when the skin is active, the quantity
of water discharged by the kidneys is proportionally diminished.

Sodium Chloride. — Sodium chloride is next in importance, as an inor-
ganic constituent of the organism, 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 sol-
ids of the body, with the single exception of the enamel of the teeth. The
exact quantity in the entire body has never been ascertained ; nor, indeed,

432 NUTRITION— ANIMAL HEAT AND FORCE.

has any accurate estimate been made of the quantity contained in the vari-
ous 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 quanti-
ties found in some of the most important of the fluids and solids :

TABLE OF QUANTITIES OF CHLORIDES.

Parts per 1,000.
In blood, human (Lehmann) 4-210

In chyle (Lehmann) 5-310

In lymph (Nasse) 4-120

In milk, human (Lehmann) 0-870

In saliva, human (Lehmann) 1-530

- In perspiration, human (mean of three analyses, Piutti) 3-433

In urine (maximum) } ( 7'280

In urine (mean) ?• Valentin. < 4-610

In urine (minimum) ) \ 2-400

In faecal matters (Berzelius) 3-010

Uses of Sodium Chloride. — The uses of sodium chloride are undoubtedly
important, but are not yet fully understood. While it enters into the com-
position of the organized solids and semi-solids, as an important and essential
constituent, it seems to exercise its chief office in the liquids. It is the so-
dium chloride particularly which regulates the quantity of water entering
into the composition of the blood-corpuscles, thereby preserving their form
and consistence ; and it seems to perform an analogous office with regard to
the other semi-solids of the body. The following brief statement expresses
the general uses of this substance in the economy :

" Common salt is intermediate in certain general processes and does not
participate by its elements in the formation of organs " (Liebig).

In the first place, the fluids of the body are generally intermediate in their
uses, containing nutritious matters, which are destined to be appropriated by
the tissues and organs, and excrementitious matters, which are to be separated
from the body. In the blood and chyle, sodium chloride is found in greatest
abundance. In the nutrition of tissues and orgaiis, sodium chloride is not
deposited in any considerable quantity, but it seems to regulate the general
process, at least to a certain extent. In all civilized countries salt is used ex-
tensively as a condiment, 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 intermediate agent. There is nothing more
general among men and animals than this desire for common salt. In the
experiments made by Dailly on sheep and by Boussingault on bullocks, de-
priving these animals as nearly as possible of common salt for a number of
months, the general nutrition was affected without any marked change in
special tissues or organs.

It is significant that the quantity of sodium chloride existing in the blood
is not subject to variation, but that an excess introduced with the food is
thrown oif by the kidneys. The quantity in* the urine, then, bears a relation
to the quantity introduced with food, but the proportion in the blood is nearly

SUBSTANCES WHICH PASS THROUGH THE ORGANISM. 433

constant. This is another fact in favor of the view that the presence of a
definite quantity of common salt in the circulating fluid is essential to normal
nutrition.

Origin and Discharge of Sodium Chloride. — Sodium chloride is always
introduced with food, in the condition in which it is found in the body. It
is contained in the substance 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 esti-
mates are not entirely accurate, for the quantity thrown off in the perspira-
tion has never been directly ascertained. It exists in the blood in connection
with potassium phosphate, and a certain quantity is lost in a double decom-
position which takes place between these two salts, resulting in the forma-
tion'of potassium chloride and sodium phosphate. It also is supposed to
furnish sodium to all the salts which have a sodium base, and a certain quan-
tity, therefore, disappears in this way.

Existing, as it does, in all the solids and fluids of the body, sodium chlo-
ride is discharged in all the excretions, being thrown off in the urine, fasces,
perspiration and mucus.

Potassium Chloride. — Potassium chloride, although neither so important
as sodium chloride nor so generally distributed in the economy, seems to
have analogous uses. It is found in the muscles, liver, milk, chyle, blood,
mucus, saliva, bile, gastric juice, cephalo-rachidian fluid and urine. It is
very soluble, and in these situations it exists in solution in the fluids. Its
quantity in the fluids has not been accurately ascertained, as it has gen-
erally been estimated in connection with sodium chloride. In the muscles
it exists, however, in a larger proportion than common salt. In cpw's milk,
Berzelius found 1-7 part per 1,000. Pfaff and Schwartz found 1*35 per
1,000 in cow's milk and 0*3 per 1,000 in human milk. Of the uses of this
salt, little remains to be said after what has been stated with regard to sodi-
um chloride. The uses of these two salts are probably identical, although
sodium chloride, on account of its greater quantity in the fluids and its uni-
versal distribution, is by far the more important.

Origin and Discharge of Potassium Chloride. — 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 potassium phosphate and sodi-
um chloride, forming potassium chloride and sodium phosphate. That this
decomposition takes place in the body, is evident from the fact that the in-
gestion of a considerable quantity of common salt has been found, in the
sheep, to increase the quantity of potassium chloride in the urine, without
having any influence upon the quantity of sodium chloride. Potassium chlo-
ride is discharged from the body in the urine and in mucus.

Calcium Phosphate. — 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 constitution, it is hardly second in importance to water.

434: NUTRITION-ANIMAL HEAT AND FORCE.

It differs in its uses so essentially from the chlorides, 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 carbon dioxide, the bicarbonates and sodium chlo-
ride. In the solids and semi-solids, the condition of its existence is the same
as that of water ; i. e. it is incorporated with the organic substance character-
istic of the tissue, is one of its essential constituents, and can not be com-
pletely 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 with regard to water.

The following table gives the relative quantities of calcium phosphate in
various situations :

TABLE OF QUANTITIES OF CALCIUM PHOSPHATE.

Parts per 1,000.

In arterial blood. ( p ia}e and Marchal j 0'79

In venous blood. ( ( 0-76

In milk, human (Pfaff and Schwartz) 2-50

In saliva (Wright) 0-60

In urine, proportion to weight of ash (Fleitmann) .... 25-70

In excrements (Berzelius) 40-00

In bone (Lassaigne) 400*00

In the vertebrae of a rachitic patient (Bostock) 136-00

In teeth of an infant one day old . "j f 510-00

In teeth of the adult I I 610-00

In teeth, at eighty-one years f LassaiSne- 1 860-00

In the enamel of the teeth j [ 885-00

By this table it is seen that calcium phosphate exists in very small quan-
tity 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, for
example, being more than .twice that in bone. The variations in quantity
with age are very considerable. In the teeth of an infant one day old, Las-
saigne 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 constituents of the bones, teeth etc., in old age is very marked :
and in extreme old age they are deposited in considerable quantity in situa-
tions where there existed but a small proportion in adult life. The system
seems to gradually lose the property of appropriating to itself organic mat-
ters ; and although articles of food may be 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 dislocations are
almost unknown. Inasmuch as the efficiency of organs depends mainly upon
organic matters, the system actually wears out, and this progressive change
finally unfits certain parts for their various offices. An individual, if he
escape accidents and die of old age, passes away by a simple wearing out of
some essential part or parts of the organism.

Uses of Calcium Phosphate. — This substance, as before remarked, enters
largely into the constitution of the solids of the body. In the bones its office
is most apparent. Its existence, in suitable proportion, is necessary to the

SUBSTANCES WHICH PASS THROUGH THE ORGANISM. 435

mechanical uses 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 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 calcium phosphate in the bones
is made evident by cases of disease. In rachitis, where, as is seen by the
table, its quantity is very much diminished, the bones being unable to sus-
tain the weight of the body become deformed ; and finally, when calcium
phosphate is deposited, they retain their distorted shape.

Origin and Discharge of Calcium Phosphate. — The origin of calcium
phosphate is exclusively from the external world. It enters into the consti-
tution of food and is discharged in the faeces, urine and other matters thrown
off by the body. Its proportion in the urine is very variable.

Calcium Carbonate. — This salt exists in the bones^ teeth, cartilage, internal
ear, blood, sebaceous matter and sometimes in the urine. It exists as a nor-
mal constituent of the urine in some herbivora but not in the carnivora or
in man. It is most appropriately considered immediately after calcium phos-
phate, 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 phosphates, and it has analo-
gous uses. In the fluids it exists in small quantity and is held in solution
by virtue of free carbon dioxide and potassium chloride.

Calcium carbonate is the only example of an inorganic salt existing un-
combined and in a crystalline form in the body. In the internal ear it is
found in this form and has some office connected with audition.

TABLE OF QUANTITIES OF CALCIUM CARBONATE.

Parts per 1,000.

In bone, human (Berzelius) 113-00

" " " (Marchand) 102-00

" " " (Lassaigne) 76-00

In teeth of an infant one day old j ( 140-00

In teeth of an adult > Lassaigne. •< 100-00

In teeth of an old man, eighty-one years . ) ' 10*00

In urine of the horse (Boussingault) 10*82

Origin and Discharge of Calcium Carbonate. — This salt is introduced into
the body with food, held in solution in water by the carbon dioxide, which is
always present in small quantity. It is also formed in the body, particularly
in the herbivora, by a decomposition of the calcium tartrates, malates, citrates
and acetates contained in the food. These salts, meeting with carbon diox-
ide, are decomposed and calcium carbonate is formed. It is probable that
in the human subject some of it is changed into calcium phosphate and in
this form is discharged in the urine ; but it has not been definitely ascertained
when and how this change takes place.

Sodium Carbonate. — 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

436 NUTRITION— ANIMAL HEAT AND FORCE.

alkaline without being ammoniacal ; in the urine of the herbivora ; and in
the lymph, cephalo-rachidian fluid and bone. The analyses by different
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 quanti-
ties which have been found in some of the fluids and solids :

TABLE OF QUANTITIES OF SODIUM CAKBOSTATE.

Parts per 1,000.

In blood of the ox (Marcet) 1-62

In lymph (Nasse) 0-56

In cephalo-rachidian fluid (Lassaigne) 0-60

In compact tissue of the tibia in a male of 38 years (Valentin) 2'00

In spongy tissue of the same (Valentin) 0*70

Uses of Sodium Carbonate. — This substance has a tendency to maintain
the fluidity of the albuminoid constituents of the blood, and it assists in pre-
serving the form and consistence of the blood-corpuscles. Its office in nutri-
tion is rather accessory, like that of sodium chloride, than essential, like cal-
cium phosphate, in the constitution of certain structures.

Origin and Discharge of Sodium Carbonate. — This substance is not intro-
duced into the body as sodium carbonate, but it is formed, as is calcium
carbonate in part, by a decomposition of the malates, tartrates etc., which
exist in fruits. It is discharged occasionally in the urine of the human sub-
ject, and a great part of it is decomposed in the lungs, carbon dioxide being
set free, which latter is discharged in the expired air.

Potassium Carbonate. — This salt exists particularly in herbivorous ani-
mals. It is found in the human subject under a vegetable diet. Under the
heads of uses, origin and discharge, what has been said with regard to sodium
carbonate will apply to potassium carbonate.

Magnesium Carbonate and Sodium Bicarbonate. — It is most convenient
to take up these two salts in connection with the other carbonates, though
they are among the least important of the inorganic constituents of the
body. Traces of magnesium carbonate 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 indicated the presence of sodium bicarbonate in the blood.
In this form a certain quantity of carbon dioxide is carried to the lungs, to
be exhaled in the expired air.

Magnesium Phosphate, Sodium Phosphate (neutral) and Potassium
Phosphate. — These salts are found in all the fluids and solids of the body,
though not in a very large proportion as compared with calcium phosphate.
In their relations to organized structures, they are analogous to calcium
phosphate, 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 are in great part the
result of the decomposition by carbon dioxide of the malates, tartrates, oxa-

SUBSTANCES CONSUMED IN THE OEGANISM. 437

lates etc. With respect to their uses, it can only be said that with calcium phos-
phate they go to form the organized structures of which they are necessary
constituents. They are discharged from the body in the urine and faeces.

Sodium Sulphate, Potassium Sulphate and Calcium Sulphate. — Sodium
sulphate and potassium sulphate are identical in their situations and appar-
ently in their uses. 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 dis-
charged in the urine. Their chief office 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. Calcium sulphate 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 office is not
understood and is probably not very important.

Ammonium Chloride. — This substance has simply been indicated by
chemists as existing in the gastric juice of ruminants, the saliva, tears and
urine. It is discharged in the urine, in which it exists in the proportion of
0*41 part per 1,000 (Simon). Its origin and uses are unknown. Various
combinations of bases with organic acids taken as food, as l^he acetates, tar-
trates etc., found in fruits, undergo decomposition in the body and are trans-
formed into carbonates. In this form they behave precisely like the other
inorganic salts.

SUBSTANCES CONSUMED IN THE ORGANISM.

All of the assimilable organic matters taken as food are consumed in the
organism, and none are ever discharged from the body in health in the form
in which they entered. The matters thus consumed in nutrition have been
divided into nitrogenized and non-nitrogenized ; and although they both dis-
appear in the organism, they possess certain marked differences in their prop-
erties and probably, also, in their relations to nutrition.

Nitrogenized Constituents of the Body. — The organic nitrogenized con-
stituents of the body are composed of carbon, hydrogen, oxygen, nitrogen
and sulphur. The exact proportions of these elements are not definitely
fixed, and the nitrogenized matters may change in their general characters
without undergoing corresponding changes in their actual ultimate constitu-
tion, unless it be in the arrangement of their atoms. They are coagulable
and non-crystallizable. They possess certain properties in common with
each other, which have already been described more or less fully in connec-
tion with the physiological history of the blood, alimentation, the secreted
fluids etc. One of these properties is a tendency to decomposition by putre-
faction, under certain conditions of heat and moisture. They also undergo
certain changes under chemical manipulation, analogous to those already
described as effected by the prolonged action of the pancreatic juice. The
type of substances of this class is the albumin of white of egg, and as a
class, they are generally known as albuminoids. Artificial subdivisions of
these substances have been made into proteids and albuminoids, the latter

438 NUTRITION— ANIMAL HEAT AND FORCE.

name, in this subdivision, being restricted to certain albuminoids which
closely resemble proteids but possess some distinctive characters. Inasmuch
as proteine is an hypothetical compound and the so-called proteids do not
differ much from other nitrogenized substances, it seems better to designate
the entire class as albuminoids.

The so-called proteids are the albuminoid constituents of the blood,
lymph and chyle, and the characteristic albuminoid constituents of the vari-
ous tissues. These are sometimes called colloids. They pass through mem-
branes with difficulty, or are very slightly osmotic. In this regard they pre-
sent a striking contrast to the peptones, which are very osmotic, passing
easily through animal membranes. This distinction is important, and it has
already been fully described in connection with the physiology of digestion
and absorption.

Nitrogenized matters constitute an important class of alimentary sub-
stances, and the corresponding constituents of the body are all originally
derived from food. The condition of existence of these substances in the
body is always one of union with more or less of the class of inorganic mat-
ters. Nitrogenized matters are found in all of the tissues and liquids of the
body, except the bile and urine. They undergo changes in digestion before
they become a part of the blood, they are changed in the blood into the
nitrogenized constituents of this fluid and are again changed as they are de-
posited in the tissues in the process of nutrition. They are not discharged
from the body in health, but are destroyed or changed into excrementitious
matters, chiefly urea, and in this form are eliminated in the excretions. An
excess of these substances taken as food is not discharged in the faeces, nor
does it pass out, in the form in which it entered, in the urine ; but it under-
goes digestion, becomes absorbed by the blood, and increases the quantity of
nitrogenized excrementitious matters 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 /iot
actually needed in nutrition be changed into urea in the blood, in the so-
called luxus-consumption process, 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 nitrogen-
ized 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 ex-
crementitious matters.

The nutrition of the nitrogenized constituents of the tissues may be greatly
modified by the supply of new matter. For example, a diet composed of nitro-
genized matter in a readily assimilable form will undoubtedly affect favorably
the development of the corresponding tissues of the body ; and on the other
hand, a deficiency in the supply will produce a corresponding diminution in
power and development. The modifications in nutrition due to supply have,
however, certain well defined limits. As regards the muscular tissue, proper
exercise increases nutritive activity, the development and power of muscles

NON-NITROGENIZED CONSTITUENTS OF THE BODY. 439

and the capacity for muscular work and endurance. The nutritive activity
of other parts and organs is limited and is not sensibly affected by an excess
of nitrogenized food.

In addition to the albuminoids of the blood, lymph, chyle and secreted
fluids, and those which have been described as alimentary matters, the fol-
lowing have been found in various tissues and organs of the body.

Cystalline, a nitrogenized substance in the crystalline lens.

Myosine, a substance extracted from muscular tissue, of which it is the
chief nitrogenized constituent.

Keratine, found in the epidermis and its appendages.

Elastine, the nitrogenized constituent of the elastic tissues.

Osseine, in bones, and chondrine, in cartilage.

Gelatine, probably not a normal constituent of the body, but a substance
formed from the connective tissues by prolonged boiling in water.

Certain nitrogenized substances containing phosphorus, found in the
nervous tissues, which will be described in connection with the chemistry of
the nervous system.

The changes involved in nutrition, assimilation, or nutritive metabolism,
are apparently dependent upon properties belonging to the nitrogenized con-
stituents of the tissues. When the supply of new matter is equal to the de-
structive metabolism, the system is in what is called a condition of equilib-
rium, and the body neither gains nor loses in weight. In growth, the supply
exceeds the waste, and in the opposite condition, the waste exceeds the supply.

Certain liquids and tissues of the human body may be restored after
their destruction. The blood and its corpuscles undergo regeneration. Blood-
vessels, also, may be regenerated, being developed first as capillaries and
afterward as arteries and veins. The same is probably true of lymphatics.
The epidermis and its appendages and certain parts of the true skin may be
regenerated after destruction. Muscular substance, after certain kinds of
degeneration in disease, as in fevers, may be restored. Portions of nerves
may be regenerated after division or exsection. A divided tendon may become
reunited by connective tissue. Portions of cartilage or bone may be regen-
erated, if the perichondrium or the periosteum remain intact. When wounded
or lost parts are not absolutely restored, the divided tissue is reunited or the
lost tissue is supplied by what is called cicatricial connective tissue.

Non- Nitrogenized Constituents of the Body. — Under the head of alimen-
tation, the general properties of non-nitrogenized matters (starch, sugars
and fats) have been fully described. These are important constituents of
food, but in themselves they are incapable of supporting life. They are
introduced as food, but are destroyed in the organism and are never dis-
charged from the body in health in the form in which they entered.

The carbohydrates (starch and sugars) are all converted into glucose in di-
gestion. As glucose they are taken up by the blood and carried to the liver,
where they are in great part and probably entirely converted into glycogen.
The glycogen thus formed is stored up in the liver and is gradually transformed
into animal sugar, which passes into the blood slowly and gradually, and

NUTRITION— ANIMAL HEAT AND FORCE.

promptly disappears as sugar, usually in the passage of the blood through
the lungs. In addition to the glycogen formed from the carbohydrates of
food, the liver is capable of forming glycogen from other substances, as is
shown by the presence of glycogen in the liver of carnivorous animals. It is
probable that the glycogen thus produced is formed from albuminoid matters
and not from fats. The exact mechanism of the destruction of carbohydrates
in the organism has not been fully understood, although it is admitted that
these substances are important factors in the production of animal heat. The
presence of alcohol in very small quantity in the normal blood has been
demonstrated by Ford (1872). If this be admitted — and the accuracy of the
observations by Ford seems to have been absolute — it is reasonable to sup-
pose that the small quantity of sugar constantly discharged into the blood by
the liver is converted into alcohol, which is promptly oxidized, being con-
verted into carbon dioxide and water. The carbohydrates, in contributing to
calorification, are very important in saving destruction of the albuminoid
constituents of the body. In this process the carbohydrates and the fats act
together and in the same way ; and in this action they are capable of mutu-
ally replacing each other.

The fats taken as food are either consumed in the organism or are de-
posited 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. For a time, during absorption,
fat may exist in certain quantity in the blood ; but it soon disappears and is
either destroyed directly in the circulatory system or is deposited in the form
of adipose tissue to supply a certain quantity of this substance consumed.
That it may be destroyed directly, is proved by the consumption of fat in
instances where the quantity of adipose matter is insignificant ; and that the
adipose tissue of the organism may be consumed, is shown by its rapid dis-
appearance in starvation.

Formation and Deposition of Fat. — The question of the formation of fat
in the economy is one of great importance. Whatever the exact nature of
the changes accompanying 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 constituents 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 con-
stituents of the body are the first to be consumed, and they almost entirely
disappear before death. Sugar is never deposited in any part of the organ-
ism, and it is merely a temporary constituent of the blood. If the sugars
and fats have, in certain regards, similar relations to nutrition, and if, in addi-
tion to the mechanical uses of fat, it may be retained in the organism for use
under extraordinary conditions, it becomes important to ascertain the mech-
anism 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 ;

NON-NITROGENIZED CONSTITUENTS OF THE BODY. 441

and analogous observations have been made upon birds and mammals, by
Boussingault. Under certain conditions more fat exists in the bodies of ani-
mals than can be accounted for by the total quantity of fat taken as food
added to the fat existing at birth. In experiments with reference to the in-
fluence of different kinds of food upon the development of fat, it has been
ascertained that fat can 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 fatten-
ing is precisely that which joins to the proper proportion of albuminoid sub-
stances the greatest proportion of fatty matters " (Boussingault).

There can be no doubt with regard to the formation of fat in the organ-
ism from albuminoid matters. Where an excess of such matters is taken as
food, it is probable that the albuminoid substance is decomposed, and that a
part of it is either deposited as fat or is oxidized into carbon dioxide and
water, and a part is discharged from the body in the form of urea.

Theoretical considerations point to starch and sugar as the constituents
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 time of
grinding the cane, the laborers become excessively fat, from eating large
quantities of saccharine matter ; and although there are no exact scientific
observations upon this point, the fact is 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. Carbohydrates added in quantity to a
nitrogenized diet favor the formation of fat. The fat may be formed from
the carbohydrates either directly (Lawes and Gilbert) or indirectly. If
formed indirectly, it is probable that the carbohydrates are oxidized into car-
bon dioxide and water, and that this saves, to a certain extent, destruction of
albuminoids. The albuminoids are split up into fats, which are deposited
in the body, and into urea.

Fatty degeneration occurs in tissues during certain retrograde processes.
The muscular fibres of the uterus, during the involution of this organ after
parturition, become filled with fatty granulations. Long disuse of any part
will produce such changes in its power of appropriating nitrogenized matter
for its regeneration, that it soon becomes atrophied and altered. A portion of
the nitrogenized constituents of the tissue, under these conditions, is changed
into fatty matter. The fat is here inert, and it takes the place of the sub-
stance that gives to the part its characteristic properties. These changes are
observed in muscles and nerves that have been long disused or paralyzed.
If the change be not too extensive, the fat may be made to disappear and
the part will return to its normal constitution, under appropriate exercise ;
but frequently the alteration has proceeded so far as to be irremediable and
permanent.

It is difficult to explain the tendency to obesity observed in some indi-
viduals, which is very often hereditary. Such persons will become fat upon

442 NUTRITION— ANIMAL HEAT AND FORCE.

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 articles of
food, while the latter consume a greater proportion of nitrogenized matter.
It is not an uncommon remai^f 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. The formation of fat by any particular organ or
organs in the body has not been determined.

Condition under which Fat exists in the Organism. — It is said that fat,
combined with phosphorus, is united with nitrogenized matter in the sub-
stance of the nervous tissue ; but its condition here is not well understood.
A small quantity of fat is contained in the blood-corpuscles and is held in
solution in the bile ; but with these exceptions, fat always exists in the body
isolated and un combined with nitrogenized matter, in the form of granules
or globules and of adipose tissue. The three varieties of fat (stearine, palmi-
tine and oleine) are here combined in different proportions, which is the
cause of the differences in its consistence in different situations.

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, however, to be con-
founded with the so-called cellular or areolar tissue, and is simply associated
with it without being one of its essential parts; for the areolar tissue is
abundant in certain situations, as the eyelids and 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 me-
chanical uses. Its anatomical element is a rounded or ovoid vesicle, -g-J-g- to
g-J-g- of an inch (30 to 80 /x.) in diameter, composed of a delicate, structureless
membrane, ^-g-J-oD of an inch (1 /x) thick, enclosing fluid contents. The
membrane sometimes presents a small nucleus attached to its inner surface.
The contents of the vesicles are a minute quantity of an albuminoid fluid
moistening the internal surface of the membrane, and a mixture of oleine,
palmitine and stearine, nearly liquid at the temperature of the body but
becoming harder on cooling. Little rosettes of acicular crystals of palmitine
are frequently observed in the fat- vesicles at a low temperature. The quan-
tity of fat in a man of ordinary development equals about one-twentieth of
the weight of the body (Carpenter). The adipose vesicles are collected into
little lobules, -fa to £ of an inch (1 to 6 mm.) in diameter, which are sur:
rounded by a rather wide net- work of capillary blood-vessels. Close examina-
tion 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 elements of adipose tissue.

Conditions which influence Nutrition. — Physiologists know more con-
cerning the conditions that influence the general process of nutrition than
about the nature of the process itself. It will be seen, for example, in studying
the nervous system, that there are nerves which regulate, to a certain extent,

CONDITIONS WHICH INFLUENCE NUTRITION. 443

the nutritive forces. This does not imply that nutrition is effected through
the influence of the nerves, but it is the fact that certain nerves, by regulat-
ing the supply of blood, and perhaps by other influences, are capable of
modifying the nutrition of parts to a very considerable extent.

As regards the influence of exercise upon the development of parts, it has
been shown that this is not only desirable but indispensable ; and the proper
performance of the offices of nearly all parts involves the action of the nerv-
ous system. It is true that the separate parts of the organism and the organ-
ism as a whole have a limited existence ; but it is not true that the change
of nitrogenized substances into effete matters — 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 disassimila-
tion, but it also increases the activity of nutrition and favors development.
It is often said 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 nutri-
tion, assuming, of course, that the supply from without be sufficient. Other
things being equal, a man would live longer under a system of physiological
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. Notwithstanding all these facts', life
is self-limited. Organic substances are constantly undergoing transforma-
tion. In the living body, their metabolism is unceasing ; and after they are
removed from what are termed vital conditions, they change, first losing
excitability, and afterward decomposing into matters which, like the products
of their disassimilation, are destined to be appropriated by the vegetable
kingdom. Nutrition sufficient to supply the physiological decay of parts
can not continue indefinitely. The 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 any sufficient reason be given why,
with an adequate and appropriate supply of material, a man should not grow
indefinitely. When the being is fully developed, and during what is known
as adult life, 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 nitrogenized substance. There may be at this time, as an exception,
a considerable deposition of fat ; but the nitrogenized matter is always de-
ficient, and the proportion of inorganic matter combined with it is increased.

There can be little if any doubt that the properties which involve the
regeneration or nutrition of parts reside in the organic nitrogenized sub-
stance, the inorganic matter being passive, or having purely physical uses.
If, therefore, as age advances, the organic matter be gradually losing the
power of completely regenerating its substance, and if its proportion be pro-
gressively diminishing while the inorganic matter is increasing in quantity.

444 NUTRITION— ANIMAL HEAT AND FORCE.

a time will come when some of the organs necessary to life will be unable to
perform their office. When this occurs, there is death from old age, or physio-
logical dissolution. This may be a gradual failure of the general process of
nutrition or it may occur in some one organ or system that is essential to
life.

ANIMAL HEAT AND FORCE.

The processes of nutrition in animals are always attended with the devel-
opment and maintenance of a bodily temperature that is more or less inde-
pendent of external conditions. This is true in the lowest as well as the
highest animal organizations ; and analogous phenomena have been observed
in plants. In cold-blooded animals, nutrition may be suspended by a dimin-
ished 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 hibernation ; but in man and most
of the warm-blooded animals, the general temperature of the body can un-
dergo 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 keep-
ing up its temperature when exposed to cold, or of moderating it when
exposed to heat, death is the inevitable result.

Estimated Quantity of Heat produced by the Body. — In order to express
quantities of heat, it is necessary to fix upon some definite quantity to be
taken as a heat-unit. In what is to follow, a heat-unit is to be understood
as the heat required to raise the temperature of one pound of water 1° Fahr.
(pound-degree Fahr.).

It has been calculated that one heat-unit is equal to the force expended
in raising one pound 772 feet or 772 pounds one foot (Joule). The equiva-
lent of heat in force has been calculated by estimating the heat produced
by a certain weight falling through a certain distance, assuming the falling
force to be precisely equal to the force which has been used in raising the
weight; but physicists have not actually succeeded in so completely convert-
ing heat into force as to raise one pound 772 feet or 772 pounds one foot, by
the expenditure of one heat-unit.

The heat-unit and its equivalent in force are, of course, differently ex-
pressed according to the metric system. When heat-units or foot-pounds are
given in the text, the equivalents, according to the metric system, are given
in parantheses. These equivalents are as follows :

A heat-unit, according to the metric system, or the heat required to raise
the* temperature of one kilo, of water one degree C., will be designated as a
kilo.-degree C.

One pound-degree = 0-252 kilo.-degree C. One kilo.-degree C. = 3-96
(nearly 4) pound-degrees. A kilogrammetre represents the force required to
raise a weight of one kilogramme one metre. One foot-pound = 0-138 kilo-
grammetre. One kilogrammetre = 7'24 foot-pounds. One pound-degree =
772 foot-pounds. One pound-degree = 106-6 kilogrammetres. One kilo.-

QUANTITY OF HEAT PRODUCED BY THE BODY. 445

degree C. = 422-25 kilogrammetres. One kilo.-degree C. = 3,057 foot-
pounds.

Two methods have been employed in arriving at estimates of the actual
quantity of heat produced by the body in a definite time :

1. The direct method consists in placing an animal in a calorimeter and
measuring the heat produced, making all necessary corrections. This has
been repeatedly done, but the results obtained have been very variable and
not entirely satisfactory.

The observations of Senator (1872) seemed to fulfill the necessary experi-
mental conditions ; and as an average of five observations made on dogs at
rest and fasting, he found a production of about 4-21 heat-units per hour
per pound weight of the body (2-34 kilo.-degree C. per kilo.).

J. C. Draper (1872) estimated the heat-production in his own person by
immersing the body in water. In this observation, many errors must have
escaped correction ; but the results agreed remarkably with those obtained
by Senator. Deducting 1° Fahr. of heat lost by the body, as shown by a
reduction in the general temperature, and imparted to the water — a correc-
tion not made by Draper — about 4 heat-units were produced per hour per
pound weight of the body (2-22 kilo.-degrees C. per kilo.). According to
the estimate of Draper, a man weighing 140 pounds (63-5 kilos.) would pro-
duce 13,440 heat-units (3-383 kilo.-degrees C.) in twenty-four hours of repose.
This would be equal to 10,375,680 foot-pounds, or about 1,430,000 kilogram-
metres.

An important element of inaccuracy in all direct observations and one,
indeed, which it seems impossible to correct absolutely, is due to the great
variations in heat-production with digestion, conditions of muscular repose
or exercise, external temperature etc. Another source of error is the diffi-
culty in estimating the heat lost by the body and not actually produced dur-
ing the time of the observation. These possible inaccuracies are so impor-
tant and so evident, that the results of direct observations have not been
generally accepted by physiologists.

2. The indirect method consists in estimating the heat represented by
oxidation, calculated from the quantity of oxygen consumed in the various
processes which result in the production and discharge of carbon dioxide,
water, urea etc. These estimates have been compared with the calculated
heat- value of the food consumed, and the results very nearly correspond.

According to the estimates of Helmholtz, Ranke and others, by the in-
direct method, the heat-production is equal to about 2*5 heat-units per hour
per pound weight of the body (1'39 kilo.-degree C. per kilo.) In a man weigh-
ing 180-4 pounds (82 kilos.) the heat-production in twenty-four hours
(Helmholtz) was 10,818 heat-units (2,732 kilo.-degrees C.). According to
this estimate, a man weighing 140 pounds (63-5 kilos.) would produce 8,400
heat-units (2,118 kilo.-degrees C.) in twenty-four hours. This would be
equal to 6,484,800 foot pounds, or about 894,500 kilogrammetres.

Comparing the results of direct observations, showing a production of
about four heat-units per pound per hour (2*22 kilo.-degrees C. per kilo.),

30

446 NUTRITION— ANIMAL HEAT AND FORCE.

with those obtained by the indirect methods, 2'5 heat-units per pound per
hour (1-39 kilo.-degree 0. per kilo.), it is seen that the indirect estimates
give about 37£ per cent, less heat produced than is given by direct estimates.
It is on account of this great difference, that writers are at a loss to give
definite estimates of the actual quantity of heat produced by the body.

A study of this subject and of the details of observations both direct
and indirect has made it evident that the experimental difficulties to be
overcome and the unavoidable elements of inaccuracy are greater in the
direct than in the indirect method. In comparing the estimates of heat
actually produced with the heat value of food — which, of course, is the ulti-
mate source of heat and force in the body — the correspondence is much
closer if the indirect estimates be adopted. It therefore seems more in ac-
cordance with ascertained facts to adopt the indirect estimates, although this
can not be done without reserve. The heat produced, then, is probably
equal to about 2'5 heat-units (pound-degrees) per hour per pound weight of
the body (nearly 1-4 kilo.-degree 0. per kilo.) This is equal to about 8,400
heat-units, or about 2,120 kilo.-degrees C., in twenty-four hours ; which is
equal to about 6,500,000 foot-pounds, or about 900,000 kilogrammetres.

The normal variations in the production of heat are not absolutely and
definitely represented by variations in the actual temperature of the body
and by the consumption of oxygen. Muscular work may increase the pro-
duction of heat 60 per% cent. (Hirn) while it increases the consumption of
oxygen about 4^ times, a large part of the oxidation being expended in the
form of work. The production of heat is diminished in fasting animals
(dogs) by nearly 45 per cent. (Senator), after deprivation of food for two
days. In old age and in infancy, there is less heat produced than in adult
life. The production of heat is less in females than in males and is less dur-
ing the night than during the day. These points will be touched upon again
in connection with the normal variations in the temperature of the body.

Limits of Variation in the Normal Temperature in Man. — One of the
most common methods of taking the general temperature has been to intro-
duce a registering thermometer into the axilla, reading off the degrees after
the mercury has become absolutely stationary. N early all observations made
in this way agree with the results obtained by Gavarret, who estimated that
the temperature in the axilla, in a perfectly healthy adult man, in a temper-
ate climate, ranges between 97*7° and 99-5° Fahr. (36-5° and 37'5° C.). Davy,
from a large number of observations upon the temperature under the tongue,
fixed the standard, in a temperate climate, at 98° Fahr. (36-67° 0.) The
axilla and the tongue, however, being more or less exposed to external influ-
ences, do not exactly represent the general heat of the organism ; but these
are the situations, particularly the axilla, in which the temperature is most
frequently taken in pathological examinations. As a standard for compari-
son, it may be assumed that the most common temperature in these situa-
tions is 98° Fahr. (36'67° C.) subject to variations, within the limits of
health of about 0-5° Fahr. (0-27° C.) below and 1-5° (0-82° Fahr. C.) above.

Variations with External Temperature. — The general temperature of the

VARIATIONS IN THE HEAT OF THE BODY. 447

body varies, though within very restricted limits, with extreme changes in
climate. The results obtained by Davy, in a large number of observations in
temperate and hot climates, show an elevation in the tropics of 0-5° to 3° Fahr.
(0-27° to 1*65° C.). It is well known, also, that the human body, the surface
being properly protected, is capable of enduring for some minutes a heat
greater than that of boiling water. Under these conditions, the animal
temperature is raised but slightly, as compared with the intense heat of the
surrounding atmosphere. In the observations by Dobson, the temperature was
raised to 99-5° Fahr. (37-5° C.) in one instance, 101-5° Fahr. (38-6° C.) in
another, and 102° Fahr. (38-9° C.) in a third, when the body was exposed to
a heat of more than 212° Fahr. (100° C.). Delaroche and Berger, however,
found that the temperature in the mouth could be increased by 3° to 9°
Fahr. (1-65° to 5-05° C.) after sixteen minutes of exposure to intense heat.
This was for the external parts only ; and it is not probable that the tem-
perature of the internal organs ever undergoes such wide variations.

It is difficult to estimate the temperature in persons exposed to intense
cold, as in Arctic explorations, because 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, Currie
caused the temperature in a man to fall 15° Fahr. (8-25° C.) by immersion
in a cold bath ; but he could not bring it below 83° Fahr. (28-33° C.) This
extreme depression, however, lasted only two or three minutes, and the tem-
perature 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 more than two degrees Fahr. (1-1° C.),
the body may be exposed for a time to excessive heat or cold, and the extreme
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° Fahr. (28-33° and 41-67° C.).

Variations in Different Parts of the Body. — The blood becomes slightly
lowered in its temperature in passing through the general capillary circula-
tion, but the difference is ordinarily not more than a fraction of a degree.
This fact is not opposed to the proposition that animal heat is produced in
greatest part in the general capillary system, as one of the results of nutri-
tive action ; for the blood circulates with such rapidity that the heat ac-
quired 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.

Bernard ascertained that the blood is usually 0-36° to 1-8° Fahr. (O2° to
1° C.) warmer in the hepatic veins than in the aorta. The temperature in
the hepatic veins is 0-18° to 1-44° Fahr. (0-1° to 0-8° C.) higher than in the
portal veins. 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

448 NUTRITION— ANIMAL HEAT AND FORCE.

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 2-5° to 3-3° Fahr. (1-37° to 1-8° C.) cooler than the muscles. As regards
the temperature of the blood in the two sides of the heart, experiments upon
the lower animals have been somewhat contradictory ; but there is no positive
evidence of any considerable change in the temperature of the blood in pass-
ing through the lungs in the human subject. In the lower 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 animals
with a slight covering of hair, the blood generally is cooler in the right cavi-
ties ; but in animals with a thick covering, that probably lose considerable
heat by the pulmonary surface, the blood is cooler in the left side of the
heart.

Variations at Different Periods of Life. — The most important variations
in the temperature of the body at different periods of life are observed in in-
fants just after birth. The body of the infant and of young mammalia
removed from the mother presents a diminution in temperature of 1° to
4° Fahr. (0-55° to 2-2° C.). 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 standard in the adult, and the variations produced by external
conditions are not so great.

W. F. Edwards 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 re-
moved from the body 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 illustrated in instances 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 varia-
tion in the normal temperature ; but in old age, while the actual temperature
of the body is not notably reduced, the power of resisting refrigerating in-
fluences is diminished very considerably. There are no 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.

Variations in the Heat of the Body at different Times of the Day etc. —
Although the limits of variation in the animal temperature are not very wide,
certain fluctuations are observed, depending upon muscular repose o,r activity,
digestion, sleep etc. It has been ascertained that there are two well marked
periods in the day when the heat is at its maximum. These are at eleven
A. M. and four p. M. ; and while all observations agree upon this point, the
observations of Lichtenfels and Frohlich have shown that these periods are

VARIATIONS IN THE HEAT OF THE BODY. 449

well marked, even when no food is taken. Barensprung and Ladame have
observed that the fall in temperature during the night takes place sleeping
or waking ; and that when sleep is taken during the day, it does not dis-
turb the period of the maximum, which occurs at about four P. M. Accord-
ing 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 between 1° and 2-16° Fahr. (0-55° and 1-19° C.). The minimum
is always during the night.

The influence of defective nutrition or of inanition upon the heat of the
body is very marked. In pigeons the extreme variation in temperature during
the day, under normal conditions, was found by Ohossat to be 1*3° Fahr.
(0-7° C.). During the progress of inanition this variation was increased to
5-9° Fahr. (3-25° C.). with a slight diminution in the absolute temperature,
and the periods of minimum temperature were unusually prolonged. Imme-
diately preceding death from starvation, the diminution in temperature
became very rapid, the rate being 7° to 11° Fahr. (3'85° to 6° C.) per hour.
Death usually occurred when the diminution had amounted to about 30°
Fahr. (16-5° C.).

When the surrounding conditions call for the development of an unusual
quantity 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 (Davy). Nevertheless, the conditions of external temperature
have a remarkable influence upon the diet. It is well known that in the
heat of summer, the quantity of meats and fat taken is relatively small,
and of the succulent, fresh vegetables and fruits, large, as compared with the
diet in the winter ; but although the proportion of carbohydrates in many
of the fresh vegetables used during a short season of the year is not great,
these articles are also deficient in nitrogenized matters. During the winter
the ordinary diet, composed of meat, fat, bread, potatoes etc., contains a
large proportion of nitrogenized substances as well as a considerable propor-
tion of carbohydrates ; and in the summer the proportion of both of these
varieties of food is reduced, the more succulent articles taking their place.
This is farther illustrated by a comparison of the diet in the torrid or tem-
perate and in the frigid zones. It is stated that the daily ration of the Es-
quimaux is twelve to fifteen pounds (5-433 to 6-804 kilos.)' of meat, about
one-third of which is fat. Hayes noted that with a temperature of — 60°
to — 70°, Fahr. (about — 51° to — 57° C.), there was a continual craving for
a strong, animal diet, particularly fatty substances.

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 excessive cold. The universal testimony of scientific

450 NUTRITION— ANIMAL HEAT AND FORCE.

Arctic explorers is that the use of alcohol does not enable men to endure a
very low temperature for any considerable length of time.

As a rule, when the respiratory activity is physiologically increased — as it
is by exercise, bodily or mental, ingestion of food or diminished external
temperature — the generation of heat in the body is correspondingly raised ;
and on the other hand, it is diminished by conditions which physiologically
decrease the absorption of oxygen and the exhalation of carbon dioxide. The
relations of animal heat to the general process of nutrition 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 pro-
duction of heat. The reverse of this proposition is equally true.

Notwithstanding the fact that there is a certain correspondence between
the activity of the respiratory processes and the production of heat, this is
far from being absolute. It has been shown by Senator that digestion in-
creases heat-production rather more than it increases the exhalation of carbon
dioxide. Muscular exertion has been found to increase the quantity of oxy-
gen consumed in very much greater proportion than it increased the heat-
production (Him). Even adding to the heat produced, the work, reduced to
heat-units, the heat-production was about doubled, while the quantity of
oxygen consumed was increased about four and a half times.

Influence of Exercise etc., upon the Heat of the Body. — The most com-
plete repose of the muscular system is observed during sleep, when hardly
any of the muscles are brought into action, except those concerned in tran-
quil respiration. There is always a notable diminution in the general tem-
perature at this time. In the variations in the heat of the body, the mini-
mum is always during the night ; and 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 means of resisting 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 irre-
sistible, if yielded to, is followed by a very rapid loss of heat and almost cer-
tain death. Muscular exercise increases the production of heat; but the
variations in the actual temperature of the body in man, although distinct,
are seldom very considerable, for the reason that muscular exertion is gener-
ally attended with increased action of the skin, which keeps the heat of the
body within restricted limits. In very violent muscular exertion, as in fast
running, the increased production of heat may be so rapid that it can not
be entirely compensated by evaporation from the skin, and the temperature
may rise to 104° Fahr. (40° C.). In about an hour and a half the tempera-
ture falls to the normal standard (Billroth, quoted by Landois).

The elevation in temperature that attends muscular action is produced
directly in the substance of the muscle (Becquerel and Breschet). Intro-
ducing a thermo-electric needle into the biceps of a man who used the arm
in sawing wood for five minutes, these physiologists noted an elevation of
temperature of nearly two degrees Fahr. (1° C.). The production of heat

VAKIATIONS IN THE HEAT OF THE BODY. 451

in the muscular tissue has been observed in experiments with portions of
muscle from the frog. Not only was there an absorption of oxygen and
exhalation of carbon dioxide after the muscle had been removed from the
body of the animal, but an elevation in temperature of about one degree
Fahr. (0-55° C.) was noted following contractions artificially excited (Mat-
teucci). Observations upon the influence of mental exertion on the tempera-
ture of the body have not been so many, but they are, apparently, no less
exact in their results. Davy observed a slight but constant elevation during
" excited and sustained attention." Lombard noted an elevation of tempera-
ture in the head during mental exertion of various kinds, but it was slight,
the highest rise not exceeding 0-05° Fahr. (0-027° C.). According to Bur-
dach, the temperature of the body 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 phe-
nomena of nutrition, it must be greatly influenced by conditions of the circu-
lation. It has been a question, indeed, whether the modifications in tem-
perature, produced by operating upon the vaso-motor nerves, be not due
entirely to changes in the supply of blood. It is certain that whatever deter-
mines an increased supply of blood to any part raises the temperature ; and
whenever the quantity of blood in any organ or part is considerably dimin-
ished, the temperature is reduced. This fact is constantly illustrated in
operations 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 ves-
sels become enlarged sufficiently to supply the quantity of blood necessary
for healthy nutrition.

Influence of the Nervous System upon the Production of Animal Heat
(Heat- Centres). — The local influences of the vaso-motor nerves upon calori-
fication operate mainly if not entirely through changes in the nutrition of
parts, produced by variations in blood-supply. Theselnfluences will be fully
considered in connection with the physiology of the nervous system.

The general temperature of the body may be modified through the nerv-
ous system by reflex action, and this implies the existence of nerve-centres, or
of a nerve-centre, capable of influencing the general process of calorification.
Experiments have been made, chiefly on parts of the encephalon, with the
view of determining the existence and location of heat-centres. In a recent
publication by Ott (1887), four heat-centres are recognized, irritation of
which by puncture increases the temperature of the body in rabbits by several
degrees (4° to 6° Fahr., or 2'2° to 3-3° C.). These four centres are as fol-
lows: 1, in front of and beneath the corpus striatum (Ott); 2, the median
portion of the corpora striata and the subjacent parts (Aronsohn and Sachs) ;
3, between the corpus striatum and the optic thalamus (Ott) ; 4, the anterior
inner end of the optic thalamus (Ott). Puncture of these parts is followed
by rise in temperature, which continues for a variable time, two to four days.
A similar centre has been described as existing in the dog, in the cortex of

452 NUTRITION— ANIMAL HEAT AND FORCE.

the anterior portion of the upper surface of the brain, near the median line
(Eulenberg and Landois). The conductors connected with these centres
decussate and pass through the medulla oblongata and the spinal cord. The
question arises as to whether the effects of puncture or stimulation of these
parts be exciting or inhibitory ; but observations regarding the mechanism
of their action have not been sufficiently definite to warrant any positive con-
clusions on this point.

MECHANISM OF THE PRODUCTION OF ANIMAL HEAT.

The definite ideas of physiologists concerning the mechanism of the pro-
duction of heat by animals date from the researches of Lavoisier (1777 to
1790). As a general result of these observations, Lavoisier concluded that
animal heat was produced by an internal combustion resulting in carbon
dioxide and water. Even now there is little to be said beyond this, as regards
the general mechanism of animal calorification, although modern investiga-
tions have brought to light many important details in the heat-producing
processes.

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 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 respiratory surfaces. Variations in the activity of calori-
fication are not to be measured by corresponding changes in the tempera-
ture of the body, but are to be estimated by calculating the quantity 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.

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 Becquerel and Breschet,
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 observed that
the blood becomes notably warmer in passing through the abdominal viscera
(Bernard). 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 experiment, not only is there no
particular part or organ in the body endowed with the special office of calori-
fication, but every part in which the nutritive forces are in operation pro-
duces a certain quantity of heat ; and this is probably true of the blood-cor-
puscles 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 illus-

MECHANISM OF THE PRODUCTION OF HEAT. 453

trated in the effects of operations upon the vaso-motor nerves and in the phe-
nomena of inflammation.

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 elimina-
tion of carbon dioxide ; and consequently, respiration may be regarded 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 tempera-
ture. During the first periods of intrauterine 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. Dur-
ing adult life, animal heat and the nutritive force are co-existent. It now
becomes an important question to determine whether there be any class of
nutritive matters specially concerned in calorification or any nutritive acts-
exclusively or specially directed to the maintenance of the normal tempera-
ture of the body.

It is evident that in normal nutrition by food, the heat of the body must
be maintained by changes which take place, either directly in the blood or
indirectly in the tissues, in alimentary matters, and that these changes involve
oxidation to a very considerable extent. Under ordinary conditions of nutri-
tion, 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 main-
tained, the work must be accomplished at the expense of the substance of
the body itself, and the individual loses weight. In order to maintain the
equilibrium of the body, therefore, food should be taken in quantity sufficient
to supply, by its changes in oxidation etc., the heat and force required. In
this condition of equilibrium, the body neither gains nor loses weight. To-
furnish a positive scientific basis for calculations with reference to these
points, physiologists have burned various articles of food in oxygen, and
have estimated their heat-value in heat-units.

In 1866, Frankland 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 ani-
mal 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 quantity 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 Frankland arrived at a determination of the heat- value of
articles of food oxidized in the body.

The following selections from Frankland's table will give an idea of the
heat- value of different articles of food oxidized in the body. In this table
the heat-units are calculated as pound-degrees.

454

NUTRITION— ANIMAL HEAT AND FORCE.

HEAT-VALUE OF TEN GRAINS OF THE MATERIAL OXIDIZED INTO CARBON
DIOXIDE, WATER AND UREA IN THE ANIMAL BODY (FRANKLAND).

Articles of food. Heat-units.

Articles of food. Heat-units.

Butter 18-68

Beef -fat (dry) 23-33

Lump-sugar 8*61

Grape-sugar 8-42

Wheat-flour 9-87

Bread-crumb 5-52

Arrowroot 10-06

Ground rice 9-52

Potatoes 2-56

Cabbage 1-Q8

Milk 1-64

Egg (boiled) 5-86

Cheese 11-30

Lean beef 3-66

Ham (boiled) 4-30

Mackerel 4-14

In the following, selected from the table quoted by Chapman, the heat-
units are calculated as kilo. -degrees C.

HEAT-VALUE OF ONE GRAMME OF THE MATERIAL OXIDIZED INTO CARBON
DIOXIDE, WATER AND UREA IN THE ANIMAL BODY (FRANKLAND).

Articles of food. Heat-units.

Potatoes . , . 0-990

Articles of food. Heat-units.

Butter 7-264

Beef-fat (dry) 9-069

Lump-sugar 3-348

Grape-sugar 3-227

Wheat-flour 3-840

Bread-crumb 1-450

Arrowroot 3-912

Ground rice . . 3*760

Cabbage 0-420

Milk

0-620

Egg (boiled) 2-280

Cheese 4-360

Lean beef 1-420

Ham (boiled) 1-680

Mackerel . . . 1-610

The heat- value of one gramme of alcohol — taken from a table compiled
by Landois — is equal to 8-958 heat-units (kilo.-degrees C.), or the heat- value
of 10 grains of alcohol is equal to 23 heat-units (pound-degrees Fahr.).

As regards the processes of combustion which take place in the living
organism, the oxidation of the constituents of food produces carbon dioxide
and water, but it is probable that the quantity of heat produced bears a defi-
nite relation to the total consumption of oxygen, the heat, as far as this is
concerned, being the same whether the oxygen unite with carbon or with
hydrogen (Pfliiger). This relation between the quantity of oxygen consumed
and the production of heat seems to be disturbed by muscular exercise ; but
it has thus far been found impossible to estimate accurately the quantity of
heat represented by the force expended in muscular work, circulation, respi-
ration etc.

The heat-producing processes undoubtedly are represented mainly by the
exhalation of carbon dioxide and water, and to a less degree by the discharge
of urea, the quantity of heat produced by other chemical processes being
comparatively small. It is also true that the carbohydrates and fats are
more important factors in calorification than the albuminoids ; but it seems
beyond question that there must be heat evolved in the body by oxidation of
nitrogenized matters. When the daily quantity of food is largely increased
for the purpose of generating the immense quantity of heat required in ex-
cessively cold climates, the nitrogenized matters are taken in greater quan-

MECHANISM OF THE PRODUCTION OF HEAT. 455

tity, 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 nitrogenized
matters bear a certain share in the production of animal heat. The carbo-
hydrates and fats are not concerned in the building up of tissues and organs,
except as the fats are deposited in the form of adipose tissue. Their addition
to the food saves the nitrogenized tissues, which latter must be used in heat-
production in starvation and in a restricted diet deficient in non-nitrogenized
matters. If the non-nitrogenized constituents of food do not form tissue,
are not discharged from the body, and are consumed in some of the processes
of nutrition, it would seem that their change must involve the production of
carbon dioxide and water and the evolution of heat.

Although it may be assumed that the non-nitrogenized constituents 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 a nitrogen-
ized diet ; and it is not possible to connect calorification exclusively with the
consumption of any single class of alimentary matters or with any single
one of the acts of nutrition.

The exact mechanism of the oxidation-processes in the body is not under-
stood. All physiologists, however, are agreed that the quantity of heat pro-
duced by oxidation is the same, whether the combustion be rapid or slow.
The fact that fats are never discharged, but are either consumed entirely or
are deposited in the body as fat, leaves their oxidation and discharge as oxi-
dation-products the only alternative. The oxidation of albuminoids has
already been considered. As regards the carbohydrates, if it can be shown
that alcohol normally exists in the blood, even in very small quantity, the
idea that these matters are slowly passed from the liver as sugar, into the
general circulation, and are then converted into alcohol which is promptly
oxidized, is worthy of serious consideration. Such a theory would explain
the destination of the carbohydrates and their relations to calorification.
There can be no doubt that in certain cases of fever, alcohol administered in
large quantity may be oxidized and " feed " the fever, thus saving consump-
tion of tissue.

In a series of observations made in 1879 (Flint), it seemed impossible to
account for the heat actually produced in the body and expended as force in
muscular work etc., by the heat- value of food and of tissue consumed. The
estimates of heat-production, made by the direct method, were then adopted;
but even the indirect estimates, which were much less, presented difficulty,
though in a less degree. In these observations, it was shown that water was
actually produced in the body in quantity over and above that contained in
food and drink, during severe and prolonged muscular exertion. It was
also shown that water was produced in considerable quantity during twenty-
four hours of abstinence from food. It has been shown by Pettenkofer and
Voit that " the elimination of water is very much increased by work, and
the increase continues during the ensuing hours of sleep." As regards the

456 NUTRITION— ANIMAL HEAT AND FORCE.

oxidation of hydrogen in this formation of water, it is probable that the
hydrogen of the tissues is used and that the matter thus consumed is sup-
plied again to the tissues in order to maintain the physiological status of the
organism. Adding the heat- value of the water thus produced to the heat-
value of food, there is little difficulty in accounting for the heat and force
actually produced and expended.

The demonstration that water is actually formed within the organism,
under certain conditions, not only completes the oxidation-theory of the pro-
duction of animal heat, but it affords an explanation of certain physiological
phenomena that have been heretofore obscure. It is well known, for exam-
ple, 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 con-
taining a relatively small proportion of fat and liquids, and regular muscular
exercise attended with profuse sweating. Muscular work increases the elimi-
nation of water, while it also exaggerates for the time the calorific processes.
Muscular exercise undoubtedly favors the consumption of the non-nitrogenized
parts of the body, and a diminution of the supply of fats, carbohydrates and
water in the food prevents, to a certain extent, the new formation of fat. In
excessive muscular exertion, the production of water is increased 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 in-
creased, 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.

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 sur-
rounding atmosphere is very cold, it becomes desirable 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 moderates the loss of heat from the surface. When the body
is not exposed to currents of air, garments are useful chiefly as non-conduct-
ors, imprisoning many layers of air, which are warmed by contact with the
person. It is also important to protect the body from the wind, which greatly
increases 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. This has already been considered in treating of
the action of the skin, and facts were noted showing that men can work
when exposed to a heat much higher than that of the body itself. The
quantity of vapor that is lost under these conditions is sometimes very large

RELATIONS OF HEAT TO FORCE. 457

Tillet recorded an instance of a young girl who remained in an oven for ten
minutes without inconvenience, at a temperature of 324-5° Fahr. (162-5° C.).
Blagden, in his noted experiments in a heated room, made in connection with
Banks, Solander, Fordyce, and others, found in one series of observations, that
a temperature of 211° Fahr. (99-5° 0.) could be easily borne; and at another
time the heat was raised to 260° Fahr. (126-5° C.). Under these extraordi-
nary external conditions, the body is protected from the radiated heat by
olothing, the air is perfectly dry, and the animal temperature is kept down
by increased 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, with inflammation etc., are liable to occur. The
•explanation of this 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 ani-
mal temperature comes from causes entirely external. It is a practical ob-
servation that no ill effects are produced, under these circumstances, by sud-
denly 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 sup-
pression of the compensative action of the skin is liable to produce disturb-
ances in nutrition, often resulting in inflammations.

RELATIONS OF HEAT TO FORCE.

Since the development of the theory of the conservation of forces, which
had its origin in an essay published by J. R. Mayer, in 1842, physiologists
have applied -the laws of correlation and conservation of forces to operations
involving the production of heat and the development and expenditure of
force in animals. This theory, if applicable to what weive formerly called
vital operations, certainly affords, in its definite quantities of heat and force as
•expressed in heat-units and foot-pounds, a basis for calculating the absolute
value of material changes in the body. Without discussing the purely physi-
cal questions involved, the laws of correlation and conservation of forces, as
they are applicable to human physiology, may be briefly stated as follows :

Potential energy is something either residing in or imparted to matter,
which is capable of being converted directly or indirectly into heat. The
.animal body, for example, is a store-house of potential energy. Its tissues
may be made to unite with oxygen and heat is produced. Any body may
have potential energy imparted to it. If a weight be raised to a certain
height, when the force which has accomplished this work is exhausted, the
potential energy imparted to the weight causes it to fall, and in this fall, heat

458 NUTRITION— ANIMAL HEAT AND FORCE.

is produced. The weight may be supported at the height to which it has
been raised, for an indefinite time ; but it still possesses the potential energy
which has been imparted to it, and when the support is removed, this poten-
tial energy is converted into force which may be converted into heat. Poten-
tial energy may be converted directly into heat, as when a body is oxidized.
It is converted indirectly into heat, when movement, falling or other force is
produced, for all force may be converted into heat. This conversion into
heat, directly or indirectly, affords a convenient measure of potential energy.
Using the example of the change of potential energy into heat by oxida-
tion, the energy stored up in matter is measured by estimating the heat
produced by oxidation, as so many heat-units. Using the example of falling
force imparted to a weight, the potential energy imparted to the body is esti-
mated by calculating the heat produced by the body falling.

If the entire body of an animal were burned in a calorimeter, the heat
produced would be an exact measure of the potential energy of the tissues,
converted into heat by oxidation. If one can imagine an animal perfectly
quiescent, neither losing nor gaining weight, nourished by food, expending
no force in circulation and respiration, but supplied with oxygen, the poten-
tial energy of the food could be measured by the heat produced. In animal
organisms, heat is produced mainly by oxidation, although other chemical
processes contribute to the production of heat, to some extent. The body
contains the potential energy stored up in its tissues. The oxygen taken in
by respiration changes a certain part of this potential energy into heat. If
food be not supplied in adequate quantity, the body loses weight by this
change of tissue into certain matters, such as carbon dioxide, water and urea,
which are discharged. Food supplies the waste of tissue and is the ultimate
source of the potential energy of the body. If food be supplied in excess,
that which is not in some form discharged from the body remains and adds
to the total potential energy stored up in the organism.

Kinetic energy is mechanical force. It is the force of a falling body, or
as regards animal mechanics, it is muscular force used in respiration, circu-
lation or any kind of muscular work. In physics, kinetic energy, or force,
and heat are regarded as mutually convertible. The reasoning by which this
law was formulate'd is the following :

The force used in raising a weight to a certain height, which is imparted
to the weight as potential energy, is precisely equal to the force developed by
this body as it falls. If this force could be transmitted to another body of
equal weight, without any expenditure of energy in friction, it would raise
the second weight to an equal height. The arbitrary unit of this force is a
foot-pound or a kilogrammetre, terms which have already been defined. The
falling of a body of a certain weight through a definite distance produces a
definite quantity of heat that itself is capable of producing force ; and it is
assumed that the heat produced by a falling body, if absolutely and entirely
converted into force, would raise that body to the height from which it had
fallen, or would exactly equal the falling force. A heat-unit is therefore said
to be equal to a definite number of foot-pounds or kilogrammetres. Cal-

RELATIONS OF HEAT TO FORCE. 459

culations have been made showing the conversion of foot-pounds or kiio-
grammetres into heat-units, but mechanical difficulties have thus far pre-
vented the actual conversion of heat-units into their equivalents in foot-pounds
or kilogrammetres. As a matter of reasoning, however, it is assumed that if
a certain number of foot-pounds or kilogrammetres be equal to a certain
number of heat-units, the reverse of the equation is true ; but in the applica-
tion of this law to animal physiology, it is always by a conversion of heat-
units into foot-pounds or kilogrammetres. The experiments on which the
law rests have been made by converting foot-pounds or kilogrammetres into
heat-units.

In work by machinery a very large proportion of the force-value of fuel
is dissipated in the form of heat. This is well illustrated by Landois. If a
steam-engine burning a certain quantity of coal, but doing no work, be
placed in a calorimeter, the heat produced can be measured. If, now, the
engine be made to do a certain work, as in raising a weight, the heat, as
measured by the calorimeter, will be less and the work done is found to be
very nearly proportional to the decrease in the measured heat (Him). It is
estimated by Landois, that of the heat produced by the body, one-fifth may
be used as work. In the best steam-engine, it is possible to use only one-
eighth as work, seven-eighths being dissipated as heat.

Many elaborate and careful estimates have been made of the mechanical
work produced by the human body. The basis of such calculations is more
or less indefinite, and the reduction of the work to foot-pounds or kilogram-
metres is difficult and inexact. Even the general statement, that of the
heat-units produced by the body, four-fifths remain as heat and one-fifth is
converted into work, must be regarded as merely approximate.

In the animal organism, a part of the potential energy of the tissues may
be converted into force by voluntary effort. In fevers, an abnormally large
proportion of the potential energy of the organism is converted into heat,
and it is not possible to use much of this energy as force. These and other
peculiarities of living bodies, as regards the production of heat and force,
are difficult of explanation. In the essential fevers, the conditions which
involve the abnormal production of heat finally consume the substance of the
tissues. They involve especially an increased production of carbon dioxide
and urea and not to any great extent the formation of water. If heat-pro-
ducing alimentary substances and alcohol can be introduced and consumed,
the tissues are thereby proportionally saved from destruction and degenera-
tions.

460 MOVEMENTS— VOICE AND SPEECH.

CHAPTER XV.

MOVEMENTS— VOICE AND SPEECH.

Amorphous contractile substance and amoeboid movements — Ciliary movements — Movements due to elas-
ticity— Elastic tissue — Muscular movements — Physiological anatomy of the involuntary muscular tissue
—Contraction of the involuntary muscular tissue— Physiological anatomy of the voluntary muscula:
tissue— Connective tissue — Connection of the muscles with the tendons — Chemical composition of the
muscles — Physiological properties of the muscles — Muscular contractility, or excitability — Muscular
contraction— Electric phenomena in muscles— Muscular effort— Passive organs of locomotion— Physio-
logical anatomy of the bones— Physiological anatomy of cartilage— Voice and speech— Sketch of the
physiological anatomy of the vocal organs— Mechanism of the production of the voice — Laryngeal
mechanism of the vocal registers — Mechanism of speech — The phonograph.

THE various processes connected with the nutrition of animals involve
•certain movements; and almost all animals possess in addition the power
of locomotion, 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 respiration, the ciliary
movements in the air-passages, the muscular acts in deglutition, the peri-
staltic movements and the mechanism of defsecation and urination. There
remain, however, certain general facts with regard to various kinds of move-
ment and the mode of action of the different varieties of muscular tissue,
that will demand more or less extended consideration. As regards the varied
and complex acts concerned in locomotion, it is difficult to fix a limit between
.anatomy and physiology. A full comprehension of such movements should
be preceded by a complete descriptive anatomical account of the passive and
active organs of locomotion ; and special treatises on anatomy give the uses
and actions as well as the structure and relations of these parts.

Amorphous Contractile Substance and Amoeboid Movements. — In some of
theiowest forms of beings, in which hardly any thing but amorphous mat-
ter and a few granules can be recog-
nized 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 struct-
ures, such as the leucocytes, the eon-

PIG. 142. — Amceba diffluens, changing in form and . 1 . ,, ,. , ,, n

moving in the direction indicated by the ar- tents of the OVUm, epithelial Cells and
row (Longet). . . . . ,, rni

connective-tissue cells. These move-
ments generally are simple changes in the form of the cell, nucleus, or what-
ever it may be. They depend upon an organic principle formerly called sar-
code and now known as protoplasm ; but it is not known that such move-
ments are characteristic of any one definite constituent of the body, nor is it
easy to determine their cause and their physiological importance. In the
anatomical elements of adult animals of the higher classes, these movements
usually appear slow and gradual, even when viewed with high magnifying
powers; but in some of the very lowest forms of life, these movements

CILIARY MOVEMENTS. 461

serve as a means of progression and are more rapid. Such movements are
called amoeboid. It does not seem possible to explain the nature and cause
of the movements of homogeneous contractile substance ; and it must be ex-
cessively difficult, if not impossible, to observe directly the effects of differ-
ent stimuli, in the manner in which the movements of muscles are studied.
They seem to be analogous to the ciliary movements, the cause of which is
equally obscure.

Ciliary Movements. — The epithelium covering certain of the mucous
membranes is provided with little, hair-like processes upon the borders 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 mem-
branes to which they are attached, the direction being generally from within
outward. In man and in the warm-blooded animals generally, the ciliated
or vibratile epithelium is of the variety called columnar, conoidal or ,pris-
moidal. 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.
In general structure the ciliary processes are entirely homogeneous, and they
gradually taper from their attachment to the cell to an extremity of excess-
ive tenuity.

The presence of cilia has been demonstrated upon the following surfaces :
The respiratory 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 fimbriated
extremities of the Fallopian tubes ; the ventricles of the brain. In these
situations, on each cell of conoidal epithelium are
six to twelve prolongations, about 2g&o0 of an inch
(1 p,) in thickness at their base, and -g-gVo to ^>Vo
of an inch (5 to 6 /n) in length. Between the cilia
and the substance of the cell, there is usually a
thin, transparent disk. The appearance of the cilia
is represented in Fig. 143. When seen in situ,
they appear regularly disposed upon the surface,
are of nearly equal length and are generally slight-
ly inclined in the direction of the opening of the
cavity lined by the membrane.

When the ciliary movements are seen in a large number of cells in situ,
the appearance is well illustrated by the comparison by Henle to the undula-
tions 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 ap-
peared simply as currents, produced by movements too rapid to be studied
in detail, become revealed as distinct undulations, in which the action of
individual cilia can be readily studied. Several 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
31

462 MOVEMENTS— VOICE AND SPEECH.

to the perpendicular. The other movements, such as the infundibuliform,
in which the point describes a circle around the base, the pendulum-move-
ment etc., are not common and are unimportant.

The combined action of the cilia upon the surface of a mucous mem-
brane, moving as they do in one direction, is to produce currents of consid-
erable power. This may be illustrated under the microscope by covering the
surface with a liquid holding little, solid particles in suspension ; Avhen the
granules are tossed from one portion of the field to another, with consid-
erable 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 ^¥ to -^ of an
inch (100 to 140 //,) per second, the number of vibratile movements being
seventy-five to one hundred and fifty per minute. In the fresh-water polyp
the movements are more rapid, being two hundred and fifty or three hundred
per minute. There is no reliable estimate of the rapidity of the ciliary cur-
rents 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 spermato-
zoids, seem to be independent of nervous influence, and they are affected only
by local conditions. They will continue, under favorable circumstances, for
more than twenty-four hours after death, and they can be seen in cells entire-
ly 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 feebly alkaline solutions.
There seems to be no possibility of explaining the movement except by a
simple 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 movements, it is sufficient to refer to the physi-
ology 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 gen-
erally and in the genital passages of the female, the currents are of consid-
erable 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 mem-
branes. These are distinct from muscular movements, and are not even to
be classed with the movements produced by the resiliency of muscular tissue,
in which muscular tonicity is more or less involved. Movements of this kind
consist simply in the return of movable parts to a certain position after they
have been displaced by muscular action, and in the reaction of tubes after
forcible distention, as in the walls of the large arteries.

Elastic Tissue. — Most anatomists 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 chem-
ical composition and general properties. On account of the yellow color of
this tissue, presenting, as it does, a strong contrast to the white, glistening

MOVEMENTS DUE TO ELASTICITY.

463

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 in-
termingled with fibres of the ordinary inelastic tissue. They possess all the
chemical and physical charac-
ters of the larger fibres, but are
very fine, measuring T^^HF to
iroVo" or s 0*0 tf °^ an inch (1 to 4
or 5 /u,) in diameter. If acetic
acid be added to a preparation
of ordinary connective tissue,
the inelastic fibres are rendered
semi-transparent, but the elas-
tic fibres are unaffected and be-
come quite distinct. 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 fract-
ure, 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 ordinary
fibrous membranes. They are found in greater or less abundance in the
situations just mentioned ; in the ligaments, but not the tendons ; in the lay-
ers of non -striated muscular tissue ; the true skin ; the true vocal chords; 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 fibres, larger than the
first, ribbon-shaped, with well-defined outlines, anatomosing, undulating or
curved in the form of the letter S, presenting the same
curled ends and sharp fracture as the smaller fibres.
These measure j-^ to 3-5^5- of an inch (5 to 8 /A) in di-
ameter. Their type is found in the ligamenta subflava
and the ligamentum nuchse. They are also found in
some of the ligaments of the larynx, the stylo-hyoid liga-
ment and the suspensory ligament of the penis.

The third variety of elastic tissue is found forming
FIG.' 148. — Large elastic the middle coat of the large arteries, and it has already
^Kmbran£)"from\ehe been described in connection with the vascular system.
Carotid of \he°Lrie; The fibres are large and flat> inosculating freely with
fe?s SSmkCT) diame~ each other by short, communicating branches. These
anastomosing fibres, forming the so-called fenestrated
membranes, are arranged in layers, and the structure is sometimes called the
lamellar elastic tissue.

464 MOVEMENTS— VOICE AND SPEECH.

The great resistance which the elastic tissue presents to chemical action
serves to distinguish it from nearly every other structure in the body. It is
not affected by acetic acid or by boiling with sodium hydrate. It is not soft-
ened by prolonged boiling in water, but it is slowly dissolved, without decom-
position, by sulphuric, nitric or hydrochloric acid, the solution not being
precipitable by potassium hydrate. Its organic constituent is a nitrogenized
substance called elastine, containing carbon, hydrogen, oxygen and nitrogen,
without sulphur. This is supposed to be identical with the sarcolemma of
the muscular tissue.

The purely physical property of elasticity plays an important part in
many of the animal functions. Examples of this are in the action of the
large arteries in the circulation, and in the resiliency of the parenchyma of
the lungs. The ligamenta subflava and the ligamentum nuchge 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 also is necessary to keep the body in a vertical posi-
tion.

MUSCULAR MOVEMENTS.

The muscular movements 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 cer-
tain involuntary actions, like the contractions of the heart or the movements
of deglutition, that require the rapid, vigorous contraction characteristic of
the voluntary muscular tissue, and here the structure resembles that of the
voluntary muscles. With a few exceptions, however, the anatomical division
of the muscular tissue into voluntary and involuntary is sufficiently distinct.

Physiological Anatomy of the Involuntary Muscular Tissue. — The invol-
untary muscular system presents a striking contrast to the voluntary muscles,
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 extremities to movable parts, the involuntary muscles form sheets or
membranes in the walls of hollow organs, and by their contraction, they sim-
ply modify the capacity of the cavities which they surround. On account of
the peculiar structure of the fibres, they have been called muscular fibre-cells,
smooth muscular fibres, pale fibres, non-striated fibres, fusiform fibres and con-
tractile cells. The distribution of these fibres to parts concerned in the or-
ganic functions, as the alimentary canal, has given them the name of organic
muscular fibres, or fibres of organic life. In their natural condition, the
involuntary muscular fibres are pale, finely granular, flattened, and of an
elongated spindle-shape, with a very long, narrow, almost linear nucleus in
the centre. The nucleus generally has no distinct nucleolus, and it is some-
times curved or shaped like the letter S. The ordinary length of these fibres
is about -g^-g- (50 /u.) and their breadth, about -ffais °^ an iRcn (6 A1)- ^n tne
gravid uterus they undergo remarkable hypertrophy, measuring here -fa to-fa
of an inch (300 to 500 /*) in length, and ^-^ of an inch (12 /x) in breadth.

MUSCULAE MOVEMENTS.

465

In the contractile sheets formed of involuntary muscular tissue, the fibres
are arranged side by side, are closely adherent, and their extremities are, as

FIG. 148.— Muscular fibres
from the aorta of the
calf ; magnified 200
diameters (Sappey).

1,1, fibres joined with each
other; 2, 2, 2, isolated
fibres.

FIG. 149.— Muscular fibres from the uterus oj
a woman who died at the ninth month oj
utero-gestation ; magnified 350 diameters
(Sappey).

1, 1, 2, short, wide fibres ; 3, 4, 5, 5, longer and
narrower fibres ; 6, 6, two fibres united
at 7 ; 8, small fibres in process of develop-
ment.

FIG. 147.— Muscular fibres
from the urinary blad-
der of the human subject;
magnified 200 diameters
(Sappey).

1, 1, 1, nuclei ; 2, 2, 2, bor-
ders of some of the
fibres : 3, 3, isolated
fibres ; 4, 4, two fibres
joined together at 5.

it were, dove-tailed into each 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. The fibres seldom
exist in a single layer except in the very smallest arterioles. 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 the nuclei more distinctly into view.

Contraction of the Involuntary Muscular Tissue. — The mode of contrac-
tion of the involuntary muscles is peculiar. It does not take place immedi-
ately 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 intes-
tines gives an idea of the mode of contraction of these fibres, with the grad-
ual propagation of the stimulus along the alimentary canal as the food mak^s
its impression upon the mucous membrane. Another illustration is afforded
by labor-pains. These are due to the muscular contractions of the uterus,
and they last for a few seconds or one or two minutes. Their gradual access,
continuation for a certain period, and gradual disappearance coincide 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 involun-

466 MOVEMENTS— VOICE AND SPEECH.

tary. Peristaltic action is the rule, and the contraction takes place progress-
ively and without oscillations. Contractility persists for a long time after
death. Excitation of the nerves has less influence upon contraction of these
fibres than direct excitation of the muscles. The involuntary muscular tis-
sue is regenerated very rapidly, while the structure of the voluntary muscles
is restored with great difficulty after destruction or division (Legros and Oni-
mus).

Physiological Anatomy of the Voluntary Muscular Tissue. — A voluntary
muscle contains, in addition to its peculiar contractile substance, fibres of in-
elastic and elastic tissue, adipose tissue, abundant blood-vessels, nerves and
lymphatics, with certain nuclear and cellular anatomical elements. The
muscular system in a well proportioned man is equal to about two-fifths of the
weight of the body (Sappey). Its nutrition consumes a large proportion of
the reparative material of the blood, while its disassimilation furnishes a cor-
responding quantity of excrementitious matter. The condition of the mus-
cular 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 contract-
ing forcibly on the reception of a proper stimulus, and a peculiar kind of
sensibility. The relations of particular muscles, as taught by descriptive anat-
omy, involve special acts ; but the most important physiological points con-
nected with this system relate to the general properties and uses of the mus-
cles.

The voluntary muscles are made up of a great number of microscopic
fibres, known as the primitive muscular fasciculi. These are called red, stri-
ated or voluntary fibres. Their structure is complex, and they may be sub-
divided longitudinally into fibrillae and transversely into disks. In very short
muscles, some of the primitive fasciculi may run the entire length of the
muscle; but the fasciculi usually are 1-2 to 1-6 inch (30 to 40 mm.) in
length. The fasciculi, however, do not inosculate with each other, but the
end of one fasciculus is united longitudinally with the end of another by a
strongly adhesive substance, the line of union being oblique ; so that the fibres
practically run the entire length of the muscle. Each fasciculus 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. In a thin, transverse section of a muscle, the divided
ends of the fibres present an irregularly polygonal form with rounded cor-
ners. They seem to be cylindrical, however, when viewed in their length and
isolated. Their color by transmitted light is a delicate amber, resembling
the color of the blood-corpuscles.

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

MUSCULAK MOVEMENTS.

467

particular muscles have been increased in size and power by exercise, the fas-
ciculi 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-

FIG. 150.— Striated muscular fibres from the mouse ; magnified 500 diameters (from a photograph

taken at the United States Army Medical Museum).
The injected capillaries are seen, somewhat out of focus.

existing fasciculi and not to the formation of new elements. In young per-
sons the fasciculi are y^ to y^o of an incn (15 to 2° /*) in diameter. In
the adult they measure ^^ to -^ of an inch (55 to 100 ft).

The appearance of the primitive muscular fasciculi under the microscope
is characteristic. They present regular, transverse s'trise, formed of alternat-
ing dark and clear bands about ^f^ of an inch (1 /*) wide. With a high
magnifying power, a very fine transverse line is observed running through the
middle of each one of the clear bands. In addition they present longitudi-
nal striae, not so distinct, and 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, presenting this peculiar,
striated appearance, is enclosed in a very thin but elastic and resisting tubu-
lar membrane, called the sarcolemma or myolemma. This envelope can not
be seen in ordinary preparations of the muscular tissue ; but it frequently
happens that the contractile muscular substance is broken, leaving the sarco-
lemma intact, which gives a good view of the membrane and conveys an idea

468

MOVEMENTS— VOICE AND SPEECH.

of its strength and elasticity. Attached to the inner surface of the sarco-
lemma, are 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 distinct.

Water after a time acts upon the muscular tissue, rendering the fasciculi
A somewhat paler and larger. Acetic

acid and alkaline solutions efface the
striae, and the fibres become semi-trans-
parent. In fasciculi that are slightly
decomposed, there is frequently a sepa-
ration at the extremity into smaller
fibres, called fibrillae. These, when
isolated, present the same striated ap-
pearance as the primitive fasciculus ;
viz., alternate dark and light portions.
They measure about -^^or °f an incn
(1 /A) in diameter, and their number,
in the largest primitive fibres, is esti-
mated at about two thousand (Kolli-
ker). The interior of each primitive
fasciculus is penetrated by a very del-

FIG. 151. — Striated muscular fibres ; magnified 250
diameters (Sappey).

A, transverse striae and nuclei of a primitive f ascic- i pa fa m p™ hra n p r>l n«pl v «n vrnn n rl i n tt
ulus; B, longitudinal striae and fibrillae of a 1Caie .lOSGiy £ mg

the fibrillae. This arrangement may

primitive fasciculus in which the sarcolemma
has been lacerated at one point by pressure.

be distinctly seen in a thin section of
a fibre treated with a solution of common salt in water, in the proportion of
five parts per thousand (Kolliker).

Connective Tissue. — In the muscles there is a membrane surrounding a
number of the primitive fasciculi. This is called the perimysium. The
fibrous membranes that connect together the sesecondary bundles, with their
contents, are enclosed in
a sheath enveloping the
whole muscle, sometimes
called the external peri-
mysium. The peculiari-
ty of these membranes as
distinguished from the
sarcolemma is that they
have a fibrous structure
and are connected togeth-
er throughout the muscle,
while the tubes forming
the sarcolemma are struct-
ureless and each one is
distinct.

The name now most generally adopted for the ordinary fibrous tissue is

PIG. 152.— Fibres of tendon of the human subject (Rollett).

CONNECTIVE TISSUE.

469

connective 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 prin-
cipal anatomical element is a fibre of excessive tenuity, wavy and with a sin-
gle contour. These fibres are collected into bundles of 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 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 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 into

FIG. 153.— Loose net-work of connective tissue from the human subject, showing the fibres and cells

(Rollett).
a, a, a capillary blood-vessel.

view. The proportion of elastic fibres differs very much in different situa-
tions, 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
very small, they always present a double contour.

Certain cellular and nuclear elements are always found in the connective
tissue. The cells are known as connective-tissue cells. They are very irregu-
lar in size and form, some of them being spindle-shaped or caudate, and

470 MOVEMENTS— VOICE AND SPEECH.

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. It is impossible to give any accu-
rate measurements of the cells, on account of their great variations in size.
The appearance of the connective tissue, with a few cells and nuclei, is repre-
sented in Fig. 153.

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-vessels, generally by a number of small arteries with two satellite
veins. The capillary arrangement in this tissue is peculiar. From the small-
est arterioles, capillary vessels are given off, arranged in a net- work with tol-
erably 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.

The arrangement of the lymphatics in the muscles has never been defi-
nitely ascertained.' There are 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 lym-
phatics 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. — The primitive muscular
fasciculi terminate in little, conical extremities, which are received into corre-
sponding 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 arrange-
ment is quite uniform. In other muscles it is essentially the same, but the
perimysium seems to be continuous with the loose areolar tissue enveloping
the corresponding tendinous bundles.

Chemical Composition of the Muscles. — The most important nitrogenized
constituent of the muscles is myosine. 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 contains certain coagulable albuminoid substances,.
Combined with the organic constituents of the muscular substance are min-
eral salts in great variety, which can not be separated without incineration.
Certain excrementitious 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 conse-
quently detected with difficulty. The muscles also contain inosite, inosic
acid, lactic acid and certain volatile acids of fatty origin. During life the

ELASTICITY AND TONICITY OF MUSCLES. 471

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
and other acids exist in greater quantity and the reaction becomes acid.

PHYSIOLOGICAL PROPERTIES OF THE MUSCLES.

The important general properties of the striated muscles are the following :
1. Elasticity ; 2. Tonicity ; 3. Sensibility of a peculiar kind ; 4. Contractility,
or excitability. These are all necessary to the physiological action of the mus-
cles. 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 mus-
cles, which, by virtue of their elasticity, retract when the extending force is
removed. Their tonicity is an insensible and a more or less constant con-
traction, by which the action of opposing muscles is balanced when both are
in the condition of what is called repose. Their sensibility is peculiar and
is expressed chiefly in the sense of fatigue and in the appreciation of weight
and of resistance to contraction. Their contractility or excitability is the
property which enables them to contract under stimulation. All of these
general properties strictly belong to physiology, as do some special acts that
are not necessarily 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 presents a
certain number of elastic fibres ; and the sarcolemma is very elastic. It is
probably the sarcolemma that gives to the muscles their retractile power after
simple extension.

It is unnecessary to follow out in detail all of the many 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 exten-
sion that is followed by complete retraction — and this can not 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 -fa of an inch (0*5 mm.) by a weight of a little more than
300 grains (20 grammes). 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 (48-6 grammes). 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 physio-
logical action of muscles'; for it is well known that they are unusually relaxed
during fatigue after excessive exertion, and 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 depend-

472 MOVEMENTS— VOICE AND SPEECH.

cnt 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 difficult 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 can be said 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.

Sensibility of the Muscles. — The muscles possess that kind of sensibility
which gives an appreciation of the power of resistance, immobility, and elas-
ticity of substances that are grasped, or which, by their weight, are opposed
to the exertion of muscular power. It is by the appreciation of weight and
resistance that the force required to accomplish muscular acts is regulated.
These properties refer chiefly to simple muscular efforts. After long-con-
tinued exertion there is 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 a nervous stimulus
could be sent to the muscles, to which they are for the time unable to respond.

When the muscles are thrown into tetanic contraction, a peculiar sensa-
tion is produced, which is entirely different from painful impressions made
upon the ordinary sensory nerves. In the cramps of cholera, tetanus, or the
convulsions from strychnine, these distressing sensations are very marked.

If the muscles possess'any general sensibility, it is very slight. A muscle
may be lacerated or irritated without producing actual pain, although con-
traction produced by irritants and the sense of tension when the muscles are
drawn upon can always be appreciated.

Muscular Contractility, or Excitability. — During life and under normal
conditions, the muscles will always contract in obedience 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 either through voli-
tion or reflex action. Still, a muscle may be living and yet have lost its con-
tractility. For example, after a muscle has been for a long time paralyzed
and disused, the application of the most powerful stimulus will fail to induce
contraction ; but when examined with the microscope, it is found that the
nutrition of the muscle has become profoundly affected, and that the con-
tractile substance has disappeared. Muscular contractility persists for a cer-
tain time after death and in muscles separated from the body ; and this fact
has been taken advantage of by physiologists in the study of the properties
of the muscular tissue. A muscle detached from the living body continues
for a time to respire, and it undergoes some of the changes of disassimilation
observed in the organism. So long as these changes are restricted within
the limits of physical and chemical integrity of the fibre, contractility re-
mains. As these processes are very slow in the cold-blooded animals, the
excitability of all the parts persists for a considerable time after death.

MUSCULAR CONTRACTILITY, OR EXCITABILITY.

473

In the human subject and the warm-blooded animals, the muscles cease
to respond to a stimulus a few hours after death, although the time of dis-
appearance of excitability is very variable. Nysten, in a number of experi-
ments upon the disappearance of excitability in the human subject after de-
capitation, found that different parts lost their contractility at different peri-
ods, but that generally this depended upon exposure to the air. With the
exception of the right auricle of the heart, the striated muscles were the last
to lose their excitability. In one instance, certain of the voluntary muscles
that had not been exposed retained their contractility seven hours and fifty
minutes after death. Longet and Masson found that an electric shock, suf-
ficiently powerful to produce death instantly, destroyed the excitability of
the muscular tissue and of the motor nerves.

The experiments of Longet (1841) presented almost conclusive proof of
the independence of muscular excitability. He resected the facial nerve and
found that it ceased to respond to mechanical and electric stimulus, or in
other words, lost its excitability, after the fourth day. Operating, however,
upon the muscles supplied exclusively with filaments from this nerve, he
found that they responded promptly to me-
chanical and electric stimulation, and that
this continued for more than twelve weeks.
In other experiments it was shown that while
the contractility of the muscles could be seri-
ously influenced through the nervous system,
this was effected only by modifications in their
nutrition. When the mixed nerves were di-
vided, the nutrition of the muscles was gener-
ally disturbed; and although muscular con-
tractility persisted for some time after the
nervous excitability had disappeared, it be-
came very much diminished at the end of six
weeks. Some varieties of curare destroy the
excitability of the motor nerves, leaving the
sensitory filaments intact. If a frog be poi-
soned by introducing a little of this agent
under the skin, stimulation, electric or me-
chanical, applied to an exposed nerve, fails to
produce muscular contraction ; but if the Fl»- 15*TJW? leg-s PrePa™d so as^to

r . . show the effects of curare (Bernard).

Stimulus be applied directly to the mUSCleS, Faradization of the nerves in this ani-

, -, .-,, . , T , , . , T mal, which has been poisoned with

they Will Contract Vigorously. In this Way the curare, has no effect ; while the

nerves are, as it were, dissected out from the muscles8 (seePdotteddiirnes)yproduces
muscles ; and the discovery of an agent that

will paralyze the nerves without affecting the muscles affords conclusive
proof that the excitability of these two systems is distinct. If a frog be
poisoned with potassium sulphocyanide, precisely the contrary effect is ob-
served ; that is, the muscles will become insensible to excitation, while the
nervous system is unaffected. This fact may be demonstrated by apply-

MOVEMENTS— VOICE AND SPEECH.

ing a tight ligature around the body in the lumbar region, involving all the
parts except the lumbar nerves. If the poison be now introduced beneath
the skin above the ligature, only the anterior parts are affected, because the
vascular communication with the posterior extremities is cut off. If the
exposed nerves be now stimulated, the muscles of the legs are thrown into
contraction, showing that the nervous excitability remains. Reflex move-
ments in the posterior extremities may also be produced by irritation of the
parts above the ligature. These experiments leave no doubt of the existence
of an inherent and independent excitability in the muscular tissue (Bernard).
Contractions of muscles, it is true, are normally excited through the nervous
system, and artificial stimulation of a motor 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 electric, mechanical, or chemical irritation of the muscles
themselves will produce contraction, after the nervous excitability has been
abolished. The conditions under which muscular contractility 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 paralysis, their excitability disappears
and can not be restored.

Experiments have been made with regard to the influence of the cir-
culation upon muscular excitability, chiefly with reference to the effects of
tying large vessels. Longet tied the abdominal aorta in five dogs and found
that voluntary motion ceased in about a quarter of an hour, and that the
muscular excitability was extinct in two hours and a quarter. When the
circulation was restored, after three or four hours, by removing the ligature,
the excitability, and finally voluntary movement, 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 excitability of the muscles.
In dogs in which this experiment was performed, the lower extremities pre-
served 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 excitability to the circulation have been farther
illustrated in the following experiments by Brown-Sequard : The first ob-
servations were made upon two men executed by decapitation. Thirteen
hours and ten minutes after death, when the muscular excitability had disap-
peared and was succeeded by cadaveric rigidity, a quantity of fresh, defibri-
nated venous blood from the human subject was injected into the arteries of
one hand and was returned by the veins. It was afterward re-injected sev-
eral times during a period of thirty-five minutes. The whole time occupied
in the different injections was ten to fifteen minutes. Ten minutes after the
last injection, and about fourteen hours after death, the excitability 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 excitability could not
be demonstrated. Three hours after, the excitability still existed, but it disap-
peared a quarter of an hour later. The second observation was essentially
the same, except that defibrinated blood from the dog was used and the ex-

MUSCULAR CONTRACTION. 475

periments were made upon the muscles of the arm. The excitability was re-
stored in all of the muscles, and it persisted, the cadaveric rigidity having
disappeared, twenty hours after decapitation.

MUSCULAR CONTRACTION.

The stimulus of the will, conveyed through the conductors of motor im-
pulses from the brain to a muscle or set of muscles, excites the muscular
fibres and causes them to contract. In muscles that have been exercised
and educated, this action is regulated with great nicety, so that the most
delicate and rapid as well as powerful contractions may be produced. Cer-
tain 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 sensory 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 dif-
ferent 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 important.

The most prominent of the phenomena accompanying muscular action is
shortening and hardening of the fibres. It is necessary only to observe the
action of any well developed muscle to appreciate these changes. The active
shortening is shown by the approximation 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 matter, such as fat. It is the muscular substance alone which has
the property of contraction ; and this action increases the consumption of
oxygen and probably of other matters, the formation of carbon dioxide and
some other excrementitious products, and develops heat.

Notwithstanding the marked and constant changes in the form and con-
sistence of the muscles during contraction, their actual volume undergoes
modifications so slight that they may practically be disregarded. The ex-
ceeding slight change which has been observed in recent experiments (Valen-
tin, Landois) is a diminution in volume.

Changes in the Form of the Muscular Fibres during Contraction. — All
physiologists are agreed that in muscular contraction there is an increase in
the thickness of the fibre, nearly 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 en-
largement, its duration, the means by which it may be excited, and its physi-
ological modifications. These questions have been made the subjects of in-
vestigation by Helmholtz, Du Bois-Reymond, Aeby, Marey and others ; and
although it is hardly necessary to follow these experimenters through till the
details of their observations, many important points have been developed,
particularly by the methods of registering the muscular movements.

One essential condition in the study of the mechanism of muscular con-

476 MOVEMENTS— VOICE AND SPEECH.

traction 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 the most perfect method that can
be employed for this purpose. In this way a single contraction may be pro-
duced, or by employing a rapid succession of impulses, so-called tetanic
action may be excited. While the electric current is not identical with the
nervous force, it is the best substitute that can be used in experiments
upon muscular contractility, and it has the advantage of affecting but little
the physical and chemical integrity of the nervous and muscular tissues.

There are two classes of phenomena that may be produced by electric
excitation of motor nerves : 1. When the stimulus is applied in the form of
a single discharge, it is followed by a single muscular contraction. 2. Un-
der a rapid succession of discharges, the muscle is thrown into a state of
permanent, or tetanic contraction. It will facilitate a comprehension of the
subject to study these phenomena separately and successively.

Mechanism of a Single Muscular Contraction. — 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 relaxa-
tion. Under this stimulation, the muscle shortens by about three-tenths of
its entire length. The form of the contraction, as registered by the appa-
ratus of Helmholtz, Marey and others who have applied the graphic method
to the study of muscular action, presents certain peculiarities.

According to Helmholtz, the whole period of a single contraction and
relaxation of the gastrocnemius muscle of a frog is a little less than one-third
of a second. The muscles 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
in the gastrocnemius of a frog :

Interval between stimulation and contraction (latent period) 0"-020

Contraction 0"-180

Relaxation.. . 0"-105

0"-305

The latent period in man is 0-004 to O'Ol of a second, the contraction oc-
cupies 0*03 to 0'4 of a second, and the period of relaxation is a little shorter
than the period of contraction. The duration of the electric current is only
O^'OOOS. 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 well established, how-
ever, that a single fibre, with its excitability unimpaired, becomes contracted
and swollen at the point where the stimulation is applied. The question
now is whether, in normal contraction of the fibres in obedience to the nat-
ural nervous stimulus, 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.

MUSCULAR CONTRACTION. 477

The experiments of Aeby, which have been repeated and extended by
Marey, have shown that when one extremity of a muscle is excited, a con-
traction occurs at that point and is propagated along the muscle, in the form
of a wave. The estimated rapidity of this wave is 33 to 43 feet (10 to 13
metres) per second (Hermann). Applying this principle to the physio-
logical action of muscles, Aeby proposed 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 different point of stimulation. Although this view of the physiological
action of the muscular fibres is very probable, it can not be assumed that it
has been absolutely demonstrated ; but it is certainly more satisfactory and
better sustained by experimental facts than any other theory that has yet
been advanced.

Mechanism of Tetanic Muscular Contraction. — By a voluntary effort a
muscular contraction may be produced, of a certain duration and of a power,
within certain limits, proportionate to the amount of force required ; but
after a time the muscle becomes fatigued, and it may become exhausted
to the extent that it will no longer respond to the normal stimulus. This
normal muscular action in obedience to impulses conveyed by motor nerves
may be closely imitated by electric stimulation. When a single electric dis-
charge is applied to a nerve, there is a single muscular contraction ; but a
rapid succession of discharges produces a persistent contraction, which is
called tetanic.

During the passage of a feeble galvanic current through a nerve, there is
no contraction in the muscles to which the nerve is attached ; and it is only
when the circuit is closed or opened that any action is observed. The inter-
rupted galvanic current, the induced current, or a succession of discharges of
statical electricity, when they do not follow each other too rapidly, produces
a corresponding succession of muscular contractions. As the rapidity of
these electric impulses is increased, the individual contractions become less
and less distinct, until finally the contraction is persistent. Distinct single
contractions occur with ten excitations per second, a partial fusion of the
different acts takes place with twenty per second, and a complete fusion, or
tetanus, with twenty-seven per second (Marey). When the contraction be-
comes continuous, there is an elevation of the line marked on a registering
apparatus, showing increased power as the excitations are more and more
rapid. This is artificial tetanus ; but it probably is the kind of contrac-
tion that occurs in the physiological action of the voluntary muscles.

It is probable that the normal nervous stimulus in voluntary muscular
action is a succession of impulses, which produce a power of muscular con-
traction that is proportionate to their rapidity. Vibrations, which are more
or less regular, actually occur during the contraction of muscles (Wollaston,
Haughton, Helmholtz). Helmholtz, indeed, has recognized a musical note
produced by contracting muscles, which exactly corresponds to the number
of excitations per second applied to the nerve. This can be heard in the
temporal and masseter muscles by filling the ears with wax and causing these

32

478 MOVEMENTS— VOICE AND SPEECH.

muscles to contract. The number of vibrations noted by Helmholtz was
per second ; but the sound heard was the first overtone, or the octave, the
fundamental tone being too low to be appreciated by the ear.

Some physiologists have denied the supposed identity between the tetanic
contraction produced by a rapid succession of stimuli applied to a motor
nerve and voluntary muscular contraction. Complete fusion of contraction
occurs with twenty-seven or more stimuli per second applied to a nerve ;
but it is stated that stimuli applied to the motor cerebral centres, even when
very rapid, do not produce more than eight to thirteen muscular contrac-
tions, the average being ten per second (Horsley and Schafer, 1887). The
average in voluntary muscular contraction is about the same. From these
observations it is argued that the rate of so-called vibration in voluntary
muscular contraction has an average of about ten per second. This conclu-
sion is based upon actual myographic tracings. It is difficult, however, to rec-
oncile these results with those obtained by Marey, Helmholtz and others.
It is a fact, also, that distinct muscular contractions may be produced very
rapidly by an effort of the will. It is not difficult for any one to make five
taps of the finger per second for a few seconds, and skillful performers on
musical instruments are able, by using the same muscle or set of muscles, to
make movements that are very much more rapid, each movement presumably
requiring a distinct nervous impulse. It may be that in an unweighted mus-
cle, the contractions are discontinuous, and that the average number of
waves is about ten per second ; but it is probable that the estimate of Helm-
holtz— 19£ waves per second — is nearly correct for muscles in a condition of
powerful contraction. In a series of observations by Griffiths (1888), it was
found that voluntary contraction of the biceps weighted with a little more
than eleven pounds (5,000 grammes), for one hundred seconds, gave an aver-
age of eighteen waves per second, the average for the unweighted muscle
being fourteen waves per second for thirty-three seconds.

The nerves are not capable of conducting an artificial stimulus for an in-
definite 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 excitability ; and
these properties become gradually extinguished, the parts becoming fatigued
before they are completely exhausted. Precisely the same phenomena are
observed in the physiological action oi muscles. When a muscle is fatigued
artificially, a tetanic condition is excited more and more easily, but the power
of the contraction is proportionally diminished. 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 in-
tensity ; but it is certain that the vigor of contraction at the same time pro-
gressively diminishes.

The phenomena of muscular contraction thus far considered are those
produced by voluntary effort or by stimulation of motor nerves ; but many
important phenomena have been observed in muscles detached from the body

ELECTRIC PHENOMENA IN MUSCLES.

479

FIG. 155. — Diagram of the myograph of Helmholtz (Lan-

dois).

Mi muscle fixed by the clamp (K) by a portion of the fe-

mur . F recorjdiu? point^ P? counterpoise used to bai-

ance^lever ; V^, pan for weights ; S, S, supports for

and stimulated directly. These observations have generally been made on

the gastrocnemius of the frog, the phenomena being recorded by a register-

ing apparatus, the simplest form

of which is the myograph of

Helmholtz. This instrument is

used in recording muscular con-

tractions by causing the record-

ing point to play upon a smoked

paper moving at a known rate.

If the muscle of the frog, slight-

ly weighted, be stimulated by a

single induction-shock, there is

first a latent period, when there

is no contraction, then a con-

traction followed by relaxation,

and finally a slight, elastic vibra-

tion before the muscle becomes

. f-f,-. ,

quiescent. These phenomena

ova illncfrtifprl in f no onrvp crivpn

are illustrated in tne curve gi\en

rn Fig. 156 in which, however,

the latent period is not measured.

In a muscle prepared in this way, the maximum of stimulation and the
maximum of power measured by a weight lifted can readily be ascertained,
and certain phenomena due to fatigue of the muscle have been observed. In
a fatigued muscle, the latent period is lengthened and the elevation of the
curve of contraction is not so high, showing a slower and longer action.
When a muscle is excited to tetanic contraction by a rapidly interrupted
current of considerable strength, the elevation produced by the initial con-

traction is nearly vertical,
and is followed by a hori-
zontal straight line which
marks the tetanic condi-
tion. The phenomena in-
duced by direct stimulation
of muscles are somewhat

PY«0-cypratprl whpn fhp qfim
exaggerated Wnen tne Stim-

ujug jg applied to the mo-

tor nerve.

Electric Phenomena in Muscles. — It was ascertained a number of years
ago, by Matteucci, that all living muscles present electric currents. The
direction of these currents is from the longitudinal surface to the transverse,
or cut surface of the muscle, as is shown in Fig. 157. A simple method
of demonstrating the muscular 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 connection is made, a contraction of the leg takes place. The current

FIG. 156. -Curve of a single muscular contraction (Landois).
A F, abscissa ; A C, ordinate ; A B, latent period : B D, period of
contraction ; D E, period of relaxation ; E F, elastic vibra-
tion.

480

MOVEMENTS— VOICE AND SPEECH.

may also be demonstrated with an ordinary galvanometer ; but the evidence

obtained by the frog's leg is sufficiently conclusive.

Matteucci constructed out of the fresh muscles from the thigh of the frog,

what is sometimes called a frog-battery; which is made by taking the

muscles of the lower half

n ^SS^NT^----^- °^ t^ie thigh from several

/^--Vv^^^^^fe, fa* frogs, remoying the bones,

and arranging them in a
series, each with its coni-
cal extremity inserted into
the central cavity of the
one below. In this way
the external surface of
each thigh except the last
is in contact with the in-
ternal surface of the one
below. If the two extrem-
ities of the pile be con-
nected with a galvanome-
ter, quite a powerful cur-
rent from the internal to
the external surface of the

FIG. 157.— Muscular current in the frog (Bernard). muscle may be demon-

Fig. 1, portion of the thigh, with the skin removed ; a, surface of -i y ,~:i« *„„ ,1

the muscles; 6, section ; the direction of the current is indi- Strated. In a pile lormed

Fig C2, the nervl XTfrog's leg (the leg enclosed in a glass tube) is °f ten elements, the nee-
applied to the section and the surface of the muscle. There is Jla ~f a fralva-nnm&i-av waa
no contraction, because it is necessary that a portion of the Ult! U1 " g«"*"
nerve should be raised up. rlpvia+prl 30° +n 4.0°

Fig. 3, a portion of the nerve is raised with a glass rod. The con- L

traction of the galvanoscopic leg occurs at the making of the Tn'lpp+rir* nnrrpnfa «TP

circuit, because the current follows the course of the nerve, or

observed in all living mus-
cles, 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 cur-
rent, 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°, or it may
even return to zero. This phenomenon, which is called negative variation of
the muscular current, is observed only during a continued muscular contrac-
tion and it does not attend a single contraction.

Muscular Effort. — The mere voluntary movement of parts of the body,
when there is no obstacle to be overcome or no great force is required, is
very different from a muscular effort. For example, in ordinary progression
there is simply a movement produced by the action of the proper muscles,
almost without consciousness, and this is unattended with any considerable
modification in the circulation or respiration; but in attempting to lift a
heavy weight, to jump, to strike a powerful blow or to make any vigorous

at the breaking of the circuit,
because the direction of the current is opposite the course of

PHYSIOLOGICAL ANATOMY OF THE BONES. 481

effort, the action is different. In the latter instance, a certain preparation
for the muscular effort is made by inflating the lungs, closing the glottis
and contracting more or less forcibly the expiratory muscles so as to render
the thorax rigid and unyielding ; and by a concentrated effort of the will, the
proper muscles are then brought into action. This action of the muscles of
the thorax and abdomen, due to simple effort and independent of the partic-
ular muscular act that is to be accomplished, compresses the contents of the
rectum and bladder and obstructs very materially the venous circulation in the
large vessels. It is well known that hernia frequently is produced in this
way ; the veins of the face and neck become turgid ; the conjunctiva may be-
come ecchymosed ; and sometimes aneurismal sacs are ruptured. An effort
of this kind is generally of short duration, and it can not, indeed, be pro-
longed beyond the time during which respiration can be conveniently arrested.
There are degrees of effort which are not attended with this powerful ac-
tion 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 impossible, does not interfere with certain acts that
require considerable muscular power. If the glottis be exposed in a dog,
when he makes violent efforts to escape, the opening is firmly closed. This
is often observed in vivisections ; but Longet has shown that dogs with an
opening into the trachea are frequently able to run and leap with " astonish-
ing 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 consid-
ered in connection with the functions of which they form a part; but
others are purely anatomical questions. Associated and antagonistic move-
ments, automatic and reflex movements etc., belong to the history of the
motor nerves and will be fully considered in connection with the physiology
of the nervous system.

The study of locomotion involves a knowledge of the physiological anat-
omy of certain passive organs, such as the bones, cartilages and ligaments.
Although a complete history of the structure of these parts trenches some-
what upon the domain of anatomy, a brief description of their histology will
practically complete the account of the tissues of the body, with the excep-
tion 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, mov-
able parts. These are the bones, cartilages, ligaments, aponeuroses and ten-
dons. The fibrous structures have already been described, and it only remains
to study the structure of bones and cartilages.

Physiological Anatomy of the Bones. — The bones are composed of what is
called the fundamental substance, with cavities and canals of peculiar form.

482

MOVEMENTS— VOICE AND SPEECH.

«'-*MH^4

The cavities contain 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, con-
taining vessels and nerves, called
the periosteum.

The fundamental substance is
composed of an organic matter,
called osseine, combined with vari-
ous inorganic salts, in which calci-
um phosphate largely predomi-
nates. In addition to calcium phos-

the bones contain calcium

FIG. 158.— Vascular canals and lacunae, seen in a lon-
gitudinal section of the humerus ; magnified 200 carbonate, calcium fluoride,
diameters (Sappey).

o, a, a, vascular canals ; b, 6, ft, lacunge and canaliculi nesium phosphate, sodium. pllOS-
in the fundamental substance. , -. -, . i i • j mn

phate and sodium chloride. The

relative proportions of the organic and inorganic constituents 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.

Anatomically, the fundamental
substance of the bones is arranged in
the form of regular, concentric lam-
ellae, about -g-oVir of an inch (8 /*) in
thickness. This matter is of an in-
definitely and faintly striated appear-
ance, but it can not be reduced to dis-
tinct fibres. In the long bones the
arrangement of the lamellae is quite
regular, surrounding the Haversian
canals and forming what are some-
times called the Haversian rods, fol-
lowing in their direction the length
of the bone. In the short, thick
bones the lamellae are more irregular, frequently radiating from the central
portion toward the periphery.

FIG. 159.— Longitudinal section of bone, from the
shaft of the human femur ; magnified 180 di-
ameters (from a photograph taken at the Unit-
ed States Army Medical Museum).

PHYSIOLOGICAL ANATOMY QF THE BONES.

483

The Haversian canals exist in the compact bony structure. They are
either absent or are very few in the spongy and reticulated portions. Their
form is rounded or ovoid, the larger canals being sometimes quite irregular.
In the long bones their direction is generally longitudinal, although they
anastomose by lateral branches. Each one of these canals contains 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 arteries penetrate and the veins emerge. Their size,
of course, is variable. The largest are about -fa of an inch (400 //,) and the
smallest, -^ of an inch (30 /x) in diameter (Sappey). Their average size
is -pfa to ¥fg- of an inch (100 to 125 //,). In a transverse section of a long
bone, the Haversian canals may be seen cut across and surrounded by twelve
to fifteen lamellae.

Lacuna. — The fundamental substance is everywhere marked by irregular,
microscopic excavations, of a peculiar form, called lacunae. They are con-
nected with little canals, giving them a stellate appearance. These canals
are most abundant at the sides of the lacunae. The lacunae measure y^^ to
-5^-5- of an inch (20 to 30 /x) in their long diameter, by about -£-£$-$ of an inch
(10 /*) in width.

Canaliculi. — These are little, wavy canals, connecting the lacunae with
each other and presenting a communication between the first series of lacunas
and the Haversi-
an canals. Each
lacuna presents
eighteen to twen-
ty canaliculi radi-
ating from its
borders. The
length of the can-
aliculi is -gfo to
-inhr of an inch
(30 to 40 /x), and
their diameter is
about ^^ of an
inch (1 //,). The
arrangement and
relations of the
Haversian canals,
lacunae and cana-
liculi are shown
in Fig. 160.

Bone-cells or Corpuscles. — These structures are stellate, granular, with a
large nucleus and several nucleoli, and are of exactly the size and form of
the lacunae. They send out prolongations into the canaliculi, but it has
been impossible to ascertain positively whether or not they form membranes
lining the canaliculi throughout their entire length.

FIG. 160. — Vascular canals and lacunce. 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 di-
vided at the point of its anastomosis with a transverse canal. Around the
canals, cut across perpendicularly, are seen the lacunae (with their canali-
culi), forming concentric rings.

484

MOVEMENTS— VOICE AND SPEECH.

Marrow of the Bones. — The marrow is found in the medullary cavities of
the long bones, filling them completely and moulded to all the irregularities

of their walls. It is also found filling
the cells of the spongy portion. In
other words, with the exception of
the vascular canals, lacunae and cana-
liculi, the marrow fills all the spaces,
in the fundamental substance. The
cavities of the bones are not lined
with a membrane corresponding to
the periosteum, and the marrow is
applied directly to the bony sub-
stance. In the foetus and in very
young children the marrow is red
and very vascular. In the adult it is
yellow in some bones and gray or
gelatiniform in others. It contains

FIG. 161.— Transverse section of bone, from the shaft r>pri-mn r»pr>nliav nplle aiirl rmnloi ™ifVi

of the human humerus ; magnified 180 diame- Certain peculiar C611S and. nuclei, Wltn

ters (from a photograph taken at the United arnnrrYhrma. rrmtfpr arlinrusp vp«inlp«

States Army Medical Museum). mailer, adipose Vesicles,

connective tissue, blood-vessels and

nerves. Eobin has described little bodies, existing both in the form of cells
and free nuclei, called medullocells. These are found in greater or less num-
ber in the bones at
all ages, but they are
more abundant in
proportion as the
amorphous matter
and fat-cells are de-
ficient. The nuclei are
spherical, sometimes
with irregular bor-
ders, generally with-
out nucleoli, finely
granular, and -^
to -g-j^-fr of an inch (5
to 8 //,) in diameter.
They are insoluble in
acetic acid. The cells,
which are less abun-
dant than the free nu-
clei, are spherical or
slightly polyhedric,
contain a few pale granulations, are rendered pale but are not dissolved
by acetic acid, and they measure about 3-^5- of an incn (15 ft) in diameter.
Irregular, nucleated patches, described by Eobin under the name of myelo-
plaxes, more abundant in the spongy portions than in the medullary canals,

FIG. 162.— Bone-corpuscles, with their prolongations (Rollett).

PHYSIOLOGICAL ANATOMY OF THE BONES. 485

are found applied to the internal surfaces of the bones. They are very irreg-
ular in size and form (measuring -j-gVs to -vfa of an inch, or 20 to 100 \L in
diameter), are finely granular, and present two to twenty or thirty nuclei.
The nuclei are clear and ovoid and are generally provided with a distinct
nucleolus. The myeloplaxes are rendered pale by acetic acid, and the nuclei
are then brought distinctly into view. They are particularly abundant in
the red marrow.

In addition to the anatomical elements just described, the marrow con-
tains a few very delicate bundles of connective tissue, most of which accom-
pany the blood-vessels. In the foetus the adipose vesicles are few or may
be absent ; but in the adult they are quite abundant, and in some bones they
seem to constitute the whole mass of the marrow. They do not differ ma-
terially from the fat-cells in other situations. Holding these different struct-
ures together, is a variable quantity of semi-transparent, 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 chief physiological interest connected with the marrow of the bones
is in its relations to the formation of blood-corpuscles. This question has
already been discussed in connection with the development of the corpuscular
elements of the blood.

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 incrusta-
tion. It is composed mainly of ordinary fibrous tissue with small elastic
fibres, blood-vessels, nerves and a few adipose vesicles.

The arterial branches ramifying in the periosteum are quite abundant,
forming a close, anastomosing plexus, which sends 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 itself 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 and regeneration 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

486

MOVEMENTS— VOICE AND SPEECH.

regenerated. The importance of the
periosteum has been still farther illus-
trated by the experiments of Oilier
and others, upon transplantation of
this membrane in the different tissues
of living animals, which has been fol-
lowed by the formation of bone in
these situations.

Physiological Anatomy of Carti-
lage. — In this connection the structure
of the articular cartilages presents the
chief physiological interest. The ar-
ticular surfaces of all the bones are

.m.-sectionof cartilage from the nb of the encrusted with a layer of cartilage,

ox, showing the homogeneous fundamental
substance, cartilage - cavities and cartilage-
cells; magnified 370 diameters (from a photo-
graph taken at the United States (Army Medical

Qr>rl
and

B

Trorvno- n
Varying m

1_ nf sm i-nr»Vi (C\~^ onrl 1 mm \
& (- 1 mm.).

cartilaginous substance is white, opal-
ine, and semi-transparent when examined in thin sections. It is not
covered with a membrane, but in the
non - articular cartilages it has an
investment analogous to the perios-
teum.

Examined in thin sections, cartilage
is found to consist of a homogeneous
fundamental substance, marked with
excavations, called cartilage-cavities or
chondroplasts. The intervening sub-
stance has a peculiar organic constitu-
ent, called chondrine. The organic
matter is united with a certain propor-
tion of inorganic salts. This funda-
mental substance is elastic and resist-
ing. The cartilages are closely united
to the subjacent bony tissue. The
free articular surface has already been
described in connection with the syn-
ovial membranes.

Cartilage- Cavities. — These cavities
are rounded or ovoid, measuring y^-
to -g-j-fr of an inch (20 to 80 /x) in diam-
eter. They are generally smaller in

the articular cartilages than in other FlG. 164._Perpen^.cw,arsecf,ono/ad,ar^rod,a,
situations, as in the costal cartilages.

rr,! . , .. ,,

They are Simple excavations in the
» i Jiii i i • •

f Undamental Substance, have 110 lining

membrane, and they contain a small

cartilage (Sappey).

1, 1, osseous tissue ; 2, 2, superficial layer of osse-
ous tissue treated with hydrochloric acid; 8,3,
cavities and cells of the deep layer of carti-
lage ; 4, 4, cavities and cells of the middle lay.

5' cavities and cells of the 8uperficial

PHYSIOLOGICAL ANATOMY OF CARTILAGE.

487

quantity of a viscid liquid with one or more cells. They are analogous to the
lacunae 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 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 carti-
lages the cavities are not abundant but are rounded and quite large. The
cells contain generally a certain quantity of fatty matter. The appearance
of the ordinary articular cartilage is represented in Fig. 164.

The ordinary cartilages have neither blood-vessels, lymphatics nor nerves,
and are nourished by imbibition from the surrounding parts. In the develop-
ment of the body, the anatomy of the cartilaginous tissue possesses peculiar
importance, from the fact that the deposition of cartilage, with a few excep-
tions, precedes the formation of bone.

Fibro- Cartilage. — This variety of cartilage presents certain important
peculiarities in the structure of its fundamental substance. It exists in the
synchondroses, the cartilages of the ear and of the Eustachian tubes, the
interarticular disks, the intervertebral cartilages, the cartilages of Santorini
and of Wrisberg, and the epiglottis.

Fibro-cartilage is composed of true fibrous tissue with a great predomi-
nance of elastic fibres, fusiform, nucleated fibres, a certain number of adipose

FIG. 165.— Section of the cartilage of the ear of the human subject (Rollett).
a, flbro-cartilage ; &, connective tissue. In this preparation, the cartilage had been boiled and dried.

vesicles, cartilage-cells, blood-vessels and nerves (Sappey). The fibrous ele-
ments above mentioned take the place of the homogeneous fundamental sub-
stance 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

488

MOVEMENTS— VOICE AND SPEECH.

of the acts of walking, running, leaping, swimming etc. ; but it has been
thought better to omit these subjects, rather than to enter so minutely as

would be necessary into anatomical details
and to give elaborate descriptions of move-
ments that are simple and familiar.

VOICE AND SPEECH.

The principal organ concerned in the pro-
duction of the voice is the larynx. The ac-
cessory organs are the lungs, trachea, expi-
ratory muscles, the mouth and the 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 expiration.
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 it may assist, by resonance, in
modifying the quality of the voice. Most
of the variations in the tone and quality,
however, are effected by the action of the
larynx itself and of the parts situated above
the larynx.

Sketch of the Physiological Anatomy of
the Vocal Organs. — The vocal chords are
stretched across the superior opening of the
larynx from before backward. They consist

K^s'of^^ri^o^y of two pairs- The suPeri°r> cailed the false

vocal chords »r the ventricular bands, are not
concerned in the production of the voice.
They are less prominent than the inferior
chords, although they have nearly the same
direction. They are covered by a thin mu-
cous membrane, which is closely adherent to
the subjacent tissue. The chords themselves are composed of ordinary
fibrous tissue, with a few elastic fibres.

The true vocal chords, or vocal bands, 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 arytenoid 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 are much larger than the false vocal chords, and they contain a great
number of elastic fibres. Like the superior vocal chords, they are covered
with a very thin and closely adherent mucous membrane. The mucous
membrane over the borders of the chords is covered with flattened epithelium

19

FIG. 166. — Longiiuaiuai section of the
human larynx, showing the vocal
chords (Sappey).

1, ventricle of the larynx ; 2, superior
vocal chord ; 3, inferior vocal chord ;
4, arytenoid cartilage ; 5, sectiorj of
the arytenoid muscle ; 6, 6, inferior

,

the cricoid cartilage ; 8, section of
the anterior portion of the cricoid
cartilage ; 9, superior border of the
cricoid cartilage ; 10, section of the
thyroid cartilage ; 11, 11, superior
portion of the cavity of the larynx ;
12, 13, arytenoid gland ; 14, 16, epi-
glottis : 15, 17, adipose tissue ; 18,
section of the hyoid bone ; 19, 19, 20,
trachea.

MUSCLES OF THE LARYNX.

489

without cilia. There are no mucous glands in the membrane covering either
the superior or the inferior chords. The inferior vocal chords alone are con-
cerned in the production of the voice.

Muscles of the Larynx. — The muscles of the larynx are classified as ex-
trinsic 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 concerned 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 vocal chords 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 posteriorly,
present a movable articulation with the
cricoid cartilage ; and the cricoid, which
is narrow in front, and is wide behind,
where the arytenoid cartilages are attached,
presents a movable articulation with the
thyroid cartilage. It is evident, therefore,
that muscles acting upon the cricoid car-
tilage can cause it to swing upon its two
points of articulation with the inferior
cornua of 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 at-
tachments 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 certain 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 cartilages may be approximated to each other posteriorly, 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-arytenoid muscles.
The thyro-arytenoid muscles, the most complicated of all the intrinsic mus-
cles in their attachments and the direction of their fibres, are important in
regulating the tension and capacity of vibration of 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

FIG. 167 .—Posterior view of the muscles of
the larynx (Sappey).

1, posterior crico-arytenoid muscle ; 2, 3, 4,
different fasciculi of the arytenoid mus-
cle ; 5, aryteno-epiglottidean muscle.

4:90

MOVEMENTS— VOICE AND SPEECH.

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 move-
ments during inspiration.

The muscles mainly concerned in the
modifications of the voice by their action
upon 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 ac-
tion:

Crico-thyroid Muscles. — These muscles
are situated on the outside of the larynx, at
the anterior and lateral portions of the cri-
coid cartilage. Each muscle is of a triangu-
lar form, the base of the triangle presenting
posteriorly. It arises from the anterior and
lateral portions of the cricoid cartilage, and
its fibres diverge to be inserted into the in-
FIO. 168.— Lateral view of the muscles of ferior border of the thyroid cartilage, extend-

the larynx (Sappey). . J . c

i, body of the hyoid bone ; 2, vertical mg ±rom the middle of this border postenor-

, as far back as the inferior cornua. Lon-

roid muscle ; 4, facet of articulation
of the small cornu of the thyroid car-
tilage with the cricoid cartilage ; 5,
facet on the cricoid cartilage ; 6, su-
perior attachment of the crico-thy-
roid muscle ; 7, posterior crico-aryt-
enoid muscle ; 8, lateral crico-aryte-
noid muscle ; 9, thyro - arytenoid
muscle ; 10, arytenoid muscle ; 11,
aryteno - epiglottidean muscle ; 12,
middle thyro - hyoid ligament ; 13,
lateral thyro-hyoid ligament.

get, after dividing the nervous filaments dis-
tributed to these muscles, noted a certain de-
gree of hoarseness of the voice due to relaxa-
tion of the vocal chords; and by imitating
their action mechanically, he approximated
the cricoid and thyroid cartilages in front,
carried back the arytenoid cartilages and ren-
dered 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 the articulations of the arytenoid carti-
lage 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 in-
terior 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 the filaments of the recurrent laryn-
geal nerves, except those distributed to these muscles, and then stimulating
the nerves, Longet has shown that they act to approximate the vocal chords,
and that they constrict the glottis, particularly in its interligamentous por-
tion. "These muscles, with the arytenoid, act as constrictors of the larynx.

MOVEMENTS OF THE GLOTTIS DURING PHONATION. 491

Tkyro-arytenoid Muscles. — These 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 aryt-
enoid cartilages. Stimulation of the nervous filaments distributed to these
muscles renders the vocal chords tense. The great variations that may be
produced in the pitch and quality of the voice by the action of muscles oper-
ating -directly or indirectly upon the vocal chords render the problem of de-
termining the precise mode of action of the intrinsic muscles of the larynx
complicated and difficult. It is certain, however, that in these muscular
acts, the thyro-arytenoids play an important part. Their contraction regu-
lates the thickness of the vocal chords, while at the same time it modifies
their tension. The swelling of the chords, which may be rendered regular
and progressive under the influence of the will, is one of the most important
elements in the formation of the timbre of the voice.

Mechanism of the Production of the Voice. — If the glottis be examined
with the laryngoscope during ordinary respiration, the wide opening of the
chink during forced inspiration, due to the action of the posterior 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 so
soon as an effort is made to produce a vocal sound, the appearance of the
glottis undergoes a change, and it becomes modified in the most varied man-
ner with the different changes in pitch and intensity that the voice can be
made to assume. Although sounds may be produced, and even words may
be articulated, with the act of inspiration, true and normal phonation takes
place during expiration only. It is evident, also, that the inferior vocal
chords alone are concerned in this act.

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 notes ; but the patience and skill
of Manuel Garcia, a celebrated teacher of singing, enabled him to overcome
most of these difficulties, and to settle, by autolaryngoscopy, certain impor-
tant questions with regard to the action of the larynx in singing. It is for-
tunate that these observations were made by one versed theoretically and
practically in music and possessed of great control over the vocal organs.

Garcia, after having observed the respiratory movements of the larynx,
as they have just been briefly described, 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 for the passage of air

492 MOVEMENTS— VOICE AND SPEECH.

into the lungs but entirely inactive in expiration, has now become a musi-
cal instrument, presenting a slit with borders capable of accurate vibra-
tions.

The approximation of the posterior extremities of the vocal chords and
their tension by the action of certain of the intrinsic muscles are accom-
plished just before the vocal effort is actually
made. The glottis being thus prepared for the
emission of a particular sound, the expiratory
muscles force air through the larynx with the re-
quired power. The power of the voice is due
simply to the force of the expiratory act, which
is regulated chiefly by the antagonistic relations
of the diaphragm and the abdominal muscles.
From the fact that the diaphragm, as an inspira-

FIG 169 — Glottis seen with the torv muscle, is exactly opposed to the muscles

which have a tendency to push the abdominal
Bon)- organs, with the diaphragm over them, into the

1, 2, base of the tongue ; 3, 4, epi- ,,° . . , *, a; ' • • TJJL

glottis; 5, 6, pharynx ; 7. aryte- thoracic cavity and thus to diminish the pulmo-

noid cartilages ; 8, opening be- ., xl . -, .

tween the true vocal chords ; nary capacity, the expiratory and mspiratory acts

9, aryteno-epiglottidean folds ; i i i " n • -i ^ ^ , i V

10, cartilage of Santorini ; ii, may be balanced so nicely that the most delicate

cuneiform cartilage ; 12, supe- i -i , • i -, -, rrn n j.^.-

rior vocal chords ; 13, inferior vocal vibrations can be produced, ihe glottis,
thus closed as a preparation to a vocal act, pre-
sents a certain resistance 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 bands ; but aside from what is technically known as quality,
the pitch is dependent 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 illustrated by Garcia in the fol-
lowing, which relates to what is known as the chest-voice :

"If we emit veiled and feeble sounds, the larynx opens at the notes
i3 anc^ we see tne glottis agitated by large and loose vibra-

' ' tions throughout its entire extent. Its lips comprehended

in their length the 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—Q — — i
they finish by touching each other throughout their whole j^n- p^~1 |
extent ; but their summits are only solidly fixed one against *J •pr'?
the other at the notes . Q — . In some organs these summits are a

little vacillating when [^__p~ | _[ they form the posterior end of the glot-
tis, and two or three cJ S^- ^ half-tones which are formed show a cer-
tain want of purity and strength, which is very well known to singers. From

MOVEMENTS OF THE GLOTTIS DURING PHONATION. 493
the vibrations, having become rounder and purer, are accom-

I | I plished by the vocal ligaments alone, up to the end of the

^V- ^^ -WI^/T-I ci4-/-kt*

fj |«p*- ^ register.

" The glottis at this 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 others who have applied the laryngoscope to the study of the
voice in singing.

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 mus-
cles are more feeble ; but the quality of the vocal sounds at this period of
life is peculiarly penetrating. While there are certain characters that dis-
tinguish the voices of boys before the age of puberty, they present, as in
the female, the different qualities of the soprano and contralto. After the
age of puberty, the female voice does not commonly undergo any very
marked change, except in the development of additional strength and in-
creased 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. This change does not usually take
place if castration be performed in early life ; and this operation was fre-
quently resorted to in the seventeenth century, for the purpose of preserving
the qualities of the male 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 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.. 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. The
different voices in the male are the bass, the tenor, and an intermediate voice
called the barytone. The female voices are the contralto, the soprano, and
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 do not possess the same quality as the
corresponding notes of the tenor. The same remarks apply to the contralto
and soprano.

The following scale (Landois) gives the ordinary ranges of the different
kinds of voice; but it must be remembered that there are individual in-
stances in which these limits are exceeded :

494:

MOVEMENTS— VOICE AND SPEECH.

256

Soprano.

1024

171

Contralto. 684 ^

EFGrAB cdefgab

c'd'e'f'g'a'b

'•T t

~~~

0 I

f

1 1

/ i

m

K5 J

vsy i J

1

J i f

1

c" d" e" f" g/x a/7 b"

c'"

80 Bass.

342

128

Tenor.

512

The accompanying figures indicate the number of vibrations per second in the corresponding tone. It
is evident that from c' to /' is common to all voices ; nevertheless, they have a different timbre.
The lowest note or tone, which, however, is only occasionally sung by bass singers, is the contra-F,
with 42 vibrations ; the highest note of the soprano voice is a"', with 1,708 vibrations (Landois and
Stirling).

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 conforma-
tion 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 practice,
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 surprisingly natural manner.

Action of the Intrinsic Muscles of the Larynx in Phonation. — In the
production of low chest-notes, in which the vocal chords are elongated and
are at the minimum 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 ligaments. It will be remembered
that the crico-thyroids, by approximating the cricoid and thyroid cartilages
in front, increase the distance between the arytenoid cartilages and the an-
terior attachment of the vocal chords.

As the notes produced by the larynx become higher in pitch, the pos-
terior attachments of the chords are approximated, and at this time the lat-
eral crico-arytenoids are probably brought into vigorous action.

The uses of the thyro-arytenoids are more complex ; and it is probably in
great part by the action of these muscles that the varied and delicate modi-
fications in the rigidity of the vocal chords are produced.

The differences in singers as regards the purity of their notes are due in
part to the accuracy with which some put the vocal chords upon the stretch ;
while in those in whom the voice is of inferior quality, the action of the
muscles is more or less vacillating and the tension is frequently incorrect.

ACTION OF ACCESSORY VOCAL ORGANS. 495

The fact that some 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 mathematical equality of the
sonorous vibrations and the comparative absence of discordant waves.

Action of Accessory Vocal Organs. — A correct use of the accessory organs
of the voice is of great importance in singing ; but the action of these parts
is simple and does not require a very extended description. The human
vocal organs, indeed, consist of a vibrating instrument, the larynx, and of
certain tubes and cavities by which the sound is re-enforced and modified.

The trachea serves, not only to conduct air to the larynx, but to re-enforce
the sound to a certain extent by the vibrations of the column of air in its
interior. When a powerful vocal effort is made, it is easy to feel, with the
finger upon the trachea, that the contained air is thrown into vibration.

The capacity of the cavity of the larynx 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 di-
ameter may be reduced by the action of the inferior constrictors of the
pharynx upon the sides of the thyroid cartilage.

The epiglottis, the superior vocal chords and the ventricles are by no
means indispensable to the production of vocal sounds. In the emission of
high notes the epiglottis is somewhat depressed, and the superior chords are
brought nearer together ; but this affects the form of the resonant cavity only
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 action is not absolutely necessary or even very important, as
has been shown in experiments of excising the part in living animals.

The most important modifications of the laryngeal sounds are produced
by the resonance of air in the pharynx, mouth and nasal fossae. This reso-
nance 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 the opening into the
mouth is closed, and all of the cavities resound. As the notes are raised in
pitch, the isthmus contracts, the part immediately 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
re-enforced entirely by the pharynx and mouth. At the same time the
tongue — a very important organ to singers, particularly in the production
of high notes — is drawn backward. The point being curved downward, its
base projects upward posteriorly and assists in diminishing the capacity of
the bucco-pharyngeal cavity. In the changes which the pharynx thus under-

496 MOVEMENTS— VOICE AND SPEECH.

goes 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, a
singer changes into what is sometimes called the head-voice (falsetto), the
velum palati is drawn forward instead of backward, and the resonance takes
place chiefly in the naso-pharyngeal cavity.

Laryngeal Mechanism of the Vocal Registers. — One difficulty at the very
beginning of a discussion of this subject is in fixing upon clear definitions of
what are to be recognized as different vocal registers. In the first place it
must be understood that the singing voice is very different from the speaking
voice. Without being actually so far discordant as to offend a musical ear, the
ordinary voice in speaking never has what may strictly be called a musical
quality, while the perfect singing voice produces true musical notes. This is
probably due to the fact that the inflections of the voice in speaking are not
in the form of distinct musical intervals, that the vibrations follow each
other and are superimposed in an irregular manner, and that no special effort
is made to put the vocal chords upon any definite tension, unless to meet a
more powerful expiratory effort when the voice is increased in force. A
shout or a scream is entirely different from a powerful, singing note. This
difference is at once apparent in contrasting recitative with ordinary dialogue
in operatic performances.

The divisions of the voice into registers, made by physiologists, are some-
times based upon theories with regard to the manner of their production ;
and if these theories be not correct, the division into registers must be equally
faulty. Again, there are such marked differences between male and female
voices, that it does not seem possible to apply the same divisions to both sexes.
There is no difficulty, however, in recognizing the qualities of voice, called bass,
barytone and tenor, in the male, or contralto, mezzo and soprano, in the
female. A division of the voice into registers should . be one easily recog-
nizable by singers and singing teachers ; and this must be different for male
and female voices. If a division were made such as would be universally
recognized by the ear, irrespective of theories, it would remain only to as-
certain as nearly as possible the exact vocal mechanism of each regis-
ter. It must be remembered that the voice of a perfect singer shows no
recognizable break, or line of division between the vocal registers, except
when a difference is made apparent in order to produce certain legitimate
musical effects. One great end sought to be attained in training the voice
in singing is to make the voice as nearly as possible uniform throughout the
extent of its range ; and this has been measurably accomplished in certain
singers.

Judging of different registers entirely by the effect produced upon the ear,
both by cultivated and uncultivated singers, the following seem to be the
natural divisions of the male voice :

1. The chest-register. This is the register commonly used in speaking.
Though usually called the chest-voice, it has, of course, no connection with
any special action of the chest, except, perhaps, with reverberation of air in

MECHANISM OF THE VOCAL REGISTERS. 497

the trachea and the larger bronchial tubes. This register is sensibly the same
in the male and in the female.

2. The head-register. In cultivated male voices, a quality is often produced,
probably by diminished power of the voice, with some modification in the
form and capacity of the resonant cavities, which is recognized as a " head-
voice," by those who do not regard the head-register as equivalent to the
falsetto.

3. The falsetto-register. By the use of this register, the male may imitate
the voice of the female. Its quality is different from that of the chest-voice,
and the transition from the chest to falsetto usually is abrupt and quite
marked. It may be called an unnatural voice in the male ; still, by very
careful cultivation, the transition may be made almost imperceptibly. The
falsetto never has the power and resonance of the full chest-voice. It
resembles the head-voice, but every good singer can recognize the fact that
he employs a different mechanism in its production.

Applying an analogous method of analysis to the female voice, the
natural registers seems to be the following :

1. The chest-register. This register is the same in the female as in the
male.

2. The lower medium register, generally called the medium. This is the
register commonly used by the female in speaking.

3. The upper medium register. This is sometimes called the head-regis-
ter and is thought by some to be produced by precisely the same mechanism
as the falsetto-register in the male. It has, however, a vibrant quality, is full
and powerful, and is not an unnatural voice like the male falsetto.

4. The true head-register. This is the pure tone, without vibrant qual-
ity, which seems analogous to the male falsetto.

Vocal Registers in the Male. — According to the division and definitions
just given of the vocal registers, in the male voice there is but one register,
extending from the lowest note of the bass to the
falsetto, and this is the chest-register. In the low
notes, the vocal chords vibrate, and the arytenoid
cartilages participate in this vibration to a greater
or less extent. In the low notes, also, the larynx
is open ; that is, the arytenoid cartilages do not
touch each other. As the notes are raised in pitch,
the arytenoid cartilages are approximated more
and more closely, and they touch each other in the

highest notes, the vocal chords vibrating alone. ffijS?~WtCe' after Mandl
It is probable that the degree of approximation
of the arytenoid cartilages is different in different singers, and that the part
of the musical scale at which they actually touch is not invariable. This
appears to be the case in the observations made by Mills.

What has been called, in this classification, the head-register of the male,
is not a full, round voice, but the notes are more or less sotto voce. This
peculiar quality of voice does not seem to have been made the subject of

498

MOVEMENTS— VOICE AND SPEECH.

laryngoscopic investigation. It has a vibrant character, which is undoubtedly
modified by peculiar action of the resonant cavities, which latter has not been
described. It is not probable that its mechanism differs essentially, as re-
gards the action of the glottis, from that of the full chest-register, shown in
Fig. 170.

The falsetto-register in the male undoubtedly involves such a division of
the length of the vocal chords that only a portion is thrown into vibration.
There is always an approximation of the chords in their posterior portion,
and sometimes also in their anterior portion. This is illustrated in Fig. 171.
I II

FIG. 171. — Appearances of the vocal chords in the production of the falsetto-voice (Mills).
I. The larynx during falsetto-production ; after Mandl.

II. The larynx during the emission of falsetto-tones ; middle range ; after Holmes.
III. The larynx of the female during the production of head-tones, as seen by the author (Mills).

The mechanism by which the vocal chords are approximated in portions
of their length has not been satisfactorily explained ; but laryngoscopic ex-
aminations leave no doubt of the fact of such action. The extent of this
shortening of the chords must vary in different persons and in the same per-
son, probably, in the production of falsetto-notes of different pitch. Accord-
ing to Mrs. Seiler, the shortening is due to the action of a muscular bundle,
called the internal thyro-arytenoid, upon little cartilages extending forward
from the arytenoid cartilage, in the substance of the vocal chords, as far as
the middle of the glottis ; but dissections made by Mills failed to confirm
this view.

Some singers, especially tenors, have been able by long practice to pass
from the chest to the falsetto so skillfully that the transition is scarcely ap-
parent, but the falsetto is devoid of what is called vibrant quality.

Vocal Registers in the Female. — There is absolutely no difference between
the vocal mechanism of the chest-voice in the sexes. In the best methods of
teaching singing, one important object is to smooth the transition from the
chest-voice to the lower medium. The full chest-notes, especially in con-
traltos, closely resemble the corresponding notes of the tenor.

According to the laryngoscopic observations of Mills, the mechanism of
the lower medium and upper medium in females does not radically differ
from the mechanism of the chest-voice. In these registers, the arytenoid
cartilages become more and more closely approximated to each other as the
voice ascends in the scale until, in the higher notes, they probably are firmly

MECHANISM OF THE VOCAL REGISTERS. 499

in apposition. It is probable that the vocal chords alone vibrate in the lower
and upper medium, while the apophyses of the arytenoid cartilages partici-
pate in the vibrations in the female chest-voice.

The vocal chords are much shorter in the female than in the male. Ac-
cording to Sappey, the average length in the male is about -J of an inch (22
mm.) and in the female, about £ of an inch (17 mm.). If the chords alone
vibrate, without the apophyses of the arytenoid cartilages, the difference in
length would account for the differences in pitch of the voice in the sexes.
The tenor can not sing above the chest-range of the female voice without
passing into the falsetto, to produce which he must actually shorten his vocal
chords so that they are as short or shorter than the vocal chords of the female.
This is shown by the scale of range of the different voices compared with
the length of the vocal chords ; and this idea is sustained still farther by a
comparison of "the larynx during falsetto production" (Fig. 171,1). In
the male falsetto, produced by this shortening of the vocal chords, the more
nearly the resonant cavities are made to resemble, in form and capacity, the
corresponding cavities in the female, the more closely will the quality of the
female voice be imitated. It is probable that the vocal bands in the female
present a thinner and narrower vibrating edge than the chords in the male,
although there are no exact anatomical observations on this point. This
would account for the clear quality of the upper registers of the female
voice as compared with the male voice or with the female chest-register.
Analogous differences exist in reed-instruments, such as the clarinet and the
bassoon. This comparison of the female upper registers with the male
falsetto does not necessarily imply a similarity in the mechanism of their
production, as is assumed by some writers. The vocal chords, in the female
lower and upper medium, vibrate in their entire length ; in the male falsetto,
the chords are artificially shortened so that they are approximated in length
to the length of the chords in the female.

To reduce to brief statements the views just expressed, based partly upon
laryngoscopic examinations — that are far from complete — by a number of
competent observers, the following may be given as the mechanism of the
vocal registers in the female, taking no account of the changes in form and
capacity of the resonant cavities :

1. The chest-voice is produced by " large and loose vibrations " (Garcia)
of the entire length of the vocal chords, in which the apophyses of the aryt-
enoid cartilages participate to a greater or less extent, these cartilages not
being in close apposition.

2. In passing to the lower medium, the arytenoid cartilages probably are
not closely approximated, but they do not vibrate, the vocal chords alone
acting.

3. In passing to the upper medium, the arytenoid cartilages probably are
closely approximated, and the vocal chords alone vibrate, but they vibrate in
their entire length.

4. The head-register, which may be called the female falsetto, bears the
same relation to the lower registers in both sexes. The notes are clear hut

500 MOVEMENTS— VOICE AND SPEECH.

deficient in vibrant quality. They are higher in the female than in the
male because the vocal chords are shorter. Laryngoscopic observations dem-
onstrating this fact in the female are as accurate and definite as in the male.
(See Fig. 171.)

The reasons why the range of the different vocal registers is limited are
the following : Within the limits of each register, the tension of the vocal
chords has an exact relation to the pitch of the sound produced. This tension
is of course restricted by the limits of power of the muscles acting upon the
vocal chords, for high notes, and by the limit of possible regular vibration of
chords of a certain length, for low notes. The higher the tension and the
greater the rigidity of the chords, the greater is the force of air required to
throw them into vibration ; and this, also, has, of course, certain limits. It
is never desirable to push any of the lower registers in female voices to their
highest limits. All competent singing teachers recognize this fact. The
female chest-register may be made to meet the upper medium, particularly
in contraltos ; but the singer then has practically two voices, a condition
which is musically intolerable. In blending the different registers so as to
make a perfectly uniform, single voice, the arytenoid vibrations should be
rendered progressively and evenly less and less prominent, until they imper-
ceptibly cease when the lower medium is fully reached ; the arytenoid car-
tilages should then be progressively and evenly approximated to each other,
until they are firmly in contact and the upper medium is fully reached.
The female vocal apparatus is then perfect. AVhile single notes of the
chest, lower medium and upper medium, contrasted with each other, have
different qualities, the voice is even throughout its entire range, and the
proper shading called for in musical compositions can be made in any part of
the scale. The blending of the male chest-register into the falsetto and of the
upper medium into the female falsetto, or true head- voice, is more difficult,
but it is not impossible. Theoretically, this must be done by shortening the
vocal chords gradually and progressively and not abruptly, unless the latter
be required to produce a legitimate effect of contrast.

Even in singing identical notes, there are distinctly recognizable differ-
ences in quality between the bass, barytone and tenor, and between the con-
tralto, mezzo and soprano. For the female, these may be compared to the
differences in identical notes played on different strings of the violin. For
the male, they may be compared to the qualities of the different strings of
the violoncello. Falsetto-notes may be compared to harmonics produced on
these instruments.

These ideas with regard to the mechanism of the different vocal registers
have resulted from a study of these registers, first from an aesthetic point of
view ; endeavoring then to. find explanations of different qualities of sound
appreciated by the ear, in laryngoscopic and other scientific observations, and
not by reasoning from scientific observations, as to what effects upon the ear
should be produced by certain acts performed by the vocal organs. It ma}
be stated, in this connection, that the works of Bach, Beethoven and other
old masters were composed, exactly in accordance with purely physical laws,

MECHANISM OF SPEECH. 501

long before these laws were ascertained and defined, as has lately been done,
particularly by Helmholtz.

MECHAKISM OF SPEECH.

Articulate language consists in a conventional series of sounds made for
the purpose of conveying certain ideas. There being no universal language, it
will be necessary to confine the description of speech to 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 ad-
vanced, certain differences in the accuracy and elegance with which ideas are
expressed have become associated with the degree of development and culti-
vation of the intellectual faculties. Philologists have long since established
a certain standard — varying, to some extent, it is true, with usage and the ad-
vance of knowledge, but still sufficiently definite — by which the correctness
of modes of expression is measured. It is not proposed to discuss the science
of language, or to consider, in this connection at least, the peculiar mental
operations concerned in the expression of ideas, but to take the language as
it exists, and to describe briefly the mechanism of the production of the
most important articulate sounds.

Almost every language is imperfect, as far as an exact correspondence be-
tween its sounds and written characters is concerned. The English language
is full of incongruities in spelling, such as silent letters and arbitrary and
unmeaning variations in pronunciation ; but these do not belong to the sub-
ject 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, «, e, i, 0, «, can all be sounded
alone and may be prolonged in expiration. These are the sounds chiefly em-
ployed in singing. The differences in their characters are produced by changes
in the position of the tongue, mouth and lips. The vowel-sounds are neces-
sary to the formation of a syllable, and although they generally are 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
qualities, the chief differences being as they are made long or short. In addi-
tion to the modifications 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 diph-
thongs, as 0?, in voice, the two vowels are sounded. In the improper diph-
thongs, as ea, in heat, and in the Latin diphthongs, as ce, in Caesar, 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 conso-
nant ; but in other positions it is pronounced as e or i.

An important question relates to the differences in the quality of the dif-
ferent vowel-sounds when pronounced with equal pitch and intensity. The

502 MOVEMENTS- VOICE AND SPEECH.

cause of these differences was studied very closely in the latter part of the
last century, but it has lately been rendered clear by the researches of Helm-
holtz and of Koenig. In this connection it will be sufficient to indicate the'
results of the modern investigations very briefly. It will be seen in studying
the physics of sound in connection with the sense of hearing, that nearly all
sounds, even when produced by a single, vibrating body, are compound. Helm-
holtz, by means of his resonators, has succeeded in analyzing the apparently
simple sounds into different component parts, and he has shown that the qual-
ity of such sounds may be modified by re-enforcing certain of the overtones, as
they are called, such as the third, fifth or octave. For those who are famil-
iar with the physics of sound, the explanation of the mechanism of the pro-
duction of vowel-sounds will be readily comprehensible. The reader is re-
ferred, however, to the remarks upon overtones in another part of this work,
under the head of audition, for a more thorough exposition of this subject.
The different vowel-sounds may be emitted 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 ascer-
tained experimentally that the overtones in each instance are different, as they
are re-enforced by the vibrations of air in the accessory vocal organs, in some
instances the third, in others, the fifth etc., being increased in intensity.
This can hardly be better illustrated than by the following quotation from
Tyndall, in which modern researches have been applied to the vowel-sounds
of the English language :

" For the production of the sound U (oo 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 re-enforced, 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 fun-
damental 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 com-
paratively strong, the third very feeble, but the fourth, which is characteris-
tic of this vowel, must be intense. A moderate fifth tone may be added.
No 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 I the higher overtones come princi-

MECHANISM OF SPEECH. 503

pally into play ; the second tone may be entirely neglected ; the third ren-
dered very 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, produc-
ing innumerable composite colors by their admixture. Out of violet and red
we produce purple, and out of yellow and blue we produce white. Thus 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 com-
bining 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 J,
d, Jc, p, t, and c and g hard. Their office in the formation of syllables is suf-
ficiently apparent.

The consonants known as semi- vowels are /, Z, 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 /*, from the facility with
which they flow into other sounds, are called liquids. Orthoepists have far-
ther divided the consonants with reference to the mechanism of their pronun-
ciation : d,j, s, #, 2, and g soft, being pronounced with the tongue against the
teeth, are called dentals ; d, g, /, k, /, n, and q are called palatals ; Z>, p, /, v
and m are called labials ; m, n and ng are called nasals ; and &, g, and c and
g hard are called gutturals. After the description already 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. All are acquainted
with the modifications in articulation in persons in whom the nasal cavi-
ties resound unnaturally from imperfection of the palate ; and the slight
peculiarities observed after loss of the teeth and in harelip 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 pro-
nunciation in different persons and the difficulty of acquiring foreign lan-
guages after the habits of speech have been formed show that the organs of
articulation must perform their office with great accuracy, their movements
are simple, and they vary with the peculiarities of different languages.

Whispering. — Articulate sounds may be produced by the action of the res-
onant cavities, the lips, teeth and tongue, in which the larynx takes no part

504 MOVEMENTS— VOICE AND SPEECH.

This action occurs in whispering and it can not properly be called vocal. It
is difficult to make any considerable variations in the pitch of a whisper, and
articulation in this way may be produced in inspiration as well as in expira-
tion, although the act in expiration is more natural and easy. The character
of a whisper may be readily distinguished from that of the faintest audible
sound involving vibration of the vocal chords. In aphonia from simple pa-
ralysis of the vocal muscles of the larynx, patients can articulate distinctly in
whispering; but in cases of chronic bulbar paralysis (glosso-labio-laryngeal
paralysis), speech is entirely lost.

The Phonograph. — In 1877, a remarkable invention was made in this
country, by Mr. Thomas A. Edison, which possesses considerable physiologi-
cal importance. Mr. Edison constructed a very simple instrument, called the
phonograph, which will repeat, with a certain degree of accuracy, the pecul-
iar characters of the human voice both in speaking and singing, as well as the
pitch and quality of musical instruments. This demonstrates conclusively
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 instrument : It consists of a cylinder of iron provided with very fine,
shallow grooves in the form of an exceedingly close spiral. Upon the 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 vi-
brating plate is connected with a mouth-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 vi-
brations 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 indenta-
tions 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 dis-
tinctness. The improvements that have lately been made in the phonograph
do not involve any modifications in the principles of its construction.

DIVISIONS AND STRUCTURE OF THE NERVOUS TISSUE. 505

CHAPTER XVI.

PHYSIOLOGICAL DIVISIONS, STRUCTURE AND GENERAL PROPERTIES OF
THE NERVOUS SYSTEM.

Divisions and structure 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-
Termination of the nerves in the muscular tissue— Termination of the nerves in glands— Modes of
termination of the sensory nerves — Corpuscles of Vater, or of Pacini— Tactile corpuscles — End-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 —
Degeneration and regeneration of the nerves — Motor and sensory nerves — Mode of action of the motor
nerves — Associated movements — Mode of action of the sensory nerves — Physiological differences be-
tween motor and sensory nerve-fibres — Nervous excitability — Different means employed for exciting
the nerves— Rapidity of nervous conduction— Personal equation— Action of electricity upon the nerves
— Law of contraction— Induced muscular contraction — Electrotonus, anelectrotonus and catelectrotonus
— Negative variation.

THE nervous system is anatomically and physiologically distinct from all
other systems 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 their actions; but its physiological properties
are inherent, and it gives to no tissue or organ its special excitability or the
power of performing its particular office in the economy. The nervous sys-
tem connects into a co-ordinated organism all parts of the body. It is the
medium through which all impressions are received. It animates or regu-
lates all movements, voluntary and involuntary. It regulates secretion,
nutrition, calorification and all the processes of organic life.

In addition to its action as a medium of conduction and communication,
the nervous 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 co-ordination of different parts
of the organism without nerves, there can be no unconscious reception of
impressions giving rise to involuntary movements, no appreciation of impres-
sions, general, as in ordinary sensation, or special, as in sight, smell, taste
or hearing, no instinct, volition, thought or even knowledge of existence,
without nerve-centres.

DIVISIONS AND STRUCTURE OF THE NERVOUS TISSUE.

The nervous tissue presents two great divisions, each with distinct ana-
tomical as well as physiological differences. One of these divisions is com-
posed 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 composed of cells, and this kind of nervous matter, while it may
act as a conductor, is capable of generating the so-called nerve-force.

The nerve-fibres and cells are also 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 functions of relation, or of animal life. The centres pre-

506 NERVOUS SYSTEM.

side over general sensation, the special senses, voluntary and some involun-
tary movements, intellection, and, in short, all of the functions that charac-
terize the animal. The nerves serve as the conductors of impressions known
as general or special sensations and of the stimulus that gives rise to volun-
tary and certain involuntary movements, the latter being the automatic
movements connected with animal life.

2. The sympathetic, or organic system. This system is specially con-
nected 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 system 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 move-
ments and ordinary sensation, and centres capable of receiving impressions
connected with the special senses, such as sight, audition, olfaction and gusta-
tion. The nerves which receive these special impressions and convey them
to the appropriate centres are more or less insensible to ordinary impressions.
The organs to which these special nerves are distributed are generally of a
complex and peculiar structure, and they present accessory parts which are
important and essential in the transmission of the special impressions to the
terminal branches of the nerves.

The physiological division of the nervous system into nerves and nerve-
centres is 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 cells of the nerve-centres, while they may transmit impressions and
impulses, are the only parts capable, under any circumstances, of generating
the nerve-force ; and as a rule, they do not receive impressions in any other
way than through the nerve-fibres. There are, however, many exceptions
to this rule, as in the case of movements following direct stimulation of the
sympathetic ganglia and certain centres in the brain and spinal cord ; but
the cells of many of the ganglia belonging to the cerebro-spinal axis are
insensible to direct stimulation and can receive only 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 filaments conducting these to the muscles and
the sensory filaments conveying the impressions 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 conveyed to them by sensory nerves and conduct to the
motor nerves the stimulus generated by nerve-cells.

In the most natural classification of the nerve-fibres, they are divided intc

STRUCTUKE OF THE NERVOUS TISSUE. 507

two groups ; one embracing those fibres which have the conducting element
alone, and the other presenting this anatomical element surrounded by cer-
tain 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 i j the nerve-centres, they lose one or another of their coverings,
These two varieties are designated as medullated and non-medullated fibres.

Medullated Nerve-fibres. — These fibres are so called because, in addition
to the axis-cylinder, or conducting element, they contain, enclosed in a tubu-
lar sheath, a soft substance called medulla. This substance is strongly re-
fractive and gives the nerves a peculiar appearance under the microscope,
from which they are sometimes called dark-bordered nerve-fibres. As the
whole substance of the fibre is enclosed in a tubular membrane, these are fre-
quently called nerve-tubes.

If the nerves be examined while perfectly fresh and unchanged, their ana-
tomical elements appear in the form of simple fibres with strongly accentu-
ated borders. The diameter of these fibres is ^W *° i Ao ot an incn (10 to
15 /A). In a very short time the borders become darker and the fibres assume
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, the neurilemma, is a somewhat
elastic, homogeneous membrane, never striated or fibrillated, and generally
presenting oval nuclei with their long diameter in the direction of the tube.
This is sometimes called the sheath of Schwann. In its chemical and gen-
eral 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,
and the trunk of the auditory nerve. It possibly exists in the non-medullated
fibres, although its presence here has never been satisfactorily demonstrated.

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 ori-
gin of the nerves in the gray substance of the nerve-centres or at the periph-
eral 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
altered by desiccation, the action of water, acetic acid and various other
reagents, it coagulates into an opaque, granular mass. In the white sub-
stance of the encephalon and spinal cord, the neurilemma is wanting and
the fibres present only the axis-cylinder surrounded with the white substance
of Schwann. As a post-mortem condition, these fibres present, under the
microscope, varicosities at irregular intervals, which give them a peculiar
and characteristic appearance.

The medullated nerve-fibres do not have regular outlines, but present con-

508

NERVOUS SYSTEM.

strictions at various points in their length, called the constrictions or nodes
of Eanvier. At these nodes the medullary substance is wanting and the

neurilemma is in contact with the axis-
cylinder. It is at these points that the
transverse lines of Fromann, produced by
the action of silver nitrate upon the axis-
cylinder, are particularly prominent.

When a medullated nerve - fibre is
slightly stretched, a number of oblique
cuts are observed running across the fibre
and extending to the axis-cylinder, called
incisures. These involve the medullary
substance only, and are best observed when
this substance has been stained with os-
mic acid. It is not known that they pos-
sess any physiological importance.

The axis-cylinder, which occupies one-
FIG. m.-Nerve-fibres from the human sub- fifth to one-f ourth of the diameter of the

ject; magnified 350 diameters (Kolliker). nerve-tube, is probably the Conducting
Four small fibres of which two are varicose, J

one medium-sized fibre with borders of portion of the nerve. In the ordinary

single contour, and four large fibres. Of r J

the latter, two have a double contour, and medullated fibres, the axis-cylinder can

two contain granular matter. . , , . .

not be seen in the natural condition, be-
cause it refracts in the same manner as the medullary substance; and it
can not easily 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 retract, leaving the axis-cylinder, which
latter 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 intervals. It is somewhat granular and very finely
striated in a longitudinal direction. This band is elastic but not very resist-
ing. What serves to distinguish it from all other portions of the nerve-fibre
is its insolubility in most of the reagents employed in anatomical investiga-
tions. It is slightly swollen by acetic acid but is dissolved after prolonged
boiling. If nerve-tissue be treated with a solution of carmine, the axis-cyl-
inder only is colored. It has been observed that the nerve-fibres treated with
silver nitrate present in the axis-cylinder well marked, transverse striations
(Fromann) ; and some anatomists regard both the nerve-cells and the axes
of the fibres as composed of two substances, the limits of which are marked
by the regular striae thus developed. This, however, is a point of purely
anatomical interest. The presence of regular and well marked striae in the
axis-cylinder after the addition of a solution of silver nitrate and the action
of light can not be doubted ; but it has not yet been determined whether
these markings be entirely artificial or whether the axis-cylinder be really
composed of two kinds of substance.

For some time it has been known that the axis-cylinders in the organs of
special sense, in the final distribution of sensory nerves and in some other

STRUCTURE OF THE NERVOUS TISSUE.

509

(Ranvier).
A. Intercostal nerve of the mouse, treated with sil-

B. Nerve-fibre from the sciatic nerve of a full-grown
rabbit. A, node of Ranvier ; M, medullary sub-
stance rendered transparent by the action of
glycerine ; CY, axis-cylinder presenting the lines
of Fromann, which are very distinct near the
node. The lines are less marked at a distance
from the node.

situations, break up into fibrillae. A
fibrillated appearance, indeed, is often
observed in nerves in their course, and
it is now the general opinion that the
axis-cylinders are composed of fibrillae ~
held closely together by connective
substance. This fibrillated structure
of the nerves is quite prominent in
some of the lower orders of animals.

The various appearances which
the nerve-fibres present under differ-
ent conditions are represented in
Figs. 172 and 173.

Non-nwdullated Nerve - Fibres. —
These fibres, which are largely dis-
tributed in the nerVOUS System, ap- FlG. m.-Nodes of Ranvier and lines of Fromann

pear to be simple prolongations,

without alteration, of the axis-cylin- ver nitrate.

ders of the medullated fibres. They

are found chiefly in the peripheral

terminations of the nerves and in the

filaments of origin of the fibres from

the nerve-cells. Some anatomists think that they have a
delicate investing membrane, but this has not been satis-
factorily demonstrated.

Gelatinous Nerve -Fibres (Fibres of Remak). — There
has been some difference of opinion with regard to the
physiology of the so-called gelatinous nerve-fibres. Some
anatomists have regarded them simply as elements of con-
nective tissue, and others have described them as axis-cyl-
inders surrounded with a nucleated sheath ; but the fibres
do not present the lines of Fromann when treated with sil-
ver nitrate. While elements of connective tissue may have
been mistaken for true nerve-fibres, there are in the nerves,
particularly in those belonging to the sympathetic system,
fibres resembling the nerve-fibres of the embryon. These
are the true, gelatinous nerve-fibres, or fibres of Remak-
All the nerves have this structure until about the fifth
month of intraiiterine life, and in the regeneration of
nerves after division or injury, the new elements usually
assume this form before they arrive at their full develop^

FIG. 174. — Fibres of rn pr) t
Remak ; magnified L

300 diameters (Rob- The true, gelatinous nerve-fibres present the following

With the gelatinous characters : They are flattened, with regular and sharp bor-

seeiTtwo oTthe^ ders, grayish, pale and always fibrillated, with very fine

derednerdver-fibresr" granulations, and a number of oval, longitudinal nuclei, a

34

510 NERVOUS SYSTEM.

characteristic which has given them the name of nucleated nerve-fibres.
The diameter of the fibres is about Tr^ulr of an inch (3 /*). The nuclei have
nearly the same diameter as the fibres and are about -^^ of an inch (20 /A)
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 connect-
ive tissue. They are found chiefly in the sympathetic system and in that
particular portion of this system connected with involuntary movements.
They are not usually found in the white filaments of the sympathetic.

Accessory Anatomical Elements of tlie Nerves. — The nerves present, in
addition to the different varieties of true nerve-fibres just described, certain
accessory anatomical elements common to nearly all of the tissues of the
organism, such as connective tissue, blood-vessels and lymphatics.

Like the muscular tissue, the nerves are made up of their true anatomical
elements — the nerve-fibres — held together into primitive, secondary and terti-
ary bundles, and so on, in proportion to the size of the nerve. The primitive
fasciculi are surrounded with a delicate membrane, described by Robin, under
the name of perinevre, but which had been already noted by other anatomists,
under different names, and is now frequently called the sheath of Henle.
This membrane is homogeneous or very finely granular, sometimes marked
with longitudinal striae, and possessing elongated, granular nuclei. Accord-
ing to Ranvier, there are three kinds of nuclei either attached to or situated
near the sheath. These are (1) nuclei attached to the inner surface of the
sheath ; (2) nuclei belonging to the nerve-fibres within the sheath ; and (3)
nuclei of connective-tissue elements near the sheath. Treated with silver
nitrate, the sheath presents the borders of a lining endothelium. The sheath
of Henle begins 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 mem-
brane generally envelops a primitive fasciculus of fibres, branching as the bun-
dles divide and pass from one trunk to another, and is sometimes found
surrounding single fibres. It usually is not penetrated by blood-vessels, the
smallest capillaries of the nerves ramifying in its substance but seldom pass-
ing through to the individual nerve-fibres. Within the sheath of Henle are
sometimes found elements of connective tissue, with very rarely a few capil-
lary blood-vessels in the largest fasciculi.

The quantity of fibrous tissue in the different nerves- is very variable and
depends upon the conditions to which they are subjected. In the nerves
within the bony cavities, where they are entirely protected, the fibrous tissue
is very scanty ; but in the nerves between muscles, there is a tolerably strong
investing membrane or sheath surrounding the whole nerve and sending into
its interior processes which envelop smaller bundles of fibres. This sheath
is formed of ordinary fibrous tissue, with small elastic fibres and nucleated
connective-tissue cells. These latter may be distinguished from the gelati-
nous nerve-fibres by the action of acetic acid, which swells and finally dissolves
them, while the nerve-fibres are but slightly affected.

TERMINATIONS OF THE MOTOR NERVES.

511

The greatest part of the fibrous sheath of the nerves is composed of bun-
dles of white inelastic tissue, interlacing in every direction ; but it contains
also many elastic fibres, adipose tissue, a net- work of arteries and veins, and
" nervi nervorum," which are to these structures what the vasa vasorum are
to the blood-vessels. The adipose tissue is constant, being found even in ex-
tremely emaciated persons (Sappey).

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, longi-
tudinal meshes surrounding the fasciculi of fibres ; but they rarely penetrate
the sheath of Henle, and they do not usually come in contact with the ulti-
mate nervous elements. The veins are rather more voluminous and follow
the arrangement of the arteries. Lymph-spaces, lined by delicate endothe-
lium, are found in the connective-tissue sheaths of the bundles of fibres.

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 in-
osculation. 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 themselves maintaining
throughout their course their individual physiological properties. The
nerve-fibres do n9t branch or inosculate except near their termination. When
there is branching of medullated fibres, it is always at the site of one of the
nodes of Ranvier. The branching
and inosculation of the ultimate
nerve-fibres will be fully described
in connection with their final dis-
tribution to muscles and sensitive
parts.

Termination of Nerves in Vol-
untary Muscles. — The mode of L.
termination of motor nerves in
voluntary muscles was indicated
by Doyere, in 1840, was quite fully
described by Rouget, in 1862, and
has since been studied by anato- FlG
mists, who have extended and
elaborated these researches. It is
the general opinion that but one
nerve-ending exists in each mus-

175.— Mode of termination of the motor nervzs

(Rouget).

A, primitive fasciculus of the thyro-hyoid muscle of the
human subject, and its nerve-tube: 1, 1, primitive
muscular fasciculus ; 2, nerve-tube ; 3, medullary
substance of the tube, which is seen extending to the
terminal plate, where it disappears ; 4, terminal
plate situated beneath the sarcolemma, that is to
say, between it and the elementary fibrillse ; 5, 5,
, ,,, , sarcolemma.

CUlar nbre in the mammalia, While 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 ; 3, 3,
sarcolemma becoming continuous with the sheath ;
4, medullary substance of the nerve-tube, ceasing
abruptly at the site of the terminal plate; 5, 5, ter-
minal plate ; 6, 6, 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 ; 8, 8, undulations of the sarcolemma re-
producing those of the fibril la- ; 9, 9, nuclei of the
sarcolemma.

several exist in cold-blooded ani-
mals. In man and in the warm-
blooded animals generally, the
medullated nerve - fibres divide
dichotomously near their endings
in the muscular fibres, each divis-
ion always taking place at a node of Ranvier.

The fibres finally resulting

512

NERVOUS SYSTEM.

from these divisions pass to the sarcolemma and terminate in a rather prom-
inent mass called an end-plate, with six to twelve or sometimes sixteen nuclei
which are distinct from the nuclei of the muscular fibre. The tubular mem-
brane of the nerve-fibre here fuses with the sarcolemma (Rouget) and the
medullary substance is lost. By the action of gold chloride, it has been
shown that fibrils arise from the under surface of the end-plates, which pass
into the substance of the muscular fibres, between the muscular fibrillae.

FIG. 176. — Intrafibrillar terminations of a motor nerve in striated muscle, stained with gold chloride

(Landois). .

These fibrils probably are connected with the axis-cylinders, but their exact
mode of termination in the muscular substance has not been satisfactorily
demonstrated.

Although the sensibility of the muscles is slight as compared with that
of the skin and mucous membranes, they are not insensible and they possess
nerve-fibres other than those exclusively motor. According to Kolliker,
small medullated fibres go to the muscular tissue and here give off very fine
non-medullated fibres, which terminate in fibres of the same appearance but

provided with nuclei. These form a plexus on
the sarcolemma and surround the muscular fibres.
It is not certain that they penetrate the sarco-
lemma and terminate in the muscular substance,
although this view has been advanced.

Termination of Nerves in the Involuntary
Muscular Tissue. — According to the observa-
tions of Frakenhaeuser upon the nerves of the
uterus, the nerve-fibres form a plexus in the con-
nective tissue surrounding the involuntary mus-
cles and then send 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
FIG. 177. -Termination of nerves in shown farther that in many instances, the fine,
non-stnated muscle (CaAiat). terminal nerve-fibres branch and go into the

nuclei of the muscular fibres and afterward pass out to join with other fibres
and form a plexus.

Termination of the Nerves 'in Glands. — The researches of Pfliiger upon
the salivary glands leave no doubt of 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

TERMINATIONS OF THE SENSORY NERVES.

513

FIG. 178.— Termination of the nerves in the salivary glands (Pfliiger).
I, II, branching of the nerves between the glandular cells ; III, termina-
tions of the nerves in the nuclei of the cells ; IV, multipolar nerve-
cell.

more or less branching plexus, non-medullated fibres pass directly into the
glandular cells and terminate in the nucleoli. The same observer has de-
scribed and figured multipolar cells, mixed with the glandular cells, in which
some of the nerve-fibres terminate. These, however, are not found in the
parotid. These nerve-
fibres are regarded as
glandular nerves, and
they are distinct from
the vaso-motor nerves.

Modes of Termina-
tion of the Sensory
Nerves. — There un-
doubtedly are several
modes of termination
of the sensory nerves
in integument and in
mucous membranes,
some of which have
been quite accurately
described, while others
are still somewhat un-
certain. In the first
place, anatomists now
recognize three varieties of corpuscular terminations, differing in their
structure, probably, according to the different properties connected with
sensation, with which the parts are endowed. In addition it is probable
that sensory nerves are connected with the hair-follicles, which are so largely
distributed 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 are still differences of opinion concerning these various modes of
termination of the nerves, but with regard to the terminal corpuscles, these
differences relate mainly to anatomical points. It is npt proposed, therefore,
to enter fully into the discussions upon these questions, but simply to pre-
sent what seem to be the most reliable anatomical views.

Corpuscles of Vater or of Pacini. — These bodies were called corpuscles
of Pacini, until it was shown that they had been seen about a century and
a half ago by Vater. In man, they are oval or egg-shaped and measure -fa
to -J- of an inch (1 to 4 mm.) in length. They are always found in the sub-
cutaneous layer on the palms of the hands and the soles of the feet, and are
most abundant on the palmar surfaces of the fingers and toes, particularly
the third phalanges. In the entire hand there are about six hundred, 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 extremi-

514 NERVOUS SYSTEM.

ties, 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 with-
- out exception on all of the great plexuses of the sympathetic system, in front
of and by the sides of the abdominal aorta, and behind the peritoneum, par-
ticularly in the vicinity of the pancreas. They some-
times exist in the mesentery and have been observed near
the coccygeal gland.

The corpuscles consist simply of several layers of
connective tissue enclosing one, two or three central
bulbs in which are found the ends of the nerve. These
bulbs are finely granular and nucleated, and are regarded
by most anatomists as composed of connective tissue.
At the base of the corpuscle, is a pedicle formed of con-
nective tissue surrounding a medullated nerve - fibre
which penetrates the corpuscle. Within the corpuscle
the medullary substance of the nerve-fibre is lost and
only the axis-cylinder remains.

The situation of these corpuscles, beneath the true
skin instead of in its substance, shows that they can not
be properly considered as tactile corpuscles, a name
which is applied to other structures found in the papilla

.rjr j •. • • -11,

or the conum ; and it is impossible to assign to them any
special use connected with sensation, such as the appre-
ciation of temperature, pressure or weight. All that can
be said with regard to them is that they constitute one of

nerve V2e?ve?wiiich tne seyeral modes of termination of the nerves of gen-
has lost its medullary m.Ql oa-nail-»il if XT-
substance and sheath; eial sensibility.

Tactile Corpusdes.—The name tactile corpuscles im-
P^es that t^iese bodies are connected 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 sur-
faces 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 nipples,
and a few on the anterior surface of the forearm. The largest papillae of the
skin are found on the hands, feet and nipples, precisely where the tactile
corpuscles are most abundant. Corpuscles do not exist in all papillae, and
they are found chiefly in those called compound. In an area a little more
than ^g of an inch square (2'2 mm. square), on the third phalanx of the in-
dex-finger, Meissner counted four hundred papillae, in one hundred and eight
of which he found tactile corpuscles, or about one in four. In an equal area
on the second phalanx, he found forty corpuscles ; on the first phalanx, fif-
teen ; 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

FIG. 179. - Corpuscle

Vater (Sappey).

TERMINATIONS OF THE SENSORY NERVES.

515

the skin on the middle of the sole of the foot. In the skin of the fore-arm
the corpuscles are very rare. According to Kolliker, the tactile corpuscles

FIG. 180.— Papillae 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 papillae ; 9, 9, 10, 11, tactile corpuscles.

usually occupy special papillae 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 -3^-3 to ^-$ of an inch (66 to
100 /A). In the palm of the hand they are ^¥ to rirr °^ an incn (100 *°
165 ft) long, and -fa to -g-j^ of an inch (45 to 50 /A) in thickness. They gen-
erally are situated at the summits of the secondary eminences of the com-
pound papillae. They consist of a central bulb of homogeneous or slightly
granular connective-tissue substance, harder than the central bulb of the
corpuscles of Vater, and a covering. The covering is composed of connect-
ive tissue with 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 on the surface of
the central bulb.

End-Bulbs. — Under this name, a variety of corpuscles has been described
by Krause, as existing in the conjunctiva covering the eye and in the semi-
lunar 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 rounded or
oblong enlargements at the ends of the nerves, which are composed of homo-
geneous matter with a delicate investment of connective tissue. They meas-
ure TisVo to ^iir °f an incn (25 to 100 /A) in diameter. In the parts provided
with papillae, they are situated at the summits of the secondary elevations.
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 cor-
puscles. The investing sheath of the fibres is here continuous with the con-
nective-tissue covering of the corpuscle, and the nerve-fibres pass into the
corpuscle, break up into two or three divisions, and terminate in convoluted

516

NERVOUS SYSTEM.

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, however, the terminal bulbs
are oblong, and sometimes 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 Sensory
Nerves. — The actual termination of the sensory
nerves upon the general surface and in mucous
membranes is still a question of some obscurity.
Although anatomists have arrived at a pretty definite
knowledge of the sensory 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 may be called general sensibility, as dis-
tinguished from the sense of touch, that the mode
of termination of the nerves remains to be studied.

According to Kolliker, in the immense majority
of instances the sensory 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 un-
fortunately the exact mode of connection of the
nerves with these follicles is not apparent. The
following seems to be all that is positively known
FIG. m.-End-buibs. or cow*- of the terminations of the nerves on the general sur-

cles of Krause (Ludden). face I
A, three corpuscles of Krause -nr i 11 i_ -i .m £ i • J.T

from the conjunctiva of Medullated nerve-fibres form a plexus in the
acid'; magSfieiFsoo diam° deeper layers of the true skin, and from this plex-
sr°

two nerve-fibres us, fibres, some pale and nucleated and others me-
terio^p^rtio^sof'two'p^ dullated, 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

m tS^hre^corpuscies, the number pass to papillae and terminate in tactile cor-

pusclesi and others pass to papilla? that have no tac-

B, terminal bulbs from the con- -Hlo nr»T*rmar»lcKa
junctiva9f the calf, treated T 0-rpUSCieS.

id; In t^e mucous membranes the mode of termina-

tion is' in general terms, by a delicate plexus just
of a 'nerve-fibre, with two beneath the epithelium, coming from a submucous

terminal bulbs ; a, covering

of the terminal bulbs; 6, in- plexus analogous to the deep cutaneous plexus. In

ternal bulb ; c, pale nerve- r . r . ,

fibre. certain membranes the nerves terminate in end-

bulbs, or corpuscles of Krause. In the cornea, according to the observations

STRUCTURE OF THE NERVE-CENTRES.

517

of Hoyer, Lipmann and others, branching nerve-fibres pass to the nucleoli
of the corneal corpuscles 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 in the surrounding granular substance 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, are included, anatomically 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 ganglia of the sympathetic 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, deli-
cate membranes enveloping some of the cells, with blood-vessels and lym-
phatics. The most important of these structures,
in their physiological relations, are the cells and
the prolongations by which they are connected with
the nerves and with each other.

Nerve-cells. — The following varieties of cells ex-
ist in the nerve-centres and constitute their essential
anatomical elements ; viz., unipolar, bipolar and
multipolar cells. These cells present great differ-
ences in their size and general appearance, and some
distinct varieties are found in particular portions of
the nervous system. Unipolar and bipolar cells are
found in the ganglia of the cranial nerves and in
the ganglia of the posterior roots of the spinal
nerves. Small unipolar cells are found in the sym-
pathetic ganglia. Multipolar cells present three or
more prolongations. Small cells, with three and
rarely four prolongations, are found in the posterior
cornua of the gray matter of the spinal cord. From
their situation they have been called sensory cells.
They are found in greatest number in parts known
to be endowed exclusively with sensory properties.
Large, irregularly shaped multipolar cells, with a
number of poles, or 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.

Unipolar cells, such as exist in the ganglia of FIG. vs.— unipolar ceil from the

,. .. . , _ _ Gasserian ganglion (Schwalbe).

the nerves as distinguished from the ganglia of the N, N, N, nuciei of the sheath ; T,
cerebro-spinal axis, have but a single prolongation, ^branching at a node of

518

NERVOUS SYSTEM.

FIG. 183.— Unipolar nerve-
cell with a spiral fibre
(Landois).

FIG. 184. — Bipolar
nerve-cell (Landois).

which is continuous with a nerve-fibre. These cells frequently have a con-
nective-tissue envelope, or sheath, which is prolonged as a sheath for the

nerve. Unipolar cells, with a connect-
ive-tissue sheath, the pole being sur-
rounded by a spiral fibre, have been
observed in the sympathetic ganglia of
the frog. These do not exist in the
human subject or in the mammalia and
nothing is known of the uses of the
spiral fibres.

Bipolar cells seem to be nucleated
enlargements in the course of medul-
lated nerve-fibres. Usually the medul-
lary substance does not extend over
the cell, although this sometimes oc-
curs.

Multipolar cells have a number of
poles, but there is always one pole
which does not branch and which becomes continuous with the axis-cylinder
of a nerve-fibre. This is called the axis-cylinder prolongation. Of the
other poles, some are continuous with poles of contiguous cells, connecting
numbers of cells into groups, and others,
which are sometimes called protoplasmic
prolongations, branch freely and are lost
in the intercellular substance.

With all the differences in the size
and form of the nerve-cells, they present
tolerably uniform general characters as
regards their structure and contents.
With the exception of the unipolar and
bipolar cells, they are irregular in shape,
with strongly refracting, granular con-
tents, frequently a considerable number
of pigmentary granules, and always a dis-
tinct nucleus and nucleolus. The nucleus
in the adult is almost invariably single,
although, in rare instances, two have been FlG

Observed. Cells with multiple nuclei are z, axis-cylinder prolongation ; Y, protoplas-
... , . • i mi mic branches.

often observed in young animals. The

nucleoli usually are single, but there may be as many as four or five. The
diameter of the cells is variable. They usually measure y^Vo to ^^ of an
inch (20 to 50 /w,) ; but there are many of larger size and some are smaller.
The nuclei measure ^-gW to y^Vo- of an inch (12 to 20 /*). The nerve-cells
are soft, have no true cell-membrane and are fibrillated, the fibrillation ex-
tending to the poles. The transverse striae in the axis-cylinder treated with
silver nitrate, noted by Fromann and confirmed by Grandry and others,

STRUCTURE OF THE NERVE-CENTRES.

519

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 like the substance of the axis-cylinder, it is possible that the

FIG. 186. — Transverse section of the gray substance of anterior cornua of the spinal cord of the ox,
treated with silver nitrate (Grandry).

markings may be entirely artificial, and that they do not indicate the exist-
ence of two distinct substances.

Tracing the nerve-fibres toward their origin, they are seen to lose their
investing membrane as they pass into the white portion of the centres, being
here composed only of medullary substance surrounding the axis-cylinders.
They then penetrate the gray substance, in the form of axis-cylinders, losing
the medullary substance. In the gray substance, it is impossible to make
out all their relations distinctly, and it can not be stated, as a matter of
positive demonstration, that all of them are connected with the poles of
nerve-cells. Still, it has been shown in the gray matter of the spinal cord,
that many of the fibres are actual prolongations of the cells, others probably
passing upward to be connected with cells in the encephalon.

Tracing the prolongations from the cells, it is found that at least one of
the poles in the gray substance gives origin to nerve-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 ; and it is probable that the cells are thus arranged in separate
and distinct groups, possibly connected with sets of muscles.

Accessory Anatomical Elements of the Nerve-centres. — In addition to the
cells of the gray matter and the axis-cylinder of the nerves, which are prob-

520 NERVOUS SYSTEM.

ably the only structures directly concerned in innervation, are the following
accessory anatomical elements : 1, outer coverings surrounding some of the
cells ; 2, intercellular, granular matter ; 3, peculiar corpuscles, called myelo-
cytes ; 4, connective-tissue elements ; 5, blood-vessels and lymphatics.

Certain of the cells in the spinal ganglia and in the ganglia of the sym-
pathetic system are surrounded with a 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 is composed of a layer of very delicate endothelium.
Its physiological significance is not apparent.

In the gray matter of the nerve-centres, there is a finely granular sub-
stance between the cells, which closely resembles the granular contents of
the cells themselves. In addition to this granular matter, Kobin has de-
scribed peculiar anatomical elements which he 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 be-
ing by far the more abundant. 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 poly-
hedric, pale, clear or very slightly granular, and contain bodies similar to the
free nuclei. The free nuclei are -g-gVo to ^^ of an inch (5 to 6 /x,) in diam-
eter, and the cells measure ^Vo- to ^oVo? an(^ sometimes y^Vo of an inch (10,
12 and 15 //,). These elements also exist in the second layer of the retina.

In the cerebro-spinal centres there is a delicate stroma of connective tis-
sue, chiefly in the form of stellate, branching cells, which serves in a meas-
ure, to support the nervous elements. This tissue, which is peculiar to the
white substance of the encephalon and spinal cord, is called neuroglia.

The blood-vessels of the nerve-centres form a capillary net-work with
large meshes. The gray substance is richer in capillaries than the white.

A peculiarity of the vascular arrangement in the cerebro-spinal centres
has already been described in connection with the anatomy of 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. — The chemistry of the nervous
substance, as far as it is understood, throws little light on its physiology.
Certain albuminoids have been extracted which do not possess more than a
purely chemical interest. The substance called cerebrine is composed of
carbon, hydrogen, oxygen and nitrogen, without either sulphur or phosphorus.
Protagon is a nitrogenized substance containing phosphorus (Liebreich, 1865).
By some chemists protagon is thought to be a mixture of cerebrine and
lecethine. Lecethine is regarded as a nitrogenous fat. Other substances
which have been extracted — xanthine, hypoxanthine, inosite, creatine and
various volatile fatty acids — have no special physiological interest connected
with the nervous system and are found in many other situations. Cholester-

DEGENERATION AND REGENERATION OF NERVES. 521

ine, which always exists in considerable quantity in the nervous tissue, has
been considered in connection with the physiology of excretion. The ordi-
nary fats are in combination with other fats or with peculiar acid substances,
The reaction of nerve-tissue is either neutral or faintly alkaline under normal
conditions, soon becoming acid after death.

Degeneration and Regeneration of Nerves. — The degenerations observed
in nerves separated from the centres to which they are normally attached,
first studied by Waller, in 1850, are now used in following out certain
nervous connections too intricate to be revealed by ordinary dissection.
This is known as the Wallerian method. If an ordinary mixed nerve be
divided in its course, both the motor and sensory fibres of the peripheral
portion undergo fatty degeneration and lose their excitability. As regards
the spinal nerves, degeneration occurs in the motor fibres only, when the
anterior spinal root has been divided, and the nerve has degenerated fibres
(motor) mixed with the sensory fibres, which latter retain their anatomical
and physiological characters. The motor fibres of the spinal nerves are
degenerated when separated from their connections with the anterior cornua
of gray matter of the cord. If the posterior roots of the spinal nerves be
divided beyond the ganglia, the peripheral sensory fibres degenerate ; but if
the ganglia be exsected, the central as well as the peripheral portions degen-
erate. These experiments show the existence of centres which preside over
the nutrition of the nerves. The centres for the motor filaments of the
spinal nerves are in the anterior cornua of gray matter of the cord. The
centres for the sensory fibres are the ganglia of the posterior roots. The
centres for the sensory cranial nerves are the ganglia on their roots ; and
the centres for the motor cranial nerves are probably the gray nuclei of
origin of these nerves. The Wallerian method has been found useful in
studying the paths of conduction in the encephalon and spinal cord, as will
be seen in connection with the physiology of these parts.

The excitability of the motor nerves disappears in about four days after
their section. 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 about the fourth day, stimulation of the nerve
will produce no contraction in the muscles, although the latter retain their
contractility. This loss of excitability is gradual, and it continues, whether
the nerve be exposed and stimulated from time to time or be left to itself,
progressing from the centres to the periphery. In the researches of Longet
upon this subject, it was found that the lower portion of the peduncles of the
brain lost their excitability 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 terminations 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 anaesthet-
ics. 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*

522 NERVOUS SYSTEM.

Nerves that have been divided may be regenerated if anatomical union of
the divided ends can be obtained ; and this sometimes takes place several
months after injury to the nerves, the regeneration occurring by the forma-
tion of new fibres. Mixed nerves are regenerated in this way, and conduction
is finally restored in both directions. The sensory conduction appears first,
and next, the conduction of motor impulses. The restoration of the physio-
logical properties of the nerves occupies several weeks. The central end of a
mixed nerve has been made to unite with the peripheral end of another
mixed nerve, but it is doubtful whether a divided end of a motor nerve is
ever united to the divided end of a sensory nerve. Experiments upon this
latter point are not entirely satisfactory.

MOTOR AKD SENSORY NERVES.

Aside from the nerves possessing special properties, such as the nerves of
sight, hearing, smell, taste and, according to some physiologists, nerves of
touch, temperature, sense of weight and muscular sense, the cerebro-spinal
nerves present two kinds of fibres. These are (I) centrifugal, or motor
fibres, and (2) centripetal, or sensory fibres. The motor fibres conduct im-
pulses from the centres to the muscles and excite muscular action. The sen-
sory fibres conduct impressions from the periphery to the centres, which are
appreciated either as ordinary sensation or as pain. As regards the nerves
arising by two roots from the spinal cord, the exact anatomical and physio-
logical divisions into motor and sensory were first made by Magendie, in
1822. As will be seen farther on, this division is distinct for the cranial
nerves, so that it is universal in the cerebro-spinal system. The importance
of the discovery of the distinct properties of the two roots of the spinal
nerves is such that it merits at least a brief historical account, particularly
as this discovery is quite generally attributed to Charles Bell.

The first definite statement with regard to distinct properties of the two
roots of the spinal nerves was made by Alexander Walker, in 1809, who said
that th£ posterior roots were for motion and the anterior roots for sensation,
the exact reverse of the truth.

In a pamphlet privately printed by Charles Bell, probably in 1811, and
" submitted for the observations of his friends," the view was advanced that
the anterior roots are both motor and sensory and that the posterior preside
over " the secret operations of the bodily frame, or the connections which
unite the parts of the body into a system."

In 1822, Magendie, as the result of experiments upon the exposed roots
in living dogs, stated that " he was able at that time to advance 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 particu-
larly destined to sensibility, while the anterior seem more specially con-
nected with motion."

It is now universally admitted that the mixed nerves arising from the
spinal cord derive their motor properties from the anterior roots and their
sensory properties from the posterior roots.

MOTOR AND SENSORY NERVES. 523

The anterior roots possess a certain degree of sensibility in addition to
their motor properties (Magendie). This sensibilitity, which is slight, is de-
rived from fibres from the posterior roots, which turn back to go to the an-
terior roots. This fact has been positively demonstrated by the Wallerian
method. When a posterior root is divided beyond the ganglion, the sensi-
bility of the corresponding anterior root is lost, and degenerated fibres appear,
after a few days, in the anterior roots (Schiff). This sensibility of the an-
terior roots is called recurrent sensibility. Similar relations are observed
between certain of the motor and sensory cranial nerves.

Mode of Action of the Motor Nerves. — As regards the normal action of
the motor nerves, a force, the nature of which is unknown, 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 inter-
rupted, and motion in these parts, in obedience to the natural stimulus, be-
comes impossible. While, however, it is not always possible to induce gen-
eration 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 thus respond to direct stimulation is said to be excitable.

If a motor nerve be divided, electric, mechanical, or other stimulus ap-
plied to the extremity connected with the centres produces no effect ; but the
same stimulus applied to the extremity connected with the muscles is fol-
lowed 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 distributed ; 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 individual nerve-
fibres are entirely independent ; and the relations which they bear to each
other in nervous fasciculi and in the so-called anastomoses of nerves involve
simple contiguity. Comparing 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 it is more than probable that the axis-cylinder is the only
conducting element.

The generation of a motor impulse maybe induced by an impression
made upon sensory nerves and conveyed by them to the centres. If, for
example, a certain portion of the central nervous system, as the spinal cord,
be isolated, leaving its connections with the motor and sensory nerves
intact, these phenomena may be readily observed. An impression made
upon the sensory nerves will be conveyed to the gray matter of the cord
and will induce the generation of a motor impulse by the cells of this part,

524 NERVOUS SYSTEM.

which will be conducted to the muscles and give rise to contraction. As the
impulse, in such observations, seems to be reflected from the cord, through
the motor nerves, to the muscles, this action has been called reflex. These
phenomena 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 mus-
cles 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 restraining the movements of the
others ; and the action of certain sets of muscles of the extremities 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 associ-
ated movements, the question arises as to how far they are due to the ana-
tomical relations of the nerves to the centres and their connections with
muscles, and how far they depend upon habit and exercise. 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 anatomi-
cal arrangement that might render a separate action of these cells impossi-
ble. 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 would afford a ready explanation of
the fact that it is impossible, as a rule, by an effort of the will, to cause only a
portion of a single muscle to contract ; yet some of the larger muscles receive
a considerable number of motor nerve-fibres which are probably connected
with gray matter composed of many anastomosing nerve-cells.

Many of the associated movements may be influenced to a remarkable
degree by education, of which no better example can be found than in the
case of skillful 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 pianists frequently execute at the same
time scales with both hands, the action being entirely opposed to the natural
association of movements.

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 impulse or an effort of the
will can not be conducted to a portion only of a muscle, but must act upon
the whole muscle, and the same is true, probably, of certain restricted
sets of muscles ; but the association of movements of corresponding mus-
cles upon the two sides of the body, with the exception, perhaps, of the mus-

MOTOR AND SENSORY NERVES. 525

cles of the eyes, is due mainly to habit and may be greatly modified by edu-
cation.

Mode of Action of the Sensory Nerves. — The sensory nerve-fibres, like
the fibres of the motor nerves, are entirely independent of each other in
their action ; and in the so-called anastomoses that take place between
sensory nerves, the fibres assume no new relations, except as regards con-
tiguity.

As motor fibres convey to their peripheral distribution the impulse pro-
duced by a stimulus applied in any portion of their course, so an impression
made upon a sensory 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 hu-
merus. 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 neuralgic affections dependent upon disease of or pressure upon
the, trunk of a sensory nerve. In such cases, excision of the nerve is often
practised, but no permanent relief follows unless the section be made be-
tween the affected portion of the nerve and the nerve-centres ; and the pain
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 impressions. The explanation of this is that the nerves are paralyzed
near their terminal distribution, so that an impression made upon the skin
can not be conveyed to the sensorium ; but 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 the very common
operation of restoring the nose by transplanting skin from the forehead,
after the operation has been completed, the skin having been entirely sepa-
rated, and united in its new relations, the patient feels that the forehead is
touched when the finger is applied to the artificial nose. After a time, how-
ever, 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 physi-
ological interest, presented in persons who have suffered amputations. It
has long been observed that after loss of a limb, the sensation of the part re--
mains ; and pain is frequently experienced, which is referred to the ampu-
tated 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. After a
time the sense of presence 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 for years. Examples have been
reported by Muller, in which the sense was undiminished thirteen, and in
one case, twenty years after amputation. In a certain number of cases,

35

526 NERVOUS SYSTEM.

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 impression being
that the limb is gradually becoming shorter. It was noted by Gueniot, that
the sense of the limb becoming shorter exists in about half of the cases of am-
putation in which cicatrization goes on regularly ; and in these cases, the pa-
tient finally experiences a feeling as though the hand or foot were in direct
contact with the stump,

Physiological Differences between Motor and Sensory Nerve-Fibres. — It
has not been shown that there is any essential anatomical difference between
the conducting elements of motor and sensory nerve-fibres ; but the physio-
logical differences are sufficiently distinct, as has already been seen. Under
normal conditions, motor fibres conduct motor impulses in but one direction,
and these fibres are insensible. Sensory fibres conduct impressions always in
the opposite direction, and they do not conduct motor impulses. Certain
experiments, however, have led some physiologists to adopt the view that the
conducting properties of the nerves themselves, both motor and sensory, are
identical, and that the direction of conduction depends upon the kind of
centres with which nerves are connected. These experiments are the fol-
lowing :

It is said that the peripheral end of a divided motor nerve, the sublin-
gual, can be made to unite with the central end of a sensory nerve, the
lingual branch of the fifth ; and that after a time motor impulses are con-
ducted by the sensory fibres and sensory impressions, by the motor fibres. A
careful study of these experiments, however, shows that the results are far
from satisfactory.

Another experiment is grafting the end of the tail of a rat into the
skin of the back (Bert). When the union has become complete, the tail is
divided at its root and the sensory conduction, after five or six months, takes
place in a direction opposite to the normal. While this experiment may be
regarded as showing that sensory fibres may be made to assume such rela-
tions with other sensory fibres as to change, after a time, the direction of
conduction, it has no absolutely direct bearing upon the question of the
physiological identity of motor or sensory fibres.

The experiments just mentioned seldom succeed, and the results of
union of motor with sensory nerves are quite indefinite ; but the divided
ends of mixed nerves readily reunite, and it is not difficult to establish a
union between the central and peripheral ends of two different mixed
nerves. It is hardly reasonable to assume that in these instances, each and
every divided end of a motor fibre selects another motor fibre with which it
unites, and that the same occurs with sensory fibres ; but it would seem that
in a divided mixed nerve, a certain number of fibres of each kind must
unite with certain fibres that have similar physiological properties. Com-
plete physiological regeneration of divided nerves is always slow, and fre-
quently the regeneration never becomes complete. The fact, also, that
curare destroys the physiological properties of motor nerves, leaving the sen-
sory nerves intact, has a very important bearing upon the question under

NERVOUS EXCITABILITY. 527

consideration ; and anaesthetics temporarily abolish the physiological proper-
ties of the sensory nerves without necessarily affecting the motor nerves.

Until the results of experiments upon the artificial union of motor
and sensory nerves become much more positive than they now are, it must
be assumed that these two kinds of nerve-fibres have distinct physiological
properties, both as regards the kind of impulse or impression produced by
excitation or stimulation and the direction of conduction. It is possible,
however, that these properties may be modified by altered relations for a
long time with the trophic centres that influence the nutrition of the differ-
ent kinds of nerve-fibres.

Nervous Excitability. — Immediately or soon after death, when the excit-
ability of the nerves is at its maximum, they may be stimulated by mechani-
cal, chemical or galvanic irritation, all of these agents producing contraction
of the muscles to which the motor filaments are distributed. Mechanical irri-
tation, 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 disorgan-
ize its fibres, that portion of the nerve will no longer conduct an impulse.
Among the irritants of this kind, are extremes of heat and cold. If an ex-
posed nerve be cauterized, 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, except common salt, which is sometimes used
when it is desired to produce tetanic action. Mechanical stimulation and
the action of certain chemicals are capable of exciting the nerves ; but 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 such 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 ex-
periments is by means of electricity. This may be employed without dis-
organizing the nerve-tissue, and it 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 considered
under a separate head.

Rapidity of Nervous Conduction. — The first accurate estimates of the
rapidity of nervous conduction were made by Helmholtz, in 1850, and were
applied to the motor nerves of the frog. These estimates were arrived at by
an application of the graphic method, which was afterward considerably ex-
tended and improved by Marey. The process employed by Marey, which is
essentially the same as that used in all recent investigations, is the following :

To mark small fractions of a second, a tuning-fork vibrating at a known
rate (five hundred times in a second) is so arranged that a point connected
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,

528 NERVOUS SYSTEM.

each curve representing -^^ of a second. If a lever be attached to a muscle
and be so arranged as to indicate upon the paper, moving at the same rate.
the instant when contraction takes place, it is evident that the interval be-
tween two contractions produced by stimulating the nerve at different points
in its course may be accurately measured ; and if the length of the nerve be-
tween 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 nerve is stimulated successively at two points, the distance between them
being measured.

Employing the myograph of Marey, Baxt, in the laboratory of Helmholtz,
succeeded in measuring the rate of nervous conduction in the human sub-
ject. In these experiments, the swelling of the muscle during contraction
was limited by enclosing the arm in a plaster-mould, and the contraction
was observed through a small opening. By then exciting the contraction by
stimulating the radial nerve successively at different distances from the mus-
cle, the estimate was made. The rate in the human subject was thus esti-
mated at one hundred and eleven feet (33*9 metres) per second.

The method used in determining the rate of conduction in motor nerves
— 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 made the first attempt
to solve this question, in 1861. He employed the delicate chronometric in-
struments 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
(33-9 metres) per second as the rate of sensory conduction.

It is not necessary to describe fully the complicated apparatus by means
of which the most recent estimates of the rate of nervous conduction have
been made. The general results of the observations of Helmholtz, Marey,
Baxt, Schleske and of many others nearly correspond with the estimates just
given, and they show that the rate is about the same for motor and sensory
nerves. This rate is modified by various conditions. It is diminished in
the anelectrotonic and increased in the catelectrotonic condition of nerves.
In the frog Helmholtz observed that the rate was very much reduced by
cold, at 32° Fahr. (0° C.) being not more than one-tenth as rapid as at 60°
or 70° Fahr. (15-5° or 21-11° C.).

The rate of transmission of impulses and impressions through the spinal
cord has been investigated by calculating the distances between nerves as
they are given off at different points and measuring the time required for
the appreciation of certain impressions and the beginning of certain move-
ments (Burkhardt). While these observations are not absolutely exact, their
general results are of considerable physiological interest. According to Burk-
hardt, the rate of motor conduction in the cord is about one-third of the nor-

ACTION OF ELECTRICITY UPON THE NERVES. 529

mal rate in the motor nerves. As compared with the sensory nerves, the
cord conducts tactile impressions a little faster and painful impressions less
than one half as fast.

Attempts have been made to estimate the duration of acts involving the
central nervous system, such as the reflex phenomena of the spinal cord or
the operations of the cerebral hemispheres. These have been partially suc-
cessful, 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 impor-
tant fact ; although the duration of these acts has not been measured with
absolute accuracy. As the general result of experiments upon these points,
it has been found that the reflex action of the spinal cord occupies more than
twelve times the period required for the transmission of stimulus or impres-
sions through the nerves. Bonders found, in experiments upon his own
person, that an act of volition required -fa of a second, and one of simple
distinction or recognition of an impression, -fa of a second. These esti-
mates, however, are merely approximate, and until they attain greater cer-
tainty, it is unnecessary to describe in detail the apparatus employed.

Personal Equation. — In recording astronomical observations, it has been
found that a certain time elapsed between the actual observation of a phe-
nomenon and the moment of its record. This error, which is equal to the
interval of time between the impression made upon the retina and the mus-
cular act by which a record is made, is not the same in different persons or
even in the same person at all times. It may amount to -J of a second or
even more, and it may be as low as -fa of a second. If this difference be due
to different rates of nervous conduction, and not entirely to variations in the
rapidity of mental operations, it is evident that the velocity of the nerve-cur-
rent must vary very considerably in different individuals.

Action of Electricity upon the Nerves. — So long as the nerves retain their
excitability and anatomical integrity, they will respond to properly regulated
electric stimulus. Experiments may be made upon the exposed nerves in
living animals or in animals just killed ; and of all classes, the cold-blooded
animals present the most favorable conditions, on account of the persistence
of nervous and muscular excitability for a considerable time after death.
Experimenters most commonly use frogs, on account of the long persistence
of the physiological properties of their tissues and the facility with which
certain parts of the nervous system can be exposed. For ordinary experi-
ments upon 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 (25 or
50 mm.) in length, attached to the muscles, which will respond to a feeble
electric stimulus. It is by experiments made upon frogs prepared in this
way that most of the important facts with regard to the action of electricity
upon the nervous system have been developed.

In physiological experiments it is sometimes necessary to use different
forms of electrical apparatus in order to study different properties and

530 NERVOUS SYSTEM.

phenomena of nerve and muscle. A full description of the apparatus thus
used would be out of place in this work, and it will be necessary only to
enumerate and describe the diiferent currents used and the manner of their
application. Many of the phenomena, also, described by electro-physiolo-
gists, although curious and interesting, have little apparent application to
human physiology or to the practice of medicine. A description of such
phenomena may well be very brief in a work for the use of students and
practitioners of medicine.

In studying the action of nerve and muscle, observers often use what is
called a single Faradic, or induction shock. The duration of this stimulus
is about y^ (0-0008) of a second (Helmholtz). The excitation, therefore,
is practically instantaneous. These single shocks are produced by Du Bois-
Reymond's apparatus, which is a modification of the Faradic, or induction
battery. It will be seen farther on that somewhat different effects are pro-
duced by the stimulus due to closing and opening the circuit, and that with
a feeble current, no contractions occur at any other time. The contractions
thus produced are known respectively as opening and closing contractions.
By the use of Du Bois-Reymond's keys, either the closing or the opening ex-
citation may be diverted from the nerve, and a single closing or opening
shock may be applied at will.

What is commonly known as an interrupted current is a Faradic, or in-
duced current, in which the closing and opening excitations follow each
other with greater or less rapidity, and the intervals may be regulated so
that they occur at a regular rate. A rapid succession of induction-shocks
produces a more or less prolonged muscular action, called tetanic contrac-
tion. The number of successive shocks in a second, required to produce a
tetanic condition of a muscle, varies in different animals and in different
muscles in the same animal. The minimum seems to be about sixteen per
second, with a very considerable range of variation. Very rapid stimuli,
even more than 24,000 per second, will produce tetanic contraction.

The Faradic, or induced current is different in its effects, under certain
conditions of the nerves and muscles, from an interrupted galvanic, or pri-
mary current. This question is important in practical medicine, in deter-
mining the so-called " reaction of degeneration " of nerve and muscle.

The constant current, under certain conditions, has no effect that is in-
dicated by muscular phenomena, contraction occurring only on closing or
opening the circuit. This is known as the galvanic, or primary current.
It produces, however, a peculiar condition of nerves and muscles, which will
be described under the head of electrotonus. The primary current is de-
rived directly from the cells of a galvanic battery, and this is to be distin-
guished from the Faradic, or induced current. The Faradic current is
induced in a coil of small, insulated wire brought near and parallel to and
partly or entirely surrounding a coil of larger wire carrying the primary
current. When the circuit of the primary current is closed, the direction
of the induced current is the reverse of that of the primary current.
When the primary circuit is opened, the induced current has the same

ACTION OF ELECTRICITY UPON THE NERVES. 531

direction as the primary current. The direction of the primary current is
uniform, but the direction of the induced current alternates with every in-
terruption of the primary current. These induced currents are of momen-
tary duration, being produced only when the primary current is closed and
opened. A rapid interruption of the primary current is produced by what
is called a rheotome, or current-interrupter, which is attached to all induc-
tion-batteries.

The points or surfaces used in closing a circuit in which a portion of
nerve or muscle is included are called electrodes. They are usually desig-
nated as the copper, or positive electrode or pole, and the zinc, or negative
electrode or pole. The positive pole is also called the anode, and the nega-
tive pole, the cathode. The direction of the current, when the circuit is
closed, is from the anode to the cathode.

When a galvanic current is passed through a liquid or a moist, animal
tissue, decomposition occurs, by what is known as electrolysis or internal
polarization. The results of this decomposition, called ions, are of course
different in different liquids or moist tissues. These accumulate at the poles
and after a time disturb the currents and the phenomena produced. In ani-
mal tissues, acids accumulate at the anode, and alkalies, at the cathode. The
ions which go to the anode are called anions, and those which accumulate at
the cathode are called cations. In physiological experiments, it is often de-
sirable to eliminate electrolysis, or internal polarization, and this is done by
using the non-polarizable electrodes devised by Du Bois-Reymond. These
may be described as follows : " The researches of Regnault, Matteucci and
Du Bois-Reymond have proved that such electrodes can be made by taking
two pieces of carefully amalgamated pure zinc wire, and dipping these in
a saturated solution of zinc sulphate contained in tubes, their lower ends
being closed by means of modeller's clay, moistened with a 0*6 per cent,
normal saline solution. The contact of the tissues with these electrodes
does not give rise to polarity." (Landois and Stirling.)

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 have been called respectively descending and ascending
currents. When the positive pole (copper) is placed nearer the origin of the
nerve, and the negative pole (zinc), below this point in the course of the
nerve, the galvanic current follows the normal direction of the motor con-
duction, and this is called the descending current. When the poles are re-
versed and the direction is from the periphery toward the centre, it is called
the ascending current. It will be convenient to speak of these two currents
respectively as descending and ascending, in detailing experiments 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, the phe-
nomena observed on closing and opening the circuit, and the effects of an
interrupted current.

532 NEEVOUS SYSTEM.

During the passage of a feeble constant current through a nerve, what-
ever be its direction, there are 110 convulsive movements and no evidences of
pain. This fact has long been recognized by physiologists, who at first lim-
ited the effects of electricity upon the nerves to two periods, one at the clos-
ing of the circuit and the other at its opening. It will be seen, however, that
the passage of electricity through a portion of a nervous trunk produces a
peculiar condition in the nerve, which has been described under the name
of electrotonus ; but the fact remains that neither motion nor sensation is
excited in a mixed nerve during the actual passage of a feeble constant cur-
rent.

Law of Contraction. — All who have experimented upon the action of
galvanism upon the nerves have noted the fact alluded to above, that con-
traction occurs only on closing or on opening the circuit. Take, for exam-
ple, a frog's leg prepared with the nerve attached : Place one pole of a gal-
vanic apparatus on the nerve and then make the connection, including a
portion of the nerve in the circuit. With the feeblest current, contraction oc-
curs only on closing the circuit. With what is called the " weak " current
(Pfluger), contraction occurs only on closing the circuit, for currents in
either direction. With the " moderate " current, contraction occurs both on
closing and on opening the circuit, for currents in either direction. 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 phenomena constitute what is called Pfliiger's ie law of
contraction." The explanations of this law are the following :

The stimulus which gives rise to the closing contraction occurs at the
cathode, when the electrotonus produced by the passage of the current be-
gins. The stimulus which produces the opening contraction occurs at the
anode, when the electrotonus disappears. The impulse is always stronger
when the electrotonus begins than when it disappears. Therefore, when the
current is so feeble that but one contraction is produced, this contraction
occurs only on closing the circuit, for both ascending and descending currents.

With the " moderate " current, the strength of the opening impulse is
sufficient to produce a contraction ; and contractions therefore occur both on
opening and closing the circuit, for both ascending and descending currents.

Strong currents produce closing contraction with the descending current,
for the reason that the current destroys the conducting power of that portion
of the nerve included between the poles of the battery, and, the stimulus
occurring only at the cathode (see above), and the cathode being applied to
that portion of the nerve nearest the muscle, the closing impulse only is
conveyed to the muscle. The opening impulse (at the anode) is cut off from
the muscle by the loss of conducting power in the intrapolar portion of the
nerve. With the ascending current, the opening impulse, occurring at the
anode, which is nearest the muscle, produces an opening contraction, and
the closing impulse, which is at the cathode, is not conducted to the muscle.

While the constant current does not usually excite contractions during
the time of its passage through a nerve, with a certain strength of current,

ACTION OF ELECTRICITY UPON THE NERVES. 533

the muscle is thrown into a tetanic condition. This is called " closing teta-
nus." When a constant current, not of sufficient strength to produce closing
tetanus, is passed for several minutes through a long extent of nerve, a very
vigorous contraction occurs on opening the circuit, which is followed by teta-
nus lasting for several seconds. This is called " opening tetanus." After a
time, this varying with the excitability of the nerve and the strength of the
current, the descending current will destroy the nervous excitability, but it
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 con-
traction follows the opening of the circuit ; and this contraction, within cer-
tain limits, is more vigorous the longer the current is passed. At the same
time, the prolonged passage of the ascending current increases the excitabil-
ity of the nerve for any kind of stimulus.

After a certain time, which varies in different animals, the nervous excita-
bility becomes somewhat enfeebled by exposure of the parts. The phenom-
ena then observed belong to the conditions involved in the process of " dying "
of the nerve. In the later stages of this condition, the phenomena may be
formulated 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. With 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 excitability of the parts has become somewhat diminished by exposure or
by electric stimulation of the nerve.

If a sufficiently powerful constant current be passed through a nerve, dis-
organization of its tissue takes place, and the nerve finally loses its excita-
bility, 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 generally accepted by physiologists.

The muscular contraction produced by electric stimulation of a nerve is
more vigorous the greater the extent of the nerve included between the poles
of the battery. This fact has long been observed, and its accuracy may easily
be verified. It would naturally be expected that the greater the amount of
stimulation, the more marked would be the muscular action ; and the stimu-
lation seems to be increased in proportion to the extent of nerve through
which the current is made to pass.

The excitability of a nerve, it is well known, may be exhausted by the
repeated application of electricity, whatever be the direction of the current,
and it is more or less completely restored by repose. When it has been ex-
hausted for the descending current, it will respond to the ascending current,
and vice versa ; and after it has been exhausted by the descending current,

534

NERVOUS SYSTEM.

it is restored more promptly by stimulation with the ascending current than
by absolute repose, and vice versd. This phenomenon, observed by Volta, is
known as " voltaic alternation."

Many of the phenomena illustrating the law of contraction may be ob-
served without the use of complicated apparatus. A form of battery, very

convenient for some of these experiments,
is the one described by Bernard. It con-
sists 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
(20 centimetres) long, which, when moist-
ened with water slightly acidulated with
acetic acid, will give a constant current of
about the required strength.

The law of contraction is applicable to
inhibitory nerves, as the inhibitory nerve of
the heart, the difference being that the
stimulation produces inhibition instead of

FIG. 187.— Electric forceps (LiSgeois).
c, copper ; z, zinc.

FIG. 188. — Arrangement of frog^s legs prepared so as to
show induced contraction (Liegeois).

contraction. It also holds good for sensory nerves, the effects being observed
by noting the reflex contractions produced '(Pfliiger).

A peculiar phenomenon, discovered by Matteucci, has been called " in-
duced muscular contraction." If the nerve of a galvanoscopic frog's leg be
placed in contact with the muscles of another leg prepared in the same way,
stimulation of the nerve, giving rise to contraction of the muscles with which
the nerve of the first leg is in contact, will induce contraction in the muscles
of both. This experiment may be extended, arid contractions may thus be
induced in a series of legs, the nerve of one being in contact with the mus-
cles of another. It is shown that " induced contraction " is not due to an
actual propagation of the electric current but to a stimulus attending the

ELECTROTONUS. 535

muscular contraction itself, by the fact that the same phenomena occur when
the first muscular contraction is produced by mechanical or chemical excita-
tion of the nerve.

Galvanic Current from the Exterior to the Cut Surface of a Nerve. — Be-
fore studying 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
with a direction from the exterior to the cut surface. It has been roughly
estimated that the nerve-current has one-eighth to one-tenth the intensity of
the muscular current (Matteucci). The existence of the nerve-current has,
as far as is known, no more physiological significance than the analogous
fact observed in the muscular tissue. Galvanic currents also exist in the
skin and in mucous membranes, the direction being from the outer surface,
which is positive, to the inner surface, which is negative.

Electrotonus, Anelectrotonus and Catelectrotonus. — When a constant gal-
vanic current is passed through .a portion of a freshly prepared nerve, a large
part of the entire nerve is brought into a peculiar electric condition (Du
Bois-Eeymond). While in this state, the nerve will deflect the needle of a
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. There
is also a peculiar condition of that portion of the nerve near the anode,
differing from the condition of the nerve near the cathode. Near the anode
the excitability of the nerve is diminished, and this condition is called ane-
electrotonus. Near the cathode the excitability is increased, and this condi-
tion is called catelectrotonus (Pfluger). These phenomena have been the
subject of extended investigation by electro-physiologists ; and although the
conditions are not to be included in the physiological properties of the
nerves, they have considerable pathological and therapeutical importance.
It is well known, for example, that electricity is often one of the most effi-
cient agents at command for the restoration of the properties of nerves
affected with disease ; and the constant current has been extensively and
successfully used as a therapeutical 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, in a measure explains how this result may
be obtained.

The electrotonic condition is marked in proportion to the excitability of
the nerve, and it is either entirely absent or extremely feeble in nerves that
are dead or have lost their excitability. If a strong ligature be applied to the
extrapolar portion of a 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 that the phenomena of electrot-
onus depend upon the physiological integrity of nerves. A dead nerve or

536

NERVOUS SYSTEM.

one that has been divided or ligated 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 these phenomena are not to be compared with those ob-
served in nerves that retain their physiological properties.

As stated above, the electrotonic condition is not restricted to that por-
tion of the nerve included between the poles of the battery. The condition
of the portion between the poles is called intrapolar electrotonus, and the
condition of the nerve outside of the poles is called extrapolar electrotonus.

When a portion of a nerve is subjected to a moderately strong constant
current, the conditions of the extrapolar portions corresponding to the two
poles of the battery are entirely different. Near the anode the excitability
of the nerve and the rate of nervous conduction are diminished. If, how-
ever, a galvanometer be applied to this portion of the nerve, its electromo-
tive power, measured by the deflection of the galvanometric needle, is in-
creased. On the other hand, near the cathode the excitability of the nerve
is increased, as well as the rate of nervous conduction, but the electromo-
tive power is diminished.

The anelectrotonic condition, on the one hand, and the catelectrotonic
condition, at the other pole of the battery, are marked in extrapolar portions
of the nerve and are to be recognized, as well, in that portion through
which the current is passing ; but between the the poles, there is a point
where these conditions meet, as it were, and where the excitability is un-
changed. This has been called the neutral point. When the galvanic cur-
rent 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 cur-
rent the negative pole rules over a wider territory
than the positive pole, whereas in a strong current
the positive pole prevails " (Rutherford).

The conditions of extrapolar excitability vary
with the direction of the current applied to the
nerve. A convenient stimulus with which to meas-
ure this excitability is a solution of common salt,
which excites more or less powerful tetanic contrac-
tions of the muscles. These variations are illus-
trated in Fig. 189.

In Fig. 189, A, a descending constant current is
applied to the nerve. When the circuit is open, the
salt applied to the nerve at R produces contrac-
tions of the muscle. If the circuit be closed, the
contractions either become much less vigorous

or

Fro. 189.— Method of testing the

excitability in electrotonus

(Landois).
The positive poles are + and

the negative poles are — ;

b ' ?ne^kuneSiHtionXcited cease> on account of the diminished excitability near

the anode. This is called descending extrapolar an-

electrotonus. If the salt be applied at R1} the contractions are increased in

ELECTROTONUS. 537

vigor by closing the circuit, on account of the increased excitability of the
nerve near the cathode. This is called descending extrapolar catelectronus.

In Fig. 189, B, the conditions are reversed. The polarizing current here
must be very weak, as a strong current may destroy the conducting power of
the intrapolar portion of the nerve and thus prevent the conduction of the
stimulus to the muscle when the salt is applied at E. On closing the cir-
cuit, there is ascending extrapolar catelectronus at R, and ascending extra-
polar anelectronus at RJ.

Within certain limits, the greater the strength of the constant current
applied to the nerve and the greater the length of nerve included between
the poles of the battery, the greater is the deflection of the galvanoscopic
needle, by which the electrotonic condition is measured.

Electrotonic conditions in sensory nerves are measured by reflex move-
ments produced by the action of a stimulus applied to these nerves. The
variations in excitability of inhibitory nerves, produced by a constant current,
are indicated by increase or diminution in the inhibitory action. The phe-
nomena in sensory and inhibitory nerves are analogous to those observed in
motor nerves. The influence of a constant current upon the muscle current
is distinct though feeble, producing a kind of electrotonic condition of
muscle.

Negative Variation. — When a rapidly interrupted current is applied to a
nerve so as to produce a tetanic condition of the muscles to which it is dis-
tributed, the normal or tranquil nerve-current is overcome, and a galvano-
scopic needle applied to the nerve, which was first deviated by the nerve-
current, will be observed to retrograde and will finally return to zero (Du
Bois-Reymond). This may also be observed to a slight degree under the in-
fluence of mechanical or chemical stimulation of the nerve, the proper nerve-
current being diminished, but generally not abolished. The variation of the
needle under the influence of the tetanic condition has been called negative
variation. It is not known that this has any important physiological or
pathological significance.

538 NERVOUS SYSTEM.

CHAPTER XVII.

SPINAL AND CRANIAL

Spinal nerves— Cranial nerves— Anatomical classification— Physiological classification— Motor oculi cora-
munis (third nerve)— Physiological anatomy— Properties and uses— Influence upon the movements of
the iris— Patheticus, or trochlearis (fourth nerve)— Physiological anatomy— Properties and uses— Motor
oculi externus, or abducens (sixth nerve)— Physiological anatomy— Properties and uses— Nerve of mas-
tication (the small, or motor root of the fifth)— Physiological anatomy— Properties and uses— Facial,
or nerve of expression (seventh nerve) — Physiological Anatomy — Intermediary nerve of Wrisberg —
Alternate paralysis— General properties— Uses of the chorda tympani— Influence of various branches
of the facial upon the movements of the palate and uvula— Spinal accessory (eleventh nerve)— Physio-
logical anatomy— Uses of the internal branch from the spinal accessory to the pneumogastric— Influ-
ence of the spinal accessory upon the heart— Uses of the external, or muscular branch of the spinal
accessory— Sublingual, or hypoglossal (twelfth nerve)— Physiological anatomy— Properties and uses
— Trifacial, or trigeminal (fifth nerve)— Physiological anatomy— Properties and uses— Pneumogastric
(tenth nerve)— Physiological anatomy— Properties and uses— General properties of the roots— Prop-
erties and uses of the auricular nerves— Properties and uses of the pharyngeal nerves— Properties
and uses of the superior laryngeal nerves — Properties and uses of the inferior, or recurrent laryngeal
nerves— Properties and uses of the cardiac nerves— Depressor nerve of the circulation— Properties and
uses of the pulmonary nerves— Properties and uses of the oesophageal nerves— Properties and uses of
the abdominal nerves.

WITH a knowledge of the general properties of the nerves belonging to the
cerebro-spinal system, it is easy to understand the uses of most of the special
nerves, 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 sphincters and the integument covering these
parts, the posterior segment of the head, and to certain mucous membranes.
It is evident, therefore, that an account of the exact office 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 treatises
on descriptive anatomy.

SPINAL NERVES.

There are thirty-one pairs of spinal nerves ; eight cervical, twelve dorsal,
five 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 possessed of motor and sensory properties. It divides outside of the spinal
canal into two branches, anterior and posterior, both containing motor and
sensory filaments, which are distributed respectively to the anterior and the pos-
terior 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.

The anterior branches of the upper four 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 excep-
tion 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. The ante-
rior branches of the upper four lumbar nerves form the lumbar plexus. The
anterior branch of the fifth lumbar nerve and a branch from the fourth

CRANIAL NERVES.

539

unite with the anterior branch of the first sacral, forming the lumbo-sacral
nerve, and enter into the sacral plexus. The upper three anterior sa-
cral 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 muscles of
the anus. The fifth
anterior sacral and
the coccygeal are
distributed to parts
about the coccyx.

The posterior
branches of the spi-
nal nerves are very
simple in their dis-
tribution. With
one or two excep-
tions, which have
no great physiolog-
ical importance,
these nerves pass
backward from the
main trunk, divide

into two branches, FlQ m.-Cervical por- FIG. 191.
pvi-prnal ?mrl infpv tion of the spinal cord tion o

(Hirschfeld) cord (Hirschfeld). and

nal, and their fila- (Hirschfeld).

.a j • A -U *' antero-inferior wall of the fourth ventricle ; 2, superior peduncle of the
ineiltS OI UlStriDU- 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 ; 13, 13, anterior roots
of the nerves ; 14, division of the nerves into two branches ; 15, lower ex-

Fio.

192.— Inferior por-
l cord,
equina

tion of the spinal cord,
cauda

tremity of the cord : 16, 16, coccygeal ligament ; 17, 17, cauda equina ;
I- VIII, cervical nerves ; I, II, in, IV-XII, dorsal nerves ; I, II-V, lumbar

tion go to the mus-
cles and to integu-
ment behind the
spinal column.

It is farther im-
portant to note, that all of the cerebro-spinal nerves anastomose with the
sympathetic.

CRANIAL NERVES.

Many of the cranial nerves are peculiar, either as regards their general
properties or in their distribution to parts concerned in special functions.
In some of these nerves, the most important facts concerning their distribu-
tion have been ascertained only by physiological experimentation, and their
anatomy is inseparably connected with their physiology. It would be desira-
ble, if it were possible, to classify these nerves with reference strictly to their
properties and uses ; but this can be done only to a certain extent. The
classification of the cranial nerves adopted by most anatomists is the arrange-

540

NERVOUS SYSTEM.

FIG. 193.— Roots of tl

al nerves (Hirschfeld).

I. Olfactory.
II. Optic. '

III. Motor oculi communis.

IV. Patheticus.

V. Nerve of mastication and trifacial.
VI. Motor oculi externus.
VII. Facial.
VIII. Auditory.
IX. Glosso-pharyngeal.
X. Pneumogastric.
XI. Spinal accessory.
XII. Sublingual.

The numbers 1 to 15 refer to branches which will be de-
scribed hereafter.

Spinal accessory. (Eleventh pair.)
Sublingual. (Twelfth pair).

ment of Sommerring, in which the
nerves are numbered from before
backward, in the order in which
they pass out of the skull, making
twelve pairs.

CLASSIFICATION OF THE CRANI-
AL NERVES.

Nerves of Special Sense.
Olfactory. (First pair.)
Optic. (Second pair.)
Auditory. (Eighth pair.)
Gustatory, comprising a part
of the glosso-pharyngeal (ninth
pair) and a small filament from
the facial (seventh pair) to the lin-
gual branch of the fifth pair.

Nerves of Motion.

Nerves of motion of the eye-
ball, comprising the motor oculi
communis (third pair), the pathet-
icus (fourth pair), and the motor
oculi externus (sixth pair).

Nerve of mastication, or motor
root of the fifth pair.

Facial, sometimes called the
nerve of expression. (Seventh
pair.)

Nerves of General Sensibility.

Trifacial, or large root of the fifth pair.

A portion of the glosso-pharyngeal. (Ninth pair.)

Pneumogastric. (Tenth pair.)

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 pneumo-
gastric and the inferior maxillary branch of the trifacial.

The nerves of special sense have little or no general sensibility ; 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 capable of conveying to the nerve-centres only certain peculiar impres-
sions, such as odors, for the olfactory nerves, light, for the optic nerves, and

MOTOR OCULI COMMUNIS.

541

sound, for the auditory nerves. The proper transmission of these impres-
sions, however, involves the action of accessory parts, more or less complex ;
and the properties of these nerves will be fully considered in connection with
the physiology of the special senses.

MOTOE OCULI COMMUNIS (THIKD NERVE).

The third cranial nerve is the most important of the motor nerves dis-
tributed to the muscles of the eyeball. Its physiology is readily understood
in connection with its distribution, the only point at all obscure being its re-
lations to the movements of the iris, upon which the results of experiments
are somewhat contradictory.

Physiological Anatomy. — The apparent origin of the third nerve is from
the inner edge of the crus cerebri, directly in front of the pons Varolii, mid-
way between the pons and the corpora albicantia. It presents here eight or
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 en-
cephalon 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 mid-
dle filaments passing inward, the anterior,
inward and forward, and the posterior,
inward and backward. It is probable
that the middle filaments pass to the me-
dian line and decussate with correspond-
ing fibres from the opposite side. The
anterior filaments pass forward and are
lost in the optic thalamus. The posterior
filaments on either side pass backward to
a gray nucleus beneath the aqueduct of
Sylvius and here decussate with fibres
from the opposite side, This decussation
of the fibres of origin of the third nerves
is important in connection with the har-

. .

mony 01 action 01 the ins and the mus-
cles of the eyes upon the two sides.

The distribution of the third nerve is

vorv airnrVlp A« it -na««P« into thp nrhit
Very Simple. AS It passes into tne OrDlt,

Vw7 tVtP a-nnPTinirlal fiaanra it rlivirlpa into

by tne spnenoiaai nssure, it divides into
two branches. The superior, which is the
smaller, passes to the superior rectus mus-

cle of the eye, and certain of its filaments are continued to the levator palpe-
brae superioris. The inferior division breaks up into three branches. The
internal branch passes to the internal rectus muscle ; the inferior branch, to
the inferior rectus ; the external branch, the largest of the three, is distribu-
ted to the inferior oblique muscle, and in its course, it sends a short and
36

FIO. 194.— Distribution of the motor ocuii

communis (Hirschfeld).

trunjc 0/ the motor ocuii communis ; 2, su-
f (i &/£££ £*£ S&

inferior rectus ; 6, branch to the inferior
oblique muscle ; 7, branch, to the lenticular
ganglion ; 8, motor ocuii externus ; 9, fila-

g^ of tht; motor oculi externus knksto-
the sympathetic ; 10, ciliary

542 NERVOUS SYSTEM.

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 influence 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 Uses of the Motor Oculi Communis. — Stimulation of 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 stimulus, however, be applied a
little farther on in the course of the nerve, there are evidences of sensibility ;
and this is readily explained by its communications with the ophthalmic
branch of the trifacial. At its root, therefore, this nerve is exclusively motor,
and its office is connected entirely with the action of muscles.

The phenomena which are observed after section of the motor oculi com-
munis in living animals are the following :

1. Falling of the upper eyelid, or blepharoptosis.

2. External strabismus, immobility of the eye except in an outward di-
rection, inability to rotate the eye on its antero-posterior axis in certain
directions, with slight protrusion of the eyeball.

3. Dilatation of the pupil, with a certain degree 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 animal in which the nerve has been divided can not
raise the lid, but can press the lids together by a voluntary effort. In the
human subject the falling of the lid gives to the face a peculiar and char-
acteristic expression. The complete loss of power shows that the levator
palpebrae superioris muscle depends upon the third nerve entirely for its mo-
tor filaments. In pathology, external strabismus is frequently observed with-
out falling of the lid, the filaments distributed to the levator muscle not be-
ing affected.

The external strabismus and the immobility of the eyeball except in an
outward direction are due to paralysis of the internal, superior, and inferior
recti muscles, the external rectus acting without its antagonist. This condi-
tion requires no farther explanation. These points are 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 outward, the
globe remains motionless.

It is somewhat difficult to note the effects of paralysis of the inferior
oblique muscle, which also is supplied by the third nerve. This muscle, act-
ing 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,

MOTOR OCULI COMMUNIS. 543

having no antagonist, rotates the globe upward and inward, directing the pupil
downward and outward. The action of the oblique muscles is observed
when the head is moved alternately toward one shoulder and the other. In
the human subject, when the inferior oblique muscle on one side is paralyzed,
the eye can not 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 supe-
rior 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 can not 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.

The third nerve sends a filament to the ophthalmic ganglion of the sym-
pathetic, and from this ganglion, the short ciliary nerves take their origin
and pass to the iris. 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.

Herbert Mayo (1823) made experiments on thirty pigeons, living or just
killed, upon the action of the optic, the third and the fifth nerves, on the
iris. When the third nerves were divided in the cranial cavity in a living
pigeon, the pupils became fully dilated and did not contract on the admission
of intense light ; and when the same nerves were pinched in the living or
dead bird, the pupils were contracted for an instant on each stimulation of
the nerves. The same results followed division or stimulation of the optic
nerves, under similar conditions ; but when the third nerves had been
divided, no change -in the pupil ensued upon stimulating the entire or
divided optic nerves.

The third nerves animate the muscular fibres that contract the pupil, the
contraction produced by stimulation of the optic nerves being reflex in its
character. Longet divided the motor oculi and the optic nerve upon the right
side. He found that stimulation 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 amaurosis 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

5M NERVOUS SYSTEM.

its operations are rather characteristic of the action of the sympathetic sys-
tem and the non-striated muscular tissue. It has been found, also, by Ber-
nard, in experiments upon rabbits, that the pupil is not immediately 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 op-
eration, however, the pupil is generally found dilated, and it may slowly con-
tract when the eye is exposed to the light. In one experiment this occurred
after the eye had been exposed for an hour. Farther experiments have shown
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 stimulation of the fifth nerve
produces contraction of the pupil. This takes place after as well as before di-
vision 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 stimulation of the motor oculi itself did not pro-
duce contraction of the pupil, but this result followed when he stimulated
the ciliary nerves coming from the ophthalmic ganglion. Chauveau, in experi-
ments upon horses, did not observe contraction of the pupil following stimula-
tion of the motor oculi, although it was sometimes seen 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 stimulation of the trunks of
the third pair. When the eye is turned inward by a voluntary effort, the pu-
pil is contracted ; and when the axes of the two eyes are made to converge
strongly, as in looking at near objects, the contraction is very considerable
(Miiller).

The third nerve contains filaments which preside over voluntary move-
ments of the ciliary muscle in the accommodation of the eye to vision at dif-
ferent distances.

The following case illustrates, in the human subject, nearly all of the
phenomena following paralysis 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, com-
plete 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 paral-
lel, 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

PATHETICUS, OR TROCHLEARIS. 545

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 NERVE).

The physiology of the patheticus is very simple and resolves itself into
the action of a single muscle, the superior oblique.

Physiological Anatomy. — The apparent origin of the patheticus is from
the superior peduncles of the cerebellum ; but it may be easily followed to the
valve of Vieussens. The deep roots can be traced, passing from without in-
ward, to the following parts : One filament is lost in the substance of the
peduncles ; other filaments pass from before backward into the valve of Vieus-
sens and are lost, and a few pass into the f renulum ; a few filaments pass
backward 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 fibres can be traced to a nucleus in the floor of the aque-
duct of Sylvius, beneath the nucleus of the third nerve. The decussation of
the fibres of origin of the fourth nerve 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
sensory and coming from the ophthal-
mic branch of the fifth. It also re-
ceives a few filaments from the sympa-
thetic.

Properties and Uses of the Pathet-
icus.— Direct observations upon the pa-
theticus in living animals have shown
that it is motor, and its stimulation ex-
cites contraction of the superior oblique
muscle only. This muscle arises just
above the inner margin of the optic fo-
ramen, passes forward, along the upper FIG. lOS.— ^Distribution of the patheticus (Hirsch-

wall of the orbit at its inner angle, to a Ii0lfactory nerve. jrj^ nerves; m, motor
little, cartilaginous ring which serves as ^^^^SSS^^^S, and
a pulley. From its origin to this point S^^S^^^i^onSf^l
it is muscular. Its tendon becomes ?i3'A?< 6' 7< 8' 9, 10, ophthalmic division of

the fifth nerve, with its branches.

rounded just before it passes through

the pulley, where it makes a sharp curve, passes outward and slightly back-
ward, and becomes spread out to be attached to the globe, at the superior and

546

NERVOUS SYSTEM.

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 ro-
tates the eye upon an oblique, horizontal axis, from below upward, from
without inward and from behind forward. By its action, the pupil is di-
rected downward and outward. It is the antagonist of the inferior oblique,
the action of which has been described in connection with the motor oculi
communis. When the patheticus is paralyzed, the eyeball is immovable, as
far as rotation is concerned. When the head is moved toward the shoulder,
the eye does not rotate to maintain the globe in the same relative position, and
there is double vision.

MOTOR OCULI EXTER^US, OR ABDUCENS (SIXTH NERVE).

Like the patheticus, the motor oculi externus is distributed to but a single

muscle. 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 separating the anterior corpus pyramidale of the medulla oblon-

gata from the pons Varolii, from the up-
per portion of the medulla and from 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 supe-
rior 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
ventricle. Vulpian followed these fibres
to within about two-fifths of an inch (10
mm.) of the median line, but they could
not be traced beyond this point. It is

FIG. m.-Distmbution^h^motor oculi e^ not known that tne fibres of the two sides

it trunk of the motor oculi communis, with- decussate. From this origin the nerve

its branches (2, 3, 4, 5, 6, 7) ; 8, motor oculi

externus, passing to the external rectus paSSCS into the 01'blt by the SphenOldal

muscle; 9, filaments of the motor oculi ex- n T •-,•,••,,-, i -IJJT

ternus, anastomosing with the sympathet- IlSSUre and IS distributed exclusively to the
ic ; 10, ciliary nerves. , .. inn TUT

external rectus muscle 01 the eyeball. In

the cavernous sinus it anastomoses with the sympathetic through the carotid
plexus and receives a filament from Meckel's ganglion. It also receives
sensory filaments from the ophthalmic branch of the fifth. It is thought by
some anatomists that this nerve occasionally sends a small filament to the
ophthalmic ganglion ; and it was stated by Longet that this branch, which
is exceptional, exists in those cases in which paralysis of the motor oculi
communis, which usually furnishes all the motor filaments to this ganglion,
is not attended with immobility of the iris.

Properties and Uses of the Motor Oculi Externus. — Direct experiments

NERVE OF MASTICATION. 547

have shown that the motor oculi externus is entirely insensible at its origin, its
stimulation producing contraction of the external rectus muscle and no pain.
The same experiments illustrate the action of the nerve, inasmuch as its
stimulation is followed by 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 converging strabismus, due to the
unopposed action of the internal rectus muscle.

With regard to the associated movements of the eyeball, it is important to
note that all of the muscles of the eye which have a tendency to direct the
pupil inward or to produce the simple movements upward and downward
(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 of the two muscles that move the globe so as to direct the pupil
outward, except the inferior oblique (the superior oblique and the external
rectus), is supplied by a special nerve. The movements of the eyeball will
be described more minutely in connection with the physiology of vision.

NERVE OF MASTICATION (THE SMALL, OR MOTOR ROOT OF THE FIFTH

NERVE).

The motor root of the fifth nerve is entirely distinct from its sensory
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 cav-
ity has demonstrated its distribution to a particular set of muscles.

Physiological Anatomy. — 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 six to eight rounded fila-
ments. If a thin layer of the pons covering these filaments be removed, the
roots will be found penetrating its substance, becoming flattened, passing
under the superior peduncles of the cerebellum and going to a gray nucleus,
with large multipolar cells, in the anterior wall of the fourth ventricle, near
the median line. At this point, the fibres change their direction, passing from
without inward and from behind forward toward the median line, the fibres
diverging rapidly. The posterior fibres pass to the median line, and cer-
tain of them decussate with 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 ante-
rior wall of the fourth ventricle. Here they lose their white color, become
gray and present a number of globules of gray substance between their fila-
ments.

From the origin above described, the small root passes beneath the gan-
glion 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. With-

548

NERVOUS SYSTEM.

in 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 sensory branch.

The inferior maxillary nerve, made up of the motor root and the inferior
maxillary branch of the sensory root, just after it passes out 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 dis-
tributed to the mus-
cles of mastication.
It gives off five
branches. The first
of these passes to
be distributed to
the masseter mus-
cle, in its course oc-
casionally giving off
a small branch to
the temporal mus-
cle and a filament
to the articulation
of the inferior max-
illa with the tem-
poral bone. The
two deep temporal
branches are dis-
tributed to the tem-
poral muscle. The
buccal branch sends
filaments to the
external pterygoid
and the temporal
muscles, and a small
branch is distribu-

FIG. 197.— Distribution of the small root of the fifth nerve (Hirschfeld).
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 ; 5, 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, auricu-
lar branches ; 11, anastomosis with the facial nerve ; 12, lingual branch ;
13, branch of the small root to the mylo-hyoid muscle ; 14, inferior den-
tal nerve, with its branches (15, 15) ; 16, mental branch ; 17, anastomosis
of this branch with the facial nerve.

ted to the internal

pterygoid muscle. From the posterior branch, which is chiefly sensory but
contains some motor filaments, branches are sent to the mylo-hyoid 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 gives in general terms the distribution of the
nerve of mastication, without taking into consideration its various anastomo-
ses, the most important of which are with the facial. 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

NERVE OF MASTICATION. 549

motor filaments only, to the external pterygoid and the temporal, its final
branches of distribution being sensory and going to integument and to
mucous membrane.

In treating of the physiology of digestion, a table has been given of the
muscles of mastication, 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 belly 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 Uses of the Nerve of Mastication. — The anatomical dis-
tribution of the small root of the fifth nerve points at once to its uses.
Charles Bell, whose ideas of the nerves were derived almost entirely from
their anatomy, called it the nerve of mastication, in 1821, although he did
not state that any experiments were made with regard to its action. All ana-
tomical and physiological writers since that time have adopted this view. It
would be difficult if not impossible to stimulate the root in the cranial cav-
ity in a living animal ; but its Faradization in animals just killed determines
very marked movements of the lower jaw. Experiments have demonstrated
the physiological properties of the small root, which is without doubt solely
a nerve of motion.

The observations upon section of the fifth pair in the cranial cavity
are most important in connection with the uses of its sensory branches and
will be referred to in detail in treating of
the properties of the large root. In addi-
tion to the loss of sensibility following sec-
tion of the entire nerve, Bernard noted
the effects of division of the small root,
which can not be avoided in the operation.
In rabbits the paralysis of the muscles of
mastication upon one side, and the con-
sequent action of the muscles upon the
unaffected side only, produce, a few days
after the operation, a remarkable change ^/feV^t^
in the appearance of the incisor teeth. A ^^ormai condition.

As the teeth in these animals are p-radu- B> indsors, seven days after section of the

nerve on one side.

ally worn away in mastication and repro-
duced, the lower jaw being deviated by the action of the muscles of the
sound side, the upper incisor of one side and the lower incisor of the other
touch each other but slightly and the teeth are worn unevenly. This makes
the line of contact between the four incisors, when the jaws are closed, ob-
lique instead of horizontal.

550 NERVOUS SYSTEM.

There is little left to say with regard to the uses of the motor root of the
fifth nerve, in addition to the description of the action of the muscles of mas-
tication, contained 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 can not be well
performed unless the mouth be closed by 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, animat-
ing all of the muscles concerned in this act, except two of the most unimpor-
tant depressors of the lower jaw (the genio-hyoid and the platysma myoides),
but it is concerned indirectly in deglutition.

FACIAL, OB NERVE OF EXPRESSION (SEVENTH NERVE).

The anatomical relations of the facial nerve are quite intricate and it
communicates freely with other nerves. As far as can be determined by exper-
iments 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.

Physiological Anatomy. — The facial nerve, has its apparent origin from
the lateral portion of the medulla oblongata, in the groove between the oli-
vary and restiform bodies, just below the border of the pons Varolii, its
trunk being internal to the trunk of the auditory nerve. It is separated from
the auditory by the two filaments constituting what is known as the interme-
diary nerve of Wrisberg, or the portio inter duram et mollem. As this little
nerve joins the facial, it is usually included in its root.

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 satisfactory. Its fibres pass inward, with one or two de-
viations 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
certain 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 decus-
sate ; the course of most of the fibres, however, has not been satisfactorily
established. The fibres of origin of the intermediary nerve of Wrisberg have
been traced to the nucleus of the glosso-pharyngeal.

It is evident from physiological experiments, that the decussation of the
fibres in the floor of the fourth ventricle itself is not very important. Vul-
pian 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 decus-
sation 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

FACIAL NERVE.

551

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 affected upon
the same side, and
not upon the side
of the hemiplegia.
This is called alter-
nate paralysis. In
view of these facts,
the phenomenon of'
hemiplegia upon
one side and facial
paralysis upon the «i
other is regarded
as indicating, with
tolerable certainty,
that the injury to
the brain has oc-
curred upon the
same side as the
facial paralysis,
either within or
posterior to the
pons Varolii.

As already stat-
ed, the fibres of or-
igin of the facial
have been traced to
the floor of the
fourth ventricle,
where a few decus-
sate but most of
them are lost. The
question now is,
whether or not the

. 199.— Superficial branches of the facial and the fifth (Hirschfeld).
lrunk of the facial ; 2, posterior auricular nerve ; 3, branch which it re-
ceives from the cervical plexus ; 4, occipital branch ; 5, 6, branches to the
muscles of the ear ; 7, digastric branches ; 8, branch to the stylo-hyoid
muscle ; 9, superior terminal branch ; 10, temporal branches ; 11, frontal
branches ; 12, branches to the orbicularis palpebrarum ," 13, nasal, or sub-
orbital branches ; 14, buccal branches ; 15, inferior terminal branch ; 16,
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, 31, 32, branches of the cer-
vical nerves.

fibres pass up through the pons and decussate above, as the pathological facts
just noted would seem to indicate. Anatomical researches upon this point
are not satisfactory, and the existence of such a decussation has never been
clearly demonstrated. The pathological observations, nevertheless, remain ;
and however indefinite anatomical researches may have been, there can be
no doubt that lesions in one lateral half of the pons affect the facial upon
the same side, while lesions above have a crossed action. The most that can
be said upon this point is that it is a reasonable inference from pathological
facts that the nerves decussate anterior to the pons.

552 NERVOUS SYSTEM.

The main root of the facial, the auditory nerve and the intermediary
nerve of Wrisberg pass together into the internal auditoYy meatus. At the
bottom of the mejitus, the facial and the nerve of Wrisberg enter the aquge-
ductus Fallopii, following its course through the petrous portion of the tem-
poral bone. In the aqueduct the nerve of Wrisberg presents a little, ganglio-
form enlargement (geniculate ganglion) 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 aquseductus Fallopii the facial gives off the following branches :

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 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 communicat-
ing branch passes between the facial and the pneumogastric, connecting these
nerves by a double inosculation.

The five branches above described are given off in the aquseductus Fal-
lopii. The following branches are given off after the nerve has emerged
from the cranial cavity :

1. Just after the facial has passed out at the stylo-mastoid foramen, it
sends a small, communicating branch to the glosso-pharyngeal nerve. Thi&
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 re-
trahens aurem and the attollens aurem, In its course this nerve receives a.
communicating branch of considerable size from the cervical plexus, by the
auricularis magnus. It sends some filaments to the integument. The in-
ferior, or occipital branch, the larger of the two, is distributed to the occipi-
tal portion of the occipito-frontalis muscle and to the integument.

3. The digastric branch is given off near the root of the posterior auricu-
lar. It is distributed to the posterior belly of the digastric muscle. In ita
course it anastomoses with filaments from the glosso-pharyngeal nerve.
From the plexus formed by this anastomosis, 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,
delicate branch is given off, which is not noticed in many 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

FACIAL NERVE. 553

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 a number of filaments with the glosso-pharyngeal. It
then sends filaments of distribution to the mucous membrane and finally
passes to the stylo-glossus and palato-glossus muscles.

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 distributed to the superficial muscles of the upper part of the face ; viz.,
the attrahens aurem, the frontal portion of the occipito-frontalis, the orbicu-
laris palpebrarum,. corrugator supercilii, pyramidalis nasi, levator labii supe-
rioris, levator labii superioris alaeque nasi, the dilators and compressors of the
nose, part of the buccinator, the levator anguli oris and the zygomatic mus-
cles. In its course it receives branches of communication from the auriculo-
temporal branch of the inferior maxillary nerve. It joins also with the tem-
poral branch of the superior maxillary and with branches of the ophthalmic.
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
inferioris, depressor anguli oris and platysma.

General Properties 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 produces paralysis of motion and no marked effects upon
sensation. It is evident, also, from the communications of the facial with
the fifth, that it probably contains in its course sensory fibres. Indeed, all
who have operated upon this nerve have found that it is slightly sensory
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 muscles ; but this root is joined by the intermediary nerve
of Wrisberg, which presents a small, ganglionic enlargement, that is analo-
gous to the ganglia upon the posterior roots of the spinal nerves. The testi-
mony 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 cer-
tain anatomical resemblance to the sensory nerves, chiefly by reason of its
ganglioform enlargement ; but direct experiments are wanting to show that
it is sensory.

Uses of the Branches of the Facial given off within the Aqueduct of Fal-
lopius. — 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 petrosal, 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 second and third
branches will be again considered, in connection with the physiology of the

554 NERVOUS SYSTEM.

internal ear. The fourth branch, the chorda tympani, is so important that
it demands special consideration. 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. In this branch, sensory filaments pass
from the pneumogastric and constitute a part of the sensory connections of
the facial.

Uses of the Chorda Tympani. — This nerve passes between the bones of
the ear and through the tympanic cavity, to the lingual branch of the infe-

rior maxillary division of the fifth^
which it joins at an acute angle, be-
tween the pterygoid muscles. As
regards the portion of the facial
which furnishes the filaments of the
chorda tympani, it is nearly certain
that these come from the intermedi-
ary nerve of Wrisberg.

There can be no doubt with re-
gard to the influence of the chorda
tympani upon the sense of taste in
the anterior two - thirds of the
tongue. In cases of disease or in-

FIG. 2QQ.—Chorda-tympani nerve (Hirschfeld). JUYJ in which the root of the facial

1, 2, 3, 4, facial nerve passing through the aqueeduc- • i-nvrklv£»fl on fhai fVio nV-nrrla fvm
tus Fallopii ; 5, ganglioform enlargement (genie- 1S involved SO mat me CHOraa tm-

Pani 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 two-thirds of the tongue, upon the side
corresponding to the lesion. The action of the chorda tympani will be con-
sidered again, in connection with the physiology of gustation.

Influence of Various Branches of the Facial upon the Movements 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 flaccid and the uvula is drawn to the opposite side ; but these phe-
nomena do not occur unless the nerve be affected at its root or within the
aquaeductus Fallopii. It is true that the uvula frequently is drawn to one
side or the other in persons unaffected 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. The filaments of the facial which influence the levator
palati and azygos uvulae muscles are derived from the large petrosal branch
of the nerve, passing to the muscles through Meckel's 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 (Longet). As regards the branches of communication from the
glosso-pharyngeal, Longet has mentioned a preparation by Richet, in the
museum of the Ecole de medecine, of Paris, in which branches of the facial

FACIAL NERVE. 555

upon one side pass directly to the palato-glossus and the palato-pharyngeus,
without any connection with the glosso-pharyngeal nerve. In the anatomical
description of the branches of the facial, it has already been noted that a
filament, described by Hirschfeld, passes to the stylo-glossus and the palato- .
glossus muscles. This is the filament affected when there is deviation of the
point of .the tongue.

In view of the 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 stimulation of the facial and the reflex action through
the glosso-pharyngeal and the facial, there can be little doubt that the mus-
cles of the palate and uvula are animated by filaments derived from the sev-
enth nerve. The effects of paralysis of these muscles are manifested by more
or less trouble in deglutition and in the pronunciation or certain words, with
great difficulty in the expulsion of mucus collected in the back part of the
mouth and the pharynx.

Uses of the External Branches of the Facial. — The general action of the
branches of the facial going to the superficial muscles of the face is suffi-
ciently evident, in view of what is known of the distribution of these branches
and the general properties of the nerve. Throughout the writings of 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 su-
perficial muscles of the face, not including those directly concerned in the act
of mastication. This being its general action, it is easy to assign to each of
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 action of which
has just been mentioned in connection with the movements of the palate.

The posterior auricular branch, becoming partly sensory 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-fron-
talis muscle. It animates the retrahens and the attollens aurem, muscles that
are little developed in man but are very important in certain of the inferior
animals. It also animates the posterior portion of the occipito-frontalis
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 action.
Both of these branches are slightly sensory, from their connections with
other nerves, and are distributed 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, on account of paralysis of the orbicularis muscle. In
cases of long standing, the globe of the eye may become inflamed from con-

556

NERVOUS SYSTEM.

stant 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 mus-
cles is inability to corrugate the brow upon one side.

Paralysis of the muscles that dilate the nostrils has been shown to have
an important influence upon respiration through the nose. It was the syn-
chronism between the acts of dilatation of the nostrils and the movements of
inspiration which first led 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, even in the human subject.

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.

FIG. 204. FIG. 205. FIG. 206.

Expressions of the face produced by contraction of the rmiscles under electrical excitation (Le Bon,

after Duchenne).

Fig. 201, front view of the face in repose.
Fig. 202, profile view.

Fig. 203, expression of laughter upon one side, produced by contraction of the zygomaticus major.
Fig. 204, expression of fear, produced by contraction of the frontal muscle and the depressors of the

lower jaw.

Fig. 205, expression of fear, profile view.
Fig. 206, expression of fear and great pain, produced by contraction of the corrugator supercilii and

the depressors of the lower jaw.

The influence of the nerve in the act of conveying odorous emanations to the
olfactory membrane is sufficiently evident, after what has been said con-
cerning 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, on account of the unopposed
action of the muscles upon the sound side, a phenomenon which is suf-

SPINAL ACCESSORY NERVE. 557

ficiently familiar. 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 prehension, 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 puffing movement with each act of expi-
ration, as if the patient were smoking a pipe.

The buccinator is not supplied by filaments from the nerve of mas-
tication but is animated solely by the facial. Paralysis of this muscle inter-
feres 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 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 action of the external branches of the facial is thus sufficiently sim-
ple ; and it is only as its deep branches affect the sense of taste, the move-
ments 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 aspect is remarkable, the face being absolutely expres-
sionless and looking as if it were covered with a mask.

SPIRAL ACCESSORY (ELEVENTH NERVE).

The spinal accessory nerve, from the great extent of its origin, its impor-
tant anastomoses with other nerves and its peculiar course and distribution,
has long engaged the attention of anatomists and physiologists, who have
advanced many theories with regard to its office. Its physiological history,
however, begins with comparatively recent experiments, which alone have
given a positive knowledge of its properties and uses.

Physiological Anatomy — The origin of this nerve is very extensive. 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 the bulbar portion, the roots from the cord constituting
the spinal portion. Inasmuch as there is a marked difference between the
uses of these two portions, the anatomical distinction just mentioned is im-
portant.

The superior roots arise by four or five filaments, from the lower half of
the medulla oblongata, below the origin of the pneumogastrics. These fila-
ments of origin pass to a gray nucleus in the medulla, below the origin of
the pneumogastric.

The spinal portion of the nerve arises from the upper part of the spinal
37

558

NERVOUS SYSTEM.

cord, between the anterior and posterior roots of the upper four or five cervi-
cal nerves. The filaments of origin are six to eight in number. The most
inferior of these is generally single, the other filaments frequently being
arranged in pairs. These take their origin from the lateral portion of the
cord and are connected with the anterior cornua of gray matter.

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 cav-
ity by the foramen magnum, and passes to the jugular foramen, by which it
emerges, 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 upper two-
cervical nerves. These filaments, how-
ever, are not constant. It frequently
though not constantly sends a few fila-
ments to the superior ganglion, or the
ganglion of the root of the pneumogas-
tric. After it has emerged by the jug-
ular foramen it sends a branch of con-
siderable size to the pneumogastric, from
which nerve it also receives a few fila-
ments of communication. In its course
it also receives filaments of communica-
tion from the anterior branches of the
second, third, and fourth cervical
nerves.

In its distribution the spinal acces-
sory presents two branches. The inter-
nal, or anastomotic branch, passes to-
the pneumogastric just below the plexi-
form enlargement which is sometimes
called the ganglion of the trunk of the
pneumogastric. This branch is com-
posed principally if not entirely of the
FIG. wr.-spinai accessory nerve (Hirechfeid). niaments that take their origin from

1, trunk of the facial nerve ; 2, 2, glosso-pharyn- . . .

geal nerve ; 3, 3, pneumogastrie ; 4, 4, 4, trunk the medulla ODlongata. As it TOinS the
of the spinal accessory ; 5, sublingual nerve ; , . . , , ... . , . .

6. superior cervical ganglion ; 7, 7, anasto- pneumogastric it Subdivides into tWO
mosis of the first two cervical nerves ; 8, ca- ,, , ml „ „ ,

rotid branch of the sympathetic; 9,10, 11,12, smaller branches. The first of these

13, branches of the glosso-pharyngeal; 14, 15, „ .. „ ,, -, -,

branches of the facial ; 16, otic ganglion ; 17, f Orms a portion of the pharyngeal

auricular branch of the pneumogastric ; 18, , , „ , , , . m,

anastomosing branch from the spinal acces- branch of the pneumogastric. I lie S6C-

ond becomes intimately united with the
pneumogastric, lying at its posterior
Portion, and furnishes filaments to the
inferior, or recurrent laryngeal branch,
which is distributed to all of the muscles of the larynx except the crico-

nerve ; 24, middle cervical ganglion.

SPINAL ACCESSORY NERVE. 559

thyroid. The passage of the filaments from the spinal accessory to the pharyn-
geal branch of the pneumogastric is easily observed ; but the fact that fila-
ments from this nerve pass to the larynx by the recurrent laryngeal has been
ascertained by physiological experiments.

The external, or large branch of the spinal accessory, called the muscular
branch, penetrates and passes through the posterior portion of the upper
third of the sterno-cleido-mastoid muscle, and goes to the anterior surface of
the trapezius, 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 receive motor fila-
ments from the spinal accessory, they are also supplied from the cervical
nerves; and consequently they are not entirely paralyzed when the spinal
accessory is divided.

Properties and Uses of the Spinal Accessory. — Notwithstanding the great
difficulty in exposing and operating upon the roots of the spinal accessory,
it has been demonstrated that their stimulation produces convulsive move-
ments in certain muscles. By stimulating the filaments that arise from the
medulla oblongata, contractions of the muscles of the pharynx and larynx
are produced, but no movements of the sterno-mastoid and trapezius. Stim-
ulation of the roots arising from the spinal cord produces movements of the
two muscles just mentioned and absolutely no movements in the larynx (Ber-
nard). 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 distributed to the muscles of the
pharynx and larynx, while the filaments from the spinal cord go to the ster-
no-cleido-mastoid and trapezius.

The trunk of the spinal accessory, after the nerve has passed out of the
cranial cavity, has a certain degree of sensibility. If the nerve be divided,
the peripheral extremity manifests recurrent sensibility, but the central end
is also sensible, probably from direct filaments of communication from the
cervical nerves and the pneumogastric.

Uses of the Internal Branch from the Spinal Accessory to the Pneumo-
gastric.— Bischoff attempted to ascertain the uses 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 sec-
tion of the nerves, that no satisfactory results were obtained. In two suc-
ceeding 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

560 NERVOUS SYSTEM.

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 neuti-
quam vox appellari potuit"). This experiment was made in the presence of
Tiedemann and Seubertus and was not repeated.

Bernard, who determined exactly the influence of the spinal accessory
over the vocal movements of the larynx, first repeated the experiments of
Bischoff ; but the animals operated upon died so soon, from haemorrhage or
other causes, that his observations were not satisfactory. After many unsuc-
cessful 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
forceps and drawing it out by the roots. The operation is generally most
successful in cats, although Bernard succeeded frequently in other animals.

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 partial paralysis of the sterno-mastoid and trapezius
muscles, the voice becomes extinct. Animals operated upon in this way
move the jaws and make evident eiforts to cry, but no vocal sound is emitted.
Bernard kept animals, with both nerves extirpated, for several months and
did not observe any return of the voice. His observations, which have been
fully confirmed, show that the internal branch of the spinal accessory is the
nerve of phonation. The filaments which preside over the vocal movements
of the larynx pass in greatest part through the recurrent laryngeal branches
of the pneumogastrics ; but the recurrent laryngeals also contain motor fila-
ments from other sources, which latter are concerned in the respiratory move-
ments of the glottis.

Influence of the Internal Branch of the Spinal Accessory upon Degluti-
tion.— 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 can not be completely closed to prevent the entrance
of foreign bodies into the air-passages. In rabbits particularly, it has been
noted that particles of food penetrate the trachea and find their way into the
lungs. 2. The spinal accessory furnishes filaments to the pharyngeal 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 tendency 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 difficulty 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. — The spinal accessory
furnishes to the pneumogastric the inhibitory fibres which influence the
action of the heart. A sufficiently powerful Faradic current, passed through
one pneumogastric only, will in some animals arrest the cardiac movements.
Waller found that if he extirpated the spinal accessory upon one side, after
four or five days the action of the heart could not be arrested by stimulating

SPINAL ACCESSORY NERVE. 561

the pneumogastric upon the same side ; but inhibition followed stimulation
of the pneumogastric upon the opposite side, on which the connections with
the spinal accessory were intact. In these observations, it seemed necessary
that a sufficient time should elapse after extirpation of the spinal accessory
for the excitability of the filaments that join the pneumogastric to become
extinct ; but the experiments are sufficient to show the direct inhibitory in-
fluence of the spinal accessory upon the heart. After extirpation of the spi-
nal accessory, degenerated fibres are found in the trunk of the pneumogastric.
The mechanism of inhibition of the heart has already been considered in
connection with the physiology of the circulation.

Uses of the External, or Muscular Branch of the Spinal Accessory. —
Observations have shown that the internal branch of the spinal accessory,
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 irregularity of the movements of the
anterior extremities and suffer from shortness of breath after violent muscu-
lar exertion. The use of the corresponding extremities in the human subject
is so different, that it is not easy to make a direct application of these experi-
ments ; still, certain inferences may be drawn from them with regard to the
action of the external branch in man.

In prolonged vocal efforts, the vocal chords are put upon the stretch, and
the act of expiration is different from that in tranquil breathing. In sing-
ing, for example, the shoulders frequently are fixed ; and this is done to some
extent by the action of the sterno-cleido-mastoid and the trapezius. It is
probable, then, that the action of the 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 regu-
lated by the expiratory muscles, and the other acting upon the vocal chords.

In what is known 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 probably due to the want of syn-
chronous action of the sterno-cleido-mastoid and trapezius. The irregularity
in the movements of progression in animals in which either both branches
or the muscular branches alone have been divided is due to anatomical pecul-
iarities. 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 opportuni-
ties^for illustrating these points in the human subject.

SUBLINGUAL (TWELFTH NERVE).

The last of the motor cranial nerves is the sublingual ; and its action is
intimately connected with the physiology of the tongue in deglutition and

562 NERVOUS SYSTEM.

articulation, although the sublingual is also distributed to certain of the
muscles of the neck.

Physiological Anatomy. — The apparent origin of the sublingual 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 ten to twelve filaments, which extend from
the inferior portion of the olivary body to about the junction of the upper
with the middle third of the medulla. These filaments of origin are sepa-
rated 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 ante-
rior 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 sympa-
thetic 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 peculiarities :

Its first branch, the descendens noni, passes down the neck to the sterno-
hyoid, sterno-thyroid and omo-hyoid muscles.

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 mus-
cles in the infra-hyoid region, the action of which is to depress the larynx
and the hyoid bone after 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.

Properties and Uses of the Sublingual. — The fact that the sublingual
nerve 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 acces-
sory— when the origin of the sublingual is necessarily exposed — Longet has
irritated the roots in the dog, without any evidence of pain on the part of

SUBLINGUAL NERVE.

563

the animal. Such experiments, taken in connection with the anatomical
characters of the nerve, render it almost certain that its root is devoid of

FIG. 208.— Distribution of the subliminal nerve (Sappey).

1, root of the fifth nerve ; 2, ganglion of Gasser ; 3, 4, 5, 6, 7, 9, 10, 12, branches and anastomoses of the
fifth nerve ; 11, submaxillary ganglion ; 13, anterior belly of the digastric muscle ; 14, section of the
mylo-hyoid muscle ; 15, glosso-pharyngeal nerve ; 16, ganglion of Andersch ; 17, 18, branches of the
glosso-pharyngeal nerve ; 19, 19, pneumogastric ; 20, 21, ganglia of the pneumogastric ; 22, 22, su-
perior laryngeal branch of the pneumogastric ; 23, spinal accessory nerve ; 24, sublingual nerve ;
25, descendens noni ; 26. thyro-hyoid branch ; 27, terminal branches ; 28, two branches, one to the
genio-hyo-glossus and the other to the genio-hyoid muscle.

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 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 the nerve is seen as it crosses its course.
On applying a feeble Faradic current at this point, there are evidences of
sensibility, and the tongue is moved at each stimulation.

The phenomena following section of both sublingual nerves point directly
to their uses. 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. The phenomena which follow division of
these nerves consist simply in loss of power over the tongue, with considera-
ble difficulty in deglutition.

564

NERVOUS SYSTEM.

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 protrudes the tongue, directs the point toward
the side affected with paralysis.

A disease of rather rare occurrence has been described under the name
of glosso-labio-laryngeal paralysis, characterized by paralysis of the muscles
of the lips, tongue, soft palate, pharynx, and frequently the intrinsic muscles
of the larynx. The phenomena 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 addi-
tion there is some interference with articulation, which can not be observed
in experiments upon animals.

TRIFACIAL (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 nerve is impor-
tant, not only as the great sensitive
nerve of the face, but from its con-
nections with other nerves and its re-
lations to the organs of special sense.
Physiological Anatomy. — The ap-
parent 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 trans-
verse 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 with-
out inward and from before back-
ward, without any connection with
the fibres of the pons itself. By this
course the fibres reach 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 fibres
of the auditory nerve. The other
bundles, which are posterior, pass, the

FIG. 209.— Principal branches of the large root of
the fifth nerve (Robin).

a, ganglion of Gasser ; a-w, ophthalmic division
of the fifth ; 6, ophthalmic ganglion ; c,
branch from the ophthalmic division of the
fifth to the ophthalmic ganglion • d, motor
oculi communis ; e, carotid ; /, ciliary nerves ;
gr, cornea and iris ; a-7i, superior maxillary di-
vision 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 malleus ; i,
naso-palatine ganglion ; m. otic ganglion ; ?i,
small superficial petrosal nerve ; o, branches
of the fifth to the submaxillary ganglion ; p,
branches to the sublingual gland ," ' q, facial
nerve ; ?•, sympathetic ganglion ; s, nerve of
mastication ; t, chorda tympani, joining the
lingual branch of the fifth ; u, Vidian nerve ;
v, branch from the motor root, to the internal
pterygoid muscle ; w, branch of the fifth to
the lachrymal gland ; x. bend of the facial
nerve ; ?/, middle rneningeal artery ; z, fila-
ment from the carotid plexus, to the ophthal-
mic ganglion ; (1 and 2 are not in the figure) 3,
external spheno-palatine filaments ; 4, spheno-
palatine ganglion ; 5, naso-palatine nerve ; 6,
anterior palatine nerve ; 7. inferior maxillary
division of the fifth ; 8, nerve of Jacobson.

TRIFACIAL NERVE.

565

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 3
in the petrous portion of the tem-
poral bone, on the internal portion
of its anterior face.

The Gasserian ganglion is semi-
lunar in form, with its concavity
looking upward and inward. At
the ganglion the nerve receives
filaments of communication from
the carotid plexus of the sym-
pathetic. This 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.

At the ganglion of Gasser,
from its anterior and external por-
tion, are given off a few small and unimportant branches to the dura mater
and the tentorium.

From the convex border of the ganglion the three great divisions, or
branches arise, which have given to the nerve the name of trifacial or tri-
geminal. These are : 1, the ophthalmic ; 2, the superior maxillary ; 3, the
inferior maxillary. The ophthalmic and superior maxillary branches 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 recurrent branch which passes between the
layers of the tentorium.

Just before the ophthalmic branch enters the orbit by the sphenoidal fis-
sure 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,

FIG. 210.— Ophthalmic division of the fifth (Hirschfeld).

1, ganglion of Gasser ," 2, ophthalmic division of the
fifth ; 3, lachrymal branch ; 4, frontal branch ; 5,
external frontal ; 6, internal frontal ; 7, supratro-
chlear ; 8, nasal branch ; 9, external nasal ; 10, in-
ternal nasal ; 11, anterior deep temporal nerve ;
12, middle deep temporal nerve ; 13, posterior deep
temporal nerve; 14. origin of the superficial tempo-
ral nerve; 15. great superficial petrous nerve.

I to XII, roots of the cranial nerves.

566

NERVOUS SYSTEM.

to which certain of its filaments are distributed, and its terminal filaments
go to the conjunctiva and to the integument of the upper eyelid.

The frontal branch, the largest of the three, divides into the supratroch-
lear and supraorbital nerves. The supratroachlear passes out of the orbit

between the supraorbital
foramen and the pulley of
the superior oblique mus-
cle. It sends in its course
a long, delicate filament to
the nasal branch and is
finally lost in the integu-
ment of the forehead.
The supraorbital passes
through the supraorbital
foramen, sends a few fila-
ments to the upper eye-
lid, and supplies the fore-
head, the anterior and the
median portions of the
scalp, the mucous mem-
branch ; 7, hrane of the frontal sinus,

FIG. 211.— Superior maxillary division of the fifth (Hirschfeld).
1, ganglion of Gasser ; 2, lachrymal branch of the ophthalmic di-
vision ; 3, superior maxillary division of the fifth ; 4, orbital
branch ; 5, lachrymo-palpebral filament ; 6, malar I

temporal branch; 8, spheno- palatine ganglion; 9, Vidian Qrifi fup -npvipranin™ n/™
10, great superficial petrosal nerve; 11, facial nerve ; ana tne peilCramum COV-

nerve

alveolar processes ; 15, terminal branches of the superior max-
illary division ; 16, branch of the facial.

12, branch of the Vidian nerve ; 13, anterior and two posterior pvir>o- fV»o frnn+«l nnrl T^QT-I
dental branches; 14, branch to the mucous membrane of the eimS LJ lildi HMl.pBn-

etal bones.

The nasal branch, be-
fore it penetrates the orbit, gives off a long, delicate filament to the ophthal-
mic ganglion. It then gives off the long ciliary nerves, which pass to the
•ciliary muscle and iris. Its trunk finally divides into the external nasal, or
infratrochlearis, and the internal nasal, or ethmoidal. The infratrochlearis
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 inter-
nal nasal is distributed to the mucous membrane and also in part to the in-
tegument of the nose.

The superior maxillary branch of the fifth passes out of the cranial cav-
ity by the foramen rotundum, traverses the infraorbital canal, and emerges
upon the face by the infraorbital foramen. Branches from this nerve are
given off in a spheno-maxillary fossa and the infraorbital canal, before it
emerges upon the face. In the spheno-maxillary 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

TRIFACIAL NERVE.

567

molar and bicuspid teeth, the mucous membrane of the corresponding alve-
olar processes and to the antrum.

In the infraorbital canal, a large branch, the anterior dental, is given off
to the teeth and mucous membrane of the alveolar processes not supplied
by the posterior den-
tal branches. This
branch anastomoses
with the posterior
dental.

The terminal
branches upon the
face are distributed
to the lower eye-
lid (the palpebral
branches), to the
side of the nose
(the nasal branch-
es), anastomosing
with the nasal
branch of the oph-
thalmic, and to the
integument and the
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 distribu-
tion of the motor
filaments has al-
ready been described. This nerve passes out of the cranial cavity by the for-
amen 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 the following branches :

1. The auriculo-temporal nerve supplies the integument in the temporal
region, the auditory meatus, the integument of the ear, the temporo-maxillary
articulation and the parotid gland. It also sends branches of communica-
tion 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 a branch from the facial
(the chorda tympani) which has already been described. From this nerve,

Fm. 212.— Inferior maxillary division of the fifth (Hirschfeld).
branch from the motor root to the masseter muscle ; 2, filaments from
this branch to the temporal muscle ; 3, buccal branch ; 5, 6, 7, branches
to the muscles ; 8, auriculo-temporal nerve ; 9, temporal branches ; 10,
auricular branches ; 11, anastomosis with the facial nerve ; 12, lingual
branch; 13, branch of the motor root to the mylo-hyoid muscle ; 14, 15,
15, inferior dental nerve, with its branches ; 16, mental branch ; 17,
anastomosis of this branch with the facial nerve.

568

NERVOUS SYSTEM.

FIG. 218.-Limtte of cutaneous distri- Volving Other parts, but all
button of sensory nerves to the
face, head and neck (Beclard).

also, are given off two or three branches which pass to the submaxillary

ganglion.

3. The inferior dental nerve, the largest of the three, passes in the sub-

stance of the inferior maxillary bone, beneath the teeth, to the mental fora-

men, where it emerges upon the face. The most
important sensory branches are those which sup-
ply 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 and the lower lip. It also
sends certain filaments to the mucous membrane
of the mouth.

Properties and Uses of the Trifacial. — The
trifacial is the great sensory nerve of the face
and of the mucous membranes lining the cavi-
ties about the head. It is impossible to stimu-
late this nerve at its origin without seriously in-

observations with

regard to the properties of the large root go to
show that it is an exclusively sensory nerve and
that its sensibility is very acute as compared with

nf>,Ar TIPVVPC Tf waa rlivirl^rl in fno cranial r>av

omer Bives. it was ai\mea in me cranial cav-

ifv V»\r Mavn M899 '9^\ Tfnrlora /1893\ anrl Ma
irJ "J Mayo (ISxJ/S- £6), V OQera (IS/^j ana Ma-

c3a?^errvesbranches °f the cervi" £endie (1824). Magendie divided the nerve at

its root by introducing a small, cutting stylet

through the skull. He succeeded in keeping the animals alive for several
days or weeks and noted in his experiments immediate loss of sensibility in
the face on the side on which the nerve was divided. The operative proced-
ure employed by Magendie has been followed by other physiologists, particu-
larly Bernard, who made a number of important observations on the immedi-
ate and remote effects of section of the nerve. The section is usually made
through the ganglion of Gasser. The operation is difficult on account of
the danger of wounding large blood-vessels. When this operation is per-
formed without accident, the cornea and the integument and mucous mem-
brane 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 the small root of the fifth
is divided as well as the large root, and the muscles of mastication are para-
lyzed upon one side ; but with this exception, there is no paralysis of motion,
sensation alone being destroyed upon one side.

Immediate -Effects of Division of the Trifacial. — This 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 to be exquisitely sensitive. Physiologists have ex-
posed the roots in animals immediately after death, and have found that

n

of the inferior maxillary divis-

ion; 4, distribution of the ante-

rior branches of the cervical
nerves; 5,5, distribution of the

TRIFACIAL NERVE. 569

stimulation of the large root carefully insulated produces no muscular con-
traction. All who have divided this root in living animals must have recog-
nized, not only that it is sensitive, but that its sensibility is far more acute
than that of any other nervous trunk in the body.

As far as audition and olfaction are concerned, there are no special effects
immediately following section of the trifacial ; but there are certain impor-
tant phenomena observed in connection with the eye and the organs of
taste.

At the instant of division of the fifth, the eyeball is protruded and the
pupil becomes strongly contracted. This occurs in rabbits, and the contrac-
tion of the pupil was observed in the first operations of Magendie. The
pupil, however, usually is restored to the normal condition in a few hours.
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, even after extirpation of both lachrymal glands
(Magendie). 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 influ-
ence of this nerve over the general sensibility and the sense of taste in the
tongue have been made by dividing the lingual branch of the inferior maxil-
lary 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 portion of the tongue. It will be remembered,
however, that the chorda tympani joins the lingual branch of the fifth as it
passes between the pterygoid muscles, and that section of this branch of the
facial abolishes the sense of taste in the anterior two-thirds 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 the physiology of gustation.

Among the immediate effects of section of the fifth, is an interference
with the reflex phenomena of deglutition. In a series of observations upon
the action of the sensory 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 section 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 the velum upon the corre-
sponding 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 sen-
sory nerve, conveying the impression from the velum palati to the nerve-cen-

570 NERVOUS SYSTEM.

tres. This action probably takes place through filaments which pass from
the fifth to the mucous membrane, through Meckel's ganglion.

Remote Effects of Division of the Trifacial. — After section of the fifth
nerve in the cranial cavity, the immediate loss of sensibility of the integu-
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. After a period varying between a few
hours and one or two days after the operation, the eye upon the affected side
becomes the seat of purulent inflammation, the cornea becomes opaque and
ulcerates, the humors are discharged and the organ is destroyed. Conges-
tion 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 operation, although these are not so-
prominent. Animals affected in this way usually die in fifteen to twenty
days.

In the early experiments of Magendie, it was 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 instances. Magendie offered no satisfactory
explanation of the differences in the consecutive phenomena coincident with
the place of section of the nerve. The facts, however, have been repeatedly
verified. In a number of experiments in which the nerve was divided in the
cranial cavity (Flint), the consecutive inflammatory effects were almost always
observed ; but in an experiment made in 1868, the nerve was completely
divided on the left side, as was shown by total loss of sensibility of the parts
to which it is distributed, and the animal (a rabbit) lived nearly four months.
Four days after the operation 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 difficulty. 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
disappeared. 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 operation, and there was no inflammation
of the organs of special sense. It died at that time of inanition, having
become extremely emaciated. The animal never recovered power over the
muscles of the left side, and the incisors grew to a great length, interfering
very much with mastication.

Longet, in 1842, gave an explanation of the absence of inflammation in
certain cases of division of the fifth. He attributed the consecutive inflam-

TRIFACIAL NERVE. 571

mation in most experiments to lesion of the ganglion of Gasser and of the
sympathetic connections, which are very abundant at this point. These
sympathetic filaments are avoided when the section is made behind the gan-
glion.

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 when the loss of sensibility
is complete after division of the nerve behind the Gasserian ganglion, these
results may not follow. They are not explained by deficiency in the lachry-
mal secretion, for they are not observed when both lachrymal glands have
been extirpated. They are not due to exposure of the eyeball, for they da
not follow section of the facial. They are not due simply to an enfee-
bled general condition, for in the experiment just detailed, the animal died
of inanition after section of the nerve, without any evidences of inflam-
mation. In view of the fact that section of the sympathetic filaments i&
well known to modify nutrition of parts to which they are distributed,
producing congestion, increase in temperature and other phenomena, it i&
rational to infer that the modifications in nutrition which follow section of
the fifth after it receives filaments from the sympathetic system, not occur-
ring 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 simply produces exaggeration
of the nutritive processes, as evidenced chiefly by local increase in the animal
temperature, and not the well-known phenomena of inflammation.

It was 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 deli-
cate organs, like the eye, so as to induce those changes which are called
inflammatory. The following observation (W. H. Mason) has an important
bearing on this question :

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 nutri-
tion was maintained at a high standard, and no inflammation of the eye
occurred for about four weeks. The supply 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 following explains, in a measure at least, the consecutive inflamma-
tory effects of section of the fifth with its communicating sympathetic fila-
ments : By dividing the sympathetic, the eye and the mucous membranes of

572 NERVOUS SYSTEM.

the nose, mouth and ear are rendered hyperaemic, the temperature probably
is 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 inflammation was 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, particularly those of modified nutri-
tion, are more or less contradictory.

In nearly all works upon physiology, are references to cases of paralysis
of the fifth in the human subject. Two cases have been reported by Noyes,
in both of which 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. A notable 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 cases in which the
fifth nerve alone is involved in the disease, without the facial, there is simply
loss of sensibility upon one side, the movements of the superficial muscles
of the face being unaffected. When the small root is involved, the muscles
of mastication upon one side are paralyzed ; but in certain reported 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 inflam-
mation, are little if at all disturbed in uncomplicated cases. The sense of
taste in the anterior portion of the tongue is perfect, except in those cases in
which the facial, the chorda tympani or the lingual branch of the fifth after
it had been joined by the chorda tympani is involved in the disease. In
some cases there is 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 diffi-
cult, in most of them, to exactly limit the boundaries of the lesion.

PNEUMOGASTRIC (TENTH NERVE).

Of all the nerves emerging from the cranial cavity, the pneumogastric
presents the greatest number of anastomoses, the most remarkable course and

TNEUMOGASTRIC NERVE. 573

the most varied uses. Arising from the medulla oblongata by a purely senso-
ry root, it communicates with at least five motor nerves, and it is distributed
largely to muscular tissue, both of the voluntary and the involuntary variety.

Physiological Anatomy. — 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 the spinal accessory.
The deep origin is mainly from what is 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 ap-
pear to be in the main identical. Tracing the filaments from without in-
ward, they may be followed in four directions : (1) The anterior filaments
pass from without inward, first very superficially, in the direction of the
olivary body ; but they then turn and pass deeply into the substance of the
restiform body, in which they are lost. (2) The posterior filaments are
superficial, and they pass, with the fibres of the restiform body, toward the
cerebellum. (3) Of the intermediate filaments, the anterior pass through
the restiform body, the greatest number extending to the median line, in
che floor of the fourth ventricle. A few fibres are lost in the middle fascic-
uli of the medulla and a few pass toward the brain. (4) The posterior
intermediate filaments traverse the restiform body, to the floor of the fourth
ventricle, when some pass to the median line, and others descend in the sub-
stance of the medulla. It is difficult to follow the fibres of origin of the
pneumogastrics beyond the median, line ; but recent observations leave no
doubt of 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, one-
sixth to one-fourth of an inch (4-2 to 6*4 mm.) in length, called the jugular
ganglion, or the ganglion of the root. This is united by two or three fila-
ments with the ganglion of the glosso-pharyngeal. It is a true ganglion,
containing nerve-cells. After the nerve has emerged from the cranial cav-
ity, it presents on its trunk another grayish enlargement, half an inch to an
inch (12 to 25 mm.) in length, called the ganglion of the trunk. This has
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 acces-
sory, the glosso-pharyngeal nerve and the internal jugular vein.

Anastomoses. — There are occasional filaments of communication which
pass from the spinal accessory to the ganglion of the root of the pneumogas-
tric, but these are not constant. After both nerves have emerged from the
cranial cavity, an important branch of considerable size passes from the spi-
nal accessory to the pneumogastric, 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.

38

574

NERVOUS SYSTEM.

In the aquseductus Fallopii, the facial nerve gives off a filament of com-
munication to the pneumogastric, at the ganglion of the root. This filament,

joined at the ganglion by sensory fila-
ments from the pneumogastric and
some filaments from the glosso-pha-
ryngeal, 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 sublin-
gual to the ganglion of the trunk of
the pneumogastric.

At the ganglion of the trunk, the
pneumogastric generally receives fila-
ments of communication from the ar-
cade 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 a num-
ber of filaments of communication from

FIG. 214.— Anastomoses of the pneumogastric

(Hirschfeld).

1, facial nerve ; 2, glosso-pharyngeal nerve ; £
anastomoses of the glosso-pharyngeal wit
the facial ; 3, 3, pneumogastric, with its two
ganglia ; 4, 4, spinal accessory ; 5, sublingual
nerve ; 6, superior cervical ganglion of the
sympathetic ; 7, anastomotic arcade of the
first two cervical nerves ; 8, carotid branch

ganglia ; 4, 4, spinal accessory ; 5, sublingual the SUpeiioi Cervical ganglion, passing1

nerve ; 6, superior cervical ganglion of the

sympathetic ; 7, anastomotic arcade of the in part Upward toward the ganglion

first two cervical nerves; 8, carotid branch

of the superior cervical ganglion of the sym- of the root of the pneumOgastriC, and

pathetic ; 9, nerve of Jacobson ; 10, branches .

of this nerve to the sympathetic ; ii, branch in part transversely and downward.

to the Eustachian tube ; 12, branch to the

fenestra ovaiis ; is, branch to the fenestra These filaments frequently are short,

rotunda ; 14, external deep petrous nerve ; , . , . ,
15, internal deep petrous nerve ; 16, otic gan- and they bind the Sympathetic gan-
glion ; 17, a uricular branch of the pneumo- ,. ., , „ ., 7™
gastric ; 18, anastomosis of the pneumogas- gllOn to the trunk 01 the nerve. The
trie with the spinal accessory ; 19, anastomo- . , „ , ! . .

sis of the pneumogastric with the sublingual; main trunk of the pneumogastric and

20, anastomosis of the spinal accessory with
the second pair of cervical nerves ; 21, pha-
ryngeal plexus ; 22, superior laryngeal nerve.

its branches receive a few filaments
of communication from the middle
and inferior cervical and the upper dorsal ganglia of the sympathetic.

The pneumogastric frequently sends a slender 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. — Although the pneumogastric nerves upon the two sides do
not present any important differences in the destination of their filaments,
as far down as the diaphragm, the distribution of the abdominal branches is
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.

PNEUMOGASTRIC NERVE.

575

The auricular nerves are sometimes described in connection with the
facial. They are given off from the ganglion of the trunk of the pneumo-
gastric and are com-
posed 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 membrana tym-
pani.

The pharyngeal
nerves are given off
from the superior
portion of the gan-
glion of the trunk,
and they contain a
large number of the
filaments of com-
munication which
the pneumogastric
receives from the
spinal accessory. In

their COUrse bv the
Kir!p« nf thp aniipn'nr
pon «;t-ri otnr mn «pl P«

nf tliPT^VmrvTiY
OItnepnarynX,

Tiprvp«j
81 VeS

With filaments from

sympathetic ganglia.

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 pneumo-
gastric 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

FIG. 215.- -Distribution of the pneumogastric (Hirschfeld).

left pneumogastric ; 2, ganglion of the trunk ; 3, anastomo-
sis with the spinal accessory ; 4, anastomosis with the sublingual ; 5,
pharyngeal branch (the auricular branch is not shoivn 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 ; 16, glosso-
17, spinal accessory ; 18, 19, 20. spinal nerves ; 21, phrenic

23' Spinal nerves ;

576 NERVOUS SYSTEM.

point of junction of the pneumogastric with the communicating branch
from the spinal accessory, so that probably the superior laryngeals contain
few if any motor fibres from the eleventh nerve. The superior laryngeal
gives off the external laryngeal, a long, delicate branch, which sends a few
filaments 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 branch anastomoses with the inferior laryn-
geal nerve and with the sympathetic. The internal branch is distributed to
the mucous membrane of the epiglottis, the base of the tongue, the aryteno-
epiglottidean fold and the mucous membrane of the larynx as far down as
the true vocal chords. A branch from this nerve, in its course to the larynx,
penetrates the arytenoid 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, de-
scribed 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. It passes down the neck by the side
of the sympathetic, and in the chest, it joins filaments from the thoracic
sympathetic, to pass to the heart, between the aorta and the pulmonary
artery. This nerve is not isolated in the human subject, but it is probable
that analagous fibres exist in man in the trunk of the pneumogastric.

It is important from a physiological point of view to note that the supe-
rior laryngeal nerve is the nerve of sensibility of the upper part of the larynx,
as well as of the supralaryngeal 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 up-
ward 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 intercartilaginous
muscular tissue of the trachea, one or two filaments to the inferior constric-
tor 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 in-
trinsic 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 essentially the same course
and distribution as upon the left side, except that it is smaller and has fewer
filaments of distribution.

The important physiological point connected with the anatomy of the re-
current laryngeals is that they animate all of the intrinsic muscles of the
larynx, except the crico-thyroid. Experiments have shown that these nerves
contain a large number of motor filaments derived from the spinal accessory

PNEUMOGASTRIC NERVE. 577

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 sympa-
thetic. The thoracic cardiac branches are given off from the pneumogas-
trics, 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 car-
diac 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 ter-
minations in the air-cells. The posterior pulmonary branches are larger and
more abundant than the anterior. They communicate freely with sympa-
thetic 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 inferior and posterior portion of the trachea, a few pass to the mus-
cular 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 filaments of the anterior
branches. The pulmonary branches are distributed to the mucous mem-
brane, and not to the walls of the blood-vessels.

The oesophageal branches take their origin from the pneumogastrics,
above and below the pulmonary branches. These branches from the two
sides join to form the cesophageal 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 here anterior to the cardiac
opening of the stomach, immediately after its passage by the side of the
oesophagus into the abdomen, divides into a number of 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 direc-
tion 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 suie and with the sympathetic.

The right pneumogastric, situated posteriorly, at the oesophageal open-
ing of the diaphragm, 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 (Kollmann). The anatomical researches by Kollmann (1860)
have been fully confirmed by physiological experiments. Before the nerves
pass to the intestines, there is a free anastomosis and interchange of fila-
ments between the right and the left pneumogastric.

General Properties of the Roots of Origin of the Pneumogastrics. — The
sensibility of the pneumogastrics in the neck, while it is dull as compared

578 NERVOUS SYSTEM.

with the properties of other sensory nerves, is nevertheless distinct. It is
impossible, however, to expose the roots of the nerves in living animals, be-
fore they have received communicating motor filaments, without such muti-
lation as would interfere with accurate observations; but in animals just
killed, if the roots be exposed and divided, so as to avoid reflex movements,
and if care be taken to avoid stimulation of motor filaments from adjacent
nerves, it is found that the application of electricity to the peripheral end of
the root, from its origin to the ganglion, gives rise to no movements. It may
therefore be assumed that the true filaments of origin of the pneumogastrics
are exclusively sensory or at least that they have no motor properties.

Properties and Uses of the Auricular Nerves. — There is very little to be
said with regard to the auricular nerves after a description of their anatomy.
They are sometimes described with the facial and sometimes with the pneu-
mogastric. 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 tym-
pani.

Properties and Uses of the Pharyngeal Nerves. — The pharyngeal branches
of the pneumogastric are mixed nerves, their motor filaments being derived
from the spinal accessory ; and their direct action upon the muscles of deglu-
tition belongs to the physiological history of the last-named nerve. As
already stated in treating of the spinal accessory, the filaments of communica-
tion 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
one 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 the experiments of Waller and Prevost, upon the reflex phenomena of
deglutition, it is shown that the action of the pharyngeal muscles can not be
excited by stimulation of the mucous membrane of the supralaryngeal region
and the pharynx, after section of the fifth and of the superior laryngeal
branches of the pneumogastrics. This would seem to show that yie pharyn-
geal branches of the pneumogastrics are of little importance in these reflex
phenomena.

Properties and Uses of the Superior Laryngeal Nerves. — 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 influence of the
nerves upon the muscles resolves itself into the action 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 in-
ferior muscles of the pharynx are few and comparatively unimportant. The

PNEUMOGASTRIC NERVE. 579

superior laryngeals do not receive their motor filaments from the spinal acces-
sory.

The sensory filaments of the superior laryngeals have important uses con-
nected with the protection of the air-passages from the entrance of foreign
matters, particularly in deglutition, and they are also concerned in the reflex
action of the constrictors of the pharynx. When both superior laryngeals
have been divided in living animals, liquids often pass in small quantity into
the larynx, owing to the absence of the reflex closure of the glottis when
foreign matters are brought in contact with its superior surface and the occa-
sional occurrence of inspiration during deglutition.

Aside from the protection of the air-passages, the superior lauyngeal 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 membrane of the epiglottis, of the aryteno-epiglot-
tidean fold and of the larynx as far down as the true vocal chords. 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.

If the superior laryngeal nerves be divided and a stimulus 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.

Properties and Uses of the Inferior, or Recurrent Laryngeal Nerves. —
The anatomical distribution of these nerves shows that their most important
action is connected 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 membrane of the upper part of the
oesophagus and trachea, and one or two branches are sent to the inferior
constrictor of the pharynx. The action of these filaments is sufficiently
evident.

The inferior laryngeals contain chiefly motor filaments, as is evident
from their distribution as well as from the effects of direct stimulation. All
who have experimented upon these nerves have noted little or no evidence
of pain when they are irritated or divided.

One of the most important uses of the recurrents relates to the production
of vocal sounds. In connection with the physiology of the internal, or com-
municating branch from the spinal accessory to the pneumogastric, it has
been shown that this branch of the spinal accessory is the true nerve of
phonation. Before the uses 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 loss of voice follows 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

580 NERVOUS SYSTEM.

recurrents contain as well motor filaments which preside 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 respiratory muscles, and these are not affected
by extirpation of the spinal accessories, but the glottis is still capable of dilata-
tion, 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 irritated. If the inferior laryn-
geals be then divided, the glottis is mechanically closed with the iiispiratory
act, and the animals often die of suffocation. In view of 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.

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 divis-
ion 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 instant death.

Feeble stimulation of the central ends of the inferior laryngeals, after
their division, produces rhythmical movements of deglutition, generally coin-
cident 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 probably is dependent upon the communicating
filaments which they send to the superior laryngeal nerves.

Properties and Uses of the Cardiac Nerves. — The chief uses of the cardiac
branches relate to the influence of the pneumogastrics on the action of the
heart. This has already been considered in connection with the physiology of
the circulation. The effect of dividing the pneumogastrics in the neck is to
remove the heart from the influence of its inhibitory nerves ; but at the same
time, the operation profoundly affects the respiratory movements, and this
latter effect must be eliminated as far as possible in studying the influence
of the pneumogastrics on the circulation. The same remark applies to the
experiment of Faradization of the pneumogastrics in the neck. The cardiac
branches are operated upon with difficulty, and most experiments have been
made upon the cervical portion of the pneumogastric itself.

Faradization of the pneumogastrics in the neck arrests the action of the
heart in diastole (the brothers Weber, 1846). This is a direct action and is
due to the excitation of the inhibitory fibres, which are derived from the
spinal accessory nerves. The phenomena following stimulation of these
nerves have already been described in connection with the physiology of the
circulation and the properties and uses of the spinal accessories.

Depressor Nerve. — While this nerve, which lias been described in the
rabbit (Cyon and Ludwig, 1867), is not isolated in the human subject, it is
probable that fibres, the actLon of which is analogous to the action observed

PNEUMOGASTRIC NERVE. 581

in animals in which the nerve is anatomically distinct, exist in the trunk of
the pneumogastric. The action of the depressor nerves, which is reflex, has
already been described in connection with the physiology of the circulation.

Properties and Uses of the Pulmonary Nerves. — The trachea, bronchia
and the pulmonary structure are supplied with motor and sensory filaments
by branches of the pneumogastrics. The recurrent laryngeals supply the
upper part, and the pulmonary branches, the lower part of the trachea, the
lungs themselves being supplied by the pulmonary branches alone. The
sensibility of the mucous membrane of the trachea and bronchia 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 respira-
tory passages was irritated, after division of the pneumogastrics there was
no evidence of sensibility, even when the tracheal mucous membrane was
treated with strong acid or cauterized. He also saw the muscular fibres of
the small bronchial tubes contract when an electric stimulus was applied to
the branches of the pneumogastrics.

Effects of Division of the Pneumogastrics upon Respiration. — Section of
both pneumogastrics in the neck, in mammals and birds, is usually followed
by death, in two to five days. In very young animals, death may occur
almost instantly from paralysis of the respiratory movements of the glottis.
It has been found by all experimenters that animals survived and presented
no very distinct abnormal phenomena after section of one nerve. Accord-
ing to Longet, animals operated upon in this way present hoarseness of the
voice and a slight increase in the number of respiratory acts. Some observ-
ers have found the corresponding lung partly emphysematous and partly en-
gorged with blood, and others have not noted any change in the pulmonary
structure.

When both nerves are divided in full-grown dogs, the effect upon the
respiratory movements is very marked. For a few seconds the number of
respiratory acts may be increased ; but so soon as the animal becomes tran-
quil, the number is very much diminished and the movements change their
character. The inspiratory acts become unusually profound and are at-
tended with excessive dilatation of the thorax. The animal generally is quiet
and indisposed to move. Under these conditions the number of respirations
may 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 condition is not the result of inflammation of the pulmonary
parenchyma, although this was the view formerly entertained and is even now
held by some physiologists. Bernard found that the pulmonary lesion did
not exist in birds, although section of both nerves was fatal. It had previ-
ously been ascertained that in some animals death takes place with no altera-
tion of the lungs. When the entrance of the secretions into the air passages
was prevented by the introduction of a canula into the trachea, the solidifica-
tion of the lungs was nevertheless observed. Without detailing all of the

582 NERVOUS SYSTEM.

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 actu-
ally seen when the pleura is exposed in living animals. As a result of this
excessive distention of the air-cells, the pulmonary capillaries are ruptured in
different parts, the blood becomes coagulated and the lungs are finally solidi-
fied. This can not occur in birds, because the lungs are fixed, and their rela-
tions are such that they are not exposed to excessive distention in inspiration.

The pneumogastrics sometimes reunite after division. The following
observation (Flint, 1874) illustrates this fact, which has frequently been
noted : Both pneumogastrics were divided in the neck 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 oblon-
gata, and the reunion of the divided ends of the nerves was found to be
nearly complete.

The relations of the pneumogastrics to the respiratory nervous centre
have been fully considered in connection with the physiology of respiration.

Effects of Faradization of the Pneumogastrics upon Respiration. — Fara-
dization of the pneumogastrics in the neck, if the current be sufficiently
powerful, arrests respiration. This arrest may be produced at any time with
reference to the respiratory act, either in expiration or inspiration, although
it is more readily effected in expiration. During the passage of the current
the general movements of the animal are also arrested. Although respira-
tion may always be arrested in this way, quite a powerful current is required.
During the passage of a very feeble current, the respirations are accelerated.
They are then retarded as the current is made stronger, until they finally
cease (Bert).

The following are the phenomena, observed by Bert, during the passage
of a powerful Faradic current :

" If an excitation be employed sufficiently powerful to arrest respiration
in inspiration, all respiratory movements may be made to cease at the very
moment when the excitation is applied (inspiration, half-inspiration, expira-
tion), 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 pow-
erful excitation of the pneumogastrics, of the superior laryngeal, of the nasal
branch of the infraorbital, 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."

The above expresses the most important experimental facts at present
known with regard to the influence of stimulation of the pneumogastrics

PNEUMOGASTRIC NERVE. 583

upon respiration. TJie pulmonary branches themselves are so deeply situated
that they have not as yet been made the subject of direct experiment, with
any positive and satisfactory results.

Properties and Uses of the (Esopliageal Nerves. — The muscular walls and
the mucous membrane of the oesophagus are supplied entirely by branches
from the pneumogastrics. 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 cesopha-
geal 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 pneumogastrics, 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 oesopha-
gus is paralyzed by dividing the nerves in the neck. When the pneumogas-
trics are divided in the cervical region in dogs, if the animals attempt to
swallow a considerable quantity of food, the upper part of the O3sophagus 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 in-
stant 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 Uses of the Abdominal Nerves. — In view of the exten-
sive distribution of the terminal branches of the pneumogastrics to the ab-
dominal organs, it is evident that the action of these nerves must be very
important, particularly since it has been shown that the right nerve is dis-
tributed to the whole of the small intestine.

Influence of the Pneumogastrics upon the Liver. — There is very little
known with regard to the influence of the pneumogastrics upon the se-
cretion of bile ; and the most important experiments upon the innervafion
of the liver relate to the production of glycogen. If both pneumogastrics be
divided in the neck, and if the animal be killed at a time varying between a
few hours and 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 concluded that the glycogenic pro-
cesses are suspended when the nerves are divided. The experiments, how-
ever, made by irritating the pneumogastrics, were more satisfactory, as in
these he looked for sugar in the blood and in the urine and did not confine
his examinations for sugar to the substance of the liver.

584 NERVOUS SYSTEM.

After division of pneumogastrics in the neck, if the peripheral ends be
stimulated there is no effect upon the liver ; but if the stimulus be applied
to the central ends, the glycogenic processes become exaggerated, and sugar
makes its appearance in the blood and in the urine. Bernard made a num-
ber of experiments illustrating this point, upon dogs and rabbits. The cur-
rent employed was generally feeble, and it was continued for five or ten min-
utes, two or three times in an hour. In some instances the stimulation was
kept up for thirty minutes. From these experiments, it is assumed that the
physiological production of glycogen by the liver is reflex and is due to an
impression conveyed to the nerve-centres through the pneumogastrics. The
inhalation of irritating vapors and of anaesthetics produces an increased gly-
cogenic action in the liver.

The effects of irritating the floor of the fourth ventricle, by which tem-
porary diabetes is produced, have been considered in connection with the
glycogenic action of the liver. This effect is not due to a direct transmis-
sion of the irritation to the liver through the pneumogastrics, for the phe-
nomena are observed in animals upon which this operation has been per-
formed 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 sympa-
thetic going to the solar plexus have been divided. The operation, however,
of dividing the sympathetic nerves in this situation is so serious, that it may
interfere with the experiment in some other way than by the direct influence
of the nerves upon the liver.

Influence of the Pneumogastrics upon the Stomach and Intestines. — Lit-
tle or nothing is known with regard to the action of the pneumogastrics on
the spleen, kidneys and suprarenal capsules. The influence of these nerves
upon the stomach and intestine will be considered under the following heads :

1. The effects of Faradization of the nerves.

2. The effects of section of the nerves upon the movements of the stom-
ach in digestion.

3. The influence of the nerves upon the small intestine.

Effects of Faradization. — The stomach contracts under stimulation of
the pneumogastrics in the neck, not instantly, but after the lapse of five or
six seconds (Longet). Longet explained some of the contradictory results
obtained by other observers by the fact that these contractions are very
marked during stomach-digestion, while they are wanting " when the stom-
ach is entirely empty, retracted on itself and in a measure in repose." Stim-
ulation of the splanchnic nerves, while it produces movements of the intes-
tines, 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 assumed that the motor action of the pneumogas-
trics is due, not to the proper filaments of these nerves, but to filaments de-
rived from the sympathetic.

PNEUMOGASTRIC NERVE. 585

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 intro-
duced through the fistula, it will be firmly grasped by the contractions of the
muscular walls. When the pneumogastrics are divided, 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 (Bernard).

Notwithstanding the apparent arrest of the movements of the stomach in
digestion, by section of the pneumogastrics, it has been shown 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 by the experiments of Schiff, who attributed the move-
ments occurring after section of the nerves to local irritation of the intra-
muscular terminal nervous filaments.

The influence of the pneumogastrics upon the general processes of diges-
tion, the sensations of hunger and thirst and upon absorption from the ali-
mentary canal have already been considered in connection with the physiol-
ogy of digestion and absorption.

Influence of the Pneumogastrics upon the Small Intestine. — Physiologists
have given but little attention to the influence of the pneumagastrics 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 semi-
lunar 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.

The experiments of Wood have shown that the pneumogastrics influence
intestinal as well as gastric secretion. After section of the nerves in the
cervical region, the most powerful cathartics (croton-oil, calomel, podophyl-
lin, 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 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 distribution of the nerves to the small intestine. 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 inject-
ing it under the skin. Reid made five experiments, and in all but one, it is
stated that diarrhoea existed after division of the nerves. In twenty experi-
ments by Wood, there was no purgation after division of the nerves, in one

586 NERVOUS SYSTEM.

there was free purgation, and in one there was " some slight muco-faecal dis-
charge." From these, Wood concluded 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 riot observed.

It would be interesting to determine whether the pneumogastrics influ-
ence the intestinal secretions through their own fibres or through filaments
received from the sympathetic system ; but there are no experimental facts
sufficiently definite to admit of a positive answer to this question. If the
action take place through the sympathetic system, as in the case of the stom-
ach, the filaments of communication join the pneumogastrics high up in the
neck.

The cranial nerves that have been considered in this chapter are the
third, fourth, fifth, sixth, seventh, tenth, eleventh and twelfth. The ana-
tomical and physiological history of the olfactory (first), optic (second),
auditory (eighth), gustatory (branch of the seventh and a part of the ninth)
and of the general sensory nerves, as far as they are concerned in the sense
of touch, belongs properly to the chapters on the special senses.

CHAPTEE XVIII.

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— Columns of the Cord— Direction of the
nerve-fibres in the cord — General properties of the spinal cord — Motor paths in the cord — Sensory paths
in the cord — Relations of the posterior white columns of the cord to muscular co-ordination — Nerve-centres
in the spinal cord — Reflex action of the spinal cord — Exaggeration of reflex excitability by decapitation,
poisoning with strychnine etc.— Reflex phenomena observed in the human subject.

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 system is composed
of white and gray matter. The fibres of the white matter act solely as con-
ductors. The gray matter constitutes a chain of ganglia, which act as nerve-
centres, receiving impressions and generating the so-called nerve-force. Cer-
tain parts of the gray matter also serve as conductors.

The cerebro-spinal axis is enveloped in membranes, which are for its pro-
tection and for the support of its nutrient vessels. It is surrounded to a cer-
tain extent with liquid, and it presents cavities, as the ventricles of the brain
and the central canal of the cord, 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

SPINAL COED. 587

internal. In the white substance of the brain, also, are collections of gray
matter. The white matter of the cerebro-spinal axis is composed largely of
fibres. The gray substance is composed chiefly of cells.

The encephalon is contained in the cranial cavity and consists of the
cerebrum, cerebellum, pons Varolii and medulla oblongata. In the human
subject and in many of the higher animals, its surface is marked by convo-
lutions, by which the extent of its gray substance is much increased. The
cerebrum, the cerebellum and most of the encephalic ganglia are connected
with the white substance of the encephalon and with the spinal cord. All
of the cerebro-spinal nerves are connected with the encephalon and the cord.
The cerebro-spinal axis acts as a conductor, and its different collections of
gray matter, or ganglia, receive impressions conveyed by the sensory conduct-
ing fibres, and generate motor impulses which are 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.

The dura mater of the encephalon is a dense membrane, in two layers,
composed chiefly of ordinary fibrous tissue, which lines the cranial cavity
and is adherent to the bones. In certain situations its two layers are sepa-
rated 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 in-
to the longitudinal fissure and is called the f alx cerebri ; another lies between
the cerebrum and the cerebellum and is called the tentorium ; another is sit-
uated between the lateral halves of the cerebellum and is called the falx cere-
belli. 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 ad-
herent 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 a delicate membrane, resembling the serous membranes,
with the exception that it presents but one layer. Its inner surface is cov-
ered with a layer of tesselated endothelium. There is a considerable quantity
of liquid between the arachnoid and the pia mater, surrounding the cerebro-
spinal axis, in what is called the subarachnoid space. This is called the cer-
ebro-spinal, or cephalo-rachidian fluid. The arachnoid does not follow the
convolutions and fissures of the encephalon or the fissures of the cord, but it
simply covers their surfaces. Magendie described a longitudinal, incom-
plete, 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, very vas-
cular, seeming to present, indeed, only a skeleton net-work of fibres for
the support of the vessels going to the nervous substance. This membrane
covers the surface of the encephalon immediately, follows the sulci and fis-

588 NEKVOUS SYSTEM.

sures, 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 the membrane is thicker,
stronger, more closely adherent to the subjacent parts, and its blood-vessels
are not so abundant. In this situation many of the fibres are arranged in
longitudinal bands. This membrane lines the anterior fissure arid a portion
of the posterior fissure of the cord. At the foramina of exit of the cranial
and the spinal nerves, the fibrous structure of the pia mater becomes contin-
uous 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 holding 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 circula-
tion in these parts presents certain peculiarities. In the. first place, the en-
cephalon being contained in an air-tight case of invariable capacity, it has been
a question whether or not the vessels be capable of contraction and dilatation,
or whether the quantity of blood in the brain be subject to modifications in
health or disease. These questions may certainly be answered in the affirm-
ative. 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 quantity of blood is increased in expiration and dimin-
ished in inspiration ; but it is not probable that the cerebro-spinal axis under-
goes any considerable movements. The important peculiarities in the cere-
bral circulation have already been fully considered in connection with the
physiology of the circulation. It has been shown that the encephalic capilla-
ries are surrounded or nearly surrounded by canals (perivascular canal-sys-
tem), which 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 quantity of liquid in the brain, as the blood-vessels are dis-
tended or contracted.

Cephalo-RacJiidian Fluid. — The greatest part of the fluid in the cranium
and in the spinal canal is contained in the subarachnoid space. The ventri-
cles of the encephalon are in communication with the central canal of the
cord, and are also connected with the general subarachnoid space, by a narrow,
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 cer-
ebro-spinal axis, and the pressure upon these parts is equalized.

PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. 589

As far as is known, the office of the cephalo-rachidian fluid is simply
mechanical, and its properties and composition have no very definite physio-
logical significance. Its quantity was estimated by Magendie, in the human
subject, at about two fluidounces (60 c. c.) ; but this was the smallest quan-
tity obtained by placing the subject upright, making an opening in the lum-
bar 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 esti-
mated in this way ; and it is difficult, indeed, to see how any thing more than
a foughly approximate idea could be obtained. The quantity obtained by
Magendie probably does not represent all the liquid contained in the ventri-
cles and in the subarachnoid space, but it is 4he most definite estimate that
has been given.

The general properties and composition of the cephalo-rachidian fluid
are in brief the following : It is transparent and colorless, free from viscid-
ity, of a distinctly saline taste, an alkaline reaction, and it resists putrefaction
for a long time. It is not affected by heat or acids. It contains a large pro-
portion of water (981 to 985 parts per thousand), a considerable quantity of
sodium chloride, a trace of potassium chloride, sulphates, carbonates and alka-
line and earthy phosphates. In addition it contains traces of urea, glucose,
sodium lactate, fatty matter, cholesterine and albumen.

As a summary of the office of the cephalo-rachidian fluid, it may be
stated in general terms that it serves to protect the cerebro-spinal axis,
chiefly by equalization of the pressure in the varying condition of the blood-
vessels, filling the space between the centres and the bony cavities in which
they are contained. That the blood-vessels of the cerebro-spinal axis are sub-
ject 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 be affected only through the blood-vessels.

PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD.

The spinal cord, with its membranes, the roots of the spinal nerves and
the surrounding liquid, occupies the spinal canal and is continuous with the
encephalon. Its length is fifteen to eighteen inches (38'1 to 45'7 centi-
metres) and its weight is about an ounce and a half (42'5 grammes). Its
general form is cylindrical, but it is slightly flattened in certain portions.
It extends from the foramen magnum to the lower border of the body of the
first lumbar vertebra. It presents, at the origin of the brachial nerves, an
elongated ovoid enlargement flattened antero posteriorly, and a correspond-
ing enlargement at the origin of the nerves which supply the lower extremi-
ties. It terminates below in a slender, gray filament, called the filum termi-
nale. The §acral 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 composed of white and gray matter, the white matter being external.
The inferior, pointed termination of the cord consists entirely of gray matter.

39

590

NERVOUS SYSTEM.

The cord is marked by an anterior and a posterior median fissure, and
by imperfect and somewhat indistinct anterior and posterior lateral grooves,

FIG. 216.— Transverse section of the spinal cord of a child six months old, at the middle of the lumbar
enlargement, treated with potassium-auric chloride and uranium nitrate ; magnified 20 diame-
ters. By means of these reagents, the direction of the fibres in the gray substance is rendered un-
usually distinct (Gerlach).

a, anterior columns ; 6, 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 an-
terior columns ; g, central canal with its epithelium ; /i, surrounding connective substance of the
central canal ; i, transverse fasciculi of the gray commissure in front of the central canal ; k, trans-
verse fasciculi of the gray commissure behind the central canal ; I, transverse section of the two
central veins ; m, anterior cornua ; n, great, lateral cellular layer of tl» anterior cornua ; o, lesser,
anterior cellular layer ; p, smallest, median cellular layer ; g, posterior cornua ; r, ascending fas-
ciculi in the posterior cornua ; s, substantia gelatinosa.

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 fis-
sure 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 vas-
cular 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 septum posteriorly, between the lateral
halves of the cord. The posterior median fissure extends nearly to the cen-
tre of the cord, as far as the posterior gray commissure.

The arrangement of the white and the gray matter in the cord is seen in a
transverse section. The gray substance is in the form of a letter H, present-
ing two anterior and two posterior cornua connected by what is called the
gray commissure. The anterior cornua are short and broad, and they do not

PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. 591

reach to the surface of the cord. The posterior cornua are longer and nar-
rower, and they extend nearly to the surface, at the point of origin of the
posterior roots of the spinal nerves. In the centre of the gray commissure, is
a narrow canal, lined by cells of ciliated epithelium, called the central canal.
This is in communication above with the fourth ventricle, and it extends be-
low to the filum terminale. 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 cen-
tral canal is immediately surrounded by connective tissue. In front of the
gray commissure, is the anterior white commissure.

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 up-
ward throughout the whole extent of the cord. In the dorsal region, the
gray matter is least abundant, and it exists in greatest quantity in the lumbar
enlargement.

The white substance of the cord is composed of nerve-fibres, connective-
tissue elements (neuroglia) and blood-vessels, the latter arranged in a very
wide and delicate plexus. The nerve-fibres are variable in size and are com-
posed of the axis-cylinder and the medullary substance, without the tubular
membrane.

The anterior cornua of gray matter contain blood-vessels, connective-tis-
sue elements (neuroglia), very fine nerve-fibres, and large multipolar nerve-
cells, which are sometimes called motor cells. The posterior cornua are com-
posed of the same elements, the cells being much smaller, and the fibres ex-
ceedingly 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
small cells and fibres, called the substantia gelatinosa. The connections
between the nerve-cells and the nerve-fibres have already been described in
connection with the general structure of the nervous system. The multi-
polar nerve-cells are supposed to present certain prolongations which do not
branch and are directly connected with the medullated nerve-fibres. These
are called axis-cylinder prolongations. In addition, fine, branching poles are
described under the name of protoplasmic prolongations. In both the white
and the gray substance of the cord, is a ground-work of delicate connective-
tissue fibres and cells, called neuroglia. This supports the nerve-cells, nerve-
fibres, vessels etc. The neuroglia is particularly abundant in that part of the
posterior cornua of gray matter, called the substantia gelatinosa.

The division of the spinal cord into columns, has a physiological as well
as an anatomical basis. Anatomists usually recognize, on either side of the
cord, an anterior column, bounded by the anterior median fissure and the
line of origin of the anterior roots of the spinal nerves, a lateral column,
bounded by the lines of origin of the anterior and of the posterior roots of
the nerves, and a posterior column, bounded by the line of the posterior roots
of the spinal nerves and the posterior median fissure. As the anterior or

592 NERVOUS SYSTEM.

posterior columns include either the white or the gray matter, they are called
respectively the anterior or posterior white and gray columns. Physiological
and pathological researches, however, have shown that the cord may prop-
erly be farther divided as follows :

1. Columns of Tiirck. — By the sides of the anterior median fissure, are
two narrow columns of white matter, one on either side, extending to the
white commissure (A, in Fig. 217), called the columns of Tiirck, the direct,
or the uncrossed pyramidal tracts. The fibres of these columns descend,
probably decussate in the cervical region of the cord, and the columns are
lost in the lower dorsal region. Destruction of certain motor parts in the
brain is followed by descending secondary degeneration of the fibres of these
columns.

2. Crossed Pyramidal Tracts. — These are situated, one on either side, in
the posterior portion of the lateral columns (G, G, in Fig. 217), and are
bounded internally by the posterior cornua of gray matter and externally by
a narrow band called the direct cerebellar tract. In following the columns
upward, it is found that they pass forward in the upper part of the cervical
region and decussate in the lower portion of the anterior pyramids of the
medulla oblongata. These are descending tracts, and their fibres undergo
descending secondary degeneration as the result of destruction of certain
motor parts in the brain.

3. Anterior Fundamental Fasciculi. — These fasciculi (B, in Fig. 217),
are bounded internally by the columns of Tiirck and externally by the ante-
rior cornua of gray matter and the anterior roots of the spinal nerves. Their
fibres are supposed to connect the gray matter of the anterior cornua of the
cord with the gray matter of the medulla oblongata.

4. Anterior Radicular Zones. — These columns (E, E, in Fig. 217) are in
the anterior portion of the lateral columns. Their fibres are supposed to
connect the gray matter of the cord with the gray matter of the medulla
oblongata.

5. Mixed Lateral Columns. — These columns (F, F, in Fig. 217) are in
the lateral columns of the cord, next the gray matter. With the anterior
fundamental fasciculi and the anterior radicular zones, they probably connect
the gray matter of the cord with the gray matter of the medulla oblongata.

The fibres of the anterior fundamental fasciculi, the anterior radicular
zones and the mixed lateral columns do not degenerate in either direction as
the result of section of the cord. Their fibres seem to connect nerve-cells with
each other, and their trophic cells exist at both extremities, which accounts
for the absence of degeneration, just mentioned.

6. Direct Cerebellar Fasciculi. — These fasciculi (H, H, in Fig. 217) are
situated at the outer and posterior portion of the lateral columns. Their
fibres pass to the funiculi graciles, or posterior pyramids of the medulla
oblongata, and thence to the cerebellum, by the inferior peduncles. They
connect the cells of the posterior cornua of gray matter with the cerebellum.
These columns make their appearance first in the lumbar region of the cord,
and they increase in size from below upward. After section of the spinal

PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. 593

AR

H

cord, the fibres of the direct -cerebellar fasciculi show ascending secondary
degeneration. Their trophic centres probably are the cells of the posterior
cornua of gray matter of the cord.

7. Columns of Burdach. — These columns (D, in Fig. 217) are in the pos-
terior columns of the cord, between the columns of Goll and the posterior
cornua of gray matter. Their fibres connect some of the cells of the gray
matter of the posterior cornua with the

cerebellum ; or at least the fibres pass up-
ward and are connected with the restiform
bodies, going to the cerebellum through
the inferior peduncles. The fibres also
connect nerve-cells of different portions of
the cord with each other. No secondary
degenerations have been noted in these
columns.

8. Columns of Goll — These delicate
columns (C, in Fig. 217) are situated on
either side of the posterior median fissure.
They are lost in the lower dorsal or upper
lumbar region. Their fibres pass upward

and are lost in the funiculi graciles of the \

medulla oblongata. After section of the
cord, ascending secondary degeneration is FlG' **r- Diagram. of
observed in the fibres of these columns.

Directions of Nerve - Fibres in the
Cord. — Many of the points in the descrip-
tion of the course and connections of the
fibres in the cord are given as probable.
Anatomical observations have been some-
what contradictory, but these have been
corrected or verified by following the paths
of degeneration. What is called secondary degeneration is the anatomical
change in the nerve-fibres which follows separation of the fibres from the
cells which act as their trophic centres, or the centres presiding over their
nutrition, these changes being secondary to the destruction or degeneration
of the centres.

The fibres of the anterior roots of the spinal nerves, following these fibres
inward and upward, pass directly to the large, multipolar motor cells of the
anterior cornua of gray matter and have no direct connection with the white
columns. Their direction through the white columns of the cord is oblique
and slightly upward. They are continuous with the axis-cylinder prolonga-
tions of the cells. From the nerve-cells, prolongations are given off, by
branching processes, in two bundles, median and lateral. The fibres of the
median bundle pass to the anterior white commissure, in which they decus-
sate. They then go each one to the column of Tiirck on the opposite side
and pass upward in the so-called direct pyramidal tracts. The fibres of the

ducting paths in
upper dorsal region (enlarged and modi-
fied from Landois).

AR, AR, anterior roots of the spinal nerves ;
PR, PR, posterior roots ; A, columns of
Tiirck ; B, anterior fundamental fascicu-
li ; C, columns of Goll ; D, columns of
Burdach ; E. E, anterior radicular zones ;
F, F, mixed lateral columns ; G, G,
crossed pyramidal tracts ; H, H, direct
cerebellar fasciculi. The gray matter of
the cord is in black. The figure also
shows the anterior and posterior median
fissures, the white and gray commissures
and the central canal.

594 NERVOUS SYSTEM.

lateral bundle go to the crossed pyramidal tract in the lateral column of the
same side and pass upward to decussate at the medulla oblongata.

The fibres of the columns of Tiirck and the crossed pyramidal tracts are
the only fibres of the cord which are known to convey motor impulses from
the brain. Destruction of certain parts of the brain produces descending
secondary degeneration of these fibres.

It is probable that fibres arise from the cells' of the gray matter of the
cord, which connect these cells with- each other and are concerned in cer-
tain reflex phenomena involving the action of the cord alone. These fibres
are in the anterior fundamental fasciculi, the anterior radicular zones and
the mixed lateral columns. They present no secondary degeneration.

The fibres of the posterior roots of the spinal nerves pass to the small,
sensory cells of the posterior cornua of gray matter of the cord and are con-
nected by branching processes with branching prolongations of these cells.
Processes from these cells pass to the gray commissure and decussate around
the central canal, conducting sensory impressions to the brain, in the gray
matter of the opposite side of the cord. The sensory conductors therefore
decussate all along the cord. Some of the fibres go to the. columns of Goll
and pass upward to and are continuous with the funiculi graciles of the
medulla, oblongata. Fibres also pass to the direct cerebellar fasciculi and a
few, perhaps, to the columns of Burdach, to go upward to the cerebellum.
Section of the cord produces ascending secondary degenerations in the col-
umns of Goll and the direct cerebellar fasciculi. Fibres originating in the
nerve-cells of the posterior cornua pass in and ou't, along the cord, and con-
nect the cells with each other. These may properly be called longitudinal
commissural fibres. They probably constitute the greater part of the col-
umns of Burdach and they present no secondary degeneration.

GENERAL PROPERTIES OF THE SPIRAL CORD.

As regards the general properties of the cord, as shown by the effects of
stimulus applied to its exterior or to its cut surface, the term excitability will
be used to express a property indicated by direct muscular contraction follow-
ing stimulation of the cord, and sensibility, a property which enables it to
receive impressions which produce pain. In exciting different parts of the
cord with electricity, it is necessary to carefully guard against an extension
of the current beyond the points which it is intended to stimulate. Some
physiologists regard the cord as absolutely inexcitable and insensible, both on
its surface and in its deeper portions. With this view, it is supposed that
parts of the cord will conduct motor impulses received from the centres
situated above, but are not excited by a stimulus applied directly. In the
same way, it is thought, parts of the cord will convey sensory impressions
received through the nerves, but are insensible to direct irritation.

The results of the observations of Van Deen, Brown-Sequard, Schiff and
others, were simply negative ; but the positive results obtained by Longet,
Fick, Vulpian and those who regard parts of the cord as excitable and sen-
sible, show that certain of the columns react under direct stimulation.

PATHS OF CONDUCTION IN THE COED. 595

In some experiments made in 1863 (Flint) upon a living dog, the cord
having been exposed in the lumbar region and stimulated mechanically and
with an electric current two hours after the operation, certain positive results
were obtained, which led to 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 pro-
duces convulsive movements 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
the general properties of the nerves in their course are demonstrated.

Motor Paths in the Cord. — What has been said regarding the direction
of the fibres in the cord and the situation and course of the degenerations
following destruction of motor cerebral centres conveys a definite idea of the
motor paths in the cord. This idea is sustained by experiments in which
different columns of the cord have been divided in living animals.

The motor paths are in the direct pyramidal tracts (columns of Tiirck)
and in the crossed pyramidal tracts of the lateral columns. The motor im-
pulses are conveyed by the fibres of these tracts to the multipolar cells in the
anterior cornua of gray matter and are thence transmitted to the anterior
roots of certain spinal nerves. In the lower dorsal region the conduction
is confined to the crossed pyramidal tracts in the lateral columns, while
above, the direct pyramidal tracts participate in this action.

The motor fibres decussate in the anterior pyramids of the medulla oblon-
gata (crossed pyramidal tracts), and in the cervical region, to a comparatively
slight extent, before the direct pyramidal tracts (columns of Tiirck) pass to
the encephalon. In the cervical region the decussation takes place probably
in the anterior white commissure. The fact of this decussation of motor
conductors is sustained by pathology — paralysis of motion following brain-
lesions, occurring on the opposite side of the body — and by experiments in
which the fibres as they cross are divided by a longitudinal median section
in the medulla and in the cervical region of the cord.

Vaso-motor nerve-fibres exist in the lateral columns of the cord and
probably are connected with the cells of the gray matter. They pass out in
the anterior roots of the spinal nerves and go to the blood-vessels either
from the branches of the spinal nerves directly or through filaments sent to
the sympathetic.

Sensory Paths in the Cord. — The gray matter of the cord is the part
concerned in the conduction of sensory impressions (Bellingeri, 1823). This
fact has been verified by recent experiments ; but it is thought that some of

596 NERVOUS SYSTEM.

the sensory conductors run in the columns of Goll (Flechsig). The columns
of Goll, however, exist only in the cervical and dorsal regions.

The sensory conductors do not decussate at any particular point as do the
motor conductors in the crossed pyramidal tracts. The fibres from the pos-
terior roots of the spinal nerves pass to the sensory cells of the posterior cor-
nua and decussate throughout the entire length of the cord (Brown-Sequard).
If the cord be divided longitudinally in the median line, there is complete
paralysis of sensation on both sides in all parts below the section (Fodera,
1822, and Brown-Sequard). In this section, the only fibres that are divided
are those passing from one side of the cord to the other. This decussation
is by fibres prolonged from the cells of the posterior cornua, which cross in
the gray commissure, around the central canal.

When one lateral half of the cord is divided in a living animal, sensibil-
ity is impaired or lost on the opposite side of the body, below the section,
but there is hyperassthesia on the side corresponding to the section. The
exaggeration of sensibility has not been satisfactorily explained.

Relations of the Posterior White Columns of the Cord to Muscular Co-
ordination.— It was noticed by Todd, many years ago (1839-1847), in cases
of that peculiar form of muscular inco-ordination now known as locomotor
ataxia, that the posterior white columns of the cord were diseased. Eeason-
ing from this fact, Todd made the following statement with regard to the
office of these columns :

" I have long been impressed with the opinion, that the office of the pos-
terior 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
co-ordinating the movements necessary for perfect locomotion."

The view thus early advanced by Todd has been sustained by the results
of experiments on living animals. If the posterior columns be completely
divided, by two or three sections made at intervals of about three-fourths of
an inch to an inch and a quarter (20 to 30 mm.), the most prominent effect
is a remarkable trouble in locomotion, consisting in a want of proper co-ordi-
nation of movements (Vulpian). Experiments upon the different columns
of the cord in living animals, however, are so difficult that physiologists have
preferred to take the observations in cases of disease in the human subject as
the basis of their ideas with regard to the office of the posterior white col-
umns.

The characteristic phenomenon of locomotor ataxia is inability to co-ordi-
nate muscular movements, particularly those of the extremities. There is
not of necessity any impairment of actual muscular power ; and although
pain and more or less disturbance of sensibility are usual, these conditions
are not absolutely invariable and they are always coincident with disease of
sensory conductors. The characteristic pathological condition is disease of
the posterior white columns (columns of Burdach). This is usually followed
by or is co-existent with disease of the posterior roots of the spinal nerves

NERVE-CENTRES IN THE SPINAL CORD. 597

and disease of the cells of the posterior gray matter of the cord. As the
cells are affected, there follows ascending secondary degeneration of the col-
umns of Goll. It is fair to assume that the disease of the cells of the gray
matter of the cord and of the posterior roots of the spinal nerves is con-
nected with the disorders of general sensibility. The disease of the columns
of Burdach produces the disorder in movements.

Reasoning from the characteristic phenomena and the essential patholog-
ical conditions of the cord in typical cases of locomotor ataxia, the posterior
white columns of the cord, connecting cells of the gray matter in different
planes with each other, assist in regulating and co-ordinating the voluntary
movements. The fibres of these columns also connect the cord with the
cerebellum, which has an important office in muscular co-ordination. It is
probable that the appreciation of the muscular sense and the sense of press-
ure, if these can be separated from what is known as general sensibility,
are connected with the action of the fibres of the posterior white columns.

NERVE-CENTRES IN THE SPINAL CORD.

It has long been known that decapitation of animals does not arrest mus-
cular action ; and the movements observed after this mutilation present a
certain degree of regularity and have been shown to be in accordance with
well defined laws. Under these conditions, the regulation of such move-
ments is effected through the spinal cord and the spinal nerves. If an ani-
mal be decapitated, leaving only the cord and its nerves, there is no sensa-
tion, f 01 the parts capable of appreciating sensation 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 generat-
ing a motor impulse 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 mus-
cular movements are abolished, except as they may be produced by direct
stimulation of the muscular tissue or of individual motor nerves.

The gray matter of the brain and spinal cord is a connected chain of
ganglia, capable of receiving impressions through the sensory nerves and of
generating motor impulses. The cerebro- spinal axis, taken as a whole, has
this general office ; but some parts have separate and distinct properties and
can act independently of the others. The cord, acting as a conductor, con-
nects 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 cen-
tre, independently of the brain • but the encephalon has no communication
with the parts supplied with nerves from the cord, and it can act only upon
the parts which receive nerves from the brain itself.

When the cord is separated from the encephalon, an impression made
upon the general sensory nerves is conveyed to its gray substance, and this
gives rise to a stimulus, which is transmitted to the voluntary muscles, pro-
ducing certain movements, independently of sensation and volition. This

598 NERVOUS SYSTEM.

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 con-
sequence of an impression received by a nerve-centre ; and it is evident that
reflex phenomena are by no means confined to the action of the spinal cord.
The movements of the iris are reflex, and ye.t they take place in many in-
stances 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 cer-
tain 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 impressions as an exciting
cause ; but it is evident, from a little reflection, that this is often the case.

Reflex Action of the /Spinal Cord. — Simple reflex action involves the
existence of an afferent (sensory) nerve, a collection of nerve-cells, and an
efferent (motor) nerve, the nerves being connected with the nerve-cells. In
a decapitated animal, not only are the movements independent of sensation
and volition, but no movements occur if the sensory nerves be protected
from any kind of impression or stimulation (Marshall Hall, 1832 and 1833).
If the cord be destroyed, however, no movements follow stimulation of the
surface ; and if either the afferent and the efferent nerves be divided, no
reflex movements can take place. Experiments upon decapitated animals
are in accord with the results of observations upon acephalous foetuses and
in cases of complete paraplegia from injury to the cord.

In the simplest form of a reflex movement, the muscular contraction is
confined to the muscle or muscles which correspond, in their nervous supply,
to the afferent nerve stimulated ; but when the stimulus is sufficiently power-
ful or when the cord is in a condition of exalted excitability, the impression
is disseminated throughout the gray matter, and the entire muscular system
may be thrown into action. With feebler stimulation, one side only of the
muscular system may respond. When the reaction extends to the opposite
side, it is called crossed reflex. The extension of a stimulus conveyed by a
single afferent nerve throughout the cord is called irradiation.

When a feeble stimulus applied to an afferent nerve is repeated frequently
and at short intervals, general muscular movements are produced. This fol-
lows stimuli applied three times in a second, and the effect is increased up
to sixteen shocks in a second, but not beyond this number (Rosenthal).

In studying the paths of conduction in the cord it has been seen that
sensory conduction takes place through the gray matter and possibly through
the columns of Goll, that motor impulses are conducted by the direct and
the crossed pyramidal tracts, and that the columns of Burdach are connected
with muscular co-ordination. The fibres of the cord that are specially con-

REFLEX ACTION OF THE SPINAL CORD.

599

nected with reflex action are probably in the anterior fundamental fasciculi,
the anterior radicular zones and the mixed lateral columns.

It is well known that the reflex excitability of the cord is exaggerated by
removal of the encephalon. According to Setschenow (1863), certain parts
in the encephalon, particularly the optic lobes in frogs, exert an inhibitory
influence over the reflex acts of the cord, and as a consequence, the reflex
phenomena are more marked when this influence is suppressed.

Various poisons, especially strychnine, have a remarkable influence over
reflex excitability. In a frog ^decapitated and poisoned with strychnine, no
reflex movements occur unless an impression be made on
the sensory nerves ; but the slightest irritation, such as a
breath of air, throws the entire muscular system into a
condition of violent tetanic spasm. The same phenome-
na are observed in cases of poisoning by strychnine or
of tetanus in the human subject.

The inhalation of anaesthetic agents may abolish all
of the ordinary reflex phenomena. 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 move-
ments of respiration continue; but these also may be
arrested, as has been observed by all who have experi-
mented with anaesthetics, especially with chloroform. A
common way of determining that an animal is complete-
ly under the influence of an anaesthetic is by noting an
absence of the reflex act of closing the eyelids when the
cornea is touched.

It is only necessary, after what has gone before, to in-
dicate in a general way certain phenomena observed in
the human subject which illustrate the reflex action of
the cord. It is a common observation, in cases of para-
plegia in which the lower portion of the cord is intact,
that movements of the limbs follow titillation of the soles
of the feet, these movements taking place independently
of the consciousness or the will of the subject experi-
mented 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 of
this kind are so familiar that they need not be cited in detail. Experiments
have also been made upon criminals after decapitation ; and although the re-
flex phenomena are not so well marked and can not be excited so long after
death as in cold-blooded animals, they are sufficiently distinct.

General muscular spasms following stimulation of sensory * nerves are
pathological and take place only when the reflex excitability of the cord is
much exaggerated. Examples of this action are the spasms observed in teta-
nus or in poisoning by strychnine. In experiments on the lower animals,

l~

600 NERVOUS SYSTEM.

particularly frogs, co-ordinate reflex movements are often observed, such as
the movements of jumping or swimming. This is sometimes called purposive
reflex action, as the movements seem to have a definite purpose or object. The
following well known experiment illustrates a co-ordinate, or purposive reflex :

Pfliiger (1853) removed the entire encephalon from a frog, leaving only
the spinal cord. He then touched the surface of the thigh, over the inner
condyle, with acetic acid. The animal thereupon rubbed the irritated sur-
face with the foot of the same side, apparently appreciating the seat of the
irritation, and endeavoring, 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 movements of
the limbs, rubbed the spot with the foot of the opposite side.

It has been thought that this experiment shows a persistence of sensa-
tion and the power of voluntary movements after removal of the entire en-
cephalon ; but it must be remembered that the cord contains cells connected
together by fibres probably into groups which correspond to sets of muscles
concerned in co-ordinate movements, and that many movements set in action
by an effort of the will continue in an automatic manner, as the ordinary
movements of progression. It is more reasonable to suppose that a persist-
ent stimulation of the surface, such as is produced by the action of acetic
acid upon the skin of a frog, can give rise to co-ordinate movements of a
purely reflex character than to assume that the movements in Pfliiger's ex-
periment are voluntary efforts to remove a painful impression. It is certain
that in the higher classes of animals after removal of the encephalon, in ex-
periments on decapitated criminals and in patients suffering from paraplegia,
there is no evidence of true sensation or volition in the spinal cord. In man
and the higher animals, all muscular movements which depend solely upon
the reflex action of the cord must be regarded as automatic and entirely in-
dependent of consciousness and of the will.

Certain reflex movements may be restrained by an effort of the will, as is
well known ; provided, always, that these be movements that can be exe-
cuted by voluntary effort. Nevertheless, if the sensory impression be suffi-
ciently powerful or be very frequently repeated, it is often impossible to con-
trol such movements by the will. Movements that are never in themselves
voluntary, such as the ejaculation of semen, when excited by reflex action
can not be restrained by a voluntary effort ; while the reflex act of coughing,
for example, may be measurably controlled. It is hardly proper to speak of
inhibition of the reflexes, in the sense in which the term inhibition is gener-
ally used in physiology, for the reason that there are probably no special in-
hibitory nerves for these movements.

Various reflexes are made use of in pathology as means of diagnosis.
The superficial reflexes are those produced by tickling the soles of the feet
or by exciting other parts of the skin. The most prominent of the deep re-
flexes is the patellar reflex, or the knee-jerk, produced by percussion of the
ligamentum patellae.

PHYSIOLOGICAL DIVISIONS OF THE ENCEPHALON. 601

The gray matter of the cord is not a single centre, but consists of a num-
ber of centres connected with each other and with the brain. Some of these
have already been described in connection with the history of various physi-
ological processes, and others will be considered hereafter under appropriate
heads. In addition to those already described, are centres for defsecation, at
the fifth lumbar vertebra in dogs (Budge), the erection-centre, in the lumbar
region (Eckhard), and the parturition-centre (Korner), at the first and sec-
ond lumbar vertebrae. All of the spinal centres act in accordance with the
general laws of reflex phenomena.

CHAPTER XIX.

THE ENCEPHALIC GANGLIA.

Physiological divisions of the encephalon— Weights of the encephalon and of certain of its parts— The
cerebral hemispheres— Cerebral Convolutions— Basal ganglia— Corpora striata, optic thalami and inter-
nal capsule— Tubercular quadrigemina— Pons Varolii— Directions of the fibres in the cerebrum— Cere-
bral localization — General uses of the cerebrum — Extirpation of the cerebrum — Facial angle — Pathologi-
cal observations — Reaction-time — Centre for the expression of ideas in language — The cerebellum —
Physiological anatomy— Extirpation of the cerebellum— Pathological observations— Connection of the
cerebellum with the generative function— Medulla oblongata (Bulb)— Physiological anatomy— Uses of
the medulla oblongata— Respiratory nerve-centre— Cardiac centres— Vital point (so called)— Rolling and
turning movements following injury of certain parts of the encephalon.

THE encephalic ganglia are collections of gray matter found in the en-
cephalon, or what is commonly known as the brain. This part of the cerebro-
spinal axis is situated in the cranial cavity. It is provided with membranes,
which are similar to the membranes of the spinal cord and have been de-
scribed in connection with the cord and the general arrangement of the cere-
bro-spinal axis. The gross anatomical divisions of the encephalon are the
cerebrum, cerebellum, pons Varolii and medulla oblongata. As regards their
physiological uses, the cerebellum, pons and medulla are to a certain extent
subordinate to the cerebrum. In treating of the physiology of these parts,
it will be convenient to take up first the cerebrum, or the cerebral hemi-
spheres, with their anatomical and physiological connections and their rela-
tions to the other parts of the encephalon.

All parts of the encephalon which act as nerve-centres are more or less
intimately connected with each other anatomically, and are finally connected,
through the medulla oblongata, with the spinal cord. The exceptions to this
rule are the centres of olfaction, vision, audition and gustation, which will
be considered fully in connection with the physiology of the special senses.
The spinal cord, as has been seen, is capable of independent action as a
nerve-centre or collection of nerve-centres, also serving as a means of connec-
tion between the brain and the parts, through the spinal nerves. The motor
and sensory cranial nerves are directly connected with the encephalon.

A detailed anatomical description of the brain would be out of place in

602

NEEVOUS SYSTEM.

this work, as there are many anatomical parts, the exact physiological rela-
tions of which are not understood ; still, there are certain parts which will
be referred to by name, a general knowledge of the arrangement of which
is necessary. The general relations of these parts are shown in Fig. 219,
slightly reduced and modified, from Harrison Allen, which represents a ver-
tical longitudinal section of the brain, in the median line.

As bearing upon certain points in the physiology of the brain, it is im-
portant to note the weight of the entire encephalon and of its great divisions.

FISSURE OFROLANDC

CALLOSO-MARGINAL SULCUS

SE PTU M
LUC

ANTERIOR CRUS
OF FORNIX
I

TRANSVERSE
FISSURE

VALVE
OF VIEUSS ENS

PINEAL GLAND.
CORPORA OUADRIGEMINA1

"?io. 219.— View of the structures displayed upon the right side of a median longitudinal section of the

brain — semi-diagrammatic.

Weights of the Encephalon and of Certain of its Parts. — Most of the
tables of weights of the healthy adult brain of the Caucasian, given by differ-
ent observers, give essentially the same figures, the differences amounting
to only one or two ounces (28-3 or 56-7 grammes) for the entire encepha-
lon. The average weight given by Quain, combining the tables of Sims,
Clendinning, and Reid, is 49£ ounces (1,408-3 grammes) for the male, and 44
ounces (1,247*4 grammes) for the female. The number of male brains
weighed was 278, and of female brains, 191. In males the minimum weight
was 34 ounces (963-9 grammes), and the maximum, 65 ounces (1,842'7
grammes). In 170 cases out of the 278, the weights ranged between 46 and
53 ounces (1,304-1 and 1,502-5 grammes), which may be taken as the average
limits. In females the minimum was 31 ounces (878-8 grammes), and
the maximum, 56 ounces (1,587*6 grammes). In 125 cases out of the 191,
the weights ranged between 41 and 47 ounces (1,162*3 and 1,332-4 grammes).

Quain assumed, from various researches, that in new-born infants, the

THE CEREBRAL HEMISPHERES. 603

brain weighs 11-65 ounces (327'8 grammes), for the male, and 10 ounces
(283-5 grammes), for the female. In both sexes, " the weight of the brain
generally increases rapidly up to the seventh year, then more slowly to be-
tween 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 progressive diminution in weight of about one
ounce (28-3 grammes) during each subsequent decennial period ; thus con-
firming the opinion, that the brain diminishes in advanced life."

The comparative weights of the several parts of the encephalon, calcu-
lated 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 fol-
lows :

Divisions of the encephalon.

Males.

Females.

Average weight of the cerebrum
Average weight of the cere-
bellum

43-98 oz. (1,247-3 grammes).
5-25 " (148-8 grammes).

38-75 oz. (1,098-6 grammes).
4-76 " (134-9 grammes).

Average weight of the pons and
medulla oblono'ata

0-98 " (28-2 grammes).

1-01 " (28-6 grammes).

Average weight of the en-
tire encephalon

50-21 oz (1 423'5 grammes).

44-52 oz. (1,262-1 grammes).

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).

THE CEREBRAL HEMISPHERES.

'Cortical Substance. — The surface of the cerebral hemispheres is marked
by fissures, sulci, and convolutions, which serve to increase the extent of the
gray substance. The sulci between the convolutions vary in depth in dif-
ferent parts, the average being about an inch (25-4 mm.). The grcy mat-
ter, which is external and follows the convolutions, is ^ to -J of an inch
(2-1 to 3-2 mm.) in thickness. Anatomists have described this substance as
existing in several layers, but this division is mainly artificial. In certain
parts, however, particularly 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 super-
ficial cells are small and present a net-work of delicate, anastomosing fibres.
The deepest cells are much larger. Between these two extremes, in the
intermediate layers, there is a gradual transition in the size of the cells.
Fig. 220 shows the layers of cells in a vertical section of a cerebral convolu-
tion. The most superficial layer is very thin. It contains much neuroglia
and a fine net-work of fibrils, with a few small nerve-cells. The second layer
presents a large number of small, so-called pyramidal cells. The third layer

604:

NERVOUS SYSTEM.

FIG. 220.— Vertical section of the third cerebral
convolution in man (Meynert).

1, superficial layer ; 2. layer of small pyramidal
cells ; 3. layer of large pyramidal cells ; 4, lay-
er of small irregular cells ; 5, layer of spindle-
shaped cells ; M, white substance.

is the thickest of all and contains
large, pyramidal cells, which become
larger in its deeper portions. The
fourth layer contains a large number
of smaller cells, irregular in form and
with branching prolongations. The
fifth layer presents spindle - shaped
cells with branching poles and this
layer is just above the white sub-
stance. The pyramidal cells present
a long process above, which passes to-
ward the surface, lateral branches,
which form a plexus of fine fibrils,
and an unbranched prolongation be-
low, which passes to the white sub-
stance, in the form of an axis-cylin-
der. The cells vary somewhat in their
appearances in different parts of the
brain. The largest pyramidal cells
are found in the anterior central con-
volution, in the upper part of the pos-
terior central convolution and the par-
acentral lobule. Large cells with few
prolongations are found in the poste-
rior part of the occipital lobes. The
cells in this part are connected to-
gether by communicating poles. The
mode of connection of the cells with
each other and with the fibres of the
white substance has already been de-
scribed and does not demand farther
mention.

Cerebral Convolutions. — The cere-
brum presents a great longitudinal
median fissure by which it is partially
divided into two lateral halves. Figs.
221 and 222, based on the well-known
diagrams of the brain by Ecker, show
three great fissures, the fissure of Syl-
vius, the fissure of Rolando and the
parieto-occipital fissure. The lobes of
the cerebrum are (1) the frontal lobe,
lying in front of and above the fissure
of Sylvius and in front of the fissure
of Rolando, (2) the parietal lobe, be-
hind the frontal lobe and in front of

CEREBRAL CONVOLUTIONS.

605

and above the occipital lobe, (3) the occipital lobe, and (4) the temporo-
sphenoidal lobe. The parietal lobe is bounded in front by the fissure of

FIG. 221.— Diagram of the external surface of the left cerebral hemisphere (modified from Ecker).

Rolando and below by the fissure of Sylvius and the parieto-occipital fissure
(shown in Fig. 222). The occipital lobe lies below the parieto-occipital fis-

FIG. 222.— Diagram of the internal surface of the right cerebral hemisphere, shoivn in a longitudinal

section in the median line (modified from Ecker).
40

606 • NERVOUS SYSTEM.

sure. The temporo-sphenoidal lobe is situated below the fissure of Sylvius
and in front of the occipital lobe.

While the convolutions are not exactly the same in all human brains, or
even in both sides of the brain, their arrangement and relations may be
described in a general way with sufficient accuracy to enable one to recognize
easily the most important physiological points in the descriptive anatomy of
the cerebral surface. The diagrammatic Figs. 221 and 222 give a general
view of the fissures and of the most important convolutions.

The first frontal convolution is bounded internally by the great longi-
tudinal fissure and externally by a shallow fissure nearly parallel to the longi-
tudinal fissure. The second frontal convolution lies next the first frontal
convolution, and is bounded externally by two shallow fissures lying in front
of the fissure of Sylvius. The third frontal convolution curves around the
short branch of the fissure of Sylvius. On either side of the fissure of Ro-
lando, are the anterior central convolution and the posterior central convolu-
tion. Curving around the posterior extremity of the fissure of Sylvius, is
the supramarginal convolution, which is continuous with the first temporal
convolution, the latter lying behind and parallel with the fissure of Sylvius.
Internal to the posterior portion of the intraparietal sulcus is the angular
convolution, which is continuous with the second temporal convolution. At
the inferior border of the temporo-sphenoidal lobe, below the first and second
temporal convolutions, is the third temporal convolution. The superior pari-
etal convolution lies by the side of the median fissure and is the posterior
continuation of the first frontal convolution. The situation of the occipital
convolutions is indicated in Fig. 221. In addition to these convolutions
upon the general surface of the cerebrum, there are convolutions on the sur-
face of the base of the brain and in the gray matter of the sides of the great
longitudinal 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.

Fig. 222 shows the most important parts observed on the inner surface
of the right hemisphere. These parts do not demand any explanation beyond
that given in the diagram itself.

Basal Ganglia. — The ganglia at the base of the brain are the olfactory
ganglia, the corpora striata, optic thalami, tubercula quadrigemina and the
gray matter of the pons varolii. The olfactory ganglia will be described in
connection with the physiology of the sense of smell. The corpora striata
and the optic thalami are important in their relations to the internal capsule
and the paths of motor and sensory conduction.

Corpora Striata, Optic Thalami and Internal Capsule. — The corpora
striata are pear-shaped bodies, situated at the base of the brain, with their
rounded bases directed forward, and the narrower ends, backward and out-
ward. Their external surface is gray, and they present, on section, alternate
striae of white and gray matter. Between the posterior and narrow extremi-
ties of these bodies, are the optic thalami. The corpora striata have what is

BASAL GANGLIA OF THE ENCEPHALON.

GOT

called an intraventricular portion, projecting into the anterior part of the
lateral ventricles, and an extraventricular portion, which is embedded in the
white substance at the base of the brain.

The optic thalami are oblong bodies situated between the posterior ex-
tremities of the corpora striata and resting upon the crura cerebri on the two
sides. These are white externally, and in their interior they present a mixt-
ure, of white and gray matter.

If a horizontal section be made through the brain, involving the corpora
striata and the optic thalami, the corpora striata present a division into two
nuclei. These are the
caudate nucleus, which
is internal, and the
lenticular nucleus,
which is external to
and behind the cau-
date nucleus. Exter-
nal to the lenticular
nucleus, is a band of
white substance, called
the external capsule, in
which there is a band
of gray matter, called
the claustrum. Exter-
nal to the external cap-
sule, at its anterior
portion, is the insula,
or island of Reil.

Between the cau-
date nucleus and the
lenticular nucleus in
front, is a broad band
of white fibres, which
is continuous with a
band of white fibres
lying posteriorly, be-
tween the lenticular
nucleus and the optic
thalamus on either
side. This band is the
internal capsule. The
portion of the internal
capsule which lies between the caudate nucleus and the lenticular nucleus is
called its anterior division. The portion of the internal capsule situated
between the lenticular nucleus and the optic thalamus is its posterior divis-
ion. The bend where the posterior division of the internal capsule joins the
anterior division is called the knee of the capsule.

FIG. 223. — Horizontal section of the hemispheres, at the level of the cere'
bral ganglia (Dalton).

1, great longitudinal fissure between the frontal lobes ; 2, great longi-
tudinal fissure between the occipital lobes ; 3, anterior part of the
corpus callosum : 4, fissure of Sylvius ; 5, convolutions of the insu-
la ; 6, caudate nucleus of the corpus striatum ; 7, lenticular nucleus
of the corpus striatum ; 8. optic thalamus ; 9, internal capsule ; 10.
external capsule ; 11, claustrum.

608

NERVOUS SYSTEM.

FIG. 224. — Diagram of the human brain in a transverse vertical section
(Dalton).

1, pons Varolii ; 2, 2, erura cerebri ; 3, 3, internal capsule ; 4, 4, corona
radiata ; 5, optic thalamus ; 6, lenticular nucleus ; 7, corpus cal-
losum.

The directions of the fibres of the internal capsule are in general terms the
following : Fibres from the crura cerebri go directly into the corpora striata

in front and into the
optic thalami behind.
This is the course of
greater part of.
fibres, but some

the
the

fibres go directly
through the internal
capsule, and thence
to the gray matter of
the cerebral convolu-
tions. Most of the
fibres, however, which
form the internal cap-
sule, come from the
gray matter of the
corpora striata and
optic thalami and
curve outward and
upward to go to the
gray matter of the
hemispheres. As they
pass from the internal capsule to the internal surface of the cerebral convo-
lutions, they form the corona radiata.

In the human subject, lesions affecting the anterior two-thirds of the pos-
terior division of the internal capsule produce paralysis of motion only, and
are followed by descending degenerations. The fibres in this part are con-
nected with the corpora striata. Lesions affecting both the anterior two-
thirds and the posterior third of the posterior division of the internal capsule
produce paralysis of motion and sensation. The fibres in the posterior third
are connected with the optic thalami. Ascending degenerations have not
been observed in the fibres of the cerebrum.

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 apparent origin of the optic
nerves and are connected by commissural fibres with the optic thalami. In
birds the tubercles are two in number, instead of four, and are called tuber -
cula bigemina. The anatomical and physiological relations of these bodies
will be fully described in connection with the sense of sight.

Crura Cerebri. — The crura are short, thick, rounded bands which pass
from the cerebral hemispheres to the upper border of the pons Varolii,

BASAL GANGLIA OF THE ENCEPHALON. 609

They are rather broader above than below and are about three-quarters of an
inch (19 mm.) in length. They are composed of longitudinal white fibres
connecting various parts with the cerebrum. Each crus is divided into a
superficial and a deep band, by a layer of gray substance called the locus
niger. The locus niger contains small, multipolar nerve-cells and abundant
pigmentary granules. The lower, or superficial band of the crus is called
the crusta. The deep band is called the tegmentum. The crusta consists
of white fibres only. In the tegmentum the fibres are mixed with masses
of gray matter.

Pons Varolii. — The pons Varolii, called the tuber annulare or the meso-
cephalon, is situated at the base of the brain, just above the medulla oblon-
gata. It is white externally and contains in its interior a large admixture
of gray matter. It presents both transverse and longitudinal white fibres.
Its transverse fibres connect the two halves of the cerebellum. Its longi-
tudinal fibres are connected below with the anterior pyramidal bodies and
the olivary bodies of the medulla oblongata, the lateral columns of the
cord and a certain portion of the posterior columns. The fibres are con-
nected above with the crura cerebri and pass to the brain. The super-
ficial transverse fibres are wanting in animals in which the cerebellum has
no lateral lobes.

If the cerebral hemispheres, the olfactory ganglia, the optic lobes, the
corpora striata and the optic thalami be removed, the animal loses the spe-
cial senses of smell and sight and the intellectual faculties, there is a certain
degree of enfeeblement of the muscular system, but voluntary motion and
general sensibility are retained. As far as voluntary motion is concerned,
an animal operated upon in this way is in nearly the same condition as one
simply deprived of the cerebral hemispheres. There are no voluntary move-
ments which show any degree of intelligence, but the animal can stand, and
various consecutive movements are executed, which are different from the
simple reflex acts depending exclusively upon the spinal cord. The co-ordi-
nation of movements is perfect, unless the cerebellum be removed. As re-
gards general sensibility, an animal deprived of all the encephalic ganglia,
except the pons Varolii and the medulla oblongata, undoubtedly feels pain.
This has been demonstrated by Longet, Vulpian and others. In rabbits, rats
and other animals, 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 Longet and Vulpian have insisted upon the char-
acter of these cries as indicating the actual perception of painful impressions,
and as very different from cries that are purely reflex, according to the ordi-
nary acceptation of this term. Longet alluded to the voluntary movements
and the cries observed in persons subjected to painful surgical operations,
when incompletely under the influence of an anaesthetic, concerning the
character of which there can be no doubt. He regarded 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 impres-
sion, although they have apparently experienced great suffering. As far as

610 NERVOUS SYSTEM.

can be judged from what is positively known of the action of the encephalic
centres, the pain under these conditions is perceived by some nerve-centre,
probably in the pons Varolii, 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 action of the pons Varolii
as a nerve-centre :

It is an organ capable of originating impulses 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 intel-
lectual effort, are made in obedience to a stimulus transmitted from the cere-
brum, through conducting fibres in the pons Varolii, to the motor conduc-
tors of the cord and the general motor nerves.

The gray matter of the ports Varolii is also capable of perceiving painful
impressions, which, when all of the encephalic ganglia are preserved, are
conducted to and are perceived by the cerebrum, and are remembered ; but
there are distinct evidences of the perception of pain, even when the cere-
brum has been removed.

Directions of the Fibres in the Cerebrum. — Fibres pass from the cerebral
hemispheres to the cerebellum. Commissural fibres connect the cerebrum
and certain of the basal ganglia on the two sides. Fibres connect the gray
matter of the cerebral convolutions on the same side with each other. Fibres
pass from the inner surface of the gray matter of the cerebrum to the inter-
nal capsule, corpora striata, optic thalami and pons Varolii, to the medulla ob-
longata and thence to the spinal cord. The directions of these four sets of
fibres have been quite accurately described.

1. Fibres connecting the Cerebrum with the Cerebellum. — (A) Fibres from
the gray matter of the frontal lobe, in front of the anterior central convolution,
pass through the anterior division of the internal capsule and thence through
the inner portion of the outer layer of the crus cerebri (crusta) to the pons,
where they seem to go to the cells of the gray matter. From the pons, fibres
go to the lateral and posterior regions of the cerebellum on the opposite side.
(B) Fib'res from the occipital and temporo-sphenoidal lobes pass in the outer
portion of the crusta and go to the upper portion of the cerebellum, near
the middle lobe. This connection is probably crossed. (C) Above the
pyramidal tract of the crusta, is a small tract of fibres which connect the
caudate nucleus of the corpus striatum, through the cells of the pons, with
the cerebellum on the opposite side (Gowers).

2. Fibres connecting the Two Sides of the Brain. — (A) Fibres coming from
the inner surface of the gray matter of the cerebral convolutions pass from
one side to the other, through the corpus callosum, and connect the two cere-
bral hemispheres with each other. These are the transverse fibres of the
corpus callosum. (B) Fibres from the gray matter of the temporo-sphenoidal
lobe on either side pass through the corpora striata to the anterior com-
missure. These fibres connect the temporo-sphenoidal lobes, and probably

DIRECTION OF THE FIBRES IN THE CEREBRUM. 611

also the corpora striata, on the two sides. (C) Fibres from the deeper portion
of the crus cerebri (tegmentum) pass to the optic thalamus on either side and
thence to the temporo-sphenoidal lobes. These fibres form the posterior com-
missure and connect the temporo-sphenoidal lobes and the optic thalami of
the two sides.

3. Fibres connecting Different Cerebral Convolutions on the same Side. —
(A) The so-called arcuate fibres, passing in a curved direction from one con-
volution to another, connect adjacent convolutions. (B) Other fibres, called
longitudinal or collateral fibres, connect distant convolutions with each other.
The fibres of the fornix connect the optic thalamus with the hippocampus
major and the unicate gyrus. Fibres in the corpus callosum connect the an-
terior and posterior extremities of the gyrus f ornicatus. These are the longi-
tudinal fibres of the corpus callosum. Other longitudinal fibres, connecting
parts more or less distant from each other, are found in the tsenia semicircu-
laris, the unicate fasciculus, the fillet of the gyrus fornicatus and the inferior
longitudinal fasciculus. The last-mentioned fasciculus connects the gray
matter of the temporo-sphenoidal and occipital lobes.

4. Fibres connecting the Brain ivith the Spinal Cord. — If these fibres be
followed from the cortex of the brain downward, they are called converg-
ing, and if they be followed from below upward, they are called radiating
fibres.

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. In studying the course of the con-
verging fibres arising from all points in the concave surface of the cerebral
gray matter, it is found that they take various directions. The fibres from
the anterior region of the cerebrum pass backward and form distinct fascic-
uli which converge to the gray substance of the corpora striata. The fibres
from the middle portion converge regularly to the middle region of the ex-
ternal portions of the optic thalami. The fibres from the posterior portion
pass from behind forward and are distributed 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 the course of most of these fibres toward the corpora
striata and the optic thalami, they pass through the internal capsule.

The fibres from the anterior and middle portions of the cerebrum, espe-
cially the middle portion, contribute largely to the formation of the anterior
two-thirds of the posterior division of the internal capsule. The fibres from
the posterior portion of the cerebrum are found in the posterior third of the
posterior division of the internal capsule. The posterior fibres are probably
sensory. The middle and anterior fibres are motor. The latter undergo de-
scending degenerations following lesions of the anterior and posterior central

612 NERVOUS SYSTEM.

convolutions (Charcot). A few of the converging fibres from the hemispheres
pass directly through the internal capsule and have no connection with the
corpora striata and optic thalami.

From the internal capsule, the fibres pass in the crus cerebri to the upper
border of the pons Varolii. The motor fibres pass through the pons as lon-

FIG. 225.— Diagrammatic representation of the direction of some of the fibres in the cerebrum (Le Bon).

gitudinal fibres, go to the anterior pyramids of the medulla oblongata, where
most of them decussate, and thence to the pyramidal tracts of the spinal
cord. The sensory fibres go to the posterior part of the cord. The converg-
ing cerebral fibres are re-enforced, in their downward course, by fibres from
the tubercular quadrigemina and the gray matter of the pons Varolii. Cer-
tain fibres go to the olivary bodies in the medulla oblongata. A more extend-
ed description of these fibres will be given in connection with the physiologi-
cal anatomy of the medulla.

Cerebral Localization. — The observations of Flourens (1822 and 1823) and
his immediate followers, which seemed to show that the cerebrum was neither
excitable nor sensible to direct stimulation, have been so completely contra-
dicted by the experiments of Fritsch and Hitzig (1870), Ferrier, Munk, Hors-
ley and many others, that the question of the existence of motor and sensory
centres — especially motor centres — hardly admits of discussion. The negative
results obtained by Floureus were probably due to severe haemorrhage, which,

CEREBRAL LOCALIZATION.

613

according to Ferrier, rapidly destroys the excitability of the motor cortical
areas. Some of the experiments of Goltz, by which it has been attempted to
prove that circumscribed and invariable motor areas do not exist, are an-
swered by observations showing descending secondary degenerations following
injury of certain parts of the cerebral cortex. The earlier observations on cere-
bral localization were made on dogs. Later, experiments have been made
on monkeys, and the results of these have been to a certain extent confirmed
by pathological observations on the human subject. Beginning with the ob-
servations in which descending degenerations have been noted as a consequence
of destruction of parts of the cerebral cortex, it may be assumed that a distinct
area exists which presides over certain localized muscular movements.

Motor Cortical Zone. — The motor cortical zone is on either side of the
fissure of Rolando. It is usually described as including the anterior and pos-

Fio. 226.— Motor cortical zone, on the outer surface of the cerebrum (Exner).

terior central convolutions (see Fig. 221) and the paracentral lobule (see Fig.
222). Faradization of parts in this zone is followed by localized muscular
movements. In fact, the motor areas seem to be subject to nearly the
same laws, as regards their reactions to Faradic stimulation, as are the
motor nerves. Forty Faradic shocks per second produce a corresponding
number of single muscular contractions. Forty-six shocks per second pro-
duce a tetanic contraction (Franck and Pitres). Destruction of motor areas
is followed by partial loss of power in certain sets of muscles, and by descend-
ing secondary degeneration of nerve-fibres, extending through the corona
radiata, the internal capsule, the crura cerebri, the anterior pyramids of the
medulla oblongata and finally the pyramidal tracts of the spinal cord.

614

NERVOUS SYSTEM.

It remains now to locate the distinct motor areas. This has been done
on the brain of the monkey, by Ferrier, who has applied his observations as

PIG. 227.— Paracentral lobule, on the inner surface of the cerebrum (Exner).
The shaded area in the diagram is the paracentral lobule.

nearly as possible to the human brain. While the divisions made by Ferrier
can not be taken as absolute, experiments on monkeys have been followed by

FIG. 228.— Lateral view of the human brain, with certain motor cortical areas (modified from Ferrier)

CEREBRAL LOCALIZATION. 615

results so nearly constant, that the localizations may be accepted as nearly cor-
rect. In the diagram (Fig. 228) and descriptions, the centres for the special
senses have been omitted, to be taken up in connection with the physiology
of olfaction, vision, audition and gustation.

In the following description, the numbers and letters refer to Fig. 228 :
(1). This, which is on the precuneus (compare Fig. 222), indicates the
position of the centres for movements of the opposite leg and foot, such as
are concerned in locomotion.

(2), (3), (4). These numbers, which are over the convolutions bounding
the upper extremity of the fissure of Rolando (including the paracentral
lobule — compare Fig 222), include centres for various complex movements
of the arms and legs, such as are concerned in climbing, swimming, etc.

(5) Situated at the posterior extremity of the first frontal convolution, at
its junction with the anterior central convolution, is the centre for the ex-
tension forward of the arm and hand, as in putting forth the hand to touch
something in front.

(6) Situated on the anterior central convolution, just behind the upper
end of the posterior extremity of the second frontal convolution, is the cen-
tre for the movements of the hand and forearm, in which the biceps is par-
ticularly engaged ; viz., supination of the hand and flexion of the forearm.

(7), (8). Just below (6), on the anterior central convolution, are centres
respectively for the elevators and depressors of the mouth.

(9), (10). These numbers taken together, on the third frontal convolu-
tion, mark the centre for the movements of the lips and tongue, as in articu-
lation. " This is the region, disease of which causes aphasia, and is gener-
ally known as Broca's convolution."

(11). This, which is on the lower end of the posterior central convolution,
marks " the centre of the platysma, retraction of the angle of the mouth."

(12) This, which is on the posterior part of the first and second frontal
convolution, marks " a centre for lateral movements of the head and eyes,
with elevation of the eyelids and dilatation of pupil."

(«), (#), (c), (d). These letters, on nearly the whole of the posterior cen-
tral convolution, " indicate the centres of movement of the hand and wrist."

The above description is quoted from Ferrier, with certain changes in
the nomenclature of the convolutions. Schiifer and Horsley in the main
have confirmed and have somewhat extended the researches of Ferrier.
These observers have shown that the centres on the outer surface of the
cerebrum, near the great longitudinal fissure, extend to the inner surface. In
the first frontal convolution, in front of the paracentral lobule, is a centre
for movements of the trunk (Tr., Fig. 229), and in front of this, is a centre
for the movements of the arm and shoulder. Other parts of the inner cere-
bral surface, except the paracentral lobule, are inexcitable.

In man lesions of parts of the motor-cortical zone produce localized paral-
ysis, or what is called monoplegia, the action being crossed. " The following
forms of monoplegia have been observed to attend localized cortical lesions :
1, oculo-motor monoplegia (isolated ptosis) ; 2, facial monoplegia, sometimes

616

NEEVOUS SYSTEM.

FIG. 229. — Inner surface of the right cerebral hem-
isphere (Schafer and Horsley).
A. S., area governing the movements of the arm i^ a-p-noval forma tVmf

and shoulder ; Tr., area for movements of the ln gel

trunk ; LEG, (paracentral lobule) area

movements of the leg.

combined with paralysis of the hypoglossal nerve ; 3, brachial monoplegia,
or paralysis of the opposite arm ; 4, crural monoplegia, or paralysis of the

opposite leg ; 5, brachio-facial mono-
plegia, or paralysis of the arm and
face " (Flint's " Practice of Medi-
cine ").

It is possible that there may be
sensory centres in the cerebral cortex,
but they have not been satisfactorily
localized, although attempts have been
made to limit such areas by studying
reflex phenomena following stimula-
tion of certain parts. It may be stated

nnnirn'tal anrl

for temporo - sphenoidal lobes, the fibres
from which pass through the posterior
third of the posterior division of the internal capsule, are specially connected
with sensation.

One of the most important of the cerebral centres is the centre for
speech, which will be fully described after the consideration of the general
uses of the cerebral hemispheres.

GENERAL USES OF THE CEREBRUM.

The cortical gray substance of the cerebral hemispheres not only is capable
of generating motor impulses of the kind known as voluntary, and of receiv-
ing sensory impressions, including those connected with the special senses,
but its anatomical and physiological integrity, and its connections, especially
with sensory conductors, are essential to what are known as mental opera-
tions. The existence of the mind and the possibility of normal operations
of the intelligence depend upon the existence of the gray matter of the cere-
bral cortex and its normal physiological condition and relations. This prop-
osition does not imply that the mind is a force which operates through the
brain, or even, strictly speaking, that the brain is the seat of the intellectual
faculties. Mental operations involve a slight elevation of temperature and
slightly increase some of the excretions. It is probable, therefore, that they
involve changes of matter ; and these changes, if they occur, can be effected
only by the cells of the brain. Without defining or analyzing the intellec-
tual faculties or attempting to locate different faculties in special parts, it is
sufficient to state that certain of these faculties reside probably in that por-
tion of the brain which is anterior to the motor cortical zone ; that is, in the
frontal lobes. These lobes, as far as is known, do not present motor or sen-
sory areas.

The brain and the intellectual power of man are so far superior in their
development to 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 degree. Although physiologists do not generally accept this prop-

GENERAL USES OF THE CEREBRUM. 617

osition, regarding the intelligence of man as simply superior in degree to
that of the lower animals, it is evident that this difference in the degree of
development is so great as to render the human mind hardly comparable
with the intellectual attributes of animals low in the scale. Still, there can
be no doubt with regard to the identity of the nature of the faculties of the
brain in man and in some of the lower animals, however much these facul-
ties may differ in their degree of development. If this proposition be true,
it is reasonable to apply experiments on the brain in the lower animals to the
physiology of corresponding parts in the human subject.

Extirpation of the Cerebrum. — Experiments upon different classes of
animals show clearly that the brain is less important, as regards the ordinary
manifestations of animal life, in proportion as its relative development is
smaller. For example, if the cerebral hemispheres be removed from fishes
or reptiles, the movements which are called voluntary may be but little
affected ; while if the same mutilation be performed in birds or some of the
mammalia, the diminished power of voluntary motion is much more marked.
It would be plainly unphilosophical 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 js not destroyed by the operation. It is not only possible
but probable that in the very lowest of the vertebrates, the operations of the
nervous centres are not the same as in higher animals. There is, for exam-
ple, a fish (the lancet-fish, Amphioxus 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, therefore, in endeavoring to apply the results of
experiments upon the brain in the lower animals to human physiology, to
isolate, as far as possible, the distinct manifestations of intelligence from
automatic movements.

Flourens (1822 and 1823) made a series of important observations upon
the different parts of the encephalon. 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 in-
stinctive acts. Animals thus mutilated retained general sensibility and the
power of voluntary movements, but were thought to be deprived of the spe-
cial senses of sight, hearing, smell and taste. As regards general sensibility
and voluntary movements, Flourens was of the opinion that animals de-
prived of their cerebral lobes possessed sensation, 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 an effort of the will. One of the most remark-
able phenomena observed was entire loss of memory and of the power of
connecting ideas. The voluntary muscular system was enfeebled but not
paralyzed. Removal of one hemisphere produced, in the higher classes of
animals experimented upon, enfeeblement of the muscles upon the opposite
side, but the intellectual faculties were in part or entirely retained.

618 NERVOUS SYSTEM.

The observations of Flourens have been repeated by many physiologists,
and were in the main confirmed, except as regards the special senses. Bouil-
laud (1826) made a large number of observations upon pigeons, fowls, rab-
bits and other animals, in which, after removal of the hemispheres, he noted
the persistence of the senses of sight and hearing. Longet finally demon-
strated the fact that both sight and hearing are retained after extirpation 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 remarkable, 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 deter-
mine their presence than to ascertain that the senses of sight and hearing are
retained. It is probable, 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 extirpation 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 concentrated
solution of colocynth into the mouth, as distinctly as in the same animals
under normal conditions.

Comparative Development of the Cerebrum in the Lower Animals. — It is
only necessary to refer very briefly to the development of the cerebrum in
the lower animals as compared with the human subject, to show the connec-
tion of the hemispheres with intelligence. In man the cerebrum presents a
large preponderance in weight over other portions of the encephalon ; and
in some of the lower animals the cerebrum is even less in weight than tho
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
has cited a number of observations made upon the brains of elephants, in
which the weights ranged between nine and ten pounds (about 4,000 and
4,500 grammes). Rudolphi gave the weight of the encephalon. of a whale,
seventy-five feet long (about 23 metres), as considerably over five pounds
(about 2,300 grammes). 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 cere-
bral convolutions in certain animals, by which the relative quantity of gray
matter is increased. In fishes, reptiles and birds, the surface of the hemi-
spheres is smooth ; but in many mammalia, especially in those remarkable for
intelligence, the cerebrum presents a greater or less number of convolutions,
as it does in the human subject.

GENERAL USES OF THE CEREBRUM. 619

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 cerebrum 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 exceptions. 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 co-existent 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
(170 grammes) of cerebral substance ; and while many women are far superior
in intellect to many men, such instances are not sufficiently frequent to
invalidate the general law, that the greatest intellectual capacity and mental
vigor is coincident with the greatest quantity of cerebral substance. If the
view, which is in every way reasonable, be accepted, that the gray substance
alone of the cerebral hemispheres is directly connected with the mind, it
would be necessary, in comparing different individuals with the view of
establishing a definite relation between brain-substance and intelligence, to
estimate the quantity 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, irrespective of the size of the cerebral hemispheres.
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 train-
ing, to the extraordinary development, in some individuals, of certain quali-
ties, to intensity and pertinacity of purpose, capacity for persistent labor in
certain directions, a fortunate direction of the mental efforts, opportunity and
circumstances, etc. ; but aside from these considerations, it is exceedingly
probable that there are important individual differences in the quality of
nervous matter.

Facial Angle. — It is not necessary to enter into an extended discussion
of the relations of the facial angle to intelligence. 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 ex-
tremity 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. A number of
observations upon the facial angle in different races has been made by Camper
and by other physiologists and ethnologists. These show, in general terms,

G20 NERVOUS SYSTEM.

that the angle is larger in man than in any of the inferior animals and is
largest in those races that possess the greatest intellectual development.

Pathological Observations. — It is a fact now generally admitted in pathol-
ogy, that loss of cerebral substance from repeated haemorrhage is sooner or
later followed by impairment of the intellectual faculties. This point is
frequently difficult to determine in an individual 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 phenomena denoting abnormally feeble intel-
lectual power, following any considerable disorganization of cerebral sub-
stance. In short, pathological conditions of the brain all go to show that
the intellectual faculties are directly connected with the cerebral hemispheres.

In idiots the brain usually is of small size, although there are exceptions
to this rule. In two cases of adult idiots, reported by Tiedemann, the brain
was about one-half of the normal weight. The brain of an idiotic woman,
forty-two years of age, reported by Gore, weighed ten ounces and five grains
(about 284 grammes). It has been observed, also, that the cerebellum is
not proportionally diminished in size in idiots (Bradley). In one instance
reported, the proportion of the cerebellum to the cerebrum was as 1 to 5*5.
In the healthy adult male of ordinary weight, the proportion is as 1 to 8^.
The statements just made with regard to the brains of idiots refer to cases
characterized 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. Lelut has reported 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 encepha-
lon weighed 48'32 oz. (1,369-8 grammes). 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, is
a report of the case of a congenital imbecile, aged thirty years, height five
feet and eight inches (172-7 centimetres), died of phthisis, whose brain
weighed 70J- oz. (2,000 grammes). This is heavier than the heaviest normal
brain on record. The normal brain- weight is 49£ oz. (1,408*3 grammes).

Reaction-Time. — The time which elapses between the application of a
stimulus and its appreciation by the individual experimented upon is known
as reaction-time. In experiments with reference to this point, the person
observed makes an electric signal when the sensation is perceived. The reac-
tion-time is 0-12 of a second for a shock on the hand, 0-13 for the forehead,
0-17 for the toe and 0-13 for a sudden noise (Exner). The duration is about
0-16 of a second for impressions made on the nerves of special sense. This is
the time of conduction of the impression to the brain, its appreciation by the
individual, the generation of the voluntary impulse and the conduction of
this impulse to the muscles concerned in making the signal. It is probably

CENTRE FOR SPEECH. 621

subject to variations analogous to those observed in the "personal equa-
tion."

Centre for the Expression of Ideas in Language. — The location of this
centre depends entirely upon the study of cases of disease in the human sub-
ject. It is evident that there must be a comprehension of the significance of
words, the formation of an idea more or less complex, and a co-ordinate action
of the muscles concerned in speech, as conditions essential to expression in
spoken words. One or more of these conditions may be absent in cases of
disease ; and the general absence of the power of verbal expression, when
this depends on cerebral lesion, is known as aphasia. This is quite different
from aphonia, which is simply loss of voice. If the comprehension of the
meaning of words be absent, the individual is incapable of receiving ideas
expressed in language. In cases of aphasia it often is difficult to determine
this point. In certain cases it is possible that the individual may under-
stand what is said and may form ideas to which he is unable to give verbal
expression. In such instances he can neither speak nor write. There are
certain cases in which the written or printed words convey no idea, while
spoken words are understood, but there is no loss of intelligence and words
are spoken without difficulty. This condition is called word-blindness. If
there be simple want of co-ordination of the muscles concerned in speech,
words are spoken which may have no connection with the idea to be con-
veyed, but the individual may be able to express himself in writing. This
condition is known as ataxic aphasia. The inability to express ideas in writ-
ing is called agraphia, and this is usually an indication of the condition
known as amnesic aphasia, in which it is impossible to put ideas into words
in any way. Persons affected with purely ataxic aphasia may understand
and write perfectly, but they can not read aloud or repeat words or sentences
spoken to them. In cases of simple amnesic aphasia, patients can sometimes
repeat dictated words. In cases in which hemiplegia is marked, the aphasia
usually is ataxic. In cases in which there is no hemiplegia, the aphasia usu-
ally is amnesic. The ataxic and amnesic forms of aphasia may be combined.
A full description, however, of the many and varied forms of aphasia would
be out of place in this work.

In 1766, Pourfour du Petit reported a case of aphasia, with lesion of the
left frontal lobe of the cerebrum, in which the patient could pronounce
nothing but " non"

Marc Dax (1836) indicated loss or impairment of speech in one hundred
and forty cases of right hemiplegia. These observations attracted little at-
tention, until 1861, when the subject was studied by Broca. Since then,
many cases of aphasia with lesion of the left frontal lobe have been reported
by various writers. In 1863, M. G. Dax, a son of Marc Dax, limited the
lesion to the middle portion of the left frontal lobe. It was farther stated,
by Broca and Hughlings Jackson, to be that portion of the brain nourished
by the left middle cerebral artery (the inferior frontal branch). According
to recent observers, the most frequent lesion is in the parts supplied by the
left middle cerebral artery, particularly the lobe of the insula, or the island

41

622 NERVOUS SYSTEM.

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 the cerebral lesion in aphasia involves the left frontal lobe in the
great majority of cases, there are instances in which the right lobe alone is
affected, and these occur in left-handed persons. Aside from the anatomi-
cal arrangement of the arteries, which seem to furnish a greater quantity of
blood to the left hemisphere, it is evident that as far as voluntary move-
ments are concerned, the right hand, foot, eye etc., are used in preference
to the left, and that the motor operations of the left hemisphere are superior
in activity to those of the right. Bateman has quoted 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 important, as showing that a person may use the right side of the
brain in speech, as in the other motor acts. Although most anatomists have
failed to find any considerable difference in the weight of the two cerebral
hemispheres, Boyd has shown by an "examination of nearly two hundred
cases at St. Marylebone, in which the hemispheres were weighed separately,
that almost invariably the weight of the left exceeded that of the right by
at least the eighth of an ounce (4-5 grammes)."

Broadbent has reported an examination of the encephalon 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 convolution was of " comparatively small
size and simple character."

Taking into consideration all of the pathological facts bearing upon the
question, it seems certain that in the great majority of persons, the organ or
part presiding over the faculty of language is situated on the left side, at or
near the third frontal. con volution and the island of Reil, mainly in the parts
supplied by the middle cerebral artery. In some few instances the organ
seems to be in the corresponding part upon the right side. It is possible
that originally both sides preside over speech, and the superiority of the left
side 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 action of the
right side of the brain, in connection with speech, simply from disuse. This
view, however, is purely hypothetical. In some cases of aphasia from lesion
of the speech-centre in the left hemisphere, recovery takes place, and occa-
sionally " speech has been again lost when a fresh lesion occurred in this
part of the right hemisphere " (Gowers). In the ataxic form of aphasia, tho
idea and memory of words remain, and there is loss of speech simply from
inability to co-ordinate the muscles concerned in articulate language. Pa-
tients affected in this way can not speak but can write with ease and correct-
ness. In the amnesic form of the disease, the idea and memory of language
are lost ; patients can not speak, and are affected with agraphia, or inability
to write. The motor tracts from the centre for speech pass to the anterior
portion of the posterior division of the internal capsule and thence through
the left crus, into the pons Varolii, where they decussate and go to the right
side of the medulla oblongata.

THE CEREBELLUM.

623

THE CEREBELLUM.

It is not necessary in order to comprehend the uses of the cerebel-
lum, as far as these are known, to enter into a full description of its
anatomical characters. The points, in this connection, that are most im-
portant are the following : the division of the substance of the cerebellum
into gray and white matter; the connection between the cells and the
fibres ; the connection of the fibres with the cerebrum and with the prolon-
gations of the columns of the spinal cord ; the passage of fibres between the
two lateral lobes. These are the only anatomical points that will be con-
sidered.

Physiological Anatomy. — The cerebellum, situated beneath the posterior
lobes of the cerebrum, weighs about 5-25 ounces (148-8 grammes) in the male,
and 4*7 ounces (135 grammes) in the female. The proportionate weight to
that of the cerebrum is as 1 to 8f in the male, and as 1 to 8£ in the female.
The cerebellum is separated from the cerebrum by a strong process of the
dura mater, called the tentorium. Like the cerebrum, the cerebellum pre-
sents an external layer of gray matter, the interior being formed of white, or
fibrous nerve-tissue. The extent of the gray substance is much increased
by abundant, fine convolutions and is farther extended by the penetration,
from the surface, of arborescent processes of gray matter. Near the centre
of each lateral lobe, embedded in the white substance, is an irregularly den-
tated mass of gray
matter, called the
corpus dentatum.
The convolutions
are finer and more
abundant and the
gray substance is
deeper in the cere-
bellum than in the
cerebrum. These
convolutions, also,
are present in many
of the inferior ani-
mals in which the
surface of the cere-
brum is smooth.

The cerebellum
consists of two lat-
eral 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 unne-
cessary to describe. Beneath the cerebellum, bounded in front and below by
the medulla oblongata and pons Varolii, laterally, by the superior peduncles,
and above, by the cerebellum itself, is a lozenge-shaped cavity, called the

FIG. 230.— Cerebellum and medulla oblongata (Hirschfeld).
1,1, corpus deiitatum ; 2, pons Varolii ; 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 extremity of the spinal cord.

624 NERVOUS SYSTEM.

fourth ventricle. The crura, or peduncles, will be described in connection
with the direction of the fibres.

The gray substance of the convolutions is divided quite distinctly into an
internal and an external layer. The internal layer presents an exceedingly
delicate net-work of fine nerve-fibres which pass to the cells of the external
layer. The external layer is somewhat like the external layer of gray sub-
stance of the posterior lobes of the cerebrum and is more or less sharply di-
vided into two or more secondary layers. The most external portion of this
layer contains a few small nerve-cells and fine filaments of connective tissue.
The rest of the layer contains a great number of large cells, rounded or ovoid,
with two or three and sometimes four prolongations. The mode of connec-
tion between the nerve-cells and the fibres has already been described under
the head of the general structure of the nervous system.

Directions of the Fibres in the Cerebellum. — Fibres from the gray sub-
stance of the convolutions and their prolongations, and from the corpus denta-
tum, converge to form the three cerebellar peduncles on either side. The
superior peduncles pass forward and upward to the crura cerebri and the
optic thalami. These connect the cerebellum wkh the cerebrum. Beneath
the tubercular quadrigemina, some of these fibres decussate with the corre-
sponding fibres from 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 cerebral hemisphere of the opposite side. The connections
between the cerebrum and the cerebellum, through the pons Varolii, have
already been described (see page 610).

The middle peduncles arise from the lateral hemispheres of the cerebel-
lum, pass to the pons Varolii, where they cross, connecting the two sides of
the cerebellum.

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 is sufficiently evident. By the superior peduncles, the cerebellum
is connected, as are all of the encephalic ganglia, with the cerebrum ; by the
middle peduncles, the two lateral halves of the cerebellum are intimately con-
nected with each other ; and by the inferior peduncles, the cerebellum is
connected with the posterior columns of the spinal cord.

Extirpation of the Cerebellum. — 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 (Flourens). The intelli-
gence, general and special sensibility, the involuntary 'movements and the
simple faculty of voluntary motion remain. The movements are always
exceedingly irregular and inco-ordinate ; the animal can not maintain its
equilibrium ; and on account of the impossibility of making regular move-
ments, it can not feed. This want of equilibrium and of the power of co-or-

THE CEREBELLUM. 625

d mating 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. Calling this want of equi-
libration, of co-ordination, of " muscular sense," an indication of vertigo, or
by any other name, the fact remains, that regular and co-ordinate muscular
action in standing, walking or flying, is impossible, although voluntary power
is retained. It is well known that many muscular acts are more or less auto-
matic, as in standing, and to a certain extent, in walking. These acts, as
well as nearly all voluntary movements, require a certain co-ordination of the
muscles, and this, and this alone, is affected by extirpation of the cerebellum.
It is true that destruction of the semicircular canals of the internal ear pro-
duces analogous disorders of movement, but this is the only mutilation, except
division of the posterior white columns of the spinal cord, which produces
anything resembling the results of cerebellar injury.

When a portion only of the cerebellum is removed, there is slight disturb-
ance of co-ordination, and the disordered movements are marked in propor-
tion to the extent of the injury. After extirpation of even one-half or two-
thirds of the cerebellum, the disturbances in co-ordination immediately fol-
lowing the operation may disappear, and the animal may entirely recover,
without any regeneration of the extirpated nerve-substance. This important
fact enables one to understand how, in certain cases of disease of the cere-
bellum in the human subject, when the disorganization of the nerve-tissue
is slow and gradual, there may never be any disorder in the movements.

If there be a distinct nerve-centre which presides over the co-ordination
of the general voluntary movements, experiments upon the higher classes of
animals show that this centre is situated in the cerebellum. If the cerebellum
preside over co-ordination, as a physiological necessity, 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 would be followed by loss of co-ordinating power.
From the anatomical connections of the cerebellum, it appears that the main
communication between this organ and the general system is through the
posterior white columns of the spinal cord. 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.
When the posterior white columns are divided at several points, there is
want of co-ordination of the general muscular system. When the posterior
white columns are disorganized in the human subject, there is loss or impair-
.ment of co-ordinating power, even though the general sensibility be not af-
•fecced, as in the disease called locomotor ataxia.

Pathological Observations. — Records of cases of lesion of the cerebellum
in the human subject have accumulated until the number is very large. A
study of cases in which the phenomena referable to cerebellar injury are not
complicated by paralysis, coma or convulsions, shows that serious lesion of
the middle lobe is almost always attended with marked muscular inco-ordina-
tion. Cases in which only a portion of one or of both hemispheres is involve:!

626 NERVOUS SYSTEM.

may not present any disorder in the muscular movements. These facts are
in accord with the results of experiments upon the lower animals.

The phenomena observed in 'the few cases of cerebellar inco-ordination
which have been carefully observed are notably different from those presented
in simple locomotor ataxia. In cerebellar disease, the gait is staggering,
much as it is in alcoholic intoxication. The chief difficulty seems to be in
maintaining the equilibrium in progression, even with the greatest care and
closest attention on the part of the patient. With the idea in mind that
there is a co-ordinating centre for the muscles of progression, and that this
centre acts imperfectly, it seems as though an efficient effort at co-ordination
were impossible. In locomotor ataxia, patients seem to make co-ordinating
efforts, but the paths by which these efforts find their way to the muscles are
disturbed and the co-ordinating process, which is more or less automatic in
health, requires peculiar care and attention. By the aid of the sense of sight
and by artificial supports, progression may be safely though irregularly accom-
plished. The movements are jerky, and each step seems to require a distinct
act of volition. It is possible to imagine that in disorganization of the paths
of co-ordination in the spinal cord, the co-ordinating centre may act in some
degree through the motor paths in the direct and crossed pyramidal tracts
of the cord. It is certain that the want of normal co-ordinating power is
supplemented by ordinary voluntary acts and by the sense of sight.

Vertigo is not a necessary accompaniment of cerebellar ataxia. Disease
of the semicircular canals of the internal ear (Meniere's disease) is attended
with vertigo, and this is the main cause of the disturbances of equilibrium.

Connection of the Cerebellum with the Generative Function. — The fact
that the cerebellum is the centre for equilibration and the co-ordination of
certain muscular movements does not necessarily imply that it has no other
office. The idea of Gall, that " the cerebellum is the organ of the instinct
of generation," is sufficiently familiar; and there are facts in pathology
which show a certain relation between this nerve-centre and the organs of
generation, although the view that it presides over the generative function is
not sustained by the results of experiments upon animals or by facts in com-
parative anatomy.

In experiments upon animals in which the cerebellum has been removed,
there is nothing pointing directly to this part as the organ of the generative
instinct. Flourens removed 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, on account of 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 been 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 certain cases of disease or injury of the cerebellum, irritation of this
part has been followed by persistent erection and manifest exaggeration of

MEDULLA OBLONGATA. 627

the sexual appetite, and in others, its extensive degeneration or destruction
has apparently produced atrophy of the generative organs and total loss of
sexual desire. Serres reported several cases in which irritation of the cere-
bellum was followed by satyriasis or nymphomania, but in other cases there
were no symptoms referable to the generative organs. In the well known
case reported by Combette, the patient had the habit of masturbation.
Fisher, of Boston, reported (1838) two cases of diseased or atrophied cere-
bellum, with absence of sexual desire, and one case of irritation, with saty-
riasis. Similar instances have been given by other writers. The observa-
tions of Budge, in which mechanical irritation of the cerebellum was followed
by movements of the uterus, testicles etc., have not been satisfactorily ex-
plained.

Although there are many facts in pathology which are opposed to the
view that the cerebellum presides over the generative function, there are
cases which 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 can be said upon this point. It is certain that the facts are not
sufficiently definite and invariable to sustain the notion that the cerebellum
is the seat of the sexual instinct.

It is not necessary to discuss the vague theories with regard to the uses
of the cerebellum advanced by writers anterior to the publication of the ob-
servations of Flourens. There is no evidence 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
co-ordination of certain muscular movements, and is, perhaps, in some way
connected with the generative function.

MEDULLA OBLONGATA (BULB).

The medulla oblongata, or bulb, connects the spinal cord with the
encephalic ganglia. It is composed of white and gray matter and presents,
in its substance, a number of important nerve-centres. It is not necessary
to give anything like a complete anatomical description of the medulla. Its
most important conducting parts are those which are continuous with the
columns of the cord and which pass to the cerebrum and cerebellum. The
nuclei of origin of certain of the cranial nerves in the floor of the fourth ven-
tricle have already been mentioned.

Physiological Anatomy. — The medulla oblongata is pyramidal in form,
with its broad extremity above, and rests in the basil ar groove of the occipital
bone, extending from the lower border of the pons Varolii to the atlas. It
is about an inch and a quarter (31-8 mm.) in length, three-quarters of an
inch (19-1 mm.) broad at its widest portion and half an inch (12-7 mm.)
thick. It is flattened antero-posteriorly. Like the cord, it has an anterior
and a posterior median fissure.

Apparently continuous with the anterior columns of the cord, are the

628

NERVOUS SYSTEM.

two anterior pyramids, one on either side. Viewed superficially, the inner-
most fibres of these pyramids are seen to decussate in the median line ; but
if the fibres be traced from the cord, it is found that they come from the
crossed pyramidal tracts of the 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 direct pyramidal tracts 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 sur-
rounded by a distinct groove. They are white
externally and contain a gray nucleus called
the corpus dentatum.

External to the corpora olivaria, are the
restiform bodies, formed chiefly of white mat-
ter and constituting the postero-lateral portion
of the medulla. They are continuous with
the posterior white 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. Some fibres
from the restiform bodies pass to the cere-
brum.

Beneath the olivary bodies and between
the anterior pyramids and the restiform bod-
ies, are the lateral tracts of the medulla, some-
times called the intermediary or lateral fascic-
view of the medulla uli, or the funiculi of Rolando. These are

oblongata (Sappey). . .

i, infundibuium ; 2, tuber cinereum ; 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
d£tSS±S°f M u PJ^mids. They are usually described as parts
! ?hiasmcofd kl5' optic of the restiform bodies, but they are peculiarly
nerves 17, motor ocuiicommunis; important, from the fact that they contain

18, patheticus ; 19, fifth nerve ; 20, J

motor ocuii externus ; 21, facial the gray centre presiding over respiration ;

nerve : 22, auditory nerve ; 23, nerve c J

ofwrisberg;24,giosso-pharyngeai and for that reason they are here described as

nerve ; 25, pneumogastric ; 26, 26, . . . *

spinal accessory ; 27, sublingual distinct f aSClCUU.

nerve ; 28, 29, 30, cervical nerves. . . ,„.-,. ., x

Ine posterior pyramids (luniculi graciles)

are the smallest of all. They pass upward to the cerebellum, without decus-
sating, joining the restiform bodies above. They are composed chiefly of
white matter. As they pass upward in the medulla, they diverge, leaving a
space at the fourth ventricle.

THE MEDULLA OBLONGATA.

629

The fourth ventricle is the cavity between the pons Varolii, the medulla
oblongata and cerebellum. It is lozenge-shaped, the acute angles being
above and below. The upper angle extends to the upper border of the
pons, and the lower angle, to the lower border of the olivary bodies. The
triangles which form this lozenge are of nearly equal size. The superior
triangle is bounded laterally by the superior peduncles of the cerebellum, as
they converge to meet at the corpora quadrigemina. The inferior triangle
is bounded laterally by the funiculi graciles and the restiform bodies of
the medulla, which diverge at its lower angle. The arched roof of the ven-
tricle is formed by the valve of Vieussens, which is stretched between the
superior peduncles of the cerebellum and covers the anterior triangle,
arid the cerebellum, which covers the posterior triangle. Beneath the
cerebellum, is a reflection of the pia mater. The fourth ventricle com-
municates above with the third ventricle, by the aqueduct of Sylvius, below
with the subarachnoid space, by the foramen of Magendie, and by a small
opening below with the central canal of the cord. The floor of the ventri-
cle is formed by the posterior surface of the pons above and the medulla
below. It presents a fissure in the median line, which terminates below
in the calamus scriptorius. By the sides of the median fissure, are the
fasciculi teretes, which correspond to the intermediary fasciculi of the me-
dulla. Little eminences in the floor indicate the situation of nuclei of
origin of cranial nerves. The floor is composed mainly of a layer of gray
matter, continuous with the
gray commissure of the cord.
The lower portion of the floor
is marked by transverse lines
of white matter emerging from
the median fissure.

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
intermediary fasciculi, passing
obliquely, in a curved direction
from behind forward, to the
raphe in the median line. There

are also fibres passing from be-

fnrp Vmnlrwnrrl +n fr»rm n rmc
I0re DaCKWdra, tO lOrm a pOS-

tprinr pnmmi«?<3iirp anrl fihrp«
16, ana nDreS

arisino- frnrn flip ppll« nf thp

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 bod-
ies, and the olivary bodies with the cerebellum, their fibres forming part of
the inferior peduncles of the cerebellum. In addition it is probable that

FIG. 232.— Floor of the fourth ventricle (Hirschfeld).
1> median fissure, between the fasciculi teretes ; 2, trans-
verse whjte gtrige . 3 inferior peduncle of the cerebel-
lum ; 4, posterior pyramid (funiculus gracilis) ; 5, 5, su-
perior peduncles (divided) of the cerebellum; 6,6, bands
to the side of the crura cerebri ; 7, 7, lateral

the crura cerebri ; 8, corpora quadrigemina.

grooves of

630 NEEVOUS SYSTEM.

fibres, taking their origin from all of the gray nodules of the medulla, pass
to the parts of the encephalon situated above.

The uncrossed pyramidal tracts of the spinal cord (columns of Tiirck)
pass to the encephalon, by direct fibres situated at the outer border of the
anterior pyramids of the medulla.

The crossed pyramidal tracts of the cord decussate in the lower portion
of the medulla and constitute the greatest part of the anterior pyramids.

Fibres from the anterior fundamental fasciculi, the anterior radicular
zone and from the mixed lateral columns of the cord, probably pass to the
gray matter of the medulla.

The direct cerebellar fasciculi of the cord are continuous with the funic-
uli graciles of the medulla.

The columns of Burdach are continuous with the restiform bodies of
the medulla.

The columns of Goll pass to the medulla and are lost in the funiculi
graciles.

As far as the fibres of origin of the cranial 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 sen-
sory nerves arising from gray matter in the posterior portions.

USES OF THE MEDULLA OBLONGATA.

It is hardly necessary to discuss the action of the medulla oblongata as a
conductor of sensory impressions and of motor stimulus to and from the
brain. It is evident 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 relations, and which
is demonstrated by its section in living animals. Nor is it necessary to
dwell upon the general properties of the medulla, 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 observing
the phenomena which follow its stimulation in living animals has rendered
it impossible 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 me-
dulla 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 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 important reflex
phenomena are instantly abolished. From its connection with various of
the cranial nerves, one would expect it to play an important part in the
movements of the face, in deglutition, in the action of the heart and of vari-

RESPIRATORY NERVE-CENTRE. 631

ous glands etc., important points which are fully considered in their appro-
priate place. The various reflex centres in the medulla have been located
chiefly by a study of the relations of the gray matter to the deep fibres of
origin of certain of the cranial nerves. The centre for the orbicularis oculi
muscle is related to the origin of the large root of the fifth nerve and the
origin of the facial ; and the integrity of these two nerves is necessary to the
reflex act of closure of the eyelids. The impression which produces the act
of sneezing is conveyed to the medulla through the nasal branch of the
fifth — possibly sometimes through the olfactory nerves — and excites certain
of the expiratory muscles. Impressions conveyed to the medulla by certain
sensory branches of the pneumogastrics give rise to the reflex acts of cough-
ing. The reflex acts of swallowing and vomiting also depend upon centres
in the medulla oblongata. There are centres, also, which influence the
glycogenic action of the liver, the secretion of saliva and the secretion of
sweat. The vaso-motor centres will be considered in connection with the
physiology of the vaso-motor nerves. The centres connected with respira-
tion are so important that they demand special description.

Respiratory Nerve-Centre. — In 1809, Legallois made a number of ex-
periments upon rabbits, cats and other animals, in which he showed that
respiration depends upon the medulla oblongata and not upon the brain ;
and he farther located the part which presides over the respiratory move-
ments, 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 quar-
ter of an inch (6-4 mm.) 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 centre does n*>t occupy
the whole of the medulla included between the two planes first 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 respi-
ration persists in animals after division of the anterior pyramids and the
restiform bodies. Subsequently, Flourens restricted the limits of the respir-
atory 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 Flourens have found that the spinal
cord may be divided below the medulla oblongata, and that all of the en-
cephalic ganglia above may be removed, respiratory movements still persist-
ing. It is a very common thing in vivisections to kill an animal by break-
ing up the medulla. When this is done there are no struggles and 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.

The relations of the respiratory centre have already been fully considered

632 NERVOUS SYSTEM.

in connection with the physiology of respiration. Under normal condi-
tions, the centres on the two sides probably operate through the pneurnogas-
tric nerves and the respiratory movements on the two sides are synchronous.
That there is a respiratory centre on either side, is shown by the experiment
of dividing the medulla longitudinally in the median line, the respiratory
movements afterward continuing with regularity. If, now, the pneumogas-
tric be divided on one side, the respiratory movements on that side become
slower and are no longer synchronous with the movements on the opposite
side. This shows that while the respiratory centres on the two sides nor-
mally act together, being undoubtedly connected with each other by com-
missural fibres, each one has independent connections with the pneumo-
gastric on the corresponding side of the body.

Cardiac Centres. — There can be scarcely any doubt with regard to the
existence of cardiac centres in the medulla — perhaps an inhibitory centre
and an acceleratory centre — but the situation of these centres has not been
exactly determined. The influence of the nerves and nerve-centres over the
movements of the heart has been fully considered in connection with the
physiology of the circulation.

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 movements,
Flourens and others have called this centre the vital knot, destruction of
which is immediately followed by death. With the existing knowledge of the
properties and uses of the different tissues and organs of which the body is
composed, it is almost unnecessary to present any arguments to show the un-
philosophical character of such a proposition. One can hardly imagine such
a thing as instantaneous death of the entire organism ; and still less can it be
assumed fhat 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 ; but even then it is by no means certain that some parts do not for a
time retain their physiological properties. In apparent death, the nerves
and the heart may be shown to retain their characteristic properties ; the
muscles will contract under stimulus, and will appropriate oxygen and give
oil carbon dioxide, or respire ; the glands may be made to secrete, etc. ; and
no one can assume that under these conditions, the entire organism is dead.
There seems to be 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 being simply a blank, as far as the recollection of
the individual is concerned. It is as utterly impossible to determine the ex-
act 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

ROLLING AND TURNING MOVEMENTS. 633

being. Death is nothing more than a permanent destruction of so-called
vital physiological properties ; and this occurs successively, and at different
times, for different tissues and organs.

When it is seen that frogs will live for weeks, and sometimes for months,
after destruction of the medulla oblongata, and that in mammals, by keep-
ing up artificial respiration, many of the most important physiological acts,
such as the movements of the heart, may be prolonged for hours after de-
capitation, one 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.

There is little to be said concerning certain ganglia and other parts of
the brain that have not yet been considered. The olfactory ganglia preside
over olf action and will be treated of fully in connection with the special
senses. The pineal gland and the pituary body, in their structure, present a
certain resemblance to the ductless glands, and their anatomy has been con-
sidered in another chapter. Passing over the purely theoretical views of the
older writers, who had very indefinite ideas of the action of any of the en-
cephalic ganglia, it can only be said 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, hippo-
campi and various other parts that are necessarily described in anatomical
works. It is useless to discuss the early or even the recent speculations with
regard to the uses of these parts, which are entirely unsupported by experi-
mental or pathological facts and which have not advanced positive knowledge.

ROLLING AND TURNING MOVEMENTS FOLLOWING INJURY OF CERTAIN
PARTS OF THE ENCEPHALON.

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 uses of the brain, and they are rather to
be classed among the curiosities of experimental physiology. These move-
ments 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 has enumerated 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 thalami (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 por-
tions of the cerebellum (Magendie) ;

" 8. Olivary bodies, restiform bodies (Magendie) ;

634: NERVOUS SYSTEM.

" 9. External part of the anterior pyramids (Magendie) ;

" 10. Portion of the medulla from which the facial nerve arises (Brown-
Sequard) ;

"11. Optic nerves;

" 12. Semicircular canals (Flourens) ; auditory nerve (Brown-Sequard )."

To the parts above enumerated, Vulpian added 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 the movements be due to paralysis or enfeeblement
of certain muscles upon one side of the body, to a direct or reflex irritation
of the parts of the nervous system involved or to both of these causes com-
bined. The experiments of Brown-Sequard and others show that tjie move-
ments may be due to irritation alone, for they occur when parts of the en-
cephalon and the upper portions 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 phe-
nomena produced by simple irritation. The most satisfactory explanation
of these movements is the one proposed by Brown-Sequard, who attributed
them to a more or less convulsive action of muscles on one side of the body,
produced by irritation of the nerve-centres. He regarded the rolling as
simply an exaggeration of the turning movements, and places both in the
same category.

It is not necessary to enter into an extended discussion of the above ex-
periments. In some of them, the movements have been observed toward
the side operated upon, and in others, toward the sound side. These differ-
ences probably depend upon the fact that in certain experiments, tho 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 generally is reflex.

GENERAL ARRANGEMENT OF THE SYMPATHETIC SYSTEM. 635

CHAPTER XX.

SYMPATHETIC NERVOUS SYSTEM— SLEEP.

General arrangement of the sympathetic system— General properties of the sympathetic ganglia and nerves
Direct experiments on the sympathetic — Vaso-motor centres and nerves — Reflex vaso-motor phenom-
ena—Vaso-inhibitory nerves— Trophic centres and nerves (so-called)— Sleep— Condition of the brain
and nervous system during 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 — Condition of the organism during sleep.

LIKE the cerebro-spinal system, the sympathetic is composed of centres,
or ganglia, and nerves, at least as far as can be seen from its anatomy. The
ganglia contain nerve-cells, most of which differ but little from the cells of
the encephalon and spinal cord. The nerves are composed of fibres, some
of which are nearly identical in structure with the ordinary motor and sen-
sory fibres, while many are the so-called gelatinous 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 continu-
ous chain on either side of the body, beginning above, by the ophthalmic gan-
glia, 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 filaments pass from the sympathetic to the cerebro-spinal
system. The general distribution of the sympathetic filaments is to mucous
membranes — and possibly to integument — to non-striated muscular fibres,
and particularly to the muscular coat of the arteries. As far as has been
shown by 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 large numbers of ganglionic cells.

The general arrangement of the sympathetic ganglia and the distribution
of the nerves may be stated very briefly ; but a knowledge of certain anatom-
ical points is indispensable as an introduction to an intelligent study of the
physiology of this system.

In the cranium, are the four cranial 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 tho-
racic ganglia, corresponding to the twelve ribs. The great semilunar ganglia,
the largest of all and sometimes called the abdominal brain, are in the abdo-
men, by the side of the creliac axis. In the lumbar region, in front of
the spinal column, are the four lumbar ganglia. In front of the sacrum, are
the four orw five sacral, or pelvic ganglia ; and finally, in front of the coccyx,
is a small, single ganglion, the last of the sympathetic chain, called the gan-
glion impar. Thus, the sympathetic cord, as it is sometimes called, consists
of twenty-eight to thirty ganglia on either side, terminating below in a
single ganglion.

636

NERVOUS SYSTEM.

FIG. 233.— Cervical and thoracic portion of the sympathetic (Sappey).

.1, 1, 1, right pneumogastric ; 2, glosso-pharyngeal ; 3, spinal accessory ; 4, sublingual ; 5, 5, 5, chain of
ganglia of the sympathetic ; 6, superior cervical ganglion ; 7, branches to the carotid ; 8, nerve of
Jacobson ; 9, filaments from the facial, to the spheno-palat ine and to the otic ganglion ; 10, motor
oculi externus ; 11, ophthalmic ganglion ; 12, spheno-palat ine ganglion ; 13, otic ganglion ; 14, lin-
gual branch of the fifth nerve ; 15, submaxillary ganglion ; 16/17, superior laryngeal nerve : 18, ex-
ternal laryngeal nerve ; 19, 20, recurrent laryngeal nerve ; 21, 22, 23, anterior branches of the upper
four cervical nerves ; 24, anterior branches of the fifth and sixth cervical nerves ; 25, 20, anterior
branches of the seventh and eighth cervical and the first dorsal nerves ; 27, middle cervical gangli-
on ; 28, cord connecting the two ganglia ; 29, inferior cervical ganglion ," 30, 31, filaments connect-
ing this with the middle ganglion ; 32, superior cardiac nerve ; 33, middle cardiac nerve ; 34, infe-
rior cardiac nerve : 35, 35, cardiac plexus ; 36, ganglion of the cardiac plexus : 37, nerve following
the right coronary artery: 38, 38, intercostal nerves ; 39, 40,41, great splanchnic nerve ; 42, lesser
splanchnic nerve ; 43, 43, solar plexus ; 44, left pneumogastric ; 45, right pneumogastric ; 46, phrenic
nerve ; 47, right bronchus ; 48, aorta ; 49, right auricle ; 50, right ventricle ; 51,52, pulmonary artery ;
53, stomach ; 54, diaphragm.

GENERAL ARRANGEMENT OF THE SYMPATHETIC SYSTEM. 637

FIG. 234.— Lumbar and sacral portions of the sympathetic (Sappey).

1, section of the diaphragm ; 2, lower end of the oasophagus ; 3, left half of the stomach ; 4, small
intestine ; 5, sigmoid 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 great splanchnic nerve ; 13, lower end of the lesser splanchnic nerve ; 14, 14, last two tho-
racic ganglia ; 15, 15, the four lumbar ganglia ; 16, 16, 17, 17, brandies from the lumbar ganglia ; 18,
superior mesenteric plexus; 19, 21. 22, 23, aortic lumbar plexus; 20. inferior mesenteric plexus ;
24. 24, sacral portion of the sympathetic ; 25, 25, 26, 26, 27. 27, hypogastric plexus ; 28, 29, 30, tenth,
eleventh and twelfth dorsal nerves ; 31, 32, 33, 34, 35, 36, 37, 38, 39, lumbar and sacral nerves.

Cranial Ganglia. — The ophthalmic, lenticular, or ciliary ganglion is sit-
uated 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 ophthalmic division of the fifth. It is also
connected with the cavernous plexus and with MeckePs ganglion. Its so-
called motor and sensory roots from the third and the fifth pair have already

42

638 NERVOUS SYSTEM.

been described in connection with these nerves. Its filaments of distribution
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 uses of the ophthalmic ganglion are related mainly to the action of
the ciliary muscle and iris ; and it is only necessary here to indicate its ana-
tomical relations, leaving its physiology to be taken up in connection with
the physiology of the sense of sight.

The spheno-palatine, or Meckel's ganglion, is the largest of the cranial
ganglia. It is triangular in shape, reddish in color, and is situated in the
spheno-maxillary fossa, near the spheno-palatine foramen. It receives a mo-
tor 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.
It has a large number of branches of distribution. 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 uvulae 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 mo-
tor 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 Eustachian tube and to the tensor tym-
pani and tensor palati muscles. Reasoning from the general mode of distribu-
tion of the sympathetic filaments, those going to the striated muscles are de-
rived from the facial. It also sends branches to the carotid plexus.

The submaxillary ganglion, situated on the submaxillary gland, is small,
rounded, and reddish-gray in color. It receives motor filaments from the
chorda tympani 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 and seventh cervical vertebras respectively. The middle ganglion
is sometimes wanting, and the inferior ganglion is occasionally fused with
the first thoracic ganglion. These ganglia are connected together by the so-
called sympathetic cord. They have a number of filaments of communica-
tion above, with the cranial and the cervical nerves of the cerebro-spinal sys-
tem. 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 distribution. Branches from this ganglion pass to the cra-
nial ganglia. There are also branches which unite with filaments from the

GENERAL ARRANGEMENT OF THE SYMPATHETIC SYSTEM. 639

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 arteries, 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 cardiac 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 wanting; and the inferior nerve
arises from the inferior cervical ganglion or the first thoracic. These nerves
present frequent communications with various of the adjacent cerebro-spinal
nerves, penetrate the thorax, and form the deep and superficial cardiac plex-
uses and the posterior and the anterior coronary plexuses. In these various
plexuses, there are found ganglioform enlargements ; and upon the surface
arid in the substance of the heart, are collections of nerve-cells connected
with the fibres.

Tfioracic Ganglia. — The thoracic ganglia are situated in the chest, be-
neath 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 to-
gether 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 gan-
glia 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 semi-
lunar ganglion, sending a few filaments to the renal plexus and the suprare-
nal 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 re-
nal plexus. The three splanchnic nerves present frequent anastomoses with
each other.

Ganglia in the Abdominal and the Pelvic Cavity. — The semilunar gan-
glia on the two sides send off radiating branches to form the solar plexus.
They are situated by the side of the coeliac axis and near the suprarenal capsules.
These are the largest of the sympathetic ganglia. From these arise plexuses
distributed to various parts in the abdomen, as follows : The phrenic plexus
follows the phrenic artery and its branches to the diaphragm. The coeliac
plexus subdivides into the gastric, hepatic and splenic plexuses, which are
distributed to organs, as their names indicate. From the solar plexus differ-
ent 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 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.

640 NERVOUS SYSTEM.

The lumbar ganglia, four in number, are situated in the lumbar region,
upon the bodies of the vertebrae. They are connected with the ganglia above
and below and with each other by the sympathetic cord, receiving, like the
other ganglia, filaments from the spinal nerves. Their branches of distribu-
tion form the aortic lumbar plexus and the hypogastric plexus and follow the
course of the blood-vessels.

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 they receive fila-
ments from the sacral nerves, there being generally two branches of commu-
nication for each ganglion. The filaments of distribution go to all of the
pelvic viscera and blood-vessels. The inferior hypogastric, or pelvic plex-
us is a continuation of the hypogastric plexus above, and receives a few fila-
ments from the sacral ganglia. The uterine nerves 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 sympathetic filaments are
prolonged into the upper and lower extremities, following the course of the
blood-vessels and terminating in their muscular coat.

The filaments of the sympathetic, at or near their terminations, are con-
nected with ganglionic cells, not only in the heart and the uterus, but in the
blood-vessels, lymphatics, the coccygeal gland, the submucous and the mus-
cular 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,
thymus, 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.

General Properties of the Sympathetic Ganglia and Nerves. — The sym-
pathetic ganglia and nerves possess a dull sensibility, which is particularly
marked in the ganglia. That the nerves contain afferent fibres, is shown by
certain reflex phenomena.

Stimulation of the sympathetic produces muscular movements, but these
are confined generally to non-striated muscular fibres, to which these nerves
are largely distributed. The muscular movements do not immediately follow
stimulation of the nerves, but there is a long, latent period. The muscular
contraction, also, persists for a time and the subsequent relaxation is slow.
The induced current applied to the splanchnic nerves does not produce
movements of the intestines, but these movements are excited by the con-
stant current (Legros and Onimus). The properties of the vaso-motor
nerves will be considered separately.

The sympathetic ganglia are connected with the motor and sensory
divisions of the cerebro-spinal system. Some of the ganglia and nerve-
plexuses are directly dependent for their action upon the cerebro-spinal
system, while others are capable, at least for a time, of independent action.
Among the latter, are the ganglia of the heart, the intestinal plexuses, the

DIRECT EXPERIMENTS ON THE SYMPATHETIC. 641

plexuses of the uterus and Fallopian tubes, of the ureters and of the blood-
vessels.

Direct Experiments on the Sympathetic. — The experiments of Pourfour
du Petit (1712-1725) were the first to give any positive information regard-
ing the action of the sympathetic system ; and these observations may be
taken as the starting-point of a definite knowledge of the physiology of the
sympathetic, although they showed only the influence of the cervical portion
upon the eye. In 1816, 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 divided the sympathetic in the neck on one side in rabbits, and
noted on the corresponding side of the head and the ear, increased vascularity
and an elevation in temperature of 7° to 11° Fahr. (4° to 6° C.). This con-
dition of increased heat and vascularity continues for several months after
division 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 an important advance in
the history of the sympathetic, by demonstrating that its section paralyzed
the muscular coat of the arteries, and farther, that Faradization of the nerve
in the neck caused the vessels to contract. This was the discovery of
the vaso-motor nerves, 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 ex-
planation of the phenomena observed.

The important points developed by the first experiments of Bernard and
of Brown-Sequard 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 mus-
cular coats of the alimentary canal.

When the sympathetic is divided in the neck, the local increase in tem-
perature 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 tem-
perature is due to a local exaggeration of the nutritive processes, apparently
dependent directly upon the hypersemia. There are many instances in
pathology, of local increase in temperature attending increased supply of
blood to restricted parts. In an experiment by Bidder, after excising about
half an inch (12-7 mm.) of the cervical sympathetic 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.

It is 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 de-
scribed an intense hyperaemia of the mucous membrane of the stomach and

NERVOUS SYSTEM.

intestines, following extirpation of the coeliac plexus. By comparative ex-
periments it was shown that this did not result from the peritonitis pro-
duced 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 sup-
ply of blood is much increased and an abundant flow of the secretion follows
(Bernard). Peyrani has shown that the sympathetic has an influence upon
the secretion of urine. When the nerves in the neck are stimulated, the
quantity of urine and of urea is increased, and this increase is greater with
the induced than with the constant current. When the sympathetic is
divided, the quantity of urine and of urea sinks to the minimum.

Moreau published in 1870 a series of observations on the influence of the
sympathetic nerves upon the secretion of liquid by the intestinal canal, which
are important as affording a possible explanation of the sudden occurrence
of watery diarrhoea. In these experiments, the abdomen was opened in a
fasting animal, and three loops of intestine, each loop four to eight inches
(100 to 200 mm.) long, were isolated by 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 Centres and Nerves. — The principal or dominating vaso-
motor centres are situated in the medulla oblongata, one on either side,
about one-tenth of an inch (2*5 mm.) from the median line. Each centre, in
the rabbit, is about one-eighth of an inch (3 mm.) long and about one-six-
teenth of an inch (1/5 mm.) wide. Its lower border is about one-fifth of an
inch (5 mm.) above the calamus scrip torius. Each side of the body has its
special vaso-motor centre, and very few if any of the vaso-motor fibres decus-
sate. The situation of the vaso-motor centres in the medulla has been de-
termined by successive removal of the nerve-centres above. If the central
end of a large cerebro-spinal nerve be stimulated in an animal poisoned with
curare, the vaso-motor nerves produce contraction of the blood-vessels, by
reflex action, and there is a rise in the blood -pressure. The action is not
interfered with by removal of the encephalic ganglia from above downward,
until the part of the medulla containing the vaso-motor centres is reached.
When these centres are removed, the reflex vaso-motor action is permanently
arrested.

Subordinate vaso-motor centres exist in the spinal cord. When the
vaso-motor centre in the medulla is destroyed, there is a fall in the blood-
pressure ; but if the circulation be continued, after a time the blood-vessels
regain their " tone " and the pressure may then be affected by reflex action,
It is probable that these spinal centres exist throughout the dorsal region
and in the upper part of the lumbar region of the cord.

VASO-MOTOR CENTRES AND NERVES. 643

All the vaso-motor nerves are derived from the medulla oblongata and
the spinal cord. Some of the vaso-motor fibres to the head pass in the
trunks of the motor cranial nerves, but most of them come from the ante-
rior roots of some of the spinal nerves and pass to the head by the filaments
of distribution of the cervical sympathetic. The vaso-motor fibres pass in
the lateral columns of the cord, and from the cord, in the anterior roots of
the spinal nerves, in the dog, as far down as the second pair of lumbar
nerves. These fibres are medullated but are of small size. They pass to
the blood-vessels either through branches from the sympathetic ganglia or
through the ordinary cerebro-spinal nerves. They are therefore not confined
to branches of the sympathetic, as Bernard has shown by the following ex-
periment : 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 mo-
tion 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 decided increase in temperature. This
experiment, which is only one of a large number, shows that the ordinary
mixed nerves contain vaso-motor fibres, which are entirely independent of
the nerves of motion and sensation, a fact which is now well known to physi-
ologists and has frequently been illustrated in cases of disease in the human
subject.

The vaso-motor nerves are capable of influencing local circulations,
probably through distinct centres for different parts. Direct stimulation of
the principal vaso-motor centre (10 to 12 or more single induction shocks
per second for strong currents or 20 to 25 for moderate currents) increases
the blood-pressure to the maximum.

The contractile coats of the veins and lymphatics probably are influenced
by vaso-motor nerves, but there is little known of the mechanism of this action.

Reflex Vaso- Motor Phenomena. — The most important physiological acts
connected with the vaso-motor nerves are reflex. It is evident from experi-
ments on the inferior animals and observations on the human subject that
there are afferent as well as efferent nerves. The reflex acts connected with
secretion have already been considered ; but there are other phenomena that
demand a brief description.

As regards animal heat, the phenomena of which are intimately con-
nected with the supply of blood to the parts, it is important to note the ob-
servations of Brown-Sequard and Lombard, who found that pinching of the
skin on one side was attended with a diminution in the temperature in the
corresponding member of the opposite side, and that sometimes, when the
irritation was applied to the upper extremities, changes were produced in
the temperature of the lower limbs. Tholozan and Brown-Sequard found,
also, that lowering the temperature of one hand produced a considerable de-
pression 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. (5° C.) the temperature of the other foot
was diminished by about 7° Fahr. (4° C.) in the course of eight minutes.

644 NERVOUS SYSTEM.

These experiments show that certain impressions made upon the sensory
nerves affect the animal heat, by reflex action. As section of the sympa-
thetic filaments increases the heat in particular parts, with an increase
in the supply of blood, and their Faradization reduces the quantity of blood
and diminishes the temperature, it is reasonable to infer that the reflex
action takes place through the vaso-motor nerves. If it be assumed 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, it remains only to determine the situation of
the centres which receive the impression and generate the stimulus. These
centres are situated 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 acts may be distinctly located, as
the genito-spinal centre, in the spinal cord opposite the fourth lumbar verte-
bra, and the cilio-spinal centre, in the cervical region of the cord. An im-
pulse generated in these centres, sometimes as the result of impressions re-
ceived 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 this way. This action is
also illustrated in cases of reflex paralysis, in inflammations as the result of
" taking cold," and in many other pathological conditions.

It remains only 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 rare to observe traumatic injury confined to the
sympathetic in the neck. A single case, however, apparently of this kind,
has 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. Bartholow has reported several cases of
unilateral sweating of the head (two observed by himself), in several of
which there probably was 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 obser-
vations by Wagner, upon the head of a woman, eighteen minutes after
decapitation, powerful stimulation of the sympathetic produced great en-
largement of the pupil. In such a case as this, it would not be possible to

TROPHIC CENTRES AND NERVES. 645

make any observations on the influence of the sympathetic upon the tem-
perature.

Vaso- Inhibitory Nerves. — There are certain nerves, the direct action of
which under Faradic stimulation is to dilate certain blood-vessels. These
nerves may also be excited by reflex action through the sensory nerves. In
many nerves, as the chorda tympani, the nervi erigentes etc., the existence
of inhibitory fibres has been demonstrated (Dastre and Morat, Eckhard,
Laffont, Vulpian and others). For example, division of the nervi erigentes
has no immediate effect on the penis, but Faradization of the peripheral
ends of the nerves dilates the blood-vessels and produces erection. Fibres
possessing this property undoubtedly exist throughout the body, in the sym-
pathetic and in the motor and mixed nerves ; and it is possible that there are
vaso-motor inhibitory centres, although such centres have not been located.
The mode of action of these nerves is analogous to that of the inhibitory
nerve of the heart, restraining and regulating the action of the vaso-motor
nerves and allowing the pressure of blood to dilate the vessels. It does
not, however seem proper to call them " vaso-dilator " nerves, any more than
it would be correct to call the inhibitory nerve of the heart the cardiac dilator
nerve.

Trophic Centres and Nerves (so-called). — Collections of nerve-cells act as
centres presiding over the nutrition of the nerve-fibres with which they are
connected ; but it has been found that the nutrition of certain parts may be
profoundly affected through the nervous system. Many pathologists, 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. These views, however, rest almost entirely upon pathological
observations. 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 a sympathetic nerve is
divided, there is an apparent exaggeration of the nutritive processes in par-
ticular parts, and there may be inflammatory phenomena, but atrophy of
muscles is not observed. Atrophy of muscles, indeed, follows division of
cerebro-spinal nerves only, or as cases of disease have shown, disorganization
of cells belonging to what are recognized 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 : There may be progressive atrophy of
certain muscles, uncomplicated with paralysis except in so far as there is
weakness of these muscles due to partial and progressive destruction of their
contractile elements. The only constant 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 corre-
sponding anterior roots of the nerves. It has never been assumed that there
are cells in the cord, presenting anatomical peculiarities by which they may be

646 NERVOUS SYSTEM.

distinguished from the ordinary motor or sensory elements ; but the fact of
the degeneration of certain cells, others remaining normal, has led to the dis-
tinction by certain writers, of trophic cells, and, of course, these must be
connected with the parts by trophic nerves.

There can be no doubt of the fact that the cells of the antero- lateral
columns of the spinal cord are connected with motion, and that impulses
generated in these cells are conveyed to the muscles by the anterior roots of
the spinal nerves. It also is a fact, no less definite, that when a muscle or a
part of a muscle is for a long time deprived of the motor influence by which
it is brought into action, its fibres undergo atrophy, become altered in struct-
ure and lose their contractility. Starting with these two propositions, and
assuming that certain of the ordinary motor cells of the cord are destroyed,
it is easy to predict the phenomena to be expected as a consequence of such
a lesion.

The destruction of certain motor nerve-cells connected with the anterior
roots of the spinal nerves would certainly produce degeneration of the nerve-
fibres to which they give origin. This occurs when any motor nerves are
separated from their cells of origin, and it involves no necessity of assuming
the existence of special trophic cells or nerves.

If a few of the motor cells be affected with disease, and if the degenera-
tion be gradual and progressive, there would necessarily be 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 weakening of the muscles,
and the phenomena would not be those observed in complete paralysis pro-
duced by section of the motor nerves. These are the phenomena observed
in progressive muscular atrophy, preceding the paralysis which is the final
result of the disease ; and these do not of necessity involve the action of any
special centres or nerves.

As regards the muscular atrophy itself, if- the nervous stimulus be grad-
ually destroyed, the muscular tissue will necessarily undergo progressive de-
generation and atrophy.

With the above considerations', the question of the trophic cells and
nerves may be left to the pathologist ; and the existence of centres and
nerves specially and directly influencing the nutrition of the muscular sys-
tem can be admitted only when it has been demonstrated that there are
lesions of particular structures in the nervous system, which produce phe-
nomena that can not be explained by the action of ordinary motor and sen-
sory nerves and of the vaso-motor system. In thus dismissing the question,
however, it is not intended to assume that the existence of trophic centres
and nerves is impossible. There are certain peculiar changes in tissue in
progressive muscular atrophy, and section of nerves produces degenerations
of glandular and other structures that are not muscular. Future observations
may show that there are special parts of the nervous system presiding over
nutrition ; but at present, such parts have not been accurately described and
isolated, either anatomically or physiologically.

SLEEP. 647

SLEEP.

When it is remembered that about one-third of each day 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 im-
portance 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 modifications in
function are observed in the cerebro-spinal axis and nerves. Eepose is as
necessary to the nutrition of the muscular system as proper exercise ; but re-
pose of the muscles 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. 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
concerned in circulation and respiration, are never completely arrested, sleep-
ing 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 and digest. In adult life, under perfectly physiological condi-
tions, a person requires about eight hours of sleep ; some need less, but 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 com-
pletely incapacitates one for mental or muscular effort, especially the former,
than loss of natural 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. One of the most severe methods of torture is long-continued
deprivation of sleep ; and persons have been known to sleep when subjected
to acutely painful impressions. Severe muscular effort, even, may be con-
tinued during sleep. In forced marches, regiments have 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 one has become accustomed may
fail to disturb natural rest. Those who have been long habituated to the
noise of a crowded city frequently find difficulty in sleeping in the stillness
of the country. Prolonged exposure to intense cold induces excessive som-
nolence, and if this be not resisted, the sleep passes into stupor, the power

648 NERVOUS SYSTEM.

of resistance to cold becomes rapidly diminished, and death is the result.
Intense heat often produces drowsiness, but, as is well known, is not favor-
able to natural sleep.

Sleep is preceded by a feeling of drowsiness, an indisposition to mental or
physical exertion, and a general relaxation of the muscular system. It then
requires a decided effort to keep awake. In sleep the voluntary muscles
are inactive, the lids are closed, the ordinary impressions of sound are not
appreciated, and sometimes there is a dreamless condition, in which all
knowledge of existence is lost.

There may be, during sleep, mental operations of which there is no con-
sciousness or recollection, unconscious cerebration, as it was called by Car-
penter. It is well known that dreams are vividly remembered immediately
on awakening, but that the recollection of them rapidly fades away, unless
they be brought to mind by an effort to recall and relate them. Whatever
be the condition of the mind in sleep, if the sleep be normal, there is repose
of the cerebro-spinal system and an absence of voluntary effort, which re-
store 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 the
organism is so subject to unusual mental conditions, that it is difficult to
determine with exactness the phenomena of sleep that are absolutely physio-
logical and to separate those that are slightly abnormal. It can not be as-
sumed, for example, that a dreamless sleep, in which existence, is as it were
a blank, is the only normal condition of repose of the system ; nor is it pos-
sible to 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 influences, disordered
digestion, etc. It may be assumed, however, that an entirely refreshing sleep
is normal.

That reflex ideas originate during sleep, as the result of external im-
pressions, there can be no doubt ; and many remarkable experiments upon
the production of dreams of a definite character, by subjecting a person dur-
ing sleep to peculiar influences, have been recorded. The hallucinations
produced in this way are called hypnagogic, and they occur usually when
the subject is not in a condition favorable to sound sleep.

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 per-
sonal 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 dreams, actually occur in the brain within a few seconds. A person
is awakened by a certain impression, which undoubtedly has given rise to
a dream that seemed to occupy hours or days, and yet the period of time be-
tween the impression and the awakening was 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 and apparently of great length. It is unnecessary
to cite the accounts of literary compositions of merit, the working out of

CONDITION OF THE BRAIN DURING SLEEP. 649

difficult mathematical problems in dreams, etc., some of which are undoubt-
edly accurate. If it be true that the mind is capable of forming consecu-
tive ideas during sleep — which can hardly be doubted — there is no good rea-
son why these phenomena should not occur and the thoughts should not be
remembered and noted immediately on awakening. In most dreams, how-
ever, the mind is hardly in a normal condition, and the brain generally loses
the power of concentration and of accurate reasoning.

Condition of the Brain and Nervous System during Sleep. — During
sleep the brain may be in a condition of absolute repose — at least, as far as
there is any subjective knowledge of mental operations — or there may be
more or less connected trains of thought. There is, also, as a rule, absence
of voluntary effort, although movements may be made to relieve discom-
fort 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. There is every reason to believe that the
action of the sympathetic system is not disturbed or affected by sleep, if
the influence of the vaso-motor nerves upon the circulation in the brain be
excepted.

Two opposite theories have long been in vogue with regard to the imme-
diate cause of sleep. In one, this condition is attributed to venous conges-
tion and increased pressure 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 in
the former the action of the brain is entirely suspended, there is no con-
sciousness, no dreaming, and the condition is manifestly abnormal. In ani-
mals rendered comatose by opium, the brain when exposed is found deeply
congested with venous blood. The same condition often obtains in pro-
found anaesthesia by chloroform, but a state of the brain very nearly resem-
bling normal sleep is observed in anaesthesia by ether. These facts have been
demonstrated by experiments upon living animals, 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 unneces-
sary to discuss the theory that sleep is attended with or is produced by con-
gestion of the cerebral vessels.

The idea that the circulation in the brain ist diminished during sleep has
long been entertained by some physiologists ; but until within a few years,
it has rested chiefly upon theoretical considerations. The experiments of
Durham (1860) seem to demonstrate that the supply of blood to the brain is
always greatly diminished during sleep. These experiments were made
upon dogs. A piece of the skull 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 were awake, the vessels

650 NERVOUS SYSTEM.

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 appearance of the brain during its period
of functional activity and during its state of repose or sleep was most re-
markable." There can be hardly any doubt, after these experiments, that
the cerebral circulation is considerably diminished in activity during sleep.

The influence of diminished supply of blood to the brain has been illus-
trated by compression of both carotid arteries. In an experiment performed
upon his own person, Fleming produced immediate and profound sleep in
this way, and this result invariably followed in subsequent trials upon him-
self and others. Waller produced anaesthesia in patients by pressure upon
both pneumogastric nerves ; but the nerves are so near the carotid arteries
that* they could hardly be compressed, in the human subject, without inter-
fering 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 instances in which both carotid arteries have
been tied 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 condi-
tions involving 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 persons. These, as well as experi-
ments on animals, all go to show that the supply of blood to the brain is
diminished during natural sleep, and that sleep may be induced by retarding
the cerebral circulation by compressing the vessels of supply. When the cir-
culation is interfered with by compressing the veins, congestion is the result
and there is 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 physio-
logical anaemia 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, diminishing 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 being well established by observations upon other parts of the circu-
latory system.

Little is known of the intimate nature of the processes of nutrition of
the brain during its 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 one is awake.
Although the mental processes are much less active during sleep, even at this
time, the operations of the brain are not always suspended. It is equally
well established that exercise of the brain is attended with physiological
wear of nervous tissue, and like other parts of the organism, its tissue re-
quires periodic repose for regeneration of the substance consumed. Analo-

CONDITION OF THE BRAIN DURING SLEEP. 651

gies to this are to be found in parts that are more easily subjected to direct
observation. The muscles require repose 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 supply of blood to
their tissue is much diminished. It is probable, also, that the muscles 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 activity of
parts, while it is attended with an increased supply of blood, is a condition
more or less opposed to the processes of repair, the hyperaemia being, appar-
ently, a necessity for the marked and powerful manifestations of their pecul-
iar action. When the parts are active, the blood seems to be required to keep
at the proper standard the so-called irritability 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 blo'od passing through the tissue
carries away carbon dioxide and other products of disassimilation, which axe
increased in quantity, until it gradually uses up its capacity for work. Then
follows repose; the supply of blood is reduced, but under normal condi-
tions, the tissue repairs the waste which has been excited, by action, the blood
furnishing nutritive matter and carrying away a comparatively small quan-
tity of effete products.

It may safely be assumed that processes analogous to those just described
take place in the brain. By absence of voluntary effort, the muscles have
time for rest and for the repair of physiological waste, and their action is for
the time suspended. As the activity of the brain involves consciousness,
volition, the generation of thought, and, in short, the mental condition ob-
served while awake, complete repose of the brain is characterized by the
opposite conditions. It is true that the brain may be rested without sleep,
by abstaining from mental effort, by the gratification of certain of the senses,
and by mental distraction of various kinds, and that the mind may work
to some extent during sleep ; but during the period of complete repose — that
condition which is so necessary to perfect health and full mental vigor — con-
sciousness and volition are lost, 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 renewed work.
The exhaustion of the muscles produces a sense of fatigue of the muscular
system, indisposition to muscular exertion, and a desire for rest, not neces-
sarily involving drowsiness. Fatigue of the brain is manifested by indisposi-
tion to mental exertion, dullness of the special senses and a desire for sleep.
Simple repose will relieve physiological fatigue of muscles ; and when a par-
ticular set of muscles has been used, the fatigue often disappears when these
muscles alone are at rest, though others be brought into action. Sleep, and
sleep alone, relieves fatigue of the brain.

652 SPECIAL SENSES.

During sleep nearly all of the physiological processes, except those di-
rectly 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 in connection with the physiology of circulation and
respiration. Physiologists 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 persons experience after a full
meal is probably due to a determination of blood to the alimentary canal and
a consequent diminution in the supply to the brain.

CHAPTER XXL

SPECIAL SENSES— TOUCH, OLF ACTION AND GUSTATION.

General characters of the special senses— Muscular sense (so called)— Sense of touch— Variations in tactile
sensibility in different parts (sense of locality of impressions) — Table of variations measured by the
sesthesiometer— Appreciation of temperature— Tactile centre— Olfaction— Nasal fossje— Schneiderian
and olfactory membranes— Olfactory (first nerve)— Physiological anatomy— Olfactory bulbs— Olfactory
cells and terminations of the olfactory nerve-fibres — Properties and uses of the olfactory nerves— Mechan-
ism of olfaction— Relations of olfaction to the sense of taste— Reflex acts through the olfactory nerves
—Olfactory centre— Gustation— Savors— Nerves of taste— Chorda tympani— Glosso-pharyngeal (ninth
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
—Papillae of the tongue— Taste-beakers— Connections of the nerves with the organs of taste— Taste-
centre.

THE description of the nerves thus far has included motion and what is
known as general sensibility ; and knowledge of these properties of the nerv-
ous system has been derived mainly from experiments upon the inferior ani-
mals. As regards sensation, the experiments have referred to impressions
recognized as painful ; and these are conveyed to the centres by nerve-fila-
ments, anatomically as well as physiologically distinct from those which con-
vey to the contractile parts the impulses that give rise to motion. In regard
to the sensory nerves, simple impressions only have been described ; but it
is evident that the filaments of peripheral distribution of these nerves are
capable of receiving a variety of impressions, by which, to a certain extent,
the form, size, character of surface, density and temperature of objects are
recognized. There is also 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 adapted to receive the impressions
of smell, taste, sight and hearing.

The senses of olfaction, gustation, vision and audition belong to peculiar
organs, provided with nerves which have special properties and usually are
not endowed with general sensibility. These nerves have been omitted in

GENERAL CHARACTERS OF THE SPECIAL SENSES. 653

the general description of the nervous system, as well as the accessory organs
to which they are distributed.

The senses of touch, temperature and pain are all conveyed to the nerve-
centres by what have been described as sensory nerves, the touch being per-
fected in certain parts by peculiar arrangements of the terminal nerve-fibres.
Although it is possible that each one of these impressions is transmitted by
special and distinct fibres, this is not yet a matter of positive demonstration.
The so-called muscular sense, by which weight, resistance etc., are appreci-
ated, undoubtedly depends to a great extent upon the muscular nerves. What
are generally recognized as sensory impressions have been thus subdivided.
These subdivisions are sufficiently distinct, as far as the character of the
sensations themselves are concerned, but as regards their paths of conduc-
tion, as before intimated, exact and positive data are wanting. It is impossi-
ble to study with advantage the different varieties of ordinary sensation in
the lower animals, for evident reasons ; and physiologists rely mainly upon
observations on the human subject, in the form of experiments and of patho-
logical phenomena.

There are two ways of regarding the different varieties of general sensa-
tion : One is to look at each as a peculiar impression conveyed by special
nerve-fibres, and the other is to regard the nerves of general sensibility as
capable of conducting impressions of different kinds. It has never been
assumed that special fibres for each variety of sensation have been demon-
strated, and it is possible only to reason as to this from what is actually
known of the general properties of sensory nerves.

The general sensory nerves are sufficiently distinct in their properties
from the true nerves of special sense. The latter convey peculiar impressions
only, such as those of sight, hearing, smell and taste. The former, when
strongly stimulated or irritated, always convey impressions of pain. Separat-
ing, then, all other senses, except the venereal sense, from the true special
senses, it is proper to inquire whether it be reasonable or necessary to assume
that any of the varieties of general sensation require special nerves for their
conduction.

It is well known that a relatively powerful stimulation of a sensory nerve
or of sensitive parts is necessary to the production of a painful impression ;
and it is also well known that very painful impressions overpower impressions
of touch, weight, pressure, temperature and the so-called muscular sense. In
cases of disease, it is sometimes observed that tactile sensibility is retained in
parts that are insensible as regards pain. It is possible that sensory nerve-
fibres may become so altered in their properties as to be incapable of con-
ducting painful impressions, while they still conduct sensations that are
appreciated only as impressions of contact. This is observed in certain cases
of artificial anaesthesia. In hyperaesthesia, or exaggerated sensibility to pain-
ful impressions, the tactile sense is necessarily overpowered in a greater or
less degree. Impressions made on a sensory nerve in its course are always
appreciated as painful, and the pain is referred to the terminal distribution
of the nerve, this being a law of sensory perception. There is no sense of

43

654 SPECIAL SENSES.

contact at the ends of the nerve, and there is no contact. The impression,
in order to be perceived at all, must be painful. These facts may be in a
measure applied to local impressions produced by extremes of heat and cold
or by chemical or electric stimulation of sensitive parts.

The internal organs have as a rule no tactile sensibility, although they
may be sensitive ; and feeble impressions may not be appreciated, while
stronger impressions are painful.

Titi Ration is the result of unusual, feeble impressions or of slight impres-
sions frequently repeated in the peripheral ends of certain sensory nerves.
These impressions are not precisely tactile nor are they painful. They pro-
duce peculiar sensations, and they frequently give rise to violent reflex move-
ments, by what is known as a summation of sensory stimulations.

Muscular Sense (so called}. — It is difficult to define exactly what is meant
by the term muscular sense, as it is used by some physiologists. In all proba-
bility, the sense which enables one to appreciate the resistance, immobility
and elasticity of substances that are grasped or stood upon or which are in
any way opposed to the exertion of muscular power, may be greatly modified
by education and habit. It is undoubtedly true, however, that general sensi-
bility regulates the action of muscles to a considerable extent. If, for exam-
ple, the lower extremities be paralyzed as regards sensation, the muscular
power remaining intact, frequently the person so aifected can not walk unless
he be able to see the ground. This difficulty occurs for the reason that the
limbs have lost the sense of contact. 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 Charles Bell by Dr. Ley. The
patient was affected 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 surrounding objects withdrew her
from the notice of the state of her arm, the flexors gradually relaxed, and the
child was in hazard of falling." This is like certain of the phenomena
observed in cases of locomotor ataxia. In this disorder there is disease of
the posterior white 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 frequently are 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 considerable power. Habit and education enable
some persons to appreciate with great nicety slight differences in weight ; but
this is due chiefly to the sense of resistance to muscular effort and has little
dependence upon the sense of touch.

In general those parts which are most sensitive to the impressions of
touch, as the fingers, enable one to appreciate differences in pressure and
weight with greatest accuracy. The sense of simple pressure, unaided by
the estimation of weight by muscular effort, generally is more acute upon

SENSE OF TOUCH. 655

the left side. 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 most
persons 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 if the weights be successively tested with the same hand than
when two weights are placed, one on either hand. When the interval be-
tween the two trials is more than forty seconds, slight differences in weight
— the difference between fourteen and a half and fifteen ounces (411 and
425 grammes), for example — can not 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.

SENSE OF TOUCH.

The different modes of termination of the sensory nerves have already
been described; 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 the tactile sensibility in different parts — differ-
ences which are very 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 (Sense of Local-
ity of Impressions). — In certain parts of the cutaneous 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 peculiarly sensitive. The appreciation of tempera-
ture 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 titillation. The sense of touch, also, by which the size,
form, character of the surface, consistence etc., of objects are appreciated,
is developed to a greater degree in some parts than in others. The tips of
the fingers generally are used to ascertain those properties of objects revealed
by the sense of touch. This sense is capable of education and is almost
always extraordinarily developed in persons who are deprived of some other
special sense, 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 was said to model
excellent likenesses, being guided entirely by the sense of touch. Other
instances of this kind are on record. The blind have been known to become
proficients in conchology and botany, guided entirely by the 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 facility by passing the fingers over raised letters but little
larger than the letters in an ordinary folio Bible.

An easy method of determining the relative delicacy of the tactile sen-
sibility of different portions of the cutaneous surface was devised a num-

656

SPECIAL SENSES.

ber of years ago (1829) by E. H. Weber. This method consists in the
application to the skin, of two fine 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 carefully adjusting
the distance between the points, a limit will be reached where the two im-
pressions upon the surface are appreciated as one ; i. e., by gradually approx-
imating 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 measure of the delicacy of
the tactile sensibility of different parts. Of course the instrument used
may be very simple — a pair of ordinary dividers will answer — but it is co.n-
venieiit to have some ready means of ascertaining the distances between the
points. An instrument, consisting simply of a pair of dividers with a grad-
uated 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 an gethesiometer. The experiments of Weber were made upon his own
person. They showed some slight variations with the direction of the line
of the two points, but these are not very important. The table which follows
is made of selections from the observations of Weber, taking those that are
most likely to be useful as a guide in pathological investigations. The ex-
periments of Valentin and others on different persons do not vary much in
their results from the figures given in the table.

TABLE OF VARIATIONS IN THE TACTILE SENSIBILITY OF DIFFERENT POR-
TIONS OF THE SKIN (WEBER).

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 linos (fa of an
inch, or a little more than 2 mm.).

PART OF SURFACE.

Lines.

Mm.

Tip of tongue ....

0-50

1-05

Palmar surface of third phalanx of forefinger

1-00

2-10

Red surface of under lip

2-00

4-20

Palmar surface of second phalanges of fingers

2-00

4-20

Dorsal surface of third phalanges of fingers .

3-00

6-30

Tip of nose

3-00

6-30

Palmar surface of metacarpus ...

3-00

6-30

End. of great toe

5-00

10-50

Palm of hand

5-00

10-50

Skin of cheek, over buccinator

5-00

10-50

Skin of cheek over anterior part of malar bone

7-00

14-70

Dorsal surface of first phalanges of fingers ...

7-00

14-70

Lower part of forehead
Back of hand

10-00
14-00

21-00
29-40

Patella and surrounding part of thigh

16-00

33-60

Dorsum of foot near toes

18-00

37-80

Upper and lower extremities of forearm

18-00

37-80

Upper and lower extremities of leg

18-00

37-80

Penis . .

18-00

37-80

Acromion and upper part of arm

18-00

37-80

Grluteal region and neighboring part of thigh . . .

18-00

37-80

Middle of forearm where its circumference is greatest

30-00

63-00

Middle of thigh where its circumference is greatest

30-00

63-00

APPRECIATION OF TEMPERATURE. 657

. By comparing the distribution of the tactile corpuscles with the results
given in the table, it will be seen that the sense of touch is most acute in
those situations in which the corpuscles are most abundant. In the space of
a little more than ^ of an inch (2'2 mm.) square, on the palmar surface of
the third phalanx of the index-finger, Meissner counted the greatest num-
ber of corpuscles ; viz., one hundred and eight. In this situation the tactile
sensibility is more acute than in any other part of the skin, the mean dis-
tance indicated by the aesthesiometer being 0*603 of a line, or 1*27 mm.
(Valentin). In the same space on the second phalanx, forty corpuscles were
counted, the aesthesiometer marking 1-558 line, or 3*27 mm. (Valentin), this
part ranking next in tactile sensibility after the red surface of the lips.
One can readily understand how the tactile corpuscles, embedded in the
amorphous substance of the cutaneous papillae, might increase the delicacy of
appreciation of slight impressions, by presenting hard surfaces against
which the nerve-filaments can be pressed.

As regards those portions of the general cutaneous surface in which no
tactile corpuscles have been demonstrated, it is not easy to connect the varia-
tions in the tactile sensibility with the nervous distribution, as little is
known of the comparative richness of the terminal nervous filaments in
these situations.

Appreciation of Temperature. — It is not known that the sense of tem-
perature, either of the surrounding medium or of bodies applied to different
parts of the skin, is appreciated through any nerves other than those of gen-
eral 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 state-
ment 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 comparatively insensible to temperature ; and the same is
true of those who often expose the hands, face or other parts to heat. The
variations in the sensibility of different parts of the surface to temperature
depend, also, upon special properties of the parts themselves. The differ-
ences, however, are not so marked as to be of any great importance, and the
experiments made upon this point are simply curious.

The experiments of Weber and others show that the skin is the chief
organ for the appreciation of temperature, if the mouth, palate, vagina and
rectum, by which the differences between warm and cold substances is
readily distinguished, be excepted. In several instances in which larger por-
tions of the skin were destroyed by burns and other injuries, experiments
have been made by applying spatulas of different temperatures. In one of
these, a spatula plunged in water at 48° to 55° Fahr. (9° to 12° C.) was
applied to a denuded surface, and again, a spatula at 113° to 122° Fahr. (45°
to 50° C.). When the patient was requested to tell which was the warmer.

658 SPECIAL SENSES.

the answers were as frequently incorrect as they were correct ; but the dis-
crimination was easy and certain when the applications were made to the
surrounding healthy skin. When applications at a higher temperature were
made to the denuded part, the patient suffered only pain.

The venereal sense is unlike any other sensation, and is general as well
as referable to the organs of generation. In this connection, however, it is
important to note that the tactile sensibility of the palmar surface of the
third phalanx of the fingers, measured by the sesthesiometer, compared with
the sensibility of the penis, is as 0-802 to 0-034, or between twenty-three and
twenty-four times greater.

Ferrier has described a diffused tactile centre in the " hippocampal re-
gion," the action of which is crossed ; but the observations to determine the
loss of the sense of touch after destruction of this part, which were made
on monkeys, are by no means satisfactory. It must be very difficult to study
tactile sensibility in the inferior animals.

OLFACTION.

The nerves directly connected with the senses of olfaction, vision and
audition, have little or no general sensibility. As regards the olfactory
nerves, the parts to which they are distributed are so largely supplied with
branches from the fifth, that it is difficult to determine the fact of their sen-
sibility or insensibility to ordinary impressions. The olfactory nerves, how-
ever, are distributed to the mucous membrane of that portion only of the
nasal cavity, endowed with the special sense of smell.

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, are called the nasal fossae. The membrane lining
these cavities is generally called the Schneiderian mucous membrane, and
sometimes, the pituitary membrane. This membrane is closely adherent to
the fibrous coverings of the bones and cartilages by which the nasal fossse
are bounded, and it is thickest over the turbinated bones. It is continuous
with the membrane lining the pharynx, the nasal duct and lachrymal 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 alone receives the terminal filaments of the olfactory nerves, but physio-
logical experiments have demonstrated that it is the only part capable of ap-
preciating odorous impressions. If a tube be introduced into the nostril,
placed horizontally over an odorous substance so that the emanations can not
penetrate its caliber, no odor is perceived, though the membrane below the
end of the tube might receive the emanations ; but if the tube be 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

OLFACTORY NERVES.

659

membrane, extends from the cribiform plate of the ethmoid bone downward
a little less than an inch (25 mm.). It is soft and friable, very vascular,
thicker than the rest of the Schneiderian membrane, and in man, it has rather
& yellowish color. It is covered by long, delicate, columnar cells, nucleated,
and each one provided with three to eight ciliary processes, the movements of
which are from before backward. The olfactory membrane is provided with
a large number of long, racemose, mucous glands, which secrete a fluid that
keeps the surface moist, a condition essential to the accurate perception of
odorous impressions.

* OLFACTORY (FIRST NERVE).

The apparent origin of the olfactory nerve is by three roots, from the
inferior and internal portion of the frontal lobe of the 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, pass-
ing outward, across the
fissure of Sylvius, to
the temporo-sphenoidal
lobe. The internal white
root is thicker and short-
er than the external root,
.and it arises from the
most posterior portion
of the frontal lobe. The
middle, or gray root
arises from a little em-
inence of gray matter
situated on the posterior and inner portion of the inferior surface of the
frontal lobe.

The deep origin of these three roots of the olfactory nerves is still a matter
of discussion. The external root passes through the gray substance of the
island of Reil, to a gray nucleus in the temporo-sphenoidal lobe, in front of
the pes hippocampi. The fibres of the middle root have not been traced
farther than the gray eminence from which it arises. The fibres of the inter-
nal root probably are connected with the fibres of the gyrus fornicatus. The
three roots converge to form a single cord at the inner boundary of the fissure
of Sylvius. This cord passes forward and slightly inward, in a deep groove be-
tween two convolutions on the under surface of the frontal lobe, covered by
the arachnoid membrane, to the ethmoid bone. This portion of the nerve is
soft and friable. It is composed of both white and gray matter, the propor-

Fio. 235.— Olfactory ganglion and nerves (Hirschfeld).
1, olfactory ganglion and nerves ; 2, branch of the nasal nerve ; 3,
spheno-palatine ganglion ; 4, 7, branches of the great palatine
nerve ; 5, posterior palatine nerve ; 6, middle palatine nerve ; 8, 9,
branches from the spheno-palatine ganglion ; 10, 11, 12, Vidian
nerve and its branches ; 13, external carotid branch, from the su-
perior cervical ganglion.

660

SPECIAL SENSES.

tions 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, fifteen to eighteen nervous filaments are given on%
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 olfac-
tory nerves, the cord leading from the olfactory
bulb to the cerebrum being properly a commis-
sure. 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 fossae ; and an
outer group, to the mucous membrane covering
the superior and middle turbiuated bones and a
portion of the ethmoid.

The mode of termination of the olfactory
FIG. 236.— Terminal filaments of the nerves differs from that of the ordinary sensory

olfactory nerves ; magnified 30 ,. ,. ,, .. ...

diameters (Koiiiker). nerves, and is peculiar and characteristic, as it is

in the other organs of special sense. The olf ac-
tory mucous membrane contains terminal nerve-
cells> called the olfactory cells, which are situated

ceil of the sheep. between the cells of epithelium. These are long>

delicate, spindle-shaped, varicose structures, each one containing a clear,
round nucleus. In the frog there is a fine, hak-like process projecting from
each cell, beyond the mucous membrane, which has not been observed in
man or the mammalia. The delicacy of the structures entering into the
composition of the olfactory membrane renders the investigation of the ter-
mination of its nervous filaments exceedingly difficult.

Properties and Uses of the Olfactory Nerves. — It is almost certain that
the olfactory nerves possess none of the general properties of the ordinary
nerves belonging to the cerebro-spinal system, and are endowed with the
special sense of smell alone. The filaments coming from the olfactory bulbs
and distributed to the pituitary membrane have not been exposed and stimu-
lated in living animals ; but experiments upon the nerves behind the olfac-
tory bulbs show that they are insensible to ordinary impressions. Attempts
have been made to demonstrate, in the human subject, the special properties
of these nerves, by passing an electric current through the nostrils ; but the
situation of the nerves is such that these observations are of necessity indefi-
nite and unsatisfactory.

of va?fcJse°Sbri£d

MECHANISM OF OLF ACTION. 661

Among the experiments upon the higher orders of animals, in which the
olfactory nerves have been divided, may be cited, as open to no objections,
those of Vulpian and Philipaux, upon dogs. It is well known that the sense
of smell usually is very acute in these animals. Upon dividing or extirpating
the olfactory, bulbs, " after the animal had completely recovered, it was de-
prived 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, suc-
cessfully operated upon, then taken into the laboratory, never found the bait ;
and nevertheless, care had been taken to select hunting-dogs." This experi-
ment is conclusive ; more so than those in which animals deprived of the
olfactory bulbs were shown to eat faeces without disgust, for this sometimes
occurs in dogs that have not been multilated.

Comparative anatomy shows that the olfactory bulbs generally are devel-
oped in proportion to the acuteness of the sense of smell. Pathological facts
show, in the human subject, that impairment or loss of the olfactory sense is
coincident with injury or destruction of these ganglia. 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.

Mechanism of Olfaction. — Substances that have odorous properties give
off material emanations, which must come in contact with the olfactory mem-
brane before their peculiar odor is appreciated. This membrane is situated
high up in the nostrils, is peculiarly soft, is abundantly provided with glands,
by the secretions of which its surface is kept in proper condition, and it pre-
sents the peculiar nerve-terminations of the olfactory filaments.

In experimenting upon the sense of smell it has been found difficult to
draw an 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 overpower their odorous
qualities. It is unnecessary in this connection to discuss the different varie-
ties of odors recognized by some of the earlier writers, as the fragrant, aro-
matic, 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 subject and in different animals are evidence of this fact. Hunt-
ing-dogs recognize odors to which most persons are absolutely insensible ;
and certain races of men are said to possess a remarkable delicacy of the sense
of smell. Like the other special senses, olfaction may be cultivated by atten-
tion and practice, as is exemplified in the delicate discrimination of wines,
qualities of drugs etc., by experts.

After what has been said concerning the situation of the true olfactory
membrane in the upper part of the nasal fossae and the necessity of particles
impinging upon this membrane in order that their odorous properties may

662 SPECIAL SENSES.

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 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 emanations 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 therefore it is not appreciated.
This is an apparently satisfactory explanation, for it could hardly be supposed
that the direction of the emanations, provided they came in contact with the
membrane, could modify their effects. Longet has cited 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 im-
pression 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 im-
portant a part, that it can hardly be separated from gustation. The
common practice of holding the nose when disagreeable remedies are swal-
lowed is an 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 im-
pressions.

It is undoubtedly true that the delicacy of the sense of taste is lost when
the sense of smell is abolished. The experiment of tasting wines blind-
folded and with the nostrils plugged, and the partial loss of taste during a
severe coryza, are sufficiently familiar illustrations of this fact. In the great
majority of cases, when there is complete anosmia, the taste is sensibly im-
paired ; 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 spe-
cial impressions.

It is unnecessary, in this connection, to describe fully the reflex phenom-
ena which follow impressions made upon the olfactory membrane. The
odor of certain sapid substances, 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 im-
pressions of various kinds are sufficiently familiar.

According to Ferrier, the olfactory centre is on the inner surface of
the anterior extremity of the unicate gyrus ; but this location of the centre

GUSTATION. 663

is not regarded as definitely determined. Stimulation of this part in mon-
keys simply produces peculiar movements of the nostril and lip of the same
side.

GUSTATION.

The special sense of taste gives the appreciation of what is known as the
savor of certain 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-pharyngeal nerves.

It is assumed by some physiologists, that the true tastes are quite simple,
presenting the qualities which are recognized as sweet, acid, saline and bit-
ter ; while the more delicate shades of what are called flavors nearly always
involve olfactory impressions, which it is difficult to separate entirely from
gustation. Applying the term savor exclusively to the quality which makes an
impression upon the sense of taste, it is evident 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 circum-
stances. 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 condi-
tions. Chlorotic females, for example, frequently crave the most unnatural
articles, and their morbid tastes may disappear under appropriate treatment.
Inhabitants of the frigid zones crave fatty articles of food and will even
drink rancid oils with avidity. Patients often become accustomed to the
most disagreeable remedies and take them without repugnance. Again, the
most savory dishes may even excite disgust, when the sense of taste has be-
come cloyed, while abstinence sometimes lends a delicious flavor to the sim-
plest articles of food. The taste for certain articles certainly is 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. It is easy to recognize that certain articles are bitter or
sweet, empyreumatic or insipid, acid or alkaline, etc., but beyond these sim-
ple distinctions, the shades of difference are closely connected with olfac-
tion and are too delicate and too many for detailed description. Some per-
sons are comparatively insensible to nice distinctions of taste, while others
recognize 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

664 SPECIAL SENSES.

regarded as a violation of strictly hygienic principles, but it none the less
exemplifies the cultivation of the sense of taste.

Nerves of Taste. — Two nerves, the chorda tympani and the glosso-pharyn-
geal, are endowed with the sense of taste. These nerves are distributed to
distinct portions of the gustatory organ. The chorda tympani has already
been referred to as one of the branches of the facial ; the glosso-pharyngeal
has not yet been described.

Chorda Tympani. — In the description already 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 can not be followed farther by dis-
section. The filaments of this branch probably originate from the interme-
diary nerve of Wrisberg.

The course of the filaments of the chorda tympani, after this nerve has
joined the fifth, is shown by the effect upon the sense of taste and the altera-
tion of the nerve-fibres following its division. Vulpian and Prevost, by the
so-called Wallerian method, after dividing the chorda tympani, found degen-
erated 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. Observations upon the sense of taste show that the
chorda tympani is distributed to the anterior two-thirds of the tongue.

The general properties of the chorda tympani have been ascertained only
by observations made after its paralysis or division. All experiments in
which a stimulus has been applied directly to the nerve in living animals
have been negative in their results. According to Longet, when the nerve
has been isolated as completely as possible and all reflex action is excluded,
its stimulation produces no movement in the tongue.

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 many cases
illustrating this fact have been recorded. Aside from cases of paralysis of
the facial with impairment of taste, in which the general sensibility of the
tongue is intact, instances are on record of affections of the fifth pair, in
which the tongue was absolutely insensible to ordinary impressions, the
sense of taste being preserved. 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 de-
rived from the chorda tympani.

Passing from the consideration of pathological facts to experiments
upon living animals, 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,

GLOSSO-PHARYNGEAL NERVES. 665

the sense of taste is abolished in the anterior two-thirds of the tongue on
the side of the section. In a case reported by Moos, the introduction of an
artificial membrana tympani in the human subject 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 disappeared when the
membranes were removed, and the phenomena were referred to pressure
upon the chorda tympani. Other instances of this kind are on record.

As regards 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 addi-
tion, the lingual branch of the fifth contains filaments, derived from the
large root of this nerve, which give general sensibility to the mucous mem-
brane.

GLOSSO-PHARYNGEAL (NINTH NERVE).

The glosso-pharyngeal is 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 question of its other uses will be
considered in connection with its general properties, as well as the differences
between this nerve and the chorda tympani.

Physiological Anatomy. — The apparent origin of the glosso-pharyngeal
is from the groove between the olivary and restiform bodies of the medulla
oblorigata, between the roots of the auditory nerve above and the pneumo-
gastric below. The deep origin is in a gray nucleus in the lower part of the
floor of the fourth ventricle, between the nucleus of the auditory nerve and
the nucleus of the pneumogastric. From this origin the filaments pass for-
ward and outward, to the posterior foramen lacerum, by which the nerve
emerges with the pneumogastric, the spinal accessory and the internal jugu-
lar 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 ganglion, or the ganglion of Andersch.

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.

The distribution of the glosso-pharyngeal is quite extensive. The tym-
panic 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 mem-
brane surrounding the fenestra ovalis ; two anterior are distributed, one to

666

SPECIAL SENSES.

the carotid canal, where it anastomoses with a branch from the superior cer-
vical ganglion, and the other to the mucous membrane of the Eustachian

FIG. 237.— 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
filaments of the chorda tympani ; 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 Andersch ; 17, branches from the glosso-
pharyngeal to the stylo-glossus and the stylo-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.

tube ; two superior branches are distributed to the otic ganglion and, as is
stated by some anatomists, 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 mus-
cle. 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 a number of ganglionic points,
and filaments of distribution from the three nerves go to the mucous mem-
brane and to the constrictors of the pharynx. The mucous membrane proba-
bly is supplied by the glosso-pharyngeal. It is probable, also, that the mus-
cles of the pharynx are supplied by filaments from the pneumogastric, which
are derived originally from the spinal accessory.

MECHANISM OF GUSTATION. 66T

Near the base of the tongue branches are sent to the mucous membrane
covering the tonsils and the soft palate.

The lingual branches penetrate the tongue about midway between its
border and centre, are distributed to the mucous membrane at its base and
are connected with certain of the papillae.

General Properties of the Glosso-Pharyngeal. — To ascertain the general
properties of this nerve, it must be stimulated at its root, before it has con-
tracted anastomoses with other nerves, and the nerve must be divided in
order to avoid reflex phenomena. Taking these precautions it has been
found that stimulation of the peripheral end of the nerve does not give rise
to muscular movements (Longet). There can be no doubt of the fact that
the nerve is sensory, although its sensibility is somewhat dull. In experi-
ments in which the nerve has seemed to be insensible to ordinary impressions,
it is probable 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.

Experiments upon the glosso-pharyngeal are not very definite and satis-
factory 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 branches of the fifth, passing to the mucous membrane,
through Meckel's ganglion. Experiments show, also, that the reflex phe-
nomena 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.

Relations of the Glosso-Pharyngeal Nerves to Gustation. — Relying upon
experiments on the inferior animals, particularly dogs, it seems certain that
there are two nerves presiding over the sense of taste : The chorda tympani
gives this sense to the anterior two-thirds portion of the tongue exclusively ;
the glosso-pharyngeal supplies this sense to the posterior portion of the
tongue ; the chorda tympani seems to have nothing to do with general sensi-
bility ; 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 of 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. — Articles which make the special impression
upon the gustatory organ 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 usually more or less mastication, which in-
creases the flow of the parotid saliva ; and during the acts of mastication and
the first stages of deglutition, the sapid substances are distributed over the

668

SPECIAL SENSES.

gustatory membrane, so extensively, indeed, that it is difficult to exactly locate
the seat of 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 some confusion in the 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 exactly as possible. This has been done, with the result of
showing that the true gustatory organ is quite restricted in its extent.

Physiological Anatomy of the Organ of Taste. — Anatomical and physio-
logical researches
have shown that,
at least in the hu-
man subject, the
organ of taste
probably is con-
fined to the dorsal
surface of the
tongue and the
lateral portion of
the soft palate.
The upper surface
of the tongue pre-
sents a large num-
ber of special pa-
pillae, called, in
contradistinction
to the filiform pa-
pillae, fungiform
and circumval-
late. These are
not found on its
under surface or
anywhere except
on the superior
portion ; and it is
now well estab-
lished that the
circumvallate and
fungiform papillae
alone contain the

FIG. 238.— Papillae of the tongue (Sappey).
1, 1, circumvallate papillae ; 2, median circumvallate papilla, which entirely

fills the foramen caecum ; 3, 3, 3, 3,

pillae ; 5, 5, vertical folds and furrow

6, glands at the base of the tongue ; 7, 7, tonsils ; 8, epiglottis ;

glosso-epiglottidean fold.

foramen caecum ; 3, 3, 3, 3, fungiform papillae ; 4, 4, filiform pa- ..„,, .„,_ _.c
pillae ; 5, 5, vertical folds and furrows of the border of the tongue ; 6, 6, 6, 01 gans o:t

"

median Experiments up-
on the gustatory
organs, by the application of solutions to different parts through fine, glass

MECHANISM OF GUSTATION. 669

tubes, have shown that the mucous membrane around a papilla has no gusta-
tory sensibility, but that different savors can.be distinguished when a single
papilla is touched (Camerer).

In Fig. 238, which represents the dorsal surface of the tongue, the large,
circumvallate papillae, usually seven to twelve in number, are seen in the
form of an inverted V, occupying the base of the tongue. The fungiform
papillae are scattered over the surface but are most abundant at the point and
near the borders. Both of these varieties of papillae are distinguishable by
the naked eye.

The circumvallate papillae simply are enlarged, fungiform papillae, each
one surrounded by a circular ridge, or wall, and covered by small, secondary

FIG. 239. — Medium-sized circumvallate FIG. 240. — Fungiform, filiform, and hemi-

papilla (Sappey). spherical papillae (Sappey).

FIG. 239.— 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. 240. — 1, 1, two fungiform papillae covered with secondary papillae ; 2, 2, 2, filiform papillae ; 3, 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, filiform
papillae with striations at their bases ; 7, 7, hemispherical papillae, slightly apparent, situated
between the fungiform and the filiform papillae.

papillae. The fungiform papillae have each a short, thick pedicle and an en-
larged, rounded extremity. According to Sappey, one hundred and fifty to
two hundred of these can easily be counted. These, also, present small, sec-
ondary papillae on their surface. When the mucous membrane of the tongue
is examined with a low magnifying power, particularly after maceration in
acetic or in dilute hydrochloric acid, their structure is readily observed.
They are abundantly supplied with blood-vessels and nerves.

Several glandular structures are found beneath the mucous membrane of
the tongue. On either side of the frenum, near the point, is a gland about
three-quarters of an inch (20 mm.) long and one-third of an inch (8*5 mm.)
broad, which has five or six little openings on the under surface of the
tongue (Blandin and Nuhn). Near the taste-beakers, are small, racemose
glands, which discharge a watery secretion, by minute ducts which open into
the grooves within the walls of the circumvallate papillae (Ebner).

Taste-Beakers. — Loven and Schwalbe (1867) described, under this name,
peculiar structures which are supposed to be the true organs of taste. They
are found on the lateral slopes of the circumvallate papilla? and occasionally

44

6TO

SPECIAL SENSES.

on the fungiform papillae. Their structure 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 each flask, is a rounded opening, called the taste-pore. Their length
ig T^O" t° y}~o °^ an inch (71 to 83 /x), and their transverse diameter, about
•g-J-Q- of an inch (41 /A). 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. Accord-
ing to Engelmann, delicate, hair-like processes are connected with the taste-
cells and extend through the taste-pores, in the form of very fine filaments.

Bodies similar to the taste-beak-
ers have been found on the pa-
pillae of the soft palate and uvula,
the mucous membrane of the epi-
glottis and some parts of the top
of the larynx. As regards these
structures in the tongue, it has
been found that four or five
months after section of the glosso-
pharyngeal on one side in rabbits,

Tio.ZU.-Taste-bealcers, from the lateral taste-organ of ^ taste-buds On the COTOSpOnd-
the rabbit (Engelmann). jng gj^g Qf the posterior portion of

the tongue disappear, while they remain perfect on the sound side (Vintsch-
gau and Honigschmied).

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 the taste-cells, these cells
being directly connected with the terminal filaments of the gustatory nerves.

Ferrier has described a taste-centre near the so-called olfactory centre in
the unicate gyrus ; but his observations are not very definite, and the location
of a centre for gustation must be regarded as undetermined.

OPTIC NERVES. 671

CHAPTER XXII.

VISION.

General considerations— Optic (second nerve)— Genera) properties of the optic nerves— Physiological anat-
omy of the eyeball— Sclerotic coat— Cornea— Choroid coat— Ciliary muscle— Iris— Papillary 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— Certain laws of refraction, dispersion etc.,
bearing upon the physiology of vision— Refraction by lenses— Visual purple and visual yellow and ac-
commodation of the eye for different degrees of illumination— Formation of images in the eye— Mechan-
ism 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— Accommoda-
tion of the eye for vision at different distances— Changes in the crystalline lens in accommodation —
Changes in the iris in accommodation — Erect impressions produced by images inverted upon the retina
— Field of indirect vision — The perimeter— Binocular vision — Corresponding points — The horopter —
Duration of luminous impressions (after-images) — Irradiation — Movements of the eyeball — Muscles of
the eyeball— Centres for vision— Parts for the protection of the eyeball— Conjunctival mucous membrane
— Lachrymal apparatus — Composition of the tears.

THE chief important points to be considered in the physiology of vision
are the following :

1. The physiological anatomy and the general properties and uses 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 uses of accessory parts, as the muscles
which move the eyeball.

7. The physiological anatomy and uses of the parts which protect the
eye, as the lachrymal glands, eyelids etc.

OPTIC (SECOND NERVE).

The bands which pass from the tubercula quadrigemina to the eyes are
divided into the optic tracts, which extend from the tubercula on either side
to the chiasm, or commissure ; the chiasm, or the decussating portion ; and
the optic nerves, which pass from the chiasm to the eyes.

The optic tracts arise each one by two roots, internal and external. The
internal roots, which are the smaller, arise from the anterior tubercula quadri-
gemina, and pass through the internal corpora geniculata, to the optic chiasm.
The external roots, which are the larger, arise from the posterior part of the
optic thalami, pass to the external corpora geniculata, from which they receive
fibres, and thence to the chiasm.

Partly by anatomical researches (Wernicke) and partly by experiments on
the cerebral cortex in the lower animals and pathological observations on the
human subject, it has been shown that fibres from the apparent origin of the
optic tracts pass backward to the gray matter of the occipital lobes of the
cerebrum. It has also been stated by Stilling that fibres pass to the medulla

672

SPECIAL SENSES.

oblongata, extend down as far as the decussation of the pyramids, and proba-

bly are concerned in the reflex movements of the iris.

The two roots of each optic tract unite
above the external corpus geniculatum, form-
ing a flattened band, which takes an oblique
course around the under surface of the crus
cerebri, to the optic commissure.

The optic commissure, or chiasm, is situ-
ated just in front of the corpus cinereum,
resting upon the olivary process of the sphe-
noid 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 ad-
dition, the commissure contains filaments pass-
ing 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 op-
tic tract upon either side to the eye of the op-
posite side. The greatest part of the fibres
take this direction. Their relative situation is
internal.

2. External fibres, 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.

The fibres of the optic tracts upon the two
sides are connected with distinct portions of the
retina. This fact is illustrated in cases of hemi-
anopsia, which show that the decussating fibres
have the following directions and distribution :

From the left side of the encephalon, fibres FIG ^.-Diagram of the
pass to the right eye, supplying the inner, or na-
sal mathematical half of the retina, from a ver- The
tical line passing through the macula lutea. Fi-

bres also pass to the left eye, supplying the outer, or temporal half of the
retina. The macula lutea, then, and not the point of entrance of the optic
nerve, is in the true line of division of the retina.

FIG. 242.— Optic tracts, commissure
and nerves (Hirschfeld).

1, infundibulum : 2, corpus cinereum ;
3, corpora albicantia ; 4, cerebral
peduncle ; 5, pons Varolii ; 6, optic
tracts and nerves, decussating at
the commissure, or chiasm ; 7, mo-
tor oculi communis ; 8, patheticus ;
9, fifth nerve ; 10, motor oculi ex-
ternus ; 11, facial nerve ; 12, aud-
itory nerve ; 13, nerve of Wris-
berg ; 14, glosso-phary ngeal nerve ;
15, pneumogastric ; 16, spinal ac-
17, sublingual nerve.

at the opiic com'
^

OPTIC NERVES. 673

With the exception of a few grayish filaments, the fibres of the optic
tracts and the optic nerves are of the ordinary, medullated variety, and they
present no differences in structure from the general cerebro-spinal nerves.

The optic commissure is covered with a fibrous membrane and is more
resisting than the optic tracts. The optic nerves are rounded and are enclosed
in a double sheath derived from the dura mater and the arachnoid. They
pass into the orbit upon either side and penetrate the sclerotic, at the pos-
terior, 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 sphenoidal fissure, 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 a number of 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, mammillated 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 £ to f of an inch (8*5 to 19-1 mm.) 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 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
corresponding with the extent of the lesion. It is important, 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 their
stimulation produces luminous impressions. This was stated in the remark-
able paper, Idea of a New Anatomy of the Brain, 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 beefi. exposed. If an electric current be
passed through the optic nerves, a sensation of light is experienced. The

674

SPECIAL SENSES.

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 certain muscles. It is surrounded by a
thin, serous sac, the capsule of Tenon, which exists in two layers. The outer
layer lies next the fatty layer in which the globe is embedded, and the inner
layer invests the sclerotic coat. When the axis of the eye is directed for-
ward, 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 external 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 varia-
tions 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 has given comparative measure-
ments made three hours and twenty-four hours after death, the results of
which presented very considerable differences.

In measurements made by Sappey, one to four hours after death, of the
eyes of twelve adult females and fourteen adult males, of different ages, the
following mean results were obtained :

SUBJECTS EXAMINED.

Diameters (inch, and mm. in parentheses).

Antero-posterior.

Transverse. Vertical.

Oblique.

Mean of 12 females, 18 to 81 years of age.
Mean of 14 males, 20 to 79 years of age . .

0-941 (23-9 mm.)
0-968 (24-6 mm.)

0-911 (23-4 mm.) 0-905 (23'0 mm.)
0-941 (23-9 mm.) 0-925 (23'5 mm.)

0-937 (23-8 mm.)
0-949 (24-1 mm.)

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,

ANATOMY OF THE EYEBALL. 675

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 ^ of
an inch (1 mm.) It is thinnest at the middle portion of the eye, measuring
about -fa of an inch (0-5 mm.), and is a little thicker again near the cornea.
This membrane is composed chiefly of bundles of ordinary connective tissue.
The fibres are slightly wavy, and are arranged in flattened bands, which are
alternately longitudinal and transverse, giving the membrane a lamellated
appearance, although it can not be separated into distinct layers. Mixed
with these bands of connective-tissue fibres, are 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 scle-
rotic 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 -fa of an inch (0-8 mm.),
in its central portion, and about ^ of an inch (1 mm.) 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 whit-
ish 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 very pale, flattened bun-
dles of fibres, interlacing with each other in every direction. Their arrange-
ment is lamellated, although they can not be separated into complete and
distinct layers. Between the bundles of fibres, lie a great number of stellate,
anastomosing, connective-tissue corpuscles. In these cells and in the inter-
vals 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 can not 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, nu-

676

SPECIAL SENSES.

cleated epithelium. At the circumference of the cornea, a portion of this
membrane passes to the anterior surface of the iris, in the form of a number
of 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 foatal 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 ex-
treme edge.

In the cornea fine nerve-fibres terminate in the nuclei of the posterior
layer of the epithelium of its convex surface. The cornea also contains
lymph-spaces and the so-called " wandering cells," The surface of the cor-
nea is exquisitely sensitive.

Choroid Coat. — Calling the sclerotic and the cornea the first coat of the
eyeball, the second is the choroid, with the ciliary processes, the ciliary mus-
cle and the iris. This was
called by the older anato-
mists the uvea, a name
which was later applied,
sometimes to the entire iris,
and sometimes to its pos-
terior, or pigmentary layer.
The choroid and ciliary
processes will be described
together as the second coat.

•'••UP-- -:-..Jp The ciliary muscle and the

iris will be described sepa-
rately.

The choroid is distin-
guished from the other coats
of the eye by its dark color
and its great vascularity. It

FIG. 244.— Choroid coat of the eye (Sappey). • **. *.• £ ru

1, optic nerve ; 2, 2, 2, 2, 3, 3. 3, 4, sclerotic coat, divided and turned OCCUpieS that portion Of the

back to show the choroid ; 5, 5, 5, 5, the cornea, divided into pvpV,all pnrrp«r»nnrlino- fr» tViP

four portions and turned back ; 6, 6, canal of Schlemm ; 7, ^yvL mg IL

external surface of the choroid, traversed by the ciliary oplprnfin Tf i« r»prfnrafpd

nerves and one of the long ciliary arteries ; 8, central vessel, k AG'

into which open the vasa vorticosa ; 9, 9, 10, 10, choroid zone ; nnsfprinrlv hv thp rvntio

11, 11, ciliary nerves ; 12, long ciliary artery ; 13, 13, 13, 13, P0> )rV DJ

anterior ciliary arteries ; 14, iris ; 15, 15, vascular circle of the nerve and is Connected in
iris ; 16, pupil.

front with the iris. It is

very delicate in its structure and is composed of two or three distinct layers.
Its thickness is -fa to ^ of an inch (0-3 to 1 mm.) Its thinnest portion is
at about the middle of the eye. Posteriorly it is a little thicker. Its thick-
est portion is at its anterior border.

The external surface of the choroid is connected with the sclerotic by
vessels and nerves (the long ciliary arteries and the ciliary nerves), and very
loose, connective tissue. This is sometimes called the membrana fusca, al-
though it can hardly be regarded as a distinct layer. It contains, in addi-

ANATOMY OF THE EYEBALL. 677

tion to blood-vessels, nerves and fibrous tissue, a few irregularly shaped pig-
ment-cells.

The vascular layer of the choroid consists of arteries, veins and capillaries,
arranged in a peculiar manner. The layer of capillary vessels, which is
internal, is sometimes called the tunica Kuyschiana. The arteries, which
are derived from the posterior short ciliary arteries and are connected with
the capillary plexus, lie just beneath the pigmentary layer of the retina.
The plexus of capillaries is closest at the posterior portion of the membrane.
The veins are external to the other vessels. They are very abundant 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 vorti-
cosa. The pigmentary portion is composed, over the greatest part of the
choroid, of a single layer of regularly polygonal cells, somewhat flattened,
measuring -^-Q to y^-jr of an inch (12 to 16 /*) in diameter. These cells are
filled with pigmentary 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 abundant near their centre, where a clear nucleus
can readily be observed. In the anterior portion 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 occu-
pied by stellate pigment-cells. The cells next the layer of rods and cones
are regarded as constituting the outer, or pigmentary layer of the retina.
These cells send little, hair-like processes downward between the rods and
cones.

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 ^ of an inch (£-5 mm.) in length. They
are sixty to eighty in number. The larger folds are of nearly uniform size
and are regularly arranged around the margin of the crystalline lens. Be-
tween 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 anteriorly 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 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 it is essential, in the
study of accommodation, to have an exact idea of its relations to the coats
of the eye and to the crystalline lens.

The form and situation of the ciliary muscle are as follows : It surrounds

678

SPECIAL SENSES.

the anterior margin of the choroid, in the form of a ring about -J of an inch
(3*2 mm.) wide and ^ of an inch (0-5 mm.) in thickness at its thickest por-

FIG. 245.— Ciliary muscle ; magnified 10 diameters (Sappey).

1, 1, crystalline lens ; 2, hyaloid membrane ; 3, zone of Zinn ; 4, iris ; 5. 5, one of the ciliary processes ;
6, 6, radiating fibres of the ciliary muscle ; 7, section of the circular portion of the ciliary muscle ;
8, venous plexus of the ciliary process ; 9, 10, sclerotic coat ; 11, 12, cornea ; 13, epithelial layer of
the cornea ; 14, membrane of Descemet ; 15, ligamentum iridis pectinatum ; 16, epithelium of the
membrane of Descemet ; 17, union of the sclerotic coat with the cornea ; 18, section of the canal of
Schlemm.

tion, which is its anterior border. It becomes thinner from before backward,
until its posterior border apparently fuses with the fibrous structure of the
choroid. It is semi-transparent and of a grayish color. Its situation is just
outside of the ciliary processes, these processes projecting in front of its
anterior border, about ^ of an inch (1 mm.). 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 ligamentum iridis pecti-
natum. 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 longitudinal fibres. Some of these fibres have an
oblique direction.

The ciliary muscle is composed mainly of muscular fibres. These fibres,
anatomically considered, belong to the non-striated variety. They are pale,
present a number of oval, longitudinal nuclei, and have no striae.

ANATOMY OF THE EYEBALL. 679

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 scle-
rotic and cornea and the circumference of the choroid, compressing the vitre-
ous humor and relaxing the suspensory ligament of the crystalline lens. This
action enables the lens to change its form, and 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. It
is a circular membrane, situated just in front of the crystalline lens, with a
round perforation, the pupil, near its centre.

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 backward to be inserted into the choroid, and the former pass-
ing directly over the crystalline lens. The diameter of the iris is about half
an inch (12-5 mm.). The pupil is subject to considerable variations in size.
When at its medium of dilatation, the diameter of the pupil is -j- to -j- of an
inch (3-2 to 4-2 mm.). The pupillary orifice is not in the mathematical cen-
tre 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 differ-
ent 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 prop-
erty of the crystalline lens, called fluorescence, which enables an observer , 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 chamber is very small and exists only near the margins of the lens
and the iris.

The color of the iris is 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 membrane of the aqueous humor. At the great circumference, it
presents little, fibrous prolongations, forming a delicate, dentated membrane,
called the ligamentum iridis pectinatum. The membrane covering the gen-
eral anterior surface of the iris is extremely thin and is covered by cells of
tessellated epithelium. Just beneath this membrane are a number of irregu
larly shaped, pigmentary cells.

The posterior layer of the iris is very thin, easily detached from the middle
layer, and contains a number of small cells rich in pigmentary granules.
Some anatomists recognize this membrane only as the uvea.

The middle layer constitutes by far the greatest part of the substance of

680 SPECIAL SENSES.

the iris. It is composed of connective tissue, muscular fibres of the non-
striated variety, many blood-vessels, and probably nerve-terminations. Di-
rectly surrounding the pupil, forming a band about -^ of an inch (0-5 mm.)
in width, is a layer of non-striated muscular fibres, called the sphincter of the
iris. The existence of these fibres is admitted by all anatomists. It is differ-
ent, however, for the radiating muscular fibres. Most anatomists describe,
in addition to the sphincter, non-striated fibres, which can be traced from
near the great circumference of the iris almost to its pupillary border, ly-
ing both in front of and behind the circular fibres. 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 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 ves-
sels 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 membrane 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 transparent, 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 atro-
phies, and 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 pro-
longations from the nerve-cells. 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 a delicate, trans-
parent membrane covering the posterior portion of the vitreous humor. A
short time after death it becomes slightly opaline. It extends over the pos-

ANATOMY OF THE RETINA. 681

terior portion of the eyeball, to a distance of about -^ of an inch (1/7 mm.)
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 TJ-g- of an inch (200 //,). It
becomes thinner nearer the anterior margin, where it measures only about -g-j-^
of an inch (80 //,). Its external surface is in contact with the choroid, and
its internal, with the hyaloid membrane of the vitreous humor.

The optic nerve penetrates the retina about -J of an inch (3*2 mm.) within
and ^ of an inch (2'1 mm.) below the antero-posterior axis of the globe,
presenting at this point a small, rounded elevation upon the internal sur-
face of the membrane, perforated in its centre for the passage of the central
artery of the retina. At a point ^ to -J of an inch (2'1 to 3 '2 mm.) external
to the point of penetration of the nerve, is an elliptic spot, its long diameter
being horizontal, about -J of an inch (2-1 mm.) long and -fa of an inch (0-7
mm.) 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 de-
pression 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 im-
portance 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 is known,
except the pigment cells, that are directly concerned in the reception of
optical impressions, and they will be described rather minutely, while the
intermediate layers will be considered more briefly.

Most anatomists recognize nine layers in the retina :

1. Layer of pigment-cells (already described in connection with the
choroid).

2. Jacob's membrane, the bacillar membrane, or the layer of rods and
cones.

3. The external granule-layer.

4. The inter-granule layer (cone-fibre plexus of Hulke).

5. The internal granule-layer.

6. The granular layer.

7. The layer of nerve-cells (ganglion-layer).

8. The expansion of the fibres of the optic nerve. •

9. 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 sur-
face a regular, mosaic appearance ; and between these, are a greater or less
number of flask-shaped bodies, the cones. This layer is about -§%-$ of an inch
(76 /A) in thickness at the middle of the retina ; -ffa of an inch (62 /A), about
midway between the centre and the periphery; and near the periphery,
about ^^ of an inch (55 /*). At the macula lutea the rods are wanting, and
the layer is composed entirely of cones, which are here very much elongated.

SPECIAL SENSES.

Over the rest of the membrane the rods predominate, and the cones be-
come less and less frequent toward the periphery.

The rods are regular cylinders, their length corresponding to the thick-
ness of the layer, terminating above in truncated extremities, and below in
points which are probably continuous with the filaments of connection with
the nerve-cells. Their diameter is about ls}00 of an inch (2 /*). They

are clear, of rather a fatty lustre, soft and plia-
ble, but somewhat brittle, and so alterable that
they are with difficulty seen in a natural state.
They should be examined in perfectly fresh prep-
arations, moistened with liquid from the vitreous
humor or with serum. 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 extrem-
ity of the inner segment, is a hemispherical body,
with its convexity presenting inward, called the
lentiform body (linsenformiger Korper). The
entire inner segment is somewhat granular, and
it often presents a granular nucleus at its inner
extremity. The outer segment apparently differs
B. Rods from the frog : i. Fresh, in its constitution from the inner segment and

magnified 500 diameters ; a, in- . ., , „„ . , , „,

ner segment ; b, outer segment ; is not similarly affected by reagents. Treated

c, lentiform body; d, nucleus. • ,-, 1M , ,. . n ,, . ,

2. Treated with dilute acetic acid witn dilute acetic acid, the outer segment be-
comes broken up transversely into thin disks.

The cones are probably of the same constitution as the rods, but that
portion called the inner segment is pyriform. 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 constitution 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. 247,
which shows the different layers of the retina.

At the fovea centralis, Jacob's membrane is composed entirely of elon-
gated 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 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) re-
main, in the fovea, while the internal granule-layer and the granular layer are
wanting. At the fovea, indeed, those elements of the retina which may be

FIG. 246.— Rods of the retina

(Schultze).

From the monkey.— A. Rods, after
maceration in iodized serum, the
outer segment (6) truncated, the
inner segment (a) coagulated,
granular, and somewhat swol-
len ; c, filament of the rods ; d,
nucleus.

ANATOMY OF THE RETINA.

683

regarded as purely accessory 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 yy^nr to 60*00 of an inch (2 to 4 /*) in diameter. The
inter-granule layer (cone-fibre plexus) is composed apparently of minute
fibrillee 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 prob-

Fio. 247.— Vertical section of the retina FIG. 248.— Connection of the rods and cones
(H. Miiller). of the retina with the nervous elements

(Sappey).

FIG. 247.— 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 ; 13, membrana limitans. (The pig-
mentary layer is not shown in this figure.)

FIG. 248.— 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 con-
nected 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, 23, 24, 25, 26, a rod and a cone, con-
nected with the cells of the granule-layers, with the nerve-cells and with the nerve-fibres.

ably connected with the filaments of the rods and cones. The granular
layer is situated next the layer of ganglion-cells.

The layer of ganglion-cells is composed of multipolar nerve-cells, measuring
TcW to -rfa of an inch (8 to 32 /A) in 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 cen-

684 SPECIAL SENSES.

tre, and the larger, near the periphery. Each cell sends off several fila-
ments (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, ^J-oij- to s^imr of an incn (0'5 to 1 p) in
diameter. These do not require special description.

The limitary membrane is a delicate structure, with fine striae and nuclei,
composed of connective- tissue elements. It is about ggio0 of an inch (1 /x.)
in thickness. From this membrane, connective-tissue elements are sent into
the various layers of the retina, where they form a framework for the sup-
port of the other structures.

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.

The following is the probable mode of connection between the rods and
cones and the ganglion-cells : The filaments from the bases of the rods and
cones pass inward, presenting in their course the corpuscles which have
been described in the granule-layers, and finally become, as is thought,
directly continuous with the poles of the ganglion-cells. The cells 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.
248.

The following description of the blood-vessels of the retina, with Fig.
249, was furnished by Loring :

" 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 membrane. The vessels lie so superficially
that in a cross-section examined with the microscope, they are seen to pro-
ject 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 appear-
ance 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. 249 than by any detailed description.
The figure represents the ophthalmoscopic appearance 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 vascular twigs which, coming from above and below, extend
toward the spot in the centre of the oval which marks the position of the
fovea centralis. In opposition, then, to the general opinion, which is that

CRYSTALLINE LENS. 685

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 dis-
tinctly seen even
with the ophthal-
moscope ; and mi-
croscopical exam-
ination shows that
the capillary plex-
us in the macula
lutea is closer and
richer than in any
other part of the
retina."

The arteries of
the retina send
branches to the
periphery, where
they supply a wide
plexus of very
small capillaries in
the ora serrata-
These capillaries

empty into an in- FIQ 24$.-Blood-vessels of the retina ; magnified TJ diameters (Loring).

complete venous

circle, branches from which pass back by the sides of the arteries, to the vena

centralis.

Crystalline Lens. — The crystalline is a double-convex lens, which is per-
fectly transparent and very elastic. Its action in the refraction of the rays
of light is analogous to that of convex lenses in optical instruments. It is
situated behind the pupil, in what is called the hyaloid fossa of the vitreous
humor, which is exactly moulded to its posterior convexity. In the foetus
the capsule 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 (8*5 mm.) transversely and £ of an inch (6*4 mm.)
antero-posteriorly. The convexity is greater on its posterior than on its
anterior surface. In fretal life the convexities of the lens are 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.

45

686

SPECIAL SENSES.

The capsule of the lens is a thin, transparent membrane, which is very
elastic. This membrane generally is from

FIG. 250.— Crystalline lens ; anterior view (Babuchin).

to -3-^ of an inch (10 to
17 /M.) thick ; but it is very
thin at the periphery, meas-
uring here only ^5^5- of an
inch (4 /A). Its thickness is
increased in old age. The
anterior portion of the cap-
sule is lined on its inner sur-
face with a layer of exceed-
ingly delicate, nucleated epi-
thelial cells. The posterior
half of the capsule has no
epithelial lining. The cells
are regularly polygonal,,
measuring -^V?r to y^- of
an inch (12 to 20 /u) in di-
ameter, 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 supposed 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
its surfaces, a star with nine to sixteen radi-
ations extending from the centre to about
half or two-thirds of the distance to the pe-
riphery. 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 homogeneous
substance, which extends, also, between the
fibres.

The greatest part of the substance of the
lens is composed of very delicate, soft and plia-
ble fibres, which are transparent, but perfect-
ly distinct. These fibres are flattened, six-

sided prisms, Closely packed together, SO that

their transverse section presents a regularly

tesselated appearance. They are -^^ to ^-gW of an incn (5 to 10 /*) broad,
and y^fjj-g- to ^Vrr of an mcn (2 to 3 /*) in thickness. Their flat surfaces are
parallel with the surface of the lens. The direction of the fibres is from

. CRYSTALLINE LENS. 687

the centre and from the *rays of the stellate 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, contain exceedingly
distinct, oval nuclei, with one or two nucleoli. These become smaller in
passing more deeply into the substance of the lens, and gradually they dis-
appear.

The regular arrangement of the fibres of the lens makes it possible to
separate its substance into laminae, 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 nitrogenized substance, called crystalline, com-
bined with various inorganic salts. One of the constant constituents of this
body is cholesterine. In an examination of four fresh
crystalline lenses of the ox, cholesterine was found in the
proportion of 0-907 of a part per 1,000 (Flint). In some
cases of cataract cholesterine exists in the lens in a crys-
talline form ; but under normal conditions it is united
with the other constituents.

Suspensory Ligament of the Lens (Zone of Zinri). —
The vitreous humor occupies about the posterior two- FIG. 252.— zone
thirds of the globe, and is enveloped in a delicate capsule, lt crystamneTiens
called the hyaloid membrane. In the region of 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 an- ggjf of the zone of
terior 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 pos-
terior 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 corrugated portion
is called the zone of Zinn. The two layers thus surround the lens and are
properly called its suspensory ligament. As the two layers of the suspensory
ligament separate at a certain distance from the lens, one passing to the ante-
rior and the other to the posterior portion of the capsule, there remains a
triangular canal, about -^ of an inch (2-5 mm.) 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.

The membrane forming the suspensory ligament is composed of pale, lon-
gitudinal 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,

688 SPECIAL SENSES.

by the crystalline lens and the anterior face of its ' suspensory ligament, and
at its circumference, by the tips of the ciliary processes, is known as the aque-
ous 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 between 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 posi-
tion 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 periphery or when the iris is very much
dilated. The liquid filling the chambers of the eye 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 with the same index of refraction as that
of 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 small proportions in this liquid. It also
contains traces of urea and glucose.

The anterior and posterior chambers of the eye are regarded as lymph-
spaces communicating with the lymphatics of the conjunctiva, cornea, iris
and ciliary processes. In addition a lymph-space is described as existing be-
tween the choroid and the sclerotic. This space is supposed to communicate
with a perivascular canal-system around the vasa vorticosa, and through these
vessels, with the space between the capsule of Tenon and the sclerotic
(Schwalbe). The latter is connected with lymph-channels which surround
the optic nerve (Key and Eetzius).

Vitreous Humor. — The vitreous humor is a clear, glassy substance, occupy-
ing about the posterior two-thirds of the globe. It is enveloped in a delicate,
structureless capsule, called the hyaloid membrane, which is about -g-^Vo" of
an inch '(4 /u,) in thickness. This membrane adheres rather strongly to the
limitary membrane of the retina. In front, at the ora serrata, the hyaloid
membrane is thickened and becomes continuous with the suspensory ligament
of the lens.

The vitreous humor itself is gelatinous, of feeble consistence and slightly
alkaline in its reaction, with a specific gravity of about 1005. Upon section
there oozes from it a watery and slightly mucilaginous liquid. This humor
is not affected by heat or alcohol, but it is coagulated by certain mineral
salts, especially lead acetate. 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 a number of 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 adult, the vitreous humor being then entirely without blood-

SUMMARY OF THE ANATOMY OF THE EYE.

689

The vitreous humor is divided into compartments formed by deli-
cate 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, something like
the half of an orange, by about one hundred and eighty membranous pro-
cesses of extreme delicacy, which do not interfere with its transparency.

SUMMARY OF THE ANATOMY OF THE GLOBE OF THE EYE.

This summary is intended simply to indicate the relations and the physio-
logical importance of the various parts of the eye, in connection with Fig.
253.

The eyeball is nearly spherical in its posterior five-sixths, its anterior sixth

— SUPERIOR RECTUS

CILIARY PROCESSES

SUSPENSORY LIGAMENT

SUSPENSORY LIGAMENT

CILIARY PROCESSES

CHOROID

OPTIC NEflVE
CHOROID

-INFERIOR RECTUS
FIG. 253.— Section of the human eye.

being formed of the segment of a smaller sphere, which is slightly projecting.
It presents the following parts, indicated in the figure.

The sclerotic ; a dense, fibrous membrane, chiefly for the protection of
the more delicate structures of the globe, and giving attachment to the mus-
cles which move the eyeball. Attached to the sclerotic are the tendons of
the recti and the oblique muscles.

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 epi-
thelial cells.

The choroid coat ; lining the sclerotic and extending only as far forward

690 SPECIAL SENSES.

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.

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.

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 ciliary 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.

The iris ; dividing the space in front of the lens into two chambers occu-
pied by the aqueous humor. The anterior chamber is much the larger.
The iris, in its central portion surrounding the pupil, is in contact with the
lens. Its circumference is just in front of the line of origin of the ciliary
muscle.

The retina ; a delicate, transparent membrane, lining the choroid and ex-
tending to about ^ of an inch (1*7 mm.) behind the ciliary processes, the
anterior margin forming the ora serrata. The optic nerve penetrates the
retina a little internal to and below the antero-posterior axis of the globe.
The layer of rods and cones is situated next the pigmentary layer, which is
external. Internal to the layer of rods and cones, are the four granular lay-
ers ; 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 vitre-
ous humor, is the limitary membrane.

The crystalline lens; elastic, transparent, enveloped in its capsule and
surrounded by the suspensory ligament.

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 be-
tween the folds of the ciliary processes, is called the zone of Zinn. The tri-
angular canal between the anterior and the posterior layers of the suspen-
sory ligament and surrounding the equator of the lens is called the canal of
Petit.

The vitreous humor ; enveloped in the hyaloid membrane, which mem-
brane is continuous in front, with the suspensory ligament of the lens.

REFRACTION IN THE EYE.

In applying some of the elementary laws of 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 a perfect optical instrument, looking at it from a purely

REFRACTION IN THE EYE. 691

physical point of view. This statement, however, should not be understood
as implying that the arrangement of the parts is not such aa to adapt them
perfectly to their uses 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.

The refracting apparatus is not exactly centred, a condition so essential
to the satisfactory performance of perfect optical instruments. For example,
in a compound microscope or a telescope, the centres of the different 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 exactly with the axis of the cornea ; but this is not the case. The
visual line — a line 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 mathe-
matical centre of the eye is observed both in the horizontal and in the verti-
cal planes. The horizontal deviation varies by two to eight degrees (Schuer-
man), and the vertical, by one to three degrees (Mandelstamm). Of course
this want of exact centring of the optical apparatus, in normal eyes, does
not practically affect distinct 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 mathemati-
cal calculations connected with the physics of the eye.

The area of distinct vision is quite restricted ; but were it larger, it is
probable that the mind would become confused by the extent and variety of
the impressions, and that it would not be so easy to observe minute details
and fix the attention upon small objects.

Although certain objects are seen with absolute distinctness only in a re-
stricted field, the angle of vision is very wide, and rays of light are admitted
from an area equal to nearly the half of a sphere. Such a provision is emi-
nently adapted to visual requirements. The eyes are directed to a particular
point and a certain object is seen distinctly, with the advantage of an image
in the two eyes, exactly at the points of distinct vision ; the rays coming 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 atten-
tion is for the moment directed ; but even while looking intently at any ob-
ject, the attention may be attracted 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 but few objects are seen
distinctly at one time, the area of indistinct vision is very large ; and the at-
tention may readily be directed to unexpected or unusual objects that come
within any portion of the field of view. The small extent of the area of dis-

692 SPECIAL SENSES.

tinct vision, especially for near objects, may readily be appreciated in watch-
ing a person who is 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 regular-
ity. When it is considered that in addition to these qualities, which are not
possible in artificial optical instruments, the eye may be accommodated at
will to vision at different distances, and that there is correct appreciation of
form, etc., by the use of the two eyes, it is evident that the visual organ gains
rather than loses in comparison with the most perfect instruments that have
been constructed.

Certain Laws of Refraction, Dispersion etc., bearing upon the Physiology
of Vision. — Physiologists have little to do with the theory of light, except as
regards the modifications of luminous rays in passing through the refracting
media of the eye. It will be sufficient to state that nearly all physicists of
the present day agree in accepting what is known as the theory of undula-
tion, rejecting the emission-theory proposed by Newton. It is necessary to
the theory of undulation 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 the mechanism of its propagation ;,
but in sound the waves are supposed to be longitudinal, or to follow the line
of propagation, while in light the particles are supposed to vibrate trans-
versely, or at right angles to the line of propagation. It must be remem-
bered, however, that the undulatory theory of sound is capable of positive
demonstration, and that the propagation of sound by waves can take place
only through ponderable matter, the vibrations of which can always be ob-
served ; but the theory of luminous vibrations involves the existence of an
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 the theory of luminous undulation seems to
be 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 (297,725 kilometres) in a second, and the highest,
at about 195,000 miles (313,818 kilometres). The rate of propagation is
usually assumed to be about 192,000 miles (309,000 kilometres).

The intensity of light is in proportion to the amplitude of the vibrations.
The intensity 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 decom-
posed by prisms, it is assumed to be 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 medium denser than the
air.

The analysis of white light into the different colors of the spectrum shows

REFRACTION IN THE EYE. 693

that it is compound ; and by synthesis, the colored rays may be brought to-
gether, 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 re-
flecting the rays of light. A perfectly smooth, polished surface, like a mir-
ror, may reflect all of the rays ; and the object then has no color, only the re-
flected light 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.

A mixture of different colors in certain proportions will result in white.
Two colors, which, when mixed, result in white, are called complementary.
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 affords an illustration of the law of complementary colors. If
a disk, presenting divisions with two complementary colors, be made to
revolve so rapidly that the impressions made by the two colors are blended,
the resulting color is white.

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 supposed to consist of an infinite number of such rays. In
studying the physiology of vision, it is important to recognize the laws of re-
fraction of rays by transparent bodies bounded by curved surfaces, with par-
ticular reference to the action of the crystalline lens.

The action of a double-convex lens, like the crystalline, in the refraction
of light, may readily be understood by a simple application of the well known
laws of refraction by 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 prism to the air, it is again refracted, but the de-
viation is then from the perpendicular of the second surface of the prism.
In passing through a prism, therefore, the pencil of light is bent, or refracted,
toward the base.

A circle is equivalent to a polygon with an infinite number of sides. A
regular, double-convex lens is a transparent body bounded by segments of a
sphere. Theoretically a double-convex lens may be assumed to be composed
of an infinite number of sections of prisms .(Fig. 254, 1.), or to make the com-

694

SPECIAL SENSES.

parison with prisms more striking, although less accurate, the lens may be
assumed to be composed of prisms (Fig. 254, II., Weinhold).

If these prisms or sections of prisms be infinitely small, so that the sur-
face of each receives but a single infinitely small pencil of light, these pencils
will be refracted toward the bases of the prisms, and different rays of light
from all points of an object may be brought to an infinite number of foci, all
these foci, for a plane object, being in the same plane. If the number of
sections be equal on every side of the centre of the lens, the bases looking
toward the axis of the lens, the rays of light will cross at a certain point, and
the image formed by the lens will be inverted. This is illustrated in Fig.

II

FIG. 254.— Refraction by convex lenses.

254, which represents a section of a lens theoretically dissected into six sec-
tions of prisms. fc

If the lens A B (Fig. 254) be assumed to be free from what is known as
spherical aberration, the rays from the point 0 will be refracted, and brought
to a focus at the point D. In the same way the rays from E will be brought
to a focus at F, the two sets of rays crossing before they reach their focal
points. The same is true for all the rays from every point in the image C E,
which strike the lens at an angle, but the ray Gr H, which is perpendicular to
the lens, is not deviated. The rays of light are refracted in this way by the
cornea and by the crystalline lens. The retina is normally at such a distance
from the lens that the rays are brought to a focus exactly at its surface. In-
asmuch as the rays cross each other before they reach the retina, 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 con-
ditions :

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 F II D, or behind the retina ; and as a conse-
quence the image is confused. In optical instruments the adjustment is
made for objects at different distances by moving the lens itself. In the eye,

REFRACTION IN THE EYE. 695

however, the adjustment is effected by increasing or diminishing the curva-
tures 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
crystalline lens is called accommodation. This power, however, is restricted
within certain well denned 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 remedied for distant ob-
jects, 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 (hyper metropia), is such that the rays
are brought to a focus behind the retina. This is corrected by converging
the rays of incidence, by placing 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 presbyopia. 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
hypermetropia, 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 " indolent." It is only
when an effort is made to see near objects distinctly, that the agents of ac-
commodation 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, Monochromatic Aberration. — In a convex lens in which the
surfaces are segments of a 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 the crystalline lens had regular curva-
tures, the rays refracted by its peripheral 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. It is also called monochromatic aberration, because it
is to be distinguished from an aberration which involves decomposition of
light into the colors of the spectrum. If an object be examined under the
microscope with an imperfectly corrected objective, 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

696 SPECIAL SENSES.

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 portion of the lens, near its centre. The iris corresponds to the
diaphragm of optical instruments, and it corrects the spherical aberration of
the crystalline in part, by eliminating a portion of the rays that would other-
wise fall upon its peripheral portion. This correction, however, is not suffi-
cient for 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 light is pre-
cisely opposite to the aberration of converging lenses. In a compound lens,
therefore, it is possible to fulfill the conditions necessary to the convergence
of all the incident rays to a focus on a uniform plane, so that the image pro-
duced 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 points are in the
plane of the retina renders the image indistinct. If a concave or a plano-
concave lens be placed in front of this convex lens, which will diverge the
rays more or less, the inequality 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 periphery, the rays near the
periphery, which are most powerfully converged by the convex 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. It is evident that if all the rays were equally converged by the con-
vex lens and equally 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 opposite to the aberration of the other,
there will be perfect correction. Mechanical art has not effected correction
of every portion of very powerful convex lenses in this way ; but by a com-
bination of lenses and diaphragms together, highly magnified images, nearly
perfect, have been produced. Lenses in which spherical aberration has been
corrected are called aplanatic.

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 curva-
tures of the lens itself, and by certain differences in the consistence of differ-
ent portions of the lens, which will be fully considered hereafter.

Chromatic Aberration. — A refracting medium does not act equally upon
the different colored rays into which pure white light may be decom-
posed ; 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.

REFRACTION IN THE EYE. 697

A

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 com-
posed 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 dis-
tinct, and an image produced by a simple convex lens will thus be surrounded
by a circle of colors, like a rainbow.

In prisms the chromatic dispersion may be corrected by allowing the
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 constitute, 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 ; and in the concave lens the colored
rays are diverged in the opposite direction. If, then, a convex be combined
with a concave lens, the white light decomposed by the one will be recom-
posed 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 con-
vergence by the one will be neutralized by the divergence of the other, and
there will be no amplification of the object. Newton supposed that dis-
persion, or decomposition of light, by lenses was always in exact proportion
to refraction, so that it would be impossible to correct chromatic aberration and
retain magnifying power ; but it has been ascertained that there are great
differences in the dispersive power of different kinds of glass, without corre-
sponding differences in refraction. This discovery rendered it possible to con-
struct achromatic lenses (Dollond, 1757). According to Ganot, Hall was the
first to make achromatic lenses, in 1753, but his discovery was not published.
In the construction of modern optical instruments, the chromatic aberra-
tion is corrected, with a certain diminution in the amplification, by cement-
ing together 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, a convex lens of crown-glass be combined with a 'concave or plano-
concave lens of flint-glass, the chromatic aberration of the convex lens may

be corrected by a concave lens with a curvature
which will reduce the magnifying power about
one-half. A compound lens, with the spherical
aberration of the convex element corrected by the

FLINT GLASS 111'

FIG. 255.— Achromatic lens. curvature of a concave lens, and the chromatic
aberration corrected in part by the curvature, 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 ; but the chromatic aberration
is practically corrected in the crystalline lens, probably by differences in the
consistence and in the refractive power of its different layers.

698 SPECIAL SENSES.

FORMATION OF IMAGES IN THE EYE.

It is necessary only to call to mind the general arrangement of the differ-
ent structures in the eye and to apply the simple laws of refraction, in order
to comprehend precisely how images are formed upon the retina.

The eye corresponds to a camera obscura. Its interior is lined with a
dark, pigmentary membrane (the choroid), the immediate action 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 quantity of light is
diminished. In the accommodation of the eye, the pupil is dilated for dis-
tant objects and contracted 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 dia-
phragm, 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 aberra-
tion, 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 impressions of light being conveyed to the brain
by the optic nerves. This layer is situated next the pigmentary layer of
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 shown that the rods and cones are the only structures capa-
ble of directly receiving visual impressions, by the following experiment,
first made by Purkinje : With a convex lens of short focus, an intense light
is concentrated on the sclerotic, 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. In then looking at a
dark surface, the field of vision presents a reddish-yellow illumination, with
a dark, arborescent appearance produced by the shadows of the large retinal
vessels ; and as the lens is moved slightly, the shadows of the vessels move
with it. Without going elaborately into the mechanism of this phenomenon,
it is sufficient to state that Heinrich Miiller has arrived at a mathematical
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 explanation is generally accepted and is regarded as positive
proof of the peculiar sensibility of this portion of the retina.

Theoretically, an illuminated object placed in the angle of vision would
form upon the retina an image, diminished in size and inverted. This fact
is capable of demonstration by means of the ophthalmoscope ; as with this
instrument the retina and the images formed upon it may be seen during life.

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.

FORMATION OF IMAGES IN THE EYE. 699

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 opposite border of the retina. 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, the 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. One has 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 it is desired 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 fact, with what is
known 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, it is necessary
to bring the axis of the eye to bear upon it directly.

In examining the bottom of the eye with the ophthalmoscope, the yellow
spot, with the fovea centralis, can be seen, free from large blood-vessels, and
composed chiefly of those elements of the retina which are sensitive to light.
If at the same time, an image for which the eye is perfectly adjusted be ob-
served, 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, there is 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 Helmholtz, " It is only in
the immediate vicinity of the ocular axis that the retinal image possesses
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 dis-
tinctness in indirect vision, in addition, depends also upon diminished sensi-
bility of the retina : at a slight distance from the fixed point, the distinct-
ness 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 ; or at least, its sensibility is here so obtuse as to be
entirely inadequate for the purposes of vision. This point is called the punc-
tum caecum ; and its want of sensibility was demonstrated many years" ago
(1668) by Mariotte. The classical experiment by which this important fact
was ascertained is generally known as Mariotte's experiment. The following
account is quoted 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 OpticJc

700 SPECIAL SENSES.

Nerve of my Eight 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
Eight Eye fixt and very steddy upon the same ; and being about 10. foot
distant, the second paper totally disappear'd."

In this experiment the i,;ays of light from the paper which has disap-
peared from view are received upon the punctum caecum, 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
•caecum. With the ophthalmoscope, the point of penetration of the optic
nerve may readily be 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 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 distance between the sensitive elements of the retina
at which he supposed that two parallel lines would appear as one. In the
axis of vision, the distance was 0-00029 inch (7*366 /x), and at a deviation in-
ward of 8°, it was 0-03186 inch (809-244 /*), a diminution of acuteness of
more than a hundred times.

Visual Purple and Visual Yellow, and Accommodation of the Eye for
Different Degrees of Illumination. — The outer segments of the rods of the
retina sometimes present a peculiar red or purple color, which disappears
after ten or twelve seconds of exposure to light. This was first observed by
Boll (1876) in the retinae of frogs that had been kept for a certain time in
the dark. From his preliminary researches, Boll concluded that this colora-
tion of the retina exists only during life and persists but a few moments after
death ; that it is constantly 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. Kuhne and others have since confirmed and extended the original
observations of Boll ; and the visual purple (rhodopsine) has been noted in
the mammalia and in man. It has been extracted from the retinae of frogs
and dissolved in a five-per-cent. solution of crystallized ox-gall, still present-
ing in solution its remarkable sensitiveness to light (Ayres). 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.

The visual purple is produced by the cells of the pigmentary layer of the
retina and from them is absorbed by the outer segments of the rods. It is
not present in any part of the cones and does not exist, therefore, in the area
of distinct vision, at the fovea centralis. The rapid disappearance of the
oolor under the influence of actinic rays of light renders it necessary to ex-
amine the retina under a non-actinic (monochromatic) sodium-flame (Ayres).
When thus examined and gradually exposed to actinic rays, the color quickly
iades into a yellow and finally disappears, being restored, however, in the dark.

VISUAL PURPLE AND VISUAL YELLOW. 701

If the choroid and the pigmentary layer of the retina be removed, the rods
are bleached, and the color is restored in the dark when the choroid is re-
placed. In the eye of the frog, kept in the dark, the hair-like processes
which extend from the pigmentary layer of the retina downward between the
rods and cones are retracted, and the pigment is then contained chiefly in the
cells themselves. After prolonged exposure of the retina to light, these pro-
cesses, loaded with pigment, extend between the cones as far as the limitary
membrane (Kiihne).

The fact that visual purple has never been found in the fovea centralis is
opposed to the theory that its existence is directly essential to distinct vision ;
nevertheless, certain phenomena observed in passing from a bright light to
comparative obscurity, and the reverse, show that the purple has, at least, an
important indirect action. In passing from the dark to bright light, the eye
is dazzled and distinct vision is difficult. It may be assumed that this is due
to unusual general sensitiveness of the retina to light, on account of the ex-
cessive quantity of visual purple which has accumulated in the dark, and
that distinct vision is restored when the retina is bleached to a yellow, which
seems to be the most favorable condition for the exact appreciation of visual
impressions, under full illumination. On the other hand, it requires time for
the eye to become accustomed to a dim light ; and during this time the yel-
low is changing to purple. These changes in the color of the retina have
been actually observed (Ayres). Investigations of the absorption-spectra of
the purple and yellow have shown that the purple allows the actinic rays to
pass perfectly, while the yellow completely absorbs these rays (Kuhne). The
existence of visual purple seems to be most favorable to the imperfect and
shadowy vision which occurs under dim illumination, when the exact appre-
ciation of minute details is impossible. In the condition known as night-
blindness, it is probable that the visual purple has become exhausted beyond
the possibility of prompt restoration such as is normal ; and persons so affected
can not see at night, although minute vision under a bright light may not be
affected. In certain cases of this kind, the normal conditions may be re-
stored by a few days' seclusion in the dark. What is called functional night-
blindness frequently occurs in sailors during long, tropical voyages, and is
due to the excessive action of diffused light upon the retina. " That the
affection is local, is shown by the fact that darkening one eye, with a band-
age, during the day, has been found to restore its sight enough for the ensuing
night's watch on board ship, the unprotected eye remaining as bad as ever "
(Nettleship).

The change of the- visual purple to yellow is readily effected, but the
farther change to white is slower and more difficult. Conversely, the change
from white to yellow is slow and the change from yellow to purple is com-
paratively prompt. One use of the colors purple and yellow seems to be to
accommodate the retina for vision under different degrees of illumination.
The purple adapts the eye to a feeble illumination, and the yellow, to a full
illumination. This being the case, it is manifestly proper to speak of a
visual yellow (Kiihne) as well as of visual purple.
46

T02 SPECIAL SENSES.

That the accommodation of the eye to different degrees of illumination is
due to the changes in the colors produced by the pigmentary layer of the
retina and not to different degrees of dilatation of the pupil, is shown by the
fact that a person does not see better in the dark when the pupil has been
dilated by atropine (Loring). In a very dim light there is no possibility of
exact accommodation for near objects, which, when small, can not be seen
distinctly ; and the contraction of the pupil which attends accommodation
for near vision does not occur. It is possible that under dim illumination,
parts outside of the fovea, which are insensible to vision under a bright light,
receive visual impressions. Under these conditions the pupil is dilated
and rays impinge on portions of the retina not used in direct vision. A
natural extension of this idea would confine distinct vision and the apprecia-
tion of minute details to the action of the fovea centralis, in which there is
no visual purple, other parts of the retina, under full illumination, not being
used. To express this in a few words, the fovea centralis is used by day, and
the adjacent parts of the retina, by night.

MECHANISM OF REFKACTION IN THE EYE.

An object that is seen reflects rays from every point of its surface, to the
cornea. If the object be near, the rays from each and every point are diver-
gent 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, it may be stated
simply that the important agents in refraction in the eye are the surfaces
of the cornea and the crystalline lens. Calculations have shown that the
index of refraction of the aqueous humor is sensibly the same as that of
the substance of the cornea, so that practically the refraction is the same
as if the cornea and the aqueous humor were one and the same substance.
The index of refraction of the vitreous humor is practically the same as
that of the aqueous humor, both being about equal to the index of refrac-
tion 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 por-
tions of its substance. In view of these facts, the conditions of refraction
in the eye in distinct vision may be simplified by assuming the following
arrangement :

The cornea presents a convex surface upon which the rays of light are
received. 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 chromatic aberration. This lens is practically suspended in a
liquid with an index of refraction equal to that of pure water, as both the
aqueous humor in front and the vitreous humor behind have the same refract-
ive power. Behind the lens, in its axis and exactly in the plane upon which
the rays of light are brought to a focus by the action of the cornea and the

MECHANISM OF EEFEACTION IN THE EYE. 703

lens, is the fovea centralis, which is the centre of distinct vision. . The an-
atomical elements of the fovea are capable of receiving visual impressions,
which are conveyed to the brain by the optic nerves. All impressions made
upon other portions of the retina are comparatively indistinct ; and the point
of entrance of the optic nerve is insensible to light. Inasmuch as the punc-
tum caecum is situated in either eye upon the nasal side of the retina, in nor-
mal vision, rays from the same object can not fall upon both blind 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 pre-
vent any notable interference in vision, even with one eye. The sclerotic
coat is for the protection of its contents and for the insertion 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 cili-
ary muscle, are for the fixation of the lens and its accommodation for distinct
vision at different distances. The choroid is a dark membrane, for the ab-
sorption 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 -^ of an inch (10 mm.) behind the
retina. Without the crystalline lens, therefore, distinct, unaided vision gen-
erally is impossible, although the sensation of light is appreciated. In cases
of extraction of the lens for cataract (aphakia), 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 refraction, dependent upon the differences
in the various strata of the lens. These modifications have not been accu-
rately 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 point 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 inverted.

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 formulae, 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 these calculations are not
very important in a purely physiological consideration of the sense of sight.

In most calculations of the size of images, the positions of conjugate foci,
etc., in normal and abnormal eyesv a schematic eye reduced by Donders, after

704 SPECIAL SENSES.

the example of Listing, is regarded as sufficiently exact for all practical pur-
poses. This simple scheme represents the eye as reduced to a single refract-
ing surface, the cornea, and a single liquid assumed to have an index of re-
fraction 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 sys-
tem of the eye is so small, amounting to hardly -^ of an inch (0-254 mm.),
that it can be neglected. In this simple eye, there is assumed to be a radius
of curvature of the cornea of about -J- of an inch (5 mm.) and a single optical
centre situated \ of an inch (5 mm.) back of the cornea, the " principal
point " being in the cornea, in the axis of vision. The posterior focal dis-
tance, that is, the focus, at the bottom of the eye, for rays that are parallel in
the air, is about f of an inch (20 mm.). The anterior focal distance, that is,
for rays parallel in the vitreous humor, is about f of an inch (15 mm.). The
measurements in this simple schematic eye can easily be remembered and
used in calculations.

ASTIGMATISM.

In the normal human eye the visual line does not coincide exactly with
the mathematical axis ; but there is still another normal deviation from
mathematical exactness in the refraction of rays by the cornea and the crys-
talline lens, which is of considerable importance. If two threads, crossing
each other at right angles in the same plane, be placed before the eyes, 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 denned. In other words, when the eye is accommodated
for the vertical thread, the horizontal thread is indistinct, and vice versa. If
the horizontal line be seen distinctly, in order to see the vertical line 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 accommodation, a certain difference in 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 dis-
tinct 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 Donders, if the astigmatism amount to -fa or more, it is to be
considered abnormal ; which simply means that beyond this point the aber-
ration interferes with distinct vision.

From the simple definition of regular astigmatism, it is evident that this

MOVEMENTS OF THE IRIS. 705

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 curva-
ture. Indeed, the curvature of a cylindrical glass which will enable a person
to distinguish vertical and horizontal lines with perfect distinctness at the
same time, is an exact indication of the degree of aberration. Regular
astigmatism, such as just described, may be so exaggerated as to interfere
very seriously with vision, when it becomes abnormal. This kind of aberra-
tion, 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, there are irregular variations in the curva-
tures 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 irregu-
larly 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 a card with a very small opening be placed before the eye and be
moved in front of the lens, so that the pencil of light falls successively upon
different sectors, it can be shown that the focal distance is different for dif-
ferent portions. The radiating 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 be perfectly
corrected by placing cylindrical glasses before the eyes, it is impossible, in the
great majority of cases, to construct glasses which will remedy what has been
called irregular astigmatism.

MOVEMENTS OF THE IRIS.

There are two physiological conditions under which the size of the pupil
is modified : The first of these depends upon the degree of illumination to
which the eye is exposed. When the illumination is dim, the pupil is widely
dilated. 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 con-
tracted is characteristic of the smooth muscular fibres, as can be readily seen
by exposing an eye, in which the pupil is dilated, to a bright light. Con-
traction 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.

706 SPECIAL SENSES.

The effort of converging the axes of the eyes, by looking at a very near ob-
ject, contracts the pupils ; and 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.

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 dis-
tances ; but it is nevertheless true that the muscular tissue of the iris will
respond directly to the stimulus of light. Harless noted, in subjects dead of
various diseases, five to thirty hours after death, that the iris contracted un-
der the stimulus of light ; and he regarded this as probably due to direct
action upon its muscular tissue. It is not reflex, for the reason that the irri-
tability 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 con-
traction, 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 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 considered in connection with the physi-
ology 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. When light is admitted to the retina, the pupil con-
tracts, 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
dilatation of the pupil, the iris responding, only in the slow and gradual man-
ner already indicated, to the direct action of light.

Taking all the experimental facts into consideration, it is certain that the
third nerve has an important influence upon the iris. Filaments from the
ophthalmic ganglion animate the circular fibres, or sphincter, and these fila-
ments are derived from the third cranial nerve. If this nerve be divided,
the iris becomes permanently dilated and is immovable, except that it re-
sponds 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.

Most anatomists admit the existence of radiating muscular fibres in the
iris, the action of which is antagonistic to the circular fibres, and which dilate

MOVEMENTS OF THE IRIS. TOT

the pupil. That these fibres are subjected to nervous influence, is rendered
certain by experiments upon the sympathetic system. 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 muscular fibres ;
and the only question to determiners 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 sec-
tion 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 experi-
ment ; and the varying results obtained in observations upon different ani-
mals probably depend upon differences in the anatomical relations of the
nerves. It is probable, however, that the filaments of the sympathetic which
animate the radiating 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 sufficiently simple. An impression is made upon the retina, which is
conveyed by the optic nerves to the centre, and in obedience to this impres-
sion, the sphincter of the iris contracts. If the optic nerves be divided, so
that the impression can not be conveyed to the centre, or if the third nerve
be divided, no movements of the iris can take place. The centres which
preside over the reflex phenomena of contraction of the pupil are situated in
the medulla oblongata. The action of these centres is crossed in animals in
which the decussation of the optic nerves is 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. It has been observed that when one eye only is exposed to light, the
pupil becoming contracted under this stimulus, the pupil of 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 indirect, or " consen-
sual " movement of the iris upon the opposite side. The consensual con-
traction occurs about f of a second later than the direct action, and the con-
sensual 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 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 vice versa. This
does not occur when the sympathetic in the neck has been divided. In ad-
dition to the inferior cilio-spinal centre, there is a superior centre, which is

708 SPECIAL SENSES.

in communication with the superior cervical ganglion and is situated near
the sublingual nerve. The influence of this centre over the pupil can not be
demonstrated by direct stimulation, because it is too near the origin of the
fifth, irritation of which affects the iris ; but it is shown by division of its.
filaments of communication with the iris.

ACCOMMODATION OF THE EYE FOR VISION AT DIFFERENT DISTANCES.

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 reti-
na, 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 conditions 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 infi-
nite distance, be brought to bear upon a 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 dis-
tance, it is found that the image of a flame, placed at the same distance, is
produced with perfect distinctness upon the retina, and, at the same time,
upon the illuminated plane of the image, the vessels and the other anatomi-
cal 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 infinite distance, and that for the distinct perception of near objects,
the transparent media must be so altered in their arrangement or in the cur-
vatures of their surfaces, that the refraction will be greater ; for without this,
the rays would be brought to a focus beyond the retina.

The changes in the eye by which accommodation is effected are now
known to consist mainly in an increased convexity of the lens for near ob-
jects ; 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 study-
ing 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.

VISUAL ACCOMMODATION,

709

The ordinary range of accommodation varies between a distance of about
five inches (12-7 centimetres) and infinity.

Changes in the Crystalline Lens in Accommodation. — It is important to
determine the extent and nature of the changes of the lens in accommoda-
tion ; and these changes have been accurately measured in the living subject.
As the general results of these measurements (Helmholtz), 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 in-
creased, 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 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 two persons, are as follows :

Persons examined.

Radius of curvature of the anterior surface of
the lens.

Displacement of the pupil in ac-
commodation for near objects.

Distant vision.

Near vision.

0. H.
B. P.

0-4641 in. (11-9 mm.)
0-3432 in. (8-8 mm.)

0-3354 in. (8-6 mm.)
0-2701 in. (5-9 mm.)

0-0140 in. (0-36 mm.)
0-0172 in. (0-44 mm.)

The mechanism of the changes in the thickness and in the curvatures of
the lens in accommodation can be understood only by keeping clearly in
mind the physical properties of the lens itself and its anatomical relations.
In situ, in what has been called the indolent state of the eye, the lens is ad-
justed to vision at an infinite distance and is flattened by the tension of its
suspensory ligament. After death, indeed, it is easy to produce changes in
its form by applying traction to the zone of Zinn. Remembering the exact
relations of the suspensory ligament, the ciliary muscle and the lens, and
keeping 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 any near object be fixed with the eye there is
a conscious effort, and the prolonged vision of near objects produces a sense
of fatigue. This may be illustrated by the very familiar experiment of look-
ing at a distant object through a gauze. When the object is seen distinctly,
the gauze is scarcely perceived ; but by an effort the eye can be brought to
see the meshes of the gauze distinctly, when the impression of the distant
object is either lost or becomes very indistinct.

710

SPECIAL SENSES.

. The ciliary muscle arises from the circular line of junction of the cornea
and sclerotic, passes backward, and is lost in the tissue of the choroid, ex-
tending as far 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 forward, with probably a slightly spiral
motion of the lens, the contents of the globe, situated behind the lens, are
compressed, and the suspensory ligament is relaxed. The lens itself, the
compressing and flattening action of the suspensory ligament being dimin-

FIG. 256.— 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 con-
tracted and the suspensory ligament of the lens consequently relaxed.

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 diminished.

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 perfectly adapted to the requirements of vision. In early life the
lens is soft and elastic, and the accommodating power is at its maximum ;
but in old age the lens becomes flattened, harder and less elastic, and the
power of accommodation necessarily is 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 reported a
case in which the iris was completely paralyzed, the power of accommoda-
tion remaining perfect ; and he described another case, reported by Von
Oraefe, in which accommodation was not disturbed after loss of the entire
iris.

It has already been noted 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 evident that convergence of the eyes occurs in looking at very near ob-
jects. It has been shown by Bonders, that increased convergence of the vis-
ual lines without change of accommodation makes the pupil contract, as is
easily proved by simple experiments with prismatic glasses, and that when

VISUAL ACCOMMODATION. 711

accommodation is effected without converging the visual axes, " each stronger
tension is combined with contraction of the pupil." Contraction of the
pupil, therefore, occurs both in convergence of the visual axes without ac-
commodation and in accommodation for near objects without convergence of
the eyes.

The action of the iris, as is evident from the facts just stated, is to a cer-
tain extent under the control of the will ; but it can not be disassociated,
first, from the voluntary action of the muscles which converge the visual
axes, and second, from the action of the ciliary muscle. Bonders, by alter-
nating the accommodation for a remote and a near object, was able to volun-
tarily contract and dilate the pupil more than thirty times in a minute.
Brown-Sequard, in discussing the voluntary movements of the iris, has men-
tioned 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 accommoda-
tion with muscular action, cases are cited in works on ophthalmology, in
which there is paralysis of the ciliary muscle, as well as cases in which the
act of accommodation is painful.

A curious phenomenon connected with accommodation may be observed
in looking at a near object through a very small orifice, like a pinhole. The
shortest distance at which one can see a small object distinctly is about five
inches (12'7 centimetres) ; but in looking at the same object through a pin-
hole in a card, it can be seen distinctly at the distance of about one inch
(25-4 mm.), 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
probably is due to the fact that its distance from the eye is many times less
than the distance at which distinct vision is possible under ordinary condi-
tions. 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 peculiar distinctness.

Erect Impressions produced by Images inverted upon the Retina. — The
images which make visual impressions are necessarily inverted upon the
retina ; but the cerebral visual centre takes no cognizance of this, and objects
are seen in their actual position. It seems almost absurd to enter into a seri-
ous discussion of this fact. In the words of Helmholtz, " our natural con-
sciousness 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 ? "

Field of Indirect Vision. — If the eye be kept fixed upon a certain point,
and an object be moved from this point as a centre in lines radiating in dif-
ferent directions until it passes from the field of view, the limits of indirect
vision are indicated. Eight or ten such points of limit, connected by a
curved line, give a map of the visual field. This may be done roughly upon a
flat surface, such as a blackboard, placed at a distance of .twelve to eighteen
inches (3 to 4-5 centimetres) from the eye, or a chart may be made with an

712

SPECIAL SENSES.

instrument called the perimeter, by which the field is marked on the inner
surface of a hemisphere. The field of vision thus delineated is an irregular

oval, extending from the
fixed point, farther to
the temporal side than
to either the nasal side
or above and below. The
extent from the fixed
point is about 90° on
the temporal side, and
about 70° to the nasal
side and above and be-
low. The field for white
is larger than for colors,,
especially on its nasal
side, as is seen in Fig.
257. The field is small-
est for green, a little
larger for red, and is
larger still for blue. In-
vestigation of the field
of indirect vision with
the perimeter is very
useful in ophthalmolo-
gy, but the chief physi-
ological interest, as regards the sensibility of the retina, is connected with
direct vision.

FIG. 257. — Field of vision of the right eye, as projected by the pa-
tient on the inner surface of a hemisphere, the pole of which
forms the object of regard — semi-diagrammatic (Nettleship,
after Landolt).

T, temporal side ; N, nasal side ; w, boundary for white ; B, bound-
ary for blue ; R, boundary for red ; a, boundary for green.

BINOCULAR VISION. .

Thus far the mechanism of the eye and its action as an optical instru-
ment, in monocular vision only, have been described ; but it is evident that
both eyes are habitually used, and that their axes are practically parallel in
looking at distant objects and are converged when objects are approached to-
the nearest point at which there is distinct vision. In fact an image is
formed simultaneously upon the retina of each eye, but it is nevertheless-
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
in the retina of each eye, 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 external rectus muscle, when both eyes are normal,,
there is double vision. When the strabismus 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 but one eye is capable of fixing
objects accurately, images are formed upon the fovea of this eye only. Images
formed upon the retina of the other eye are indistinct, and in many instances-
are habitually disregarded ; so that practically the subject uses but one eye,.

BINOCULAK VISION. 713

and presents the errors of appreciation which attend monocular vision, such
as a want of exact 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. This is explained upon the supposition that the perceptive 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
f ovea centralis of each eye ; that is, upon corresponding points, which are,
for each eye, the centres of distinct vision. 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 visual centre receives a
correct impression of a single object. When vision is perfect, the sensation
of the situation of any single object is referred to one and the same point ;
and the impression of a double image can not be received unless the condi-
tions of vision be abnormal.

Corresponding Points. — While it is evident, after the statements just
made, 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. It is almost certain that for absolutely perfect, single vision with the
two eyes, the impressions must be made upon exactly corresponding points,
even to the ultimate, sensitive elements of the retina. It may be assumed,
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 and in correspond-
ing directions from the visual axis. When the two images of an object are
formed upon these corresponding 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 necessity they appear
double.

The effect of a slight deviation from the corresponding points may be
illustrated by the following experiment : If a small object, like a lead-pencil,
held at a distance of a few inches, be fixed with the eyes, it is seen distinctly
as a single object. Holding another small object in the same line, a few
inches farther removed, when the first is seen distinctly, the second appears
double. If the second object be fixed with the eyes, the first appears double.
It is evident here, that when the axes of the eyes bear upon one of these ob-
jects, the images of the other must be formed at a certain distance from the
corresponding retinal points.

The Horopter. — The above-mentioned experiment affords an explanation
of the horopter. If both eyes be fixed upon a point directly in front and be
kept in this position, an object moved to one side or the other, within a cer-
tain area, may be seen without any change in the direction of the axis of vis-
ion ; but the distance from the eye at which there is single vision of this
object is fixed, and at any other distance the object appears double. The
explanation of this is that at a certain distance from the eye, the images are
formed upon corresponding points in the retina ; but at a shorter or longer

714

SPECIAL SENSES.

distance, this can not occur. This illustrates the fact that there are corre-
sponding points in a large part of 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 cer-
tain 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 horop-
ter. It was supposed at one time to be a regular curve, or 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.

If the visual areas of the two retinae be superimposed, the fixation-points
coinciding, it becomes evident that a portion only of the two fields can have

corresponding points. This
is the light portion shown in
Fig. 258, which may be called
the binocular field of vision. '
Binocular vision must be im-
possible in the temporal por-
tion of each visual area (Net-
tleship).

It is undoubtedly true that
education and habit have a
great deal to do with the cor-

FIG. 258.— Binocular Held of vision (Nettleship, after Forster.) vppfinn of visual imnrp«?m'rmR
F, fixation-point ; B, B, blind spots.

and the just appreciation of

the size, form and distance of objects. In the remarkable case of Casper
Hauser, who is said to have been kept in total darkness and seclusion, from
the age of five months until he was nearly seventeen years old, the appreciation
of size, form and distance were acquired by correcting and supplementing the
sense of sight, by experience. This boy at first had no idea of the form of
objects or of distance, until he had learned by touch, by walking etc., that
certain objects were round and others were square, and had actually traversed
the distance from one object to another. At first all objects appeared as if
painted upon a screen. Such points as these it would be impossible to accu-
rately observe in infants ; but young children often grasp at remote objects,
apparently under the impression that they were within reach. It must be
admitted, however, that the account of the case of Casper Hauser is rather
indefinite ; but it is certain that even in the adult, education and habit
greatly improve the faculty of estimating distances.

Careful observations 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 either retina, that vision is absolutely perfect. The sum of actual
knowledge upon this important point is expressed in the following quotation
from Giraud-Teulon :

BINOCULAR VISION. 715

" 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 physioiogical action of a single eye, in order to arrive at an idea
of the distance 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, experi-'
ence.

" 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 degree of difficulty, although it is very near.
This difficulty 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 can
not be obtained except by the use of both eyes> and this fact will partly ex-
plain the errors of monocular vision in looking with one eye upon objects in
relief ; for under these conditions, it is impossible to determine with accu-
racy 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 is obtained 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,

716 SPECIAL SENSES.

in the second century — that in looking at any solid object not so far re-
moved as to render the visual axes practically parallel, a portion of the sur-
face, seen with the right eye, 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 and produce the impression of a single image, when
vision is perfectly normal ; and this gives the idea of relief or solidity, and
an exact appreciation of 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 consequent 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 retinae. 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, but a single
image is seen, 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. 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 occa-
sjons little or no inconvenience.

Although an opposite opinion is held by some experimenters, Helmholtz,
with many others, has stated that when one color is seen with one eye and
another color, with the 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 combination ob-
served in ordinary experiments. One additional point of importance, how-
ever, 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 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 ap-
pearance of dark, brilliant crystals, like graphite.

Duration of Luminous Impressions (After-images). — The time re-
quired for a single visual stimulation of the retina is exceedingly short. The
letters on a printed page are distinctly seen when illuminated by an electric
spark, the duration of which is not more than forty billionths of a second
(Rood). An impression made upon the retina, however, endures for a length
of time that bears a certain relation to the intensity of the luminous excita-

IRRADIATION. 717

%

tion. If the eyes be closed after looking steadily at a very bright object, 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 there is a rapid succession
of images, they may be 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 necessary 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 experi-
ments made with revolving disks 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 produced by a combination of the black and white.
The effects of an artificial combination of colors may be produced in this way,
the resultant color appearing precisely as if the individual colors had been
ground together. 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, Q'22 of a second ; and
for blue, 0'21 of a second.

The impressions which remain on the retina after an object has been
looked at steadily are called after-images. When these are bright and of the
same character as the object, they are called positive after-images. When
the stimulation of the retina has been very powerful and prolonged, the
after-image frequently is dark. Such images are called negative after-images.

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 illustra-
tions, are sufficiently familiar, as well as many scientific toys producing opti-
cal 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 some-
times 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 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 por-
tion will appear larger, for the same reason. These phenomena are due to
what has been called 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 in-
volved. In looking at powerfully illuminated objects, the irradiation is con-
siderable, as compared with objects which send fewer luminous rays to the eye

47

718

SPECIAL SENSES.

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. In looking steadily at a red spot or figure
on a white ground, a faint areola of a pale-green soon appears surrounding
the red object ; 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 por-
tion, upon a bed of adipose tissue, which is never absent, even in extreme
emaciation. Outside of the sclerotic, is a fibrous membrane, the tunica vag-
inalis oculi, or capsule of Tenon, which is useful in maintaining the equilib-
rium of the globe. This fibrous membrane 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 tendin-
ous 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

10

FIG. 259.— 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 ; 3, internal rectus ; 4,
inferior rectus ; 5, superior rectus ; 6, superior oblique ; 7, pulley and reflected portion of the supe-
rior oblique : 8, inferior oblique ; 9, levator palpebri superioris ; 10, 10, middle portion of the levator
palpebri superioris ; 11, optic nerve.

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

MOVEMENTS OF THE EYEBALL. 719

the sides of the globe and are inserted by short, tendinous bands into the scle-
rotic, at a distance of one-fourth to one-third of an inch (6-4 to 8*5 mm.)
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. Fro*m the pulley, or trochlea, the tendon becomes flattened,
passes outward and backward beneath the superior 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 rec-
tus and between the external rectus and the eyeball, taking a direction out-
ward 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 Fig. 259.

The various movements of the eyeball are easily understood by a study of
the associated movements of the muscles just enumerated, at least as far as
is necessary to the comprehension of the mechanism by which the eyes are
directed toward any particular object. The centre of exact vision is in the
fovea ; and it is evident that in order to see any object distinctly, it is neces-
sary 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, in
every direction, it is necessary only to note the exact mode of action of each
of the muscles, in order to comprehend how the different movements are
accomplished ; and it is sufficient for practical purposes to admit that ap-
proximately 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 pro-
trusion 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.

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 di-
minished. Helmholtz stated that, in his own person, with the greatest effort
that he was capable of making, he could move the line of vision in the hori-
zontal plane to the extent of about fifty degrees, and in the vertical plane, about
forty- five degrees; but he added that these extreme rotations were very
forced, and that they could not be sustained for any considerable length of

720

SPECIAL SENSES.

lime. It is probable that the eyeball is seldom moved to an angle of forty-
live degrees, the direction of the visual line being more easily accomplished
by movements of the head.

Action of the Recti Muscles. — The internal and external recti rotate the
globe upon a vertical axis, which is perpendicular 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 con-
nection with the history of the cranial nerves.

The superior and inferior recti rotate the globe upon an horizontal axis,
which is 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 arrangement, their action is not so
simple as that of the internal and external recti. The insertion of the supe-
rior rectus in 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 may
be made to perform a great variety
of rotations, and the line of vision
may be turned in nearly every direc-
tion, by the action of the recti mus-
cles alone.

Action of the Oblique Muscles. —
It is sufficient for all practical pur-
poses to assume that the superior and
the inferior oblique muscles act as
direct antagonists to each other.
The most exact measurements show
that the axis of rotation for these
muscles is horizontal and has an ob-
lique direction from before backward
and from without inward. The an-
gle formed by the axis of rotation of
the oblique muscles with the axis of
the globe is thirty-five degrees ; and
the angle between the axis of the
oblique muscles and the axis of the
superior and inferior recti muscles is
°f the seventy-five degrees.

The heavy lines represent the muscles of the eye- Given the direction of the axis of

ball, and the fine lines, the axes of the superior , , ,. . „ ,-,

and the inferior recti and the axes of the oblique rotation and the direction 01 the SU-

perior oblique muscle, it is easy to

understand the effects of its contraction. As this muscle, passing obliquely
backward and forward over the globe, acts from the pulley near the inner

MOVEMENTS OF THE EYEBALL. 721

angle of the eye, to its insertion just behind the anterior half of the globe on
its external and superior surface (7, Fig. 259), 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 insertion 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
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 corre-
sponding points on the retina, and that they should bear, for the two eyes,
corresponding relations to the perpendicular. Thus it is that when the head
is inclined to one side, the eyes are twisted upon an oblique, antero-posterior
axis ; as can be readily seen by observing little spots upon the iris, during
these movements.

The superior oblique muscle is supplied by a single nerve, the patheticus.
When this muscle is paralyzed, the inferior oblique acts without its antago-
nist, and the eyeball is immovable, as far as the twisting of the globe, just
described, is concerned. When the head is moved toward the shoulder, the
globe can not rotate to maintain a position corresponding to that of the other
eye, and there is double vision. This point has already been touched upon
in connection with the physiology of the nerves of the eyeball and the situa-
tion of corresponding points in the retina.

Associated Action of the Different Muscles of the Eyeball. — It is almost
unnecessary to add, after the description just given of the actions of the indi-
vidual muscles of the globe, that their contractions may be associated so as
to produce a great variety of movements. There is no consciousness, under
ordinary conditions, of the muscular action by which the globe is rotated
and twisted in various directions, except that by an effort of the will the line
of vision is directed toward different objects. By a strong effort the axis of
the eyes may be converged by contracting both internal recti, and some per-
sons 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.
In looking at near objects the effort of accommodation is attended with the
degree of convergence necessary to bring the visual axes to bear upon iden-
tical points. In looking around at different objects the head is moved more
or less and the globes are rotated 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-poste-
rior axis there must be an associated action of the oblique muscles and
the recti.

722 SPECIAL SENSES.

An important point, not to be lost sight of in the study of the associated
action of the muscles of the globe, relates to the associated movements of the
two eyes. 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 retinae act
practically as a single organ. The same is true in deviation of the globe in
the vertical plane. If it be supposed, 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, the obliquity of the assumed square of the retina
must be exactly the same for the two eyes, or the coincidence of the corre-
sponding points would be disturbed and there would be double vision. De-
viation of one eye in the horizontal or the vertical plane disturbs the relation
of the corresponding points, and a deviation from exact coincidence of action
in torsion of the globes, twists, as it were, the corresponding points, so that
their relation is also disturbed. It is evident, therefore, that the varied move-
ments of the globes, by the combined action of the recti and oblique muscles,
must correspond for each eye, in the movements of torsion upon an antero-
posterior axis as well as in movements of rotation upon the horizontal or the
vertical axis.

CENTRES FOR VISION.

Experiments have been made upon the lower animals by Terrier, Munk,
Exner, Dalton and many others, with the object of locating in the cerebrum
a centre for vision. It is important, however, to compare the results of such
experiments with cases of cerebral lesions in the human subject. As the
general result of experiments, both on dogs and monkeys, and of pathological
observations, the present opinion is that the centres for vision are in the
occipital lobes. The convolutions immediately above and below the calcarine
fissure, on the inner surface of the cerebrum (compare Figs. 221 and 222,
page 605), seem to be the cerebral terminations of fibres that are continuous
with the optic tracts. These fibres are not crossed in the cerebrum, but the
conductors decussate at the optic chiasm, as they pass to the eyes. Cases
have been observed in the human subject, in which lesion of these parts on
one side has been followed by loss of vision in one lateral half of the retina
in either eye. This condition is called hemianopsia. In these instances the
blindness is confined to the temporal side of the retina corresponding to the
lesion and the nasal side of the retina of the opposite eye. This is called
lateral homonym ous hemianopsia, and this is the form which always occurs
in unilateral cerebral lesion. In dogs and in monkeys destruction of both
occipital lobes and both angular convolutions produces total and permanent
blindness of both eyes.

The complete and perfect perception of visual impressions involves intel-
lectual action connected with the simple visual sense. An individual may

PARTS FOR THE PROTECTION OF THE EYEBALL. 723

see objects and yet not be able to appreciate their significance. In the con-
dition known as word-blindness, words are seen, but they convey no idea.
A dog with part of the occipital lobes removed may see objects, such as food,
but does not recognize their character. There are, apparently, psychical
centres, which elaborate the impressions received by the visual centres.

What seems at present to be the most rational view to take in regard
to the location and action of the visual centres is the following :

1. The centre for simple visual impressions is on the inner surface of the
cerebrum, on either side of the calcarine fissure, between the cuneus and the
lobulus lingualis. This part is connected with homonymous halves of the
retina of each eye, the temporal half of the retina of the same side and the
nasal half of the retina of the opposite side. The part above the calcarine
fissure is connected with the upper portion of the retina, and the part below,
with the lower portion of the retina (Henschen).

2. The action of the cortex of the convex surface of the temporal lobe
(perhaps only on the left side) is necessary for full visual perception and
recognition and for the production of visual memories (Hun). This may
be called the psychical visual centre. Psychical blindness may exist, indeed,
without loss of visual sensation.

3. The angular convolution is not a visual centre, as was claimed by Fer-
rier. It is related to visual perception only in so far as it affects " the
memories of the appearance of written or printed words " (Hun). In cases
of word-blindness, lesions have been found in this situation (Stirling).

The situation of the visual centres, as indicated above, is in parts supplied
by the third branch of the posterior cerebral artery.

Perception of Colors. — Physical researches have shown that different colors
have different wave-lengths. It is evident that they are appreciated by the
visual centres, as distinct impressions for each color and shade of color, al-
though, under what may be called normal conditions, the delicacy of color-
perception varies in different individuals. Color-blindness is an abnormal
condition, in which the power of discrimination between different colors is
impaired or lost. Some persons are entirely insensible to colors ; and cases
have been reported in which one eye was color-blind, while the other eye was
normal (Becker and Hippel). The latter is called unilateral color-blindness.

Before the visual centres had been described, various theories were pro-
posed to account for the perception of colors. Some physiologists assumed
the existence of separate and distinct retinal elements for the reception of
impressions made by different colors ; but this and other theories have been
far from satisfactory. Cases of disease of the brain, in which ordinary visual
sensations remain but the sense of color is destroyed, seem to show that a
part of the visual centre is specially connected with the appreciation of colors.
Beyond this, nothing is known of the mechanism of color-perception.

PARTS FOR THE PROTECTION OF THE EYEBALL.

The orbit, formed by the union of certain of the bones of the face, re-
ceives the eyeball, the ocular muscles, the muscle of the upper lid, blood- ves-

724 SPECIAL SENSES.

sels, nerves and a part of the lachrymal apparatus ; and it contains, also, a cer-
tain quantity 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 compara-
tively fragile. The upper border of the orbit (the superciliary ridge) is pro-
vided 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 a large number of
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 in greater number and longer than the
lower cilia. The curve of the lashes is from the eyeball. They serve to pro-
tect 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 (25'4 mm.). The
central portion of the upper cartilage is about one-third of an inch (8'5 mm.)
broad, and the corresponding part of the lower cartilage measures about one-
sixth of an inch (4-2 mm.). At the inner canthus, or angle of the eye, is a
small, delicate ligament, 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 can-
thus the cartilages are attached to the malar bone, by the external tarsal liga-
ment. The tarsal cartilages receive additional support from the palpebral
ligament, a fibrous membrane attached to the margin of the orbit and the
convex 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 lying just beneath the conjunctiva, are the Meibomian glands. The
structure and uses of these glands have already been described in connec-
tion with the physiology of secretion. They produce an oily fluid, which
smears the edges of the eyelids and prevents the overflow of tears.

Muscles which open and close the Eyelids. — The corrugator supercilii
draws the skin of the forehead downward and inward ; the orbicularis palpe-
brarum closes the lids ; and the levator palpebrae superioris raises the upper
lid. The tensor tarsi, called the muscle of Homer, is a very thin, delicate
muscle, which is regarded by some anatomists as a deep portion of the orbic-
ularis. Considering this as a distinct muscle, it consists of two delicate
slips, which pass from either eyelid, behind the lachrymal sac, uniting here

CONJUNCTIVAL MUCOUS MEMBRANE. 725

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 dis-
tance 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 maxillary 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.

The levator palpebrae 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 action is to raise the upper lid. This muscle and its relations are shown
in Fig. 259 (9, 10, 10), page 718.

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 muscles 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. Never-
theless there is hardly a conscious effort usually in keeping the eyes open,
and an effort is required to close the eyes. During sleep the eyes are closed
and the globes are turned upward. The contractions of the orbicular mus-
cles which take place in winking usually are 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 usually is
simultaneous, although they may be educated 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.

Conjunctival 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 periphery 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 conjunctiva presents a superior and an inferior fold, where it is reflected
upon the globe. In the superior conjunctival fold, are 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 form-
ing a part of the lachrymal gland. At the inner can thus there is a vertical
fold, the plica semilunaris, with a reddish, spongy elevation at its inner por-
tion, called the caruncula lacrymalis. The caruncula presents a collection of

726

SPECIAL SENSES.

follicular glands, with a few delicate hairs on its surface. The conjunctiva
is continuous with the membrane of the lachrymal ducts, of the puncta lacry-
malia 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, fur-
rowed, and presents small, isolated papillae near the borders of the lids, which
increase in number 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 papillae. It is covered by conical and rounded epithelial
cells, in two to four layers. Over the cornea the epithelium of the sclerotic
portion is continued in delicate, transparent layers, without a distinct base-
ment-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 Meibo-
mian 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
apparatus.

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 ante-
rior portion is separated
from the rest by a well
marked groove, is com-
paratively thin and ad-
heres to the upper lid.
It presents six to eight
(usually seven) ducts,
which form a row of
openings into the con-
junctival 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 importance as distinguished from the ordinary racemose glands.

FIG. 261. — Lachrymal and Meibomian glands (Sappey).
1, 1, internal wall of the orbit ; 2, 2. internal portion of the orbicularis
palpebrarum ; 3, 3, attachment of this muscle to the orbit ; 4,
orifice for the passage of the nasal artery ; 5, muscle of Horner ;

6, 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 ducts.

THE LACHRYMAL APPARATUS

727

It receives nervous filaments from the fifth cranial nerve and the sympa-
thetic.

The channels by which the excess of tears is conducted into the nose be-
gin by two little points, situated on the margin of the upper and the lower
lid, near the inner canthus? 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 caruncula, the 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 (12*7 mm.) in length and empties
into the inferior meatus of the nose, taking a direction nearly vertical
and inclined slightly outward and backward. This 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 over-
hanging 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 cov-
ered 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 disposition of the apparatus just described is shown in Fig.
262.

The Tears. — The secretion of the lachrymal glands is constant, although
the quantity of fluid may be increased under various conditions. The actual
quantity of the secretion has never been estimated. During sleep it is much
diminished ; and when the eyes are open, the quantity
is sufficient to moisten the eyeball, the excess being
carried into the nose so gradually that this process is
not appreciated. That this drainage of the excess of
tears takes place, is shown by cases of obstruction of
the nasal duct, when the liquid constantly overflows
upon the cheeks, producing considerable inconven-
ience.

It is probable that the openings at the puncta
lacrymalia take up the lachrymal fluid, 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 compressed
in the act of winking, by the contractions of the mus-
cle of Horner, and that this, while it empties the sac,
may in the subsequent relaxation assist the intro-
duction of liquid from the orbit.

Very little is known with regard to the chemical composition of tears, be-

FIG. 262.— Lachrymal canals,
lachrymal sac and nasal
canal, opened by their ante-
rior portion (Sappey).

1, walls of the lachrymal pas-
sages, smooth and adher-
ent ; 2, 2, walls of the lach-
rymal sac, presenting deli-
cate folds of the mucous
membrane; 3, a similar fold
belonging to the nasal mu-
cous membrane.

728 SPECIAL SENSES.

yond the analysis made many years ago by Frerichs. According to this
observer the following is the composition of the lachrymal secretion :

COMPOSITION OF THE TEARS.

floater 990-GO to 987*00

Epithelium 1-40 " 3-20

Albuinm ...... 0-80 " 1*00

Sodium chloride. • . . ]
Alkaline phosphates.

Earthy phosphates.. L 7'20 " 8'80

Mucus . .

Fat

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 albumin given in the table is called by some authors, lachrymine, three-
nine or dacryoline. This substance, whatever it may be called, resembles
mucus in many regards and probably is secreted by the conjunctiva and not
by the lachrymal glands. Unlike ordinary mucus, it is coagulated by water.

The secretion of tears is readily influenced through the nervous system.
Aside from the increased flow of this secretion from emotional causes, which
probably operate through the sympathetic, a hypersecretion almost imme-
diately follows irritation of the mucous membrane of the conjunctiva or of
the nose. The same result follows violent muscular effort, laughing, cough-
ing, sneezing etc. The secretion of tears following stimulation of the mu-
cous membrane is reflex.

CHAPTEE XXIIL

A UDITION.

Auditory (eighth nerve)— 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— General arrangement of
the bony labyrinth— Physics of sound— Noise and musical sounds— Pitch of musical sounds— Musical
scale — Quality of musical sounds — Harmonics, or overtones— Resultant tones — Summation tones — Har-
mony— Discords — Tones by influence— Uses of different parts of the auditory apparatus — Structure of the
membrana tympani— Uses of themembrana tympani— Mechanism of the ossicles of the ear— Physiologi-
cal anatomy of the internal ear— General arrangement of the membranous labyrinth— Liquids of the
labyrinth — Distribution of nerves in the labyrinth — Organ of Corti — Uses of different parts of the inter-
nal ear — Centres for audition.

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

AUDITORY NERVES. 729

the physiology of the auditory nerves. The auditory nerves conduct impres-
sions of sound, as the optic nerves conduct impressions of light ; but there
is an elaborate arrangement of parts by which the waves are collected, con-
veyed to a membrane capable of vibration, and finally carried to the nerves,
by which the intensity and the varied qualities of sound are appreciated.

AUDITORY (EIGHTH NERVE).

The origin of the auditory nerve can easily be traced to the floor of the
fourth ventricle, where it presents two roots. The external, or superficial
root, sometimes called the posterior root, can be seen usually without prepara-
tion. It consists of 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 a number of distinct filaments
arising from the gray matter of the fourth ventricle, two or three of which
pass to the median line, to decussate with corresponding filaments from the
opposite side. Filaments from this root have been traced to a gray nucleus
in the inferior peduncle of the cerebellum and thence to the white substance
of the cerebellum itself. The deep root passes around the restiform body
inward, so that this portion of the medulla is encircled 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 membrane, which envelops it in
a common sheath with the facial. It finally penetrates the internal audi-
tory 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 anterior and a posterior branch, the anterior being distributed to the
cochlea, and the posterior, 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 auditory nerves are grayish in color, 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 super-
ficial root, is a small, ganglioform enlargement, containing fusiform nerve-
cells. The filaments of the trunk of the nerve consist of very large axis-
cylinders, surrounded by a medullary sheath, but having no tubular mem-
brane. 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 eighth, that it is the only nerve capable of receiving and convey-
ing to the brain the special impressions produced by waves of sound ; but it
is an important 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 has been sustained by direct experiments. In
experiments made by passing electric currents through the ears, some physi-

730 SPECIAL SENSES.

ologists have thought that auditory sensations were produced ; but it is proba-
ble that the sensations observed were due to clonic spasm of the stapedius
muscle and not to impressions of sound produced by the action of the stimu-
lus upon the auditory nerves. In cases of complete facial paralysis from
otitis, in which paralysis of the auditory nerve could be positively excluded,
it has not been possible to produce subjective auditory sensations, even by
powerful Faradization by means of a catheter passed through the Eustachian
tube into the tympanic cavity or by the external meatus (Wreden). In addi-
tion there are well established clinical observations which sustain the theory
of muscular contraction and are opposed to the idea of impressions of sound
produced by direct stimulation of the auditory nerves. The results, then,
as regards stimulation of the auditory nerves, have been simply negative.
Were it practicable to subject the nerves to mechanical or electric stimula-
tion, in the human subject, without involving other parts, it might be pos-
sible to arrive at a definite conclusion ; but the difficulties in the way of
such an experiment have thus far proved insurmountable.

TOPOGRAPHICAL ANATOMY OF THE PARTS ESSENTIAL TO THE APPRE-
CIATION OF SOUND.

"Perfect audition involves the anatomical integrity of a complex appa-
ratus, which, for convenience of anatomical description, may be divided into
the external, middle and internal ear.

1. The external ear includes the pinna and the external auditory meatus,
and is bounded 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 it 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 tympanum. The parts entering into the structure of the middle ear
are accessory, and are analogous in their uses to the refracting media of the
eye. Structures contained in the labyrinth constitute the true sensory organ.

The External Ear. — The pinna, or auricle, is that portion projecting from
the head, which first receives the waves of sound. The outer ridge of the
pinna is called the helix. 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 antihelix ; 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, immediately surrounding the
opening of the meatus, is called the concha. A small lobe projects pos-
teriorly, covering the anterior portion of the concha, which is called the

THE EXTERNAL EAR. 731

tragus ; 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.

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.
The structure of this kind of cartilage has already been described.

The integument covering the ear does not vary much from the integu-
ment of the general surface. It is thin, closely attached to the subjacent
parts, and possesses small, rudimentary hairs, with sudoriparous and seba-
ceous glands.

The muscles of the external 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 cartilagi-
nous 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 (3 1/8. mm.)
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 considerably 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. 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 por-
tion. Around the inner extremity of the canal, except at its superior por-
tion, 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 cover-
ing the pinna. It is very delicate, becoming thinner from without inward.
In the osseous portion 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 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 in connection
with the physiology of the glands of the skin.

General Arrangement of the Parts composing the Middle Ear. — Without
a very elaborate description, fully illustrated by plates, it is difficult to give a

732

SPECIAL SENSES.

clear idea of the structure and relations of the complex anatomical parts in
the middle and the internal ear. Such a minute and purely anatomical de-
scription would be out of place in this work, where 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. It will be useful, however, to give a general outline of
the different parts, with their names.

The arrangement of the parts constituting the external ear is sufficiently
simple. The middle ear presents a narrow cavity (Fig. 263, 11), of irregular
shape, situated between the external ear and the labyrinth, in the petrous
portion of the temporal bone. The general arrangement of its parts is shown
in Fig. 263. The outer wall of the tympanic cavity is formed by the mem-
brana tympani (Fig. 263, 6). This membrane is concave, its concavity look-
ing outward, and oblique, inclining usually at an angle of forty-five degrees

with the perpendicu-
lar. This angle, how-
ever, varies considera-
bly in different indi-
viduals. The roof is
formed by a thin plate
of bone. The floor is
bony and is much nar-
rower than the roof.
The inner wall, sepa-
rating the tympanic
cavity from the laby-
rinth, is irregular, pre-
senting several small
elevations and forami-
na. The f enestra ova-
lis, an ovoid opening

FIG. 263.— General view of the organ of hearing (Sappey). . , .

1, pinna ; 2, cavity of the concha, on the walls of which are seen the near "8 Upper portion,
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 ; 6, membrana tympani and

the elastic fibrous membrane which forms its border ; 7, anterior cfafphvfhp hi«5P nf
portion of the incus ; 8, malleus; 9, handle of the malleus, applied to ^ ' UJ LJ
the internal surface of the membrana tympani, which it draws in-
ward toward the projection of the promontory ; 10, tensor tympani
muscle, the tendon of which is reflected at a right angle, to become lip;ament.
attached to the superior portion of the handle of the malleus; 11, 6
tympanic cavity; 12, Eustachian tube, the internal, or pharyngeal smaller opening the
extremity of which has been removed by a section perpendicular to
its curve ; 13, superior semicircular canal ; 14, posterior semicircu-
lar canal ; 15, external semicircular canal ; 16, cochlea ; 17, internal
auditory canal : 18, facial nerve ; 19, large petrosal branch, given
off from the ganglioform 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.

+ • +1, _ na • x „ ^-c
my ui

ru ^ Trp«tiVmlp Tlii« i«
T e * esu lie'

HIP

«rifl its

Below IS a

f enestra rotunda,which
leads to the cochlea.
This is closed in the
natural state by a
In addition the poste-

membrane called the secondary membrana tympani.

rior wall presents several small foramina leading to the mastoid cells, which

cells are lined by a continuation of the mucous membrane of the tympanic

THE MIDDLE EAR.

733

cavity. The tympanic cavity also presents an opening leading to the Eusta-
chian 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 malleus, the incus,
and the stapes, forming a chain and connected together by ligaments (D, Fig.
264:). These bones are situated in the upper part of the tympanic cavity. The
handle of the malleus (A, 2, Fig. 264) is closely attached to the membrana
tympani, and the long process (A, 3, Fig. 264) is attached to the Glasserian
fissure of the temporal bone. The malleus is articulated with the incus. The
incus (B, Fig. 264) is connected with the posterior wall of the tympanic cav-
ity, near the openings of the mastoid cells. It is articulated with the malleus,
and by the extremity of its long process (B, 2, Fig. 264), with the stapes.
The stapes (C, Fig. 264) is the most internal bone of the middle ear. It is
articulated by its smaller extremity with the long process of the incus. Its
base is oval (C', Fig. 264) 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. 265). Some anato-
mists describe a fourth bone as existing between the long process of the incus
and the stapes, but this is seldom dis-
tinct, usually being united either with
the incus or with the stapes.

There are two well defined muscles
connected with the ossicles of the mid-
dle ear. One of these is attached to the
malleus, and the other, to the stapes.
The so-called laxator tympani probably
is not composed of muscular fibres and
should not be enumerated with the mus-
cles of the tympanum.

The larger of the two muscles is the
tensor tympani. Its fibres arise from
the cartilaginous portion of the Eusta-
chian 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
fenestra ovalis it turns nearly at a right
angle over a bony process, and its ten-
don 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 (12'7 mm.) in length (10, Fig. 263). 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 membrana

48

FIG. 264.— Ossicles of the tympanum of the right
side ; magnified 2 diameters (Arnold).

A, malleus ; 1, its head ; 2, the handle ; 3, long,
or slender process ; 4, short process ; B, in-
cus ; 1, its body ; 2, the long process, with the
orbicular process ; 3, short, or posterior pro-
cess ; 4, articular surf ace, receiving the head
of the malleus ; C, stapes ; 1, head ; 2, pos-
terior cms ; 3, anterior crus ; 4, base ; C',
base of the stapes; D, the three bones in their
natural connection, as seen from the outside;
A, malleus ; B, incus ; C, stapes.

734:

SPECIAL SENSES.

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.

The stapedius muscle is sit-
uated in the descending por-
tion of the acquseductus Fallo-
pii and in the cavity of the
pyramid on the posterior wall
of the tympanic cavity. Its
tendon emerges from a fora-
men at the summit of the pyra-
mid. In the canal in which
this muscle is lodged, its direc-
tion is vertical. At the sum-
mit 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 mus-
cles of the ear, this is enveloped
in a fibrous sheath. Its action
to draw the head of the

is

FIG. 265. — The right temporal bone, the petrosal portion re-
moved, showing the ossicles seen from within. From a

photograph (Riidinger).
4, the incus, the short process of which is directed nearly

in a 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 Glasse-

rian 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.

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 a number of 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 cir-
culation 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. 263) is partly bony and partly cartilagi-
nous. Following its direction from the tympanic cavity, it passes forward,
inward and slightly downward. Its entire length is about an inch and a
half (38-1 mm.). 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 trian-
gular cartilage, bent upon itself above, forming a furrow with its concav-
ity 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

GENERAL ARRANGEMENT OF THE BONY LABYRINTH. 735

of the Eustachian tube is intermediate between the hyaline and the fibro-
cartilage.

The circumflexus, or tensor palati muscle, which has already been de-
scribed in connection with deglutition, is attached to the anterior margin,
or the hook of the cartilage. The attachments of this muscle have been ac-
curately described by Riidinger, who called it the dilator of the tube.

The action of certain of the muscles of deglutition dilates the pharyngeal
opening of the Eustachian tube. If the mouth and nostrils be closed and
several repeated acts of deglutition be made, air is drawn from the tympanic
cavity, and the atmospheric pressure renders the membrane of the tympanum
tense, increasing its concavity. By one or two lateral movements of the
jaws, the tube is opened, the pressure of air is equalized and the ear returns
to its normal condition. The nerves animating the dilator tubse come from
the pneumogastric and are derived from the spinal accessory.

A smooth, mucous membrane forms a continuous lining for the Eusta-
chian 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 tym-
panum it is very thin. In the cartilaginous portion of the Eustachian tube
there are mucous glands, which are most abundant near the pharyngeal ori-
fice and gradually diminish in number toward the osseous portion, in which
there are no glands. Throughout the tube the surface of the mucous mem-
brane 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
and the inner surface of the membrana tympani, is prolonged into the mas-
toid cells and covers the ossicles and those portions of the muscles and ten-
dons 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
lymphatics, a plexus of nerve-fibres and nerve-cells, with some peculiar cells,
the physiology of which is not understood.

The above is merely a general sketch of the physiological anatomy of the
middle ear, and it will not be 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 con-
sidered in connection with the physiology of these parts.

General Arrangement of the Bony Labyrinth. — 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 semi-
circular canals (13, 14, 15, Fig. 263) and the cochlea (16, Fig. 263). The
general arrangement of these parts in situ and their relations to the adja-
cent structures are shown in Fig. 263. Fig. 266, showing the bony labyrinth
isolated, is from a photograph in Riidinger's atlas.

736 SPECIAL SENSES.

The vestibule is the central chamber of the labyrinth, communicating
with the tympanic cavity by the fenestra ovalis, which is closed in the nat-
ural state by the base of the stapes. This is the central, ovoid opening
shown in Fig. 266. The inner wall of the vestibule presents a round depres-
sion, the fovea hemispherica, perforated by a number of 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. 266
(6, 7, 8, 9, 10, 11, 12).

The arrangement of the cochlea, the anterior division of the labyrinth, is
shown in Fig. 266 (1, 3, 4). This is a spiral canal, about an inch and a half
(38-1 mm.) long, and one-tenth of an inch (2-5 mm.) wide at its beginning,
gradually tapering to the apex, and making in its course, two and a half
turns. Its anterior presents a central pillar, around which winds a spiral
lamina of bone. The fenestra rotunda (2, Fig. 266), 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. 266. — The left bony labyrinth of a new-born child, forward and outward vieiv. From a photograph

(Rudinger).

1, the wide canal, the beginning of the spiral canal of the cochlea : 2, the fenestra rotunda ; 3, the sec-
ond turn of the cochlea ; 4, the final half-turn of the cochlea : 5, the border of the bony wall of the
vestibule, situated between the cochlea and the semicircular canals ; 6, the superior, or sagittal
semicircular canal; 7, the portion of the semicircular canal bent outward; 8, the posterior, or trans-
verse semicircular canal ; 9, the portion of the posterior connected with the superior semicircular
canal ; 10, point of junction of the superior and the posterior semicircular canals ; 11, the ampulla
ossea externa ; 12, the horizontal, or external semicircular canal. The explanation of this figure
has been modified and condensed from Riidinger.

What is called the membranous labyrinth is contained within the bony
parts just described. Some of the anatomical points connected with its
structure and the distribution and connections of the auditory nerve have

PHYSICS OF SOUND. 737

direct and important relations to the physiology of hearing, while many are
of purely anatomical interest. Such facts as bear directly upon physiology
will be considered fully in connection with the uses of the internal ear.

PHYSICS OF SOUND.

The sketch just given of the general anatomical arrangement of the
auditory apparatus conveys a general idea of the uses of the different parts of
the ear. The waves of sound must be transmitted to the terminal extremi-
ties of the auditory nerve in the labyrinth. These waves are collected by the
pinna, are conducted to the membrana tympani through the external auditory
meatus, produce vibrations of the membrana tympani, are conducted by the
chain of ossicles to the openings in the labyrinth and are communicated
through the fluids of the labyrinth to the ultimate nervous filaments. The
free passage of air through the external meatus and the communications
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 mem-
brana tympani ; the integrity of the ossicles and of their ligaments and mus-
cles 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 mea-
tus, to the auditory centre in the brain, where the auditory impressions are
appreciated.

Most of the points in acoustics which are essential to the comprehension
of the physiology of audition are definitely settled. The theories of the prop-
agation of sound involve wave-action, concerning which there is no dispute
among physicists. For the conduction 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,
though 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 is called melody. Again, there is appreciation, not only
of the intensity of sounds, both noisy and musical, but of pitch and different
qualities, particularly in music. Still farther, musical notes may be resolved
into certain invariable component parts, such as the octave, the third, fifth
etc. These components of what were formerly 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 pro-
duction of others which correspond to certain of the components of the pre-
dominating note. For example, if there be added to a single note, the third,

Y38 SPECIAL SENSES.

fifth and octave, the result is a major chord, the sound of which is very dif-
ferent from that of a single note or of a note with its octave. If the third
be diminished by a semitone, there is a different quality, which is peculiar to
minor chords. In this way a great variety of musical sounds may be made
upon a single instrument, as the piano ; and by the harmonious combinations
of the notes of different instruments and of different registers of the human
voice, as in choral and orchestral compositions, shades of effect, almost in-
numerable, may be produced. The modification of sounds in this way con-
stitutes harmony; and an educated ear not only experiences pleasure from
these musical combinations, 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 by transition-notes, may 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 ways. These
regular transitions constitute modulation. The ear becomes fatigued by long
successions of notes or chords always in one key, and modulation is essential
to the enjoyment of elaborate musical compositions; otherwise the notes
would not only become monotonous, but their correct appreciation would be
impaired, as the appreciation of colors becomes less distinct after looking for
a long time at an object presenting a single vivid tint.

Laws of Sonorous Vibrations. — Sound is produced by vibrations in a
ponderable medium ; and 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 care-
fully arranged in vacuo. Although the stroke and the vibration can readily
be seen, there is no sound ; and if air be gradually introduced, the sound will
become appreciable, and progressively more intense as the surrounding
medium is increased in density. The oscillations of sound are to and fro in
the direction of the line of conduction and are said to be longitudinal. 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 sqund-wave.

It is evident that vibrating bodies may be made to perform and impart to
the atmosphere oscillations of greater or less amplitude. The intensity of
sound is in proportion to the amplitude of the vibrations. 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 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. The sound, as the waves recede from the sonorous

LAWS OF SONOROUS VIBRATIONS. 739

body, becomes distributed over an increased area. The propagation of sound
has been reduced also to the formula, that the intensity diminishes in pro-
portion to the square of the distance.

Sonorous vibrations are subject to many of the laws of reflection of light.
Sound may be absorbed by soft and non- vibrating surfaces, in the same way
that certain surfaces aborb the rays of light. By carefully arranged convex
surfaces, the waves of sound may readily be collected to a focus. These laws
of the reflection of sonorous waves explain echoes and the conduction of
sound by confined strata of air, as in tubes. To make the parallel between
sonorous and luminous transmission 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 carbon dioxide. 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 fact that sound is transmitted with much less rapidity than light. At a
short distance the view of the body is practically instantaneous ; but there is
a considerable interval between the blow and the sound. This interval re-
presents the velocity of sonorous conduction. This fact is also illustrated by
the interval between a flash of lightning 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 freezing-
point of water, is about 1,090 feet (332 metres) per second. This rate pre-
sents comparatively slight variations for the different gases, but it is very
much more rapid in liquids and in solids.

Noise and Musical Sounds. — There is a well defined physical as well as
an aesthetic distinction between noise and music. Taking as examples, sin-
gle sounds, a sound becomes noise when the air is thrown into confused and
irregular vibrations. A noise may be composed of musical sounds, when
these are not in accord with each other, and sounds called musical are not
always entirely free from discordant vibrations. A noise possesses intensity,
varying with the amplitude of the vibrations, and it may have different
qualities depending upon the form of its vibrations. A noise may be called
dull, sharp, ringing, metallic, hollow etc., these terms expressing qualities
that are readily understood. A noise may also be called sharp or low in
pitch, as the rapid or slow vibrations predominate, without answering the
requirements of musical sounds.

A musical sound consists of vibrations following each other at regular in-
tervals, provided that the succession of waves be not too slow or too rapid.
When the vibrations are too slow, there is an appreciable succession of im-
pulses, and the sound is not musical. When they are too rapid, the sound
is excessively sharp, but it is painfully acute and has no pitch that can be ac-
curately determined by the auditory apparatus. Such sounds may be occa-
sionally employed in musical compositions, but in themselves they are not
strictly musical.

Musical sounds have the characters of duration, intensity, pitch and

740 SPECIAL SENSES.

quality. Duration depends simply upon the length of time during which
the vibrating body continues in action. Intensity depends upon the ampli-
tude of the vibrations, and it has no relation whatsoever to pitch. Pitch de-
pends absolutely upon the rapidity of the regular vibrations, and quality,
upon the combinations of different notes in harmony, the character of the
harmonics of fundamental tones and the form of the vibrations.

Pitch of Musical Sounds. — 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 note
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 com-
bination 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 a great variety of qualities, but all notes
of the same pitch have absolutely equal rates of vibration. ' Notes equal in
pitch are said to be in unison. An educated ear can distinguish slight differ-
ences in pitch in ordinary musical notes ; but this power of appreciation of
pitch is restricted within well defined limits, which vary slightly in different
individuals. According to Helmholtz, the range of sounds that can be legit-
imately employed in music is between 40 and 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 can not be exactly appreciated by the
ear.

Musical Scale. — A knowledge of the relations of different notes to each
other lies at the foundation of the science of music ; and without a clear
idea of certain of the fundamental laws of music, it is impossible to thor-
oughly comprehend the mechanism of audition.

It requires very little cultivation of the ear to enable one to comprehend
the fact that the successions and combinations of notes must obey certain
fixed laws ; and long before these laws were subjects of mathematical demon-
stration, 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.

The most convenient sounds for 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. Take, to
begin with, a string vibrating 48 times in a second. If this string be divided
into two equal parts, each part will vibrate 96 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 contains eight notes, of which the first is the low-

LAWS OF SONOROUS VIBRATIONS. 741

est, and the last, the highest. The half may be divided again, producing a
second octave, and so on, within the limits of appreciation of musical sounds.
If the string be divided so that f of its length will vibrate, there are 72 vibra-
tions in a second, and this note is the 5th in the scale. If the string be
divided again, so as to leave £ of its length, there are 60 vibrations, which
give the 3d note in the scale. These are the most natural subdivisions of
the note; and the 1st, 3d, 5th and 8th, when sounded together, make what
is known as the common major chord. Three-fourths of the length of the
original string make 64 vibrations, and give the 4th note in the scale.
With f of the string, there are 54 vibrations, and the note is the 3d in the scale.
With | of the string, there are 80 vibrations, or the 6th note in the scale.
With ^ of the string, there are 90 vibrations, or the 7th note in the scale.
The original note, which may be called C, is the key-note, or the tonic. In
this scale, which is called the natural, or diatonic, there is a regular mathe-
matical progression from the 1st to the 8th. This is called the major key.
Melody consists in an agreeable succession of notes, which may be assumed,
for the sake of simplicity, to be pure. In a simple melody every note must
be one of those in the scale. When a different note is sounded, the melody
passes into a key which has a different fundamental note, or tonic, with a
different succession of 3ds, 5ths etc. Every key, therefore, has its 1st, 3d,
5th and 8th, as well as the intermediate notes. If a note formed by a string $-
the length of the tonic instead of f , be substituted for the major 3d, the key
is converted into the minor. The minor chord, consisting of the 1st, the
diminished 3d, the 5th and the 8th, is perfectly harmonious, but it has a
quality quite different from that of the major chord. The notes of a melody
may progress in the 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, which may be assumed to be the scale of O
major :

1st. 2d. 3d. 4th. 5th. 6th. 7th. 8th.

Note CDEFGABC

Lengths of the string 1 f $ f f £ -fa £

Number of vibrations 48 54 60 64 72 . 80 90 96

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 semi-
tones. The other intervals are either full perfect tones or small perfect
tones. Although there are semitones, not belonging to the key of C, between
C and D, D and E, F and G-, Gr 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, with D as the tonic, the 5th would be A. It is assumed
that D has 54 vibrations, and A, 80, giving a difference of 26. With C as
the tonic and G as the fifth, there is a difference of 24. It is on account of
these differences in the intervals, that each key in music has a more or less
peculiar and distinctive character.

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

742 SPECIAL SENSES.

most pleasing effects, to change the tonic, by what is called modulation, re-
turning afterward to the original key.

Quality of Musical Sounds. — Nearly all musical sounds, which seem at
first to be simple, can be resolved into certain well defined constituents ; but
with the exception of the notes of great stopped pipes in the organ, there are
few absolutely simple sounds used in music. These simple sounds are pure,
but are of an unsatisfactory quality and wanting in richness. Almost all
other musical sounds have a fundamental tone, which is at once recognized ;
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. A string vi-
brating a certain number of times in a second, if the vibrations were abso-
lutely simple, would produce, according to the laws of vibrating bodies, a
simple, musical tone ; but as the string subdivides itself into different por-
tions, one of which gives the 3d, another, the 5th, and so on, of the funda-
mental tone, it is evident that the form of the vibrations must be consid-
erably modified, and with these modifications in form, the quality, or timbre
of the note is changed.

From what has just been stated, it follows that nearly all musical notes
consist, not only of a fundamental sound, but of harmonic vibrations, sub-
ordinate to the fundamental and qualifying it in a particular way. These
harmonics may be feeble or intense ; certain 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 pre-
sent an infinite variety. This is one of the elements entering into the com-
position of notes, and it affords a partial explanation of quality.

Another element in the quality of notes depends upon their re-enforce-
ment by resonance. The vibrations of a stretched string not connected with
a resonant body are almost inaudible. In musical instruments the sound is
taken up by some mechanical arrangement, as the sound-board of the organ,
piano, violin, harp or guitar. In the violin, for example, the sweetness of
the notes depends chiefly upon the construction of the resonant part of the
instrument, and but little upon the strings themselves, which latter are
frequently changed ; and the same is true of the human voice.

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 consequently are inharmonious. Nearly all notes
that are spoken of in general terms as musical are composed of musical, or
harmonic, aliquot tones with the discordant elements to which allusion has
just been made.

Aside from the relations of the various component parts of musical notes,

LAWS OF SONOROUS VIBRATIONS. 743

the quality depends largely upon the form of the vibrations. To quote the
words of Helmholtz, " 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 before stated, nearly all sounds are compos-
ite, 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 analogies in nearly all varieties of musical sounds. If a stretched
string be made to vibrate, the secondary tones, which qualify the funda-
mental, are called harmonics, or overtones.

While it is difficult at all times to distinguish by the ear the individual
overtones of vibrating strings, their existence can be demonstrated by certain
simple experiments. Take, for example, a string, the fundamental tone of
which is C. If this string be damped with a feather at one-fourth of its
length and a violin-bow be drawn across the smaller section, not only the
fourth part of the string across which the bow is drawn is made to vibrate,
but the remaining three-fourths ; and if little riders of paper be placed upon
the longer segment at distances equal to one-fourth of the entire string, they
will remain undisturbed, while riders placed at any other points on the string
will be thrown off. This experiment shows that the three-fourths of the
string have been divided. 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 in-
creased tension, into three, four, and go on. By damping a string with the
light touch of a feather, it is possible to 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 the
string is damped at its centre, the fundamental tone is, quenched and there
are overtones an octave above ; damping it at a distance of one-fourth, there
is the second octave above, and so on. When the string is damped at ajlis-
tance of one-fifth from the end, the four-fifths sound the 3d of the funda-
mental, with the second octave of the 3d. If it be damped at a distance of
two-thirds, there is the 5th of the fundamental, with the octave of the 5th.
Every vibrating string thus possesses a fundamental tone and overtones.
Qualifying the fundamental there is 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 can not easily be distinguished
by the unaided ear, unless the fundamental be quenched in some way. In

744

SPECIAL SENSES.

the same way the harmonic 5ths and 3ds overpower other overtones ; for the
string is subdivided 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 resonators. 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 a note identical with that produced by the vibra-
tions of the column of air, the air in the tube will resound in consonance
with the note, while no other note will have this effect. The resonators of
Helmholtz are constructed upon this principle. A glass globe or tube (Fig.
267) is constructed so as to produce a certain note. This has a larger open-
ing (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 re-enforced by the resonator and is greatly increased in intensity, while
all other notes are heard very faintly. By using resonators graduated to the
musical scale, it is easy to analyze a note and distinguish its overtones. The
resonators of Helmholtz, which are open at the larger extremity, are much
more delicate than those in which this is closed by a membrane.

A very striking and instructive point in the present discussion is the fol-
lowing : All the overtones are produced by vibrations of divisions of the
string, included between the comparatively still points, called nodes ; and if
a string be thrown into vibration by plucking or striking it at one of these

nodal points, the overtones
which vibrate from this
node at a fixed point are
abolished. It is readily
understood that when a
string is plucked at any
point, it will vibrate so vig-
orously 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 explana-
tion. Performers upon
stringed instruments ha-
bitually attack the strings near their extremities. In the piano, where the
strings may be struck at almost any point, the hammers are placed at a dis-
tance of -J- to \ of the length of the strings, from their extremities ; and it has
been ascertained by experience that this arrangement gives the richest notes.
The nodes formed at these points would produce the 7ths and 9ths as over-
tones, which do not belong to the perfect major chord, while the nodes for
the harmonious overtones are undisturbed. The reason, then, why the notes.

FIG. 267. — Resonators of Helmholtz.

LAWS OF SONOROUS VIBRATIONS. 745

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 dis-
cordant overtones are suppressed.

When two harmonious notes are produced under favorable conditions,
one 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 a har-
monic, 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 blend-
ing of colors in optics, except that the primary sounds are 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, C, with 48 vibrations, and its 5th,
with 72 vibrations in a second, give a resultant tone equal to the difference,
which is 24 vibrations, and it is consequently the octave below C. These result-
ant tones are very feeble as compared with the primary tones, and they can
be heard under only the most favorable experimental conditions. In addition
to these sounds, Helmholtz has discovered sounds, even more feeble, which he
calls additional, or summation tones. The value of these is equal to the sum
of vibrations of the primary tones. For example, C (48) and its 5th (72)
would give a summation tone of 120 vibrations, or the octave of the 3d ; and
C (48) with its 3d (60) would give 108 vibrations, the octave of the 2d.
These tones can be distinguished by means of resonators.

It is thus seen that musical sounds are complex. With single sounds
there is an infinite variety and number of harmonics, or overtones, and in
chords there are series of resultants, which are lower than the primary
notes, and series of additional, or summation tones, which are higher ; but
both the resultant and the summation tones bear exact mathematical relations
to the primary notes of the chord.

Harmony. — Overtones, resultant tones and summation tones of strings
have been discussed rather fully, for the reason that in studying the physiol-
ogy of audition, it will be seen that the ear is capable of recognizing single
sounds or successions of single sounds ; but at the same time certain com-
binations of sounds are appreciated and are even more agreeable 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 different vibrations entering into their composition being
simultaneously appreciated by the ear. The blending of tones which bear
to each other certain mathematical relations is called harmony ; but two or
more tones, though each one be musical, are not necessarily 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 a knowledge
of the relations of overtones, it might be inferred that the re-enforcement
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

746 SPECIAL SENSES.

the pleasing impression produced by such combinations was explained mathe-
matically.

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. In sounding C and its 8th, for example, there are 48
vibrations of one to 96 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 there are 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 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 vi-
bration between different tones, the more perfect is their harmony. Sounded
with the 1st, the 4th is more harmonious than the 3d ; but its want of har-
mony with the 5th excludes it from the common chord. The 1st, 4th and
8th are harmonious, but to make a complete chord the 6th must be added.

Discords. — A knowledge of the mechanism of simple accords leads natu-
rally to a comprehension of the rationale of discords. The fact that certain
combinations of musical notes produce a disagreeable impression was ascer-
tained empirically, with no knowledge of the exact cause of the dissonance;
but the mechanism of discord may now be regarded as settled.

The sounds produced by two tuning-forks giving precisely the same num-
ber of vibrations in a second are in perfect unison. If one of the forks be
loaded with a bit of wax, so that its vibrations are slightly reduced, and if
both be put in vibration at the same instant, there is discord. Taking the
illustration given by Tyndall, it may be assumed that one fork has 256, and
the other, 255 vibrations in a second. While these two forks are vibrating,
one is 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 moving in exactly opposite directions ; and as a con-
sequence, the sounds neutralize each other, and there is an instant of silence.
The perfect sounds, as the two forks continue to vibrate, are thus alternately
re -enforced and diminished, and this produces what is known in music as beats.
As the difference in the number of vibrations in a second is one, the instants
of silence occur 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; and dissonance is marked by
successive beats, or pulses. If the forks be loaded so that one will vibrate
240 times in a second, and the other 234, there will be six times in a second

LAWS OF SONOROUS VIBRATIONS. Y47

when the interference will be manifest ; or in other words in £ of a second,
one fork will make 40 vibrations, while the other is making 39. This will
give 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 undulations is observed in optics, when waves of light are made to inter-
fere and produce darkness.

It is evident that the number of beats will increase as two discordant
notes are produced 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 there is only a general sensation of dissonance. Beats,
then, are due to interference of sound-waves. There is no interference of the
waves of tones in unison, provided that waves start at the same instant ; the
intensity of the sound being increased by re-enforcement. The differences
between the 1st and 8th, the 1st and 5th, the 1st and 3d, and other harmo-
nious combinations, is so great that there are no beats and no discord, the
more rapid waves re-enforcing 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. Taking 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 an harmonious
tone.

It is evident that the laws just stated are applicable to overtones, resultant
tones and additional tones, which, like the primary notes, have their beats
and dissonances.

Tones by Influence. — After what has been stated in regard to the laws of
musical vibrations, it will be easy to comprehend the production of sounds
by influence. If a l$ey of the piano be lightly touched, so as to raise the
damper but not to sound the string, and then a note be sung in unison, the
string will return the sound, by the influence of the sound-waves of the voice.
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 a string at any particular point. If
instead of a note in unison, any of the octaves be sounded, the string will re-
turn the exact note sung ; and the same is true of the 3d, 5th etc. If a
chord in harmony with the undamped string be struck, 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 com-
binations. To carry the observation still farther, the string will return, not
only a note of its exact pitch and its harmonics, but notes of the peculiar
quality of the primary note. This is a very important point in its applica-
tions to the physiology of hearing and can be readily illustrated. Taking
identical notes in succession, produced by the voice, trumpet, violin, clarinet
or any other musical instrument, it can easily be 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. These laws of tones by influence have been

748 SPECIAL SENSES.

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 difficulty than others.
A thin membrane, like a piece of bladder or thin rubber, stretched over a
circular orifice, such as the mouth of a wide bottle, may readily be tuned to
a certain note. 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 funda-
mental, thus obeying the laws of vibrations of strings, although the har-
monic sounds are produced with greater difficulty.

The account just given of some of the laws of sonorous vibrations and
their relations to musical effects and combinations, although by no means
complete, may seem rather extended for a work on physiology ; but it should
be borne in mind that the mechanism of the appreciation of musical sounds
includes the entire physiology of audition. This subject can not be compre-
hended without a general knowledge of the physics of sound and of some of
the laws of harmony ; for not only is there a perception of single notes by
the auditory apparatus, but the most intricate combinations of sounds in
harmony are all appreciated together and at one and the same instant, as will
be seen in studying the action and uses of different parts concerned in audi-
tion. Many of the laws of musical combinations are directly applicable to
the physiology of hearing.

USES OF DIFFERENT PARTS OF THE MIDDLE EAR.

The uses of the pavilion and of the external auditory meatus are suffi-
ciently apparent. The pavilion serves to collect the waves of sound, and
probably it inclines them toward the external meatus as they come from vari-
ous directions. Although this action is simple, it has a certain degree of
importance, and the various curves of the concavity of the pavilion tend more
or less to concentrate sonorous vibrations. Such 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
probably is 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. It is not known precisely how the
obliquity and the curves of this canal affect the waves of sound, but it is
probable that the deviation from a straight course protects, to a certain
extent, the tympanic membrane from impressions 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 topo-
graphical anatomy of the auditory apparatus. The membrane is elastic,
about the thickness of ordinary gold-beater's skin, and is subject to various
degrees of tension by the action of the muscles of the middle ear and under

STRUCTURE OF THE MEMBRANA TYMPANI.

749

different conditions of atmospheric pressure within and without the tympanic
cavity. Its form is nearly circular ; and it has a diameter in the adult,
according to Sappey, of a little more than f of an inch (10 to 11 mm.) verti-
cally and about % of an inch
(10 mm.) antero-posteriorly.
The excess of the vertical
over the horizontal diame-
ter is about -fa of an inch
(0-5 mm.)

The periphery of the
tympanic membrane is re-
ceived into a little ring of
bone, which may be sepa-
rated by maceration in early
life, but which is consoli-
dated with the adjacent
bony structures in the adult.
This bony ring is incom-
plete at its superior portion,
but aside from this, it re-
sembles 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 supe-
rior portion.

The concavity of the
membrana tympani presents
outward, and it may be in-
creased or diminished by
the action of the muscles of the middle ear. The point of greatest concav-
ity, where the extremity of the handle of the malleus is attached, is called
the umbo. 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 consisting of a process of the fibrous
layer. This, which is called the posterior pocket, is open below and extends
from the posterior upper border of the membrane, to the handle of the mal-
leus, which it assists in holding in position. " 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 pro-
cess turned toward the neck of the malleus, by the mucous membrane, by the
bony process of the malleus, by its anterior ligament, the chorda tympani
and the anterior tympanic artery. The handle of the malleus is inserted

49

FIG. 268.— Right membrana tympani, seen from within. From
a photograph, and somewhat reduced (Rudinger).

1, head of the malleus, divided ; 2, neck of the malleus : 3, han-
dle of the malleus, with the tendon of the tensor tympani
muscle ; 4, divided tendon of the tensor tympani ; 5, 6, por-
tion 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.

750 SPECIAL SENSES.

between the two layers of the fibrous structure of the membrana tympani
and occupies the upper half of its vertical diameter, extending from the pe-
riphery to the umbo.

The membrana tympani, though thin and translucent, presents three dis-
tinct layers. Its outer layer is a very thin extension of the integument lining
the external meatus, presenting, however, neither papillae nor glands. The
inner layer is a delicate continuation of the mucous membrane lining the
tympanic cavity and is covered by 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 described the mem-
brane, examined in this way, as translucent, 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 portions 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 addi-
tion there is 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 direction, and -^ to ^ of an inch (1-6 to
2-1 mm.) broad at its base. This appearance is regarded by physiologists as
very important, as indicating a normal condition of the membrane. It is
undoubtedly due to reflection of light and not to a peculiar structure of that
portion of the membrane upon which it is seen.

Uses of the Membrana Tympani. — It is unquestionable that the mem-
brana 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 waves of sound, is shown by the
relief which is experienced by those patients who can tolerate the presence of
an artificial membrane of rubber. As regards the mere acuteness of hearing,
aside from the pitch of sounds, the explanation of the action of the mem-
brane 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 vibrations are received by a membrane, under the conditions of the
membrana tympani, 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 well 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

USES OF THE MEMBRANA TYMPANI. 751

tension, and vibrates under the influence of the waves of sound. Attached
to this membrane, is the angular chain of bones, which conducts its vibra-
tions, like the bridge of a violin, to the liquid of the labyrinth. The mem-
brane is fixed at its periphery and has air upon both sides, so that it is under
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 varia-
tions in tension, due to the contraction of the tensor tympani. It is also evi-
dent 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 an
attempt be made to breathe forcibly by expanding the chest, the external
pressure tightens the membrane. In this condition the ear is rendered in-
sensible to grave sounds, but high-pitched sounds appear to -be more intense.
If the tension be removed, as may be done by an act of swallowing, the grave
sounds are heard with normal distinctness. This experiment, tried at a con-
cert, produces the curious effect of abolishing 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 observed by otologists ; and in these, by bringing this muscle into action,
the limit of the perception of high tones is greatly increased. In two in-
stances of this kind, recorded by Blake, the ordinary limit of perception was
found to be three thousand single vibrations, and by contraction of the mus-
cle, this was increased to five thousand single vibrations.

The concave form of the membrana tympani and the presence of a bony
process between its layers, which is part of the chain of bones of the middle
ear, are conditions under which it is impossible that it should have a single,
fundamental tone. This has been shown by experiments with stretched
membranes depressed in their central portion by means of a solid rod. No
membrane can have a single, fundamental tone unless it be in a condition of
uniform tension, like a string, and this is impossible in the membrana tym-
pani. Nevertheless the membrana tympani repeats sounds by influence, and
it is capable of repeating in this way a much greater variety of sounds than
if it had itself a fundamental tone and were capable of a uniform degree of
tension. This has been shown by experiments with stretched, elastic mem-
branes made to assume a concave form. If the membrana tympani had a
single, fundamental tone, it would vibrate by influence only with certain tones
in unison with it, and the overtones would be eliminated. It would then act
like a resonator closed by a membrane, and the tone with which it happened
to be in unison would overpower all other tones. The fact is that all tones,
the vibrations of which reach the membrane, are appreciated at their proper
value as regards intensity. Again, if the membrana tympani had its own
fundamental tone, it would have overtones of the fundamental, which would
produce errors and confusion in auditory appreciation. The chain of bones,
also, attached to the membrane, acts as a damper and prevents the persist-

752 SPECIAL SENSES.

ence of vibrations after the waves of sound cease in the air. This provision
enables rapid successions of sounds to be distinctly and acurately repeated.

The arrangement of the muscles and bones of the middle ear is such that
the tension of the membrtina tympani may be regulated and graduated with
great nicety. It does not seem to be necessary to perfect audition that this
should be done for every single note or combination of notes, but the mem-
brane probably is brought by voluntary effort to a definite degree of tension
for notes within a certain range as regards pitch or for successions and pro-
gressions of sounds in a particular key. As far as the consciousness of this
muscular action is concerned, it may be revealed only by the fact of the cor-
rect' appreciation of certain musical sounds. Some persons can educate the
ear so as to acquire what is called the faculty of absolute pitch ; that is, with-
out the aid of a tuning-fork or any musical instrument, they can give the ex-
act musical value of any given note. A possible explanation of this is that
such persons may have educated the muscles of the ear so as to put the tym-
panic 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 from the general volume of sound, can distinguish the
faintest discords and can designate a single instrument making a false note.

Destruction of both tympanic membranes 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, although
this is done imperfectly. In a case reported by Astley Cooper, one membrana
tympani was entirely destroyed, and the other was nearly gone, there being
some parts of its periphery remaining. In this person the hearing was some-
what impaired, although he could distinguish ordinary conversation without
much difficulty. 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 ex-
cellent 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."

There is an important consideration that must be kept in view in study-
ing the uses of any distinct portion of the auditory apparatus, like the
membrana tympani. This membrane, like all other parts of the apparatus,
except the auditory nerves themselves, has simply an accessory action. If the
regular waves of a musical sound be conveyed to the terminal filaments of
the auditory nerves, these waves make their impression and the sound is cor-
rectly appreciated. It makes no difference, except as regards intensity, how
these waves are conducted ; the sound 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

MECHANISM OF THE OSSICLES OF THE EAR. 753

focus as they impinge upon the retina ; but as far as the action of the acces-
sory parts of the ear are concerned, the waves of sound are unaltered ; that
is, the rate of their succession remains absolutely the same, though they be
reflected by the concavities of the concha and repeated by the tympanic
membrane. Even if it be assumed that the membrane under normal condi-
tions repeats musical sounds by vibrations produced by influence, and that
sounds are exactly repeated, the position of these sounds in the musical scale
is not and can not be altered by the action of any of the accessory organs of
hearing. The fact that a person may retain his musical ear with both mem-
branes destroyed is not really an argument against the view that the mem-
brane repeats sounds by influence ; for if musical sounds or noisy vibrations
be conducted to the auditory nerves, the impression produced must of neces-
sity be dependent exclusively upon the character, regularity and number of
the sonorous vibrations. And, again, the physical laws of sound teach that
a membrane, like the membrana tympani, must reproduce sounds with which
it is more or less in unison much more perfectly than discordant or irregular
vibrations. In a loud confusion of noisy sounds, one can readily distinguish
melody or harmony, even when the vibrations of the latter are comparatively
feeble.

It has been shown that the appreciation of the pitch of sounds bears a
certain relation to the degree of tension of the tympanic membrane. When
the membrane is rendered tense, there is insensibility to low notes. When
the membrane is brought to the highest degree of tension by voluntary con-
traction of the tensor tympani, the limit of appreciation of high notes 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 ; and it has been ob-
served that the membrane has a position more nearly vertical in musicians
than in persons with an imperfect musical ear (Troltsch).

Experiments have shown that the tympanic membrane vibrates more
forcibly when relaxed than when it is tense. In certain cases of facial palsy,
in which it is probable that the branch of the facial going to the tensor tym-
pani was affected, the ear has been found painfully sensitive to powerful im-
pressions of sound. This probably has no relation to pitch, and most sounds
that are painfully loud are comparatively grave. Artillerists are in danger of
rupture of the membrana tympani from sudden concussions. To guard
against this injury, it is recommended to stop the ear, draw the shoulder up
against the ear most in danger, and particularly to inflate the middle ear
after Valsalva's method. " This method consists in making a powerful ex-
piration, with the mouth and nostrils closed " (Troltsch).

Mechanism of the Ossicles of the Ear. — The ossicles of the middle ear, in
connection with the muscles, have a twofold office : First, by the action of
the muscles the membrana tympani may be brought to different degrees of
tension. Second, the angular 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

754 SPECIAL SENSES.

lower end. Near the short process — which is a little, conical projection at
the root of the handle — the attachment is looser and there is even an incom-
plete 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. 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 compared 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 (Helmholtz). 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.

The body of the incus is attached to the posterior bony wall of the tym-
panic 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-cartilage, which is closely united to the bony wall of the
labyrinth, by an extension of the periosteum.

The articulations between the malleus and the incus and between the
incus and the stapes are so arranged that when the membrana tympani is
forced outward, as it may be by inflation of the tympanic cavity, there is no
danger of tearing the stapes from its attachment to the fenestra ovalis ; for
when the handle of the malleus is drawn outward, the cog-joint between the
malleus and the incus is loosened and no considerable traction can be exerted
upon the stapes.

The tensor tympani is by far the more important of the two muscles of
the middle ear. Its action is to tighten the cog-like joint between the malleus
and the incus, to tighten, also, all the ligaments of the incus, to draw the
long process of the malleus inward, thereby increasing the tension of the
membrana tympani, and to press the base of the stapes against the fenestra
ovalis. By the action of this muscle the chain of ossicles becomes prac-
tically a solid and continuous, angular, bony rod.

Although experiments have demonstrated the mechanism of the ossicles
and the action of the tensor tympani, 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 them-

PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. T55

selves 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
vibrations. Practically, then, the ossicles have no independent vibrations
that can be appreciated. 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 as the tension
of the membrane is increased, it would seem that when the tensor tympani
contracts, it must render the conduction of sound-waves to the labyrinth
more delicate than when the auditory apparatus is in a relaxed condition,
which may be compared with the " indolent " condition of accommodation of
the eye. When the membrana tympani is relaxed and the cog-like articula-
tion between the malleus and the incus is loosened, the vibrations of the
membrane and of the malleus may have a greater amplitude ; 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
sounds, puts the chain of bones in the condition best adapted to the conduc-
tion 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 vesti-
bule, semicircular canals and cochlea. The general arrangement of these
parts has already been described ; and it remains only to study the structures
contained within the bony labyrinth, in so far as their anatomy bears directly
upon the physiology of audition. Passing inward from the tympanum, the
first division of the internal ear is the vestibule. 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, nuclei and blood-vessels, with spots of calcareous
concretions. This membrane adheres closely to the bone and extends over
the fenestra ovalis and the fenestra rotunda. Its inner surface is smooth and
is covered with a single layer of cells of endothelium, which in some parts is
segmented and in others forms a continuous, nucleated sheet. In certain
portions of the vestibule and semicircular canals, the periosteum 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 by an extension of the periosteum lining the cochlea,

756

SPECIAL SENSES.

on 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 pos-
terior portion of the cavity, and a smaller, rounded sac, the saccule, situated
in its lower and anterior portion. These two sacs communicate with each

other through a small
canal in the form of
the letter Y, which is
represented in the up-
per diagram in Fig.
269. The utricle com-
municates with the
three semicircular ca-
nals, and the saccule is
connected with the
true membranous coch-
lea by the canalis re-
uniens. At a point in
the utricle correspond-
ing to the entrance of
a branch of the audi-
tory 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 sim-
ilar spot, containing
otoliths, exists in the
saccule, at the point of
entrance of its nerve.
Otoliths are also found
in the ampullae of the
semicircular canals. These calcareous masses are composed of crystals of
calcium carbonate, which are hexagonal and pointed at their extremities.
Nothing definite is known of the uses 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 small, ovoid dilatations, called
ampullae, corresponding to the ampullate enlargements of the bony canals.
They are held in place by a large number of little, fibrous bands extending
to the bony labyrinth.

The membranes of the cochlea include the periosteum lining the bony

FIG. 269.— Diagram of the labyrinth (vestibule and semicircular
canals). From a photograph, and somewhat reduced (Riidinger).

Upper figure : 1, utricle ; 2, saccule ; 3, 5, membranous cochlea ; 4,
canalis reuniens ; 6, semicircular canals.

Lower figure : I, utricle ; 2, saccule ; 3, 4, 6. ampullse ; 5, 7, 8, 9, semi-
circular canals ; 10, auditory nerve (partly diagrammatic); 11, 12,
13, 14, 15, distribution of the branches of the nerve, to the vesti-
bule and the semicircular canals.

PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 757

canal of the cochlea and the true membranous cochlea. Viewed externally, the
true membranous cochlea appears as a single tube, following the turns of the
bony cochlea, beginning below by a blind extremity and terminating in a blind
extremity at the summit of the cochlea. If a section of the cochlea be made in
a direction vertical to the spiral, it will be seen that the bony 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 terminating above in a hook-shaped extremity, called the
hamulus. The free edge of this bony lamina is thin and dense. Near the
central column it divides into two plates, with an intermediate, spongy struct-
ure, in which are lodged
vessels and nerves. The
surface of the bony lamina
looking toward the base
of the cochlea is marked
by a number of regular,
transverse ridges.

Attached to the free
margin of the bony
lamina is a membrane,
the membrana basilaris,
which extends to the out-
er wall of the cochlea.
In this way the bony coch-
lea is divided into two
portions, one above and
the other below the sep-
tum. The portion below
begins at the fenestra ro-
tunda and is called the
scala tympani. The por-
tion 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. Between 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 true membra-
nous cochlea.

In the anatomical description of the contents of the bony cochlea, the
scalae and membranous parts may be designated as follows :

FIG. ZrQ.—Otolithsfrom various animals (Riidinger).
from the goat ; 2, from the herring ; 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.

758 SPECIAL SENSES.

1. The portion below the bony and membranous septum, called the
scala tympani. This is bounded by the periosteum lining the correspond-
ing portion of the bony cochlea and the under surface of the bony lamina
and by the membrana basilaris.

FIG. 271.— Section of the first turn of the spiral canal of a cat newly-born.— Section of the cochlea of a
human fo2tiis at the fourth month. From a photograph, and somewhat reduced (Riidinger).

Upper figure : 1, 2, 6, lamina spiralis ; 2, lower plate ; 3, 4, 5, 5, nervus cochlearis ; 7, membrane of
Reissner ; 8, membrana tectoria ; 9, epithelium ; 10, 11, pillars of Corti : 12, inner hair-cells ; 13,
outer hair-cells ; 14, 16, membrana basilaris ; 15, epithelium in the sulcus spiralis ; 17, 18, 19, liga-
mentum spirale ; 20, spiral canal, below the membrana basilaris.

Lower figure : S T, S T, 5, 5, 7, 7, 8, 8, scala tympani ; S V, S V, 9. 9, scala vestibuli ; 1, base of the coch-
lea ; 2, apex ; 3, 4, central column ; 10, 10, 10, 10, ductus cochlearis ; 11, branches of the nervus
cochlearis ; 12, 12, 12, spiral ganglion ; 13, 14, limbus laminae spiralis ; 15, membrane of Reissner ;
16, epithelium; 17, outer hair-cells; 18, epithelium of the membrana basilaris; 19, nervous filaments;
20, union of the membrana basilaris with the ligamentum spirale ; 21, epithelium of the peripheral
wall of the ductus cochlearis ; 22, 23, membrana tectoria ; 24, spiral canal, below the membrana
basilaris.

2. The scala vestibuli. This is bounded by the periosteum lining the
corresponding portion of the bony cochlea and the upper surface of the
bony septum and by the membrane of Reissner.

3. The true membranous cochlea. This is the spiral, triangular canal>

PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR 759

bounded externally by the periosteum of the corresponding portion of the
wall of the cochlea, internally, by the membrane of Reissner, and on the
other side, by the membrana basilaris. What is thus called the membranous
cochlea is divided by the limbus laminae spiralis and the membrana tectoria
into two portions ; a triangular canal above, which is the larger, and a quadri-
lateral canal below, between the limbus and membrana tectoria and the mem-
brana basilaris. The quadrilateral canal contains the organ of Corti and
various complex anatomical structures. The relations of these divisions of
the cochlea are shown in Fig. 272.

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 mem-
branous cochlea to each other and to the scalae of the cochlea are shown in
Pig. 271.

Liquids of the Labyrinth. — The labyrinth contains a certain quantity of
a clear, watery liquid, called the humor of Cotugno or of Valsalva. A por-
tion of this liquid surrounds the utricle and saccule, the semicircular canals
and the true membranous cochlea ; and this is known as the perilymph of
Breschet. Another portion of the liquid fills the true membranous labyrinth ;
and this is sometimes called the humor of Scarpa, but it is known more gen-
erally as the endolymph of Breschet. The perilymph occupies about one-
third of the cavity of the bony vestibule and semicircular canals and both
scalae of the cochlea. Both this liquid and the endolymph are clear and wat-
ery, becoming somewhat opalescent on the addition of alcohol. The spaces
in the labyrinth are directly connected with the lymphatic system. The
space occupied by the perilymph communicates with lymphatics, chiefly
through the aqueduct of the cochlea, but there is also a communication
through the internal auditory meatus, with the space beneath the dura mater.
The endolymph passes to the subarachnoid space, beneath the arachnoid cov-
ering of the auditory nerve. As far as is known, 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 con-
nected.

Distribution of the Nerves in the Labyrinth. — As the auditory nerves
enter the internal auditory meatus, they divide into an anterior, or cochlear,
and a posterior, or vestibular 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 dis-
tributed to the utricle, the superior semicircular canal and the external semi-
circular canal. The middle branch is distributed to the saccule. The pos-
terior branch passes to the posterior semicircular canal. The nerves distrib-
uted to the utricle and saccule penetrate at the points occupied by the
otoliths, and the nerves going to the semicircular canals pass to the ampullae,
which also contain otoliths. (See Fig. 269.) In each ampulla, at the point

760

SPECIAL SENSES.

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 ves-
tibule and the ampullae of the semicircular canals. At the points where the
nerves enter, in addition to the otoliths, are cylindrical cells of various forms,
which pass gradually into the general endothelium of the cavities. In addi-
tion to these cells, are fusiform, nucleated bodies, the free ends of which are
provided with hair-like processes, called fila acustica. These are about ^
of an inch (31 //,) in length and are distributed in quite a regular manner
around the otoliths. The nerves form an anastomosing plexus beneath the
endothelium, and they probably terminate in the fusiform bodies just de-
scribed 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
maculae acusticae and the ampullae.

The cochlear division of the auditory nerve breaks up into a number of
small branches, which pass through foramina at the base of the cochlea, in
what is called the tractus spiralis foramiiiulentus. 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 bipolar cell, these
cells together forming a
spiral ganglion, known as
the ganglion of Corti. Be-
yond this ganglion the
nerves form an anastomos-
ing plexus and finally enter

FIG. 272.— Distribution of the cochlear nerve in the spiral lamina ft,.-. ~,10/l™lof rv^ol r>onol ^»
of the cochlea. The cochlea is from the right side and is seen tne quadrilateral Canal, Or

nf finrti
Ol UOrtL

is from the right

from its ant ero-inferior part (Sappey).

1, trunk of the cochlear nerve ; 2, 2, 2, membranous zone of the i ,

spiral lamina : 3, 3, 3, terminal expansion of the cochlear paSS into this Canal
nerve, exposed in its whole extent by the removal of the su- r
perior plate of the lamina spiralis ; 4. orifice of communica- Suddenly become pale and
tion of the scala tympani with the scala vestibuli. , . , mi

exceedingly fine. They

probably are connected finally with the organ of Corti, although their exact
mode of termination has not yet been determined. The course of the nerve-
fibres to their distribution in the cochlea is shown in Fig. 272.

Organ of Corti. — In the quadrilateral canal, bathed in the endolymph,
throughout its entire, spiral course, is an arrangement of pillars, or rods, which
are regular, like the strings of a harp in miniature. These are the pillars of
Corti. These pillars are external and internal, with their bases attached to the
basilar membrane and their summits articulated above, so as to form a regu-
lar, spiral arcade, enclosing a triangular space which is bounded below by th*

ORGAN OF CORTI.

761

basilar memorane. The number of the elements of the organ of Corti is es-
timated at about 4,500, for the outer, and 6,500, for the inner rods. The
relations of these structures to the membranous labyrinth are seen in Fig.
271. The external pillars are longer, more delicate and more rounded than

FIG. 273.— 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 ; S,
cell on its internal side ; 4, anterior extremity ; 5, convex surface, by which it is joined to the inter-

nal pillar ; 6, prolongation of this extremity.

B, internal pillar of the organ of Corti : 1, body, or middle portion ; 2, posterior extremity ; 3, 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, tie 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 attached to the posterior extremities ; 4, 4, anterior extremities joined
together ; 5, terminal prolongation of this extremity.

the internal pillars. The form of the pillars is more exactly shown in Figs.
273 and 274, the latter figure, however, exhibiting other structures which
enter into the constitution of the organ of Corti. It will be remarked that

FIG. 274.— Vertical section of the organ of Corti of the dog ; magnified 800 diameters (Waldeyer).
i-ft, homogeneous layer of the basilar membrane ; v, tympanic layer, with nuclei, granular cell-proto-
plasm and connective tissue ; a3 , tympanic lip of the crista spiralis ; c, thickened portion of the
basilar membrane ; d. spiral vessel ; e, blood-vessel ; /, h. bundle of nerves ; g, epithelium ; i. inner
hair-cell, with its basilar process, k ; 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, <j, r, outer hair-cells, with traces of the
cilia : f, bases of two other hair-cells ; z, Hensen's prop-cell ; M,, lamina reticularis ; w, nerve-fibre
passing to the first hair-cell, p.

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

762 SPECIAL SENSES.

arrangement 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 than at the base of the
cochlea, the longest rods, at the summit, measuring, according to Pritchard,
about ^-J-g- of an inch (125 /*), and the shortest, at the base, about -g^ of an
inch (50 /*). At the base of the cochlea the two sets of rods are about equal
in length. From the base to the apex, both sets, outer and inner, progress-
ively increase in length, and the outer rods become the longer, so that near
the apex they are nearly twice as long as the inner. The anatomical rela-
tions 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 structure of the organ of Corti. The most important of these are
the inner and the outer hair-cells. These are 16,400 to 20,000 in number
(Hensen, Waldeyer). The inner hair-cells are arranged in a single row, and
the outer hair-cells, in three rows. Nothing definite is known of the uses of
these cells. The relations of these parts are shown in Fig. 274. It is sup-
posed by some anatomists that the filaments of the auditory nerves terminate
in the cells above described ; but this point is not definitely settled.

USES OF DIFFERENT PARTS OF THE INTERNAL EAR.

The precise uses of the different parts found in the internal ear are ob-
scure, 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 appa-
ratus, 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 uses of the parts composing the external and the middle ear
are chiefly accessory. The sonorous waves are collected by the pavilion and
are conveyed by the external meatus, to the middle ear ; the membrana tym-
pani vibrates under their influence ; and they are thus collected, repeated and
transmitted to the internal ear.

Uses of the Semicircular Canals. — In the experiments of Flourens, upon
pigeons and rabbits (1824), it was shown that destruction of the semicircular
canals had apparently no effect upon the sense of hearing, while destruction
of the cochlea upon both sides produced complete deafness. In addition it
was observed that destruction of the semicircular canals on both sides was
followed by remarkable disturbances in equilibration. The animals could
maintain the standing position, but so soon as they made any movements,
" the head began to be agitated ; and this agitation increasing with the move-
ments of the body, walking and all regular movements finally became impos-
sible, in nearly the same way as when equilibrium and stability of move-

USES OF THE PARTS CONTAINED IN THE COCHLEA. 763

merits 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 observations upon the human subject in the condition
known as Meniere's disease. As far as can be judged from experimental
data, it does not seem probable that the nerves directly concerned in audition
are distributed to any considerable extent in the semicircular canals. In-
deed the uses of these parts is exceedingly obscure; for it can hardly be
admitted, upon purely anatomical grounds, that they are concerned in the
discrimination of the direction of sonorous vibrations, an idea which has been
advanced by some physiologists.

Uses of the Parts contained in the Cochlea. — There can be no doubt with
regard 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 hear-
ing and which receive the impressions of sound are distributed mainly in
the cochlea. An analysis of sonorous impressions shows that they possess
various attributes, such as intensity, quality and pitch. As far as the termi-
nal filaments of the auditory nerve are concerned, it is evident that the in-
tensity of sound is appreciated in proportion to the power of the impression
made upon these nerves. With regard to quality of sound, it has been seen
that this is due to the form of sonorous vibrations, and that musical sounds
usually are compound, their quality depending largely upon the relative power
of the harmonics, partial tones etc. It has also been 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 vibrations conveyed to the ear by the atmosphere are
repeated, there is reason to believe that the quality as well as the pitch is re-
produced.

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. With the exception of the internal ear, the action of
different portions of the auditory apparatus is simply to conduct and repeat
sonorous vibrations ; and the sole use of these accessory parts, aside from the
protection of the organs, is to convey the vibrations to the terminal, nervous
filaments. Whatever be the uses of the membrana tympani in repeating
sounds by influence, it is certain that this membrane possesses no true, audi-
tory nerves, and that the auditory nerves only are capable of receiving im-
pressions 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.

In view of the arrangement of the organ of Corti, with its eleven thousand
or more rods of different lengths arranged with a certain degree of regularity,
a number more than sufficient to represent all the notes of the musical scale,
it is not surprising that they should be regarded as capable of repeating all
the notes heard in music. Helmholtz formulated this idea in the theory that

764 SPECIAL SENSES.

sounds conveyed to the cochlea throw into vibration only those elements of
the organ of Corti which are tuned, so to speak, in unison with them. Ac-
cording to this hypothesis, the rods of Corti constitute a harp of several
thousand strings, played upon, as it -were, by the sonorous vibrations. The-
ories analogous to the one proposed by Helmholtz, but of course lacking the
basis of exact anatomical and physical details developed by modern researches
and experiments, were advanced by Du Verney (1683) and by Le Cat (1767).

Viewing the question anatomically, it is by no means certain that the rods
of Corti are so attached and stretched that they are capable of separate and
individual vibrations. It has not been demonstrated that certain of these
rods vibrate under the influence of certain notes or that they are tuned in
accord with certain notes. Hensen and others have rejected the theory of
Helmholtz, basing their opinions mainly upon the anatomical arrangement
of the rods of Corti. Hensen assumed it to be a physical impossibility for
the different rods to vibrate individually, and he regarded it as improbable
that the rods are tuned in accord with different musical notes. Similar ob-
jections apply to the theory that different transverse fibres in the membrana
basilaris vibrate in accord with particular notes. There is, indeed, no theory
which affords an entirely satisfactory explanation of the mechanism of the
final appreciation of the pitch of musical sounds.

It is not absolutely necessary that sonorous vibrations should pass to the
cochlea through the external ear and parts in the middle ear. Sounds may
be conducted to the auditory nerves through the bones of the head or through
the Eustachian tube, as is shown by the simple and familiar experiment of
placing a tuning-fork in contact with the head or between the teeth, the ears
being closed.

The action of the two ears does not seem to be absolutely necessary to the
correct appreciation of auditory impressions ; but variations in the force of
such impressions, made upon either ear, aid in determining the direction of
sounds, although errors are often made in this regard.

The estimate of the distance of sounds is made by judging of the intensity,
in connection with information obtained through other senses, especially the
sense of sight. The power of estimating distance is largely influenced by
experience and education.

Centres for Audition. — The centres for audition in dogs and monkeys
are in the superior temporo-sphenoidal convolution (Ferrier, Munk). In
man these centres are in the first (superior) and second temporal convolu-
tions of the temporo-sphenoidal lobe, which are supplied by the fourth branch
of the middle cerebral artery. This has been ascertained by pathological
observations as well as by experiments on the lower animals. In man the
action of these centres is not completely crossed, and destruction of the cen-
tre upon one side does not cause complete deafness in either ear. Complete
destruction of the centres on both sides, however, produces total deafness.
Injury of the first temporal convolution is often followed by the condition
known as word-deafness, in which the subject hears the sound of words, but
these sounds convey to him no idea. This is the psychical, auditory centre,

FEMALE ORGANS OF GENERATION. 765

and it is confined to the first temporal convolution on the left side (Wer-
nicke). Word-deafness is analogous to the condition already described
under the name of word-blindness, and the centre usually is confined to the
left side of the cerebrum. It has been suggested by Westphal that this
centre may be on the right side of the cerebrum, in left-handed persons.

CHAPTER XXIV.

ORGANS AND ELEMENTS OF GENERATION.

General considerations— Female organs of generation— General arrangement of the female organs — The
ovaries — Graafian follicles — The parovarium — The uterus — The Fallopian tubes — Structure of the ovum
— Discharge of the ovum — Passage of ova into the Fallopian tubes — Puberty and menstruation — Changes
in the Graafian follicle after its rupture (corpus luteum) — Male organs of generation — The testicles —
Vesiculae seminales — Prostate — Glands of the urethra — Male elements of generation — Spermatozoids.

GENERATION is one of the most important of the animal functions, and
as such usually is treated of quite fully in works upon physiology ; but a
more or less extended account of this function is also to be found in every
complete treatise on ' anatomy and in most works on obstetrics. While the
physiological history of the human organism would not be complete without
touching upon generation and development, it does not seem desirable to
give a very full description of these processes, in which there would neces-
sarily be a repetition of what is always to be found in works upon other
subjects.

The question of so-called spontaneous generation in some of the lower
animals was formerly much discussed by physiologists. This, however, is now
of purely historical interest. As actual knowledge of facts has accumulated,
the limits of what was thought to be spontaneous generation have become
more and more restricted ; until now it is generally admitted that sponta-
neous generation does not exist in the history of animals. The entire ques-
tion, therefore, may be dismissed with this simple statement. There are,
however, certain distinct forms of generation ; but the only one that has any
considerable importance in connection with human physiology is generation
of new beings by the union of male and female elements in the fecundation of
the ovum, with the development of the fecundated ovum. This is known as
sexual generation. The two elements of generation are developed in separate
beings, male and female, and these elements are brought together normally
in what is known as sexual connection, or copulation.

FEMALE ORGANS OF GENERATION.

A knowledge of certain points in the anatomy of the female organs of
generation is essential to the comprehension of the most important of the
processes of reproduction. Following a fruitful intercourse of the sexes,

50

766 GENERATION.

the function of generation, 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, con-
tinues its development, and is nourished and grows, until the foetus at term
is brought into the world. It will not be necessary to describe minutely the
anatomy of the external parts, as these are concerned only in sexual inter-
course and in parturition ; which latter, though a purely physiological pro-
cess, forms the greatest part of the science of obstetrics, is considered elabo-
rately in treatises on this subject and usually is not 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 the ovaries.
The ovaries are the true, female organs, in which alone the female element
can be produced. The Fallopian tubes and the uterus are accessory in their
uses, 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 fecunda-
tion.

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 from 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
pelvis. With the body erect, the angle of the uterus with the perpendicular
is about forty-five degrees.

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 ante-
rior surface to the bladder ; the posterior ligament extends from the poste-
rior surface to the rectum ; the round ligaments 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 ligaments ex-
tend from the sides of the uterus to the walls of the pelvis.

The uterus and the broad ligaments partially divide the pelvis into two
portions ; and these ligaments, which are formed of a double fold of perito-
neum, present a superior, or posterior surface, and an inferior, or anterior sur-
face. The superior, or anterior border of this fold is occupied by the Fallo-
pian 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 posterior surface, is the ovary, which
is connected with the fibrous tissue between the two layers of the ligament.

THE OVARIES. 767

At the hilum of the ovary, as will be seen farther on, the structure of the
peritoneum undergoes a marked change.

The Ovaries. — The ovaries, attached to the broad ligament and project-
ing from its posterior surface, lie nearly horizontally in the pelvic cavity, on

FIG. 275.— Uterus, Fallopian tubes and ovaries ; posterior view (Sappey).

1, ovaries ; 2, 2, Fallopian tubes ; 3, 3, fimbriated extremity of the left Fallopian tube, seen from its con-
cavity ; 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.

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. By closely examining their mode of connec-
tion 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.

Each ovary is about an inch and a half (38*1 mm.) in length, half an
inch (12-7 mm.) in thickness, and three-quarters of an inch (19-1 mm.) 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 ex-
tremity 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. 275 (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 sixty to
one hundred grains (3'9 to 6-5 grammes), and these organs are largest in the
adult virgin. Its attached border is called the hilum ; and at this portion
the vessels and nerves penetrate. The surface is marked by rounded, trans-
lucent elevations, produced by distended Graafian follicles, with little cica-
trices indicating the situation of ruptured follicles. There may also be
seen, between the distended follicles, corpora lutea in various stages of
atrophy.

768 GENERATION.

After the peritoneum has reached the ovary, its fibrous layer becomes
indistinct and fuses with the fibrous stroma of the ovary itself. The peri-
toneal endothelium here undergoes a change, and the cells covering the
ovary are cylindrical. This change in the structure of the peritoneum is
abrupt and is indicated by a distinct line surrounding the hilum of the
ovary. There seems to be little difference between the epithelial cells cov-
ering the ovaries and those lining the Fallopian tubes, except that the
latter are provided with cilia.

On making a section of the ovary, it is readily seen by the naked eye that
the organ is composed of two distinct structures ; a cortical substance, for-
merly called the tunica albuginea, which is about YV °^ an inc^ (1 mm-) in
thickness, and a medullary substance containing a large number of blood-
vessels. The cortical substance alone contains the G-raafian follicles. The
external layer of this is denser than the deeper portion, but there is no
distinct fibrous membrane such as is sometimes described under the name of
the tunica albuginea.

The cortical substance of the ovary consists of connective tissue in sev-
eral layers, the fibres of which are continuous with the looser fibres of the
medullary portion. In the substance of this layer, are embedded the ova,
enclosed in the sacs called Graafian follicles. This layer contains a few
blood-vessels, coming from the medullary portion, which surround the fol-
licles.

The medullary portion of the ovary is very vascular and is composed of
small bands, or trabeculae of connective tissue, with non-striated muscular
fibres. The blood-vessels, which penetrate at the hilum, are large and con-
voluted, especially at the hilum itself, where there is a mass of convoluted
veins, forming a sort of vascular bulb (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.

In addition to the blood-vessels, the ovary receives nerves from the sper-
matic 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 DeGraaf, in 1672, and are known by his name. They contain the ova,
undergo a series of peculiar changes, enlarge, approach the surface of the
ovary, and finally are ruptured, discharging their contents into the fimbriated
extremity of the Fallopian tube. The Graafian follicles are developed ex-
clusively in the cortical substance. If the ovary be examined at any period
of life, no follicles are found 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 entire
number of follicles of all sizes in each ovary is about 36,000 (Henle). Ac-
cording to the table of measurements given by Waldeyer, the primordial fol-
licles in the human embryon, at the seventh month, measure -gfa to *icr of
an inch (30 to 100 /A) in diameter, and the primordial ova, y^r to TffW of
an inch (15 to 25 /A).

GRAAFIAN FOLLICLES. 769

The ovary appears very early in embryonic life, in the form of a cellular
outgrowth from the Wolffian body. Most of its cells are small, but as early
as the fourth or fifth day, in the chick, 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 develop-
ment of the ovary some of the peripheral cells penetrate in the form of tubes
(the so-called ovarian tubes) and at the same time, delicate processes, formed
of connective tissue and blood-vessels, extend from the fibrous stroma under-
lying the epithelium and enclose collections of cells. It is probable that
there are two modes of formation of follicles ; one, by the penetration of epi-
thelial tubes from the surface, which become constricted and divided off into
closed cavities, and the other, by the extension of fibrous processes from be-
low, which enclose little collections of cells. By both of these processes, lit-
tle cavities are formed, which contain a number of cells. In each of these
cavities, there is a single, large, rounded cell, with a large nucleus, this cell
being a primordial ovum ; and in addition, in the same cavity, there are other
cells, which are the cells of the Graafian follicle. The exact nature of the
processes just described has been studied in the chick; but it is probable
that the same kind of development occurs in mammalia aridv in the human
subject.

From birth until just before the age of puberty, the cortical substance of
the ovary contains several 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 various stages
of their development. In the adult, according to Waldeyer, the smallest
Graafian follicles measure -$fa to -g-J-g- of an inch (30 to 40 /*,), and the small-
est ova, a little more than 10*60 of an inch (26 /x,). 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 the ova ar-
rive at their full development.

The most important 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 all sizes are
observed, between the smallest primordial follicles, -^ of an inch (30 /*), and
the largest, nearly \ an inch (12 mm.) in diameter. In follicles that have
attained any considerable size, there are the fully developed ova, one in each
follicle — except in very rare instances, when there are two — and these ova
have a diameter of about -^ of an inch (200 ^). In the process which cul-
minates in the discharge of the ovum into the fimbriated extremity of the
Fallopian tube, the Graafian follicle gradually enlarges, becomes distended
with liquid and finally breaks through and ruptures upon the surface of the
ovary.

Fig. 276 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.

770

GENERATION.

The ova here present an epithelial covering and are embedded in a mass of
the epithelial lining of the follicle, the membrana granulosa, this mass being
called the discus or cumulus proligerus.

At or near the period of their maturity the Graafian follicles present
several coats and are filled with an albuminous liquid. The mature follicles

FIG. 276.— Portion of a sagittal section of the ovary of an old bitch (Waldeyer).

o, ovarian epithelium ; 6, 6, ovarian tubes ; c, c, younger follicles ; d, older follicle ; e, discus proligerus,
with the ovum ; /, epithelium of a second ovum in the same follicle ; gr, fibrous coat of the follicle ;
h. proper coat of the follicle ; £, epithelium of the follicle (membrana granulosa) ; fc, collapsed,
atrophied follicle ; I, blood-vessels ; m, m, cell-tubes of the parpvarium, divided longitudinally and
transversely ; t/, tubular depression of the ovarian epithelium, in the tissue of the ovary ; z, begin-
ning of the ovarian epithelium, close to the lower border of the ovary.

project just beneath the surface and form little, rounded, translucent eleva-
tions. The smallest follicles are near the surface, and as they enlarge, at
first they become deeper, as is seen in Fig. 276, becoming superficial only as
they approach the condition of fullest distention.

Taking one of the largest follicles as an example, two fibrous layers can
be distinguished ; an outer layer, of ordinary connective tissue, and an inner
layer, the tunica propria, formed of the same kind of tissue, with the differ-
ence that as the follicle enlarges the inner layer becomes vascular. The

THE UTERUS.

771

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 is not invariable ; sometimes it is at
the most superficial, and sometimes it is at the deepest part of the Graafian
follicle.

The liquid of the Graafian follicle is alkaline, slightly yellowish and not
viscid. It contains 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.

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 twelve to fifteen
tubes of fibrous tissue, lined by ciliated epithelium. It has no physiological
importance.

The Uterus. — The form, situation and relations of the uterus and Fallo-
pian tubes have already been indicated and are shown in Fig. 275.

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 open-

FIG. 277.— Virgin uterus. A.— anterior view. B.— median section. C.— transverse section (Sappey).

A. 1, body ; 2, 2, angles ; 3, cervix ; 4, site of the os internum ; 5, vaginal portion of the cervix ; 6, ex-
ternal os ; 7, 7, vagina.

B. 1, 1, profile of the anterior surface ; 2, vesico-uterine cul-de-sac : 3. 3. profile of the posterior surface;

4, body ; 5, neck ; 6, isthmus : 7, cavity of the body ; 8. cavity of the cervix ; 9, os internum ; 10,
anterior lip of the os externum ; 11, posterior lip ; 12, 12, vagina.

C. 1, cavity of the body ; 2, lateral wall ; 3, superior wall ; 4, 4, cornua ; 5, os internum ; 6, cavity of the

cervix ; 7, arbor vitae of the cervix ; 8, os externum ; 9, 9, vagina.

ing into the vagina, called the 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 is shown in Fig. 277 (A). It usually is about three inches
(76-2 mm.) in length, two inches (50-8 mm.) in breadth at its widest portion,
and one inch (25-4 mm.) in thickness. Its weight is one and a half to two
and a half ounces (42-5 to 71 grammes). It is somewhat loosely held in place

772

GENERATION.

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 reflected upon the urinary bladder. At the
sides of the uterus, the peritoneal covering, a little below the entrance of the
Fallopian tubes, becomes loosely attached and leaves a line for the penetra-

Fio. 278.— 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.

tion of the vessels and nerves. Fig. 277 (C), giving a view of the interior of
the uterus, shows a triangular cavity, with two cornua corresponding to the
openings of the Fallopian tubes, and very thick walls, the greatest part of
which is composed of layers and bands of non-striated muscular fibres.

The muscular walls of the uterus are composed of non-striated fibres ar-
ranged in several layers. These fibres are spindle-shaped and always nucle-
ated, the nucleus 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, there are many rounded and spindle-shaped cells of con-
nective tissue, 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 bun-
dles or fasciculi, which in certain of the layers interlace with each other in
every direction. The fibres are divided into external, middle and internal
layers.

The external, muscular layer, which is very thin but distinct, is closely

THE UTERUS.

773

attached to the peritone-
um. When the uterus is
somewhat enlarged after
impregnation, there are ob-
served oblique and trans-
verse, 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 they also extend be-
tween the layers of the
broad ligament. This ex-
ternal layer is so thin that
it can not be very efficient
in the expulsive contrac-
tions Of the Uterus ; but
from its connections with

., T, ,, ,

the I allopian tubes and

the ligaments, it is useful

in holding the uterus in place.

FIG. 280.— Inner layer of muscular fibres of the uterus

(Liegeois). '

a, a, rings around the openings of the Fallopian tubes ;
6, 6, circular fibres of the cervix.

FlG 279.— Superficial muscular fibres of the anterior surface of

the uterus (Li6geois>-

a, a, round ligaments ; 6, 6, Fallopian tubes ; c, c, c, e, e, transverse
fibres ; d, /, longitudinal fibres.

It does not extend entirely over the sides of
the uterus.

The middle, muscular layer is
the one most efficient in the partu-
rient contractions of the uterus. It
is composed of a thick and intri-
cate net- work of fasciculi interlac-
ing with each other in every direc-
tion.

The inner, muscular layer is ar-
ranged in the form of broad rings,
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 is so closely attached
to the subiacent structures that it

can not be separated to any great

, r j- ,• rm. • •

extent by dissection. There is, in-

774 GENERATION.

deed, no proper submucous, areolar tissue, the membrane being applied di-
rectly to the uterine walls. It is covered by a single layer of cylindrical epi-
thelial cells, with delicate cilia, the movements of which are from without
inward, toward the openings of the Fallopian tubes. Examination of the
surface of the membrane with a low magnifying power shows the open-
ings of a great number of tubular glands. These glands usually are sim-
ple, sometimes branched, dividing, about midway between the opening and
the lower extremity, into two and very rarely into three secondary tubules.
Their course generally is tortuous, so that their length frequently exceeds
the thickness of the mucous membrane. The openings of these tubes are
about -g^-g- of an inch (72 ^) in diameter. Their secretion, 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 very thin, structure-
less walls and are lined with cylindrical, ciliated epithelial cells.

The changes which the mucous membrane of the body of the uterus
undergoes during menstruation are remarkable. Under ordinary conditions
its thickness is ^ to -fa of an inch (1 to 1-.8 mm.) ; but it measures during
the menstrual period -J- to J- of an inch (4'2 to 6-4 mm.).

In the cervix the membrane is paler, firmer and thicker than the mem-
brane of the body of the uterus, and between these two mucous surfaces
there is a distinct line of demarkation. It is 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 vitae uteri, or plicas palmatse.
Throughout the entire cervical membrane, are mucous glands, and in addi-
tion, in the lower portion, are a few rounded, semi-transparent, closed folli-
cles, called the ovules of Naboth, which are cystic enlargements of obstructed
follicles. The upper half of the cervical membrane is smooth but the lower
half presents a large number of 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 epithe-
lium. After puberty, however, the epithelium of the lower portion changes
its character, and there are 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 impor-
tant peculiarities 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 a rich plexus of vessels, anastomosing above with
branches from the ovarian arteries, sending branches over the body of the
uterus, and finally penetrating the organ, to be distributed mainly in the
middle layer of muscular fibres. In their course these vessels present a con-
voluted arrangement and form a sort of mould of the body of the uterus.
Rouget has called this the erectile tissue of the internal generative organs.
It lacks, however, certain of the characters of true, erectile tissue. By
placing the pelvis in a bath of warm water and injecting what he called the

THE FALLOPIAN TUBES. 775

spongy bodies of the ovaries and uterus, by the ovarian veins, he produced a
distention of the vessels and a sort of erection, the uterus executing a move-
ment upward.

In the muscular walls of the uterus, are large veins, the walls of which

Fio. 281. — Blood-vessels of the uterus and ovaries ; posterior view (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, ova-
rian artery ; 7, ovarian vein ; 8, uterine artery ; 9, uterine vein ; 10, 11, uterine plexus ; 12, vaginal
plexus.

are closely adherent to the uterine tissue. During gestation these vessels
become enlarged, forming the so-called uterine sinuses.

Lymphatics are not very abundant in the unimpregnated uterus, but they
become largely developed during gestation. They exist in a superficial and
a deep layer, the deeper vessels being connected with lymph-spaces in the
muscular walls and in the mucous membrane.

The uterine nerves are derived from the inferior hypogastric and the
spermatic plexuses, 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
( Frankenhaeuser ) .

The Fallopian Tubes. — The Fallopian tubes, or oviducts, lead from the
ovaries to the uterus. They are shown in Fig. 275. These tubes are three
to four inches (7*6 to 10*1 centimetres) 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 -fs of an inch (1 mm.) in diameter. From
the cornua they take a somewhat undulatory course outward, gradually in-
creasing in size, so that they are rather trumpet-shaped. Near the ovary

776 GENERATION.

they turn downward and backward. The extremity next the ovary is marked
by ten to fifteen fimbriae, or fringes, which have given this the name of the

FIG. 282.— Section through the right Fallopian tube (Richard).

fimbriated extremity, or morsus diaboli. All of these 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, extend-
ing 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 larger than the
uterine opening. Passing from the uterus, the caliber of the tube gradually
increases as the tube itself enlarges, and there is an abrupt constriction at
the abdominal opening.

Beneath the peritoneal coat, which is formed by the layers of the broad
ligament, is 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-stri-
ated 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.

The mucous membrane of the tube is thrown into folds, which are longi-
tudinal 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 some-
times simple, but more frequently they present secondary folds, often meet-
ing as they project from opposite sides. This arrangement gives an arbores-
cent appearance to the membrane on transverse section of the tube. The
mucous membrane is covered by cylindrical ciliated epithelium, the move-
ment of the cilia being from the ovary toward the uterus. The membrane
of the tubes has no mucous glands.

It is not necessary to give 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 blad-
der and the rectum. It has a curved direction, being 3£ to 3J inches (8 to 9

STRUCTURE OF THE OVUM.

777

centimetres) long in front, and 3J to 4 inches (9 to 10 centimetres) long pos-
teriorly (Sappey). At the constricted portion of the outer opening, there is
a muscle, called the sphincter vaginae, and the tube is somewhat narrowed
at its upper end, where it embraces the cervix uteri. The inner surface pre-
sents 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 the passage of
the child. It pre-
sents a proper coat
of dense, fibrous tis-
sue, with longitud-
inal and circular
muscular fibres of
the non-striated va-
riety. Surrounding
it, is a rather loose,
so-called erectile tis-
sue, which is most
prominent at its
lower portion.

The parts com-
posing the external
organs are abund-
antly supplied with

vpccpk nnrl nprvp«
-ryes.

In thp pli+nri« wViinVi
lb'WJ

corresponds to the
penis of the male, and on either side of the vestibule, there is a true erec-
tile tissue.

Structure of the Ovum. — The description which is to follow is based
upon recent and extended researches into the minute anatomy of the
healthy human ovum (Nagel, 1888), which have been rendered possible by
the frequency with which, within the past few years, normal ovaries are
removed in surgical operations :

The ovum lies in the Graafian follicle, embedded in the mass of granu-
lar cells which form the discus proligerus. Surrounding the ovum are cells
similar to those found in other parts of the membrana granulosa, and two
or three layers of columnar cells, the latter lying next the zona pellucida.
These columnar cells constitute the corona radiata (Bischoff). The ovum
itself presents the following structures : (1) Zona pellucida ; (2) peri-
vitelline space ; (3) a clear, outer zone of the vitellus ; (4) protoplasmic
zone (formative yelk) ; (5) deutoplasmic zone (nutritive yelk) ; (6) ger-
minal vesicle (Purkinje) ; germinal spot (Wagner). The extremely thin
membrane within the zona pellucida and immediately surrounding the
vitellus, described under the name of vitelline membrane by some anato-
mists, was not observed by Nagel in the human ovum.

FIG. 283.— External erectile organs of the female CLiegeois).
A, pubis ; B, B, ischium ; C, clitoris ; D, 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.

778 GENERATION.

The ovum is globular, with a diameter of about -^ of an inch (165 to
170/x,) measured from the outer border of the zona pellucida.

The zona pellucida (zona radiata, or vitelline membrane) is -^^ to -j-^
of an inch (20 to 24 ft) in thickness. It is a strong membrane appearing
in the form of a clear zone in the mass of surrounding cells. It is marked
by striae, which are thought by some anatomists to indicate the presence of
small pores ; but the large, single opening called a micropyle, which is
found in many of the osseous fishes and in mollusks, has not been demon-
strated in the human ovum.

Between the zona pellucida and the vitellus, is a narrow space, about
26}00 of an inch (1-3 ft) in diameter. This has been called the peri vitelline
space (Nagel).

The vitellus is contained in the zona pellucida. It presents a clear, outer
zone -gTjVo to ^^5-5- of an inch (4 to 6 ft) in diameter. This can not be dis-
tinguished from the protoplasmic zone, except in perfectly fresh ova. It is
composed of clear protoplasm without granules and represents that portion
of the protoplasm of the vitellus which is not at any time converted into
deutoplasm (Nagel). Within the clear zone, is the protoplasmic zone
(formative yelk). This presents very fine granules, and the zone is -^-^
to y^nr of an inch (10 to 21 ft) in thickness. Occupying the central por-
tion of the vitellus, is the deutoplasm (nutritive yelk), forming a mass about
g-J^j- of an inch (82 to 87 ft) in diameter. The deutoplasm presents granules
of different sizes and different refractive power. Treated with eosin, the
protoplasm becomes rose-colored, but the deutoplasm is unaffected. As the
ovum reaches its final stage of development, the protoplasmic zone, as far
as that portion which forms the so-called outer zone, is gradually changed
into deutoplasm. In Plate II, Fig. 1, an ovum is represented in which this
change is in progress.

The germinal vesicle lies always in the protoplasmic zone, just out-
side of the deutoplasm. As the mass of deutoplasm extends, the germi-
nal vesicle is pushed toward the periphery of the vitellus. The vesicle
measures about 3-5^ of an inch (25 to 27 ft) in diameter.
It is globular, with a double contour. In hardened prepa-
rations, it presents a frame-work of fine anastomosing
fibres. In the fully developed human ovum, no amoeboid
movements have as yet been observed in the germinal

FiQ.v*.-p>-inwrdiai vesicle (Na£e1)' In Plate IT>. FiS' 2> the germinal vesicle
ovum with two ger- is seen Iving upon and not within the deutoplasmic zone.

minal vesicles and J x .

foincuiar epitheii- The mature ovum presents but one germinal vesicle. I wo

um ; from the ova- . n .

ry of a new-born germinal vesicles, however, are sometimes lound in primor-

child (Nagel). ° '

dial ova (see Fig. 284).

The germinal spot (Wagner) is contained in the germinal vesicle. Some
vesicles present two germinal spots. In perfectly fresh ova, the germinal
spots have been observed to undergo amoeboid movements.

Discharge of the Ovum. — A ripe Graafian follicle measures •§• to £ of an
inch (10 to 12 mm.) in diameter, and presents a rounded elevation, contain-

Plate II.

Perivitelline Space.

|p Cells of the discus
W proligerus.

•" Oorona radiata.
— - Germinal

Protoplasmic Zone

Cortina radiata

Zona pellucida.

Deutoplasmic Zone.

Perivitelline Space.

( G-erminal Vesicle,
} with an amoeboid
^germinal Spot.

FIG. 2.

Clear Outer Zone.
FIG. l.—Deutoplasm- forming ovum from a Graaftan follicle of a woman 27 years old (Nagel).

FIG. 2. -Fresh ovum from Graafian follicle of a woman 30 years old; slightly reduced from
the original figure (Nagel).

PASSAGE OF OVA INTO THE FALLOPIAN TUBES 779

ing 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 por-
tion situated at the very surface of the ovary undergoes fatty degeneration,
by which this part of the wall gradually becomes weakened. At the same
time, at the other portions of the follicle, there is a proliferation of cells
which project 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 degeneration of the macula, cause the follicle to burst ;
and with the liquid, the discus proligerus and the ovum are expelled. The
formation of a cell-growth in the interior of the follicle is the beginning of
the corpus luteum ; and this occurs some time before the discharge of the
ovum takes place.

The time at which the follicle ruptures, particularly with reference to the
menstrual period, is not definite ; but it is certain that while sexual excite-
ment probably hastens the discharge of an ovum by producing a greater or
less tendency to congestion of the internal organs, ovulation takes place in-
dependently of the action of coition. The opportunities for determining
this fact in the human female are not frequent ; but it has been fully dem-
onstrated by observations upon the inferior animals, and there is now no
doubt with regard to the identity of the phenomena of rut and of menstru-
ation. At stated periods marked by the phenomena of menstruation, one
Graafian follicle — and sometimes more than one — becomes distended and
usually ruptures and discharges its 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 seem entirely conclusive. In a woman who died on the
first day of menstruation, he found a recently ruptured follicle ; in other in-
stances, 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 rupt-
ured by very slight pressure ; and other instances were observed in which
follicles were not ruptured during the menstrual period.

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 illustrated by the occasional occurrence of
extraiiterine pregnancy, a rare accident, which shows that in all probability
the failure of unimpregnated ova to enter the tubes is exceptional. As regards
the mechanism of the passage of the ova into the tubes, however, the expla-
nation is difficult. At the present time there are two theories with regard

780 GENERATION.

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, however, is susceptible of actual demonstration ; and their value is to
be judged from anatomical facts. It is not difficult to understand, taking
into account the situation of the ovaries and the relations of the Fallopian
tubes, how an ovum may pass into the tube, without invoking the aid of
muscular action. It may be supposed, for example, that a Graafian follicle
is ruptured when the fimbriated extremity of the tube is not applied to the
surface of the ovary. One of the fimbriae, longer than the others, is at-
tached 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 epithe-
lium, as indeed, is the mucous membrane of all of the fimbriae, the move-
ments of which produce a current in the direction of the opening, which
would apparently be sufficient to carry the ovum into the tube. At the same
time there probably is a constant flow of liquid over the ovarian surface,
directed by the ciliary cur-rent toward the tube ; and when the liquid of the
ruptured follicle is discharged this, with the ovum, takes the same course
(Becker). This probably is the mechanism of the passage of the ova into
the Fallopian tubes ; and it is possible that the fimbriated extremity may be
drawn toward the ovarian surface, although it is difficult to understand how it
can be closely applied to the ovary and exert any considerable pressure upon
the distended follicle. It is proper to note, also, that the conditions depend-
ent upon the currents of liquid directed by the movements of cilia are con-
stant and could influence the passage of an ovum at whatever time it might
be discharged, while a muscular action would be more or less intermittent.

Puberty and Menstruation. — At a certain period of life, usually between
the ages of thirteen and fifteen, 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 be-
come 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 favorable to rupture and the discharge of ova. The female
becomes capable of impregnation, and continues so, in the absence of patho-
logical conditions, until the cessation of the menses.

The age of puberty is earlier in warm than in cold climates ; and many
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. It is said that
sometimes 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 appearance of the menses, this
is not very marked. When the menses appear early in life, they usually

PUBERTY AND MENSTRUATION. 781

cease at a correspondingly early period ; but this is by no means constant.
There are, also, many exceptions to the ordinary limits to the period of fe-
cundity.

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 there is 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 peri-
odical, sero-mucous discharge from the genital organs, preceding, for a few
months, the regular establishment 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 be-
come 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, lacta-
tion, and severe diseases, 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.

Removal of the ovaries, especially when this occurs before the age of
puberty, usually is 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 abso-
lute, as Storer has reported at least one case, in which menstruation contin-
ued with regularity for more than a year after removal of both ovaries.
Thomas, in three cases of removal of both ovaries from menstruating
women, which he followed for five and a half months to two years and
eleven months after the operation, noted no return of menstruation ; but in
one case, nearly six months after the operation, the patient had " a bloody
discharge from the vagina and all the symptoms accompanying the men-
strual function." Other cases of this kind are on record.

When a cow gives birth to twins, one a male and the other apparently a
female, the latter is called a free-martin and generally has no ovaries. John
Hunter, in his paper on the free-martin, gave a full description of this
anomalous animal and stated that it does not breed or show any inclination
for the bull. In an examination of a free-martin, raised and killed by the
late Prof. James R. Wood, in 1868, the uterus was found rudimentary and
there were no ovaries (Flint).

A menstrual period presents three stages : first, invasion ; second, a san-
guineous 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
malaise, a sense of fullness and weight in the pelvic organs, accompanied
51

782 GENERATION.

with a greater or less increase in the quantity of vaginal mucus, which be-
comes brownish or rusty in color and has a peculiar odor. At this time,
also, the breasts become slightly enlarged. 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 symptoms above indicated occur, the general sense of uneasi-
ness usually is relieved by the' discharge of blood. During this, the second
stage, blood flows from the vagina in variable quantity, and the discharge
continues for three to five days. With regard to the duration of the flow
there are great variations in diiferent individuals. Some women present
a flow of blood for only one or two days ; while in others the flow continues
for five to eight days, within the limits of health. A fair average, perhaps, is
four days.

It is difficult to arrive at even an approximation of the total quan-
tity of the menstrual flow. Burdach estimated it at five to six ounces (about
150 to 175 grammes). According to Longet this estimate is rather low, the
quantity ordinarily ranging between ten and twelve ounces (300 and 350
grammes), occasionally amounting to seventeen ounces (500 grammes), or
even more. It is well known that the quantity is very variable, as is the
duration of the flow ; and the difficulties in the way of 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 com-
paratively 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 epithelium from the
vagina, cylindrical cells from the uterus, leucocytes and a certain quantity
of sero-mucous secretion. Chemical examinations of the fluid have not
shown 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 is probably the same as in epistaxis.
There is a rupture of small blood-vessels, probably 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 and tenacious, and is also alkaline ; the vagi-
nal mucus is decidedly acid, creamy and not viscid, containing 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 intermen-
strual period.

When the menstrual flow has become fully established there is no very

CORPUS LUTEUM.

783

marked general disturbance, except a sense of lassitude, which may become
exaggerated if the discharge 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 Fahr. (about half a de-
gree C.).

If the mucous membrane of the uterus be examined during the menstrual
flow, it is found smeared with blood, which sometimes extends into the Fallo-
pian tubes. It is then much thicker and softer than during the intermen-
strual period. Instead of measuring about ^ of an inch (1/8 mm.) in thick-
ness, as it does under ordinary conditions, its thickness is fa to J of an inch
(4-2 to 6-4 mm.). 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, large numbers
of spherical and fusiform cells. This condition probably precedes the dis-
charge of blood by several days, during which time the membrane is gradu-
ally preparing for the reception of the ovum. There is also a fatty degenera-
tion 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 mem-
brane returns to its ordinary condition. 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 thrown off is in the form of patches.

Changes in the Graafian Follicles after their
Rupture (Corpus Luteum). — After the discharge
of an ovum, its Graafian follicle undergoes certain
retrograde changes, involving the formation of what
is called the corpus luteum. Even when the dis-
charged ovum has not been fecundated, the corpus
luteum persists for several weeks, so that, ovulation

. * Fro. 285.— Sections of two cor-

occurrmg every month, several of these bodies, in vora lutea : natural size

J » (Kolliker).

various stages of retrogression, may sometimes be i, corpus luteum eight days af-

«jppn in flip nvaripc ter conception ; a, external

m aries' coat of the ovary ; 6, stroma

at the fifth

For a certain time anterior to the discharge of
the ovum, there is a cell-proliferation from the
proper coat of the Graafian follicle, and probably
from the membrana granulosa, with a projection of
looped blood-vessels into the interior of the follicle.
This 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. Usually, at the time of rupture of the
follicle, there is a discharge of blood into its interior ; but this is not invaria-

{Orfius°uteunielope °f

784 GENERATION.

ble, although there is always 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 follicle, is surrounded by the fibrous
tunic, and its thickening is most marked at the deepest portion of the follicle.
At the end of about three weeks, the body — which is now called the corpus
luteum, on account of its yellowish or reddish- yellow color — has arrived at
its maximum of development and measures about half an inch (12*7 mm.) in
depth, by about three-quarters of an inch (19*1 mm.) in length, its form being
ovoid. The convoluted wall then contains a layer of large, pale, finely granu-
lar cells, which are internal and are supposed to be the remains of the epithe-
lium 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 (3*2 mm.) at its deepest portion.

After about the third week the corpus luteum begins to contract; 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 fecun-
dated ; and the bodies thus produced are called false corpora lutea, as distin-
guished from corpora lutea formed after conception, which latter are called
true corpora lutea.

Corpus Luteum of Pregnancy. — When a discharged ovum has been fecun-
dated, the corpus luteum passes through its various stages of development
and retrogression much more slowly than the ordinary corpus luteum of
menstruation. The retrogression begins 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 ordinarily is reduced one-half. It still
forms, however, during the first days after parturition, and in the greatest num-
ber of cases, a tubercle which has a diameter of not less than f to ^ of an inch
(7-3 to 8-5 mm.). 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
retrograde 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 " (Coste, 1849). The differences
between the corpora lutea of pregnancy and of menstruation were accurately
described by Dalton, in 1851 and 1877.

MALE ORGANS OF GENERATION.

The chief physiological interest attached to the anatomy of the male or-
gans of generation relates to the testicles, which are the organs in which the
male element of generation is developed. As regards the penis, it will be

THE TESTICLES. 785

necessary to do little more than describe the mechanism of erection and of
the ejaculation of semen.

The Testicles. — The testicles are two symmetrical organs, situated, during
a certain period of intrauterine life, in the abdominal cavity, but finally de-
scending into the scrotum. Immediately beneath the skin of the scrotum, 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 a septum. Within these two sacs the coverings of
each testicle are distinct. These organs are 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 inter-
columnar fascia, the cremaster muscle, the infundibuliform fascia, the tunica
vaginalis and the proper, fibrous coat.

The tunica vaginalis is a shut sac of serous membrane, covering the tes-
ticle and epididymis 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 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 an inch and a half to two inches (38'1 to 50-8 mm.) long, about an inch
and a quarter (31*8 mm.) from the anterior to the posterior border, and
nearly an inch (25-4 mm.) from side to side. The weight of each varies from
three-quarters of an ounce to an ounce (21/2 to 28*3 grammes), 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, inferior enlarge-
ment, called the globus minor. This too is covered with the tunica vaginalis.
Between the membrane covering the testicle and epididymis and the layer
lining the scrotal cavity, is a small quantity of serum, just enough to moisten
the serous surfaces. At the superior portion of the testicle are one or more
small, ovoid bodies, called the hydatids of Morgagni, each attached to the
testicle, by short, constricted processes. These have no physiological im-
portance 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 (1 mm.) in thickness,
and is simply for the protection of the contained structures. Sections of the
testicle, made in various directions, show an incomplete, vertical process of
the tunica albuginea, called the corpus Highmorianum or the mediastinum
testis. This is wedge-shaped, about % of an inch (4*2 mm.) wide at its su-

786

GENERATION.

perior and thickest portion, is pierced by a number of openings, and lodges
blood-vessels and seminiferous tubes. From the mediastinum, delicate, radi-
ating 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 esti-
mated at one hundred and fifty to two hundred. Their shape is pyramidal,
the larger extremities presenting toward the surface, with the pointed ex-
tremities 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-ves-
sels and delicate, connective tissue, called the tunica vasculosa, or pia mater
testis.

Lodged in the cavities formed by the trabeculae of connective tissue, are
the seminiferous tubes, in which the male elements of generation are devel-
oped. 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 median size,
three or four, and the smallest en-
close sometimes but a single tube.
Each tube presents a convoluted
mass, which can be disentangled un-
der 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 inches (7*6
decimetres), and its diameter is -g-J-g-
to ^ of an inch (125 to 166 ^). It
begins by two to seven short, blind
extremities and sometimes by anas-
tomosing loops. The caecal diverti-
cula are usually found in the exter-
nal half of the tube, and their length
is -^ to ^ of an inch (2*1 to 3*2 mm.).

FIG. 286.— Testicle and epididymis of the human sub- The anastomoses ai'6 Sometimes be-
ject (Arnold). , _ ,.,„ , , , ,

a, testicle; 6, 6, 6, &, lobules of the testicle ; c, c, vasa ™een the tubes of different lobules,
/f/,/,' cones of etne Jiobus ma jor^the epididy- sometimes between tubes in the same

mis ; gr, gr, epididymis ; 7i, 7i, vas deferens ; t, vas l/~vnillrk nrirl «r»mpfitr»p<3 Vipfwppn rlif

aberrans ; m, m, branches of the spermatic ar- AODUie ana Sometimes Derwee

tery, to the testicle and epididymis ; n,n,n, ram- fpvpnf r»ninf« in tVip «amp tnhp As

incltion of the artery upon the testicle : o, def- • l P°J D6' AS

the tubes pass toward the posterior
portion of the testicle, they unite into
about twenty straight canals, called the vasa recta, about -fa of an inch (0-33
mm.) in diameter, which penetrate the mediastinum testis. In the mediasti-
num the tubes form a close net- work, called the rete testis ; and at the upper

VAS DEFERENS. 787

portion of the posterior border they pass out of the testicle, by twelve to fif-
teen openings, and are here called the vasa efferentia.

Having passed out of the testicle, the vasa efferentia form a series of
small, conical masses, which together constitute the globus major, or head of
the epididymis. Each of these tubes when unravelled is six to eight inches
(15 to 20 centimetres) long, gradually increasing in diameter, until they all
unite into a single, convoluted tube, which forms the body and the globus
minor of the epididymis. This single tube of the epididymis, when unrav-
elled, is about twenty feet (6 metres) in length.

The walls of the seminiferous tubes in the testicle itself are composed of
connective tissue and of peculiar structures which will be fully described in
connection with the processes of development of the spermatozoids. 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, there is a
fibrous membrane, with longitudinal and circular fibres of non-striated mus-
cular tissue and a lining of ciliated epithelium. The movements of the cilia
are toward the vas deferens. In the lower portion of the epididymis the cilia
are absent. The tubular structures of the testicle, the epididymis and the
beginning of the vas deferens are shown in Fig. 286.

At the lower portion of the epididymis, communicating with the canal,
there usually is found a small mass, formed of a convoluted tube of variable
length, called the vas aberrans of Haller (i, Fig. 286). This is sometimes
wanting.

Vas Deferens. — The excretory duct of the testicle extends from the epi-
didymis to the prostatic portion of the urethra and is a continuation of the
single tube which forms the body and globus minor of the epididymis. It
is somewhat tortuous near its origin, and it becomes larger at the base of the
bladder, just before it is joined by the duct of the seminal vesicle. Near its
point of junction with this duct it becomes narrower. Its entire length is
nearly two feet (about 6 decimetres).

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 ves-

788

GENERATION.

sel may be made to undergo energetic, peristaltic movements, and this has
followed stimulation 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 longitu-
dinal folds in the greatest part of the canal, and presents a number of addi-

tional rugae in the sacculated portion,
these rugae enclosing little, irregularly
polygonal spaces. The membrane is
covered with columnar epithelium,
which is not ciliated. In the sacculated
portion are large numbers of mucous
glands.

Attached to the vas deferens, near
the head of the epididymis, is a little
mass of convoluted and sacculated tubes,
called the organ of Giraldes, or the cor-
pus innominatum. The body is -j- to ^
of an inch (4-2 to 8'5 mm.) long and ^
of an inch (2-1 mm.) broad. Its tubes
are lined with cells of pavement-epithe-
lium, which often are filled with fatty
granules. Generally the tubes present

i IT i •<• i * i •»

only blind extremities, but some of them
occasionally communicate with the tubes
of the epididymis. This part has no
physiological importance. It was re-
garded by Giraldes as the remnant of the Wolffian body, analogous to the
parovarium.

VesiculcB Seminales. — Attached to the base of the bladder and situated
externally to the vasa deferentia, are the two vesiculae seminales. These
bodies are each composed of a coiled and sacculated tube, four to six inches
(10 to 15 centimetres) in length when unravelled, and somewhat 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 cir-
cular direction, and serve as compressors, by the action of which their con-
tents may be discharged. The mucous coat is pale, finely reticulated, and
covered with cells of polygonal epithelium, which are nucleated and contain
brownish granules. The vesiculae seminales undoubtedly serve, in part at
least, as receptacles for the seminal fluid, as their contents often present a
greater or less number of spermatozoids. Although the membrane of the
vesicles seems to produce an independent secretion, the presence of mucous
glands has not been demonstrated.

FIG. 287. — Vas deferens, vesiculce seminales and

ejacuiatory ducts (Liegeois).

MALE ELEMENTS OF GENERATION. 789

The ejaculatory ducts are formed by the union of the vasa deferentia with
the ducts of the vesiculae seminales on either side, and they 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 a very dense, fibrous coat, contains
many glandular structures opening into the urethra, and presents a great num-
ber of non-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 structureless membrane branching as it pene-
trates 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, becoming tessel-
lated near their openings, and sometimes laminated.

The prostatic fluid probably is secreted only at the moment of ejaculation.
Its characters will be considered in connection with the composition of the
seminal fluid. According to Kraus the prostatic fluid has an important
office in maintaining the vitality of the spermatozoids. " The spermatozoa,
in the absence of the prostatic fluid, can not 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 bulb-
ous portion of the urethra, are two small, racemose glands, called the glands
of Mery or of Cowper. These have each a single excretory duct, are lined
throughout with cylindrical epithelium, and secrete a viscid, mucus-like fluid,
which forms a part of the ejaculated semen. Sometimes there exists only a
single gland, and occasionally, though rarely, both are absent. Their uses
are 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 be-
neath the mucous membrane into the muscular structure, presenting here
four or five acini. As these acini are surrounded by muscular fibres, it is
easy to understand how their secretion may be pressed out during erection of
the penis. They are lined throughout with columnar or conoidal epithelium,
and secrete a clear and somewhat viscid mucus, which is mixed with the
ejaculated semen.

MALE ELEMENTS OF GENERATION.

The spermatozoids are the essential, male elements of generation, and
these are produced in the substance of the testicle, by a process analogous to

790 GENERATION.

that of the development of other true, anatomical elements. The testicles
can not be regarded strictly as glandular organs. They are analogous to the
ovaries, and they are the only organs in which spermatozoids can be de-
veloped, 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 office
of the true, fecundating elements.

In the healthy male, at the climax of a normal venereal orgasm, 11 '6 to
92*6 grains (0*75 to 6 grammes) of seminal fluid are ejaculated with considera-
ble force from the urethra, by an involuntary, muscular spasm (Montegazza).
This fluid requires about four days for its complete restoration. The semen
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 reaction is faintly alkaline. It contains in
the human subject 100 to 120 parts of solid matter per 1,000.

The chemical constitution of the semen has not been very thoroughly in-
vestigated and does not present the same physiological importance as its
anatomical characters. Aside from the anatomical elements derived from
the testicles and the genital passages, it presents an organic substance
(spermatine) which has nearly the same chemical characters as ordinary
mucine. It also contains a considerable quantity of phosphates. During
desiccation, elongated, rhomboidal crystals make their appearance, frequently
arranged in groups, which are supposed to be derived from the prostatic fluid
and to consist of phosphoric acid combined with an organic base, the formula
for which, united with hydrochloric acid, is C2H3NHC1 (Schreiner). These
are sometimes called spermatic crystals.

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 vesiculae seminales there is a more
abundant secretion of the grayish fluid, with epithelium, small, colorless con-
cretions of nitrogenized matter, called by Robin, sympexions, and a few
leucocytes. The glandular structures of the prostate produce a creamy secre-
tion with 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 viscid secretion of the glands of Cowper, a certain quantity 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 just mentioned serving sim-

SPERMATOZOIDS.

Y91

FIG. 288.— Spermatozoids, spermatic crystals, leuco-
cytes etc. (Peyer).

ply as a vehicle for the introduction of these bodies into the generative

passages of the female.

Spermatozoids. — In August, 1677, a German student, named Von Ham-

men, discovered the spermatozoids in the human semen and exhibited them

to Leeuwenhoek, who studied them

as closely as was possible with the in-

struments at his command. For a

long time they were regarded as liv-

ing animalcules, although now they

are considered simply as peculiar,

anatomical elements endowed with

movements, like ciliated epithelium.

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.

The fluid taken from the vesiculae

seminales of an adult who has died

suddenly or the ejaculated semen

contains, in addition to the various

accidental or unimportant anatomical elements that have been mentioned, in-

numerable bodies, resembling animalcules, which present a flattened, conoidal
head and a long, tapering, filamentous tail. The tail 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 may
come in contact. Under favorable conditions, particularly
in the generative passages of the female, the movements
may continue for several days.

Microscropical examination does not reveal any very
distinct structure in the substance of the spermatozoids.
The head is about ^^5- of an inch (5 /A) long, -^^ of an
inch (3 /A) broad, and 2sooo of an inch (1 /x,) in thickness.
The tail is about -5^-5- of an inch (50 /A) in length. La
Vallette St. George has found in man and many of the in-
ferior animals the " intermediate segment " described first
by Schweigger-Seidel, though he does not agree with
Schweigger-Seidel that this portion is motionless. The
length of the intermediate segment is about 4o*o6 of an
inch (6 /A). It usually is described as the beginning of the
^1 » an(^ ^ne only difference between this and other por-
dia™eter8 tions is that it is a little thicker. At the extreme end, is

i, flat view ; 2, side a short and excessively fine filament, called the terminal

view ; A A, head; B B, ,,1

intermediate seg- nlament.

terminal filament! °' Water speedily arrests the movements of the sperma-

T92

GENERATION.

tozoids, 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 solutions 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 contents change their character. The walls
are then provided with spindle-shaped cells with a nucleated, protoplasmic
lining, sending prolongations into the interior of the tube. These prolonga-
tions afterward break up into little, rounded bodies called spermatoblasts, a
part of each one of which becomes the head of a spermatozoid (Ebner).
Between the prolongations, are the so-called spermatic cells. The spermato-
blasts send out each one a short process which forms the intermediate seg-

III

FIG. 290.—Spermatogenesis ; semi-diagrammatic (Landois).
I, transverse section of a seminal tubule ; A, external membrane ; B, protoplasmic lining ; c, sperma-

toblast ; s, seminal cells.
II, projection with F, spermatoblasts ; s, seminal cells.

III, spermatoblasts with spermatozoids not yet detached.

IV, spermatoblasts with a spermatozoid detached.

ment of the spermatozoid, and from this a long filament is developed, which
forms the tail. The spermatozoid is detached when its development is complete.

The spermatozoids are motionless while they are within the testicle, the
epididymis or the vasa deferentia, apparently on account of 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 of saline solutions. Once in the vesiculae seminales, and
for a certain time after ejaculation, the spermatozoids are in active motion.
When the spermatozoids have ceased their movements they are incapable
of fecundating the ovum.

The semen, thus developed and mixed with the various secretions before
mentioned, is found during adult life and sometimes even in advanced age,
and under physiological conditions it contains innumerable spermatozoiJs
in active movement; but if sexual intercourse be frequently repeated at
short intervals, the ejaculated fluid becomes more and more transparent,

FECUNDATION. 793

homogeneous and scanty, and it may consist of a small quantity of secretion
from the vesiculaa seminales and the glands opening into the urethra, with-
out spermatozoids 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, sper-
matozoids, normal in appearance and quantity, though in some the vesiculae
seminales contained either none or very few. Some of the persons in whom
the spermatozoids were normal were between seventy-three and eighty-two
years of age. These observations were confirmed by Dieu, who found sper-
matozoids in a man eighty-six years of age. The contents of the seminal
vesicles, in these cases, were examined 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 differences in the cases classed with reference
to the presence of spermatozoids. As the result of his own and of other
recorded observations, Dieu concluded that the power of fecundation often
persists for a considerable time after copulation has become impossible on
account simply of absence of the power of erection.

CHAPTER XXV.

FECUNDATION AND DEVELOPMENT OF THE OVUM.

General considerations— Fecundation— Changes in the fecundated ovum— Segmentation of the vitellus—
Primitive trace— Blastodermic layers— Formation of the membranes— Amniotic fluid— Umbilical vesicle
—Formation of the allantois and the permanent chorion— Umbilical cord— Membranse deciduae— Forma-
tion of the placenta— Uses of the placenta— Development of the ovum— Development of the cavities and
layers of the trunk in the chick— Vertebral column— Development of the skeleton— Development of the
muscles— Development of the skin— Development of the nervous system— Development of the organs
of special sense— Development of the digestive apparatus— Development of the respiratory apparatus-
Development of the face— Development of the teeth— Development of the genito-urinary apparatus —
Development of the circulatory apparatus— Description of the foetal circulation.

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 can
not be fruitful: Coitus may be impossible in old age, from absence of the
power of erection ; but spermatozoids may still exist in the vesiculae seminales,
and fecundation might occur if the seminal fluid could be discharged into
the generative passages of the female. Coitus may take place in the female
before the age of puberty or after the final cessation of the menses, but inter-
course can not then be fruitful. There are many instances of conception
following what would be called imperfect intercourse, as in cases of unrupt-
ured hymen, deformities of the male organs, etc., which show that the actual

794: GENERATION.

penetration of the male organ is not essential, and that fecundation 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 has been
insensible or entirely passive. Unlike certain of the lower animals, the human
subject presents no distinct periodicity in the development of the spermato-
zoids ; but in reiterated connection, an orgasm may occur when the ejaculated
fluid has no fecundating properties.

With regard to the mechanism of erection, little remains to be said after
the description that has been given of true, erectile tissue, in connection with
the physiology of the circulation. The cavernous and spongy bodies of the
penis usually are taken as the type of erectile organs. In these parts the
arteries are large, contorted, provided with unusually thick, muscular coats,
and are connected with the veins by vessels considerably larger than the true
capillaries. They are supported by a strong, fibrous net- work of trabeculae,
which contains non-striated muscular fibres ; so that when the blood-vessels
are completely filled the organ becomes enlarged and rigid. Eesearches with
regard to the nerves of erection show 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 constriction of the veins, except possi-
bly for a short time during the period of greatest excitement. In experi-
ments 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, and is
connected with the genito-spinal centre, in the lower part of the lumbar re-
gion of the spinal cord (Budge). In the experiments referred to, by a com-
parison of the quantity of venous blood coming 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 degree of obstruc-
tion to the outflow of blood, by compression of the veins, and that the rigid-
ity is increased by contraction of the trabecular muscular fibres of the
corpora cavernosa. At the climax of an orgasm, the semen is forcibly dis-
charged from the urethra, by spasmodic contractions of the vesiculse seminales
and the ejaculatory muscles. Although this is the physiological mechanism
of a seminal discharge, friction of the parts, which usually precedes ejacula-
tion, 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.

There are some females, in whom the generative function is performed,
even to the extent of bearing children, who have no actual knowledge of a
true venereal orgasm ; but there are others who experience an orgasm fully
as intense as that which accompanies ejaculation in the male. There is,
therefore, the important difference in the sexes, that preliminary excitement
and an orgasm are necessary to the performance of the generative act in the
male, but are not essential in the female. Still there can be scarcely a doubt

FECUNDATION. 795

that venereal excitement in the female facilitates conception, other condi-
tions being favorable. When excitement occurs in the female there is en-
gorgement of the true erectile tissues and possibly of the convoluted vessels
surrounding the internal organs. The neck of the uterus becomes hardened
and slightly elongated (Wernich) ; and it has been observed by Litzmann
and others, that there occurs a sudden opening and closing of the os, which
exerts more or less suction force. These conditions, however, are not essen-
tial to fecundation, although they may exert a favorable influence upon the
penetration of spermatozoids and may at certain times determine the rupture
of a Graafian follicle.

The spermatozoids, once within the cervix uteri, and in contact with the
alkaline mucus, which increases the activity of their movements, may pass
through the uterus into the Fallopian tubes, and even to the surface of the
ovaries. Precisely how their passage is effected, it is impossible to say. It
can only be attributed to the movements of the spermatozoids themselves, to
capillary action, and to a possible peristaltic action of the muscular structures ;
but these points have not as yet been subjects of positive demonstration. As
regards the human female, it is impossible to give a definite idea of the time
required for the passage of the spermatozoids to the ovaries or for the de-
scent of the ovum into the uterus ; and it is readily understood how these
questions hardly admit of experimental investigation. It is known, how-
ever, that spermatozoids reach the ovaries, and they have been seen in motion
on their surface, seven or eight days after connection.

Fecundation. — The ordinary situation at which the ovum is fecundated
is the dilated, or external portion of the Fallopian tube. All authorities are
agreed that fecundation does not take place in the cavity of the uterus. In
rabbits, when the ovum has descended into the uterus, it is surrounded with
a dense, albuminous coating which the spermatozoids can not penetrate
(Coste). It is possible that this occurs in the human subject. Cases of
abdominal pregnancy show that an ovum may be fecundated on the ovary,
as soon as it is discharged from the Graafian follicle.

The question of the duration of vitality of the spermatozoids, after their
passage into the uterus, has an important bearing upon the time when con-
ception is most liable to follow sexual intercourse. The alkaline mucus of
the internal organs actually favors their movements ; the movements are not
arrested by contact with menstrual blood ; and, indeed, when the spermato-
zoids 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. It seems impossible, there-
fore, to fix any limit to the vitality of these anatomical elements, under phys-
iological conditions; and it is not certain that spermatozoids may not
remain either in the vagina or in the Fallopian tubes and around the ovary,
when intercourse has taken place immediately after a menstrual period,
until the ovulation following. According to the observations of Bossi,
spermatozoids may retain their vitality in the acid mucus of the posterior
vaginal cul-de-sac, or nidus seminis, as long as seventeen days. It is prob-

796

GENERATION.

able that during the unusual sexual excitement which the female generally
experiences after a monthly period, the action of the internal organs, attend-
ing and following coitus, presents the most favorable conditions for the
penetration of the fecundating elements.

Union of the Male with the Female Element of Generation. — In the ova
of certain animals, an opening, called a micropyle, has been demonstrated in
the vitelline membrane (Barry, Keber). This has been seen in the ova of rab-
bits, although its existence is to be inferred, only, in the human ovum. The
penetration of spermatozoids has been observed in the ova of various animals,
including the rabbit (Newport, Coste, Bischoff, Weil, Hensen and others).
Weil has seen spermatozoids wedged in the substance of the zona pellucida,
has added blood to a specimen under observation, and has restored the move-
ments of the spermatozoids while in this position. Hensen has seen twenty
or more spermatozoids within the zona pellucida in rabbits. The number of

spermatozoids which penetrate the ovum,
according to the most recent researches on
fecundation in rabbits, does not seem to be
important, as only one spermatozoid forms
a direct union with the female generative
element. It is assumed that the processes
observed in rabbits nearly represent those
which take place in the human subject.

In the rabbit, spermatozoids begin to
pass through the zona pellucida about thir-
teen hours after copulation (Hensen). By
this time the vitellus usually has become
somewhat shrunken and more or less de-
formed. There is then a space, filled with
a clear liquid, between the vitellus and the vitelline membrane, in which the
spermatozoids are seen in active movement. The vitelline mass, thus sur-
rounded with liquid, undergoes usually movements of rotation. These phe-
nomena have been described as deformation and gyration of the vitellus.
At about this time the germinal vesicle, according to the older writers, dis-
appears ; but it has been lately ascertained that this body is concerned in
the formation of the polar globule. The retraction of the vitellus and the
formation of the polar globule are independent of fecundation ; but the
formation of the polar globule is a process immediately preparatory to the
union of the male with the female generative element, and may properly
be described in connection with the mechanism of fertilization of the ovum.
As the deutoplasmic zone extends from the centre toward the periphery
of the ovum, the germinal vesicle is pushed outward until it reaches the
surface of the vitellus. It then becomes spindle-shaped ; and the granules
of the vitellus near the extremities of the spindle arrange themselves in the
form of stars, forming what has been called the double star, or diaster (Fol).
The extremity of the spindle which is near the surface projects and forms
a clear, mammillated eminence upon the vitellus. This projection becomes

FIG. 291.— Ovum of the rabbit, showing pene-
tration Of spermatozoids and retraction
of the vitellus (Hensen).

FECUNDATION. 797

constricted at its base, and is finally separated in the form of a globule. A
second polar globule is afterward formed in the same way.

That portion of the altered germinal vesicle which remains embedded in
the vitellus is called the female pronucleus. At the point where the polar
globules are separated, a single spermatozoid penetrates the vitellus. The
head and intermediate segment of the spermatozoid become surrounded with
a star, swell up and form the male pronucleus. The male pronucleus unites
with the female pronucleus, and fecundation is complete. The union of the
male with the female pronucleus forms a body which passes downward into
the substance of the vitellus and is called the vitelline nucleus. The furrow
which marks the beginning of segmentation of the vitellus is always ob-
served at the point of separation of the polar globules.

Hereditary Transmission, Superfecundation etc. — The first question
which naturally arises relates to the conditions which determine the sex
of offspring. Statistics show the proportions between male and female
births ; but nothing has ever been done in the way 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 modifica-
tions under varying conditions of climate, season, nutrition etc. It has been
shown, by observations upon certain of the inferior animals, that the pre-
ponderance of sex in births bears a certain relation to the vigor and age of
the parents ; and that old and feeble females fecundated by young and vig-
orous males produce a greater number of males, and vice versa ; but no
exact laws of this kind have been found applicable to the human subject.

No definite rule can be laid down with regard to the transmission of
mental or physical peculiarities to offspring. Sometimes the progeny as-
sumes more the character of the male than of the female parent, and some-
times the reverse is the case, without any reference to the sex of the child ;
sometimes there appears to be no such relation ; and occasionally peculiari-
ties are observed, derived apparently from grandparents. This is true with
regard to pathological as well as physiological peculiarities, as in the inher-
ited tendencies to certain diseases, malformations etc.

A peculiar and, it seems to be, an inexplicable fact is that previous preg-
nancies 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
inferior male, in subsequent fecundations the young are likely to partake
of the character of the first male, even if they be afterward bred with males
of unimpeachable pedigree. 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 children
presenting some of the unmistakable peculiarities of the negro race.

Superfecundation of course does not come in the category of influences
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
52

798

GENERATION.

physical characters ; 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. Many cases illustrating this point are on record.

The following communication, with a photograph, was received in Janu-
ary, 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

FIG. 292.- Mulatto mother with twins, one white and the other black (from a photograph).

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, sleep-
ing 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 chil-
dren was white. 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 brilliant."

CHANGES IN THE FECUNDATED OVUM. 799

Reference has already been made to the curious fact that when a cow
produces twins, one male and the other female, the female, which is called a
free-martin, is sterile and presents an imperfect development of the inter-
nal organs of generation. This has led to the idea that possibly the same
law may apply to the human subject, in cases of twins, one male and the
other female ; but many observations are recorded in gynaecological works,
showing the incorrectness of this view.

It has long been a question whether impressions made upon the nervous
system of the mother can exert an influence upon the foetus in utero.
While many authors admit that violent emotions experienced by the mother
may affect the nutrition and the general development of the foetus, some
writers of authority deny that the imagination can have any influence in
producing deformities. The remarkable cases recorded as instances of- de-
formity due to the influence of the maternal mind are not entirely reliable ;
and it often happens that when a child is born with a deformity, the mother
imagines she can explain it by some impression received during pregnancy,
which she recalls only after she knows that the child is deformed. There
is, indeed, no satisfactory evidence that the maternal mind has anything to
do with the production of deformities in utero.

CHANGES IN THE FECUNDATED OVUM.

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 spermatozoids do not penetrate the vitelline membrane
near the ovary, it presents an obstacle to their passage.

After fecundation of the ovum, at least in many of the lowest forms of
animals, the appearance of the vitellus undergoes a remarkable change, by
which ova that are about to pass through the first processes of development
may readily be 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.

Segmentation of the Vitellus. — Soon after the fecundation of the ovum
and the formation of the vitelline nucleus, a furrow appears at the point of
extrusion of the polar globules. This is met by a furrow upon the opposite
side, and the vitellus is divided into two globes. One of the globes is
slightly larger than the other, and presents fewer and smaller granules.
The larger sphere subsequently forms, by its division, the epiblastic cells,
and the smaller sphere forms the hypoblastic cells. Each sphere is pro-
vided with a distinct nucleus. The two spheres resulting from the first
segmentation of the vitellus are divided, each one into two, making four
spheres. These spheres are again divided into eight — four epiblastic and
four hypoblastic spheres — each with a nucleus (Van Beneden). One of the

800

GENERATION.

hypoblastic spheres now passes to the centre of the ovum ; and the foui
epiblastic spheres, which are at the periphery, divide, each one into two,
making eight epiblastic and four hypoblastic spheres. When this has
occurred, the epiblastic spheres are .smaller and more transparent than the
hypoblastic spheres. The four hypoblastic spheres now divide into eight.
The epiblastic spheres then divide into sixteen, the hypoblastic spheres in
turn divide, and this goes on until the process of segmentation is com-
pleted. In the rabbit, this occurs usually about seventy hours after impreg-
nation (Van Beneden). As segmentation progresses, the epiblastic cells ex-

FIG. 293.— Formation of the blastodermic vesicle (Van Beneden).

A, B, C, D, sections of ova in successive stages of development in the rabbit ; zp, zona pellucida ;
ep, epiblastic cells ; hyp, hypoblastic cells.

tend over the hypoblastic cells, and become irregularly polygonal in form.
The hypoblastic cells occupy the central portion of the ovum. At first
there is a circular space upon the ovum where the epiblastic cells do not
cover the cells of the hypoblast (see Fig. 293, A) ; but this soon becomes
closed by an extension of the cells of the epiblast (see Fig. 293, B). The
hypoblastic cells, at the close of segmentation, are slightly larger than the
cells of the epiblast and are darker and more rounded. The ovum is now
called the morula, on account of its fancied resemblance to a mulberry;
and the cells of which it is composed are called collectively blastodermic

CHANGES IN THE FECUNDATED OVUM. 801

cells. The ovum is probably in this condition when it passes from the
Fallopian tube into the uterus.

Most of the phenomena of segmentation have been observed in the
lower forms of animals ; but there can be no doubt that analogous pro-
cesses take place in the human ovum. In the rabbit, forty-five and a half
hours after copulation, Weil observed an ovum with sixteen segmentations,
situated in the lower third of the Fallopian tube. He observed an ovum,
ninety-four hours after copulation, with a delicate mosaic appearance, pre-
senting 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
occupies more than eight days (Hermann).

After segmentation has been completed, a cavity filled with liquid
appears between the hypoblastic and epiblastic cells, except at that portion
which has last been covered by the epiblast. Here the cells of the hypo-
blast are in contact with the epiblast. The liquid in the interior of the
ovum gradually increases in quantity, the ovum becomes enlarged to the
diameter of -^ to -fa of an inch (O5 to 1 mm.), and is now called the
blastodermic vesicle. The epiblastic cells surround the blastodermic ves-
icle completely, forming a single layer over the greater portion ; and the
hypoblastic cells form a lenticular mass attached to the smaller portion
of the inner surface of the layer of epiblastic cells (see Fig. 293, c and D).
It is at this portion of the ovum that the embryonic spot or area afterward
appears.

The albuminous covering which the ovum has received in the upper
part of the Fallopian tube gradually liquefies and penetrates the vitel-
line membrane, furnishing, it is thought, matter for the nourishment
and development of the vitellus. In the Fallopian tube, indeed, the
adventitious albuminous covering 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 albuminous matter is almost
the sole source of nourishment in the latter and exists in large quan-
tity, while in viviparous animals the quantity is small, is generally con-
sumed as the ovum passes into the uterus, and in the uterus the ovum
forms attachments to and draws its nourishment from the vascular system
of the mother.

Primitive Trace. — Soon after the formation of the blastodermic vesicle,
at a certain point on 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, called the area opaca. The line thus
formed and surrounded by the area pellucida is called the primitive trace.
This primitive trace, or primitive groove, however, is a temporary structure.
After the groove is formed, there appears, in front of but not continuous

802

GENEKATION,

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 devel-

oped into the neural canal.
Blastodermic Layers. —
The blastodermic cells, re-
sulting originally from the
segmentation of the vitel-
lus, are first split appar-
ently into two layers, the
external, or epiblast, and
the internal, or hypoblast.
The epiblast is developed
into the epidermis and its
appendages, the glands of
the skin, the brain and
spinal cord, the organs of
special sense and possibly
some parts of the genito-

. + TK

a, primitive trace; b, area pellucida ; c, area opaca ; d, blaeto- Urinary apparatus. IJlC

re118 * *' *' ^ Beginning to appear on the vitelline

FIG. 294.— Primitive trace of the embryon (Liegeois).

memrane hypoblast is developed into

the epithelium lining the

mucous membrane and glands of the stomach and intestinal canal. There
is a thickening of both of these layers at the line of development of
the cerebro-spinal system, with a furrow that is finally enclosed by an
elevation of the ridges and their union posteriorly, forming the canal for
the spinal cord.

As the spinal canal is developed, a new layer of cells is formed between
the epiblast and the hypoblast, which is called the mesoblast. The meso-
blast itself afterward splits into two layers. All the parts not enumerated
as developed from the epiblast or hypoblast are developed from the two lay-
ers of the mesoblast. The outer layer of the mesoblast, or the epiblastic
mesoblast, unites with the epiblast, and the two membranes together form
what is sometimes called the somatopleure. The inner layer of the meso-
blast, the hypoblastic mesoblast, unites with the hypoblast xto form what is
called the splanchnopleure. The cells lining the vessels, including the
lymphatics, which exist in a single layer, are called endothelial cells. This
name is also applied to the cells lining the serous membranes.

FORMATION OF THE MEMBRANES.

In the mammalia a portion of the blastoderm is developed into mem-
branes by which a communication and union are established between the
ovum and the mucous membrane of the uterus. From the ovum two mem-
branes are developed ; one non-vascular, the amnion, and another, the allan-
tois, which is vascular. The two layers of decidua are formed from the
mucous membrane of the uterus. At a certain part of the uterus, a vascular
connection is established between the mucous membrane and the allantois,

FORMATION OF THE AMNION. 803

and the union of these two structures forms the placenta. The foetal portion
of the placenta is connected with the foetus, by the vessels of the umbilical
cord, and the maternal portion is connected with the great uterine sinuses.

The external covering of the ovum, during the first stage of its develop-
ment, 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 amorphous matter with granules. These are
the first villosities of the ovum, and they assist in fixing the egg in the uter-
ine 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. The vitelline
membrane disappears soon after the passage of the ovum into the uterus,
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, forming the
epiblast, the two layers of the mesoblast and the hypoblast. At about the
time when this thickening begins, a fold of the epiblast and of the external
layer of the mesoblast makes its appearance, which surrounds the thickened
portion and is most prominent at the cephalic and the caudal extremity of
the furrow for the neural canal. This fold increases in extent as develop-
ment advances, passes over the dorsal surface of the embryon and finally
meets so as to enclose the embryon completely. At a certain period of the
development of the amnion, this membrane consists of an external layer,
formed of the external layer of the fold, and an internal layer ; and the point
of union of the two layers, or the point of meeting of the fold, is marked by
a membranous septum.

The two amniotic layers are formed in the way just described, and a com-
plete 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 umbilicus. 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 villosities 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. It encroaches upon and takes the place of the external
amniotic membrane, and is covered with hollow villi, which take the place
of the villi of the amnion. Over a certain portion of the membrane the villi
are permanent. The mode of development of the amnion is illustrated by
the diagrammatic Fig. 295. This figure illustrates the formation of the
amnion, the umbilical vesicle and the allantois. The last two structures are
derived from the hypoblast and the internal layer of the mesoblast.

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, the

804

GENERATION.

structures of the ovum are the following : 1. The chorion, formed of the
two layers of the allantois and penetrated by blood-vessels. 2. The umbili-

--ch

sh

dg

ch

FIG. 295. — Five diagrammatic representations of the formation of the membranes in the mammalia

(Kolliker).

1 : a, a', epiblast ; d, vitelline membrane ; d', villi on the vitelline membrane ; i, hypoblast ; m, m',
mesoblast.

2 : a', external layer of the amnion ; d, d', vitelline membrane ; e, embryon ; d! s, umbilical vesicle ; v I,
k s, s s, folds of the amnion ; d d, m'. s t, hypoblast ; d d, connection of the embryon with the um-
bilical vesicle.

3 : d, d', vitelline membrane ; vl, internal amniotic layer ; e, embryon ; ah, amniotic cavity ; sh,sh,
external amniotic layer ; a m, space between the two layers of the amnion ; d d, hypoblast ; d/, s t,
i, walls of the umbilical vesicle ; d g, omphalo-mesenteric canal ; d s, cavity of the umbilical vesicle ;
a I, first appearance of the allantois.

4 : s h, external layer of the amnion ; s z, villi of the external layer of the amnion, which has now be-
come the chorion, the vitelline membrane having disappeared ; h h, a m, internal layer of the am-
nion ; e, embryon ; a h, amniotic cavity ; d g, omphalo-mesenteric canal ; d s, cavity of the umbilical
vesicle ; a Z, allantois ; r, space between the two layers of the amnion.

5 : c h, s A, c h, a I, allantois (which has now become the chorion, the external amniotic layer having dis-
appeared), with its villi ; a m, amnion ; a s, amniotic covering of the umbilical cord ; r, space between
the amnion and the allantois ; ah, amniotic cavity ; ds, umbilical vesicle ; dg, omphalo-mesenteric
canal.

PIM.

FIG. 1. — Human embryon, at the ninth week, removed from the membranes ; three times

the natural size (Erdl).
FIG. 2.— Human embryon, at the twelfth week, inclosed in the amnion; natural size (Erdl).

AMNIOTIC FLUID. 805

t

cal cord, which connects the ernbryon with the placental portion of the
chorion, and the umbilical vesicle, formed from the same layers as the allan-
tois. 3. The amnion, which is the internal layer of the amniotic fold, per-
sisting throughout foetal life. 4. The embryon itself.

During the early stages of development of the umbilical vesicle and the
allantois, the internal amniotic layer, or the true amniotic membrane, is
closely applied to the surface of the embryon, and is continuous with the epi-
dermis, at the umbilicus. It is then separated from the allantois by a layer
of gelatinous matter ; and in this layer, between the amnion and the allan-
tois, is the umbilical vesicle. At this time the umbilical cord is short and
not twisted. As development advances, however, the intermembranous gelat-
inous 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 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 resem-
bles a serous membrane, 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 amnion adheres to the chorion,
although 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 protec-
tion of the foetus and is not directly concerned in its nutrition and devel-
opment (see Plate III, Fig. 2). The gelatinous mass referred to above, situ-
ated, during the early periods of intrauteriiie life, between the amnion and
the chorion, presents a semi-fluid consistence, with very delicate, interlacing
fibres of connective tissue and fine, grayish granulations scattered through
its substance. These fibres are gradually developed as the quantity of gelat-
inous matter diminishes and the amnion approaches the chorion, until
finally they form 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 (about one litre) or less than one pint (about half a litre).
In the early periods of utero-gestation it is clear, slightly yellowish or green-
ish, and perfectly liquid. Toward the sixth month its color is more pro-
nounced and it becomes slightly mucilaginous. Its reaction usually is neutral
or faintly alkaline, though sometimes it is feebly acid in the latest periods.
It sometimes contains a small quantity of albumin, as determined by heat
and nitric acid ; and there generally is a gelatinous precipitate on the addi-
tion of acetic acid. The following table gives its chemical composition
(Robin) :

806 GENERATION.

COMPOSITION OF THE AMNIOTIC FLUID.

Water 991-00 to 975-00

Albumin and mucine 0-82 " 10-7?

Urea 2-00 " 3-50

Creatine and creatinine (Scherer, Robin and Verdeil) not estimated

Sodium lactate (Vogt, Regnauld) a trace

Fatty matters (Rees, Mack) 0-13 to 1-25

Glucose (Bernard) not estimated

Sodium chloride and potassium chloride 2-40 to 5-95

Calcium chloride a trace

Sodium carbonate a trace

Sodium sulphate a trace

Potassium sulphate (Rees) i a trace

Calcareous and magnesian phosphates and sulphates 1-14 to 1-72

The presence of certain of the urinary constituents in the amniotic fluid
has led to the view that the urine of the foetus is discharged in greater or less
quantity into the amniotic cavity. Bernard, who is cited in the table of com-
position of the amniotic fluid as having determined the presence of sugar,
has shown that in animals with a multiple placenta, the amnion has a glyco-
genic action during the early part of intrauterine 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 apparently is
too great, especially in the early months, to be derived entirely from the urine
of the foetus, and there probably is an exudation from the general surface of
the foetus and from the membranes. After the third month the sebaceous
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 pu-
trefaction and of preserving dead tissues.

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 from the abdominal cavity but which still communicates
freely with the intestine. This is the umbilical 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 forms of animals. In the human subject and in mam-
mals, however, the umbilical vesicle is not so important, as nutrition is
secured by means of vascular connections between the chorion and the uterus.
The vesicle becomes gradually removed farther and farther from the em-
bryon, 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, 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-mesen-
teric vessels. At about the fortieth day one artery and one vein disappear,

FORMATION OF THE ALLANTOIS. 807

and soon after, all vascular connection with the embryon is lost. At first
there is a canal of communication with the intestine, called the omphalo-
mesenteric canal. This is gradually obliterated, and it closes, between the
thirtieth and the thirty-fifth day. The point of communication of the vesi-
cle with the intestine is called the intestinal umbilicus ; and early in the
process of development, there is here a 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 preg-
nancy.

The umbilical vesicle presents three coats; an external, smooth mem-
brane, 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 of development of the umbilical vesicle, and as it is shut off
from the intestine, there appears an elevation at the posterior portion
of the intestine, which rapidly increases in extent, until it forihs a mem-
brane of two layers, which is situated between the internal and the external
layers of the amnion. This membrane becomes vascular early in the prog-
ress of its development, increases in size quite rapidly, and finally it 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 forma-
tion of the two layers of- the allantois is quite distinct in certain of the lower
forms of animals, in the human subject and in mammals 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 membrane, the two original layers of which can not be separated from
each other. The process of the development of the allantois is shown in the
-diagrammatic Fig. 295 (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 por-
tion of the aorta, and two veins. The two arteries persist and form the two
arteries of the umbilical cord, coming from the internal iliac arteries of the
foetus ; and one vein, the umbilical vein, which returns the blood from the
placenta to the foatus, is permanent. These vessels are connected with the
permanent, vascular tufts of the chorion.

The development of the allantois can not be well observed in human ova
before the fifteenth or the twenty-fifth day. When the allantois becomes the
permanent chorion, it is marked by a large number of hollow, branching
villi over its entire surface, which give the ovum a shaggy appearance. As
the ovum enlarges, over a certain area surrounding the point of attachment
of the pedicle which connects the chorion with the embryon, the villi are

808

GENERATION.

FIG. 296.— Human embryon at the third week, showing
villi covering the entire chorion (Haeckel).

developed more rapidly than over the rest of the surface. Indeed, as the
ovum 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 of the
allantois upon which the villi per-
sist and increase in length and in
the number of their branches is
destined to form connections with
the mucous membrane of the ute-
rus and constitutes the foetal por-
tion of the placenta. This change
begins at about the end of the sec-
ond month, and the placenta be-
comes distinctly limited at about
the end of the third month.

It must be remembered that as
the changes go on which result in
the formation of the permanent
chorion and the limitation of the
foetal portion of the placenta, the
formation of the umbilical vesicle and the enlargement of the amnion are
also progressing. The amnion is gradually 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 mem-
branes.

At about the beginning of the fifth month the ovum is constituted as
follows :

The foetus floats freely in the amniotic fluid, attached to the placenta by
the umbilical cord ; the chorion presents a highly vascular, thickened and
villous portion, the foetal portion of the placenta ; the rest of the chorion is
a simple membrane, without villi and 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 umbilical
vesicle with the intestine of the foetus has closed ; and finally the foetus has
undergone considerable development.

Umbilical Cord. — From the description given of the mode of develop-
ment 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 por-
tion 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

UMBILICAL CORD. 809

coming from the body of the foetus, which are twisted usually from left to
right, around the single umbilical vein. In addition to the spiral turns of
the arteries around the vein, the entire cord may be more or less twisted,
probably from the movements of the foetus.

The fully developed cord extends from the umbilicus of the foetus to the
central portion of the placenta, in which its insertion usually is oblique ;
although 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 (50-8 centi-
metres). It has been observed as long as sixty (152-4 centimetres), and as
short as seven inches (17'8 centimetres). 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 foetus ; and this can be accounted for only by the
movements of the foetus in utero.

The external covering of the cord is a process of the amnion ; and as it
extends over the vessels, it includes a gelatinous substance (the gelatine of
Wharton) which surrounds the vessels and protects them from compression.
This gelatinous substance is identical with the so-called membrana inter-
media, or the substance included between the amnion and the chorion. The
entire cord, covered with the gelatine of Wharton and the amnion, usually is
about the size of the little finger. According to Robin, the umbilical cord
will sustain a weight of about twelve pounds (5-4 kilos). As the amniotic
fluid accumulates and distends the amniotic membrane, this membrane be-
comes more and more closely applied to the cord. The pressure extends
from the placental attachment of the cord toward the foetus, and it gradu-
ally forces into the abdomen of the foetus the loop of intestine, which, in the
early periods of intrauterine life, forms an umbilical hernia.

The vessels of the cord, the arteries as well as the vein, are provided
with valves. These are simple inversions of the walls of the vessels, 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 half an inch to two
inches (12'7 to 58'8 mm.), 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 (10 centi-
metres), fifteen folds were found (Berger). It is not apparent that these
valvular folds have any physiological importance.

As the allantois is developed, it presents, in the early stages of its forma-
tions, 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 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 becomes the urinary blad-
der ; but there is a temporary communication between the internal portion
and the lower portion of the cord,- called the urachus. This generally is
obliterated before birth and is reduced to the condition of an impervious
cord ; but it may persist during intrauterine life, in the form of a narrow

810 GENERATION.

canal extending from the bladder to the umbilicus, which is closed soon after
birth.

MembrancB 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 chorion is for the protection of the foetus ; 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.

As the fecundated ovum descends into the uterus, it is invested with a
shaggy covering, which is either the permanent chorion or one of the mem-
branes 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 menstruation have already been
described. It has been seen that during an ordinary menstrual period, the
membrane is increased three or four times in thickness and becomes more or
less rugous. If a fecundated ovum descend into the uterus, the changes in
the mucous membrane progress. The glands enlarge and the mucous mem-
brane becomes thicker, so that at the end of the first month it measures
about two-fifths of an inch (10 mm.). This thickening is due chiefly to de-
velopment of tissue between the glands, and the membrane becomes soft and
pulpy. In the mean time the ovum has effected a lodgement between the
folds, usually at the fundus, near the opening of one of the Fallopian tubes;
and the adjacent parts of the mucous membrane extend over the ovum so
that it is at last completely enclosed. This occurs at the twelfth or thirteenth
day (Reichert). The extension of the mucous membrane which covers the
ovum becomes the decidua reflexa ; the changed mucous membrane which
lines the uterus becomes the decidua vera ; and the portion of the mucous
membrane which remains at the site of the placenta becomes the decidua
serotina. The vascular villosities of the chorion probably do not, as was
once thought, penetrate the uterine tubules, but they become surrounded by
tissues developed between these tubules. ,

As development advances, the decidua vera becomes extended, loses its
vessels and glands and is reduced to the condition of a simple membrane.
The cylindrical epithelium of the mucous membrane of the body of the ute-
rus, soon after fecundation, becomes exfoliated, and its place is supplied by
flattened cells. This change is effected at the sixth or the eighth week. The
epithelium of the cervix retains its cylindrical character, but most of the
cells lose their cilia. The decidua reflexa, which is thinner than the decidua
vera, has neither blood-vessels, glands nor epithelium.

During the first periods of utero-gestation, the two layers of decidua are
separated by a small quantity 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

FORMATION OF THE PLACENTA.

811

chorion. Sometimes, at full term, the membranes of the foetus can be sepa-
rated from the decidua ; but frequently all of the different layers are closely
adherent to each other.

The changes just described are not participated in by the mucous mem-
brane of the neck of the uterus. The glands in this situation secrete a semi-
solid, transparent, viscid mucus, which closes the os and is sometimes called
the uterine plug.

Toward the fourth month a very delicate, soft, homogeneous layer ap-
pears over the- muscular fibres of the uterus, beneath the decidua vera, which
is the beginning of a new mucous membrane. This is developed very gradu-
ally, and the membrane is completely restored about two months after partu-
rition.

Formation of the Placenta. — At about the end of the second month the
villi of the chorion become enlarged and arborescent over that part which
eventually forms the foetal portion of the placenta. They are then highly
vascular and are embedded in the soft substance of the hypertrophied mucous

FIG. 297. — Diagrammatic figure, shotting the placenta and deciduce (Liegeols).

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 ; q, q, vascular tufts of the chorion, constituting the
foetal portion of the placenta ; n',n, maternal portion of the placenta ; n, n, decidua vera ; s, decid-

membrane. At the same time the villi over the rest of the chorion are ar-
rested in their growth, and they finally disappear during the third month.
The blood-vessels penetrate the villi in the form of loops at about the fourth
week ; and the placenta is distinctly marked at about the end of the third

812 GENERATION.

month. The placenta then rapidly assumes the anatomical characters ob-
served after it may be said to be fully developed.

The fully formed placenta occupies about one-third of the uterine mu-
cous membrane, and generally is rounded or ovoid in form, with a distinct
border connected with the decidua and the chorion. It is seven to nine
inches (18 to 23 centimetres) in diameter, a little more than an inch (2-5
centimetres) in thickness at the point of penetration of the umbilical cord,
slightly attenuated toward the border, and weighs fifteen to thirty ounces
(425 to 850 grammes). Its foetal surface is covered with the smooth, amni-
otic membrane, and its uterine surface, when detached, is rough, and
divided into irregular lobes, or cotyledons, half an inch to an inch and a
half (12'7 to 38-1 mm.) in diameter. Between these lobes, are membranes,
called dissepiments, which penetrate into the substance of the placenta, and
at its border extend as far as the foetal surface.

Upon the uterine surface of the placenta, is a thin, soft membrane, the
decidua serotina. This is composed of amorphous matter, a large number of
granulations, and colossal cells with enlarged and multiple nuclei. A portion
of this membrane is not thrown off with the placenta in parturition, but pro-
cesses extend into the placenta and closely surround the foetal tufts.

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, con-
verge toward the cord and unite to form the umbilical vein. Upon the
uterine surface of the placenta are oblique openings of a large number of
veins which return the maternal blood to the uterine sinuses. There are also
the 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 the umbilical arteries be injected, the fluid is returned
by the umbilical vein, having passed through the vascular tufts of the foetal
portion of the placenta.

According to 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 lacunae. 3. Long, branch-
ing villi, which penetrate more deeply into the placenta, some extending as
far as its uterine surface.

The great vascular spaces, or lacunae of the maternal portion of the pla-
centa, present a number of trabeculae, which extend from the uterine to the
foetal surface ; and between these trabeculae, are exceedingly delicate trans-
verse and oblique secondary trabecular processes. The blood-vessels of the
foetal tufts are surrounded with a gelatinous, connective-tissue structure, and
as late as the sixth month (Heinz) are covered with a layer of chor ionic cells.

The mode of formation of the vascular spaces in the placenta has been a
subject of much discussion. The following, however, seems to be the most
reasonable view with regard to this question : That portion of the uterine
mucous membrane which becomes the maternal portion of the placenta ex-
tends from the decidua serotina and surrounds the villi, which are embedded

DEVELOPMENT OF THE OVUM. 813

in its substance. As the arborescent villi extend, they encroach upon the
blood-vessels of the prolongations from the serotina, which latter become
much enlarged and finally form the great vascular spaces traversed by the
trabeculae mentioned above. At term, however, according to Heinz (1888),
the foetal vessels have lost their covering of epithelium, which is observed in
the earlier months of pregnancy. Thus the most important parts of the
placenta are formed by an interlacement of the villi of the chorion with the
altered structures of the mucous membrane of the uterus.

In the human subject the maternal and fcetal portions of the placenta
are so closely united that they can not be separated from each other. In
parturition the curling arteries and the veins on the uterine surface of the
placenta are torn off, and the placenta then consists of the parts just de-
scribed ; the torn ends of the vessels attached to the uterus are closed by
the contractions of the surrounding muscular fibres ; and the blood which
is discharged is derived mainly from the placenta itself.

Uses of the Placenta. — The placenta is the respiratory, excretory and
nutritive organ of the foetus. Its action as a respiratory organ has already
been mentioned in connection with the physiology of respiration. It cer-
tainly serves as an organ for the elimination of carbon dioxide, and probably
also for other products of excretion. It is the only source of materials for
the development and nutrition of the foetus. It is thought that cells de-
rived from the serotina elaborate a fluid called uterine milk, which is ab-
sorbed by the fcetal tufts. This fluid has been collected from between the
fcetal tufts of the placenta of the cow, and has been found to contain fatty
matter, albuminous matters and certain salts, but no sugar or caseine (Gam-
gee). It is not probable, however, that such a fluid exists in the human
placenta; although "uterine milk" of the ruminants was mentioned dis-
tinctly by Haller, and was alluded to by even earlier writers.

DEVELOPMENT OF THE OVUM.

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 fcetus, a name
which it retains during the rest of intrauterine life. The membranes are
appendages developed for the purposes 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 vitellus.

The formation of the blastodermic cells and the appearance of the groove
which is subsequently developed into the neural canal have already been de-
scribed. At this portion of the ovum, there is a thickening of the blastoderm,
which then presents three layers, the mesoblast, the thickest and most impor-
tant, being developed from the opposite surfaces of the epiblast and the hypo-
blast. The earliest stages of development have been studied almost exclu-
sively in the chick ; and it is probable that the appearances here observed
nearly represent the earlier processes of development in the human subject.

Development of the Cavities and Layers of the Trunk, in the Chick.— As

53

814

GENERATION.

an introduction 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, which will give an idea of the ar-
rangement of the different blastodermic layers and the way in which they
are developed into the different parts of the trunk, with the mode of forma-
tion of the great cavities. The figures by which this description is illustrated
are those of Briicke, which were photographed on wood from diagrams made
from actual preparations by Seboth. These figures, therefore, can hardly be
called diagrammatic.

Fig. 298 shows one of the earliest stages of development in the chick. In
this figure, the upper layer of dark cells (B, B) represents the epiblast. The

FIG. 298.

lower layer of dark cells (D, D) represents the hypoblast. The middle layer
of lighter cells is the mesoblast, which, toward 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 (E), the
chorda dorsalis. The openings (G, G) represent the situation of the two
aortae. The other cavities are as yet indistinct in this figure.

Fig. 299 shows the same structures at a more advanced stage of develop-
ment. The dorsal, or vertebral plates, which bound the furrow (A) in Fig.

FIG. 299.

298, are closed above, and include (A) the neural canal. The chorda dorsalis
(E) is separated from the cells surrounding it in Fig. 298. The epiblast
(B, B) and the hypoblast (D, D) present certain curves which follow the
arrangement of the cells of the mesoblast. By the sides of the boundaries
of the neural canal, are two distinct masses of cells (C, C), which are devel-
oped into the vertebrae. Outside of these masses of cells, are two smaller
collections of cells, afterward developed into the Wolffian bodies. Beneath
those two masses, are two large cavities (G, G), the largest cavities shown in

DEVELOPMENT OF THE OVUM. 815

Fig. 299, presenting an irregular form, which are sections of the two primi-
tive aortae. The two openings (H, H) afterward become the pleuro-peritoneal
cavity.

In Fig. 300 the parts are still farther developed. The neural canal is
represented (A) nearly the same as in Fig. 299, 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 hypoblast. Just above D, is a
single opening (G), which is formed by
the union of the two openings (Gr, G) in
Figs. 298 and 299 ; and this is the ab-
dominal aorta, which has here become
single. The two openings (H, H) rep-
resent a section of the pleuro-peritoneal
cavity. The outer wall of this cavity is
the outer visceral plate, which is devel-
oped into the muscular walls of the ab-
domen. 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 mesoblast, 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
(#, Z>) is the amniotic cavity.

The figures just described, it must be borne in mind, represent transverse
sections of the body of the chick, made through the middle portion of the
abdomen. 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 vertebral plates ; and at about the same time, the two aortae
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. The intestinal canal is then a simple groove, and the
embryon is entirely open in front. In the farther process of development,
the visceral plates advance and close over the abdominal cavity, as the
medullary plates have closed over the neural canal. Thus there is formed a
closed tube, the intestine, lined by the hypoblast, the walls of the intestine
being formed of the inner layer of the mesoblast. This brings the external
layer of the mesoblast around the intestine, to form the muscular walls of the
abdomen, the cavity (Fig. 300, H, H) being the peritoneal cavity, and the
external covering being the epiblast. At this time the- 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 develop-
ing embryon is the chorda dorsalis, or notochord. This is situated beneath

816

GENERATION.

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
it is not itself developed into the vertebrae, which grow around it and encroach
upon its substance until it finally disappears. In many mammals the noto-
chord presents a slight enlargement at the cephalic extremity, which extends
to the auditory vesicles and it is somewhat diminished in size at the caudal ex-
tremity. By the sides of this cord are masses of cells which unite in front
of the neural canal and eventually are developed into the vertebrae. These are

called protovertebrae, or somites, and
are shown in Fig. 303 (C, in A and B).
Twelve pairs of protovertebrae are
shown in Fig. 303, C. In the chick,
two pairs are first formed in the up-
per cervical region, on the second
day. They rapidly increase in num-
ber, from above downward, until at
the fourth day there are twenty-one
or twenty-two pairs. They are not
formed in the region of the head or
at the lowest part of the vertebral
column. The vertebrae, as they are
developed, are formed of temporary
cartilaginous structure, gradually ex-
tending around the chorda dorsalis,

FIG. 301.— The first six cervical vertebrae of the em-
bryon of a rabbit one inch in length (Robin).

a, 6, cephalic portion of the notochord, exposed by
the removal of the cartilage ; b, portion of the
chorda dorsalis 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, en-
largements of the chorda dorsalis, between the
vertebrae ; g, cartilage of the lateral portion of
the atlas ; h. lateral portion of the axis ; i, t,
transverse apophyses of vertebrae.

FIG. 302. — Human embryon, about one month old,
showing the large size of the head and up-
per parts of the body, the twisted form of the
spinal column, the rudimentary condition of
the upper and lower extremities and the rudi-
mentary tail at the end of the spinal column
(Dalton).

which then occupies the axis of the spinal column. These cartilages are not
divided at the lines of separation of the protovertebrae, but the protovertebrae
fuse together and the cartilages which are to be developed into the bodies of
the vertebrae are so divided off, that one cartilage occupies the place of the
adjacent halves of two protovertebrae. Between the bodies of the vertebrae,
the chorda dorsalis presents regular enlargements surrounded by a delicate
membrane. As ossification of the spinal column advances, that portion of

DEVELOPMENT OF THE SKELETON. 817

the chorda dorsalis which is surrounded by the bodies of the vertebrae disap-
pears, leaving the enlargements between the vertebrae distinct. These en-
largements, which are not permanent, are gradually invaded by fibrous tis-
sue, their gelatinous contents disappear, and the intervertebral disks, com-
posed of fibro-cartilaginous structure, remain. These disks are permanent
between the cervical, the dorsal and the lumbar vertebrae ; but they eventu-
ally disappear from between the different parts of the sacrum and coccyx, as
these are consolidated, this occurring, in the human subject, between the
ninth and the twelfth years.

Vertebral Column, etc.— In Figs. 299 and 300 (C, C), are seen the two
masses of cells (protovertebrae) 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 extend over the neural canal, closing above, and their processes are
called the medullary, 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 verte-
brae, the various 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 upper part of the body ; but as the
inferior extremities and the pelvis are 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 dorsalis, are two cartilaginous processes, which are developed into the
so-called cranial vertebrae. 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 posterior 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 inter-
vention of pre-existing cartilaginous structure. At the time when the verte-
brae are developed, with their laminae and their spinous and transverse pro-
cesses, 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 progressively increase in length, the arms appearing near
the middle of the embryon, and the legs, at the lower portion. Each extrem-
ity is divided into three portions, the arm, forearm and hand, for the upper

818 GENERATION.

extremities, and the thigh, leg and foot, for the lower extremities. 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 articula-
tions.

Very early in intrauterine life the skeleton 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 metatarsus, and the phalanges of the fingers and
toes. At birth the carpus is entirely cartilaginous, 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 occur-
ring between the twelfth and the fifteenth years. 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 thus developing, the muscles are formed from the
outer layer of the mesoblast, and the visceral plates close over the thorax
and abdomen in front, leaving an opening for the umbilical cord. The vari-
ous 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 distinguished ; then successively, the long muscles of the neck,
the anterior straight muscles of the head, the straight and transverse mus-
cles of the abdomen, the muscles of the extremities, 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 epi-
dermis 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 con-
stitutes the vernix caseosa. At the third month the nails make their appear-
ance, 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.

It has been 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 there remains only the small,
central canal of the spinal cord, communicating with the ventricles of the
brain. As the nervous tissue is developed in the interior 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

DEVELOPMENT OF THE NERVOUS SYSTEM.

819

at about the end of the second month, while the arachnoid is not distinct
until the fifth 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. 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 dilatations are observed at the superior
and at the inferior extremities of the neural canal. The cord is nearly uni-
form in size in the dorsal region, marked only by the regular enlargements
at the sites of origin of the spinal nerves ; but there soon appears 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 posterior cerebral vesicles. These become
more and more distinct as development advances. The formation of these
parts is shown in Fig. 303. This figure, in C, shows the projections, on either
side, of the vesicles which are
eventually developed (0, Fig.
303, C) into the nervous por-
tions of the organ of vision.

The three cerebral vesicles
now undergo farther changes.
The superior, or the first prim-
itive vesicle, is soon divided
into two secondary vesicles, the
anterior of which becomes the
cerebral hemispheres, and the
posterior, the optic thalami,
which are eventually covered
by the greater relative develop-
ment of the hemispheres. The
middle, or second primitive
vesicle, does not undergo divis-
ion and is developed into the
tubercula quadrigemina. The
posterior, or third primitive vesicle, is divided into two secondary vesicles,
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 (e, Fig, 304,
A, B, C), counting from before backward, is formed by a projection of the
tubercula quadrigemina, which at this time constitute the most projecting

FIG. 303.— Development of the nervous system of the chick
(Longet, after Wagner).

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
protovertebree ; ft, posterior dilatation (the lumbar en-
largement) ; d, anterior dilatation of the neural canal ;
1, 2, 3, anterior, middle and inferior cerebral vesicles; a,
slight flattening of the anterior cerebral vesicle; o, for-
mation of the ocular vesicles.

820 GENERATION.

portion of the encephalic mass ; the second prominence (c, Fig. 304), situated
behind the tubercula quadrigemina, is formed by the projection of the cere-
bellum ; the third (d, Fig. 304, 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. 304.

The cerebrum 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 corpora
quadrigemina and the cere-
bellum. Until the end of the
fourth month, the hemi-

FIG. ^.-Development of the spinal cord and brair, of the SPher6S are Sm°°th On thelr
human subject (Longet, after Tiedemann). SUrf aC6 ; but they then begin

A, brain and spinal cord of an embryon of seven weeks ; lat- , , , n

eraiview. to present large depressions,

B, the same, from an embryon farther advanced in develop- *» •,-, • * TJ £ XT,

ment; 6, spinal cord; d, enlargement of the spinal cord, following tolds 01 the pia ma-
with its anterior curvature; c, cerebellum ; e, tubercula j.^, ,T i • i ^ <i ^ n

quadrigemina ; /, optic thalamus ; g, cerebral hemi- ter, Wllicn are tne IirSt COn-

C, braizf and spinal cord of an embryon of eleven weeks ; 6, Volutions, these increasing

spinal cord ; d, enlargement of the spinal cord, with its ,,0™/nTT ,'-~ ™,™V*™. >-^A ™»
anterior curvature ; c, cerebellum ; e, tubercula quadri- rapidly in number and COm-

feTside: "' cerebral hemispheres; °'optic nerve of the plexity, especially after the

C', the same parts in a vertical section in the median line, from apvfm f Vi ™ rm +V» Th P OOTY!- n ™

before backward ; ft, membrane of the spinal cord, turned seveiltn montn. 1 ne Septum

backward; d, second curvature of the upper portion of In pi /him i«fhpn fnrmprl hv an

the spinal cord, which has become thickened and consti- mciaum 1S men lormea, Dy an

tutes the peduncles of the cerebrum ; e. tubercula quadri- plpva+irvn r»f nprvrmc rnaffpr
gemina ; /, optic thalami, covered by the hemispheres.

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, extends 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 the aque-
duct of Sylvius, which is left in the development of the middle vesicle. At

DEVELOPMENT OF THE NERVOUS SYSTEM. 821

about the fourth month there is a deposition of nervous matter in front and
above, forming the pons Varolii.

In Fig. 304 (C, 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. The eyes are situated at first at the sides of the head, grad-
ually approaching the anterior portion. At the extremity of each of these
lateral prolongations, a rounded mass appears, which becomes the globe of the
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 de-
veloped at about the seventh week, and is at first a simple membrane, with-
out any central opening. As the pupil appears, it is closed by a vascular
membrane — which probably belongs to the capsule of the crystalline lens —
called the pupillary membrane. This membrane gradually disappears, by
an atrophy extending from the centre to the periphery. It attains its max-
imum of development 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 epiblast. At
the tenth week there is 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 formation 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 later than 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 ; and 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 appearance.
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
either 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 structure is known as the cartilage of Meckel.

There are no special points for description in the development of the

822 GENEKATION.

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 connected 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
olfactory commissures.

As far as the action of the nervous system of the foetus is concerned, it
is probable that it is restricted mainly to reflex phenomena depending
upon 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 months of
pregnancy, movements of respiration occur ; and it is well known that efforts
of respiration sometimes take place within the uterus. These are due to the
want of oxygen-carrying blood in the medulla oblongata when the placental
circulation is interrupted.

DEVELOPMENT OF THE DIGESTIVE APPABATUS.

The intestinal canal is the first formation of the digestive system. This
is at first open in the greatest part of its extent, presenting, at either extrem-
ity of the longitudinal gutter, in front of the spinal column, a rounded, blind
extremity, which is closed over in front for a short distance. The closure of
the visceral plates then extends laterally and from the two extremities of the
intestine, until only the opening remains for the
passage of the umbilical cord and the pedicle of the
umbilical vesicle. There is at first an open com-
munication between the lower part of the intestinal
tube and the allantois, which forms the canal known
as the urachus ; but that portion of this communi-
cation which remains enclosed in the abdominal
cavity becomes separated from the urachus, is di-
lated and eventually forms the urinary bladder.
When the bladder is first shut off, it communicates
with the lower portion of the intestine, which is

FIG. 30o. — Foetal pig^ showing a

loop of intestine, forming called the cloaca i but it finally loses this connec-

an umbilical hernia (Dal- . •

ton). tion and presents a special opening, the urethra.

As development advances, the intestine grows
rapidly in length and becomes convoluted. 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 abdominal cavity. In the early stages of development, a portion 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 press-
ure. An illustration of this is given in Fig. 305. This protrusion, in the
normal process of development, is gradually returned into the abdomen, as

DEVELOPMENT OF THE DIGESTIVE APPARATUS. 823

the cavity of the pedicle of the umbilical vesicle is obliterated, at about the
tenth week.

At the upper part of the abdominal cavity the alimentary canal presents
two lateral projections, or pouches. The one on the left side, as it increases
in size, becomes the greater pouch of the stomach, and the one on the right
side, the lesser pouch.

At a short distance below the attachment of the pedicle of the umbilical
vesicle to the intestine, there appears a rounded diverticulum, which is
eventually developed into the caecum. 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 caecum is developed it presents a conical appendage, which is at first
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 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 flex-
ure of the colon, at the fifth month. During this time the large intestine in-
creases more rapidly in diameter than the small intestine, while the latter
develops more rapidly in its length.

In the early stages of development the internal surface of the intestines is
smooth ; but villi appear upon its mucous membrane during the latter half
of intrauterine existence. These are found at first both in the large and
the small intestine. At the fourth month they become shorter and less
abundant 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 intes-
tinal 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.

The mesentery is first formed of two perpendicular folds, attached to the
sides of the spinal column. As the intestine undergoes development a por-
tion of the peritoneal membrane extends in a quadruple fold from the stom-
ach to the colon, to form the great omeiitum, which covers the small intes-
tine in front.

As the head undergoes development a large cavity appears, which 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 pre-
sents, during the sixth week, a large opening, which is afterward partially

824 GENERATION.

closed in the formation of the face. The rest of this cavity remains closed
until a communication 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 oesophagus is
short, the rudimentary lungs appear by its sides and the heart lies just in
front. As the thorax is developed, however, the oesophagus 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 pe-
riphery to the central portion, which latter gives passage to the vessels and
the oesophagus. When this closure is incomplete there is the malformation
known as congenital diaphragmatic hernia.

The development of the anus is very simple. At first the intestine ter-
minates below in a blind extremity ; but at about the seventh week a longi-
tudinal 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 ex-
tremity, a short distance beneath the integument. This constitutes the mal-
formation known as imperforate anus, a deformity which usually can be
relieved, without much difficulty, by a surgical operation, if the distance be-
tween 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 a large 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 fissure. 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. Its
weight, in proportion to the weight of the body at different ages, is as fol-
lows : At the end of the first month, 1 to 3 ; at term, 1 to 18 ; in the adult,
1 to 36 (Burdach). Its structure is very soft during the first months. As
development advances and as the relative size of the liver gradually dimin-
ishes, 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 glandu-
lar structure at their extremities. The spleen is developed, about the same
time, at the greater curvature of the stomach, and becomes distinct during
the second month.

There is no reason to believe that any of the digestive fluids are secreted
during intraiiterine life. At birth the intestine contains a peculiar sub-
stance, called meconium, which will be described farther on. Cholesterine,
an important constituent of the bile, is found in large quantity in the me-
conium.

DEVELOPMENT OF THE FACE. 825

DEVELOPMENT OF THE RESPIRATORY SYSTEM.

On the anterior surface of the membranous tube which becomes the
03sophagus, an elevation appears, which soon presents an opening into the
03sophagus, the projection forming at this time a single, hollow cul-de-sac.
This opening becomes the rima glottidis, and the single tube with which it
is connected is developed into the trachea. At the lower extremity of this
tube, a bifurcation appears, termi-
nating first in one and afterward
in several culs-de-sao. The bi-
furcated tube constitutes, after
the lungs are developed, the prim-
itive bronchia, at the extremities
of which are the branches of the
bronchial tree. As the bronchia
branch and subdivide, they extend

, FIG. 306.— Formation of the bronchial ramifications

downward into what becomes

eventually the cavity of the tho-
rax. The pulmonary vesicles are

developed before the trachea (Burdach). The lungs contain no air at any
period of mtraiiterine 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. 306. 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.

DEVELOPMENT OF THE FACE.

The anterior portion of the embryon remains 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. At the time that the visceral plates are
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. The
first three arches, enumerating them from above downward, correspond, in
their origin, to the three primitive cerebral vesicles. The fourth arch — which
is not enumerated by some authors, who recognize but three arches — corre-
sponds to the superior cervical vertebrae. 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 malleus 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, is finally closed in front, but an opening

GENEKATION.

remains by the side, which forms, externally, the external 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 second-
ary projections, which leave certain
permanent openings, forming the
mouth, nose etc.

In the very first stages of develop-
ment of the head there is no appear-
ance of the face. The cephalic extrem-
ity consists simply of the cerebral vesi-
cles, the surface of this enlarged por-
tion of the embryon being covered, in
front as well as behind, by the epiblast.
During the sixth week, after the cavity
of the pharynx has appeared, the mem-
brane 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 meso-
blast, extending forward. This is soon
marked by two secondary projections,

the upper projection forming the superior maxillary portion of the face, and
the lower, the inferior 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 pro-
cess. This extends from the forehead — that portion which covers the front
of the cerebrum — downward. The superior maxillary projections then ad-
vance 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 medi-
an 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 max-
illary processes advance forward, the eyes are moved, as it were, from the

embryon of twen-
days; magnified 15
iiameters (Coste).
1, median or frontal process, the inferior portion
of which is considerably enlarged ; 2, right
nostril ; 3, left nostril ; 4, 4, inferior maxil-
lary processes, already united in the median
line ; 5, 5, superior maxillary processes,
which have become quite prominent and
have descended to the level of the slope of
the frontal process ; 6, mouth ; 7, first vis-
ceral arch ; 8, second visceral arch ; 9, third
visceral arch ; 10, eye ; 11, ear.

DEVELOPMENT OF THE FACE.

827

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, the malleus and incus are
developing, 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 audi-
tory meatus, the
cavity of the tym-
panum and the
Eustachian tube.

At the same
time the second vis-
ceral 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

FIG. 308. — Mouth of a human em-
bryon of thirty-five days (Coste).
f 41^ u^-rr ^A 1, frontal process, widely sloped at

torm the body and its in^ri0r portion f 2, 2Vinci-

sor processes produced by this
sloping ; 3, 3, nostrils; 4, lower
lip and maxilla, formed by the
union of the inferior maxillary
processes ; 5, 5, superior max-
illary 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 ; 9,
tongue ; 10, 10, eyes ; 11, 12, 13,
visceral arches.

the greater cornua
of the hyoid bone.
The clefts between
the second and the
third and between
the third and
fourth arches are

FIG. 309.— Mouth of an embryon of for-
ty days (Coste).

1, first appearance of the nose ; 2, 2, first
appearance of the alae of the nose ;
3, appearance of the closure beneath
the nose ; 4, middle, or median por-
tion of the upper lip, formed by the
approach and union of the two in-
cisor processes, a little notch in the
median line still indicating the prim-
itive separation of the two process-
es; 5, 5, superior maxillary process-
es, forming the lateral portions of
the upper lip ; 6, 6, groove for the
development of the lachrymal sac
and the nasal canal ; 7, lower lip; 8,
mouth ; 9, 9, the two lateral halves
of the palatine arch, already nearly
approximated to each other in front,
but still widely separated behind.

finally obliterated.

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 elevation, which is developed into the epiglottis. The

828 GENERATION.

openings of the "nostrils appear during the second half of the second month.
A little elevation, the nose, appears between these 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.

When, by an arrest of development, the superior maxilla on one side fails
to unite with the side of the incisor process, there is the very common de-
formity known as single harelip. If this union fail 'on both sides, there is
double harelip, when the incisor process usually is more or less projecting.
As a very rare deformity, it is sometimes observed that the two sides of the
incisor process have failed to unite with each other, leaving a fissure in the
median line.

The palatine arch is developed by two processes, which arise on either
side, from the incisor process, pass backward and upward and finally meet
and unite in the median line. The union of these forms the plane of sepa-
ration between the mouth and the nares ; and want of fusion of these pro-
cesses, from arrest of development, 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. — 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 either jaw, which forms
a rounded band above and dips down somewhat into the subjacent structure.
This band is readily separated by maceration, and the removal of the portion
that dips into the maxilla leaves a groove. 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.

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 :

A rounded enlargement appears at the margin of the epithelial band.
This soon becomes directed downward — adapting the 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 en-
largement enclosed completely in a follicle. This is the dental follicle, and
it has no connection with the wedge-shaped band described first. While

DEVELOPMENT OF THE TEETH.

829

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

FIG. 310.— Temporary and permanent teeth (Sappey).

1, 1, temporary central incisors; 2, 2, temporary lateral incisors ; 3, 3, temporary canines ; 4," 4, tempo-
rary anterior molars ; 5. 5, temporary posterior molars ; 6, 6, permanent central incisors ; 7, 7, per-
manent lateral incisors; 8, 8, permanent canines; 9, 9, permanent first bicuspids ; 10, 10, permanent
second bicuspids ; 11,11, first molars.

the enamel ; the dental bulb, which is provided with vessels and nerves, be-
comes the tooth-pulp ; and upon the surface of the dental bulb, the dentine
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 sur-
face.

The permanent teeth are developed beneath the follicles of the tempo-
rary, 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

54

830 GENERATION.

of the temporary teeth. The roots of the latter are absorbed, the permanent
teeth advance more and more toward the surface, and the crown of each tem-
porary tooth is finally pushed out. The number of the temporary teeth is
twenty, and there are thirty- two permanent teeth. Thus there are three
permanent teeth on either side of both jaws, which are developed de novo and
are not preceded by temporary structures.

The first dental follicles usually appear in regular succession. The folli-
cles 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 com-
pletely formed at about the eleventh or twelfth week.

The temporary teeth appear successively, the corresponding teeth appear-
ing a little earlier in the lower jaw. The usual order, subject to certain ex-
ceptional variations, is as follows (Sappey) :

The four central incisors appear six to eight months after birth.

The four lateral incisors appear seven to twelve months after birth.

The four anterior molars appear twelve to eighteen months after birth.

The four canines appear sixteen to twenty-four months after birth.

The four posterior molars appear twenty-four to thirty-six months after birth.

The order of eruption of the permanent teeth is as follows :

The two central incisors of the lower jaw appear between the sixth and the eighth
years.

The two central incisors of the upper jaw appear between the seventh and the eighth
years.

The four lateral incisors appear between the eighth and the ninth years.

The four first bicuspids appear between the ninth and the tenth years.

The four canines appear between the tenth and the eleventh years.

The four second bicuspids appear between the .twelfth and the thirteenth years.

The above are the permanent teeth which replace the temporary teeth.
The permanent teeth which are developed de novo appear as follows :

The first molars appear between the sixth and the seventh years.

The second molars appear between the twelfth and the thirteenth years.

The third molars appear between the seventeenth and the twenty-first years.

DEVELOPMENT or THE GENITO-URINARY APPARATUS.

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, de-
velop very rapidly on either side of the spinal column and are so large as to
almost fill the cavity of the abdomen. Fig. 311 shows how large these bodies
are in the early life of the embryon, at which time their office is undoubtedly
very important.

Very soon after the Wolfnan bodies have made their appearance, there
appear 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 ex-
ternal borders, are two ducts on either side, one of which, the internal, is

DEVELOPMENT OF THE GENITO-URINARY APPARATUS. 831

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 Miiller. Behind the Wolffian
bodies, are developed the kidneys and the suprarenal

As the development of the Wolffian bodies attains
its maximum their structure becdmes somewhat com-
plex. From their proper ducts, which are applied di-
rectly to their outer borders, tubes make their appear-
ance at right angles to the ducts, which extend into the
substance of the bodies and become somewhat convo- ^anln^^mZ' ion/.
luted at their extremities. These tubes communicate J^S by !K£en pre"
directly with the ducts, and the ducts themselves open i» }«St; * 3nterister!or
into the lower part of the intestinal canal, opposite to ^emi^y ' '4' Wolfflan
the point of its communication with the allantois. The abdominal walls have

been cut away, in order

The tubes of the Wolffian bodies are simple, •termina- to show the position of

_ _., , ,,. , the Wolfflan bodies.

ting in single, somewhat dilated, blind extremities, are
lined with epithelium, and are penetrated at their extremities, by blood-ves-
sels, which form coils or convolutions in their interior. These are undoubt-
edly organs of depuration for the embryon and take on the office to be after-
ward assumed by the kidneys ; but in the female they are temporary struct-
ures, disappearing as development advances, and having nothing to do with
the development of the true, urinary organs.

The testicles or ovaries are developed at the internal and anterior surface
of the Wolffian 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 'Miiller. These at first open into the
intestine, near the point of entrance of the Wolffian ducts. In the female
their upper extremities remain free, except the single fimbria which is con-
nected with the ovary. Their inferior extremities unite with each other,
and at their point of union they form the uterus. When this union is in-
complete there is the malformation known as double uterus, which may be
associated with a double vagina. The Wolffian bodies and their ducts disap-
pear, in the female, at about the fiftieth day. A portion of their structure,
however, persists in the form of a collection 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 testicles, which are at first in the abdomen of the male, finally de-
scend into the scrotum. As the testicles descend they carry with them the
Wolffian duct, that portion of the Wolffian body which is permanent consti-
tuting the head of the epididymis. At the same time a cord appears, at-
tached 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

832 GENERATION.

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 in-
ternal abdominal ring ; and at this time a double tubular process of perito-
neum, 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 become eventu-
ally the visceral and parietal portions 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
passes from the testicle, along the base of the bladder, to open into the pros-
tatic 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 ^esiculae seminales.

As the ovaries descend to their permanent situation in the pelvic cavity,
there appears, attached to the inner extremity of each, a rounded cord, analo-
gous to the gubernaculum testis. A portion of this, connecting the ovary
with the uterus, constitutes the ligament of the ovary ; and the inferior por-
tion forms the round ligament of the uterus, which passes through the in-
guinal canal and is attached to the symphysis pubis.

Development of the Urinary Apparatus. — Behind the Wolffian bodies,
and developed entirely independently of them, the kidneys, suprarenal cap-
sules 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 they
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
time that the kidneys are undergoing development the suprarenal capsules
are formed at their superior extremities. These bodies, the uses of which are
unknown, are relatively so much larger in the foetus than in the adult that
they have been supposed to be peculiarly important in intrauterine life,
though nothing definite is known upon this point. The kidneys are rela-
tively very large in the foetus. Their proportion to the weight of the body,
in the foetus, is 1 to 80, and in the adult, 1 to 240. The ureters undoubtedly
are developed as tubular processes from the kidneys, which finally extend to
open into the bladder. This fact is shown by certain cases of malformation,
in which the ureters do not reach the bladder, but terminate in blind ex-
tremities. The development of the genito-urinary apparatus can be readily
understood, after the discription just given, by a study of Fig. 312.

Development of the External Organs of Generation. — The external organs
of generation begin to be developed at about the fifth week. At the infe-

DEVELOPMENT OF THE GENITO-URINARY APPAKATUS. 833

A

FIG. 312. — Diagrammatic representation of the genitourinary apparatus (Henle).

I, embryonic condition, in which there is no distinction of sex ; II, female form ; III, male form. The
dotted lines in II and III represent the situations which the male and female genital organs assume
after the descent of the ovaries and testicles. The small letters in II and III correspond to the cap-
ital letters in I.

Fig. 312, 1.— 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' ; H, duct of Miiller, 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. 312, II (female).— a, kidney ; b, ureter ; c, bladder ; d, urachus; e, urethra; f, remains of the Wolf-

duct of the gland of Bartholinus.

Fig. 312, III (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 Miiller ; k, testicle;

1, gubernaculum testis ; n, n', n", urethra and penis ; o, scrotum ; p, gland of Cowper ; q, prostate.

834 GENERATION.

rior 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 open-
ing above. In the male this septum is developed between the rectum and the
urethra, the generative 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 cor-
pora 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, there is the malformation known
as hypospadias. 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 analogy is farther illustrated by the
anatomy of inguinal hernia, in which the intestine descends into the labium,
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.

DEVELOPMENT OF THE CIRCULATORY APPARATUS.

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 novo in the blastodermic layers, while afterward, ves-
sels are formed as prolongations of pre-existing tubes. Soon after the epi-
blast and the hypoblast have become separated from each other and the
mesoblast has been formed at the thickened portion of the ovum, which is
destined to be developed into the embryon, certain of the blastodermic cells
undergo a transformation into blood-corpuscles. These are larger than the
blood-corpuscles of the adult and generally are 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 themselves so as to form vessels. Leucocytes probably are
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.

According to His and Waldeyer, the cells of the mesoblast do not take
part in the formation of the blood and blood-vessels, as indicated above, but
cells penetrate at the edges, between the epiblast and the hypoblast, and these,
which are called parablastic cells, are developed into blood-vessels and blood-
corpuscles. The connective tissue is also supposed to be developed from
parablastic cells. According to this view — which, however, is not generally

DEVELOPMENT OF THE CIRCULATORY APPARATUS. 835

adopted — the parablastic cells are to be distinguished from the cells of the
mesoblast, which latter are called archiblastic cells. According to Rind-
fleisch the so-called parablastic cells are derived from the area opaca.

The First, or Vitelline Circulation. — In the development of oviparous
animals, the first, or vitelline circulation is very important ; for by these ves-
sels the contents of the nutritive yelk are taken up and carried to the em-

Fio. 313.— Area vasculosa (Bisehoff).
a, a, 6, sinus terminalis ; c, omphalo-mesenteric vein ; d, heart ; e, /, /, posterior vertebral arteries.

bryon, constituting the only source of material for its nutrition and growth.
In mammals, however, nutritive matter is absorbed almostly exclusive 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 dissappear 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 vi-
tellus, around the embryon. The vessels of this plexus open into a sinus at
the border of the area, called the sinus terminalis.

In examining the ovum when the area vasculosa is first formed, the em-
bryon is seen 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 down-
ward 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

836 GENERATION.

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 enlarge-
ment of the embryon, between the inferior extremity of the pharynx and the
superior cul-de-sac of the intestinal canal. The excavation which receives
this vessel is called the fovea cardiaca. 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 currents of the circulation are estab-
lished. The time of the first appearance of the circulation in the human
embryon has not been accurately determined.

In the arrangement of the vessels for the first circulation in 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 aortae, and the single trunk formed by their
union becomes the abdominal aorta. The two aortic arches, only one of
which is permanent, are sometimes called the inferior vertebral arteries. These
vessels give off a number of branches, which pass into the area vasculosa.
Two of these branches, however, are larger than the others, pass to the um-
bilical vesicle and are called the omphalo-mesenteric arteries. In the em-
bryon 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 there are then two omphalo-mesen-
teric arteries and two omphalo-mesenteric veins. At about the fortieth day
one artery and one vein disappear, leaving 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 disappears and loses its connection with the abdom-
inal aorta ; a branch, however, persists during the whole of intrauterine life
and constitutes the ductus arteriosus, and another branch is permanent,
forming th'e pulmonary artery.

The Second, or Placental Circulation. — As the omphalo-mesenteric ves-
sels disappear and as the allantois is developed to form the chorion, two
vessels (the hypogastric arteries) 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 con-
nected 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 disap-
pears, and there is finally but one vein in the umbilical cord. It is in this
way — the umbilical arteries carrying the blood to the tufts of the foetal pla-
centa, which is returned by the umbilical vein — that the placental circulation
is established.

DEVELOPMENT OF THE CIRCULATORY APPARATUS. 837

Corresponding to the four visceral arches, which have been 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 converted into
the right and left pulmonary arteries.

The changes of the branchial arches are illustrated
in the diagrammatic Fig. 314. In this figure the three
branchial arches that remain and participate in the de-
velopment of the upper portion of the vascular system
are 1, 2, 3, on either side. The two anterior (3, 3) be-
come the carotids (c, c) and the subclavians (s, s). The
second (2, 2) is obliterated on the right side, and be-
comes 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 (c«), between
the pulmonary artery of that side and the arch of the
aorta, which is the ductus arteriosus. The anastomos-
ing vessel (cd), between the right pulmonary artery and
the aorta, is obliterated.

The mode of development of the veins is very sim-
ple. Two venous trunks make their appearance by the
sides of the spinal column, which are called the cardi-
nal veins, and run parallel with the superior vertebral
arteries, or the two aortse, emptying finally into the au-
ricular 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 re-
placed by the second. The omphalo-mesentefic 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 goes to the heart. 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 with the liver as the om-
phalo-mesenteric vein, and its blood passes through the liver before it reaches
the central organ of the circulation. As the omphalo-mesenteric vein atro-
phies, 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

FIG. 314. — Transforma-
tion of the system of
aortic arches into per-
manent 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 earliest in their
appearance ; 1, 1, the
most recent ; c, c, the
two carotids, still unit-
ed, which are separated
at a later period : .s, s,
the two subclavians, the
right arising from the
arteria innominata ; a,
a, the aorta ; p, p, the
pulmonary arteries ; ca,
the ductus arteriosus ;
cd, the left artieral ca-
nal, which is finally ob-
literated.

838 GENERATION.

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, en-
larges and becomes the vena cava descendens, receiving finally all the blood
from the head and the superior extremities. The left canal of Cuvier under-
goes atrophy and disappears. The upper portion of the superior cardinal
veins is developed into the jugulars and subclavians 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 sys-
tem 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 con-
striction, which partly separates the auricular from the ventricular portion.
At a certain period of development the heart presents a single auricle and
a single ventricle.

The division of the heart into two ventricles appears before the two auri-
cles are separated. 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 between 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 persists 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 is 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

THE FCETAL CIRCULATION.

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 capac-
ity during the latter half of intraiiterine life. The pericardium makes its
appearance during the ninth week.

Early in intraiiterine 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 as 1
to 50. This proportion, however; gradually diminishes, until at birth the
ratio is as 1 to 120. The weight in the adult is about as 1 to 160. During
about the first half of intraiiterine life the thickness of the two ventricles is
nearly the same ; but after that time the relative thickness of the left ven-
tricle gradually increases.

Peculiarities of the Fatal Circulation. — Beginning at the abdominal
aorta, the blood passes into the two primitive iliacs, and thence into the in-
ternal iliacs. From the two internal iliacs the two hypogastric arteries arise,
which ascend along the sides of the bladder, to its f undus, pass to the umbili-
cus 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 ex-
tremities passes down, by the vena cava descendens, in front of the Eustachian
valve, through the right auricle, into the right ventricle. The arrangement
of the Eustachian valve is such that the right auricle simply affords a pas-
sage for the two currents 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 natu-
ral course of the fcetal circulation.

The blood poured into the left auricle, from the vena cava ascendens,
through the foramen ovale, passes from the left auricle into the left ventricle.
The left auricle and the left ventricle also receive a small quantity of blood

840

GENERATION.

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

Pulmonary Art.

Foramen Ovale

Eustachian Valve

Right Auric.-} ent. Opening A>!

Bladder.

Pulmonary Art.
Left Auricle.

Left Auric. • Vent.

Opening.

Hepatic Vein.

Branches of the
Umbilical Vein, •
to the Liver.

Ductus Venosus.

Internal Iliac Arteries.
FIG. 315— Diagram of the foetal circulation.

through the right auricle, in front of the Eustachian valve. The two ventri-
cles, thus distended, then contract simultaneously. The blood from the

THE FCETAL CIRCULATION. 841

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 half an inch (12-7 mm.) in length, and about the
size of a goose-quill. The blood from the left ventricle 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 quantity of blood received from the lungs. After the aorta has received
the blood from the ductus arteriosus, however, it is mixed blood ; and it is
this which supplies the trunk and lower extremities.

In Fig. 315, which is diagrammatic, the foetal circulation is illustrated.
In endeavoring, in this figure, to give a clear idea of the second circulation,
no attempt has been made to preserve the exact relations or the relative size
of the organs. The Eustachian valve, the foramen ovale and the two auric-
ulo-ventricular orifices are represented by dotted lines. The liver and the
bladder are also represented by dotted lines.

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 intense to give rise to an inspiratory effort, and the first
inspiration is made. The pulmonary organs are then for the first time dis-
tended with air, the pulmonary arteries carry the greatest part of the blood
from the right ventricle to the lungs, and a new circulation is established.
During the later periods of foetal life the heart is gradually prepared for the
new currents of blood. The foramen ovale, which is largest at the sixth
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 interauricular septum, is marked by an oval
depression, called the fossa ovalis.

As a congenital malformation, the foramen ovale may remain open, pro-
ducing 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 fora-
men 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, between the third and the tenth days.

When the placental circulation is arrested at birth, the hypogastric arter-
ies, the umbilical vein and the ductus venosus contract, and they become

842 GENERATION.

impervious between the second and the fourth days. The hypogastric arter-
ies remain pervious at their lower portion and constitute the superior vesi-
cal arteries. A rounded cord, which is the remnant of the umbilical vein,
forms the round ligament of the liver. A slender cord, the remnant of the
ductus venosus, is lodged in a fissure of the liver, called the fissure of the
ductus venosus.

CHAPTER XXVI.

FCETAL LIFE— DEVELOPMENT AFTER BIRTH— DEATB.

Enlargement of the uterus in pregnancy — Duration of pregnancy — Size, weight and position of the foetus
—The foetus at different stages of intrauterine life— Multiple pregnancy— Cause of the first contractions
of the uterus, in normal parturition— Involution of the uterus— Meconium— Dextral pre-eminence— De-
velopment after birth— Ages— Death— Cadaveric rigidity (rigor mortis).

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. Immediately after birth its weight is about a pound and a
half (680 grammes) while the virgin uterus weighs less than two ounces (56-7
grammes). The neck of the uterus, while it becomes softer and more patu-
lous during pregnancy, does not change its length, even in the very latest
periods of utero-gestation (Taylor). The changes in the walls of the uterus
during pregnancy are very important. The blood-vessels become much en-
larged, and the muscular fibres increase immensely in size, so that their con-
tractions are very powerful when the fretus is expelled.

It is evident that on account of the progressive increase in the size of the
uterus during pregnancy, it can not remain in the cavity of the pelvis dur-
ing 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 down-
ward, forward and a little to the left. After this time, however, the in-
creased 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 tem-
porary hypertrophy of the heart. 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 nearly to the normal standard.

Duration of Pregnancy. — The duration of pregnancy, dating from a
fruitful intercourse, 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. Taking into account, however, the various

SIZE, WEIGHT AND POSITION OF THE FCETUS. 843

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 dura-
tion of pregnancy of not less than 40 days, the extremes being 260 and 300
days. As regards the practical applications of calculations of the probable
duration of pregnancy in individual cases, the fact must be recognized that
the period is variable. Dating from the end of the last menstrual flow, an
average of 278 days, or a little more than nine calendar months, may be
adopted.

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
intrauterine life present very wide variations ; still it is important to have
an approximate idea, at least, upon these points, and the estimates by Scan-
zoni are given, as presenting fair averages.

At the third week the embryon is two to three lines (4-2 to 6-4 mm.) 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 (19-1 mm.).
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 generation have just appeared ; the
liver is of large size ; the lungs present several lobules.

At the eighth week the embryon is ten to fifteen lines (21-2 to 31-8 mm.)
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 abdominal walls have closed over in
front.

At the third month the embryon is two to two and a half inches (50-8
to 63-5 mm.) long and weighs about one ounce (28'3 grammes). The amni-
otic fluid is then more abundant, in proportion to the size of the embryon,
than at any other period ; the umbilical cord begins to be twisted ; the vari-
ous 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 four to five inches (10-1 to 12-7 centimetres) long and weighs about
five ounces (141-7 grammes). The muscles begin to show 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 nine to twelve inches (22-8 to 30-5 centi-
metres) long and weighs five to nine ounces (141-7 to 255*1 grammes). 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.

At the sixth month the foetus is eleven to fourteen inches (27'9 to 35-5
centimetres) long and weighs one and a half to two pounds (680 to 907

844 GENERATION.

grammes). If the foetus be delivered at this time, life may continue for a
few moments ; the bones of the head are ossified, but the f ontanelles and
sutures are still wide; the prepuce has appeared; the testicles have not
descended.

At the seventh month the fcetus is fourteen to fifteen inches (35-5 to 38-1
•centimetres) long and weighs two to three pounds (907 to 1,361 grammes).
The hairs are longer and darker ; the pupillary membrane disappears, under-
going atrophy from the centre to the periphery ; the relative quantity of the
amniotic fluid is diminished, and the fcetus is not so free in the cavity of the
uterus ; the fcetus is now viable.

At the eighth month, the fcetus is fifteen to sixteen inches (38'1 to 40-9
•centimetres long and weighs three to four pounds (1,361 to 1,814 grammes).
The eyelids are opened and the cornea is transparent ; the pupillary 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 (43'2 centimetres)
long and weighs five to six pounds (2'27 to 2'72 kilos). Both testicles usu-
ally have descended, but the tunica vaginalis still communicates with the
peritoneal cavity.

At birth the infant weighs a little more than seven pounds (3-17 kilos),
the usual range being between four and ten pounds (1*81 and 4'53 kilos),
although these limits are sometimes exceeded.

The position of the foetus, in the great majority of cases, excluding ab-
normal presentations, is with the head downward. In the early months of
pregnancy the fcetus floats quite freely in the amniotic fluid ; and it is prob-
able 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 fcetus 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
passages 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.
Examples of three at a birth have been often observed.

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 having its distinct decidua, pla-

PARTURITION. 845

centa 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 com-
munication 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 to assume
that there were originally two sets of membranes, which had become fused
into one. The instances on record 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 un-
settled.

As pathological conditions, extrauterine pregnancies occur, in which the
fecundated ovum, forming its attachments in the Fallopian tube (Fallopian
pregnancy) or within the abdominal cavity (abdominal pregnancy), under-
goes 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 un-
doubtedly 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 con-
tractions of this organ is to cautiously separate a portion of the membranes,
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 degeneration, and in this way there is a gradual separation of
the outer membrane, so that the contents of the uterus gradually lose their
anatomical connection with the mother. When this change has progressed
to a certain extent, the uterus begins to contract ; each contraction then
separates the membranes more and more, the most dependent part pressing
upon the os internum; and the subsequent contractions are 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.

According to Korner, there exists in the spinal cord, at the site of the
first and second lumbar vertebrae, a reflex centre for parturition. This, like
other centres in the cord, is subordinate to a centre which is situated in the
medulla oblongata.

The mechanism of parturition, although this is entirely a physiological
process, is considered elaborately in works upon obstetrics. The first con-
tractions of the uterus, by pressing the bag of waters against the os internum,
55

846 GENERATION.

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 fol-
lows 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 considered in connec-
tion with the development of the circulatory system.

Involution of the Uterus. — At 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-pregnant condition, though it never be-
comes 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
has not participated 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 involu-
tion 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 quantity of sero-mucous secretion. This dis-
charge constitutes the lochia. It is at first red but becomes paler as it is
reduced in quantity and disappears.

Meconium. — At about the fifth month there is a certain quantity 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 it is of a dark-greenish color in the colon. The dark,
pasty, adhesive matter, which is discharged from the rectum soon after birth,
is called the meconium.

The meconium appears to consist of a thick, mucous secretion, with
abundant, grayish granules, a few fatty granules, intestinal epithelium, and
frequently crystals of cholesterine. The color seems to be due to granula-
tions of the coloring matter of the bile, but the biliary salts can not be de-
tected in the meconium, by Pettenkofer's test. The constituent of the me-
conium which possesses the greatest physiological importance, is cholesterine.
Although but few crystals of cholesterine are found upon microscopical
examination, the simplest processes for its extraction will reveal the presence
of this substance in large quantity. In a specimen of meconium in which a

DEXTRAL PRE-EMINENCE.

847

quantitative examination was made, the proportion of cholesterine was 6*245
parts per 1,000 (Flint). The meconium contains cholesterine and no ster-
corine, the stercorine, in the adult,
resulting from a transformation of
cholesterine, by the digestive fluids,
which probably are not secreted dur-
ing in trail terine life.

None of the secretions concerned
in digestion appear to be produced
in utero, and it is also probable that
the true, biliary salts are not formed
at that time; but the processes of
disassimilation and excretion are
then active, and the cholesterine of
the meconium is the product of the
excretory action of the liver. The
relations of cholesterine as an ex-

, . . . . , , , FIG. 316.— Cholesterine extracted from meconium.

crementitious product have already

been very fully discussed, in connection with the bile and with excre-
tion.

Dextral Pre-eminence. — Most persons by preference use the right arm,
leg, eye etc., instead of the left ; but exceptionally some use the left in pref-
erence to the right. 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 pre-eminence in the great majority of persons, and left-
handedness, as an exception ; but what this condition is, it is very difficult
to determine. An explanation which was 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, develop's more fully, and
therefore is generally used in preference to the left ; but the exceptional pre-
dominance of the left hand can not be explained in this way.

The most important anatomical and pathological facts bearing upon the
question under consideration are the following : Boyd has shown that the
left side of the brain almost invariably exceeds the right in weight, by about
one-eighth of an ounce (3'5 grammes). In aphasia the lesion is almost al-
ways 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 persons. Ogle gives several such instances, 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 persons. 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. Bastian has found the gray matter

848 GENERATION.

of the brain generally to be 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 explanation offered is the fact that the arteries going to the left side
usually are larger than those on the right. There are 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, Ogle has assumed that dextral pre-
eminence 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 pre-eminence. Generally it is 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, although the
right hand is more conveniently and easily used than the left. In many
feats of strength, the left arm appears less powerful than the right, because
there is less command over the muscles. As regards the cause of the superior
development of the left side of the brain, it must be admitted that the ana-
tomical explanation is not entirely satisfactory. It is a fact, however, that
the two sides of the brain generally are not exactly equal in their develop-
ment, the left side usually being superior to the right, and that the muscles
of the right side of the body generally are used in preference to those of the
left side.

DEVELOPMENT AFTER BIRTH — AGES A^D 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 little 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 are found in the adult, though ob-
servations upon the secretions of the infant are few and rather unsatisfac-
tory. 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 resist-
ance to asphyxia than the adult. The power of maintaining the animal
temperature is also much less in the newly-born. The processes of ossification,
development of the teeth etc., have already been described. 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 then 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 gradually develops, and the
milk-teeth are replaced by the permanent teeth. At puberty, which begins
between the fourteenth and the seventeenth years — a little earlier in the

CADAVERIC RIGIDITY. 849

female — the development of the generative organs is attended with important
physical and moral changes.

The different ages recognized by physiologists are the following : 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 re-
garded at his maximum of intellectual and physical development at about the
age of thirty-five, and he begins to decline after the sixtieth year, although
this rule, as regards intellectual vigor, has many exceptions.

As regards nutrition, it may be stated in general terms that the appro-
priation of new matter is a little superior to disassimilation, to about the
age of twenty-five years ; between twenty-five and forty-five these two pro-
cesses are nearly equal ; and at a later period the nutrition does not com-
pletely 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 be-
come stiff ; the special senses generally are somewhat obtuse ; and there is a
diminished capacity for mental labor, with more or less loss of 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 occur-
rence ; and, indeed, early impressions and prejudices then appear to be un-
usually 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 it sometimes occurs that there is 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 persons die, apparently of old age, at seventy, and it is rare that
life is preserved beyond one hundred years. The tissues usually die succes-
sively and not simultaneously, nearly all of them being dependent upon the
circulating, oxygen- carry ing blood, for the maintenance of their physiological
properties. It has been demonstrated, indeed, that the properties of tissues
may be restored for a time, after apparent death, by the injection of blood
into their vessels.

After death there often is a discharge of the contents of the rectum and
bladder, and parturition, even, has been known to take place. The appear-
ance 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 general rigidity of the mus-
cular system.

Cadaveric Rigidity (Rigor Mortis). — At a variable time after death, usu-

850 GENERATION.

ally five to seven hours, all of the muscles of the body, involuntary as well as
voluntary, become rigid, and can be stretched only by the application of con-
siderable 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 devel-
oped until twenty or thirty hours after death, and it then continues for six
or seven days. Its average duration is 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 com-
pletely 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 lymphatics. During what may be called the first stage the
muscles are still excitable ; but when the rigidity is complete their excita-
bility is lost and can not be restored. Cadaveric rigidity is always preceded
by loss of excitability of the motor nerves.

The rigidity first appears in the muscles which move the lower jaw. Then
it is noted in the muscles of the trunk and neck, extends to the arms, and
finally to the legs, disappearing in the same order of succession. The stiffen-
ing of the muscles is due to a coagulation of their substance, analogous to
the coagulation of the blood, and probably is attended with some shortening
of the fibres ; at all events, the fingers and thumbs generally are flexed.
That the rigidity is not due to coagulation of the blood, is shown by the fact
that it occurs in animals dead from haemorrhage.

According to John Hunter the blood does not coagulate nor do the mus-
cles 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 under-
gone extensive fatty degeneration.

Under ordinary conditions of heat and moisture, as the rigidity of the
muscular system disappears the processes of putrefaction begin. The vari-
ous 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, carbon dioxide, 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.

Absorption 272

by blood-vessels 272

by the mucous membrane of the mouth.. . 272

by the stomach 272

by the intestinal mucous membrane 273

by lacteals 285

— by parts not connected with the digestive
system 286

by the skin 286

by the respiratory surface 287

by closed cavities, reservoirs of glands etc. 288

of fats and insoluble substances 288

variations and modifications of 290

of fluids of greater density than the blood. 290

of curare, venoms etc 290

of substances which disorganize the tissues 291

influence of the condition of the blood and

of the vessels upon 291

influence of the nervous system upon 291

passage of liquids through membranes (see

Endosmosis) 292

Accelerator nerves of the heart 55

Accommodation of the eye for different degrees

of illumination 702

for different distances 708

Addison's disease 421

Adipose tissue 442

Adolescence 849

Adult age 849

^Esthesiorneter 656

After-images 716

Ages (infancy, childhood, youth, adult age, mid-
dle age and old age) 848

Agminated glands of the small intestine 239

Agraphia 621

Air, composition of 135

— in the veins (see Veins) 98

proper allowance of, in hospitals, prisons

etc 137

Air-cells of the lungs 114

Air-swallowing 210

Albumin 170

Albuminates 227

Albuminates in the blood 23

Albuminoids, characters of 170, 437

— in the body 437

Albuminose (peptones) 226

Alcohol, action of, in alimentation and nutri-
tion... .. 175

FAOB

Alcohol, elimination of 176

influence of, upon endurance, the power of

resistance to cold, etc 177, 450

formation of, in the body 440

heat- value of 454

Alcoholic beverages, influence of, upon the ex-
halation of carbon dioxide 144

Aliment (see Food) 169

Alimentation 164

Allantois, formation of 807

villosities of 807

Alternate paralysis 551

Amo2boid movements 460

Ammonia, exhalation of, by the lungs 149

Amnion, formation of 803

— villosities of 803

enlargement of ,. . 805

Amniotic fluid 805

— origin of 806

antiseptic properties of 806

Amniotic umbilicus 803

Amphioxus lanceolatus, an animal without a

brain 617

Amylopsine 246

Andersch, ganglion of 665

Anelectrotonus 535

Angle alpha of the eye 691

Animal heat 444

quantity of heat produced by the body,

estimated in heat-units 444

limits of variation in the normal tempera-
ture in man 446

— — variations of, with external temperature. . 446

variations of, in different parts of the body 447

variations of, at different periods of life. . . 448

variations of, at different times of the day,

etc.

relations of defective nutrition to 449

in inanition 449

influence of alcohol upon 449

influence of exercise etc. upon 450

— influence of mental exertion upon 451

— influence of the nervous system upon. 451, 641

centres of 451

mechanism of the production of 452

relations of non-nitrogenized and nitrogen-

ized food to 454

— equalization of 456

Antihelix of the ear ... 780

852

INDEX.

PAGE

Ano-spinal centre 270

Antiperistaltic movements of the small intestine 255

Antiscorbutics 184

Antitragus of the ear 730

Anus 261

— sphincter of 261, 269

development of 824

— imperforate 824

Aorta, development of 836

Aortae, primitive 836

Aortic valves 37

Aphasia 621

in left hemiplegia in left-handed persons.

622, 847

Appendices epiploicae 260

Appendix vermiformis 258

development of 823

Appetite for food 165

influence of climate and season upon 165

Aqueous humor of the eye 688

Arachnoid 587

first appearance of 819

Arantius, corpuscles of 37

Arbor vitae uteri 774

Archiblastic cells 835

Arctic regions, diet in 184

Area opaca of the ovum 801

Area pellucida of the ovum 801

Area vasculosa of the ovum 835

Arms, development of 817

Arnold's ganglion 638

Arrowroot 171

Arsenious hydride, effects of 136

Arteries, physiological anatomy of 60

— course of the blood in 64

— elasticity of 64

gradual diminution of the intermittency of

the current in 64

contractility of 65

influence of the resiliency of, upon the cir-
culation 65, 66

influence of the contractility of the small

vessels upon the distribution of blood in the

tissues 65, 66

locomotion of, and production of the pulse 66

— tonicity of 70

— variations in the diameter of, at different
times of the day 71

pressure of blood in 71

pressure in different vessels 73

influence of respiration upon the pressure

of blood in 74

— influence of muscular effort upon the press-
ure of blood in 74

— influence of haemorrhage upon the pressure

of blood in 75

— rapidity of the flow of blood in 76

reason why they are found empty after

death 107

development of 837

Articular cartilage 315, 487

Arytenoid muscle 490

Asphyxia, influence of, upon the circulation. 51, 85

arrest of the action of the heart in 51

power of resistance to, in the newly-born.

138, 162

PAGE

Asphyxia, phenomena of 162

influence of various conditions of the sys-
tem upon the power of resistance to 164

Association and dissociation 148, 155

Astigmatism 704

Atmosphere, composition of 135

Attollens aurem 731

Attrahens aurem 731

Audition, general considerations 728

topographical anatomy of the parts con-
nected with 730

physics of sound (see Sound) 737

— centres for 764

Auditory meatus, external 731

development of 826

— internal 729, 736

Auditory nerves, physiological anatomy of 729

general properties of 729

Faradization of .730

development of 821

Auditory vesicles 821

Auerbach's plexus 257

Auricles of the heart 32

Auriculo- ventricular valves, action of 43

Axis-cylinder 508

Azygos uvulae 204

Azygos veins, development of 838

Beats, a cause of discord 747

Bellini, tubes of 3G1

Bertin, columns of 359

Besoin de respirer 157

Bile, action of, in digestion 251

color, reaction and specific gravity of 252

variations in the flow of 252

influence of, upon the faeces and upon the

peristaltic movements of the intestine 253

influence of, upon the digestion and ab-
sorption of fats 253

absorption of the salts of, by the intestinal

canal 254

mechanism of the secretion and discharge

of 399

quantity of 401

— properties and composition of 401

— tests for 404

Biliary fistula 252

nutrition in a case of 252

Biliary salts 402

Bilirubin 404

Biliverdine 404

Binocular vision 712

— fusion of colors 716

Bitters, influence of, upon the appetite 166

" Black-hole " of Calcutta 163

Bladder, urinary, physiological anatomy of — 370

first appearance of 822

Blastodermic cells 800

Blastodermic layers 802

Blepharoptosis 542

Blind spot of the retina : 699

Blood, general considerations 1

extra-vascular tissues 1

effects of abstraction and subsequent re-
turn of 1

transfusion of . . . 2

INDEX.

853

PAGE

Blood, quantity of 2

— opacity of 3

odor of, and development of odor of, by

sulphuric acid 3

— taste of 3

— reaction of 4

specific gravity of 4

— temperature of 4

— color of 4

— variations in the color of, in the vascular
system 4

— color of, in veins coining from glands 5

— anatomical elements (corpuscles) of 5

red corpuscles of 6

relations of the size of the red corpuscles

of, to muscular activity in different animals. . 8

— enumeration of red corpuscles of 8

— post-mortem changes in the red corpuscles

of 9

—f— structure of the red corpuscles of 10

— development of the red corpuscles of . . 10, 834

— relations of leucocytes to the development

of the red corpuscles of 10

— theory of destruction of the red corpuscles

of, for the production of pigment 11

— relations of the spleen to the blood-cor-
puscles ' 11, 418

— uses of the red corpuscles of 11

— capacity of the red corpuscles of, for the
absorption of oxygen, as compared with the
plasma 12, 151

— action of the red corpuscles of, as respira-
tory organs 12, 151

— leucocytes, or white corpuscles of 12

— situations in which leucocytes are found . . 12

— appearance and characters of leucocytes . . 13

— variations in the proportion of leucocytes 13

— development of leucocytes 14

proportion of leucocytes in the blood of

the splenic veins 14

— uses of leucocytes of 15

— plaques « 15

— composition of the red corpuscles of 16

— composition of the blood-plasma 1?

— coloring matter of 17

uses of water in 20

uses of sodium chloride in 21

— uses of other inorganic salts in 21

— organic saline constituents of 21

— organic non-nitrogenized constituents of.. 21

— excrementitious constituents of 21

— fats and sugars in 21

— organic nitrogenized constituents of 22

— plasmine, fibrin, metalbumen and serine in 22

— peptones in 23

— coloring matter of the plasma of 23

coagulation of 23

albuminates in 23

— conditions which modify coagulation of,
out of the body 25

— coagulation of, in the organism 25

— coagulation of, in animals killed by light-
ning or hunted to death 25, 850

— office of the coagulation of, in the arrest of
haemorrhage 26

cause of the coagulation of 27

PAGE
Blood, action of leucocytes in coagulation of . . 27

non-coagulation of, when drawn by the

leech 28

— fibrillation of fibrin in coagulation of 28

— non-coagulation of, in the renal and he-
patic veins and in the capillaries 29

— circulation of (see Circulation) 29

— changes in, in respiration (see Respiration) 135
difference in color between arterial and

venous 150

— absorption of oxygen by the red corpuscles

of 12, 151

— gases of. .-. 151

condition of the gases in 155

— general differences in the composition of *
arterial and venous 154, 155

sources of carbon dioxide of 157

Blood-corpuscles, development of, in the ovum 834
Blood-vessels, first formation of, in the blasto-

dermic layers 834

Bones, anatomy of 481

— regeneration of, by transplantation of peri-
osteum 485

Bone-corpuscles 483

Botal, foramen of 838, 841

Bowman, capsule of 362

Brain, circulation in 101, E88

— contraction and expansion of, with the acts

of respiration 102, 588

peculiarity of the small vessels of 275, 588

— lymphatics of 275, 588

— variations in the quantity of blood in 588

— ganglia of 601

— weight of different parts of 602

difference in the weight of, in the sexes. . . 603

differences in the weight of, at different

ages 603

specific gravity of 603

fissures and convolutions of 604

basal ganglia of 606

directions of the fibres in 610

— rolling and turning movements following
injury of certain parts of 633

— development of 820

Branchial arches 837

Bread 185

Breschet, perilymph and endolymph of 759

Bronchia Ill

mucous glands of 113

— development of 825

Bronchial arteries 115

Brunner, glands of 235

Buccal glands 197

Bulb (see medulla oblongata) 627

Burdach, columns of 593

Butter 186, 336

Cadaveric rigidity 850

Caecum 258

— development of 823

Caffeine 180

Calcium oxalate in the urine 383

Calcium phosphate, uses of, in alimentation 175

Calcutta, " black hole "of 163

Canals of Cuvier 837

Cane-sugar 171

854

INDEX.

PAGE

Capillaries, circulation in 78

physiological anatomy of 79

— stomata in the walls of 79

size of 79

capacity of the system of 81

course of blood in 81

study of the circulation in, with the micro-
scope 81

"still layer" in 82

circulation in, in the lungs . . 84

pressure of blood in 84

rapidity of the flow of blood in 85

relations of the circulation in, to respira-
tion 85

causes of the circulation in 86

influence of temperature upon 87

Capriline 336

Caprine 336

Caprolne 336

Capsicum 181

Caput coli 258

Carbohydrates 170, 439

Carbon, quantity of, necessary to nutrition 183

Carbonates in the body 435, 436

Carbon dioxide, small proportion of, in the air 135

relations of the consumption of oxygen to

the production of 146

— exhalation of, in respiration (see Respira-
tion) 140

sources of, in the expired air 148

analysis of the blood for ... 151

proportion of, in the blood. 154

condition of, in the blood 155

action of sodium phosphate upon the capa-
city of absorption of, by the blood 155

sources of, in the blood 157

effects of accumulation of, in the atmos-
phere 163

Carbon monoxide, effects of 136, 164

use of, in analysis of the blood for oxygen 152

Cardiac nerve-centres 55, 632

Cardinal veins 837

Cardiograph 41

Cardiometer 72

Carotids, development of 837

Cartilage 486

— of Meckel 821, 827

Caruncula lacrymalis 727

Caseine 170, 335

vegetable 170

Casper Hauser, case of 714

Catelectrotonus 535

Cauda equina 589

Cellulose 172

Cement of the teeth.. 190

Cephalo-rachidian fluid 101, 588

Cerebellum, weight of 623

physiological anatomy of 623

course of the fibres in 624

extirpation of, in animals 624

— influence of, upon muscular co-ordination 625
recovery of co-ordinating power after re-
moval of a portion of 625

pathological facts bearing upon the uses of 625

connection of, with the generative func-
tion.... .. 626

PAGE

Cerebellum, development of 819, 820

Cerebral localization 612

Cerebral vesicles, formation of 819

Cerebrine 530

Cerebro-spinal axis, general arrangement of .. . . 586

Cerebro-spinal fluid 101, 588

Cerebrum, weight of 602

cortical substance of 603

fissures and convolutions of 604

general properties of 612

— motor cortical zone of 613

motor centres in 615

sensory centres in 616

general uses of 616

extirpation of, in animals 617

absence of, in the amphioxus lanceolatus.. 617

comparative development of, in the lower

animals 618

comparative development of, in different

races of men and in different individuals 619

pathological facts bearing upon the uses of 620

in idiots 620

centre in, for the expression of ideas in

language 621

development of 819, 820

development of the convolutions of 820

development of the ventricles of 820

Cerumen 326

Ceruminous glands 322

Chick, development of 814

Childhood 848

Chlorides in the body 432, 437

Chocolate 180

Cholesterine 266

transformation of, into stercorine 266, 407

in the bile 403

— origin of 406

elimination of, by the liver. 406

proportion of, in the blood in cases of grave

and of simple icterus 407

proportion of, in the blood in cases of cir-
rhosis » 407

poisoning by injection of, into the blood. . 408

Cholesteraemia 408

Chondrine 439, 486

Chondroplasts 486

Chorda dorsalis 815

Chorda tympani 552

influence of, upon gustation 554, 664

Chords in music 745

Chorion of the ovum, formation of 803

— disappearance of villi from a portion of 808, 811

Choroid 676

Chromatic aberration 696

Chyle, properties and composition of 299, 301

coagulation of 300

comparison of constituents of, with those

of lymph 302

microscopical characters of 302

movements of (see Lymph) 303

Cilia 461

Cilia (eyelashes) 724

Ciliary ganglion 637

Ciliary movements 461

Ciliary muscle 677

Ciliary nerves (short) 543

INDEX.

855

Ciliary processes 677

Cilio-spinal centres 707

Circulation of the blood 29

— discovery of 29

action of the heart in (see Heart) 32

effects of section of the pneumogastrics

upon 56

effects of Faradizing the pneumogastrics

or their branches upon 56

reflex influence upon, through the pneu-
mogastrics 56

in the arteries (see Arteries) 60

depressor nerve of 75, 580

— in the capillaries (see Capillaries) 78

in the veins (see Veins) 87

— in the cranial cavity 101

— in erectile tissues 102

derivative 103

pulmonary 103

in the walls of the heart 104

passage of the blood-corpuscles through the

walls of the vessels 104

general rapidity of 105

relations of the frequency of the heart's ac-
tion to the rapidity of 106

— phenomena of, after death 107

first appearance of, in the ovum 835

foetal (see Foetal circulation) 839

Circulatory apparatus, development of 834

Circumflexus, or tensor palati muscle 735

Claustruin 607

Cleft palate 828

Climate, influence of, upon the diet 184

Clitoris 777

Cloaca 822, 834

Clot of blood (see Blood) 24

Coagulation of the blood (see Blood) 23

Coccyx, consolidation of 817

Cochlea, bony 736

membranous 756

membrana basilaris of 757

membrana tectoria (membrane of Corti) of 757

membrane of Reissner of.. 757

— scala tympani and scala vestibuli of 758

— the true membranous 758

— limbus laminae spiralis of 759

— quadrilateral canal of 759

distribution of the nerves in 759

uses of, in audition 763

Cocoa 180

Coffee 178

composition of 179

influence of, upon nutrition 179

Coitus 793

— influence of, upon the rupture of the Graa-
fian follicles 779

— action of the male in 794

action of the female in 794

action of the cervix and os uteri in 795

Colloids 438

Colon 258

development of 823

Color-blindness 723

Colors 692

perception of 723

Colostrum . . 338

PAGE

Colostrum, relations of the subsequent secre-
tion of milk to the quantity of 339

Colostrum-corpuscles 338

Complemental air '. 131

Concha of the ear 730

Condiments 181

Conjunctiva 725

Connective tissue 468

development of 834

Consonance 747

Consonants 503

Contractility ' 472

Co-ordination of muscular movements, connec-
tion of the posterior white columns of the

spinal cord with 596

connection of the cerebellum with (see Cere-
bellum) 625

Cornea 675

development of 821

Corona radiata of the ovum 777

Corpora striata 606

development of 820

Corpus Highmorianum 785

Corpus innominatum (organ of Giraldes), 788

Corpus luteum 783

Corpus trigonum 371

Correlation and conservation of forces 457

Corti, ganglion of 760

— organ of 760

uses of the organ of 763

Cotugno, humor of 759

Coughing 129

Co wper, glands of 789

Cranial nerves 539

classification of 540

Cranium, circulation in 101

, development of 817

Cream 334

Creatine 382

Creatinine 383

Cremaster muscle 785

Cresol, in the faeces 264

Cretinism 422

Crico-arytenoid muscles 489

— posterior .489

— lateral 490

Crico-thyroid muscles 490

Crura cerebri 608

Crusta 609

Crystalline (organic substance of the lens) 439

Crystalline lens 685

— suspensory ligament of 687

refraction by 703

changes of, in accommodation 709

development of 821

Cumulus proligerus 770, 777

Curling arteries of the placenta 812

Cuticle (see Skin) 344

Cutis vera (see Skin) 343

Cuvk-r, canals of 837

Cyanosis neonatorum 841

Cystine 384

Cytoblastions 344

Dacryoline 728

Dartos ... . . 785

856

INDEX.

PAGE

Death 444, 632, 849

— phenomena in the circulatory system after. 107

— discharge of contents of the bladder and
rectum after 849

apparent growth of the beard after 849

— parturition after 849

Decidua vera 810

— reflexa 810

serotina 810

Deciduae, formation of 810

Defsecation 268

centre for 270, 601

Degeneration, secondary, in the cord. . 592, 593, 594

Deglutition Ill, 202

influence of the saliva upon 201

action of the tongue in 206

physiological anatomy of the parts con-
cerned in 206

mechanism of 206

first period of 206

in cases of absence of the tongue 206

second period of 207

action of the constrictors of the pharynx

in the second period of 207

protection of the posterior nares during. . . 207

protection of the opening of the larynx

during 208

action of the epiglottis in Ill, 208

influence of the sensibility of the top of

the larynx in protecting the opening during.. 208

third period of 209

action of the (Esophagus in 209

— length of time occupied in 209

character of the movements of 210

in the inverted posture 210

of air i 210

influence of the small root of the fifth •

nerve upon .550

influence of the spinal accessory nerves

upon 560

influence of the sublingual nerves upon. . . 563

influence of the trif acial upon 569

influence of the superior laryngeal branch-
es of the pneumogastrics upon 569, 579

Demours, membrane of 675

Dentals (division of consonants) 503

Dentine 189

Depressor nerve of the circulation 75, 580

Derivative circulation 103

Descemet, membrane of 675

Deutoplasm 778

Dextral pre-eminence 847

Dextrine 172, 201

Diabetes, artificial 411

Diapedesis 104

Diaphragm, action of, in inspiration 118

development of 824

Diaphragmatic hernia, congenital 824

Diaster 796

Dicrotism of the pulse 69

Diet (see Food) 169

— regulation of, in hospitals, etc 183

— influence of, upon the development of
power and endurance 183

variations in, in different climates 184

in arctic regions 184

PAGE
Digestion 188

— action of the saliva in (see Saliva) 200

— action of the gastric juice in (see Gastric
juice) 222

— duration of, in the stomach 228

conditions which influence 229

in the small intestine 233

— action of the intestinal juice in (see Intes-
tinal juice) 242

action of the pancreatic juice in (see Pan-
creatic juice) 247

— action of the bile in (see Bile) 251

Digestive fluids in the f cetus 824

Dilator tub* muscle 735

Diphthongs 501

Disassiniilation (see Urine, Faeces, Sweat and

Excretion) 428

Discords 746

Discus proligerus 770, 777

Dorsal plates 814

Dreams 648

Drinking, mechanism of 188

Ductless glands 413

Ductus arteriosus 836, 841

closure of 841

venosus 838, 842

Duodenum 233

— glands of 235

Dura mater 587

first appearance of 818

Ear, glands of 322,

uses of the hairs at the opening of

disease of the semicircular canals of . . 626,

Ear, external

muscles of

— •— uses of

Ear, middle, general arrangement of

— arrangement of the ossicles of 733,

— uses of different parts of

— development of 821,

Ear, internal, physiological anatomy of

— liquids of

distribution of the nerves in ,

— hair-cells of

— uses of different parts of

development of

731
353
763
730
731
748
731
753
748
825
755
759
759

8:21

Ejaculatory ducts 789

Elastic tissue 462

Elastine 439

Electricity, action of, upon the nerves 529

action of descending and ascending cur-
rents of, upon the nerves (law of contraction) 532

action of a constant current of, upon the

nerves 532, 535

Electrotonus 535

— of muscles 537

Embryon 802

time when it becomes the foetus 813

size, weight, and development of, at dif-
ferent periods of utero-gestation 843

Embryonic spot 801

Emulsification of fats 174

Enamel of the teeth 189

Enamel-organ 828

INDEX.

857

Encephalon (see Brain) 601

development of 820

End-bulbs 515

Endocardium 32

Endolymph of the labyrinth 759

Endosmometer 293

Endosmosis 292

Endothelium 802

Epiblast 801, 814

Epidermis (see Skin) 344

first appearance of 818

Epididymis 785, 787

development of, from a portion of the

Wolffian body 832

Epiglottis, uses of, in deglutition Ill, 208

cases of loss of Ill, 208

action of, in deglutition Ill

• removal of, from the lower animals Ill

cases of loss of, in the human subject Ill

development of 827

Epithelium, glandular 310

pavement, mucous membranes covered

with 316

. . columnar, or conoidal, mucous membranes

covered with 317

ciliated, mucous membranes covered with . 317

. . mixed, mucous membranes covered with. . 318

. influence of, upon the absorption of

venoms 320

Equilibrium of the body in nutrition 439, 453

Erectile organs, structure of 102, 794

tissues, circulation in 102, 794

Erection, mechanism of 794

Erection of the penis 794

nerve of 794

Erection-centre 601, 794

Eructation 232

Eustachian tube 734

muscular action in dilatation of 735

— development of 826

Eustachian valve 34, 838, 841

— disappearance of 34, 841

Excrementitious matters, mechanism of the

production of (see Excretion) 341

Excretine 264

Excretion, distinction of, from secretion.

307, 311, 341

— mechanism of 311, 341

— •• — general considerations 341

Excretoleic acid 264

Excretory action of the liver 405

Exercise, influence of, upon the development of

parts 443

Exosmosis 292

Expiration 123

— action of the elasticity of the parenchyma

of the lungs in 123

action of the elasticity of the thoracic walls

in 123

— table of muscles of 124

action of the abdominal muscles in 125

relations of, to inspiration 128

duration of 128

Expression, nerve of (see Facial nerve) 550

External capsule 607

Eye, physiological anatomy of 674

Eye, chambers of 688

— summary of the anatomy of the globe of . . 689

— refraction in ((see Vision) 690

— considered as an optical instrument 691

— simple schematic 703

— movements of 718

muscles of 718

— protrusion and retraction of, by muscular
action 719

— action of the recti muscles of 720

— action of the oblique muscles of 720

— associated action of the muscles of 721

— parts for the protection of 723

— development of 821

Eyebrows 353, 724

Eyelashes 353, 724

Eyelids 724

— glands of 323, 724

muscles of 725

development of 821

time of separation of, in the foetus 821

Face, development of 825

Facial angle 619

Facial nerve 550

decussation of the roots of 550

— general properties of 553

uses of the branches of, given off within

the aqueduct of Fallopius 553

influence of, upon the movements of the

palate and uvula 554

uses of the external branches of 555

— influence of, upon mastication, through the
buccinator muscle 557

Faeces, influence of the bile upon 253

— constituents of 264

— bacteria of 264

Fallopian pregnancy 845

Fallopian tubes 775

development of, from the ducts of Muller. 831

Falsetto-register 497

Fats, composition of 173, 174

— saponification of 174

emtilsification of 174

— absorption of (see Absorption) 288

relations of, to nutrition 440

— formation and deposition of 440

— anatomy of adipose tissue 442

Fatty degeneration 441

Fatty diarrhoea, cases of 250

Fauces, pillars of '203

— isthmus of 203

Fecundation, situation of 795, 799

time when it is most likely to occur 795

— mechanism of 796

Fecundity, limits of, as regards age 780

Fenestra ovalis 732, 736

Fenestra rotunda 732, 736

Ferrein, pyramids of 359, 361

Fibrin 22

of the clot 24

formation of, by decomposition of plas-

mine 27

fibrillation of, in coagulation 29

Fibrin-factors 27

Fibrin-ferment 27

858

INDEX.

PAGE

Fibrinogen 23, 27

Fibrinoplastic matter 23, 27

Fibro-cartilage 487

Fifth cranial nerve, small root of (see Mastica-
tion, nerve of) 547

large root of 564

physiological anatomy of 564

branches of 565

properties and uses of 568

operation for the division of, within the

cranial cavity 568

immediate effects of division of 568

influence of, upon deglutition 569

remote effects of division of 570

different remote effects of division of, be-
fore and behind the ganglion of Gasser 571

relations of, to the sympathetic system . . . 571

cases of paralysis of, in the human sub-
ject 572

Filum terminate 589

Flavors 663

Foetal circulation 839

— change of, into the adult circulation 841

Foetus, blood-corpuscles of 10

respiratory efforts by 161, 822

— urine of 390

determination of the sex of 797

influence of the maternal mind upon the

development of 799

— at the fifth month 808

time when this name is applied to the prod-
uct of fecundation 813

reflex movements in 822

respiratory efforts by 822

digestive fluids in 824

size, weight, and development of, at differ-
ent periods of utero-gestation 843

when viable 844

weight of, at term 844

position of, in the uterus 844

Food, definition of 169

classification of 169

— nitrogenized constituents of 169

— animal 170

vegetable 170

non-nitrogenized constituents of 170

inorganic constituents of 174

quantity and variety of, necessary to nu-
trition 181, 182

regulation of, in hospitals, etc 183

influence of, upon the capacity for labor. . 183

• necessity of a varied diet 184

— influence of climate and season upon the
quantity of 184

influence upon nutrition of single articles

of, when taken alone 187

heat-value of 453

Foot-pound 444, 458

Foramen ovale 33, 838, 841

— closure of 841

Force, relations of heat to 457

Fourth ventricle 629

Fovea cardiaca 836

centralis 681

Free-martin 781, 799

Fromann, lines of 508

PAGE

Frontal process, in the development of the
face 826

Galactose 335

Gall-bladder , . 399

development of 824

Gases of the blood 151

in the blood in different parts of the system 154

Gases in the body 429

Gasser, ganglion of 565

Gasterase 221

Gastric fistula in the Ibwer animals 217

in the human subject 216

Gastric juice 216

mode of collecting 217

secretion of 218

artificial 218

modifications of the secretion of 219

quantity of .219

properties and composition of 219

antiseptic properties of 220, 226

— table of composition of 220

organic constituent of 221

source of the acidity of 221

ordinary saline constituents of 221

action of, in digestion 222

Gelatine 439

French committee on 187

Gelatine of Wharton 809

Generation 765

spontaneous 765

sexual 765

female organs of 766

— male organs of 784

development of the internal organs of 831

development of the external organs of 834

Geniculate ganglion 552

Genito-spinal centre 373, 794

Genito-urinary apparatus, development of 830

Germinal spot 778

Germinal vesicle 778

disappearance of 796

Giraldes, organ of 788

Glands, excitability of 310

color of the blood in the veins of 5, 311

comparative quantity of blood in, during

activity and repose 5, 311

— elimination of foreign substances by 311

— anatomical classification of 313

ductless, or blood-glands 413

— -~ terminations of nerves in 512

Glandular epithelium 310

Glisson, capsule of 392, 393

Globuline 16

Glosso-labio-laryngeal paralysis 564

Glosso-pharyngeal nerves 665

— general properties of 667

relations of, to gustation 667

Glottis, movements of, in respiration Ill

development of 825

Glucose (see Sugars) 171

Gluten 185

Glutine 186

Glycocholic acid and sodium glycocholate 402

Glycogen, mechanism of the formation of, by

the liver (see Liver).... 408, 409

INDEX.

859

PAGE

Glycogen, mode of extraction of 409

Goblet cells 214

Goll, columns of 593

Goose-flesh 344

Graafian follicles 768

situation of the ovum in 771

— rupture of 769, 779

Grape-sugar 171

Gubernaculum testis 831

Gums 172

Gustation, relations of, to olfaction 662

general considerations of 663

nerves of 664

uses of the chorda tympani in 664

— uses of the glosso-pharyngeal nerve in 667

physiological anatomy of the organ of 668

centre for 670

Gutturals (division of consonants) 503

Haemadynamometer 72

Haemaglobine 17, 175

absorption of oxygen by 17

Haematine 17

Haematocrystalline 17

Haematosine 17

Hsematosis 150

Haemophilia 26

Haemorrhagic diathesis 2G

Hair-cells of the internal ear 762

Hairs, physiological anatomy of 348

growth of 352

development of 352

shedding of, in the infant 352

sudden blanching of 352

uses of 353

first appearance of 818

Haller, vas aberrans of 787

Hamulus of the cochlea 757

Harelip 828

Harmonics, or overtones 743

Harmony 745

Hauser, Caspar, case of 714

Haversian canals 482

Haversian rods 482

Head-fold of the neural canal 802

Hearing (see Audition) 728

Heart, description of the action of, by Har-
vey 30

general description of the action of 31

— - physiological anatomy of 32

comparative capacity of the right and the

left ventricle of 34

quantity of blood discharged by each ven-
tricular systole of 34

muscular tissue of 35

— comparative thickness of the ventricles of 35

valves of 36

movements of 37

action of the auricles of 38

— - action of the ventricles of 38

—S- locomotion of 39

twisting of 39

hardening of 39

shortening and elongation of 39

— impulse of 40

succession of the movements of . . . .40

PAGH
Heart, relative time occupied by the auricular

and the ventricular contractions of 42

force of 42

action of the valves of 43, 44

sounds of 44

— frequency of the action of (see Pulse) 43

influence of respiration upon the action of 51

arrest of the action of, in asphyxia 51

cause of the rhythmical contractions of . . . 52

arrest of the action of, by tying the coro-
nary arteries . 53, 58

contractions of, produced by stimulation

during its repose 53

influence of the blood in its cavities upon

the contractions of 53

influence of the density of its contents

upon the contractions of 53

ganglia in the substance of 54

accelerator nerves of 55

nerve-centre of 55, 632

influence of the sympathetic nerves upon.. 55

— direct inhibition of 56

reflex inhibition of 57

want of action of digitalis upon, after sec-
tion of the pneumogastrics 56

effects of Faradization of the pneumogas-
trics upon 56

influence of the pneumogastrics upon. . . 56, 57

influence of the spinal accessory nerves

upon 56, 560

palpitation of 57

influence of mental emotions upon 57

summary of causes of arrest of the action of 58

death from distention of 58

death from a blow upon the epigastrium . . 59

relations of the force of, to the frequency

of its pulsations 75, 107

circulation in the walls of 104

time required for the passage of the entire

mass of blood through. 106

relation of the frequency of the action of,

to the rapidity of the circulation 106

temperature of the blood in the two sides

of 4, 448

development of 836, 838

relative size of, in the foetus and at differ-
ent periods of life 839

— enlargement of, in pregnancy 842

Heart-clots 25

Heat, animal (see Animal heat) 444

Heat-centres 451

Heat-units 444, 458

Helix of the ear 730

Hemialbumose 227

Hemianopsia 722

Henle, tubes of 362

sheath of 510

Hereditary transmission 797

Hernia at the umbilicus, in the foetus. 807, 809, 822

— diaphragmatic 824

Hibernation, consumption of oxygen in 139

cholesterine in the faeces in 267

Hiccough 130

Hippuric acid and its compounds 381

Horner, muscle of 724

Horopter 713

860

INDEX.

PAGE

Hunger 165

seat of the sense of 166

after section of both pneumogastric nerves 167

after section of the hypoglossal and lingual

nerves 167

Hydatids of Morgagni 785

Hydrogen, effects of confining an animal in a

mixture of with oxygen. , 139

Hydrogen monosulphide, poisonous effects of. . 136

Hyoid bone, development of 825, 827

Hypermetropia 695

Hypnagogic hallucinations 648

Hypoblast 801, 814

Hypogastric arteries 839

closure of 842

Hypoglossal nerve (see Sublingual nerve) 561

Hypospadias 834

Hypoxanthine 384

Ileo-csecal valve 259

development of 823

Heum 234

Iliac veins, development of 838

Imbibition 291

Imperf orate anus 824

Inanition, influence of, upon the exhalation of

carbon dioxide 144

influence of age upon the power of resist-
ance to 165

— phenomena attending 166

duration of life in 168

Incisor process, in the development of the face 826

Incus 733

development of 825

Indol, production of, by action of trypsine on

albuminoids 249, 267

in the faeces 264

Induced muscular contraction 534

Inelastic fibrous tissue 469

Infancy 848

secretion of milk in 340

Infracostales, action of, in expiration 125

Innominate vein, development of 838

Inorganic alimentary substances 174

Inorganic constituents of the body 429

Inspiration 116

table of muscles of 117

auxiliary muscles of 121

relations of, to expiration 128

— duration of 128

Insula 606, 621

Intellectual faculties 616

Intercostal muscles 120

action of, in inspiration 120

action of, in expiration 124

Intermaxillary process, in the development of

the face 826

Internal capsule 607

Intestinal canal, fermentation in 262

— first appearance of 822

Intestinal digestion 233

Intestinal fistula, case of, in the human subject 242

Intestinal juice 240

Intestinal villi 237

— development of 823

Intestine, small, physiological anatomy of 233

PAGE

Intestine, movements of 255

uses of the gases in 256, 271

influence of the circulation upon the move-
ments of 256

influence of the nervous system upon the

movements of 257

distribution of the pneumogastric to 257

— - influence of the pneumogastric upon 257

development of 823

Intestine, large, physiological anatomy of 257

digestion and absorption in 262

contents of (see Faeces) 263

movements of 267

— gases of 270

development of 823

Inuline 172

Involuntary muscular tissue and movements. . . 464

Involution of the uterus 846

Iris, influence of the motor oculi communis

upon 543, 706

anatomy of 679

movements of 705

direct action of light upon 706

— action of the nervous system upon 706

influence of the sympathetic nerves upon . . 707

consensual contraction of 707

influence of the cilio-spinal centre upon . . . 707

changes of, in accommodation 710

movements of, in converging the axes of

vision 706, 710

voluntary contraction of 711

development of 821

Iron, uses of, in the organism 175

in milk and eggs 175

Irradiation in the spinal cord 598

— in vision 717

Island of Reil 606, 621

Jacobson, nerve of 665

Jacob's membrane 681

Jaws, physiological anatomy of 192

articulations of 192

Jejunum 234

Jugular veins, development of 838

Juice-canals 274

Keratine 439

Kidneys, effects of destruction of the nerves

of 313, 369

physiological anatomy of 358

— distribution of blood-vessels in 364

lymphatics of 366

nerves of 366

— extirpation of 366

extirpation of, upon one side .0 368

alternate action of, upon the two sides 369

development of 832

Kinetic energy 458

Krause, corpuscles of 515

Labia majora, development of 834

Labia minora, smegma of 325

Labial glands 197

Labials (division of consonants) 503

Labyrinth, bony 735

membranous 755

liquids of 759

INDEX.

861

PAGE

Labyrinth, distribution of the nerves in 759

— development of 821

Lachrymal apparatus 726

— glands 726

— fluid 727

_ points 727

sac and ducts 727

Lachrymine 728

Lactates in the blood 21

— in the urine 382

Lactation, modifications of (see Milk) 331

Lacteals, in the intestinal villi 238

discovery of 273

course of 279

— structure of 281

— absorption by 285

Lactoproteine 335

Lactose 171, 336

Lancet-fish, an animal without a brain 617

Language 501

— centre for the expression of ideas in 621

Laryngoscopy 491

Larynx, physiological anatomy of 110

— action of, in respiration Ill

— muscles of 489

— action of, in phonation, 491

— development of 825, 827

Laughing 130

Laxator tympani 733

Lecithene 21, 520

Lef t-handedness (see Dextral pre-eminence) ... 847

Legs, development of 817

Lenses, refraction by 693

— correction of 697

Lenticular ganglion 637

Leucine in the urine S84

— production of, by the action of trypsine on
albuminoids 249

Leucocytes (see Blood) 12

relations of, to the development of the

blood-corpuscles 10

— development of 14, 834

— passage of, through the walls of the blood-
vessels 104

— in the lymph 274, 298

Leucocy thaemia 14, 413

Levator anguli scapulae, action of, in respira-
tion 122

Levator palati 204

Levator palpebrae superioris 725

Levatores costarum, action of, in respiration. . . 121

Lichenine 172

Lieberkfihn, follicles of 236

Life, definition of, etc 427

— duration of, in man 849

Ligamentum denticulatum 588

Ligamentum iridis pectinatum 676

Light, theory of the propagation of 692

— velocity of 692

— decomposition of 693

Lingual glands 198

Lips, development of 826

Liquids (division of consonants) 503

Littre, glands of 739

Liver, circulation in the veins of 97

formation of urea in 377, 400

56

PAOB

Liver, physiological anatomy of 392

structure of a lobule of 395

— arrangement of the bile-ducts in the lobules

of 396

— anatomy of the excretory biliary passages

of 397

— racemose glands attached to the ducts of. . 397

— vasa aberrantia of 398

— gall-bladder, hepatic, cystic, and common
ducts of 398

— nerves and lymphatics of 399

— excretory action of 405

— formation of glycogen by 408

— ferment produced by, which is capable of
changing glycogen into sugar 410

action of, upon foreign and poisonous sub-
stances 413

development of 824

— proportionate weight of, at different peri-
ods of life 824

Lobule of the ear 731

Lochia 846

Locomotion, passive organs of 481

Locomotor ataxia 596, 654

Locus niger 609

Lungs, capillary circulation in 84

circulation through 103

parenchyma of 113

air-cells of 114

action of the elasticity of the parenchyma

of, in expiration 123

capacity of 130

— vital capacity of 133

absorption by the respiratory surface 287

development of 825

Luxus-consumption 438

Lymph 294

— quantity of 295

properties and composition of 295

— coagulation of 295

corpuscular elements of 274, 298

origin and uses of 299

— comparison of constituents of, with those

of chyle 302

— movements of 303

Lymphatic glands 279, 283

— uses of 285

Lymphatic trunk, right 279

Lymphatics, discovery of 273

descriptive anatomy of 273

relations of, to connective tissue 274

valves of 276, 282

structure of 281

Lymph-corpuscles 274, 298

Lymph-spaces 274

Macula folliculi 779

Macula lutea.. 681

Malleus 733

development of 825

Malpighi, pyramids of a>9

Malpighian bodies of the kidney 361, 362

— capsule of the spleen 414

bodies of the spleen 415

Maltose 201

Mammary glands 327

862

INDEX.

PAGK

Mammary secretion (see Milk) 32?

Manege, movements of 634

Mannite 172

Mariotte, experiment of 699

Marrow 484

Mastication 189

— • table of muscles of 193

— • action of the muscles of, which depress the

lower jaw 193

• action of the muscles which elevate the

lower jaw and move it laterally and antero-

posteriorly 194

action of the tongue, lips and cheeks in. . . 194

action of the orbicularis oris and buccina-
tor in 194

uses of the sensibility of the teeth to hard

and soft substances in 195

— • influence of, upon the flow of the parotid

saliva 196

— — nerve of 547

— properties and uses of the nerve of 549

influence of division of the nerve of, upon

the teeth, in the rabbit 549

— influence of, upon deglutition 550

Mastoid cells 734

Maxilla, inferior, development of 826

superior, development of 826

Maxillary bones, physiological anatomy of 192

articulations of 192

Meats 185

Meckel, cartilage of 821, 827

Meckel's ganglion 638

Meconium 824, 846

Medulla oblongata, physiological anatomy of. . 627

— general properties of 630

uses of 630

connection of, with respiration 158, 631

development of 819, 820

Medullocells 484

Meibomian glands 323, 724

secretion 326

Meissner, corpuscles of 514

Meissner's plexus 257

Melody 741

Membrana f usca 676

Membranes of the foetus, formation of 802

MenieTe's disease 626, 763

Menstruation 781

— supposed appearance of, after extirpation

of the ovaries 781

— duration of 782

characters of the flow in ... 782

— diminution in the excretion of urea in 783

M6ry, glands of 789

Mesenteric vein, development of. 837

Mesentery 233

development of . 823

Mesoblast 802, 814

Mesocaecum 259

Mesocolon 260

Metabolism 428

Metalbumin 22

Micropyle 778, 796

Micturition 372

Milk 186, 333

mechanism of the secretion of , . 330

PAGE
Milk, modifications of . 331

— quantity of 332

— general properties of 333

— coagulation of 333, 330

microscopical characters of 334

composition of 334

comparison of, from the cow and from the

human subject 336

fermentation of 330

— variations in the composition of 337

— relations of the quantity of, to the previous
secretion of colostrum 339

— of the infant. 340

Milk-globules 334

Milk-sugar 171, 336

Mind 616

Mitral valve 37

Modiolus of the cochlea 757

Molar glands 197

Monoplegias 615

Morgagni, liquid of 686

— hydatids of 785

Morsus diaboli 776

Morula 800

Motor cortical zone 613

Motor nerves, disappearance of excitability of. 521

— action of 523

Motor oculi communis 541

influence of, upon the iris 543

Motor oculi externus 546

Mouth, first appearance of 820

Movements 400

of amorphous contractile substance (amre-

boid) 460

ciliary 461

due to elasticity 462

— muscular 464

— associated 524

Mucilages 172

Mticine 319

Mucinogen 310

Mucous membranes 316

Mucus, mechanism of the secretion of 318

composition and varieties of 319

influence of, upon the absorption of ven-
oms 320

Miiller, capsule of 362

— duct of 831

Muscles, connection of, with the tendons 470

voluntary, terminations of nerves in 511

involuntary, terminations of nerves in 512

Muscular atrophy, progressive 645

Muscular current. 479

Muscular effort 480

Muscular movements (see Movements) 464

Muscular sense 654

Muscular system, development of 818

Muscular tissue, involuntary 464

contraction of 465

— voluntary 46(5

development of, by exercise 407

blood-vessels and lymphatics of 470

chemical composition of 470

reactions of 471

physioldgical properties of 471

elasticity of 471

INDEX.

863

PAGE

Muscular tissue, tonicity of 471

sensibility of 472

contractility of 472

— changes in the form of, during contraction 475

— duration of contraction of, under artificial
excitation 476

— single contraction of 476

— tetanic contraction of 477

— sound produced by contraction of 477

fatigue of 478

— electric phenomena in 479

— negative variation of 480

Musical sounds (see Sound) 739

Mustache, uses of . . 353

Mustard 181

Mutes (division of consonants) 503

Myeline 507

Myelocytes 520

Myeloplaxes 484

Myolemma 467

Myopia 695

Myosine 439, 470

Myxoedema 422

Naboth, ovules of 774

Nails, physiological anatomy of 345

connections of, with the skin 347

— growth of 347

— development of 347

— first appearance of 818

Nares, development of 828

Nasal duct 727

Nasal fossae 658

action of, in phonation 495

Nasals (division of consonants) 503

Nasmyth's membrane 189

Negative variation of the muscular current 480

— of the nerve-current 537

Nerve-cells 517

— striation of, by the action of silver nitrate. 519
connections of, with the fibres and with

each other 519

Nerve-centres, structure of 517

— accessory anatomical elements of 519

— connective tissue of (neuroglia) 520

— blood-vessels of 520

— lymphatics of (perivascular canals) 520

Nerve-current 535

Nerve- fibres 507

— medullated 507

— axis-cylinder of 508

— striation of. by the action of silver nitrate. 508

— non-medullated 509

— gelatinous, or fibres of Remak 509

Nerves, structure of 507

— blood-vessels of 511

branching and course of 511

— terminations of, in the voluntary muscles. 511

— terminations of, in the involuntary mus-
cles 512

— terminations of, in glands 512

— sensory, terminations of 513, 516

— degeneration and regeneration of 521

— trophic centres for .' 521

reunion of 522

motor and sensory 522, 526

PAGE

Nerves, motor, action of 523

— sensory, action of 525

— physiological differences between motor
and sensory 526

— artificial union of motor with sensory 526

— excitability of (see Nervous excitabil-
ity) 527

— action of electricity upon (see Electricity). 529

— process of dying of 533

galvanic current from the exterior to the

cut surface of 535

spinal 538

— cranial (see Cranial nerves) 539

— development of 819

Nervi nervorum 511

Nervous conduction, rapidity of 527

Nervous excitability 527

Nervous system, divisions of 505

physiological anatomy of the tissue of 507

development of 818

— action of, in the foetus 822

Nervous tissue, composition of 520

Neural canal 814

head-fold of 802

Neurilemma 507

Neuroglia of the nerve-centres 520

— of the spinal cord 591

Neutral point 536

Nitrogen, proportion of, in the air 135

exhalation of, in respiration 150

— quantity of, necessary to nutrition 182

Nitrogen monoxide, effects of respiration of . . . 136

Nitrogenixed alimentary substances 169

Non-nitrogenized alimentary substances 170

— action of, in nutrition 439

Nose, uses of the hairs in 353

— development of 826, 828

Notochord 815

Nutrition, quantity and variety of food neces-
sary to 181, 182

— general considerations 426

— action of inorganic substances in 428, 429

substances consumed by the organism

in 437

— action of nitrogenized substances in 438

action of non-nitrogenized substances in. . 439

modifications of, by various conditions. . . . 442

CTBeirne, sphincter of 269

Obesity 441

Obliquus externus, action of, in expiration 125

internus, action of, in expiration 125

Odors 661

(Esophagus, structure of 205

action of, in deglutition 209

alternate contraction and relaxation of — 209

— development of 824

Oils (see Fats) 173

Oken, bodies of 814, 830

Old age 849

Oleine 174

Olfaction, mechanism of 661

relations of, to the sense of taste 662

Olfactory cells 660

Olfactory centre 662

Olfactory ganglia, or bulbs 660

364:

INDEX.

PAGE

Olfactory commissures and nerves, development

of 822

Olfactory nerves 659

properties and uses of 660

Omentum 260

development of 823

Omphalo-mesenteric canal 807

Omphalo-mesenteric vessels 836

Ophthalmic ganglion 637

Optic commissure 672

Optic nerves, physiological anatomy of 671

decussation of 672

— general properties of 673

— development of 821

Optic thalami 607

development of 819. 820

Osmosis 292

Osseine (bone-corpuscles) 439

Ossicles of the ear 733

— mechanism of the action of 753

Ossification of the skeleton 818

time of, for various bones 818

Osteoplasts 483

Otic ganglion 638

Otoliths 756

Ovaries 767

— Graafian follicles of 768

— development of 769

Overtones 743

Ovules of Naboth 774

Ovum, primordial 768

Ovum, situation of, in the Graafian follicle 771

— structure of 777

— discharge of, from the Graafian follicle 778

influence of copulation upon the discharge

of 779

— relations of the discharge of, to menstru-
ation 779

— passage of, into the Fallopian tube 779

coating of, with albumen, in the Fallopian

tube 795, 799

union of spermatozoids with 796

— primitive trace on 801

development of 813

Oxygen, absorption of, by the blood-corpuscles

12, 151

proportion of, in the air 135

minimum proportion of, in the air, capable

of supporting life 136

— effects of respiration of pure 136

— consumption of (see Respiration) 136

relations of the consumption of, to the ex-
halation of carbon dioxide 146

analysis of the blood for 152

— proportion of, in the blood 154

Oxyhaemaglobine 17, 155

Pacini, corpuscles of 513

Palatals (division of consonants) 503

Palate. 203

muscles of 204

development of 828

Palmitine 174

Pancreas, physiological anatomy of 243

development of 824

Pancreatic juice 244

PAGE

Pancreatic juice, mode of secretion of 244

properties and composition of 245

quantity of 247

alterations of 247

action of, in digestion 247

action of, upon starches and sugars 247

action of, upon nitrogenized substances. . . 248

action of, upon fats 250

Pancreatic secretion, centre for 341

Pancreatine 246

Panniculus adiposus 343, 442

Parablastic cells 834

Paracentral lobule 614

Paraglobuline 23, 27

Paralytic secretion by glands 313

Parotid saliva (see Saliva) 195

Parovarium 771, 831

Parturition, cause of the first contractions of

the uterus in 845

centre for 601, 845

arrest of haemorrhage after 846

after death 849

Par vagum nerve (see Pneumogastric) 573

Patheticus 545

Pavement-epithelium (squamous epithelium). . . 316
Pectoralis major, action of the inferior portion

of, in respiration 122

Pectoralis minor, action of, in respiration 122

Pectose 172

Penis, erection of 794

development of 834

Pepper 181

Pepsine 221

Pepsinogen 310

Peptones 224, 226

in the blood 23

Pericardial secretion 32

Pericardium 32

Perilymph of the labyrinth 759

Perimeter 712

Perimysium 468

Perivitelline space 778

Periosteum 485

Peristaltic movements of the small intestine. . . 255

influence of the bile upon 253

influence of the nervous system upon 257

Peritoneal cavity, first appearance of 815, 824

Perivascular canals 275, 588

Personal equation 529

Perspiration (see Sweat) 353

Petit, canal of 687

Pettenkofer's test for bile 405

Peyer, patches of 239

Pharyngeal glands 198

Pharynx, physiological anatomy of 202

muscles of 204

mucous membrane of 204

action of the muscles of, in deglutition 207

action of, in phonation 495

— development of 823

Phenol, production of, by the action of tryp-

sine on albuminoids 249, 267

in the faeces 264

Phonation (see Voice) 491

Phonograph 504

Phosphates in the body 433, 436

INDEX.

865

PACK

Phrenic nerve 119

Pia mater 587

— first appearance of 818

Pia mater testis 786

Pineal gland 425

Pinna of the ear 730

Pituitary body 425

Pituitary membrane 658

Placenta, first appearance of 811

— development and structure of 812

uses of 813

Placental circulation 836

Plasma of the blood (see Blood) 17

Plasmine 22

Pleuro-peritoneal cavity, first appearance of ... 815
Pneumogastric nerves, influence of, upon the

action of the heart 56

want of action of digitalis upon the heart

after section of 56

effects of Faradization of, upon the circu-
lation -. 56, 57

— direct influence of, upon the heart 56, 57

— influence of, upon the movements of the
small intestine 257

— physiological anatomy of 573

branches of 574

difference in the distribution of the nerves

of the two sides, to the abdominal organs 577

general properties of the roots of 577

properties and uses of the auricular branch

of 578

properties and uses of the pharyngeal

branch of 578

properties and uses of the superior laryn-

geal branch of 578

properties and uses of the inferior, or re-
current laryngeal branch of 579

influence of the inferior laryngeal branch

of, upon the movements of the larynx 579

properties and uses of the cardiac branches

of 580

effects of section of, upon the circulation.

56, 580

properties and uses of the pulmonary

branches of 581

effects of section of, upon the respiratory

movements 581

condition of the lungs after death follow-
ing section of 581

effects of Faradization of, upon respira-
tion 582

— properties and uses of the oesophageal
branches of 583

effects of division of, upon the oesophagus. 583

properties and uses of the abdominal

branches of 583

— influence of, upon the liver 583

— influence of, upon the stomach 230, 584

distribution of, to the intestinal canal 585

— want of action of purgatives, after section

of 585

Polar globule of the vitellus 796

Pons Varolii 609

— uses of 610

— development of 819, 821

Portal vein, distribution of (see Liver) 393

PAGE

Portal vein, development of 837

Potatoes 186

Potential energy 457

Pregnancy, influence of, upon lactation 331

— influence of, upon menstruation 781

— influence of, upon the corpus luteum 784

— influence of, upon subsequent offspring.. 797

— enlargement of the uterus in 842

— enlargement of the heart in 842

— duration of §42

multiple 844

extratiterine 845'

Fallopian §45

abdominal 845

Prehension of solids and liquids 188

Prepuce, smegma of 335

Presbyopia 695

Primitive trace of the embryon 801

Progressive muscular atrophy 645

Pronucleus, male and female 797

Propeptone 227

Prostate 789

Protagon 520

Proteids 437

Proteine 170, 438

Protoplasm 460

Protovertebrae 816

Ptosis (see Blepharoptosis) 542

Pytaline 200

Puberty 780

Pulmonary artery, pressure of blood in 104

development of 836

Pulmonary circulation 103

Pulmonic semilunar valves 37

safety-valve action of 44

Pulp-cavity of the teeth 190

Pulse, frequency of, at different ages 48

in the sexes 48

— influence of digestion upon the frequency

of 49

influence of muscular exertion upon the

frequency of 49

comparative frequency of, in sitting and

standing 49

— influence of sleep upon the frequency of . . 50
influence of temperature upon the fre-
quency of 50

— production of, and locomotion of the arte-
ries 66

investigation of, by the finger 66

gradual delay of, receding from the heart. 67

— pathological varieties of 67

form of 67

movements of, in the foot when the legs

are crossed 67

traces of 68

— dicrotism of 69

influence of temperature upon the form of. 70

in the veins 94, 100

relation of the frequency of, to the respira-
tory acts 127

Pupil 679

Pupillary membrane 680, 821

Purkinje, vesicle of 778

Putrefaction of the body after death 850

Pyloric muscle 213

866

INDEX.

Quadrilateral canal of the cochlea 759

Quickening 813

Ranvier, nodes of 508

Reaction-time 620

Receptaculum chyli , 273

Rectum, physiological anatomy of 258, 261

-. — sphincter of 269

development of 823

Recurrent sensibility 523

Reflex action, time occupied by 529

definition of 598

of the spinal cord 598

— exaggeration of, by poisoning with strych-
nine 599

abolition of, by anaesthetics : 599

— . — examples of 599

— inhibition of 600

-, — operating through the sympathetic sys-
tem 643

— in the foetus 822

Reflexes, superficial and deep 600

Refraction.. 690

Regurgitation from the stomach 232

Reil, island of 606, 621

Reissner, membrane of 757

Remak, fibres of 509

Reproduction (see Generation) 765

Reserve air 131

Residual air 131

Resonators of Helmholtz. 744

Respiration, influence of, upon the action of the

heart 51

— — movements of the brain with 102

— general considerations and definition of . . . 108
essential conditions in 109

— physiological anatomy of the organs of ... 110

movements of 115

action of the ribs in 116, 120

table of muscles of, used in inspiration. . . 117

auxiliary muscles of, used in inspiration . . 121

table of muscles of, used in expiration ... 124

— action of the abdominal muscles in 125

types of 126

— difference in types of, in the sexes and at
different ages 126

frequency of the movements of 127

relations of the frequency of the movements

of, to the pulse 127

influence of age upon the frequency of the

movements of 127

relations of inspiration and expiration to

each other in 128

sounds of 128, 129

extreme breathing capacity in 133

relations in volume of the expired to the in-
spired air in 133

— diffusion of air in 134

of pure oxygen 136

— consumption of oxygen in 136

— variations in the consumption of oxygen
in, with muscular activity, external tempera-
ture and digestion 138

— quantity of oxygen consumed per hour in . 138

— variations in the consumption of oxygen
.in, with age 138

PAGB

Respiration, variations in the consumption of
oxygen in, sleeping and waking 139

variations in the consumption of oxygen

in, in lean and fat animals 139

effects upon the consumption of oxygen

in, of increasing its proportion in the air 139

effects upon the consumption of oxygen in,

of confining an animal in a mixture of oxy-
gen and hydrogen 139

changes in the air passing through the lungs 140

elevation in temperature in the air in pass-
ing through the lungs in 140

exhalation of carbon dioxide in 140

— variations in the exhalation of carbon di-
oxide with the frequency and extent of the
acts of 140, 141

quantity of carbon dioxide exhaled per

hour in 142

— influence of age upon the exhalation of car-
bon dioxide in 142

influence of sex upon the exhalation of car-
bon dioxide in 143

influence of digestion upon the exhalation

of carbon dioxide in . 143

influence of inanition upon the exhalation

of carbon dioxide in 144

influence of diet upon the exhalation of

carbon dioxide in 144

influence of alcoholic beverages, tea, and

coffee upon the exhalation of carbon dioxide
in 144

influence of exercise upon the exhalation

. of carbon dioxide in 142, 145

influence of sleep upon the exhalation of

earbon dioxide in 145

relations of the consumption of oxygen to

the production of carbon dioxide in 146

— influence of moisture and temperature upon
the exhalation of carbon dioxide in 146

influence of season upon the exhalation of

carbon dioxide in 146

relations between the quantity of oxygen

consumed and the quantity of carbon dioxide

exhaled in 146

sources of the carbon dioxide exhaled in. . 148

exhalation of watery vapor in 148

exhalation of ammonia, organic matter

etc., in 149

exhalation of nitrogen in 150

changes in the blood in 150

mechanism of the interchange of gases be-
tween the blood and the air in 156

relations of, to nutrition 156

cutaneous 161

in a confined space 163

connection of the medulla oblongata with

158, 631

Respiratory centres 631

Respiratory efforts before birth 161, 822

Respiratory excitants 144

Respiratory movements, character of, and cause

of these movements 157

Respiratory movements of the glottis Ill

Respiratory non-exciters 144

Respiratory sense 157, 631

Resultant tones 745

INDEX.

867

PAGE

Rete testis 786

Retina, physiological anatomy of 680

sensibility of the layer of rods and cones of 698

shadows of the vessels of 698

— relative sensibility of the different parts of 700

— corresponding points in 713

Rctrahens aurem 731

Rhodopsine 700

Ribs 116

Right-handedness (see Dextral pre-eminence).. . 847

Rigor mortis (gee Cadaveric rigidity) 850

Rima glottidis Ill

Rolling movements following injury of certain

parts of the encephalon etc 633

Rosenmuller, organ of 771, 831

Rut, identity of, with menstruation 781

Ruysch, tunic of 677

Saccharose 171

Saccule of the internal ear 756

Sacro-lumbalis, action of. in expiration 126

Sacrum, consolidation of 817

Saliva 195

— parotid 195

— secretion of 196

relations of the flow of, to mastication 196

— alternation in the secretion of, upon the
two sides 196

submaxillary 196

— influence of sapid substances upon the se-
cretion of 197

— sublingual 197

— influence of sapid substances upon the se-
cretion of . . 197

— fluids from the smaller glands of the mouth,
tongue, and pharynx 197

mixed 198

— influence of matters introduced into the
stomach through a gastric fistula upon the
secretion of 199

— quantity of 199

— reaction of 199

— quantity of, secreted during the intervals

of mastication 199

general properties and composition of 199

— table of the composition of 200

uses of 200

influence of, upon deglutition 201

mechanical uses of 201

Salivary glands 195

Salivary secretion, centre for 341

Saponification 174

Sarcolactates 382

Sarcolemma 467

Savors. 663

Scala tympani of the cochlea 758

Scala vestibuli of the cochlea 758

Scalene muscles, action of, in respiration 119

Scarpa, humor of. 759

Schlemm, canal of 680

Schneiderian mucous membrane 658

Schwann, sheath of 507

— white substance of 507

Sclerotic coat of the eye 675

— development of 821

Scrotum 785

PAGB

Scrotum, development of 834

Sebaceous glands 320

first appearance of 818

Sebaceous matter 324

Secreted fluids, classification of 807

Secretion, general considerations 806, 811

mechanism of 807

distinction of, from excretion 307, 311, 341

mechanism of, as distinguished from ex-
cretion 808

influence of the composition and pressure

of the blood upon 311

influence of the nervous system upon 312

— paralytic 313

— centres presiding over 340

Segmentation of the vitellus 799

Semen 790

— quantity of 790

mucous secretions mixed with 790

in advanced age 793

ejaculation of 794

— penetration of, into the uterus 795

— passage of, through the Fallopian tubes. . . 795

— time occupied by passage of, to the ova-
ries 795

Semicircular canals, bony 736

membranous 756

— uses of 762

— influence of, upon equilibration 762

— disease of (Meniere's disease) 626, 7C3

development of 821

Semilunar valves, pulmonic 37

aortic 37

— safety-valve function of 44

Seminal vesicles 788

Seminiferous tubes 786, 787

Semi-vowels 503

Sensation in amputated members etc 525

Sensory nerves, disappearance of the physio-
logical properties of 521

reappearance of sensation in 522

— action of 525

Septum lucidum, development of 820

Serine 23

Seroline 265

Serotina, cells of 812

Serous cavities 275, 315

Serous fluids 315

Serratus magnus, action of, in respiration 1£2

Serratus posticus superior, action of, in respira-
tion 122

Serum of the blood (see Blood) 24

Sex, determination of, in the fretus 797

Sexual intercourse (see Coitus) 793

Sighing 130

Sight (see Vision) 671

Sinus terminalis of the area vasculosa 835

Sinuses of Valsalva 37

Skatol, production of, by action of trypsine on

albuminoids 249, 267

in the faeces 264

Skeleton, development of 817

— ossification of 818

Skin, respiration by 161

— effects of an impermeable coating applied

to . . . . 162

868

INDEX.

PAGE

Skin, absorption by 286

physiological anatomy of 342

quantity of exhalation from 356

action of, in the equalization of the ani-
mal heat 357, 456

tactile papillse of 515

development of 818

Skull, development of 817

Sleep 647

condition of the brain and nervous system

in 649

— produced by pressure on the carotids 650

conditions of various functions in 651, 652

Smegma of the prepuce and of the labia mi-

nora 325

Smell (see Olfaction) 658

Sneezing 129

Snoring 128

Sobbing 130

Sodium chloride, uses of, in the blood . ....... 21

uses of in alimentation 175

as a condiment 181

Solitary glands of the intestine 239

Somatopleure 802

Somites 816

Sommering, yellow spot of 681

Sound, physics of 737

reflection of 739

refraction of 739

shadows of 739

rapidity of transmission of 739

— noisy and musical 739

pitch of 740

range of, in music 740

musical scale of 740

— quality of 742

harmonics, or overtones of 743

resultant tones of 745

summation tones of 745

harmony of 745

chords of 746

discords of 746

beats in 747

— — tones by influence in (consonance) 747

Sounds of the heart 44

Speech, mechanism of 501

Speech-centre 621

Spermatic crystals 790

Spermatine 790

Spennatoblasts 792

Spermatozoids 791

— duration of the vitality of, in the female
generative passages 791, 795

— development of 792

— in advanced age 793

— penetration of, through the vitelline mem-
brane 796

Spheno-palatine ganglion 638

Sphymograph 68

Sphincter of the anus 261, 269

of the rectum 269

— of the bladder 371

Spices 181

Spina bifida 817

Spinal accessory nerve 557

physiological anatomy of 557

PAGE

Spinal accessory nerve, properties and uses of.. 559
uses of the internal branch of 559

— influence of, upon phonation 560

— influence of, upon deglutition 560

— influence of, upon the heart 56, 560

uses of the external, or muscular branch

of, going to the sterno-cleido-mastoid and

trapezius muscles 561

Spinal column, development of 817

twisting of, in the embryon 817

Spinal cord, rate of conduction by 528

physiological anatomy of 586, 589

direction of the fibres in 593

general properties of 594

motor paths in 595

sensory paths in 595

hypersesthesia due to injury of portions of. 596

— uses of, in connection with muscular co-
ordination 596

• nerve-centres in 597

reflex action of 598

development of 819

Spinal nerves 538

motor and sensory roots of 522, 538

Splanchnopleure 802

Spleen, relations of, to the blood-corpuscles.

11, 418

proportion of lencocytes in the blood of

the veins of 14. 418

• physiological anatomy of 413

blood-vessels, nerves, and lymphatics of. . 415

chemical constitution of 416

variations in the volume of 417

extirpation of 417

uses of 418

development of 824

Stapedius muscle 734

Stapes 733

— development of 827

Starch 171

Steapsine 246, 250

Stearine 174

Steno, duct of 195

Stercorine 265

Stereoscope 716

Sterno-mastoideus, action of, in respiration 122

St. Martin, case of 216

Stomach, physiological anatomy of 211

— glands . . 214

closed follicles of 216

secretion of (see Gastric juice) 216

changes in the appearance of the mucous

membrane of, during the secretion of gastric

juice 218

extracts of the mucous membrane of 218

— duration of digestion in 228

— digestibility of different aliments in 229

influence of the pneumogastrics upon 230

influence of the nervous system upon 230

- — movements of 230

regurgitation of food from 232

gases of 232

— development of 823

Strabismus, external . . 542

internal 547

Sty loid ligament, development of ... 827

INDEX.

869

Subclavian arteries, development of
Subclavian veins, development of
Sublingual nerves, physiological anatomy of.

- properties and uses of

- effects of section of, upon deglutition

PAGE

837
838

.. 562
562
563

Sublingual saliva (see Saliva). .-. ................ 197

Submaxillary ganglion ....................... 638

Submaxillary saliva (see Saliva) ................ 196

Sucking, mechanism of ....................... 188

Sudoriparous glands (see Sweat) ................ 353

- first appearance of ....................... 818

Suffocation, sense of .......................... 160

Sugars ........................................ 170

Sugar of milk ................................. 336

— production of, by the liver (see Liver) ...... 408

- character of, produced by the liver ........ 410

Sulphates in the body ......................... 437

Sulphocyanide in the saliva .................... 195

Summation tones ....................... ...... 745

Superfecundation ............................. 797

Suprar.enal capsules, weight of, compared with

the kidneys, in foetus and adult .............. 419

- structure of ............................... 419

— chemical reactions of ..................... 421

— extirpation of ............................ 421

— development of ........................... 832

Sweat ......................................... 353

— mechanism of the secretion of ............. 355

- influence of the nervous system upon the
secretion of .................................. 355

- • quantity of .............................. 356

- properties and composition of ............. 357

— equalization of animal heat by ............ 357

- peculiarities of, in certain parts ........... 358

Sweat-centres ................................. 356

Sweat-glands .................................. 353

Sympathetic system ........................... 635

— general arrangement of .......... • ......... 635

— cranial ganglia of ......................... 637

- cervical ganglia of ........................ 638

- thoracic ganglia of ........................ 639

- abdominal and pelvic ganglia of ........... 639

— general properties of ...................... 640

— direct experiments upon .................. 641

- influence of division of nerves of, upon
animal heat .................................. 641

— influence of, upon the circulation ......... 641

— influence of, upon secretion ............... 642

- influence of, upon the urine ............... 642

— influence of, upon the intestines ........... 642

— reflex phenomena in ............. ....... 643

— development of ........................... 819

Sympexions ................................. 790

Synovial bursae .............................. 315

Synovial fluid ................................. 316

Synovial fringes .............................. 315

Synovial membranes ........................... 315

Synovial sheaths ............................. 31(5

Synovine ...................................... 316

Tactile centre ................................ 658

Tactile corpuscles ......................... 514, 657

Taste (see Gustation) ......................... 663

- influence of the chorda tympani upon. 554, 664

- nerves of .................................. 664

- action of the glosso-pharyngeal nerve in . 667

PAGK

Taste-beakers 669

Taste-cells 670

Taste-centre 670

Taste-pores 070

Tastes and flavors 063

Taurine in the urine 384

Taurocholic acid and sodium taurocholate 402

Tea 179

— composition of 180

Tears 727

Teeth, physiological anatomy of 189

— uses of the sensibility of, to hard sub-
stances, in mastication 195

Teeth, temporary, development of 828

— order of eruption of 830

— permanent, development of 829

order of eruption of 830

Temperature of the body 446

— sense of 657

Temporo-maxillary articulation 192

Tendons, connection of, with the muscles 470

Tenon, capsule of 674

Tensor palati 204, 735

Tensor tympani 733, 751

Testicles 785

— first appearance of 831

— descent of 831

— gubernaculum of 831

Tegmentum 609

Tetanus 477

Theine .* 180

Theobromine 180

Thirst 167

— effects of haemorrhage upon 167

— seat of sense of 168

relief of, by absorption of water by the

skin 287

Thoracic duct 273

— fistula into 294

Thorax, form of 116

— action of the elasticity of the walls of, in
expiration 123

Thraenine 728

Thymus gland 423

Thyro-arytenoid muscles 491

Thyroid gland, structure of 421

— chemical constitution of 422

— extirpation of 422

Tidal air 131

Titillation .654

Tongue, action of, in sucking 188

— action of, in mastication 194

— glands of 198

— action of, in deglutition 206

— action of, in phonation 495

— papillae of 668

— development of 827

Tonsils 198, 203

Touch, sense of 655

— variations in the sense of. in different parts 655

— extraordinary development of the sense of 655
table of variations in the sense of, in differ-
ent parts 656

centre for 658

Trachea ill

development of . . 825

870

INDEX.

PAGE

Trachealis muscle 113

Tragus of the ear 730

Transfusion of blood 2

Tran sudations 308

Transver.«alis, action of, in expiration 126

Trapezius, action of the superior portion of, in

respiration 122

Triangularis sterni, action of, in expiration — 125

Tricuspid valve 36

saf ty-valve action of 44

Trifacial, or trigeminal nerve (see Fifth cranial

nerve, large root of) 564

Trigone 371

Trioleine 174

Tripalmitine 174

Triphthongs 501

Tristearine 174

Trophic centres and nerves 645

Trypsine 246, 249

Trypsinogen 310

Tuber annulare (see Pons Varolii) 609

Tubercula quadrigemina 608

development of 819, 820

Tiirck, columns of 592

Twins, one white and the other black 798

— one male and the other female 781, 799

— question of development of, from a single
ovum or from two ova 844

Tympanic membrane, physiological anatomy
of 732, 748

— cone of light in ... 750

uses of 750

Tympanum 732

— development of 826

Tyrosine, production of, by the action of tryp-

sine on albuminoids 249

— in the urine 384

Tyson, glands of 322

Umbilical arteries and vein 807, 808

Umbilical cord 808, 836

— valves in the vessels of; 809

Umbilical hernia in the foetus 807, 809, 822

Umbilical vein, closure of 841

Umbilical vesicle 803

Umbilicus, amniotic 803

intestinal 807

Urachus 809, 822

Urea 376

— where found in the economy 376

— artificial formation of 376

— origin of 377

— formation of, in the liver 377, 400

— theory of production of, from uric acid,
creatine etc 377

influence of ingesta upon the elimina-
tion of 377

— influence of muscular exercise upon the
elimination of 378

quantity of daily excretion of .... 380

Ureters, physiological anatomy of 369

Urethra 372

— glands of 789

Uric acid and its compounds ... 380

Urinary apparatus, development of 832

Urine, mechanism of the production of 366

PAOB
Urine, influence of blood-pressure, the nervous

system etc., upon the secretion of 368

effects of destruction of the nerves of the

kidneys upon the secretion of 313, 369

alternate action of the kidneys in the secre-
tion of 369

mechanism of the discharge of 371

properties and composition of 373

table of constituents of 375

— fatty matters in 385

inorganic constituents of 385

coloring-matter and mucus of 388

gases of 388

variations in the composition of 389

variations of, with age and sex 390

— of the f cetus 390

— variations of, at different seasons and at
different periods of the day 391

influence of mental exertion upon 391

Urochrome 388

Uterine plug of mucus 811

Uterus 766

situation and position of 766

ligaments of 766

physiological anatomy of 771

blood-vessels of 774

changes in the mucous membrane of, dur-
ing menstruation 774, 783

— formation of the membrane deciduae from
the mucous membrane of 810

secretion of mucus by the cervix of, in

pregnancy 811

first appearance of the new mucous mem-
brane of, in pregnancy 811, 846

development of 831

double 831

enlargement of, in pregnancy 842

cause of the first contraction of, in normal

parturition 845

involution of 846

restoration of the mucous membrane of,

after parturition 846

Utricle of the internal ear 756

Uvea 679

Uvula 203

Uvula vesicae 371

Vagina 766, 776

double 831

Valsalva, sinuses of 37

humor of 759

Valsalva's method for protection of the mem-

brana tympani from concussion 753

Valve, tricuspid 36

— pulmonic 37

mitral 37

aortic 37

Valves of the veins, discovery of 30

uses of 31, 98

Valves of the heart, action of 43

Valves of the lymphatics 276, 282

Valvulae conniventes 235

— development of 823

Vas def erens 787

— movements of, produced by galvanization

of the lumbar portion of the spinal cord 788

INDEX.

871

PAGE

Vas deferens, development of, from the Wolf-

fian duct 831

Vasa vasorum 63, 89

Vasa vorticoea 677

Vascular arches, in the embryon 837

Vaso-dilator nerves 645

Vaso-inhibitory nerves. 645

Vaso-motor centres and nerves 642

Vaso-motor reflex phenomena 643

Vater, corpuscles of 513

Veins, variations in the color of the blood in. . . 4

— renal, color of the blood in 4

— discovery of valves of 30

— uses of the valves of 31, 98

circulation in 87

— capacity of, as compared with that of the
arteries 87

— anastomoses of 89, 99

— structure and properties of 89

— vasa vasorum of 89

— strength of the walls of 90

— elasticity and contractility of 91

— valves of 91

those in which there are no valves 92

— course of the blood in 93

— pulse in 94

— pressure of blood in 94

— rapidity of the flow of blood in 95

— causes of the circulation in 95

— obstacles to the flow of blood in 95, 100

— influence of muscular contraction upon the
How of blood in 96

— influence of the force of aspiration from
the thorax upon the circulation in 96

— of the liver, circulation in 97

— relations of respiration to the circulation

in 97, 100

— entrance of air into 98

— influence of gravity upon the circulation

in 98, 101

— influence of a suction force exerted by larg-
er upon smaller vessels upon the circulation in 98

— regurgitant pulse in 100

— development of 837

Velum pendulum palati 203

Vena innominata, development of 838

Venae cavae, development of 837

Venereal sense 658

Venoms, absorption of. 320

Ventilation of hospitals, prisons etc 137

Ventricles of the heart 34

— comparative capacity of right and left 34

— comparative thickness of right and left... . 35

shortening and elongation of 39

Verheyn, stars of 365

Vermiform appendix 258

Vernix caseosa 325, 818

Vertebrae, first appearance of 817

Vertebral arteries, development of 836

Vertebral plates 814

Vesiculae seminales 788

— development of 832

Vestibule of the ear 736, 755

Villi of the small intestine 237

— development of . 823

Vinegar .. 181

PAGE

Visceral arches 825

Visceral clefts 825

Visceral plates 815

Vision, physiological anatomy of the organs of 671

— area of 691

— laws of refraction, dispersion etc., in 692

refraction by lenses in 693

— myopic 695

— hypermetropic 695

— presbyopic 695

— formation of images in 698

— demonstration of the fact that the layer of
rods and cones is the seat of impressions in. . 698

area of distinct 699

— blind spot in the retina in 699

accommodation of, to different degrees of

illumination . . 702

mechanism of refraction in 702

— astigmatic 704

— movements of the iris in 705

— accommodation of, for different distances. 708

— through a small orifice, like a pinhole 711

erect, although the images on the retina are

inverted 711

— field of 711

binocular 712

double 712

corresponding points on the retina in 713

horopter of. 714

monocular 714

— binocular field of 714

— estimation of distance, the form and so-
lidity of objects, etc., in 715

— with the stereoscope 716

binocular fusion of colors in 716

— duration of luminous impressions in (after
images) 716

fusion of colors in 717

irradiation in 717

accidental areohe in 718

centres for 722

— perception of colors in 723

— development of the organs of 821

Visual purple and visual yellow 700

Vital capacity of the lungs 133

variations in, with stature 133

Vital point 632

Vitelline circulation 835

Vitelline membrane of the ovnm 778

— disappearance of, after fecundation 803

— villosities of 803

Vitelline nucleus 797

Vitellus 778

deformation and gyration of 796

— formation of the polar globule of 796

formation of the nucleus of 797

— bright appearance of, after fecundation. . . 799

segmentation of 799

Vitreous humor 688

— development of 821

Vocal chords 110, 488

— action of, in phonation 491

Vocal registers 496

Voice and speech 488

Voice, mechanism of the production of 491

action of the vocal chords in.. . . . 491

872

INDEX.

PAGE

Voice, varieties of 493

in boys 493

— range of 494

action of the intrinsic muscles of the larynx

in.

494

action of the accessory organs of 495

action of the trachea in 495

action of the larynx and epiglottis in 495

action of the pharynx in 495

action of the mouth in 495

action of the nasal fossae in 495

— action of the tongue in 495

— action of the velum palati in 496

different registers of 496

influence of the spinal accessory nerve

upon 560

Voltaic alternation 534

Vomiting, mechanism of 232

Vowels 501

Vowel-sounds, mechanism of 502

Wagner, corpuscles of 514

— spot of 778

Wallerian method 521

Water, uses of, in the blood 20, 430

FA6E

Water, as a product of excretion 389, 455

— uses of, in alimentation etc 431

— table of quantities of, in different tissues. . 431

— origin and discharge of 431

Watery vapor, exhalation of, by the lungs 148

Weight, appreciation of 654

Wharton, duct of 196

— gelatine of 809

Whispering. 503

Wolffian bodies 814, 830

structure of 831

time of disapearance of, in the female. . . . 831

Wolfflan ducts 831

— development of the vasa deferentia from. . 831

Word-blindness 621

Wrisberg, nerve of 550

Xanthine 384

Yawning 130

Yellow spot of SOmmerring 681

Youth 849

Zona pellucida (zona radiata) 778

Zone of Zinn 677, 687

Zymogen 215, 310

THE END.

A TEXT-BOOK

— OF —

GYNECOLOGY

Edited by CHARLES A. L. REED, A. M., M. D.

President of the American Medical Association, Gynecologist and Clinical Lecturer on
Surgical Diseases of Women at the Cincinnati Hospital, etc.

With 400 Illustrations from Original Drawings by Roy J. Hopkins.
8vo, 900 pages. Sold only by Subscription. Cloth, $5.00 ;
sheep, $6.00.

Nearly one-half of the work is from the pen of the editor, whose reputation is inter-
national. The rest is based on contributions from distinguished British and American
writers and teachers, not only of gynecology, but also of the cognate subjects of pathol-
ogy, bacteriology, neurology, dermatology, general surgery, and internal medicine,
unified and blended into a consecutive text.

" Taken all in all, this book may be said to represent all that is accepted by conser-
vative gynecologists, and is a book which can be followed with the most implicit faith
by the practitioner." — Medical Progress, Louisville, Ky.

"Students and practitioners will find this text-book a valuable guide in this im-
portant field of special work. The book is judiciously illustrated, and the illustrations
are especially well drawn and helpful." — -Journal of Medical Science, Portland, Me.

" The work of the editor in properly connecting the labors of the different contribu-
tors so that the book would not have the appearance of a collection of monographs
has been stupendous. The successful accomplishment of this reflects great credit upon
his judgment, industry, and acumen." — Western Medical Review, Lincoln, Neb.

" There are thirty-one contributors, the best talent to be found in the United States,
with the result that we have one of the very best works upon gynecology extant. The
editor is to be sincerely congratulated on the outcome of his labor, but those who know
him best could not but feel that such a book only could be produced by him." — New
England Medical Monthly, Danbury, Conn.

" Dr. Reed has placed the profession under obligations to himself for a very valuable
text-book of gynecology. For clearness of statement, exhaustiveness of treatment, and
fulness of illustration, it is not excelled by any work of its size. The author has suc-
ceeded in furnishing a text-book which will be a most valuable working manual for
practitioners and students, embracing the best approved developments of gynecology.
The work of his associates has been so woven into the text as to give it unity and
completeness without repetition." — Columbus (Ohio) Medical Journal.

" This volume is an original work of more than ordinary value, upon a subject which
can boast of many distinguished authors. Its great value lies in the fact that it is of
composite authorship. Thirty-one contributors have lent their best efforts to the suc-
cessful elaboration of this volume, and the list embraces the most widely known names
of North America and Great Britain. The editor did his work thoroughly and well, and
as a result we have a book whose contents are truly refreshing. It is up to date in every
respect, and its preparation was done quickly but not hastily. The different articles
are well considered, show much thought in their preparation, and give evidence of large
experience and information on the part of their respective authors. The editor has not
confined his labors merely to editorial supervision, but he has made many contributions
as well, and they are by no means the least important." — St. Louis Medical and
Surgical Journal.

D. APPLETON AND COMPANY, NEW YORK.

A TREATISE ON THE
DISEASES OF WOMEN.

BY ALEXANDER J. C. SKENE, M. D.,

PROFESSOR OP GYNAECOLOGY IN THE LONG ISLAND COLLEGE HOSPITAL, BROOKLYN, N. Y. ; FOR-
MERLY PROFESSOR OF GYNAECOLOGY IN THE NEW YORK POST-GRADUATE MEDICAL
• SCHOOL AND HOSPITAL, ETC.

Third Edition, revised and enlarged. 8vo, 991 pages. With 290 Fine

Wood Engravings, and Nine Chromolithographs, prepared

especially for this work.

SOLD ONLY BY SUBSCRIPTION.

THIS attractive work is the outcome and represents the experience of a long and
active professional life, the greater part of which has been spent in the treat-
ment of the diseases of women. It is especially adapted to meet the wants
of the general practitioner, by enabling him to recognize this class of diseases as
he meets them in every-day practice and to treat them successfully.

The arrangement of subjects is such that they are discussed in their natural
order, and thus are more easily comprehended and remembered by the student.

Methods of operation have been much simplified by the author in his practice,
and it has been his endeavor to so describe the operative procedures adopted by
him, even to their minutest details, as to make his treatise a practical guide to the
gynaecologist.

While attention has been given to 'the surgical treatment of the diseases of
women, and many of the operations so simplified as to bring them within the
capabilities of the general surgeon, due regard has also been paid to the medical
management of this class of diseases.

Although all the subjects which are discussed in the various text-books on
gynaecology have been treated by the author, it has been a prominent feature in
his plan to consider also those which are but incidentally, or not at all, mentioned
in the text-books hitherto published, and yet which are constantly presenting
themselves to the practitioner for diagnosis and treatment.

"In the preface of the first edition of this work the author states : 'This work was written for
the purpose of bringing together the fully matured and essential facts in the science and art of
gynaecology, so arranged as to meet the requirements of the student of medicine, and be convenient
to the practitioner for reference.1 The demand for a second edition has demonstrated how fully
this purpose has been accomplished. The reader can not fail to commend the conservatism and
honesty of the author's opinions, and the care with which the material has been collected and
arranged. The second edition contains new chapters on Ectopic Gestation, Diseases and Injuries
of the Ureters, and Vesical Hernia. The first of these subjects receives in this edition a careful
exposition, the want of which was among the few defects of the former edition. The author's
work in the positional disorders of the uterus and laceration of the perinaenm stands pre-eminent
among the contributions to this subject. His discussion of the use of pessaries throws much light upon
a subject which has suffered from the want of careful treatment, both pro and con. The publishers
deserve great credit for the illustrations and general style of the work." — Medical Neivs.

"We have very little to add to what we said of it on its first appearance, and we still regard it as
one of the few foremost books in this department in the English language. 'Ihe addition of
chapters on Diseases and Injuries of the Ureters, and on Ectopic Gestation, make it more complete.
Too' much praise can not be given to the illustrations, which are models of clearness, and, as is not
always the case, show what is meant."— Boston Medical and Surgical Journal.

D. APPLETON AND COMPANY, NEW YORK.

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