MEDICAL SCHOOL

The Lucy M. wanzer Library

With the Respects of

A. L. BANCROFT & COMPANY,

San Francisco, Cal.

A TEEATISE-

6-

HUMAN PHYSIOLOGY;

DESIGNED FOR THE USE OF

STUDENTS AND PRACTITIONERS OF MEDICINE.

BY

JOHN C. DALTON, M.D.,

PROFESSOR OP PHYSIOLOGY AND HYGIENE IN THE COLLEGE OP PHYSICIANS AND SURGEONS,

NEW YORK; MEMBER OF THE NEW YORK ACADEMY OF MEDICINE ; OF THE NEW YORK

PATHOLOGICAL SOCIETY ; OF THE AMERICAN ACADEMY OF ARTS AND SCIENCES.

BOSTON; OF THE BIOLOGICAL DEPARTMENT OF THE ACADEMY OF

NATURAL SCIENCES, PHILADELPHIA; AND OF THE NATIONAL

ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA.

SIXTH EDITION,

REVISED AND ENLARGED.
WITH

THREE HUNDRED AND SIXTEEN ILLUSTRATIONS.

PHILADELPHIA:
HE^EY 0. LEA
1875.

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

HENRY C. LEA,
in the Office of the Librarian of Congress at Washington. All rights reserved.

PHILADELPHIA:

COLLINS, PRINTER,

70f> Jayne Street.

TO MY FATHER,

JOHN C. DALTON, M.D.,

IN

HOMAGE OF HIS LONG AND SUCCESSFUL DEVOTION

TO THE

SCIENCE AND AET OF MEDICINE,

AND IN
GRATEFDL RECOLLECTION OP HIS PROFESSIONAL PRECEPTS AND EXAMPLE,

n 9 aim*

IS RESPECTFULLY AND AFFECTIONATELY

INSCRIBED.

271".

PREFACE.

IN the present edition of this book, while every part has received
a careful revision, the original plan of arrangement has been changed
only so far as was necessary for the introduction of new material. Al-
though the whole field of physiology has been cultivated, of late years,
with unusual industry and success, perhaps the most important advances
have been made in the two departments of Physiological Chemistry and
the Nervous System. The number and classification of the proximate
principles, more especially, and their relation to each other in the pro-
cess of nutrition, have become, in many respects, better understood
than formerly ; though it is evident that this fundamental part of
physiology is to receive, in the future, modifications and additions of
the most valuable kind.

In nearly every division of physiological study, a prominent feature
of recent progress has been the increased attention paid to quantitative
investigation. The conviction has apparently become general that,
in physiology as well as in other natural sciences, the knowledge
gained by any method of study is essentially imperfect until its re-
sults can be stated in figures. The chemical characters of an ingre-
dient or product of the animal system are hardly more important than
its quantity; and for determining its physiological relation to other
substances, of similar or different kinds, the knowledge of its quantity
is absolutely indispensable. Investigations of this sort, in respect to
the living body, are surrounded with difficulties ; but the results ob-
tained are steadily increasing in precision and extent, and already foiun
a most important element in the study of physiology.

In a text-book like the present, it is desirable that the reader should
not be misled by having all the frequent changes of opinion, or sub-
stitutions of theory, presented as discoveries in physiological science.
Any faithfully observed facts, however unexpected or peculiar, are of
course at once invested with a permanent value. But the theoretical
explanations, by which they are sometimes accompanied, are not of the
same importance. They often represent only a scheme of probabilities

(v)

VI , PKEFACE.

existing in the mind of the author, and may be altered at any time to
suit the requirements of more extended observation. In rendering an
account, therefore, of the state of knowledge upon any physiological
subject, the student should be informed, not only of the results now in
our possession, but also of the means of investigation by which they
have been attained. He is thus enabled to distinguish between what
is positive in physiological doctrines, and what is hypothetical ; and
when further discoveries are made, which lead to changes of opinion,
he is not confused or disappointed at apparent contradictions between
the new views and the old. This method requires a certain amount of
detail in the statement of facts; but its advantages are ample compen-
sation for the necessary expenditure of time and space.

The additions and alterations in the text, requisite to present con-
cisely the growth of positive physiological knowledge, have resulted,
in spite of the author's earnest efforts at condensation, in an increase
of fully fifty per cent, in the matter of the work. A change, however,
in the typographical arrangement has accommodated these additions
without undue enlargement in the bulk of the volume.

The new chemical notation and nomenclature are introduced into the
present edition, as having now so generally taken the place of the old,
that no confusion need result from the change. The centigrade system
of measurements for length, volume, and weight, is also adopted, these
measurements being at present almost universally employed in original
physiological investigations and their published accounts. Tempera-
tures are given in degrees of the centigrade scale, usually accompanied
by the corresponding degrees of Fahrenheit's scale, inclosed in brackets.

NEW YOKK, September, 1875.

CONTENTS.

INTRODUCTION.

PAGE

Definition of Physiology — Organization of living bodies — Functions — Mode
of study in physiology — Experiments — Their results, direct and indirect —
Vital phenomena — Their various kinds — Division of the subject . 25-32

SECTION I.
NUTEITION.

CHAPTER I.

PROXIMATE PRINCIPLES IN GENERAL.

Definition of proximate principles — Their mode of extraction — Their propor-
tions in the animal tissues and fluids — Their classification . . 33-39

CHAPTER II.

INORGANIC PROXIMATE PRINCIPLES.

Nature and source of the inorganic proximate principles — Water — Lime
phosphate — Lime carbonate — Magnesium phosphate — Sodium chloride —
Potassium chloride — Sodium and potassium phosphates — Sodium and po-
tassium carbonates — Sodium and potassium sulphates — Use and final dis-
charge of the inorganic proximate principles 40-54

CHAPTER III.

HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

Source and general character of the hydrocarbonaceous proximate principles —
Starch — Its reactions — Its production in vegetables — Its transformation
in the digestive process — Glycogen — Sugar — Glucose — Its reactions — Fer-
mentation— Lactose — Saccharose — The Fats — Their reactions — Stearine —
Palmitine — Oleine — Condition of the fats in organized tissues and fluids —
Their production in vegetables — Their decomposition in the body — Choles-
terine — Origin and destination of the hydrocarbonaceous proximate princi-
ples 55-78

( vii }

Vlll CONTENTS.

CHAPTER IV.

ALBUMINOUS MATTERS.

PAOK

Composition and general characters of the albuminous matters — Hygrosco-
picity — Coagulation — Catalysis — Putrefaction — Production of albuminous
matters — Fibrine — Albumen — Albuminose — Gascine — Ptyaline — Pepsine
— Pancreatine — Mucosine — Myosine — Collagen — Chondrine — Elasticine —
Keratine — Alteration and discharge of the albuminous matters . 79-93

CHAPTER V.

COLORING MATTERS.

General characters of the coloring matters — Hemoglobine — Melanine — Bili-
rubine — Biliverdine — Urochrome — Luteine — Chlorophylle . . 94-101

CHAPTER VI.

CRYSTALLIZABLE NITROGENOUS MATTERS.

General characters of the crystallizable nitrogenous matters — Lecithine —
Cerebrinc — Leucine — Sodium glycocholate — Sodium taurocholate — Crca-
tine — Creatinine — Urea — Sodium urate — Sodium hippurate . . 102-112

CHAPTER VII.

FOOD.

Inorganic ingredients of the food — Non-nitrogenous organic ingredients of
the food — Nitrogenous ingredients of the food — Composition of different
articles of food — Milk — Bread — Meat — Eggs — Vegetables — Eequisite
quantity of food and of its different ingredients — Results of the assimilation
and metamorphosis of the food 113-130

CHAPTER VIII.

DIGESTION.

Nature of the digestive process — Digestive apparatus — Mastication — The ^
saliva — Salivary glands — Physical properties and composition of the saliva
— Its modes of secretion — Its daily quantity — Its physiological action —
The gastric juice and stomach digestion — Mucous membrane of the sto-
mach— Physical qualities and composition of the gastric juice— Its mode
of secretion — Its daily quantity — Its physiological action — The pancreatic
juice — Structure of the pancreas — Physical character and composition of
the pancreatic juice — Its physiological properties — The intestinal juice —
Brunner's glands — Follicles of Lieberkiihn — Mode of obtaining the intes-
tinal juice — Its composition and properties — The large intestine and its
contents — Excretine — Stercorine ....... 131-188

CHAPTER IX.

ABSORPTION.

Intestinal villi — Closed follicles of the small intestine — Absorption by the
villi — Absorption by the bloodvessels — Absorption by the lacteals — Pas-
sage of absorbed materials into the circulation — Renovation of the blood
by digestion and absorption ........ 189-200

CONTENTS. IX

CHAPTER X.

THE BILE.

FAG 1C

Structure of the liver — Physical and chemical characters of the bile — Its
fluorescence — Its spectrum — Its composition — Pettenkofer's test for the
biliary salts — Mode of secretion of the bile — Its daily quantity — Decompo-
sition of the biliary matters in the intesjtine — Physiological function and
destination of the bile . 201-227

CHAPTER XI.

PRODUCTION OF GLYCOGEN AND GLUCOSE IN THE LIVER.

Glycogen — Its origin and mode of formation— Its transformation into sugar —
Rapidity of formation of sugar in the liver — Its accumulation after death —
Its proportion in the liver-tissue during life — Absorption and final disap-
pearance of the liver-sugar — Its discharge by the urine — Diabetes — Va-
rious causes of diabetes ......... 228-242

CHAPTER XII.

THE BLOOD.

Physical characters of the blood — Red globules — Their size, form, and reac-
tions— Their composition — Spectrum of blood — Yarieties of the red glo-
bules in different classes of animals — Diagnosis of blood, and distinction
between that of man and animals — White globules of the blood — Amoeboid
movements of the white globules — Plasma of the blood — Coagulation of
the blood— Quantity of blood in the body 243-269

CHA PTER XIII.

RESPIRATION.

Nature of respiration — Respiration in vegetables — Organs of respiration —
Movements of respiration — Inspiration — Expiration — Respiratory move-
ments of the glottis — Frequency of respiration — Quantity of air used in
respiration — Changes of the air in respiration— Diminution of oxygen — In-
crease of carbonic acid — Relation between the oxygen absorbed and the
carbonic acid given off— Exhalation of watery vapor — Exhalation of or-
ganic matter — Vitiation of the air by respiration — Changes in the blood
by respiration — Absorption of oxygen — Discharge of carbonic acid — Source
of the carbonic acid of the blood 270-299

CHAPTER XIV.

ANIMAL HEAT.

Temperature of the animal body — Differences of temperature in different
classes — Quantity of heat produced in the body — Normal variations of
temperature during life — Mode of production of animal heat — Local pro-
duction of heat in the different organs — Equalization of temperature by
the circulation — Regulation of the animal temperature — Resistance of the
body to cold — Resistance of the body to heat — The perspiration . 300-317

X CONTENTS.

CHAPTER XV.

THE CIRCULATION.

PAGE

Apparatus of circulation — The heart — Sounds, movement, and impulse of the
heart — Rhythm of the heart's action — The arteries — Distension of the arte-
ries by the heart's action — Arterial pulse — The sphygmograph — Dicrotic
pulse — The arterial pressure — Rapidity of the arterial current — The veins
— Movement of the blood through the veins — Rapidity of the venous circu-
lation— The capillaries — Movement of the blood through the capillaries —
Physical cause of the capillary circulation — General rapidity of the circu-
lation— Local variations in the capillary circulation . . . 318-353

CHAPTER XYI.

THE LYMPHATIC SYSTEM.

Structure and arrangement of the lymphatic system — Origin and course of*
the lymphatic vessels -The lymphatic glands — Transudation and absorp-
tion by animal tissues — Endosmosis and exosmosis — Absorption and transu-
dation in the living body — Lymph and chyle — Composition of the lymph
— The lymph globules — Movement of fluids in the lymphatic system — Daily
quantity of lymph and chyle — Internal renovation of the animal fluids 354-373

CHAPTER XVII.

THE URINE.

General character of the urine — Its physical properties — Variations in quan-
tity, density, and acidity — Ingredients of the urine — Urea — Creatinine —
Sodium and potassium urates — Sodium biphosphate — Alkaline phosphates
— Earthy phosphates — Sodium and potassium chlorides — Sodium and po-
tassium sulphates — Reactions of the urine — Heat — Acids — Alkalies — Mine-
ral salts — Abnormal ingredients of the urine — Glucose — Biliary matters —
Medicinal substances — Albumen — Deposits in the urine — Deposits of the
urates — Uric acid — Blood — Mucus — Pus — Decomposition of the urine —
Acid fermentation — Alkaline fermentation — Renovation of the body in the
nutritive process 374-397

SECTION II.
THE NERVOUS SYSTEM.

CHAPTER I.

GENERAL STRUCTURE AND FUNCTIONS OF THE NERVOUS SYSTEM.

Mode of action of the nervous system — Its structure — Nerve fibres — Tubular
sheath — Medullary layer — Axis cylinder — Course and relation of the nerve
fibres — Their peripheral termination — Physiological properties of the
nerve fibres — Nerve cells — Their relation with nerve fibres — Their physio-
logical properties — Reflex action of the nervous system . . . 399-416

CONTENTS. XI

CHAPTER II.

NERVOUS IRRITABILITY, AND ITS MODE OF ACTION.

PAGE

Nature of nervous irritability — Irritability of sensitive fibres — Irritability of
motor fibres— Identity of action in sensitive and motor nerve fibres — Ra-
pidity of transmission of the nerve force — Methods of determining its rate
of transmission — Rate of transmission in the motor nerves — In the sensitive
nerves — In the spinal cord — Rapidity of nervous action in the brain — Va-
riation of nervous rapidity in different individuals .... 417-431

CHAPTER III.

GENERAL ARRANGEMENT OF THE VARIOUS PARTS OF THE NERVOUS

SYSTEM.

Two divisions of the nervous system — Ganglionic system — Cerebro-spinal
system— Spinal cord— Brain— Brain of fish— Of reptiles— Of birds— Of
quadrupeds — Of man — Medulla oblongata — Olivary bodies— Tuber annu-
lare— Crura cerebri— Cerebral ganglia— Connection of the different parts
of the cerebro-spinal system 432-442

CHAPTER IV.

THE SPINAL CORD.

General structure of the spinal cord — Arrangement of its gray and white sub-
stance—Gray substance of the cord — White substance of the cord — Con-
nection of the spinal nerve roots with the spinal cord — Transmission of
motor and sensitive impulses in the spinal nerves and nerve roots — In the
spinal cord — Sensitive and excitable parts of the spinal cord — Channels
for sensation and motion in the spinal cord — Crossed action of the spinal
cord — Decussation of the motor tracts — Decussation of the sensitive tracts
— Various forms of paralysis from lesions of the cerebro-spinal axis — Para-
plegia— Hemiplegia — Reflex action of the spinal cord . . . 443-470

CHAPTER V.

THE BRAIN.

General structure of the brain — The hemispheres — Cerebral convolutions —
Physiological properties of the hemispheres — Intellectual faculties — Special
seat of articulate and written language — Special centres of motion in the
hemispheres — The cerebral ganglia — The cerebellum — Physiological pro-
perties of the cerebellum — The tuber annulare — Physiological properties of
the tuber annulare — Medulla oblongata — Physiological properties of the
medulla — Its action as a nervous centre — Its influence on respiration — On
deglutition — On phonation — On articulation ..... 471-510

CHAPTER VI.

THE CRANIAL NERVES.

Classification of the cranial nerves — Olfactory nerves — Optic — Oculomo-
torius — Patheticus — Trigeminus — Abducens — Facial — Auditory — Glosso-
pharyngeal — Pneumogastric — Spinal accessory — Hypoglossal — General
arrangement and mode of origin of the cranial nerves . . . 511-581

Xll CONTENTS.

CHAPTER VII.

THE SYMPATHETIC SYSTEM.

PAGE

Nerves and ganglia of the sympathetic system — Their anatomical arrange-
ment— Their physiological properties — Their influence on motion and
sensibility — Their connection with the special senses — With the circula-
tion—With reflex action 582-592

CHAPTER VIII.

THE SENSES.

General sensibility — Sensations of touch — Of temperature — Of pain — Sense
of taste — Its necessary conditions — Sense of smell — Its necessary conditions
— Sense of sight — Organ of vision — Physiological conditions of the sense
of sight — Field of vision — Line of direct vision — Point of distinct vision —
Accommodation of the eye for vision at different distances — Apparent posi-
tion of objects and binocular vision — Point of fixation — Appreciation of
solidity and projection — General laws of visual perception — Persistence of
luminous impressions — Negative images — Sense of hearing — Organ of hear-
ing— Tympanum and chain of bones — Their physiological action — Labyrinth
— Its physiological action — Office of the semicircular canals — Cochlea —
Organ of Corti — Physiological action of the cochlea — Production and per-
ception of musical notes 593-666

SECTION III.
REPRODUCTION.

CHAPTER I.

THE NATURE OF REPRODUCTION, AND THE ORIGIN OP PLANTS AND

ANIMALS.

Changes of structure and function in living organisms — Their disappearance
—Their reproduction — Reproduction by generation— Spontaneous genera-
tion— Entozoa — Infusoria — Bacteria — Influence of heat on the production
of bacteria . . . ' 667-681

CHAPTER II.

SEXUAL GENERATION AND THE MODE OF ITS ACCOMPLISHMENT.

Male and female sexes — Generative apparatus of flowering plants — Genera-
tive apparatus of animals — Ovaries and testicles — Distinction between the
sexes — Accessory organs of generation ...... 682-684

CONTENTS. Xlll

CHAPTER III.

THE EGG AND THE FEMALE ORGANS OF GENERATION.

PAGE

Constitution of the egg — Yitelline membrane — Vitellus — Ovaries and Ovi-
ducts— Action of the oviducts and female generative passages — In the frog
— In the fowl — Uterus and Fallopian tubes in quadrupeds — In the human
species 685-694

CHAPTER IV.

THE SEMINAL FLUID AND THE MALE ORGANS OF GENERATION.

The spermatozoa — Their anatomical characters — Their movement — Forma-
tion of the spermatozoa — Accessory male organs of generation — Necessary
conditions of fecundation by the seminal fluid — Union of the sexes . 695-702

CHAPTER V.

PERIODICAL OVULATION AND THE FUNCTION OF MENSTRUATION.

Periodical ovulation — Original existence of eggs — In ovipara — In vivipara —
Complete development of the ovarian egg — Condition of puberty — Ripen-
ing and discharge of the ovarian egg — OEstruation — Menstruation — Its
appearance and periodicity — Phenomena of menstruation — Ovulation at
the menstrual period 703-712

CHAPTER YI.

THE CORPUS LUTEUM, AND ITS CONNECTION WITH MENSTRUATION
AND PREGNANCY.

Origin of the corpus luteum — Corpus luteum of menstruation — Hemorrhage
into the Graafian follicle — Hypertrophy of the vesicular membrane — De-
colorization of the clot — Yellow coloration of the convoluted wall — Atrophy
and disappearance of the corpus luteum of menstruation — Corpus luteum
of pregnancy — Its growth and duration — Its disappearance after delivery —
Distinguishing marks of the corpus luteum, in menstruation and pregnancy

713-720

CHAPTER VII.

DEVELOPMENT OF THE IMPREGNATED EGG.

Changes in the egg before leaving the ovary — Deposit of albuminous layers
in the Fallopian tube — Segmentation of the vitellus — Blastoderm, or ger-
minal membrane — External and internal blastodermic layers — Formation
of organs in the embryo — Embryonic spot — Area pellucida — Primitive
trace — Medullary groove — Medullary canal — Dorsal plates — Abdominal
plates — Chorda dorsalis — Changes of form in the frog's embryo — Growth of
the limbs — Disappearance of the tail — Transformation of the tadpole into
the frog 721-728

XIV CONTENTS.

CHAPTER VIII.

FORMATION OF THE EMBRYO IN THE FOWL'S EGG.

PAGE

Development of the chick — The yolk and the cicatricula — Formation of the
blastoderm — Folds of the blastoderm — Position of the embryo in the egg —
Division of the blastodermic layers — Outer and inner lamina} of the blasto-
derm— Primitive vertebrae — Formation of the spinal column and its mus-
cles 729-737

CHAPTER IX.

DEVELOPMENT OF ACCESSORY ORGANS IN THE IMPREGNATED EGG.
UMBILICAL VESICLE, AMNION, AND ALLANTOIS.

Nature and function of the accessory embryonic organs — Umbilical vesicle —
Amnion — Allantois — Physiological action of the allantois — Exhalation of
water in the fowl's egg — Respiration and absorption of nourishment by the
allantois — Escape of the chick at maturity from the egg-shell . . 738-744

CHAPTER X.

DEVELOPMENT OF THE IMPREGNATED EGG AND ITS MEMBRANES IN
THE HUMAN SPECIES. AMNION AND CHORION.

Membranous envelopes of the human foetus — Amnion — Its enlargement —
Amniotic fluid — Chorion — Early formation of the chorion — Villosities of
the chorion — Development of bloodvessels of the chorion — Partial disappear-
ance of its villosities — Their further development at the situation of the
placenta 745.749

CHAPTER XI.

DEVELOPMENT OF THE DECIDUAL MEMBRANE, AND ATTACHMENT OF
THE EGG TO THE UTERUS.

Mucous membrane of the unimpregnated uterus — Uterine tubules — Decidua
vera — Hypertrophy of the uterine mucous membrane after impregnation —
Decidua reflexa — Enclosure of egg by the decidua reflexa — Attachment of
the egg to the uterine mucous membrane — Corresponding development of
the chorion and decidua 750-754

CHAPTER XII.

THE PLACENTA.

Source of nourishment for the foetus in man and mammalians — Relations of
the allantois and uterine mucous membrane — In the pig — In ruminating
animals — In carnivora — In man — Vascular tufts of the placenta — Vascular
sinuses of the decidua — Relation between the two — Physiological action of
the placenta 755-762

CONTENTS. XV

CHAPTER XIII.

DISCHARGE OP THE FCETUS AND PLACENTA. REGENERATION OF THE
UTERINE TISSUES.

PAGE

Enlargement of the uterus during pregnancy — Formation of the umbilical
cord — Its elongation and twisting — Disappearance of the umbilical vesicle
Contact of the decidua vera and reflexa — Separation and discharge of the
foetus and placenta — Hemorrhage at the time of delivery— Its arrest by
contraction of the uterus — Regeneration of the uterine tissues after de-
livery 763-768

CHAPTER XIY.

DEVELOPMENT OP THE NERVOUS SYSTEM, ORGANS OP SENSE, SKELETON,

AND LIMBS.

Cerebro-spinal axis — Cerebral vesicles — Their division — Hemispheres — Optic
thalami — Tubercula quadrigemina — Cerebellum — Medulla oblongata —
Organs of special sense — Ossification of the skeleton — Formation of the
limbs— The integument . 769—774

CHAPTER X Y.

DEVELOPMENT OP THE ALIMENTARY CANAL AND ITS APPENDAGES,

Formation of the intestinal canal — Stomach — Small intestine — Large intes-
tine— Convolutions of the intestine — Anus — Imperforate anus — Caput coli
Appendix vermiformis — Congenital umbilical hernia — Meconium — Liver —
Lungs, thoracic cavity and diaphragm — Urinary bladder and urethra — De-
velopment of the mouth and face 775-783

CHAPTER XYI.

DEVELOPMENT OP THE WOLFFIAN BODIES, KIDNEYS, AND INTERNAL
ORGANS OF GENERATION.

Embryonic urinary apparatus — Wolffian bodies — Their structure — The kid-
neys— Internal organs of generation — Fallopian tubes and vasa deferentia
— Descent of the testicles — Tunica vaginalis testis — Congenital inguinal
hernia — Female organs of generation — Descent of the ovaries — Formation
of the uterus, round ligaments and broad ligaments — Condition of the uterus
and ovaries at birth 784-790

CHAPTER XYII.

DEVELOPMENT OP THE VASCULAR SYSTEM.

Successive forms of the circulatory system — Yitelline circulation — Omphalo-
mesenteric vessels — Placental circulation — Umbilical arteries and vein —
Adult circulation — Development of the arterial system — Development of the
venous system — The hepatic circulation and ductus venosus — The heart
and ductus arteriosus — Foramen ovale — Eustachian valve — Crossing of
blood-currents in the foetal heart — Changes in the circulation at birth 791-808

XVi CONTENTS.

CHAPTER XVIII,

DEVELOPMENT OF THE BODY AFTER BIRTH.

PAGB

Condition of the newly-born infant — Its weight — Establishment of respira-
tion— Condition of the nervous system — Relative weight of the internal
organs in the foetus at term and the adult — Separation of the umbilical
cord and cicatrization of the umbilicus — Exfoliation of the cuticle and hairs
— Appearance of the first set of teeth — Appearance of the second or per-
manent set — Period of puberty, and complete ossification of the skeleton

809-811

LIST OF ILLUSTRATIONS.

FIG. PAGE

1. Fibula tied in a knot, after maceration in dilute acid . . .45

2. Grains of potato starch ..... ,56

3. Starch grains of Bermuda arrowroot . . . . .57

4. Starch grains of wheat flour . . ... . .57

- 5. Starch grains of Indian corn ...... 58

6. Saccharomyces cerevisiae, in its quiescent condition . . 65

7. Saccharomyces cerevisiae, during active germination . . .66

8. Stearine, crystallized from a warm solution in oleine . . .70

9. Oleaginous principles of human fat . 71

10. Human adipose tissue . . . 72

11. Chyle, from thoracic duct of the dog . 73

12. Globules of cow's milk .... ... 73

13. Cells of costal cartilages, human ..... 74

14. Hepatic cells, human ....... 74

15. Uriniferous tubules of the dog ...... 75

16. Muscular fibres of human uterus, three weeks after parturition . 75

17. Cholesterine, from an encysted tumor ..... 77

18. Cells of Bacterium termo ....... 83

19. Hemoglobine crystals, from human blood . . (Funke) 95

20. Hemoglobine crystals, from dog-faced baboon . . (Preyer) 96

21. Sodium glycocholate, from ox-bile . . . . 105

22. Sodium taurocholate, from alcoholic extract of dog's bile . .106

23. Creatine, crystallized from hot water . . . (Lehmann) 107

24. Creatinine, crystallized from hot water . . . (Lehmann) 107

25. Urea, crystallized by slow evaporation . . . (Lehmann) 109

26. Alimentary canal of fowl ...... 132

27. Compound stomach of ox . . . . . . 133

28. Human alimentary canal ...... 134

29. Skull of rattlesnake ... . (Eichard) 136

30. Skull of polar bear . .... 137

31. Skull of the horse ....... 137

32. Molar tooth of the horse ; grinding surface .... 137

33. Human teeth ........ 138

34. Lobule of parotid gland ..... (Wagner) 139

35. Salivary tubes ; from a muciparous gland . . (Kolliker) 139

36. Glandular follicles and cells ; from submaxillary gland . (Heidenhain) 140

37. Section of submaxillary gland ; from the dog . . (Kolliker) 140

38. Buccal and glandular epithelium ; deposited from saliva . . 141

39. Gastric mucous membrane ; viewed from above . . . . 152

40. Gastric mucous membrane ; in vertical section .... 152

2 ( xvii )

XV111

LIST OF ILLUSTRATIONS.

PIG.

41. Mucous membrane of pig's stomach ; vertical section

42. Gastric follicles, from pig's stomach ; pyloric portion

43. Gastric follicles, from pig's stomach ; cardiac portion .

44. Gastric follicles, from pig's stomach ; middle portion

45. Gastric follicle, from human stomach ; cardiac portion ,

46. Portion of human pancreas and duodenum

47. Longitudinal section of wall of duodenum

48. Entire Brunner's gland .....

49. Portion of one of Brunner's glands

50. Follicles of Lieberkuhn ....

51. Loop of small intestine, isolated by compressors

52. Contents of stomach, during digestion of meat .

53. Contents of duodenum, during digestion of meat

54. Contents of middle portion of small intestine

55. Contents of last quarter of small intestine

56. An intestinal villus . . .

57. Peyer's patch, from the ileum ....

58. A closed follicle of Peyer's patch ; from the pig

59. Chyle, from thoracic duct of the dog

60. Intestinal epithelium ; from the dog, fasting

61. Intestinal epithelium ; from the dog, during digestion .

62. Capillary bloodvessels of the intestinal villi

63. Panizza's experiment, on absorption from the intestine .

64. Lacteals and lymphatics, during digestion

65. Hepatic lobule, in transverse section

66. Glandular hepatic cells .....

67. Biliary canals and ducts ; from the frog's liver .

68. Hepatic lobule, transverse section ; from rabbit's liver ,

69. Spectrum of green bile . . . . .

70. Spectrum of chlorophylle ....

71. Spectrum of Pettenkofer's test, with biliary salts, in watery solution

72. Spectrum of Pettenkofer's test, with biliary salts, in alcoholic solution

73. Spectrum of Pettenkofer's test, with albumen .

74. Crystalline and resinous biliary substances

75. Duodenal fistula ......

76. Human blood-globules .....

77. Red globules of the blood, seen beyond the focus

78. Red globules of the blood, seen within the focus

79. Red globules of the blood, adhering together

80. Red globules of the blood, shrunken and crenated

81. Red globules of the blood, swollen by imbibition

82. Spectrum of hemoglobine, in aerated blood

83. Spectrum of reduced hemoglobine

84. Blood-globules of the frog ....

85. White globules of the blood, altered by acetic acid

86. Changes in form of a white globule of the blood

87. Coagulated fibrine ....

88. Bowl of recently coagulated blood . .

89. Bowl of coagulated blood, after twelve hours

90. Head and gills of Menobranchus

91. Lung of frog . . . . .

92. Human larynx, trachea, bronchi, and lungs

PAGE

153

153

. .

154

. .

154

(Kolliker)

155

(Bernard)

172

(Bernard)

180

- (Frey)

180

.

180

181

. (Colin)

182

185

.

186

t

186

186

(Leydig)

189

(Boehm)

190.

.

190

.

192

.

193

f

193

(Kolliker)

194

.

195

198

202

.

202

(Eberth)

203

(Genth)

204

.

208

210

>lution

213

c solution

214

.

215

217

.

217

.

244

244

245

..

245

.

246

.

247

.

248

250

252

255

256

„

258

,

261

261

272

272

.

273

LIST OF ILLUSTRATIONS. XIX

FIG- PAGE

93. Single lobule of human lung ...... 274

94. Capillary bloodvessels in the pulmonary vesicles . . (Frey) 274

95. Diagram illustrating the movements of respiration . . . 275

96. Human larynx, in its post-mortem condition . . . .278

97. Human larynx, with the glottis opened .... 278

98. Human larynx, posterior view ...... 278

99. Diagram of the circulation in mammalians . . . .319

100. Human heart, anterior view . . . . . .319

101. Human heart, posterior view ...... 319

102. Eight auricle and ventricle ; ventricular valves open, arterial valves

closed ......... 320

103. Bight auricle and ventricle ; ventricular valves closed, arterial valves

open ......... 321

104. Course of the blood through the heart . . . . .321

105. Production of valvular sound by fibrous tension . . . 323

106. Bullock's heart, anterior view ; showing superficial fibres . . 325

107. Converging spiral fibres at the heart's apex . . . .325

108. Transverse section of the bullock's heart in cadaveric rigidity . 328

109. Left ventricle of bullock's heart ; showing deep fibres . . 328

110. Curvatures of an artery in pulsation . . . . .332

111. Curves of pulsation, in an elastic tube ..... 333

112. Trace of the radial pulse, taken by sphygmograph . . . 334

113. )

jj^ f Variations of the radial pulse, under the influence of temperature

115] ) (Marey) 335

116. Dicrotic pulse, in typhoid pneumonia . . . (Marey) 336

117. Dicrotic pulse, in typhoid fever . . . (Marey) 336

118. Chaveau's instrument, for measuring rapidity of arterial current . 339

119. Vein, with valves open ...... 342

120. Vein, with valves closed ...... 342

121. Small artery, breaking up into capillaries .... 344

122. Capillary bloodvessel ..... (Kolliker) 345

123. Capillary plexus, from web of frog's foot .... 346

124. Capillary circulation, in web of frog's foot .... 347

125. Diagram of the circulation ...... 353

126. Lymphatic vessels and glands, of the head, neck, and thorax (Mascagni) 357

127. Section of a lymphatic gland .... (Kolliker) 358

128. Longitudinal section through a mesenteric gland . (Kolliker) 358

129. Crystals of uric acid ; deposited from urine .... 385

130. Ferment-apparatus, for saccharine urine . . . .387

131. Crystalline masses of sodium urate ; deposited from urine . . 391

132. Crystals of lime oxalate ; deposited from urine . . . 394

133. Crystals of ammonio-magnesian phosphate ; deposited from urine . 396

134. Nerve fibres, from the sciatic nerve ..... 401

135. Nerve fibres, from white substance of the brain . . . 402

136. Division of a nervous branch into fibres .... 405

137. Inosculation of nerves ....... 405

138. Division of nerve fibres .... (Kolliker) 407

139. Terminal bulb of a sensitive nerve .... (Frey) 408

140. Tactile corpuscles, from tongue of the sparrow . . (Ihlder) 408

141. Termination of a nerve fibre, in muscle . . . (Rouget) 409

142. Nerve cells, from the medulla oblongata . . (Dean) 413

XX LIST OF ILLUSTRATIONS.

FIG. PAGE

143. Frog's leg, showing galvanization of the muscles .. . . 419

144. Frog's leg, showing galvanization of the nerve . . . 419

145. Frog's legs connected, showing action of direct and inverse currents . 421

146. Diagram of registering apparatus ..... 427

147. The brain and spinal cord, in profile ..... 433

148. Transverse section of the spinal cord ..... 434

149. Brain of alligator . . . . . . .436

150. Brain of pigeon ........ 437

151. Brain of rabbit . . . . . . .437

152. Medulla oblongata and base of the brain . . (Hirschfeld) 439

153. Medulla oblongata, tuber annulare, and crura cerebri (Hirschfeld) 440

154. Diagrammatic section of the human brain . . . . 441

155. Transverse section of the spinal cord ..... 444

156. Fissures and convolutions of the human brain .... 472

157. Horizontal section of the human brain .... 476

158. Vertical section of a cerebral convolution . . (Henle) 478

159. Portraits of idiotic children ...... 482

160. Pigeon, after removal of the cerebral hemispheres . .. . 483

161. Brain of the dog ; viewed from above . . . . . 489

162. Brain of the dog ; viewed in profile ..... 489

163. Section of the cerebellum and medulla oblongata . (Henle) 493

164. Brain of healthy pigeon, profile view ..... 497

165. Brain of operated pigeon, profile view .... 497

166. Brain of healthy pigeon, posterior view .... 497

167. Brain of operated pigeon, posterior view .... 497

168. Transverse section of medulla oblongata . . (Henle) 504

169. Section of cerebral hemisphere, showing olfactory tubercle (Henle) 514

170. Brain of the cod, showing optic nerves .... 519

171. Brain of the fowl, showing optic nerves .... 519

172. Course of the optic nerves, in man ..... 520

173. Nucleus of the trigerninus nerve . . . (Henle) 527

174. Diagram of the fifth nerve, and its distribution . . . 528

175. Nucleus of the abducens and facial nerves . . (Henle) 538

176. Diagram of the facial nerve, and its distribution . . . 541

177. Portrait of facial paralysis ...... 544

178. Facial nerve and connections, in the aqueduct of Fallopius . . 548

179. Ninth, tenth, and eleventh cranial nerves . . (Hirschfeld) 558

180. Section of medulla oblongata, through lower part of olivary body

(Henle) 575

181. Section of medulla oblongata, through middle root of olivary body

(Henle) 576

182. Section of medulla oblongata, through hypoglossal nerve root (Henle) 577

183. Sections of tuber annulare, medulla oblongata, and spinal cord . 580

184. Ganglia and nerves of the sympathetic system . . . 584

185. Cat, after section of the right sympathetic .... 588

186. Tactile corpuscle of the human skin . . . (Kolliker) 594

187. Diagram of tongue, with nerves and papillae .... 601

188. Distribution of nerves in the nasal passages . . ... 605

189. Horizontal section of the right eyeball . . . .608

190. Vision without a lens ....... 614

191. Vision with a lens ....... 614

192. Indistinct image, from excessive refraction .... 615

LIST OF ILLUSTRATIONS. XXI

PIG. PAGE

193. Indistinct image, from deficient refraction . . . 615

194. Rods and cones, of human retina . . . (Schultze) 618

195. Surface of the retina, showing ends of rods and cones (Helmholtz) 619

196. Diagram, for showing blind spot of the retina . . (Helmholtz) 621

197. Section of the retina, through macula lutea and fovea . (Schultze) 624

198. Section of the eyeball, showing direct and indirect vision . . 629

199. Catoptric images in the eye .... (Helmholtz) 632

200. Change of position in catoptric images during accommodation

(Helmholtz) 633

201. Vision for distant objects . . . . . .633

202. Yision for near objects ....... 633

203. Emmetropic eye, in vision at long distances . . (Wundt) 636

204. Myopic eye, in vision at long distances . . (Wundt) 636

205. Single and double vision, at different distances . . . 639

206. Skull, as seen by the left eye . . . . . .641

207. Skull, as seen by the right eye ...... 641

208. Eood's apparatus, for measuring duration of electric spark . . 644

209. Ossicles of the human ear .... (Rudinger) 650

210. Ossicles of the ear, in situ .... (Rudinger) 651

211. Bony labyrinth of the human ear ..... 655

212. Bony cochlea of the human ear . . . (Cruveilhier) 660

213. Organ of Corti . . . . . . .662

214. Cysticercus cellulosae ..... (Davaine) 673

215. Taenia solium ........ 674

216. Trichina spiralis ; encysted ...... 675

217. Infusoria, of various kinds . . (Ehrenberg and Stein) 676

218. Stylonychia mytilus ; unimpregnated and impregnated (Stein) 679

219. Cells of Bacterium termo ...... 680

220. Blossom of Ipomoea purpurea ; showing sexual apparatus . . 682

221. Single articulation of Taenia crassicollis .... 683

222. Human ovum ........ 685

223. Human ovum, ruptured by pressure ..... 686

224. Female generative organs of frog . . . . 687

225. Mature frog's eggs ...... . 688

226. Female generative organs of fowl ..... 690

227. Diagram of the fowl's egg ...... 691

228. Uterus and ovaries of the sow .... . 692

229. Generative organs of the human female .... 693

230. Spermatozoa ........ 696

231. Graafian follicle, near the period of rupture .... 707

232. Ovary with Graafian follicle ruptured ..... 707

233. Human Graafian follicle, ruptured during menstruation . 714

234. Corpus luteum of menstruation, three weeks old . . 715

235. Corpus luteum of menstruation, four weeks old . . . 716

236. Corpus luteum of menstruation, nine weeks old ... 716

237. Corpus luteum of pregnancy, two months old . . . . 718

238. Corpus luteum of pregnancy, four months old . . . . 718

239. Corpus luteum of pregnancy, at term ..... 719

240. Segmentation of the vitellus . . . . . . 722

241. Impregnated egg, with embryonic spot .... 724

242. Impregnated egg, in an early stage of development . • . . 725

243. Impregnated egg, at a more advanced period .... 725

XX11 LIST OF ILLUSTRATIONS.

FIG. PAGE

244. Frog's egg, in an early stage of development .... 726

245. Frog's egg, in process of development . . . . . 726

246. Frog's egg, farther advanced ...... 726

247. Tadpole, fully developed . 727

248. Tadpole, with limbs beginning to be formed . . . .728

249. Perfect frog ....... 728

250. Section of the blastoderm . . . (Foster and Balfour) 730

251. Blastoderm, separating into laminae .... (His) 735

252. Chick-embryo, in different stages of development . . (His) 736

253. Egg of fish, with umbilical vesicle ..... 738

254. Human embryo, with umbilical vesicle ..... 739

255. Fecundated egg, showing formation of the amnion . . . 740

256. Fecundated egg, farther advanced ..... 741

257. Fecundated egg, with allantois nearly complete . . . 741

258. Fecundated egg, with allantois fully formed .... 742

259. Human embryo and envelopes ; end of first month . . . 745

260. Human embryo and envelopes ; end of third month . . . 745

261. Compound villosity of the chorion ..... 747

262. Extremity of a villosity of the chorion ..... 748

263. Uterine mucous membrane ; unimpregnated uterus . . . 750

264. Uterine tubules ; unimpregnated uterus .... 750

265. Impregnated uterus ; formation of decidua vera . . . 752

266. Impregnated uterus ; formation of decidua reflexa . . . 752

267. Impregnated uterus; egg inclosed by decidua rcflexa . . . 752

268. Impregnated uterus ; connection of egg and decidua . . . 753
269-. Pregnant uterus ; formation of the placenta .... 754

270. FcEtal pig, with its membranes ...... 755

271. Cotyledon, from pregnant cow's uterus . . . . 756

272. Extremity of a fcetal tuft, from human placenta . . . 757

273. Extremity of a fcetal tuft, injected . . . . .758

274. Diagram of the placenta, in vertical section .... 759

275. Human embryo and its membranes ..... 763

276. Pregnant human uterus, at the seventh month . . . 764

277. Muscular fibres of the unimpregnated uterus . . 767

278. Muscular fibres of the uterus, ten days after parturition . . 767

279. Muscular fibres of the uterus, three weeks after parturition . . 768

280. Formation of the cerebro-spinal axis . . . . . 769

281. Formation of the cerebral vesicles ..... 770

282. Foetal pig, showing brain and spinal cord .... 770

283. Fcetal pig, farther advanced . . . . . .770

284. Head of foetal pig, showing hemispheres, cerebellum, and medulla oblon-

gata ......... 770

285. Brain of adult pig . . . . . . .771

286. Human embryo, one month old . . . . . . 774

287. Formation of the alimentary canal ..... 775

288. Foetal pig, showing umbilical hernia ..... 777

289. Human embryo, showing development of the face . . . 781

290. Head of human embryo, about the sixth week . . . 782

291. Head of human embryo, at end of second month . . , 782

292. Fcetal pig, showing Wolffian bodies ..... 784

293. Fcetal pig, showing Wolffian bodies and kidneys . . . 785

294. Internal organs of generation, in the fcetal pig . . . 786

LIST OF ILLUSTRATIONS. XX111

295. Internal organs of generation, in the total pig, farther advanced . 787

296. Formation of tunica vaginalis testis . . . • . 788

297. Congenital inguinal hernia ...... 788

298. Egg of fish, showing vitelline circulation .... 791

299. Diagram of the embryo, with umbilical vesicle and allantois . . 793

300. Diagram of the embryo, showing the placental circulation . .794

301. Venous system, in its earliest condition .... 797

302. Venous system, farther advanced ..... 798

303. Venous system, more fully developed ..... 798

304. Venous system, adult condition . . ... . 799

305. Early form of the hepatic circulation ..... 799

306. Hepatic circulation, farther advanced ..... 800

307. Hepatic circulation, in latter part of foetal life . . .801

308. Hepatic circulation, adult condition ..... 801

309. Foetal heart, earliest form ...... 802

310. Fcetal heart, bent upon itself ...... 802

311. Foetal heart, divided into right and left cavities . . . 802

312. Foetal heart, farther advanced ... 802

313. Heart of infant ..... .803

314. Heart of human foetus, at sixth month . . . 804

315. Diagram of foetal circulation through the heart . , . 805

316. Diagram of adult circulation through the heart . . . 808

HUMAN PHYSIOLOGY.

INTEODUCTIOlSr.

THE study of Physiology* embraces all the active phenomena pre-
sented by living beings — such as growth, reproduction, movement,
sensation, the chemical changes manifested in the body during life, as
well as its action upon external substances and its dependence upon
external conditions.

Living bodies are distinguished, as regards their structure, from
those of the inorganic world mainly by the fact that they are organized ;
that is, they are composed of a number of different parts, or organs,
connected with each other and mutually dependent. In all the higher
orders, both of animals and plants, these various organs belonging to
the same body are quite numerous, and are very different from each
other both in their structure and properties.

In an animal, for example, there is an external integument covering
the surface of the body, bones which form a framework for the protection
and attachment of other parts, muscles by which the limbs are put in
motion, an alimentary canal for the digestion of the food, and various
glands for the secretion of the animal fluids. In a plant there are roots
which absorb the ingredients of the soil, leaves which elaborate the
vegetable juices, and the various parts of the blossom which are con-
cerned in the production of the fruit. Thus each different organ has a
special structure, and plays a distinct part in the living organism.

The peculiar action or result accomplished in this way l>y a particular
organ is called its function. There are, therefore, a variety of functions
going on in the living body, each one as distinct as the organ by which
it is performed. But no one of them is entirely independent of the rest.
The circulation of the blood, which is carried on by the organs of the
vascular system, requires that the blood should be incessantly renovated
by the process of respiration in order that it may continue undisturbed ;
and the circulation is in its turn necessary to the functions of secretion
and nutrition, for which it supplies the necessary material to all parts
of the body. Thus all the different functions are in a state of mutual
dependence, and the life of the whole body is a result of the simultaneous
and harmonious action of its different parts.

3 ( 25 )

26 INTRODUCTION.

The only method by which physiology can be studied is the observa-
tion of nature. The phenomena presented by living creatures are only
to be learned by direct examination, and cannot be inferred, by any
process of reasoning, from any other facts of a different character.
Even a knowledge of the minute structure of a part, however exact,
cannot furnish any information as to its active properties or function ;
and these properties can be learned only by examining the organ when
it is in a state of activity. Thus the muscular fibre and the nervous
fibre present certain well-defined characters of minute structure which
are easily distinguished by anatomical examination, but which could
not teach us anything of their physiological properties ; while direct
experiment shows that the muscular fibre is contractile and the nervous
fibre excitable or sensitive.

Since the vital phenomena of the entire body result from the com-
bined activity of its different parts, th«se different parts should be
studied by themselves in order to ascertain their particular properties.
This can be done by examination and experiment for each part while it
still retains its vital powers. Experience shows that after the circula-
tion has ceased, and consciousness and volition have disappeared, many
minute portions of the body continue for a time capable of manifesting
their physiological action. Thus a muscular fibre, separated from the
remaining tissues, may still be made to contract under the appropriate
stimulus; and a nerve, though cut off from its connection with the
brain, may also be called into activity by mechanical or electrical
irritation. This is because each part retains its physiological powers
so long as it retains its peculiar structure and constitution. The
general functions of the body, such as the circulation, digestion, and
respiration, have for their object to provide for the nutrition of the
tissues and organs, and thus maintain their natural constitution unim-
paired. Their cessation, accordingly, does not instantly destroy the
vitality of particular parts, but only after a sufficient time has elapsed
to alter or impair their natural constitution. The time during which
the vital powers may thus be retained varies* for different parts. Thus
the muscular fibre is capable of manifesting its excitability, as a general
rule, longer than the nervous fibre, and the nervous fibre longer than
the gray matter of a nervous ganglion. There is, also, a difference in
the same part shown by different kinds of animals. The excitability of
both nervous and muscular tissues continues longer in the cold-blooded
than in the warm-blooded animals, and in the quadrupeds longer than in
birds. In every instance, of course, the examination of such an isolated
part of the body should be made while it still preserves its physiological
properties.

On the other hand, the functions of entire organs, or the general
functions of the body as a whole, can only be studied with success
while life is going on. The anatomical relations of the various organs
may be learned by dissection after death ; but their vital actions are
not to be ascertained in this way, because they have ceased and cannot

INTRODUCTION. 27

again be put in operation. The most important facts have often
remained long unknown or misunderstood for this reason. The earlier
anatomists supposed that, the arteries were tubes for the circulation of
air, because they appeared empty when opened after death. It was
only when Galen exposed the artery of a living animal, and, opening it
between two ligatures, showed it to be full of blood, that the true func-
tion of these vessels was ascertained. The lacteal and lymphatic vessels
were discovered in the seventeenth century ; but from their small size,
and the small amount of fluid contained in them, the circulation in the
lymphatic system was thought to be very limited in quantity. Two
hundred years afterward, when the experiment was performed of
introducing a canula into the thoracic duct of the living animal and
continuing the observation while digestion and absorption were going
on, the experimenters obtained, in horses and oxen, from fifty to one
hundred pounds of lymph and chyle during twenty-four hours ; thus
demonstrating the existence of a vital activity much greater than could
have been suspected from any examination of the dead bod}^.

The observation of the physiological actions during life usually re-
quires the employment of certain contrivances and manipulations in
order to arrive at accurate results. Even the more superficial phe-
nomena, such as the changes in the air produced by respiration, can
only be studied with precision *by the aid of artificial means for meas-
uring and examining the various gases absorbed or discharged. The
processes going on in the internal organs are more especially concealed
from view, and, therefore, need for their study the use of instruments
and operations in order to bring them under observation. It is accord-
ingly necessary, in the large majority of cases, to resort to experiment*
upon animals in the study of physiology, and all the important
knowledge thus far gained has been acquired in this way. But as the
physiology of the human species is the main object of our study, and
as each different species of animals presents certain peculiarities which
distinguish it from others, it becomes essential to know how far we can
apply the results derived from experiment upon one species to the
physiology of the others, or to that of the human body itself.

All animals present certain general phenomena in common, namely,
those of nutrition, secretion, absorption, movement, and reproduc-
tion. The vertebrate animals, to which class man belongs,, are fur-
thermore constructed upon the same general plan of organization, and
their corresponding organs are evidently the same in character. The
different parts of their nervous and vascular systems, their digestive
apparatus, their organs of locomotion, of secretion, excretion, and
reproduction, have the same relative position, and can be easily recog-
nized and compared with each other. The ingredients of their solids
and fluids have the same or a similar chemical constitution, and play a
corresponding part in the vital processes. The coloring matter of the
blood is identical in all of them ; they all absorb oxygen and exhale
carbonic acid with more or less activity ; and many or most of their

28 INTRODUCTION.

secretions and excretions have the same physiological character. The
whole value of physiological experiment, as applied to different species,
depends upon this general resemblance between them, both of structure
and function.

On the other hand, the differences between species of vertebrate ani-
mals consist only in the relative size and development of particular
parts, and consequently in the relative importance of particular func-
tions. The intestine, for example, is longer and more complicated in
the herbivorous animals, shorter and simpler in the carnivora. The
muscles of the external ear are slightly developed and powerless in the
human subject, large and active in many of the inferior species. Fish
and reptiles produce but little animal heat, and are, therefore, called
cold-blooded animals ; birds and quadrupeds generate it in abundance,
and are therefore called warm-blooded. The differences between them
are, therefore, almost invariably differences in degree and not in kind.

Consequently the simple and direct result of an experiment in different
animals is the same, or varies only in degree. If we deprive an animal
of oxygen, whatever the species may be, it produces death invariably and
in the same way, because in all this element is essential to the nourish-
ment of the tissues. But death will take place rapidly in birds or
quadrupeds, more slowly in reptiles, because the vital changes are more
active in the former than in the latter. Division of the spinal cord in
all cases produces immediate paralysis of sensation and voluntary
motion in the parts below, showing that the sensitive and motor fibres
follow in all the same route and possess the same nervous endowments.
Experiments accordingly of the same kind, performed upon different
animals, have a direct result which is the same in character.

But experiments have often also certain indirect or secondary results,
dependent upon the relative importance of associated organs, and these
vary considerably in different kinds of animals. Thus division or dis-
ease of the facial nerve in all instances causes a direct paralysis of the
muscles of the face. In the human subject this produces only a loss of
expression, with some inconvenience in the retention of fluids by the
mouth. But in the horse it is followed by a partial suffocation, because
in him the expansion of the nostrils is an important part of the move-
ments of respiration. While the direct effect of an experiment, there-
fore, is always the same, its indirect effect varies with the comparative
development of different parts. It is evident, however, that this varia-
tion does not impair the value of experiment as a means of study, but,
on the contrary, enlarges its usefulness and leads to the acquisition of
greater knowledge by its means.

The physiological actions of living beings are, of course, dependent
upon natural causes, and are to be studied in a similar manner with
other natural phenomena, such as those of magnetism, gravitation,
chemical affinity, and the like. In all these cases, we observe the
character of the phenomenon, the conditions upon which it depends,
the mechanism of its production, and the quantities of force or material

INTRODUCTION. 29

expended in its manifestation. The study of physiology, therefore,
requires a certain knowledge of the chemical and physical reactions
presented in the outer world, in order that the observer may be able to
appreciate the peculiarities of similar phenomena as they occur in the
living body. As all animated beings are closely dependent on external
conditions for the maintenance of their vitality, it is evident that the
study of their vital actions cannot be disconnected from that of external
natural phenomena. The pressure and tension of the atmosphere, for
example, as well as its chemical constitution, are directly connected with
the process of respiration ; and the circulation of the blood through the
vessels exhibits the physical phenomena of an incompressible fluid flow-
ing through elastic tubes.

By the term vital phenomena, accordingly, we mean those phenomena
which are manifested in the living body, and which are characteristic of
its functions. At the same time many of them do not differ in character
from those of the outside world, but only in the peculiarity of their
conditions and their results.

Some of these phenomena are physical or mechanical in their charac-
ter ; as, for example, the play of the articulating surfaces upon each
other, the balancing of the spinal column with its appendages, the action
of the elastic ligaments. Nevertheless, these phenomena, though strictly
physical in character, are often entirely peculiar and different from those
seen elsewhere, because the mechanism of their production is peculiar in
its details. Thus the human Voice and its modulations are produced in
the larynx, in accordance with the general physical laws of sound ; but
the arrangement of the elastic and movable vocal chords, and their
relations with the columns of air above and below, the moist and flexi-
ble mucous membrane, and the contractile muscles outside, are of such
a special character that the entire apparatus, as well as the sounds pro-
duced by it, is peculiar ; and its action cannot be properly compared
with that of any other known musical instrument.

In the same manner, the movements of the heart are so complicated
and remarkable that they cannot be comprehended, even by one who is
acquainted with the anatoniy of the organ, without a direct examination.
This is not because there is anything essentially obscure or mysterious
in their nature, for they are purely mechanical in character ; but because
their conditions are so peculiar, owing to the tortuous course of the
muscular fibres, their arrangement in interlacing layers, their attach-
ments and relations, that their combined action produces an effect alto-
gether peculiar, and one which is not similar to anything outside the
living body.

A very large and important class of the vital phenomena are those of
a chemical character. It is one of the characteristics of living bodies
that a succession of chemical actions, combinations, and decompositions,
is constantly going on in their interior. It is one of the necessary con-
ditions of the existence of every animal and every vegetable, that it
should constantly absorb various substances from without, which under-

30 INTRODUCTION.

go different chemical alterations in its interior, and are finally discharged
from it under other forms. If these changes be prevented from taking
place, life is immediately extinguished. Thus animals constantly absorb,
on the one hand, water, oxygen, salts, albumen, oil, sugar, etc., and give
up, on the other hand, to the surrounding media, carbonic acid, water,
creatine, the urates, urea, and the like ; while between these two extreme
points, of absorption and exhalation, there take place a multitude of
different transformations which are essential to the continuance of life.

Some of these chemical actions are the same with those which are
seen outside the body ; but most of them are peculiar, and do not take
place anywhere else. This, again, is not because there is anything excep-
tional in their nature, but because the conditions necessary for their
accomplishment exist in the body, and do not exist elsewhere. All
chemical phenomena are liable to be modified by surrounding conditions.
Many reactions which will take place at a high temperature will not
take place at a low temperature, and vice versa. Some will take place
in the light, but not in the dark ; others will take place in the dark, but
not in the light. Because a chemical reaction, therefore, takes place
under one set of conditions, we cannot be at all sure that it will take
place under others which are different.

The chemical conditions of the living body are exceedingly compli-
cated. In the animal solids and fluids, there are many substances
mingled together in varying quantities, which modify or interfere with
each other's reactions. New substances are constantly entering by
absorption, and old ones leaving by exhalation; while the circulating
fluids are incessantly passing from one part of the body to another,
and coming in contact with different organs of different texture and
composition. All these conditions are peculiar, and so modif}^ the
chemical actions taking place in the body that they are often unlike
those met with elsewhere.

If starch and iodine be mingled together in a watery solution, they
unite with each other, and strike a deep blue color; but if they be
mingled in the blood, no such reaction takes place, because it is pre-
vented by the presence of certain organic substances which interfere
with it.

If dead animal matter be exposed to warmth, air, and moisture, it
putrefies; but if introduced into the living stomach, this process is pre-
vented, because the fluids of the stomach cause the animal substance to
undergo a peculiar transformation (digestion), after which the blood-
vessels immediately remove it by absorption. There are also certain
substances which make their appearance in the living body of animals
or vegetables, and which are not found elsewhere ; such as fibrine, albu-
men, caseine, the biliary salts, hemoglobine, chlorophyll, morphine, etc.
These substances cannot be manufactured artificially, simply because
we are unable to imitate the necessary conditions. They require for
their production the presence of a living organism.

The chemical phenomena of the living body are, therefore, not different

INTRODUCTION. 31

in their nature from any other chemical phenomena; but they are often
different in their conditions and in their results, and are consequently
peculiar and characteristic.

Another set of vital phenomena are those whiph are manifested in the
processes of reproduction and development. They are entirely distinct
from any phenomena which are exhibited by matter not endowed with
life. An inorganic substance, even when it has a definite form, as, for
example, a crystal of fluor spar, has no particular relation to any similar
form which has preceded, or any other which is to follow it. On the
other hand, every animal and every vegetable owes its origin to pre-
ceding animals or vegetables of the same kind; and the manner in
which this production takes place, and the different forms through
which the new body successively passes in the course of its develop-
ment, constitute the phenomena of reproduction. These phenomena
are mostly dependent on the chemical processes of nutrition and growth,
which take place in a particular direction and in a particular manner ;
but their results, namely, the production of a connected series of different
forms, constitute a separate class of phenomena, which cannot be ex-
plained in any manner by the preceding, and require, therefore, to be
studied by themselves.

Another set of vital phenomena are those which belong to the nervous
system. These, like the processes of reproduction and development,
depend on the chemical changes of nutrition and growth. That is to
say, if the nutritive processes did not go on in a healthy manner and
maintain the nervous system in a healthy condition, the peculiar phe-
nomena which are characteristic of it could not take place. The nutri-
tive processes are necessary conditions of the nervous phenomena. But
there is no other connection between them ; and the nervous phenomena
themselves are distinct from all others, both in their nature and in the
mode in which they are to be studied.

The study of Physiology is naturally divided into three distinct Sec-
tions : —

I. The first of these includes everything which relates to the NUTRI-
TION of the body in its widest sense. It comprises the history of the
proximate principles, their source, the manner of their production, the
proportions in which they exist in different kinds of food and drink, the
processes of digestion and absorption, and the constitution of the circu-
lating fluids ; then, the physical phenomena of the circulation and the
forces by which it is accomplished ; the changes which the blood under-
goes in different parts of the body ; all the phenomena, both physical
and chemical, of respiration; those of secretion and excretion, and the
character and destination of the secreted and excreted fluids. All these
processes have reference to a common object, namely, the preservation of
the normal structure and organization of the individual. Their results
cprnprise the phenomena of internal growth and nutrition, which are
common to the animal and vegetable kingdoms; and they are accord-
ingly known by the name of the vegetative functions.

32 INTRODUCTION.

II. The second Section, in the natural order of study, is devoted to
the phenomena of the NERVOUS SYSTEM. These phenomena are not
exhibited by vegetables, but belong exclusively to animal organizations.
They bring the animal body into relation with the external world, and
preserve it from external dangers, by means of sensation, movement,
consciousness, and volition. They are more particularly distinguished
by the name of the animal functions.

III. Lastly comes the study of the entire process of REPRODUCTION.
Its phenomena, again, with certain modifications, are met with in both
animals and vegetables ; and might, therefore, with some propriety, be
included under the head of vegetative functions. But their distinguish-
ing peculiarity is, that they have for their object the production of new
organisms, which take the place of the old and remain after they have
disappeared. These phenomena do not, therefore, relate to the preserva-
tion of the individual, but to that of the species ; and any study which
concerns the species comes properly after we have finished everything
relating to the individual.

SECTION I.
NUTRITION.

CHAPTEE I.

PROXIMATE PRINCIPLES IN GENERAL.

THE study of NUTRITION begins naturally with that of the proximate
principles, or the substances entering into the composition of the dif-
ferent parts of the body, and the different kinds of food. In examining
the body, the anatomist finds that it is composed, first, of various parts,
which are easily recognized by the eye, and which occupy distinct situa-
tions. In the case of the human body, for example, a division is easily
made of the entire frame into the head, neck, trunk, and extremities.
Each of these regions, again, is found, on examination, to contain several
distinct parts, or "organs," which require to be separated from each
other by dissection, and which are distinguished by their form, color,
texture, and consistency. In a single limb, for example, every bone and
every muscle constitutes a distinct organ. In the trunk, we have the
heart, the lungs, the liver, spleen, kidneys, spinal cord, etc., each of
which is also a distinct organ. When a number of organs, differing in
size and form, but similar in texture, are found scattered throughout
the entire frame, or a large portion of it, they form a connected set or
order of parts, which is called a " system." Thus, all the muscles taken
together constitute' the muscular system ; all the bones, the osseous
system ; all the arteries, the arterial system. Several entirely different
organs may also be connected with each other, so that their associated
actions tend to accomplish a single object, and they then form an
" apparatus." Thus the heart, arteries, capillaries, and veins, together,
form the circulatory apparatus ; the stomach, liver, pancreas, intestines,
etc., the digestive apparatus. Every organ, again, on microscopic ex-
amination, is seen to be made up of minute bodies, of definite size and
figure, which are so small as to be invisible to the naked eye, and which,
after separation from each other, cannot be further subdivided without
destroying their organization. They are, therefore, called " anatomical
elements." Thus, in the liver, there are hepatic cells, capillary blood-
vessels, the fibres of Glisson's capsule, and the ultimate filaments of the

(33)

34 PROXIMATE PRINCIPLES IN GENERAL.

hepatic nerves. Lastly, two or more kinds of anatomical elements
interwoven with each other in a particular manner form a "tissue."
Adipose vesicles, with capillaries and nerve filaments, form adipose
tissue. White fibres, elastic fibres, and connective-tissue cells, with
capillary bloodvessels and nerve filaments, form connective tissue. Thus
the solid parts of the entire body are made up of anatomical elements,
tissues, organs, systems, and apparatuses. Every organized frame, and
even every apparatus, every organ, and every tissue, is made up of dif-
ferent parts, variously interwoven and connected with each other, and
it is this character which constitutes its organization.

But beside the above solid forms, there are also certain fluids, which
are constantly present in various parts of the body, and which, from
their peculiar constitution, are termed " animal fluids." These fluids
are just as much an essential part of the body as the solids. The blood
and the lymph, for example, the pericardial and synovial fluids, the
saliva, which always exists more or less abundantly in the ducts of the
parotid gland, the bile in the biliary ducts and the gall-bladder : all
these go to make up the entire body, and are quite as necessary to its
physiological structure as the muscles or the nerves. Now, if these
fluids be examined, they are found to be made up of many different sub-
stances, which are mingled together in certain proportions ; these pro-
portions being constantly maintained at or about the same standard by
the natural processes of nutrition. Such a fluid is termed an organized
fluid. It is organized by virtue of the numerous ingredients which
enter into its composition, and the regular proportions in which these
ingredients are maintained. Thus in the plasma of the blood, we have
albumen, fibrine, water, chlorides, carbonates, and phosphates. In the
urine, we find water, urea, sodium urate, creatinine, coloring matter, and
salts. These substances, which are mingled together so as to make up,
in each instance, by their intimate union, a homogeneous liquid, are
called the PROXIMATE PRINCIPLES of the animal fluid.

In the solids, furthermore, even in those parts which are apparently
homogeneous, there is a similar mixture of various ingredients. In the
hard' substance of bone, for example, there is, first water, which may be
expelled by evaporation ; second, lime phosphate and carbonate, which
may be extracted by the proper solvents ; third, a peculiar animal matter,
with which these calcareous salts are in union ; and fourth, various other
saline substances, in special proportions. The muscular tissue contains
water, sodium and potassium chlorides, lime phosphate, creatine, vari-
ous forms of albumen, and an animal matter termed myosine. The
difference in consistency between the solids and fluids does not, there-
fore, indicate any radical difference in their constitution. Both are
equally made up of proximate principles, mingled together in various
proportions.

It is important to understand, however, exactly what are proximate
principles, and what are not such; for since these principles are ex-
tracted from the animal solids and fluids, and separated from each

PROXIMATE PRINCIPLES IN GENERAL. 35

other by the help of certain chemical manipulations, such as evapora-
tion, solution, crystallization, and the like, it might be supposed that
every substance which could be extracted from an organized solid or
fluid, by chemical means, should be considered as a proximate princi-
ple. That, however, is not the case. A proximate principle is properly
defined to be any substance, whether simple or compound, chemically
speaking, which exists, under its own form, in the animal solid or fluid,
and which can be extracted by means which do not alter or destroy its
chemical properties. Lime phosphate, for example, is a proximate
principle of bone, but phosphoric acid is not so, since it does not exist
as such in the bony tissue, but is produced only by the decomposition
of the calcareous matter ; still less phosphorus, which is obtained only
by the decomposition of the phosphoric acid.

Proximate principles may, in fact, be said to exist in all solids or
fluids of mixed composition, and may be extracted from them by the
same means as in the case of the animal tissues or secretions. Thus, in
a watery solution of sugar, we have two proximate principles, namely:
first, the water, and secondly, the sugar. The water may be separated
by evaporation and condensation, after which the sugar remains behind,
in a crystalline form. These two substances have, therefore, been sim-
ply separated from each other by the process of evaporation. They
have not been decomposed, nor their chemical properties altered. On
the other hand, the hydrogen and oxygen of the water were not proxi-
mate principles of the original solution, and did not exist in it under
their own forms, but only in a state of combination; forming, in this
condition, a fluid substance (water), endowed with sensible properties
entirely different from theirs. If we wish to ascertain, accordingly, the
nature and properties of a saccharine solution, it will afford us but
little satisfaction to extract its ultimate chemical elements; for its
nature and properties depend not so much on the presence in it of the
ultimate elements, oxygen, hydrogen, and carbon, as on the particular
forms of combination, namely, water and sugar, under which they are
present.

It is very essential, therefore, that in extracting the proximate prin-
ciples from the animal body, only such means should be adopted as will
isolate the substances already existing in the tissues and fluids, without
decomposing them, or altering their nature. A neglect of this rule
would lead to erroneous results in the pursuit of physiological chemis-
try; for by subjecting the animal tissues to the action of acids and
alkalies, of prolonged boiling, or of too intense heat, we might obtain,
at the end of the analysis, substances which would not be, properly
speaking, proximate principles, but only the remains of an altered and
disorganized material. Thus, the fibrous tissues, if boiled steadily for
thirty-six hours, dissolve, for the most part, at the end of that time,
in the boiling water; and on cooling the whole solution solidifies into a
homogeneous, jelly-like substance, which has received the name of
gelatine. But this gelatine does not really exist in the body as a

36 PROXIMATE PRINCIPLES IN GENERAL.

proximate principle, since the fibrous tissue which produces it is not at
first soluble, even in boiling water, and its ingredients become altered
and converted into a gelatinous matter only by prolonged ebullition.
So, again, an animal substance containing the alkaline acetates or lac-
tates will, upon incineration in the air, yield carbonates of the same
bases, the original acid having been destroyed, and replaced by car-
bonic acid. In either case, the analysis of the tissue, so conducted,
would be a deceptive one, and useless for anatomical and physiological
purposes, because its real ingredients have been decomposed, and re-
placed by others, in the process of manipulation.

It should, therefore, be kept constantly in view, in the examination
of an animal tissue or fluid, that the object of the operation is simply
the separation of its ingredients from each other, and not their decom-
position or ultimate analysis. Only the simplest forms of chemical
manipulation, if possible, should be employed. The substance to be
examined should first be subjected to evaporation, in order to extract
and estimate its water. This evaporation must be conducted at a heat
not above 100° (212° p.), since a higher temperature would destroy or
alter some of the animal ingredients. Then, from the dried residue,
sodium chloride, alkaline sulphates, carbonates, and phosphates may be
extracted with water. Coloring matters may be separated by alcohol,
and oils may be dissolved out by ether. When a chemical decomposi-
tion is unavoidable, it must be kept in sight and afterward corrected.
Thus the sodium glyko-cholate of the bile is separated from certain
other ingredients by precipitating it with plumbic acetate, forming lead
glyko-cholate; but this is afterwards decomposed, in its turn, by sodium
carbonate, reproducing the original sodium glyko-cholate. Sometimes
it is impossible to extract a proximate principle in an entirely unaltered
form. Thus the fibrine of the blood can be separated only by allowing
it to coagulate ; and once coagulated, it is permanently altered, and no
longer presents its original characters as an ingredient of the blood.
•In such instances as this, we can only make allowance for an unavoid-
able difficulty, and endeavor by other means to ascertain under what
form the substance originally existed in the animal fluids, being careful
that the substance suffers no further alteration. By bearing in mind
the above considerations, we may form a tolerably correct estimate of
the nature and quantity of all the proximate principles in the tissue or
fluid under examination.

The manner in which the proximate principles are associated to-
gether is also deserving of notice. In every animal solid and fluid,
there is a considerable number of proximate principles which are
present in certain proportions, and which are so united with each other
that the mixture presents a homogeneous appearance. But this union
is of a complicated character ; and the presence of each ingredient de-
pends, to a certain extent, upon that of the others. Some- of them,
such as the alkaline carbonates and phosphates, are in solution directly
in the water. Some, which are insoluble in water, are retained in solu-

PROXIMATE PRINCIPLES IN GENERAL. 37

tion by the presence of other soluble substances. Thus, the insoluble
lime phosphate of the urine is held in solution by the acid reaction of
the sodium biphosphate, which is also present as an ingredient. In the
alkaline blood-plasma, on the other hand, the lime phosphate is lique-
fied by union with the albumen, which is itself soluble in the water of
the plasma. The same substance may be fluid in one part of the body,
and solid in another part. Thus in the blood and secretions the water
is fluid, and holds in solution other substances, both animal and mine-
ral, while in the, bones and cartilages it is solid — not crystallized, as in
ice, but amorphous and solid, by the fact of its intimate union with the
animal and saline ingredients, which are abundant in quantity, and
which are themselves present in the solid form. Again, the lime phos-
phate of the blood is fluid by solution in the albumen; but in the bones
it forms a solid substance with the animal matter of the osseous tissue ;
and yet the union of the two is as intimate and homogeneous in the
bones as in the blood. A proximate principle, therefore, never exists
alone in any part of the body, but is always intimately associated with
a number of others, by a kind of homogeneous mixture or mutual solu-
tion.

Every animal tissue and fluid contains a number of proximate prin-
ciples which are present, as we have already mentioned, in certain
characteristic proportions. Thus, water is present in very large quan-
tity in the perspiration and the saliva, but in very small quantity in
the bones and teeth. Sodium chloride is comparatively abundant in
the blood and deficient in the muscles. On the other hand, potassium
chloride is more abundant in the muscles, less so in the blood. But
these proportions are nowhere absolute or invariable. There is a great
difference, in this respect, between the chemical composition of an inor-
ganic substance and the physiological constitution of an animal fluid.
The former is always constant and definite ; the latter always presents
certain variations. Thus, water is always composed of exactly the
same relative quantities of hydrogen and oxygen ; and if these propor-
tions be altered in the least, it thereby ceases to be water, and is con-
verted into some other substance. But in the urine, the proportions
of water, urea, urates, phosphates, etc., vary within certain limits in
different individuals, and even in the same individual, from one hour
to another. This variation, which is almost constantly taking place,
within the limits of health, is presented by all the animal solids and
fluids. It is even a necessary accompaniment of the actions of life, and
one of the characteristic phenomena of living beings. For all parts of
the body are composed of different ingredients which are supplied by
absorption or formed in the interior, and which are constantly given
up again, under the same or different forms, to the surrounding media
by the unceasing activity of the vital processes. Every variation, then,
in the general condition of the body, as a whole, is accompanied by a
corresponding variation, more or less pronounced, in the constitution
of its different parts. This constitution is consequently of a very dif-

38 PROXIMATE PRINCIPLES IN GENERAL.

ferent character from the chemical constitution of an oxide or a salt.
Whenever, therefore, we meet with the analysis of an animal fluid, in
which the relative quantity of its different ingredients is expressed in
numbers, we must understand that such an analysis is always approxi-
mative, and not absolute.

The proximate principles are naturally divided into five different

The first of these classes comprises all the proximate principles which
are purely INORGANIC in their nature. These principles are derived
mostly from the exterior. They are found everywhere, in the inorganic
world as well as in organized bodies ; and they present themselves under
the same forms and with the same properties in the interior of the
animal frame as elsewhere. They are crystallizable, and they present
very definite chemical characters and have a comparatively simple chemi-
cal constitution. They are compounds, in simple proportions, of the
ultimate chemical elements, hydrogen and oxygen, the metals of the
alkaline and earthy salts, sulphur, phosphorus, chlorine, and, in general
terms, of the ingredients of mineral substances. They comprise water,
which is the most abundant of its class in the animal frame, sodium
and potassium chlorides, phosphates, and sulphates, alkaline carbonates,
the salts of lime and magnesia, together with combinations of a few
other of the metallic elements in minute quantity.

The second class of proximate principles consists of the HYDROCAR-
BONACEOUS SUBSTANCES of organic origin. They are distinguished from
inorganic matters first by the fact of their containing carbon in large
proportion as one of their immediate constituents, associated always
with hydrogen and oxygen, but with no other chemical element. They
are always either crystallizable, or else readily convertible into other
crystallizable members of the same group. Their chemical composition
is less simple than that of inorganic substances, but it is still sufficiently
definite, and their chemical characters are well marked and easily recog-
nizable. They first make their appearance in the interior of organized
bodies, and are not found in the inorganic world, excepting as the
remains or products of animal or vegetable life. To this group belong
the several varieties of starch, sugar, and oil.

The third class comprises the ALBUMINOUS, or nitrogenized proximate
principles. These substances derive their name from the albumen or
white of egg, which was one of the earliest to be studied, and which
was long considered as a kind of representative of the whole class.
They differ from the substances of the two preceding groups, especially
in the fact that they contain nitrogen as an ingredient, in addition to
the three elements of the hydrocarbonaceous matters. They are exclu-
sively of organic origin, appearing only as ingredients of the living bod}T.
Their chemical constitution, furthermore, is a complicated one — that is,
their four elements are united with each other in such a way as to form
compounds of a very high atomic weight. Their chemical characters

PROXIMATE PRINCIPLES IN GENERAL. 39

are not well defined, as compared with those of inorganic substances,
and their most striking properties are not such as can be accounted
for by ordinary chemical reactions or expressed in the usual chemical
phraseology. Nevertheless, they are of the first importance as ingredi-
ents of the organized frame, since they form a large proportion of its
mass, and contribute, by their peculiar properties, to its most essential
and characteristic active phenomena. They include such substances as
albumen, fibrine, caseine, and myosine.

The fourth class is formed by the COLORING MATTERS. These sub-
stances, upon which the different tints of the solids and fluids depend,
are present, for the most part, in small quantity, the most abundant
being the red coloring matter of the blood.

Lastly, in the fifth class are comprised a group of CRYSTALLIZABLE
NITROGENOUS MATTERS, many, if not all, of which are derived from the
physiological metamorphosis of albuminous principles. They are found
in some of the solid tissues, as the brain and nerves, in the secretions
of the liver, and especially in the urine, where they represent the pro-
ducts of excretion.

CHAPTEE II.

INORGANIC PROXIMATE PRINCIPLES.

THE inorganic substances are present in the animal body in great
variety. Some of them, such as water arid the salts of lime, constitute
also a large proportion of the mass of the tissues and fluids in which
they are found ; others present themselves in comparatively small
quantity. Some of them are found universally in all regions of the
body, while others are met with only in particular tissues or fluids ; but
there are hardly any which do not appear at the same time as con-
stituents of several different parts. As their name indicates, these
substances are met with extensively in the inorganic world, and form a
large part of the crust of the earth. Notwithstanding, however, their
inorganic nature, they are also essential constituents of the animal
frame. They are accordingly necessary ingredients of the food and
drink, and no regimen would be capable of supporting life indefinitely
which did not contain these materials in due proportion.

The group of inorganic proximate principles includes the following
substances : —

Water ; Potassium phosphate ;

Sodium chloride ; Potassium sulphate ;

Sodium phosphate ; Potassium carbonate ;

Sodium biphosphate ; Lime phosphate ;

Sodium sulphate ; Lime carbonate ;

Sodium carbonate ; Magnesium phosphate ;

Potassium chloride ; Magnesium carbonate.

Beside the above-named proximate principles there are found, as
constant ingredients of the incombustible residue of various parts of
the human body, iron, silica, and fluorine ; but it is not certainly known
in what form of combination these substances originally existed in the
animal solids and fluids. Sometimes, but not always, there are indica-
tions of the presence, in minute quantity, of copper, manganese, and
lead, also in some unknown forms of combination.

The most important of the inorganic proximate principles, considered
in regard to their quantity or the part which they play in the vital
actions, are the following : —

1. Water, H20.

Water is universally present in all the tissues and fluids of the body.
It is abundant in the blood and secretions, where its presence is indis-
(40)

WATER. 41

pen sable in order to give them the fluidity which is necessary to the
performance of their functions ; for it is by the blood and secretions
that new substances are introduced into the body, and old ingredients
discharged. And it is a necessary condition both of the introduction
and discharge of substances naturally solid, that they assume, for the
time being, a fluid form ; water is therefore an essential ingredient of
the fluids, for it holds their solid materials in solution, and enables them
to pass and repass through the animal frame.

But water is an ingredient also of the solids. For if we take a muscle
or a cartilage, and expose it to a gentle heat in dry air, it loses water
by evaporation, diminishes in size and weight, and becomes dense and
stiff. Even the bones and teeth lose water by evaporation in this way,
though in smaller quantity. In all these solid and semi-solid tissues,
the water which they contain is useful by giving them the special con-
sistency which is characteristic of them, and which would be lost without
it. Thus a tendon, in its natural condition, is white, glistening, and
opaque ; and though very strong, perfectly flexible. If its water be
expelled by evaporation it becomes yellowish in color, shrivelled, semi-
transparent, inflexible, and unfit for performing its mechanical functions.
The same thing is true of the other tissues, such as that of the skin, the
muscles, the cartilages, and the glands.

The following is a list, compiled by Robin and Yerdeil from various
observers, showing the proportion of water per thousand parts, in dif-
ferent solids and fluids : —

QUANTITY OF WATER IN 1000 PARTS IN

Teeth . . . .100 Bile. . .880

Bones . . . .130 Milk . . . . 887

Cartilage . . . 550 Pancreatic juice . . 900

Muscles . . . .750 Urine . . . .936

Ligaments . . . 768 Lymph .... 960

Brain .... 789 Gastric juice . . . 975

Blood . . . .795 Perspiration . . .986

Synovial fluid . . . 805 Saliva .... 995

According to the best calculations, water constitutes, in the human
subject, about seventy per cent, of the entire weight of the body.

The water which thus forms a part of the animal frame is derived
mainly from without. It is taken in the different kinds of drink, and
also forms an abundant ingredient in the various articles of food. For
no articles of food are taken in an absolutely dry state, but all contain
a larger or smaller quantity of water, which may readily be expelled by
evaporation. The quantity of water, therefore, which is daily taken into
the system, cannot be ascertained in any case by simply measuring the
quantity of drink, but its proportion in the solid food, taken at the same
-time, must also be determined by experiment, and this ascertained
quantity added to that which is taken in with the fluids. By measuring
the quantity of fluid taken with the drink, and calculating in addition
4

42 INORGANIC PROXIMATE PRINCIPLES.

the proportion existing in the solid food, we have found, in common
with the results formerly obtained by Barral, that, for a healthy adult
man, the average quantity of water introduced into the system is about
2000 grammes per day.

There is every reason to believe that a certain quantity of water also
makes its appearance within the body by the liberation of its elements
from various organic combinations. This is shown by the fact that a
considerable quantity of hydrogen is daily introduced into the system
as a constituent element of the organic substances of the food, while
only a small part of this quantity reappears, under similar forms of
combination, in the excretions. The most reliable estimates, in this
respect, are as follows : —

AVERAGE DAILY QUANTITY OF HYDROGEN

Introduced in organic combinations with the food . . . .40 grammes.
Discharged " " " excretions . . .6

Eesidue unaccounted for 34 "

Thus not more than fifteen per cent, of the quantity introduced is
discharged in the organic ingredients of the excretions. But no hydro-
gen is exhaled from the body in a free state, nor in notable quantity in
any other form of inorganic combination except water. The surplus
must, therefore, pass out as part of the water or watery vapor which is
constantly being discharged from various organs. The estimates given
above indicate that a little over 300 grammes of water are daily pro-
duced in the body in this way. As we shall hereafter see, an important
class of the organic ingredients of the food already contain hydrogen
and oxygen in the relative quantities necessary to form water; and,
when decomposed in the system, may readily yield these elements in the
required proportions.

Furthermore, although it has not yet been proved, in any particular
case, that more water is discharged from the system than can be ac-
counted for by that introduced, yet a comparison of the average results
obtained by different observers, always tends to show a surplus of water
in the entire excretions, varying from 200 to 500 grammes over and
above that introduced with the food and drink. The quantity of water,
however, thus produced in the body is small in comparison with that
which is introduced and discharged under its own form.

While in the interior of the living body, water takes part in the vital
functions principally by its physical properties. It is the universal
solvent for all the ingredients of the animal fluids, holding them in solu-
tion either by its direct liquefying power, or by the aid of other sub-
stances which are themselves soluble. It thus enables the nutritious
elements of the food to find their way into the circulating fluid, and to
penetrate the substance of the solid organs. It permeates the organized
membranes of the body and brings into contact with each other the in-
organic and organic materials of various parts, and enables them to

LIME PHOSPHATE. 43

assume new forms by their mutual reactions. In this way it is subser-
vient to all the phenomena of absorption, transudation, exhalation, and
even of chemical union and decomposition, which make up the internal
nutritive functions of the animal frame.

After forming part of the animal solids and fluids, and playing its
part in the vital processes of the interior, the water is again discharged ;
for its presence in the body, like that of all the other proximate princi-
ples, is not permanent, but only temporary. It makes its exit from the
body by four different passages : namely, in a liquid form with the urine
and feces, and in the form of vapor by the lungs and skin. The actual
quantity which is expelled in each case is not uniform, but varies accord-
ing to circumstances. Thus, if the kidneys be unusually active, the
watery ingredients of the urine will be temporarily increased in quantity,
while the cutaneous perspiration will be diminished ; and the state of
the atmosphere and the rapidity of respiration will influence for the
time the amount of watery vapor exhaled by the lungs and skin. Still
there is a well-marked average relation between the functional activity
of the various organs and the daily quantity of their excreted fluids. It
appears from a comparison of the researches of Lavoisier and Seguin,
Valentin, and other observers, that the water which is thus discharged
from the system finds its way out by these different routes nearly in the
following proportions : —

By exhalation from the lungs 20 per cent.

By the cutaneous perspiration . .... 30 "
By the urine and feces 50 "

While only four per cent, of the water is expelled with the feces,
ninety-six per cent, passes out by the lungs, the skin, and the kidneys.
It is evident, therefore, that at least the main bulk of the water
taken in with the food does not simply pass through the alimentary
canal, but is taken up by the mucous membranes, enters the circulating
fluid, and forms a temporary constituent of the solid tissues of the
body. As it appears in the secretions it also brings with it various
ingredients which it has absorbed from the substance of the glandular
organs; and when finally discharged it is mingled in the urine and feces
with salts and excrementitious matters, which it holds in solution, and
in the cutaneous and pulmonary exhalations, with animal vapors and
odoriferous materials of various kinds. In the perspiration it also con-
tains mineral sulphates and chlorides, which it leaves behind on evapo-
ration.

2. Lime Phosphate, Ca3P408.

This substance exists as an ingredient of all the animal solids and
fluids without exception. So far as regards its mass, it is, next to
water, the most important of the inorganic constituents of the body, as
its entire quantity is far greater than that of any other of the mineral
salts. For, although it is not especially abundant in the fluids and

44 INORGANIC PROXIMATE PRINCIPLES.

the softer tissues, it forms more than one-half the substance of the bones.
It is estimated by Barral, that the osseous tissues constitute 6.4 per
cent, of the entire mass of the body ; and the lime phosphate forms on
the average from 51 to 58 per cent, of the substance of the bones. This
would give, for a man weighing 65 kilogrammes, or 143 pounds avoir-
dupois, 2400 grammes of the calcareous salt in the whole body. Its
proportion in various tissues and fluids of the human system is as
follows: —

QUANTITY OF LIME PHOSPHATE IN 1000 PARTS IN THE

Enamel of the teeth . 885 Milk .... 2.72

Dentine . . . .643 Blood .... 0.30

Bones . . . 576 Bile .... 0.92

Cartilages ... 40 Urine . . . .0,75

Notwithstanding, therefore, the large quantity of lime phosphate in
the body as a whole, it is evident, from an inspection of the preceding
list, that nearly all of it is deposited in the more solid tissues ; while it
is present in but slender proportion in the animal fluids. Of these
fluids it is the milk alone which contains lime phosphate in notable
quantity, and here it is plainly subservient to the ossification of the
growing bones of the young infant, for whom the milk is used as food.
In the circulating fluids, the internal secretions, and the urine, on the
other hand, the calcareous salt is in small amount. Its importance in
the body depends mainly upon its simple physical property of impart-
ing rigidity to the solid tissues, rather than upon its active qualities in
the general phenomena of nutrition.

In the solid tissues it is associated with other earthy and alkaline
salts, but preponderates largely over them in amount. In the bones,
the quantity of lime phosphate is from 5 to 6 times greater than that of
all the other mineral ingredients taken together.

In the bones, teeth, and cartilages, the lime phosphate exists in a
solid form ; not, however, deposited mechanically in the osseous or
cartilaginous substance as a granular powder, but intimately united
with the animal matter of the tissues, like coloring matter in colored
glass, the union of the two forming a homogeneous material. It is not,
on the other hand, so combined with the animal matter as to lose its
identity and constitute a new chemical substance, as where hydrogen
combines with oxygen to form water ; but rather as salt unites with
water in a saline solution, both substances retaining their original charac-
ter and composition, though so intimately associated that they cannot
be separated by mechanical means. The lime phosphate, therefore, may
be extracted from a bone by maceration in dilute muriatic acid, leaving
behind the animal substance, which still retains the original form of the
bone or cartilage.

In all the solid tissues the lime phosphate is useful by giving to
them their proper consistence and solidity. For example, in the ena-
mel of the teeth, the hardest tissue of the body, it predominates very

LIME PHOSPHATE.

45

Fig. 1.

much over the animal matter, and is present in greater abundance there
than in any other part of the frame. In the dentine, a softer tissue, it
is in somewhat smaller quantity, and in the bones smaller still ; though
in the bones it continues to form more than one-half the entire mass
of the osseous tissue. The importance of this substance, in com-
municating to bones their natural stiffness and consistency, may be
readily shown by the alteration which they suffer from its removal. If
a long bone be macerated in dilute muriatic acid, the
earthy salt, as already mentioned, is dissolved out,
after which the bone loses its rigidity, and may be
bent or twisted in any direction without breaking.

(Fig. 1.)

In the formation of the bony skeleton, during foetal
life, infancy, and childhood, the cartilaginous sub-
stance previously existing is replaced by osseous
matter, which contains a larger proportion of calcare-
ous salts ; while the anatomical texture of the parts is
also changed, giving rise to the characteristic forms
of bony tissue. This progressive consolidation of the
framework of the body is known as the process of
"ossification." In some instances this process is
defective, owing to partial failure in the powers of
assimilation; and as the rigidity of the skeleton, ac-
cordingly, does not increase as it should do in propor-
tion to the weight of the body and to muscular action,
the bones become gradually bent and deformed, some-
times to an extraordinary degree. This affection has
received the name of Rachitis.

A somewhat similar result is produced by a morbid
softening of the bones, which sometimes comes on in
adult life, known as Osteomalakia. In this disease
the bony fabric, after its formation, becomes altered
in texture and composition ; and, the new substance which takes its
place being deficient in calcareous matter, a progressive yielding and
deformity of the skeleton takes place, like that which happens in cases
of rachitis.

In the plasma of the blood the lime phosphate, though insoluble in
simple alkaline watery liquids, is held in solution by its union with the
albuminous ingredients. It has been shown by Fokker that the earthy
phosphates added to white of egg unite with the albuminous matter and
become soluble in considerable proportion. This explains the presence
of lime phosphate in a liquid form both in the blood and in the milk,
both fluids which have an alkaline reaction. In the urine, on the other
hand, it is held in solution by the presence of the acid sodium biphos-
phate. Accordingly, whenever the urine is rendered alkaline by the
addition of soda or potassa, the earthy phosphates are precipitated in
the form of a white turbidity.

FIBULA TIED
IN A KNOT, after
maceration in a di-
lute acid. (From a
specimen in the mu-
seum of the College
of Physicians and
Surgeons.)

4(5 INOKGANIC PKOXIMATE PRINCIPLES.

The source of the lime phosphate of the animal solids and fluids is in
the food. This substance exists in nearly every animal and vegetable
alimentary matter in common use. It is found not only in muscular
flesh, eggs, and milk, and in all the cereal grains, as wheat, rye, oats,
barley, maize, and rice, but also in peas and beans, the nutritive tubers
and roots, as potatoes, beets, turnips, and carrots, and even in the
juicy fruits, such as the apple, pear, plum, and cherry.

After forming for a time a constituent part of the body, the lime
phosphate is again discharged with the excretions, but very slowly and
in small amount. According to the observations of Neubauer and
Beneke about 0.4 gramme, on the average, is daily expelled with the
urine. A slightly larger quantity is also found in the feces, but this
may be only the residue derived from the undigested portion of the food.
Only traces of it are to be detected in the perspiration. As so large a
quantity of this salt, therefore, is contained in the body, while so small
a proportion is expelled daily with the excretions, it is evidently to be
regarded as one of the more permanent constituents of the frame ; being
comparatively inactive in the process of internal metamorphosis, and
serving for the most part as a physical ingredient of the solid tissues.

3. Lime Carbonate, CaC03.

Lime carbonate is to be found in the bones, the teeth, the blood, the
lymph and chyle, the saliva, and sometimes in the urine. In all these
situations it is normally in much smaller proportion than the calcareous
phosphate with which it is associated. In the bones, however, it is next
in importance to the lime phosphate, being on the average one-seventh
as abundant as that salt, and much more so than any of the remaining
mineral ingredients. In the animal fluids its solubility is accounted for
by the presence of the alkaline chlorides or by that of free carbonic acid.

4. Magnesium Phosphate, MgHP04.

Magnesium phosphate was formerly associated with the corresponding
lime salt under the name of the earthy phosphates, owing to certain
resemblances in their chemical relations. Like the lime phosphate, which
it everywhere accompanies, it is present in all the tissues and fluids of
the body, though this substance is for the most part in the smaller
quantity of the two. Thus in the bones the lime phosphate is in the
proportion of 516 parts per thousand, while the magnesium phosphate
forms only 12.5 parts. In the blood the calcareous salt amounts to 0.30
part per thousand, the magnesium salt to 0.22 part ; and in the milk
there are 2.72 parts of lime phosphate to 0.53 part of magnesium phos-
phate. On the other hand, the salts of magnesium have been found to
be in larger quantity than those of lime in the muscles, and nearly twice
as abundant in the substance of the brain.

The magnesium phosphate is discharged, by the urine, in the average
daily quantity of 0.6 gramme. The average amount of both the earthy

SODIUM CHLORIDE. 47

phosphates, taken together, is accordingly about 1 gramme per da}^ ;
the magnesian salt being rather the more abundant of the two.

Both the magnesium phosphate and carbonate, of which latter salt
traces occur in the blood, appear to have similar physiological relations
with the corresponding salts of lime, and almost the same things may be
said in regard to their union with the substance of the more solid tissues
and their mode of solubility in the animal fluids.

5, Sodium Chloride, NaCl.

This is undoubtedly the most important of the mineral constituents
of the body, so far as regards its general distribution and the active part
which it takes in the internal phenomena of nutrition. It is the most
abundant of all, next to the lime phosphate, and it is universally pre-
sent in all the animal tissues and fluids. Its entire quantity in the
human body is estimated by Dr. Lankester at 110 grammes, or nearly
one-quarter of a pound avoirdupois. In the blood it is rather more
abundant than all the other mineral ingredients taken together. Its
proportion in the various parts of the body is as follows : —

QUANTITY OF SODIUM CHLORIDE IN 1000 PARTS IN THE

Bones .... 7.02 Saliva .... 1.53

Blood .... 3.36 Milk .... 0.30

Bile .... 3.18 Lymph .... 5.00

Gastric juice . . . 1.70 Sebaceous matter . * . 5.00

Perspiration . . . 2.23 Urine .... 5.50

One of the most important characters of this suit in the living body
is undoubted!}' its property of regulating the phenomena of endosmosis
and exosmosis, or the transudation of nutritive fluids through the organic
membranes. This property is shared more or less by the other mineral
ingredients of the blood, but is more important in the case of sodium
chloride, owing to its preponderance in quantity as compared with the rest.

Since this substance is present in all parts of the body, it is also an
important ingredient of the food. It occurs, of course, in all animal
food, as a natural ingredient of the corresponding tissues. In muscular
flesh, however, it is very much less abundant than potassium chloride,
while, on the other hand, it is more abundant in the blood. It is present
also in various articles of vegetable food.

According to Boussingault, it exists in the following proportions in
certain vegetable substances: —

PROPORTION OF SODIUM CHLORIDE IN 1000 PARTS IN

Potatoes . . . 0.43 Oats .... 0.11

Beets .... 0.66 Peas .... 0.09

Turnips .... 0.28 Beans .... 0.06

Cabbage . . . 0.40 Meadow hay . . . 3.28

The relative quantity of sodium chloride taken in animal and vegetable
food has not been determined. In regard to the demand for this salt,

48 INORGANIC PROXIMATE PRINCIPLES.

however, there is a striking difference between the carnivorous and
many herbivorous animals. The carnivora receive a fully sufficient
supply with their natural food, and invariably show a repugnance to
salt itself, as well as to salted meats. On the other hand, the horse,
and more especially the ruminating animals, have an instinctive desire
for salt, and greedily devour it, wh.en offered to them, in addition to
that naturally contained in the vegetable matters of their food. It is
well known with what avidity the cattle, sheep, and all kinds of deer
frequent the saline springs or " salt licks" of the United States ; and it
is shown by common experience that a liberal supply of salt is important
for the healthy nutrition and development of these animals in the
domesticated condition.

The same fact has been demonstrated in a more exact manner by the
experiments of Boussingault on the ox.1 This observer made a series
of comparative investigations upon the growth of two sets of bullocks
selected from animals of the same age and vigor, and supplied equally
with an abundance of ordinary nutritious food, those of one set, how-
ever, receiving in addition each 34 grammes of salt per day. At the
end of six months the difference in the aspect of the animals of the two
sets began to be distinctly evident, and became more marked as time
went on. The experiment lasted for a year, and at the end of that time
both sets of animals had on the average equally increased in weight ;
but those fed with ordinary food alone presented a rough and tangled
hide and a dull, inexcitable disposition, while in those which had re-
ceived the additional ration of salt the hide was smooth and glistening
and the general appearance was vigorous and animated. While these
animals, therefore, may subsist for a time without inconvenience upon
the salt naturally contained in their food, an additional quantity is
required to maintain the system in good condition for an indefinite
period.

There is a similar necessity for salt as an addition to the food of the
human species. No other substance is so universally used as a condi-
ment by all races and conditions of men. This custom does not depend
simply on a fancy for gratifying the palate, but is based upon an in-
stinctive demand of the system for a substance which is necessarj^ for
the full performance of its functions. Beside its other properties, it no
doubt acts in a favorable manner by exciting the digestive fluids, and
assisting in this way the solution of the food. For food which is taste-
less, however nutritious it may be in other respects, is taken with
reluctance and digested with difficulty ; while the attractive flavor which
is developed by cooking, and by the addition of salt and other condiments
in proper proportion, excites the secretion of the saliva and gastric juice,
and facilitates consequently the whole process of digestion. The sodium
chloride is then taken up by absorption from the intestine, and is de-
posited in various quantities m different parts of the body.

1 Cliimie Agricole. Paris, 1854, p. 251.

SODIUM AND POTASSIUM PHOSPHATES. 49

Notwithstanding various surmises which have been presented from
time to time with regard to its possible decomposition and the re-com-
bination of its elements in the body, we have no certain knowledge of
such changes taking place in the sodium chloride while forming a con-
stituent of the animal frame. It passes from the alimentary canal to
the blood, from the blood to the tissues, and is finally discharged with
the urine, mucus, and cutaneous perspiration, in solution in the water
of these fluids. Under ordinary circumstances, by far the largest pro-
portion passes out by the kidneys. The quantity of sodium chloride
thus discharged with the excretions by an adult man is about 15
grammes per day j1 of which 13 grammes are contained in the urine, and
2 grammes in the perspiration. Thus, of all the sodium chloride con-
tained in the body, considerably more than ten per cent, passes through
the system in twenty-four hours. This fact plainly indicates the activity
and importance of this salt in the daily internal changes of nutrition.

6, Potassium Chloride, KC1.

This substance is found in very many if not all of the animal tissues
and fluids, accompanying the sodium chloride, many of the properties
of which it shares, and with which it is closely related in its physiological
characters. It is especially abundant, as compared with the sodium
chloride, in the muscles and in the milk, less so in the blood, the gastric
juice, the urine, and the perspiration. Both salts are neutral in reaction,
and are retained in the liquid form in the blood and secretions by solution
in the water of these fluids. The potassium chloride is introduced as
an ingredient of both animal and vegetable food, and is discharged with
the mucus, the urine, and the perspiration.

7. Sodium and Potassium Phosphates, Na2HP04 and K2HP04.

These substances, associated under the name of the alkaline phos-
phates, are of the greatest importance as ingredients of the animal body.
They exist universally in all its solids and fluids, and in the latter are
present in the liquid form by means of their ready solubility in water.
No doubt they are useful in a variety of ways, but at least one of their
most important characters is their property of exhibiting an alkaline
reaction. This reaction is essential to a large number of the vital pro-
cesses taking place in the interior, and is present, without exception, in
all the animal fluids which are actually contained in the circulatory
system, or in the closed cavities of the body. An acid reaction, on the
other hand, is found only in a very few of the organic fluids which are
either employed in the process of digestion or are discharged externally.

The following list shows the comparative frequency of alkaline and
acid reactions in the animal fluids : —

1 Neubauer und Vogel-, Analyse des Hams, Wiesbaden, 1872, p. 54. Beneke,
Pathologic des Stoffwechsels, Berlin, 1874, p. 322.

50 INORGANIC PROXIMATE PRINCIPLES.

FLUIDS WITH AN ALKALINE REACTION. FLUIDS WITH AN ACID REACTION.

1. Blood-plasma. 1. Gastric juice.

2. Lymph. 2. Perspiration.

3. Aqueous humor. 3. Mucus of the vagina.

4. Cephalo-rachidian fluid. 4. Urine.

5. Pericardial fluid.

6. Synovia.

7. Fluids of the living muscular

tissue.

8. Mucus in general.

9. Milk.

10. Spermatic fluid.

11. Tears.

12. Saliva.

13. Pancreatic juice.

14. Intestinal juice.

If we take into account the carbonic acid exhaled with the breath,
we see therefore that, while in general an alkaline condition is charac-
teristic of the internal fluids, the products of excretion, on the contrary,
present universally an acid reaction.

Of all the internal fluids the most essential is the plasma of the blood,
since it affords the materials of nutrition to the entire system ; and its
alkaline reaction, which is distinctly marked, has been found to be in-
variably present, not only in the human subject, but also in every species
of animal in which it has been examined. This reaction of the blood is
moreover necessary to life, since Bernard has shown1 that if an injection
of dilute acetic or lactic acid be made into the veins of the living animal
death always results before the point of neutralization has been reached.

The alkaline reaction of the blood-plasma gives to this fluid its extra-
ordinary capacity for dissolving carbonic acid. According to Liebig,
water which holds in solution one per cent, of sodium phosphate is
enabled to absorb and retain twice its usual proportion of carbonic acid;
and the other alkaline salts, as is well known, have a similar dissolving
action upon this gas. Consequently the blood as it circulates among
the tissues rapidly absorbs from them the carbonic acid which has been
formed in their substance, and incessantly carries it away to be elimi-
nated by the lungs. This important property of the circulating fluid
depends upon its alkaline reaction.

The alkalescence of the blood is due in great measure to the alkaline
phosphates, which are present in human blood in the proportion of 0.6 T
per thousand parts. A peculiar relation, however, exists in this respect,
for different classes of animals, between the alkaline phosphates and the
alkaline carbonates, which are to be mentioned hereafter. Both these
groups of salts have, when in solution, an alkaline reaction ; and both
contribute to the alkalescence of the blood in man and animals. But in
the carnivorous animals it is the phosphates which preponderate, while

1 Liquides de 1'Organisme. Paris, 1859, tome i. p. 412.

SODIUM AND POTASSIUM CARBONATES. 51

in the herbivora the carbonates are the more abundant of the two. In
animals fed at the same time upon both animal and vegetable food the
two kinds of salts are found to be present in nearly equal proportion,
and in the same animal either the phosphates or the carbonates may
be made to predominate by increasing the relative quantity of animal
or vegetable food respectively. This is readily understood when we
remember that muscular flesh and the animal tissues generally are com-
paratively abundant in phosphates, while vegetable matters, as we shall
hereafter see, abound also in salts of the organic acids, which give
rise by their decomposition in the system to carbonates of the same
bases.

The alkaline phosphates are taken in with the food, as they exist
widely in both animal and vegetable matters. They circulate with the
animal fluids, and are finally excreted with the perspiration, the mucus,
and the urine. In the urine a portion of the alkaline sodium phosphate
is replaced by the acid sodium biphosphate, which gives to this fluid its
property of reddening blue litmus paper, although it contains no free
acid. The manner in which this change is supposed to take place is the
following. A nitrogenous organic acid of new formation, namely, uric
acid, makes its appearance in the system, and is excreted by the urine.
It exists, however, in this fluid only in the form of combination, as
sodium urate. It is, therefore, believed to combine, at the time of its
formation, with a portion of the sodium which forms the base of the
sodium phosphate; and the remainder of this salt, converted into a
biphosphate, is then eliminated by the urine, which thus acquires an
acid reaction.

There is evidence that phosphoric acid is also generated in the inte-
rior of the body by oxidation. A substance to be described hereafter,
containing phosphorus in the form of organic combination, exists in
various parts of the system, especially in the blood and in the tissue of
the brain and nerves, and is taken with certain kinds of food ; but no
such substance is to be met with in the excretions. In the fluids dis-
charged from the body phosphorus exists only in the form of the phos-
phatic salts. It is, therefore, without doubt oxidized in the internal
transformation of the organic substances, thus becoming phosphoric
acid, which in turn unites with the alkaline bases to form neutral or acid
phosphates. In this way a certain portion of the superabundant acid
is produced, which gives rise to the acid reaction of the excreted fluids.

The sodium and potassium phosphates, including the acid biphosphate,
are discharged with the urine to the amount of about 4.5 grammes per
day.

8. Sodium and Potassium Carbonates, Na2C03 and E^CO.,.
The alkaline carbonates, as mentioned above, are associated with the
phosphates in all the more important fluids of the body. They are
readily soluble, and assist in producing the necessary alkalescence of
the blood and secretions.

52 INORGANIC PROXIMATE PRINCIPLES.

The alkaline carbonates are partly introduced as such with the food,
but are to a great extent formed within the body by the decomposition
of other salts contained in the substance of certain fruits and vegetables.
Various of these fruits and vegetables, such as apples, cherries, grapes,
potatoes, carrots, and the like, contain malates, tartrates, and citrates
of the alkaline bases. It has, furthermore, been often observed that
after the use of acescent fruits and vegetables containing the above salts,
the urine becomes alkaline in reaction from the presence of the alkaline
carbonates. Lehmann1 found, by experiments upon his own person,
that within thirteen minutes after taking 15.5 grammes of sodium lactate,
the urine had an alkaline reaction. He also observed that, if a solution
of this substance were injected into the jugular vein of a dog, the urine
became alkaline at the end of five, or, at the latest, of twelve minutes.
The conversion of these salts into carbonates takes place, therefore, not
in the intestine, but in the blood. The same observer found that, in
many persons living on a mixed diet, the urine became alkaline in two
or three hours after swallowing 0.65 gramme of sodium acetate.

The organic acid in these cases is decomposed and oxidized with the
production of carbonic acid and water ; and the original salts are thus
replaced by the alkaline carbonates, which appear in the urine and tem-
porarily modify its reaction in the manner above described.

A preponderance of vegetable food, accordingly, influences the quan-
tity of the alkaline carbonates in the system, and consequently the reac-
tion of the excretions. As a rule, the urine of man and of the carnivo-
rous animals is clear and acid, while that of the herbivora is alkaline
and turbid with calcareous deposits. This turbid and alkaline urine
will often effervesce with acids, showing the presence of carbonates in
considerable quantity. Bernard has shown that this difference depends
upon the alimentation of the animal, and that although in carnivorous
and herbivorous animals under ordinary conditions the urine is respec-
tively acid and alkaline, if they be both deprived of food for a few days
the urine becomes acid in both, since they are then, in each instance,
living upon their own tissues. Furthermore, a rabbit, whose urine is
turbid and alkaline while feeding on fresh vegetables, if kept upon a diet
of animal food, soon produces an excretion which is clear and acid. The
reverse effect is produced upon a dog by changing his food from meat
to vegetable matters. Finally, it is also shown2 that the urine of the
young calf while living on the milk of the mother is clear and acid ; but
after the animal has been weaned and feeds upon vegetable matter, its
urine becomes alkaline and turbid, like that of the adult animal.

9. Sodium and Potassium Sulphates, S04Na2 and S04K2.
The sulphates are also to be regarded as constant ingredients of the
body, as they are found in several of the animal fluids, including the

1 Physiological Chemistry. Cavendish edition. London, 1851, vol. i. p. 97.

2 Milne Edwards, Legons sur la Physiologie. Paris, 1862, tome vii. p. 471.

SODIUM AND POTASSIUM SULPHATES. 53

blood, the lymph, the aqueous humor, milk, saliva, mucus, the perspira-
tion, and the urine. They are usually, however, in small quantity, as
compared with other saline matters. In the blood and the lymph, they
are much less abundant than either the chlorides, phosphates, or car-
bonates. In the milk and the saliva, there is hardly more than a trace
of them ; and they have not been found at all in the bones, the gastric
juice, the bile, or the pancreatic juice. They are most abundant in the
urine, where they amount to rather more than one-half the quantity of the
phosphates, and they are found also, in small proportion, in the feces.

The sulphates are introduced into the body, to some extent, with the
food and drink. They are to be found, in minute quantity, in muscular
flesh and in the yolk of egg. They exist also in certain vegetable pro-
ducts, such as the cereal grains, fruits, and tuberous roots, where they are
much less abundant than the phosphates, though often more so than the
chlorides. Spring and river water, as used for drink, usually contains
sulphates, including sulphate of lime, varying in amount, according to
the tables given by Payen,1 from .003 to .06 per thousand parts. In
the water of the Croton River, with which the city of New York is sup-
plied, they amount, as shown by the analyses of Prof. Chandler,2 to a
little more than .007 per thousand parts.

Beside the sulphates, however, introduced with the food and drink, a
certain amount of sulphuric acid originates within the body by oxida-
tion, in a mode analogous to that already described for phosphoric acid.
The albuminous substances, which form so important a part of the solid
food, contain sulphur as one of their constituent elements, and a con-
siderable quantity of this substance is accordingly introduced daily into
the system in the form of organic combination. The entire quantity of
sulphur, thus forming part of the organic matters of the body of a man
of medium size, amounts, according to Payen,3 to about 110 grammes ;
and at least 1 gramme must be taken daity with the albuminous ingre-
dients of the food. A portion of these substances is expelled by the
daily exfoliation of the hair, nails, and epidermis; but no such sul-
phurous organic compound is discharged by the urine and feces except
in insignificant quantity. On the other hand, the sulphates are compar-
atively abundant in the excretions. While they are to be found in the
blood only in the proportion of 0.28 per thousand, they exist in the
urine in the proportion of from 3.00 to 7.00 parts per thousand,4 and are
discharged by this channel to the amount of about 4 grammes per day.

These facts indicate that a notable quantity of sulphuric acid is con-
stantly formed in the body, during the decomposition of albuminous
matters, by oxidation of their sulphur. This is confirmed by the fact
that the quantity of sulphuric acid in the sulphates eliminated by the
kidneys is perceptibly increased by the use of a flesh diet, and also by

1 Substances Alimentaires. Paris, 1865, p. 436.

2 Lecture on Water. Transactions of the American Institute for 1870-71.
8 Substances Alimentaires. Paris, 1865, p. 68.

4 Robin, LeQons sur les Humeurs. Paris, 1874, p. 770.

54 INORGANIC PROXIMATE PRINCIPLES.

the administration of sulphur or a sulphuret.1 Dr. Parkes estimates
the quantity of sulphuric acid thus produced in the system as about
double that taken in the form of sulphates with the food and drink. It
unites at once with the alkaline bases, displacing the weaker acids with
which they were previously combined, and thus contributes indirectly
to the general acid reaction of the excreted fluids.

The foregoing substances constitute the most important of the in-
organic proximate principles of the animal body. They are distin-
guished, as a class, by their comparatively simple chemical composition,
by their external origin, and by the part which they take in the constitu-
tion and nourishment of the animal frame They are derived for the
most part from without, being taken directly from the materials of the
inorganic world. There are some exceptions to this rule; as in the
case of the alkaline carbonates formed in the body by decomposition of
the salts of the vegetable acids ; and of the sodium biphosphate pro-
duced from the neutral phosphate, by the action of an organic acid of
internal origin. The greater part, however, of the proximate principles
belonging to this class are introduced with the food, and taken up
by the animal tissues and fluids, in the form under which they exist
in external nature. The lime carbonate of the bones, for example, and
the sodium chloride of the blood and the tissues, are the same sub-
stances as those met with in calcareous rocks, or in solution in sea
water.

In the process of internal nutrition they are also exempt, as a general
rule, from any marked chemical changes. Some of them, such as the
lime and magnesium phosphates, are mostly deposited in the solid parts,
and are renewed very slowly, contributing principally to the physical
properties of the tissues, and taking a comparatively small share in the
actions of repair and waste. Others, such as water and the alkaline
chlorides, are introduced and discharged daily in considerable abund-
ance, passing rapidly through the system, and playing an important
part in the phenomena of solution and transudation. Others still, such
as the alkaline phosphates and sulphates, are partly formed in the body
by the process of oxidation, and appear in the urine as a residue from
the decomposition of other proximate principles.

Principally, however, the inorganic substances are reabsorbed by the
blood from the tissues in which they were deposited, and discharged
unchanged with the excretions. The importance of this character will
become fully manifest when we see how different are the relations
exhibited by the proximate principles of other groups. The inorganic
substances do not, for the most part, participate directly in the chemical
changes going on in the body ; but rather serve by their presence to
enable those changes to be accomplished, in the other ingredients of the
animal frame, which are necessary to the process of nutrition.

1 Neubauer und Vogel, Analyse des Hams. Wiesbaden, 1872, pp. 356, 357.

CHAPTBE III.

HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

THE proximate principles belonging to this class are distinguished
from the preceding by their organic origin. They appear as products
of the nutritive actions of organized beings, and are not introduced
ready formed from the inorganic world. They exist both in vegetables
and in animals. In the former they are produced entirely as new com-
binations, under the influence of the vegetative process ; and even in
animals, which feed upon vegetables or upon other animals, they are so
modified by digestion and assimilation that they present themselves, as
final constituents of the body, under new and specific forms. They all
consist of carbon, hydrogen, and oxygen, of which carbon is present by
weight in especially large proportion, forming from 44 to 84 per cent,
of the entire substance. Owing to the absence of nitrogen, which is an
important element in organic substances of the following class, they are
sometimes known as the "non-nitrogenous" proximate principles. They
are naturally divided into two principal groups, namely: the carbo-
hydrates, or substances containing carbon, together with hydrogen and
oxygen in the proportions to form water ; and the fatty matters, in
which the proportions of carbon and hydrogen are both increased, while
that of oxygen is considerably diminished. The group of the carbo-
hydrates includes starch, glycogen, and sugar.

I. Starch, C6H1005.

Starch is most abundantly diffused throughout the vegetable kingdom,
and exists, for at least a certain period of vegetative life, in every plant
which has yet been examined for it. It occurs especially in seeds, in
the cot3'ledons of the young plant, in roots, tubers, and bulbs, in the
pith of stems, and sometimes in the bark. It is very abundant in corn,
wheat, rye, oats, and rice, in the parenchyma of the potato, in peas and
beans, and in most vegetable substances used as food. It constitutes
almost entirely the different preparations known as sago, tapioca, arrow-
root, and maizena, which are nothing more than varieties of starch,
extracted from different species of plants.

The following list, compiled mainly from the tables of Payen,1 shows
the percentage of starch occurring in various kinds of food : —

1 Substances Alimentaires. Paris, 1865.

(55)

56 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

QUANTITY OF STARCH IN 100 PARTS IN

Wheat .
Rye

Oats .
Barley .
Indian corn
Rice

57.88
64.65
60.59
66.43
67.55
88.65

Potatoes
Sweet potatoes
Peas
Beans .
Flaxseed
Chocolate nut

20.00
16.05
37.30
33.00
23.40
11.00

When purified from foreign substances starch is a white, glistening
powder, which gives rise to a peculiar crackling sensation if rubbed
between the fingers. It consists of minute granules of very firm con-
sistency and definite shape, presenting certain peculiarities, of both form
and size, by which its varieties, derived from different sources, may be
distinguished from each other. The young starch granules, when first
produced in the tissues of the plant, are exceedingly small, round, and
perfectly homogeneous ; but they afterward increase in size, and, as their
growth is irregular, they become ovoid, pear-shaped, lenticular, or
polygonal in form. They also show under the microscope a definite
structure, each granule being composed of a series of layers, disposed
one over the other, giving rise to the appearance of concentric markings,
which are very characteristic of most varieties of starch grains, after
they have attained a certain size. The markings are arranged round a
single point, usually more or less eccentric in position, which is called
the hilum.

The successive layers of which the starch granule is composed differ
from each other mainly in their consistency, being alternately harder

and softer in comparison with
each other; and this difference
in density produces a corres-
ponding difference in the refrac-
tive power of the layers, and
consequently an appearance of
concentric striation.

Each starch granule, further-
more, consists of two sub-
stances, intimately mingled in
every part of its mass, which re-
semble each other completely in
chemicalcomposition, but differ
greatly in solubility. These
two substances are, 1st, granu-
lose, which may be extracted

GRAINS OP POTATO STABCH. f™m the starch S™™ ^ b°U-

ing water ; and 2d, cellulose,

which remains undissolved. The granulose is usually much the more
abundant of the two, but the cellulose has so marked a consistency that
it retains the form and apparent laminated structure of the starch grain.

STARCH.

57

Fig. 3.

STARCH GRAIUS OF BERMUDA ARROW-
ROOT.

after extraction of the granulose, though it may be reduced to five or
six per cent, of its original weight.

The starch grains of the potato (Fig. 2) vary considerabl}7 in size.
The smallest have a diameter of 2.5 inmm.,1 the largest 62.5 mmm.
They are irregularly pear-shaped
in form, and their concentric
markings are very distinct. The
starch obtained from the potato,
however carefully prepared, re-
tains in connection with it traces
of an odoriferous principle which
makes it less valuable for culi-
nary purposes than many other
varieties.

The starch granules of arrow-
root (Fig. 3) are generally
smaller and more uniform in
size, than those of the potato.
They vary from 12.5 mmm. to
50 mmm. in diameter. They are
elongated and cylindrical in
form, and the concentric mark-
ings are less distinct than in the preceding variety. The hilum has here
sometimes the form of a circular pore, and sometimes that of a trans-
verse fissure or slit.

The grains of wheat starch
(Fig. 4) are still smaller than
those of arrowroot. They vary
from 2.5 mmm. to 35 mmm.
in diameter. They are nearly
circular in form, with a round
or transverse hilum, but with-
out any distinct appearance of
lamination. Many of them are
flattened or compressed later-
ally, so that they present a
broad surface in one position,
and a narrow edge when viewed
in the opposite direction.

The starch grains of Indian
corn (Fig. 5) are of nearly the
same size with those of wheat
flour. They are somewhat more irregular and angular in shape ; and

1 The sign mmm. stands for micro-millimetre ; that is, the one-thousandth part
of a millimetre. A millimetre is very nearly equivalent to one twenty-fifth of an

Fig. 4.

STARCH GRAINS OP WHEAT FLOTTR.

inch ; and a micro-millimetre, accordingly, is about
5

of an inch.

HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

Fig. 5.

STARCH GRAINS OF INDIAN CORN.

are often marked with crossed or radiating lines, as if from partial
fracture.

Starch derived from all these different sources has essentially the
same chemical composition, and may be recognized b}" the same tests.

It is insoluble in cold water, but
if it be treated with about
twenty times its weight of boil-
ing water its granules swell,
become gelatinous and amor-
phous, combine with a certain
proportion of water, and fuse
into a thick opaline liquid, which
is thinner or thicker according
to the quantity of water present.
After that they cannot be made
to resume their original form,
but on cooling they solidify into
a nearly homogeneous paste,
retaining the water in union with
the starchy matter. The starch
is then said to be amorphous or
•*' hydrated." By this process

it is not essentially altered in its chemical properties, but only in
its physical condition. If starch be treated with 100 or 150 parts of
boiling water, it makes an opaline liquid which does not gelatinize ; but
on standing, the imperfectly liquefied portions, containing the insoluble
cellulose, subside to the bottom as a turbid deposit, while the soluble
starch remains above, forming a clear, colorless, and perfectly fluid solu-
tion.

Starch is especially distinguished by its property of striking a blue
color by contact with iodine. This reaction will take place even when
the starch is in the raw condition, and starch granules may be readily
recognized under the microscope by this means. It is still more prompt
when the starch is hydrated and especially when it is in solution.
A very minute quantity of tincture of iodine added to a solution of
starch will cause the whole to assume at once a very deep and rich blue
color, which may be largely diluted without losing its characteristic
tinge. The mixture of the two substances, however, must, in the first
place, be made at a moderate temperature. If the solution be hot, no
visible reaction will occur ; and even after it has taken place if heat be
applied the blue color will disappear, to return again after cooling down
to the original temperature. Secondly, the iodine must be in a free
state. If it be used in the form of a soluble iodide, it will produce
no effect, since the starch has not sufficient affinity for it to withdraw
it from its union with other matters. No third substance, furthermore,
must be present in the mixture, which would be capable of combining
with the iodine and thus preventing its action upon the starch. All the

STARCH. 59

animal fluids more especially, such as the serum of blood, saliva, mucus,
urine, contain ingredients which prevent the reaction of starch with
iodine, and may even dissipate the blue color after it has been once pro-
duced. These substances, therefore, must be removed from the fluid
before the application of the test, or else the iodine must be added in
sufficient excess to allow a surplus for action upon the starch. With
these precautions it forms a striking and valuable test.

Starch has the property of being changed, under certain conditions,
into two other substances.

1. If subjected to torrefaction, that is, a dry heat of about 210° (about
4000 F.), it is converted into Dextrine, a gummy substance freely solu-
ble in water, so called from the fact that in solution it rotates the plane
of the polarized ray toward the right.1 Dextrine has the same chemical
composition with starch, namely C6H1005, but its properties are changed,
and it will no longer produce a blue color with iodine. The same
transformation is very quickly accomplished by boiling starch with a
dilute acid; the opaline arid gelatinous solution becoming in a few
minutes clear and liquid, and losing at the same time its power of
reaction with iodine. Finalty, in the germination of starchy seeds,
like the cereal grains, a nitrogenous substance is produced termed
" diastase ;" and this has the power, when supplied with moisture at a
moderate temperature, of effecting the transformation of the starch into
soluble dextrine.

2. Starch may be converted into Sugar. When a starch solution or
a thin starch paste is boiled with a dilute acid, it is rapidly changed,
as already mentioned, into dextrine. If the boiling be continued for
several hours it is still further transformed into sugar ; and at last the
whole of it passes over into the saccharine condition. This also hap-
pens in the process of germination and growth in plants, where sugar
makes its appearance under influence of the diastase, and at the expense
of the starch, as soon as moisture and warmth are supplied in the
requisite degree. This is the usual source' of sugar in vegetable

1 A ray of light which has passer! through certain crystalline bodies, such as a
" Nicol's prism" of Iceland spar, is found to be polarized ; that is, it has acquired
opposite and complementary properties in two different directions. For if it be
received by a second similar prism, which is equally transparent in all positions
to ordinary light, the polarized ray will pass through it only when the prin-
cipal section of the second prism is parallel with that of the first ; but when the
second prism is turned round 90°, the light is entirely arrested. Now if certain
organic substances in solution be placed between the two prisms, it is found that
they have the effect of changing the angle at which the second prism must stand
in order to arrest or transmit the light from the first. In other words, the plane
of polarization of the polarized ray has been deviated or rotated by passing
through the organic liquid. Some substances deviate in this way the plane of
polarization toward the right, others toward the left. The specific rotatory
power of each is estimated for a solution of standard strength and quantity, for
yellow light, and is indicated in degrees of the circle. The specific rotatory power
of dextrine is 118°.

60 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

juices, the starch previously stored up being at some period of growth
changed into sugar by the molecular actions going on in the vegetable
fabric. Finally, various nitrogenous animal substances produce the
same effect. The contact of human saliva or the intestinal juices at a
temperature of 37.5° (10(P F.) rapidly transforms hydrated starch into
sugar.

A special interest attaches to starch from the fact that it is the first
organic substance produced, in the process of vegetation, from inor-
ganic materials. The animal body is incapable of forming organic
matter, and must therefore be supplied with these substances in the
food. But vegetables have the power of combining inorganic ele-
ments in such a way as to produce a new class of bodies, peculiar to
the organic world, and capable of serving for the nutrition of animals.
This is shown by numerous experiments, in which seeds or young
plants, artificially cultivated in a soil of clean sand, and moistened only
with solutions of various mineral salts,1 have germinated, grown, and
fructified, increasing, many times over, the quantity of organic material
which they contained at the beginning.

This production of organic matter takes place in the green tissues,
principally in the leaves, of growing plants, under the influence of
the solar light ; and the first substance which makes its appearance
under these conditions is nearly always starch. It is produced from
two inorganic matters absorbed from without, namely, carbonic acid
and water, which are deoxidized by the green vegetable tissues, their
elements being re-combined, to form a carbo-hydrate. This is proved
by the fact that oxygen is exhaled, during the vegetative process, in
the same or nearly the same proportion as that in which it existed
originally in the carbonic acid ; and the new substance produced con-
tains hydrogen and oxygen in the relative proportions to form water.
The production of starch in growing vegetables is therefore repre-
sented by the following formula : —

Carbonic acid. Water. Starch.

(C6012 + H1005) - 012 = CCH1005.

The starch thus formed in the leaves of plants is afterward trans-
formed into other vegetable substances belonging to the group of the
carbo-hydrates, such as dextrine, sugar, and cellulose, and used for the
further nutrition of the plant. When abundantly deposited in special
organs, such as the starchy seeds of wheat or Indian corn, or the tubers
of the potato, it constitutes a reserve material of nutrition, to be after-
ward dissolved and employed for the purposes of germination and
growth. It is from such natural deposits of reserve, in the vegetable
fabric, that starch is obtained in quantity to serve as food for animals
or man.

1 Mayer, Lehrbuch der Agrikultur-Chemie. Heidelberg, 1871, Band i.
p. 10.

GLYCOGEN. — SUGAR. 61

When taken into the alimentary canal, starch is rapidly transformed
into sugar by the action of the digestive fluids ; and in this form is
absorbed into the circulation.

II. Glycogen, C6H1005.

This is an amylaceous substance of animal origin, corresponding in
character with starch derived from the vegetable world. It is found in
the livers of all vertebrate animals in the healthy condition, and in the
muscles and integument of the embryo of mammalia at an early period
of development. It has also been discovered in the oyster and the
cockle-shell. Glycogen, so called from its property of producing sugar
or glucose, has the same chemical composition as starch, and agrees
with it in all its essential characters, except that it is readily soluble
in water, and, when treated with iodine, yields a violet-red instead of
a blue color. Its watery solution is opalescent, and deviates the plane
of polarization strongly to the right, its specific power of rotation for
yellow light being about 130°. By boiling with a dilute acid it is
changed first into dextrine and afterward into sugar. It also under-
goes the saccharine transformation when in solution at the temperature
of the living body by contact with saliva, the intestinal juices, the sub-
stance of the liver, or the serum of the blood. It is the source of the
sugar produced in the animal body, as starch is the source of that
formed in vegetables.

Both starch and glycogen, accordingly, are to be regarded as tempo-
rary products, destined to undergo further transformation before being
used for the purposes of nutrition. In vegetables, the starch which.
is abundantly stored up at one period in the cellular tissues is after-
ward liquefied and altered into other substances; and although it
enters so largely into the composition of the vegetable food of ani-
malSj it is converted into sugar during digestion in the alimentary
canal.

III. Sugar.

The proximate principles designated under this name include a va-
riety of substances which have certain well-marked characters, and are
of frequent occurrence in both animal and vegetable juices. They are
crystallizable and soluble in water, and have, when in solution, a
distinctly sweet taste, which, in some varieties, is very highly de-
veloped. They are all decomposed by being heated with sulphuric
acid; their hydrogen and oxygen being driven off, while the carbon
remains behind as a jet-black deposit. In this condition they are said
to be carbonized. The proportions in which they occur in various arti-
cles of food, according to the tables of Pay en,. Yon Bibra, and a few
other observers, are as follows:. —

62 HYDROOARBONACEOUS PROXIMATE PRINCIPLES.

QUANTITY OF SUGAR IN 100 PARTS IN

Cherries . . . 18.12 Wheat flour . . . 2.33

Apricots . . . 16.48 Rye flour . . . 3.46

Peaches . . . 11.61 Barley meal . . . 3.04

Pears .... 11.52 Oatmeal . . . 2.19

Juices of sugar-cane . 18.00 Indian corn meal . . 3.71

Sweet potatoes . . 10.20 Cow's milk . . . 5.20

Beet roofs . . . 8.00 Goat's milk . . .5.80

Parsnips . . . 4.50 Beefs liver . . . 1.79

The three principal varieties of this substance which are most impor-
tant in a physiological point of view are glucose, cane sugar, and milk
sugar.

Glucose, CGH1206.

Glucose, also called grape sugar from its abundance in the juices of
the ripe grape, may be considered as the most marked and representa-
tive variety of the saccharine substances. It occurs more frequently
than any other in the animal fluids, being found in the juices of the
liver, in the chyle, the blood, and the lymph. In diabetes it is abund-
antly excreted with the urine. It is also found in the juices of many
plants, in various sweet fruits, and in honey, where it is associated with
certain other varieties. It is freely soluble in water. Its solution has
a moderately sweet taste, and deviates the plane of polarization toward
the right 53.5°.

It is this form of sugar which is produced from starch by boiling with
dilute acids, by the action of the digestive fluids of the alimentary canal,
and in the plant during the process of vegetation. The change consists
in the assumption by starch of the elements of water in due proportion,
the new substance thus produced being still a carbo-hydrate. The
transformation of starch into glucose is therefore represented as
follows : —

Starch. Water. Glucose.

C6H1005 + H20 = C6HW06-

Glucose may be recognized in solution by various well-marked tests.
First, the action of alkalies at a boiling temperature. If a solution of
glucose be treated with a solution of potassium hydrate and heat applied,
the sugar is decomposed and the liquid assumes, first, a yellowish and
then a brown color, which becomes deeper in proportion to the amount
of glucose and alkali existing in the solution. This is not a certain test
for the presence of glucose, as some other organic matters are discolored
in a similar way by the strong alkalies ; but it will serve to distinguish
it from certain varieties of sugar, which do not possess this property.

Secondly, the test most commonly employed for detecting glucose
depends upon its power of reducing the salts of copper in a boiling
alkaline solution. This test, which is known as " Trommer's test," is
applied in the following manner: A very small quantity of copper
sulphate in solution should be added to the suspected liquid, and the

SUGAR. 63

mixture then rendered distinctly alkaline by the addition of potassium
hydrate. The whole solution then takes a deep-blue color. On boiling
the mixture, if sugar be present, the copper suboxide is thrown down as
an opaque red, j^ellow, or orange-colored deposit ; otherwise no change
of color takes place. In this reaction the sugar, which is oxidized at a
high temperature under the influence of the alkali, takes a portion of
its oxygen from the copper in the copper salt, and thus reduces it to
the form of an insoluble suboxide.

Some precautions are necessary in the use of this test. As a general
rule, only a small quantity of the copper sulphate should be added to
the liquid under examination, just sufficient to give to the whole a dis-
tinct blue tinge after the addition of the alkali. If the copper salt be
used in excess, the sugar in solution may not be sufficient to reduce the
whole of it ; and that which remains as a blue sulphate may mask the
yellow color of that which is thrown down as a deposit. This diffi-
culty may be removed by due care in the proportion of the ingre-
dients.

Furthermore, there are some albuminous substances which have the
power of interfering with Trommer's test, and prevent the reduction of
the copper even when sugar is present. Certain animal matters, to be
more particularly described hereafter, which are liable to be held in solu-
tion in the gastric juice and in the blood, have this effect.

The ordinary ingredients of the urine also interfere with the complete
reaction of Trommer's test, by holding the copper oxide in solution, so
that no precipitate takes place when glucose is present, although the
liquid turns yellow on boiling. A very large proportion of glucose may
be added to fresh urine without giving rise to a pulverulent precipitate
on the application of Trommer's test; notwithstanding that, if dis-
solved in water, it will react in the proportion of one part in 10,000.
That the interference of urine with Trommer's test depends on its
retaining in solution the reduced copper oxide, and not upon its pre-
venting deoxidation, is indicated by the fact that the color of the
mixture changes, as usual, from blue to yellow although no precipitate
takes place ; and also by the experiments of Dr. Fowler,1 who has shown
that if the precipitate resulting from Trommer's test with a watery solu-
tion of glucose be added to boiling urine, it is at once redissolved. The
same observer has devised a method of applying the test successfully
notwithstanding the interference of the urine. A certain quantity of
urine can, of course, only dissolve a certain amount of copper oxide ;
and if the copper sulphate solution be added to a specimen of saccharine
urine in large proportion, the excess will be precipitated and show itself
as a deposit. A copper sulphate solution, made in the proportion of 1
part copper sulphate to T.5 parts of water, and added to saccharine urine
to the amount of one-half or one-third its bulk will generally be suffi-
cient to produce a satisfactory reaction.

1 New York Medical Journal, June, 1874, p. 632.

6i HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

All sources of error of this kind, due to the presence of extraneous
substances, may be avoided in delicate examinations, by treating the
suspected fluid with animal charcoal, or by evaporating it to dryness,
extracting the dry residue with alcohol, and then dissolving the dried
alcoholic extract in water, before the application of the test. Either of
these processes will remove the substances which interfere with the
action of Trommer's test, and will leave the glucose by itself in the
watery solution.

A more delicate form of the copper test for glucose is in the employ-
ment of " Fehling's liquor," which is an alkaline solution of a double
copper and potassium tartrate. It is made as follows : —

Take — Pure crystallized copper sulphate 40 grammes.

Neutral potassium tartrate 160 "

A solution of sodium hydrate of the specific gravity 1.12 . 650 "

The neutral potassium tartrate, dissolved in a little water, is first
mixed with the solution of sodium hydrate. Then the copper sulphate,
dissolved in 160 cubic centimetres of water, is gradually added to the
alkaline liquor, which assumes a clear, deep blue color. The whole is
finally diluted with water to the volume of 1154.4 cubic centimetres.
If one drop of this liquid be added to one cubic centimetre of a saccha-
rine solution and heat applied, it will detect one-fifteenth of a milli-
gramme of glucose by the reduction o£ the copper oxide. One advan-
tage of Fehling's liquor as a test is that the quantity of copper salt
contained in a given volume is accurately known, and consequently not
only the presence but alsd the amount of glucose in any solution may
be determined by the quantity of test liquid which it decomposes at a
boiling temperature. One cubic centimetre of Fehling's liquor is
exactly decolorized by •% J^th of a gramme of glucose.

One inconvenience connected with this test is that Fehling's liquor by
exposure to the air and light undergoes an alteration, in which some of
its tartaric acid disappears and is replaced by carbonic acid. In this
condition it will partially precipitate on boiling, even without the pres-
ence of sugar. To guard against this, it should be kept in bottles which
are quite full and protected from the light ; and, in every case where a
suspected fluid is to be examined for sugar, a small portion' of the test-
liquor should be previously boiled by itself, in order to be sure that it
has not undergone spontaneous decomposition. Although by exposure
to the air and light at a summer temperature, Fehling's liquor may become
altered at the end of a week, yet if protected from the light, in carefully
closed and full bottles, it can be kept unchanged for two or three years.

Thirdly, the most marked and distinctive property of glucose, in a
physiological sense, is its capacity for fermentation. If a watery solu-
tion of pure glucose be left to itself, even exposed to the air, no remark-
able change takes place in it. But if a small quantity of beer-yeast be
added and the mixture kept at a temperature of about 25° (77° F.), after
a short time it becomes turbid. It then develops an abundance of

SUGAR.

65

carbonic acid, which is partly dissolved in the liquid and partly rises
in the form of gas bubbles to its surface. It is this circumstance which
has given to the process the name of " fermentation" or boiling. At the
same time the sugar is gradually destroyed and alcohol appears in its
place. Finally the whole of the glucose is decomposed, having been
converted principally into alcohol, C2H60, and carbonic acid, CO.,.
Then the fermentation stops and the liquid becomes clear, its turbid con-
tents subsiding to the bottom as a whitish layer. This layer is itself
found to consist of yeast, which has increased in quantity over that
originally added, and is itself capable of exciting fermentation in another
saccharine liquid.

If, instead of a solution of pure glucose, we employ the expressed
juices of certain fruits, like those of the grape, which contain nitro-
genous albuminoid matters in addition to glucose, fermentation begins
after a certain period of exposure to the air, and goes on with the same
phenomena and results as before. This is the natural source of all the
vinous and alcoholic fluids used by man ; namely, the fermentation of
some fluid containing glucose or a similar saccharine substance.

The alcoholic fermentation of glucose is due to the vegetative
action of a microscopic fungus, known as Saccharomyces. This plant
consists entirely of cells which

multiply by a process of bud- Fig. 6.

ding, but do not produce fila-
ments, nor any compound ve-
getable fabric. The species
which is present in beer-yeast
is the " Saccharomyces cerevi-
sise." Its cells are usually
rounded in form, sometimes
oval (Fig. 6). They vary in
size, but the greater number
have an average diameter of 10
mmm. They have a very thin
investing integument, which
incloses a finely granular semi-
solid substance, often with one
or two rounded cavities or
vacuoles filled with fluid. The
cells are mostly isolated, but
occasionally two of them may

be seen adhering to each other. There is also a small amount of inter-
cellular liquid, containing albuminous matter and various mineral salts.
When a little of the yeast is added to a solution containing glucose,
the cells of the yeast-plant after a short time begin to multiply by bud-
ding. The buds increase rapidly in size, and, when the young cell has
nearly attained the size of its parent, it usually separates and begins an

SACCHAROMYCES OEREVISI^E, in its
quiescent condition ; from deposit of beer-
yeast, after fermentation.

66 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

SACCHAEOMYCES OBRKVISI^E during active
germination. From fermenting saccharine solu-
tion.

Fig. 7. independent existence. While

in this active condition the
cells are mostly oval in form,
and have an average diameter
of only a little more than 8 mmm.
Often two and three are seen
connected together, forming
moniliform chains. It is by
the active growth and develop-
ment of the cells during this
process that the glucose of the
solution is decomposed, and
alcohol and carbonic acid pro-
duced in its place. Another
species of saccharomyces forms
the fungus of bread-yeast, and
a third the ferment of grape-
juice by which it is made to un-
dergo the vinous fermentation.

When fermentation is used as a test, a little beer-yeast is added to
the supposed saccharine fluid, and the mixture kept at the temperature
of about 25° (77° P.). The gas which is given off during the process
is collected and examined, and the remaining fluid is purified by distil-
lation. If the gas be found to be carbonic acid, and if the distilled
liquid contain alcohol, there can be no doubt that a fermentable sugar
was originally present in the solution. Glucose undergoes fermenta-
tion more readily and completely than most other varieties of sugar.

Lactose, C12H24012, or Sugar of Milk.

This is the variety of sugar which is found in milk, the only fluid in
which it is known to occur. It is less freely soluble than glucose, and
its sweet taste is less marked. In watery solution it rotates the plane
of polarization to the right 58°.20. In chemical composition it is
isomeric with glucose, which it resembles in several of its reactions,
namely, in being decomposed and turned brown by boiling alkalies, in
readily reducing the copper-oxide in Trommer's and Fehling's tests,
and in undergoing the alcoholic fermentation under the influence of
yeast. It enters into fermentation, however, very slowly, as compared
with glucose, and the process is usually incomplete. If fermentation
go on in the milk itself, or in the presence of other ingredients of the
milk, a part of the sugar is converted into lactic acid, C3H603, also a
carbo-hydrate. By boiling for ^ome time with dilute sulphuric or
hydrochloric acid, lactose becomes readily and completely fermentable.
This sugar forms an important element in the food of the young
infant, being a constant ingredient of the milk. It is not known
from what substance it is formed in the tissues of the mammary gland ;

SUGAR. 67

but it is evidently a reserve material, intended for the nutrition of the
infant, and not for consumption in the body of the parent.

Saccharose, 012H220U, or Cane Sugar.

This variety, the oldest known species of sugar, is derived from the
juices of the sugar cane, where it exists in great abundance. It
solidifies on cooling from a hot concentrated solution in the well-
known white granular crystalline masses, the form in which it is
generally used for culinary purposes. If crystallized more slowly, it
furnishes large, colorless, prismatic crystals, in which form it is known
as " rock candy" or ki sugar candy." This sugar is also manufactured
from the juices of the beet-root, and, imperfectly purified, from those of
the sorghum and the sugar-maple. It exists to some extent in the
green stems of Indian corn, in sweet potatoes, in parsnips, turnips, and
carrots, and in the spring juices of the birch and walnut trees. Honey
is a mixture. of glucose and saccharose, together with various other
substances.

Cane sugar originates from glucose, in the process of vegetation, by
a change the reverse of that by which glucose itself is formed from
starch, that is, by the loss of oxygen and hydrogen in the proportions
to form water. A comparison of the chemical composition of the two
substances will show the manner in which the transformation takes
place, namely : —

Glucose. "Water. Cane sugar.

2(C6H1206) - H20 = C12H22On.

Saccharose is the most soluble of all the sugars, and has the strongest
sweet taste. It rotates the plane of polarization to the right 73°. 8 4.
It differs in its reactions from glucose by the fact that it is not turned
brown by boiling with an alkali, and does not reduce the copper-oxide
in Trommer's test, or does so very slowly and imperfectly. It may be
converted into glucose, however, by a few seconds' boiling with a trace
of dilute mineral acid, and will then react promptly both with boiling
alkalies and with Trommer's test. Cane sugar is not immediately
fermentable, but by contact with yeast it is after a time changed into
glucose, and finally enters into fermentation. As it occurs in the
tissues of the living vegetable, it is regarded as a reserve material,
which is subsequently reconverted into glucose for the purposes of
nutrition.1 When taken as food, it is transformed into glucose by the
intestinal fluids in the digestive process.

Sugar and starch, accordingly, in all their varieties, are closely allied
to each other, both in their chemical and physiological relations. Their
proportions of hydrogen and oxygen are such as to have given them, as
a class, a distinct name, and their mutual convertibility in the process
of vegetation has been shown by abundant investigations. Starch and
sugar, in the living plant, represent the same nutritive material under

1 Mayer, Agrikultur-Chemie, Band i. p. 122.

63 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

two different conditions ; starch being the substance in the form of a
solid deposit, and glucose in the form of solution and activity.1 In
the animal body, the glycogen of the liver is converted into soluble
glucose, and thus enters the circulation before it takes an active part
in the nutritive operations; and vegetable starch, when taken as food,
undergoes the same transformation in the intestinal canal. Finally
these substances, from whatever source they may be derived, are com-
pletely decomposed in the interior of the system, and do not reappear,
in any notable quantity, in the excreted fluids of the body.

IV. Fats.

The fatty matters, or fixed oils, are distinguished from the preceding
group, so far as regards their chemical composition, by the fact that they
do not contain hydrogen and oxygen in the proportions to form water,
the oxygen being present in smaller quantity ; and also by their large
proportion of carbon, which preponderates much, by weight, over the
other two elements. This fact is probably connected with the strongly
marked inflammability which constitutes one of their most useful pro-
perties, the oils being decomposed at a temperature of 300° (570° F.),
and burning with a bright flame. The peculiarly smooth consistency
of the oleaginous matters is also one of their distinguishing features,
and enables them to be employed as lubricating substances, to diminish
the friction between opposite surfaces.

The fats are all insoluble in water, slightly soluble in alcohol, and
freely soluble in ether, which is accordingly used with advantage in
extracting them from their admixture with other organic matters.
They are also readily soluble in each other. They exhibit no rotatory
action upon polarized light. They are all fluid at a high temperature,
and crystallize on being cooled down to the requisite point ; the precise
degree at which crystallization takes place varying for the different
kinds of fats.

The fats are not only insoluble in water, but they refuse to mix with
it, even after prolonged mechanical agitation ; and as soon as the two
fluids are left at rest they separate from each other, the water remain-
ing below, and the oil rising to the surface, where it collects as a dis-
tinct layer. But if the watery fluid contain a trace of free alkali, the
oil is broken up into minute particles, which are disseminated uni-
formly throughout the fluid and held in permanent suspension. Such
a fluid is called an emulsion, and presents an opaque white color, owing
to the intimate mixture of watery and oleaginous particles having
different refractive powers. In an emulsion, the oil does not suffer any
chemical modification, but is simply broken up into a state of minute
dissemination. It can be recovered, with all its original characters,
by evaporating the watery fluid and extracting the oil from the dry
residue by means of ether. Oil may also be emulsioned by contact

1 Sachs, Trait£ do Botauique. Puris, 1874, p. 840.

FATS. 69

with certain nitrogenous organic matters of an albuminous nature.
White of egg, or the serum of blood, exerts this effect in an energetic
manner, and the fatty substances of milk are held in suspension by its
liquid albuminous ingredients.

Another characteristic of the true fatty substances is their property
of saponification, that is, of forming soaps when subjected to certain
chemical influences. If either of the natural fats be boiled for a con-
siderable time in the watery solution of a free alkali, it is decomposed,
with the production of two new bodies—first, glycerine (C3H803), a neu-
tral fluid substance which is soluble in water; and secondly, a fatty
acid which combines with the alkali and forms a soap. An analogous
change is thought to take place with a portion of the fatty matters in
the animal fluids.

The fats are derived from both the animal and the vegetable world.
They are present in many of the solids and fluids of the living body,
and are found also in many varieties of vegetable food. The following
list gives the proportion of fat in various alimentary substances, accord-
ing to the tables of Payen : —

QUANTITY OF FAT IN 100 PARTS IN

Wheat . . . 2.10 Beef's flesh (average) . 5.19

Indian corn . . . 8.80 Calf's liver . . . 5.58

Potatoes . . . 0.11 Mackerel . . . 6.76

Beans .... 2.50 Salmon . . . 4.85

Peas .... 2.10 Oysters . . . 1.51

Sweet almonds . 24.28 Cow's milk . . . 3.70

Chocolate nut . . 49.00 Fowl's egg . . . 7.00

Beside entering as an ingredient into the above articles, fat is often
taken with the food in a pure, or nearly pure form, as butter, olive oil,
or the various kinds of adipose tissue.

Fat is produced in the vegetable tissues, perhaps to some extent
directly from carbonic acid and water, but certainly in considerable
quantity by transformation of the starch originally formed.1 It is from
this source that the fat so abundantly stored up in oily seeds and fruits
is mainly derived; and in this situation it is retained until required for
the purposes of germination and growth. It is accumulated in some
seeds and fruits in remarkable quantity, particularly in those of the
sweet and bitter almond, the chocolate tree, hemp, flax, ricinus com-
munis, and Croton tiglium, where it exists in the proportions of from
24 to 60 per cent.

The three most important varieties of fat are those known as Stearins,
Palmitine, and Oleine. They resemble each other in their general
characters, and differ mainly in their degree of fluidity at correspond-
ing temperatures ; stearine solidifying the most readily of the three,
while oleine remains fluid at a lower temperature than either of the
others.

1 Mayer, Agrikultur-Chemie, Band i. pp. 84, 85.

TO HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

Stearine, C57H1100C,

So called from the readiness with which it assumes the solid form, is a
main ingredient of the more consistent fats. It liquefies, when pure, at
about 60° (1400 p.^ an(j again solidifies when the temperature falls to

or a little below this point. It

•Fig- 8- crystallizes, on cooling from a

warm solution in oleine, in fine
radiating needles which often
follow a wavy or curvilinear
direction. It is rather less
freely soluble in alcohol and
ether than the other fatty sub-
stances.

Palmitine, C51H9806,
Was first recognized as an in-
gredient of palm oil, a semi-
solid fat obtained from the
seed of an African palm. It
crystallizes, on cooling from its
concentrated alcoholic or ethe-

STEABiNE,cryBtallizedJrom a warm solution in real solution, in the form of

slender needles. It liquefies

about the temperature of 46° (115° F.). It is found in considerable
abundance in a variety of animal and vegetable fats.

Oleine, C57H10406.

As its name indicates, this is the representative ingredient of the oils,
or liquid fatty substances. When pure it is transparent and colorless.
It retains its fluidity at all ordinary temperatures, and even below the
freezing point of water. It readily dissolves both stearine and palmi-
tine, its solvent power for these substances increasing writh the elevation
of the temperature.

None of these oleaginous substances occur naturally in an isolated
form, but they are mingled together in varying proportions in all the
ordinary animal and vegetable fats and oils. The consistency of the
mixtures varies with the relative quantity of their different fatty ingre-
dients. Thus the more solid fats, such as suet and tallow, consist
largely of stearine ; the softer fats, as lard, butter, and the ingredients
of human adipose tissue, contain a greater abundance of palmitine;
while the liquid fats, like the fish oils, olive oil, and nut oil, are
composed mainly of oleine. As a general rule, in the bodies of the
warm-blooded animals these mixtures are fluid, or very nearly so, in
consistency ; for, although both stearine and palmitine, when pure, are
solid at the ordinary temperature of the body, they are held in solu-
tion during life by the oleine with which they are associated. After

FATS.

71

OLEAGINOUS PBINCIPLES OP HUMAN
FAT. Steariiie and Palmitine crystallized ; Ole-
ine fluid.

death, as the body cools, the Fig. 9.

stearine and pafmitine some-
times separate in a crystalline
form, since the oleine can no
longer hold in solution so large
a quantity as it had dissolved at
a higher temperature. (Fig. 9.)

When in a fluid state, the fatty
substances present themselves in
the form of drops or globules,
which vary greatly in size, but
which may be readily recog-
nized by their optical proper-
ties. They are circular in shape,
with a sharp well-defined out-
line. They often have a faint
amber color, which is distinctly
marked in the larger globules,
less so in the smaller. As they

have a higher refractive power than the watery fluids in which they are
immersed, they act under the microscope as double convex lenses, and
concentrate the light transmitted through them, at a point above the
level of the liquid. Consequently, they present the appearance of a
bright centre surrounded by a dark border. If the lens of the micro-
scope be lifted farther away, the centre of the globule becomes brighter,
and its borders darker. These characters will usually be sufficient to
distinguish them from other fluid globules of less refractive power.

The oleaginous matters present a striking peculiarity in regard to the
form under which they occur in the living body, and one which distin-
guishes them from other ingredients of the animal solids and fluids.
The remaining proximate principles of different groups are intimately
associated together by molecular union, so as to form either clear solu-
tions or homogeneous solids. Thus the saccharine matters of the blood
or the milk are in solution in water, in company with the albumen, the
lime phosphate, sodium chloride, and the like ; all of them equally dis-
tributed throughout the general mass of the fluid. In the bones and
cartilages, the animal matters and the calcareous salts are in similarly
intimate union with each other ; and in every other part of the body the
animal and inorganic ingredients are united in a similar way. But it is
different with the fats. For, while the three principal varieties of
oleaginous matter are united with each other, they are not united, as a
general rule, with proximate principles of other kinds ; that is, with
water, saline substances, sugar, or albumen. The fats are soluble to a
certain extent in the ingredients of the bile, and they are found in small
quantity, in the saponified condition, in the plasma of the blood, as
sodium stearate, palmitate, or oleate. But in by far the larger propor-

72 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

tion of cases, instead of forming a homogeneous solid or fluid with the
other proximate principles, the oleaginous matters are* found in distinct
masses or globules, suspended in the serous fluids, interposed in the
interstices between the anatomical elements, included in the interior of
cells, or deposited in the substance of fibres or membranes. Even in
the vegetable tissues, oil is always deposited in distinct drops or
granules.

Owing to this fact, the oils can be easily extracted from the organized
tissues by the employment of mechanical processes. The tissues, animal
or vegetable, are cut into small pieces and subjected to pressure, by
which the oil is forced out from the parts in which it was entangled,
and separated, sometimes without further manipulation, in a state of
comparative purity. A moderately elevated temperature facilitates the
operation by increasing the fluidity of the oleaginous matter ; but no
chemical agency is required for its separation. Under the microscope,
oil-drops and granules can be readily distinguished from the remaining
parts of a tissue, and may also be recognized by the dissolving action
of ether, which acts upon them, for the most part, without attacking
the other proximate principles.

Oils are found, in the animal body, most abundantly in the adipose
tissue. Here they are contained in the interior of the adipose vesicles,
the cavities of which they completely fill, in a state of health. These
vesicles are transparent, and have a partly angular form, owing to their
mutual compression. (Fig. 10.) They vary in diameter, in the human sub-
ject, from 28 mmm. to 125 mmm., and are composed of a thin, structure-
less animal membrane, forming

Fig- 10. a closed sac. in the interior of

which the oily matter is con-
tained. The oil, accordingly,
is simply included mechani-
cally in the interior of the
vesicles. Sometimes, when
emaciation is going on, the oil
partially disappears from the
cavity of the adipose vesicle,
and its place is taken by a
watery serum ; but the serous
and oily fluids remain distinct,
and occupy different parts of
the cavity of the vesicle.

In the chyle, the oleaginous
matter is in a state of emul-
sion or suspension in the form
of minute particles in a serous fluid. Its subdivision is here more com-
plete, and its molecules more minute, than anywhere else in the body.
It presents the appearance of a fine granular dust, which has been known
by the name of the " molecular base of the chyle." A few of these

HUMAN ADIPOSK TISSUE.

FATS.

73

CHYLE, from commencement of Thoracic Duct,
from the Dog.

granules are to be seen which Fig. H-

measure 2.5 mmm. in diameter ;
but they are generally much
less than this, and the greater
part are so small that they can-
not be accurately measured.
(Fig. 11.) For the same reason
they do not present the bril-
liant centre and dark border of
the larger oil-globules ; but ap-
pear by transmitted light only
as minute dark granules. The
white color and opacity of the
chyle, as of all other fatty emul-
sions, depend upon this mole-
cular condition of the oily in-
oredients. The albumen and

O

salts, which are in intimate

union with each other, and dissolved in the water, would alone make a
colorless and transparent fluid; but the oily matters, suspended in
distinct particles, with a different refractive power from that of the
serous fluid, interfere" with its transparency, and give to the mixture
the white color and opaque appearance which are characteristic of emul-
sions. The oleaginous nature
of these particles is readily
shown by their solubility in
ether.

In the milk, the oily matter
occurs in larger masses than in
the chyle. In cow's milk (Fig.
12), the oil-drops, or "milk-
globules," are not quite fluid,
but have a pasty consistency,
owing to the large quantity of
palmitine which they contain, in
proportion to the oleine. When
forcibly amalgamated with each
other and collected into a mass
by prolonged beating or churn-
ing, they constitute butter. In
cow's milk, the globules vary

somewhat in size, but their average diameter is 6 mmm. They are
suspended in the serous fluid of the milk, and by heating may be more
perfectly liquefied, and made to assume a circular form.

In the cells of the laryngeal, tracheal, and costal cartilages (Fig. 13)
there is always more or less fat deposited in the form of rounded glo-
bules, somewhat similar to those of the milk.
6

Fig. 12.

GLOBULES

Cow's MILK.

74 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

Fig. 13.

CELLS OF COSTAL CARTILAGES, containing
oil-globules. Human.

Fig. 14.

In the glandular cells of the liver, oil occurs constantly, in a slate of
health. It is here deposited in the substance of the cell (Fig. 14),

generally in smaller globules
than the preceding. In some
cases of disease, it accumulates
in excessive quantity, and pro-
duces the state known as fatty
degeneration of the liver. This
is consequently only an exag-
gerated condition of that which
normally exists in health.

In the carnivorous animals
oil exists in considerable quan-
tity in the convoluted portion
of the uriniferous tubules. (Fig.
15.) It is here in the form of
granules and rounded drops,
which sometimes appear to fill
nearly the whole calibre of the
tubules.

It is found also in the secret-
ing cells of the sebaceous and
other glandules, deposited in
the same manner as in those of
the liver, but in smaller quan-
tity. It exists, beside, in large
proportion, in a granular form,
in the secretion of the seba-
ceous glandules.

It occurs abundantly in the
marrow of the bones, both un-
der the form of free oil-globules
and inclosed in the vesicles of
adipose tissue, and is found in
considerable quantity in the
substance of the yellow wall of
the corpus luteum.

It occurs also in the form of

granules and oil-drops in the muscular fibres of the uterus (Fig. 16),
in which it begins to be deposited soon after delivery, and where it
continues to be present during the whole period of the resorption or
involution of this organ.

In all these instances^ the oleaginous matters remain distinct in form
and situation from the other ingredients of the tissues, and are only
mechanically entangled among the fibres and cells, or imbedded in their
interior.

HEPATIC CELLS. Human.

FATS.

75

Fig. 15.

TJRTNIFEROUS TUBULES OF DOG, from COr-

tical portion of kidney.

Fig. 16.

A large part of the fat which is found in the animal body may be
accounted for by that which is taken in with the food, since oily matter
occurs in both animal and vege-
table substances. Fat is, how-
ever, formed in the body from
other organic substances, inde-
pendently of what is intro-
duced with the food. This
important fact has been defi-
nitely ascertained by the ex-
periments of MM. Dumas and
Milne-Edwards on bees,1 M.
Persoz on geese,3 and finally
by those of M. Boussingault
on geese, ducks, and pigs.3 The
observers first ascertained the
quantity of fat existing in the
whole body at the commence-
ment of the experiment. The
animals were then subjected to
a definite nutritious regimen,
in which the quantity of fatty
matter was duly ascertained by
analysis. The experiments
lasted for a period varying, in
different instances, from thirty-
one days to eight months;
after which the animals were
killed and all their tissues ex-
amined. The result of these
investigations showed that con-
siderably more fat had been
accumulated by the animal
during the course of the expe-
riment than could be accounted
for by that which existed in
the food ; and placed it beyond
a doubt that oleaginous sub-
stances may be, and actually

are, formed in the interior of the animal body by the decomposition or
metamorphosis of other proximate principles.

There is reason to believe that fat is produced in this way, under the
influence of the vital process, from the transformation of starchy and
saccharine substances. In the first place, as we have already seen, there

MUSCULAR FIBRES OF HUMAN UTERUS
three weeks after parturition.

1 Annales de Chira. et de Phys., 3d series, vol. xiv. p. 400. 2 Ibid., p. 408.

3 Chimie Agricole. Paris, 1854.

76 HYDROCARBONACEOUS PROXIMATE PRINCIPLES.

is no clonbt that fat is produced from starch and glucose in vegetables
during a certain period of their growth. The oily seeds of certain
plants while still immature contain starch ; but as they ripen, the starch
diminishes or disappears and oil takes its place.1

It is also a matter of common observation that articles of food, con-
sisting largely of starch or sugar, or of both, are especially apt to be
fattening, both for man and animals and in sugar growing countries,
during the short season occupied in extracting and preparing the sugar,
the horses and cattle, as well as the laborers emplo3red on the plantation,
all of whom partake freely of the saccharine juices, grow remarkably
fat, and again lose their superabundant flesh when the season is past.
It is not known, however, whether the saccharine matters in these in-
stances are directly converted into fat, or whether they pass through a
series of intermediate changes which furnish the materials for its forma-
tion. The abundant accumulation of fat in certain regions of the body
and its absence in others, and more particularly its constant occurrence
in situations to which it could not have been transported by the blood,
as the interior of the cells of the costal cartilages, make it probable that
oily matter is often formed from the metamorphosis of other proximate
principles, upon the very spot where it makes its appearance in the
solid tissues. Cases of hereditary obesity, and of obesity occurring
only after a definite period of life, indicate also that the excessive depo-
sition of fat may be due to internal causes dependent on the special
condition of the bodily system.

In the female during lactation, a large part of the oily matter intro-
duced with the food, or formed in the body, is discharged with the milk,
and goes to the support of the infant. But in the female in the inter-
vals of lactation, and in the male at all times, the oily matters almost
entirely disappear by decomposition in the interior of the body ; since
the small quantity which is discharged with the sebaceous matter by
the skin bears only an insignificant proportion to that which is intro-
duced daily with the food.

Beside the fats proper there is also contained in the body the fol-
lowing substance, which resembles fat in the general features of its
chemical composition, and in some of its reactions, but differs from
them in three important particulars, namely : 1st, in being volatile at a
high temperature ; 2d, in exerting a rotatory action on polarized light ;
and 3d, in the fact that it cannot be transformed, by the action of alka-
line solutions, into glycerine and a fatty acid — that is, it is not saponi-
fiable.

Cholesterine, C26H440,

So called from its being often precipitated as a solid deposit from the
bile, in which form it was first discovered. Cholesterine is an ingredient
in the blood-plasma and the blood-globules, in the bile, in the sebaceous

1 Prof. S. W. Johnson, How Crops Grow. New York, p. 94.

CHOLESTERINE.

77

Fig. 17.

matter of the skin, the liver, the spleen, the crystalline lens, and espe-
cially in the nerves, spinal cord, and brain, in which last it has been
found by Flint1 in the proportion on the average of about one part per
thousand. Recent observations have shown that it is also a constituent /
of various articles of food, such as the yolk of egg, and even of many 1
vegetable products, as peas, beans,3 olives, almonds, and Indian corn.3 J

Cholesterine is a cry stalliz able substance, insoluble in water, freely
soluble in ether, chloroform, boiling alcohol, and the volatile and fatty
oils. It is partially soluble in
watery solutions of the biliary
salts and of the saponified fats.
It is deposited from its alco-
holic or ethereal solution in
the form of very thin, color-
less, transparent, rhomboidal
plates, portions of which are
often cut out by lines of cleav-
age parallel to the edges of the
crystal. They frequently occur
deposited in layers, in which
the outlines of the subjacent
crystals show very distinctly
through the substance of
those placed above. It is
often found, in a crystalline
form, in the fluid of hydrocele
and other morbid exudations, in the contents of encysted tumors, and
in biliary calculi. Crystallized cholesterine melts at 145° (293° F.)?
and distils unchanged in vacuo at about 360° (680° F.). Its solutions
rotate the plane of polarization to the left 32°.

If cholesterine be triturated with strong sulphuric acid, and chloro-
form added to the mixture, a blood-red color is produced, which after-
ward disappears by exposure to the air, passing gradually from red to
violet, blue, and green, the solution finally becoming colorless.

Our knowledge with regard to the physiological relations of choleste-
rine is less definite than as to those of the true fatty substances. Its
abundant proportion in the brain and nerves, and its association in these
tissues with other important constituents, have led to the opinion that
it is an essential ingredient of the nerve substance. Whatever may be
its source in these organs, it is no doubt absorbed from the nervous
system by the blood, carried to the liver, and thence discharged with

1 American Journal of the Medical Sciences, October, 1862.

Hoppe-Seyler, Handbuch der Physiologisch- und Pathologisch-Chemischen,
Analyse. Berlin, 1870, p. 98.
3 Hardy, Principes de Chimie Biologique. Paris, 1871, p. 123.

GHOLBSTERINE, from an Encysted Tumor.

78 HYDROCARBONAOEOUS PROXIMATE PRINCIPLES.

the bile. According to the observations of Prof. Flint, Jr., on the dog,1
its quantity in the blood increases, while passing through the brain,
from 0.52 to 1.09 parts per thousand. Authorities differ as to whether
it is discharged with the feces, or is transformed in the interior of the
body.

The most important characteristic, in a physiological point of view,
of all the proximate principles of the second class, including the amyla-
ceous, saccharine, and oily substances, relates to their source and their
final destination. Not only are they of organic origin, making their
appearance first in the interior of vegetables ; but they are all produced
also, to a certain extent, from other organic materials, in the bodies of
animals ; continuing to be formed when no similar substances, or only
an insufficient quantity of them, have been taken with the food. Fur-
thermore, when introduced with the food, or formed in the body and
deposited in the tissues, these substances are not found in the secretions.
They, therefore, for the most part, disappear by decomposition in the
interior of the body. They pass through a series of changes by which
their essential characters are destroyed ; and they are finally replaced
in the circulation by other substances, which are discharged with the
excreted fluids.

1 Physiology of Man, vol. iii. New York, 1870, pp. 281, 282

CHAPTEE IV.

ALBUMINOUS MATTEES.

THE proximate principles belonging to this class are very important,
not only from their peculiar physiological properties, but also from
their comparatively abundant quantity in the animal body. They are
derived both from animal and vegetable sources. But in plants, as a
general rule, the albuminous matters, though constantly present, and
essential to the activity of vegetative life, are in small quantity as com-
pared with other ingredients of the fully developed tissues. In man and
animals, on the other hand, they constitute by far the larger part of all
the solid constituents of the body. Everywhere their chemical consti-
tution, their physical characters, and the distinctive properties which
belong to them, show that they have an intimate connection with the
more active phenomena of living beings.

The first peculiarity by which they are distinguished from the proxi-
mate principles of the preceding class, is that they contain nitrogen, in
addition to the three elements belonging to other organic bodies, namely,
carbon, hydrogen, and oxygen. They are, therefore, sometimes called
the "nitrogenous" proximate principles. But, as we shall hereafter
see, there are various other substances, of a crystallizable nature, also
containing nitrogen, which are produced in the body, and which are of a
different character from the albuminous matters.

The albuminous matters are not crystallizable. They always, when
pure, assume an amorphous condition, in which they are sometimes
solid, as in the bones ; sometimes fluid, as in the plasma of the blood ;
and sometimes semi-solid in consistency, or midway between the solid
and fluid condition, as in the muscles and the substance of the
glandular organs. Even in the fluids, the albuminous matters, when
present in considerable quantity, as in the blood-plasma, the pancreatic
juice, or the subrnaxillary saliva, give to the solution a peculiar
viscid or mucilaginous consistency. This consistency is more marked,
in proportion to the abundance of the organic ingredients. The
albuminous matters, in solution, all rotate the plane of polarization
toward the left. The precise chemical constitution of these substances
has not been in all cases determined. The apparent variation in the
exact proportion of their ultimate elements in different instances is
probably due to the readiness with which they become modified in the
processes of nutrition, many of them passing into each other under the
influence of digestion and assimilation. There are, no doubt, a great
variety of these matters existing in the body, only a certain number of

80 ALBUMINOUS MATTERS.

which have as yet been so distinctly recognized as to receive specific
names. Many of them, perhaps all, contain a small amount of sulphur
in addition to their carbon, hydrogen, oxygen, and nitrogen. Their
chemical relation to other substances has not been found sufficiently
definite, in any case, to establish the formula for their atomic constitu-
tion. The average proportion, however, by weight, of their constituent
elements, according to the tables of Hoppe-Seyler1 and Fremy, is as
follows : —

AVERAGE COMPOSITION OF ALBUMINOUS MATTERS.

Carbon 52.0

Hydrogen ...... 6.9

Nitrogen 15.6

Oxygen 24.0

Sulphur ....... 1.5

100.0

One of the simpler physical characters of the albuminous substances
is that they are hygroscopic. ' As met with in different parts of the body,
they present different degrees of consistency ; some being nearly solid,
others more or less fluid. But on being subjected to evaporation they
all lose water, and may finally be reduced to the perfectly solid form.
If after this desiccation they be exposed to the contact of moisture,
they again absorb water, swell, and regain their original mass and con-
sistency. This phenomenon is different from that of capillary attrac-
tion, by which some inorganic substances or tissues become moistened
when exposed to the contact of water ; for in the latter case the water
is simply entangled mechanically in the meshes and pores of the inorganic
body, while that which is absorbed by the albuminous matter is actually
united with its substance, and diffused equally throughout its entire
mass. Every albuminous matter is naturally united in this way with a
certain quantity of water, some with more, some with less. Thus the
albumen of the blood is in union with so much water that it has the
fluid form, while the corresponding substance of cartilage contains less
and is of a firmer consistency. The quantity of water contained in each
albuminous substance may be diminished by artificial desiccation, or by
a deficient supply ; but it cannot be increased beyond a certain amount.
Thus, if the albumen of the blood and the albuminous matter of carti-
lage be both reduced by evaporation to a similar degree of dryness, and
then placed in water, the albumen will absorb so much as again to be-
come fluid, but the cartilaginous substance only so much as to regain
its usual nearly solid consistency. Even where the organic substance,
therefore, as in the case of albumen, becomes fluid under these cir-
cumstances, it is not precisely by its solution in water, but only by its
reabsorption of that quantity of fluid with which it was naturally
associated.

1 Handbuch der Physiologisch- und Pathologisch-Chemischen Analyse. Berlin,
1870.

ALBUMINOUS MATTERS. 81

Another characteristic feature of the proximate principles of this
group is their property of coagulation. Those which are naturally fluid
suddenly assume, under certain conditions, a solid or semi-solid consist-
ency. They are then said to be coagulated ; and, when once coagulated,
they cannot usually be made to resume their original condition. This
property of coagulability is not only a marked quality of the albu-
minous matters as a class, but it often serves to distinguish them
from each other by the different special conditions under which it is
manifested by each one. Thus the substance producing fibrine coagulates
spontaneously on being withdrawn from the bloodvessels ; albumen, on
being subjected to the temperature of boiling water ; caseine, on being
placed in contact with an acid. When an albuminous substance thus
coagulates, the change which takes place is a peculiar one, and differs
from that by which a mineral salt is precipitated from its watery solu-
tion. The albuminous matter, in coagulating, appears to assume a
special condition, and to permanently change its properties; but, in
passing into the solid form, it still retains ^all the water with which it
was previously united. Albumen, when coagulated, retains the same
quantity of water in union with it which it held before. After coagu-
lation, this water may be driven off by evaporation, in the same manner
as previously ; and on being once more exposed to moisture, the organic
matter will again absorb the same quantity, though it will not assume
the liquid form. The coagulated substance may sometimes be dissolved
by certain chemical agents, as the caustic alkalies ; but it is not by
this means restored to its original condition. It rather suffers a still
further alteration.

In many instances we are obliged to resort to coagulation in order
to separate an albuminous substance from the other proximate princi-
ples with which it is associated. This is the case, for example, with
the fibrine of the blood, which is obtained in the form of flocculi, by
beating freshly-drawn blood with a bundle of rods. But when separated
in this way, it is already in an unnatural condition, and no longer
represents exactly the original fluid fibrine as it existed in the circulating
blood. Nevertheless, this is the only mode in which it can be examined,
as there are no means of bringing it back to its previous condition.

Another important property of the albuminous matters is that they
excite, in other proximate principles and in each other, those peculiar
indirect chemical changes which have been termed catalyses or catalytic
transformations. That is to say, they produce the changes referred to,
not directly, by combining with the substance which suffers alteration,
or with any of its ingredients ; but simply by their presence, which
induces the chemical change in an indirect manner. We do not under-
stand the manner in which these changes are accomplished, but the
influence thus exerted by the albuminous matters is a very marked one,
and is of great importance in many of the acts of animal and vegetable
nutrition. A comparatively small quantity of the catalytic body is
often capable of inducing a palpable change in a large quantity of

82 ALBUMINOUS MATTEKS.

another substance. The action of vegetable diastase in converting
starch into dextrine and glucose is a process of this nature ; and it is
found that one part of diastase is capable of effecting the transformation
of 2000 parts of starch. The albuminous ingredients of the saliva, of
the pancreatic and intestinal juices, exert a similar action on hyd rated
starch. The whole process of digestion and assimilation is in great
part made up of a series of such catalytic changes, in which the
nutritious matters undergo their requisite transformations, by contact
with special albuminous ingredients of the blood, the tissues, or the
secretions.

At a temperature of 300° (570° F.) or over, the albuminous matters,
like other organic substances, are destroyed and decomposed into
gaseous products. But if subjected for a certain time to a temperature
of about 125° (257° F.)? they undergo a change in addition to their
coagulation, by which a distinct and agreeable flavor is developed, and
by which they become suitable for use as human food. It is this change
which is produced in the process of cooking, and the peculiar flavor
which results always depends upon the presence of a certain quantity
of albuminous matter in the substance employed. If the temperature
at which the cooking process is carried on be too low, the characteristic
flavors are not developed; if it be too high, they are destroyed and
replaced by empyreumatic odors, from the combustion or decomposition
of the ingredients of the food.

Lastly, the albuminous matters are distinguished by the property of
putrefaction. This is a process by which dead animal substances,
when exposed to the atmosphere at a moderately warm temperature,
gradually soften and liquefy and are finally decomposed, with the pro-
duction of certain fetid and unwholesome gases, among which are
hydrogen sulphide and carbide, usually with more or less carbonic acid,
nitrogen, and ammoniacal vapors. The mixture of these emanations
causes an odor which is easily recognized as a "putrefactive odor;"
and wherever such emanations are perceived, it is an indication that
some substance containing albuminous matters is undergoing decom-
position. As these albuminous matters are more abundant in the
tissues and fluids of animals than in those of vegetables, the phenomena
of putrefaction are also most distinctly marked in the decay of animal
substances. But they will take place in both, under the requisite con-
ditions. A solution of nitrogenous vegetable matters will present all
the essential characters of putrefaction, though not developed with the
same degree of intensity as in fluids of animal origin.

In order that putrefaction may take place certain special conditions
are necessary. In the first place it requires the access of atmospheric
air, or of some fluid containing oxygen. If the putrescible substance
be first boiled so as to expel all the free oxygen contained in its fluids,
and if then, while the boiling is going on, it be inclosed in a hermetically
sealed vessel, no putrefaction takes place, but the substance remains
unaltered for an indefinite time. It is by this means that cooked meats

ALBUMINOUS MATTERS.

83

are preserved in sealed cans, for use upon long voyages or expeditions
at a distance from the usual base of supplies. So long as the cans are
kept perfectly closed, their contents remain sound. After they are
opened and the air admitted to their interior, the food must be used at
once, otherwise it will begin to putrefy after the usual interval of time.

Another essential condition for putrefaction is the presence of
moisture. Albuminous substances which are reduced to a perfectly
dry state do not undergo decomposition ; and in some regions, where a
high temperature and a dry atmosphere favor the rapid desiccation of
organic substances, this fact is also utilized for the preservation of
meats. Immediately after the animal is killed, the flesh is cut into thin
strips and hung up to dry in the air, and, desiccation being completed
before putrefaction has commenced, the food thus prepared is preserved
for an indefinite time.

The third requisite for putrefaction is a moderately elevated tempe-
rature. It goes on most rapidly between 25° and 35° (^7° to 95° F.).
Below 25° it gradually diminishes in activity, and ceases altogether
about the freezing point of water. Meats, therefore, which are kept
frozen or closely packed in ice do not putrefy. The process is also
suspended in all albuminous matters exposed to winter weather at the
freezing point. The carcass of an extinct mammoth has even been
found imbedded in ice in Northern Siberia, which was in such a state
of preservation that its flesh was used for food by dogs and other
animals.1 A temperature much above 35° is also unfavorable to the
putrefactive change, and it is completely arrested by a heat approaching
that of boiling water.

The process of putrefaction
is accompl ished by the growth
and multiplication of a micro-
scopic vegetable organism,
somewhat analogous to that
by which fermentation is ex-
cited in saccharine fluids.
If any clear solution con-
taining animal or vegeta-
ble albuminous matters be
exposed to the air at a
moderate temperature, after
a short time it becomes tur-
bid. This turbidity is due to
the development of minute
vegetable cells, of very sim-
ple organization, which mul-
tiply with great rapidity in

Fig. 18.

CELLS OF BACTERIUM TEBMO; from a
putrefying infusion.

1 M6moires de 1' Academic Imperiale des Sciences de St. Petersbourg, tome 5,
p. 440.

84 ALBUMINOUS MATTERS.

the decomposing liquid, and produce in it, by their vegetative activity,
the changes of putrefaction. These cells belong to the genus " Bacteri-
um," so called from their simple rod-like form ; and the species which
is invariably to be found in putrefying infusions is known by the
name of Bacterium termo. The cells are of an oblong form, and
average 3 mmm. in length by 0.6 mmm. in thickness. They are usually
double, consisting of two single cells placed end to end. While actively
growing in a putrefying infusion, they are in constant process of mul-
tiplication, by which their numbers are rapidly increased. The multi-
plication takes place by spontaneous division of the cell, by a trans-
verse partition which grows across its middle. After a time the two
cells, thus formed out of a single one, separate from each other, and
each repeats the process for itself.

One of the most remarkable characters of the bacterium cells is
their active spontaneous movement. During a certain period of their
development they are in incessant and rapid motion by means of a
conical rotation about their longitudinal axis, by which they are trans-
ported in various directions through the fluid in which they are contained.
This motion is often so rapid that it can hardly be followed by the eye ;
in other instances it is so slow that its mechanism may be distinguished
by careful examination. The movement and mutiplication of the bac-
terium cells go on while putrefaction continues. After all the albumin-
ous ingredients of the infusion have been decomposed, the liquid again
becomes clear, and the bacterium cells subside to the bottom in a quies-
cent whitish layer. A small portion of this layer will readily excite
putrefaction, if added to another albuminous liquid.

As the bacterium cells effect the decomposition of albuminous matters
by their own vegetative activity, it is for this reason that putrefaction
is limited by certain special conditions, already mentioned. Bacteria
belong to the group of colorless cryptogamic vegetables. Like other
plants of this kind, they assimilate directly organic substances ready
formed, and at the same time absorb oxygen and exhale carbonic
acid, after the manner of animals. Consequently oxygen is one of the
substances essential to their growth ; and, as putrefaction takes place
only by means of their vital activit}r, ox}^gen or atmospheric air must
be present in order to allow putrefaction to go on. Furthermore the
presence of moisture is necessary to their growth, as it is to that of all
other plants ; and a substance thoroughly dried cannot putrefy, since no
vegetative development is possible in the total absence of moisture. A
certain degree of warmth is also essential to the continued growth of
these bodies. Their development is suspended by a freezing tempera-
ture, and their vitality is destroyed by prolonged contact with boiling
water.

Lastly, a certain amount of albuminous matter is necessary for the
nutrition of bacteria. Their cells may remain indefinitely, in a quies-
cent condition, suspended in other fluids or even in pure water; but
for their active development and multiplication they require the pre-

FIBRINE. 85

sence of albuminous matters, which appear to supply the necessary
material for their growth. They decompose these substances therefore
by assimilating their ingredients in the process of vegetable nutrition,
and the putrefactive gases are the final result of the changes thus taking
place, just as alcohol and carbonic acid are produced in the fermenta-
tion of saccharine liquids.

Fermentation and putrefaction, accordingly, are analogous processes,
in which certain materials are decomposed under the influence of micro-
scopic vegetation. The former takes place in saccharine fluids, the
latter in those containing albuminous matter; since the yeast-plant
requires for its growth a preponderance of non-nitrogenized hydrocar-
bonaceous matter, while bacterium cells are nourished mainly by the
absorption of nitrogenous substances.

The following table shows the proportion of albuminous matter,
according to Payen, in different substances used as food : —

QUANTITY OF ALBUMINOUS MATTER IN 100 PARTS IN

Beef flesh . . . 19.50 Wheat grains . . 18.03

Fowl's eggs . . 12.35 Rye .... 12.50

Mackerel . . . 24.31 Oats .... 14.39

Salmon . . . 13.58 Indian corn . . 12.50

Oysters . . . 14.01 Rice .... 7.55

Beans (dry) . . 24.40 Potatoes . . . 2.50

Peas " . . . 23.80 Sweet potatoes . . 1.50

The first formation of albuminous matter takes place in vegetables,
subsequent to the production of the non-nitrogenous organic substances,
starch and glucose, by the union of these last with nitrogen derived
from the inorganic salts. Green plants, which have the power of gene-
rating the carbohydrates from carbonic acid and water, if supplied with
moisture containing nitrates or ammonium salts in solution, are known
to grow vigorously and increase many fold their contents of albuminous
matter.1 These salts must therefore have supplied the nitrogen requisite
for the formation of the nitrogenous substances. The sulphur, which
also enters into the composition of these substances, is derived by the
plants from a reduction of the soluble sulphates contained in the soil.

Notwithstanding the very marked and important peculiarities which
distinguish the albuminous matters as a group, there are many of these
substances which differ from each other by a variety of secondary char-
acters. It is possible that some of those now designated by specific
names may really be mixtures of two or more distinct substances ; but
the classification at present in use expresses the distinguishing marks
of the more important varieties, so far as they are yet known.

Fibrine.

Fibrine is found in the plasma of the blood, where it exists in the
proportion, on the average, of three parts per thousand. It is also

1 Mayer, Lehrbuch der Agrikultur-Chemie, Band i. pp. 145, 150.

bb ALBUMINOUS MATTERS.

present in small quantity in the lymph and in the chyle. It is this sub-
stance which is distinguished by its property of " spontaneous coagula-
tion ;" that is, it coagulates on being withdrawn from the vascular
system, without the addition of any physical or chemical reagent. It
is the coagulating element of the blood ; and the power of freshly drawn
blood to form a clot depends upon its presence as an ingredient of the
circulating fluid. The term fibrine properly represents, hot the solid
clot obtained by coagulation, but the fluid substance existing before-
hand in the blood, and which becomes solidified after its withdrawal.
It is regarded by some as generated by the union of two pre-existing
substances ; by others, as produced from the decomposition of one. As
we have, however, but little opportunity of studying it while still forming
a part of the fluid plasma, our knowledge is mainly confined to its pro-
perties in the solidified form. It is obtained by stirring the freshly
drawn blood with glass rods or a bundle of twigs, and afterward washing
the deposited clots with distilled water until the adherent coloring
matter is removed.

Coagulated fibrine is a colorless, tolerably firm, extensible, and
elastic substance, which has, under the microscope, a finely fibrillated
texture. It is insoluble in water, but in solutions of the caustic alkalies
or the alkaline carbonates it becomes gelatinous, and is after a time, by
the aid of warmth, partially dissolved. Some of the free acids, as hydro-
chloric, acetic, lactic, or phosphoric acid, have a similar effect. If it be
heated in water or in a neutral liquid to 72° (162° F.), it becomes con-
tracted, white, and opaque, and less extensible than before.

An albuminous matter very similar in its physical properties to animal
fibrine, exists in certain vegetable substances, especially in wheat flour,
where it is known as gluten. When freed from the admixture of other
ingredients, it is tenacious, extensible, elastic, insoluble in water, and
slowly soluble in dilute alkalies. Its property of tenacity and its
nitrogenous character make it an important constituent of wheat flour
in the manufacture of bread.

Albumen.

Albumen is found abundantly in the plasma of the blood, also in the
lymph, the pericardial and cephalo-rachidian fluids, and in very small
quantity in the saliva and in the milk. It is not spontaneously coagu-
lable, but coagulates promptly when heated in its liquid form to a
temperature of 72° (162° F.), and its coagulum is again soluble in the
caustic alkalies. It is also coagulated by contact with nitric or sul-
phuric acid, alcohol, or the metallic salts. The organic acids, as acetic,
lactic, or tartaric acid, do not affect it ; but if it be first slightly acidu-
lated by dilute acetic acid, it may be precipitated by a solution of
potassium ferrocyanide. This is one of the most delicate tests for the
presence of albumen, but it is usually recognized from its coagulability
by heat and nitric acid. When dissolved in a fluid of neutral reaction,
it rotates the plane of polarization to the left 56°.

ALBUMINOSE. 87

The white of the fowl's egg is mainly composed of a substance also
called albumen, and which corresponds with the albumen of blood
in its coagulability by heat, nitric acid, alcohol, and the metallic salts.
It is distinguished from the preceding mainly by its coagulability by
ether, which has no effect on the albumen of blood. It rotates the
plane of polarization to the left 35°.5.

The fresh juices of nearly all vegetables, and especially the succulent
plants, contain a substance coagulable by heat, which has been called
vegetable albumen. It may also be obtained from the cereal grains by
extraction with water, and resembles in its principal chemical reactions
the albumen derived from animal sources.

Albuminose.

This substance is closely related to albumen by its chemical composi-
tion and its general characters. It is not coagulated, however, by either
heat, nitric acid, or acidulated potassium ferrocyanide, but only by the
metallic salts and alcohol in excess. It is also distinguished by its
ready diffusibility through animal membranes or parchment paper ; while
albumen, and all other liquid albuminous matters, pass through these
membranes either not at all or only with great difficulty. Coagulated
albumen and all other digestible albuminous matters are converted
into albuminose by the action of gastric juice. They thus become
liquefied and incapable of coagulation by heat. Owing to the origin of
these products from the digestive act they are designated by several
writers under the name of peptones; and a variety of them are enume-
rated, but their distinctive' characters are not very sharply denned.
Albuminose is found in the fluids of the stomach and small intestine
during digestion, and exists also in the blood in the proportion of two
to three parts per thousand.

Albuminose in solution has the property of modifying certain well-
known chemical reactions. It interferes especially with the reduction
of the copper oxide in Trommer's test. If a small quantity of glucose
be dissolved in gastric juice containing albuminose, and Trommer's test
applied, no peculiarity is observed on first dropping in the copper
sulphate ; but on the addition of potassium hydrate, the mixture takes
a rich purple hue, instead of the clear blue tinge which is presented
under ordinary circumstances. On boiling, the color changes to claret,
cherry red, and finally to a light yellow ; but no copper oxide is
deposited, and the fluid remains clear. If albuminose be present only
in small quantity, an incomplete reduction of the copper takes place,
so that the mixture becomes opaline and cloudy, but still without any
well marked deposit. This interference will take place when sugar is
present in very large proportion. We have found that gastric juice,
drawn from the dog's stomach during digestion, may sometimes be
mixed with an equal volume of honey without giving any deposit of
copper on the application of Trommer's test. If such a mixture, how-
ever, be previously diluted with water, it will often fail to prevent the

88 ALBUMINOUS MATTERS.

reduction and deposit of the copper oxide. The peculiar action above
described depends upon the presence of albuminose, and not upon that
of any original ingredient of the gastric juice ; since it is not exhibited
by the perfectly clear and colorless juice, obtained from the empty
stomach of the fasting animal by irritation of the mucous membrane
with a glass rod or metallic catheter ; while the same fluid, if macerated
for a time with finely chopped meat at a temperature of 38° (lOQo F.),
will be found to have acquired the property in a marked degree. Gas-
tric juice, furthermore, drawn from the stomach after digestion has
been going on for half an hour or more, always contains a certain
quantity of albuminose, and consequently interferes, as above described,
with Trommer's test.

Albuminose, if present in notable quantity, will also interfere with the
mutual reaction of starch and iodine. If gastric juice, containing albu-
minose, be mingled with an equal volume of iodine water, and a solution
of starch be subsequently added, no blue color is produced ; though if
the iodine water be added in excess, or if the tincture of iodine be used
instead of its aqueous solution, the superabundant iodine then com-
bines with the starch, and produces the ordinary blue color. This
property, like that described above, is not possessed by pure, colorless
gastric juice, taken from the empty stomach, but is acquired by it on
being digested with albuminoid substances.

Accordingly, in testing for the presence of glucose in fluids which are
liable to contain albuminose or other organic substances of similar
character, the precaution must always be adopted of first eliminating
the albuminous matters which might interfere with the test. This may
be done in either of two ways : first, by evaporating the fluid to dryness
over the water bath, and extracting the dry residue with alcohol, which
takes up the sugar, but leaves behind the albuminous matters. The
alcoholic solution may then be filtered and evaporated, and the evapo-
rated residue dissolved in water, when it will respond to Trommer's test
if glucose be present. Or, secondly, the fluid may be treated with ani-
mal charcoal, which retains the albuminous matters, and allows the
glucose to pass through in watery solution.

Caseine,

This is the principal albuminous ingredient of milk, the only animal
fluid in which it is certainly known to exist. It is called caseine, be-
cause, when solidified, it forms the substance of cheese. It is not
affected by a boiling temperature, but coagulates on the addition of any
of the dilute acids, organic as well as mineral, and of magnesium sul-
phate. These characters are sufficient to distinguish it from albumen.
It is also coagulated by a temperature of 30° (860F.),'by contact with
gastric juice, or an infusion of rennet, the mucous membrane of the
fourth stomach of the calf. In solution in neutral fluids it rotates the
plane of polarization to the left 80°. Caseine is an important article
of food, being the principal nutritious ingredient in preparations of milk.

PTYALINE. — PANCREATINE. 89

A nitrogenous substance, termed vegetable caseine, exists abundantly
in peas and beans, where it is known as " legumine." It is found
also in small quantity in oats, in the potato, and in the juices of many
plants. It resembles the caseine of milk in not being affected by a
boiling temperature, and in its coagulability by the organic acids and
magnesium sulphate.

Ptyaline

Is an ingredient of the saliva, to which it communicates the property
of converting hydrated starch into glucose. From this circumstance it
has sometimes been called "animal diastase." It differs from albumen
in many of its characters, and is not coagulated by nitric acid nor by
potassium ferrocyanide in an acidulated solution. On the other hand,
it is precipitated by alcohol in excess, and by a boiling temperature ;
but while, after precipitation by alcohol, it may be redissolved in water
with all its original properties, the action of heat produces in it a per-
manent alteration, and saliva which has once been boiled and allowed
to cool is found to have lost its power of converting starch. Ptyaline
can also be thrown down by adding to the saliva dilute phosphoric acid,
and afterward neutralizing the solution with lime water. The precipi-
tate of lime phosphate thus produced brings down with it the ptyaline,
which may afterward be redissolved in water, and again separately
precipitated by alcohol. Ptyaline does not constitute the whole of the
organic ingredients of the saliva, but is mingled in the secretion with
other albuminous substances.

Fepsine

Is the albuminous matter of the gastric juice, where it is found in the pro-
portion of fifteen parts per thousand. It is this substance which effects
the conversion of nitrogenous matters into albuminose in the digestive
process. It requires, however, in order to exert this action, to be dis-
solved in an acidulated liquid. It also causes the coagulation of caseine,
when first brought in contact with that substance. It is coagulated by
a boiling temperature, and when once subjected to the action of heat
loses permanently its digestive power. It is also thrown down by alco-
hol in excess, but may be redissolved in water after removal of the
alcohol. Pepsine is produced in the glandular follicles of the stomach,
and there mingled with the other ingredients of the gastric juice.

Pancreatine.

This is the characteristic ingredient of the pancreatic juice, where it
is very abundant ; being present in the proportion of a little over ninety
parts per thousand. It is coagulable by heat, nitric acid, alcohol, and
the metallic salts ; in these respects resembling albumen. But it is
also coagulated by magnesium sulphate, which has no effect on albumen.
It is further distinguished by the fact that, after precipitation by alcohol,
it may be again dissolved in water, and its solution exhibits the same
t

90 ALBUMINOUS MATTERS.

albuminous consistency which belongs to fresh pancreatic juice. It has
the power of emulsifying fatty matters with great rapidity at the tem-
perature of the living body, and also of saponifying a certain portion of
them by the production of a fatty acid. It is believed by some observers
that the pancreatine of pancreatic juice is a mixture of several sub-
stances ; one of which, like ptyaline, is active in the conversion of starch,
while another aids in the liquefaction of albuminous matters, and a third
has the property of acting upon fats.

Mucosine.

There are a variety of secretions in the body which are designated
by the common name of " mucus," and which are distinguished by a
peculiar physical character of viscidity. This viscid consistency is
given to them by the presence of a substance termed " mucosine," or, as
it is called by some writers, " mucine." It exists in all the varieties of
mucus, some of which, like those of the bronchial tubes and intestine,
are nearly fluid, while others, like that of the cervix uteri during preg-
nancy, are gelatinous and semi-solid. It is also present in abundant
proportion in the synovia, the bile, and the saliva of the submaxillary
and sublingual glands. The secretion of the mucous follicles of the
mouth consists almost entirely of it. Mucosine is not coagulated by
heat, but is thrown down by alcohol and by the acids, both mineral and
organic. It is remarkably unaffected by the metallic salts, lead sub-
acetate being the only one that produces a distinct coagulation. In
some cases, as in the bile, it is dissolved in the fluid ingredients of the
secretion, from which it may be separated by the action of alcohol. In
others, as in the urine, it is only mechanically suspended, and subsides
as a light deposit after a few hours' repose.

Myosine.

The contractile substance of the striped muscular fibres contains an
albuminous matter which after death coagulates, like the fibrine of the
blood-plasma ; at the same time the muscles lose their contractility and
assume the condition of cadaveric rigidity. The coagulation of this
substance is retarded by the action of cold ; and it has been extracted
by Kiihne, from the muscular tissue of frogs, by the following process :
The vascular system is first deprived of blood by an injection of a ^ per
cent, solution of sodium chloride. The muscles, thoroughly washed,
are then subjected for two hours to a temperature of 7° to 10° below
0° (17OF.)? reduced to a pulp in a cold mortar, and then allowed
gradually to thaw upon a filter. The filtered liquid coagulates spon-
taneously at ordinary temperatures.

Coagulated myosine is gelatinous, and without fibrillated texture.
It is insoluble in water and in concentrated solutions of common salt ;
but is dissolved by a watery solution of salt, made in the proportion of
ten per cent, or less. It is extracted from the muscles after death by
bruising the muscular tissue to a pulp in a ten per cent, solution of

COLLAGEN. — CHONDRINE. 91

sodium chloride, filtering the expressed liquid, and then precipitating
the dissolved myosine by dropping the clear solution into distilled
water. It may also be precipitated by adding sodium chloride in sub-
stance, and thus increasing the strength of .the solution. Myosine is,
distinguished from the fibrine of the blood by its complete solubility
in saline solutions of a certain strength, as well as in dilute acids and
alkalies. When dissolved in a neutral saline fluid it is coagulable by
heat, like the albumen of blood.

The preceding substances are all naturally liquid, or nearly so, in con-
sistency, and form constituent parts of the various animal fluids and
juices. The following are ingredients of the solid tissues.

Collagen.

This substance is very widely diffused in the animal body, forming
the more or less homogeneous interstitial mass of the bones, perios-
teum, tendons, ligaments, fasciae, and connective tissues generally. All
these tissues, although at first insoluble, after long ebullition dissolve
in the boiling water ; and the substance thus dissolved solidifies on cool-
ing into a jelly-like mass. This substance is gelatine, or the animal
principle of glue. Gelatine, however, does not exist as such in the
osseous and fibrous tissues in their natural condition, but is evidently
the result of a transformation produced by long boiling. The original
body of which these tissues are mainly composed is termed "collagen ;"
that is, a substance which produces gelatine or glue. The conversion
of collagen into gelatine is a simple transformation, and neither a decom-
position nor combination, since it is not accompanied by any increase or
diminution of weight.

The gelatine produced by the action of boiling water on collagen,
when present in the proportion of ten parts per thousand, solidifies on
cooling ; below this proportion, or if the boiling be repeated, it may
remain liquid. Its solution rotates the plane of polarization to the
left 130°. It is precipitated by alcohol and by tannic acid. The last,
which is the only acid by which this substance is precipitated, is a
very sensitive test of its presence ; and, according to Hardy,1 will de-
tect one part of gelatine in 5000 parts of water. A similar combination
no doubt takes place, in the process of tanning, between tannic acid
and the original collagen of the fibrous tissues, by which they are ren-
dered harder, more impermeable to water, and incapable of putrefac-
tion. Gelatine is not affected by potassium ferrocyanide with acetic
acid, nor by lead subacetate.

Chondrine.

The amorphous intercellular substance of cartilage resembles that
of the bones and the fibrous tissues in being changed by prolonged boil-
ing with water into a substance which will gelatinize on cooling. In

1 Chimie Biologique. Paris, 1871, p. 282.

92 ALBUMINOUS MATTERS.

the case of the cartilages, however, this substance is termed chondrine,
from the source from which it is derived. Chondrine corresponds with
gelatine in most of its characters, but differs from it in being precipitated
from its watery solution by both acetic acid and lead subacetate. It
rotates the plane of polarization to the left 213°.5.

Elasticine.

The fibres of all the yellow elastic tissues, as that in the middle coat
of the larger arteries, the elastic ligaments of the spinal column, and the
ligamentum nucha3, mainly consist of a homogeneous substance which
possesses all the physical properties of the fibre itself, and is furthermore
distinguished by its extremely refractory nature toward most chemical
reagents. It is obtained by boiling the elastic fibres successively with
alcohol, ether, water, acetic acid, dilute soda solution, and dilute hydro-
chloric acid. The elasticine is thus purified from other ingredients, but
is not itself soluble in either of the above reagents. It is not converted
into gelatine even by long boiling ; and it is dissolved, but, at the
same time, decomposed, only by the concentrated acids and alkalies.
The slender elastic fibres mingled with connective tissue, and the sarco-
lemma of the striped muscular fibres, are probably composed of the
same substance.

Keratine.

Under this name is known the exceedingly resisting and indestruc-
tible substance of the hair, nails, epidermis, feathers, and all horny
tissues. It is unaffected by boiling with alcohol, ether, water, and the
dilute acids. By continuous boiling in a Papin's digester at 150° (302° F.)
it is liquefied and partly decomposed. It is distinguished from the
preceding substance by containing sulphur as an ingredient, which is
not present in elasticine. Keratine, accordingly, when decomposed by
boiling under pressure or with concentrated alkalies, gives rise to hydro-
gen sulphide vapors.

It is evident that the albuminous substances, under different forms,
constitute a large and important part of the mass of the body ; and as
they are during life in a constant state of active alteration, they require
for their maintenance an abundant supply of similar ingredients in the
food. All highly nutritious articles of diet contain more or less of
these substances. According to the estimates of Payen, which corre-
spond very closely in their gross results with our own observations, an
adult man requires a daily supply of about 130 grammes of albuminous
matter to provide for the wants of the system ; and this quantity is
actually contained in the food consumed.

But although nitrogenous matter is thus abundantly supplied to the
system from without, yet the particular kinds of albuminous substances
characteristic of the various tissues and fluids are formed within the
body in the process of digestion and assimilation, by transformation of

ALBUMINOUS MATTERS. 93

those which are introduced with the food. A large part of the albu-
minous matters of the food are derived from vegetables, and, though
closely related to the corresponding animal substances, are not pre-
cisely identical with them. Even the animal albuminous matters used
for food, as the albumen of eggs, the caseine of milk, and the sub-
stance of muscular flesh, are usually taken in the coagulated form, and
suffer still further changes before they become converted into the albu-
men of the blood. From their subsequent metamorphoses in the act
of nutrition they are transformed into the many specific varieties of
albuminous matter peculiar to the different tissues and fluids.

Only a very small proportion of these substances is discharged with
the excretions. The albuminous ingredients of the perspiration and
sebaceous matter, and the mucus of the urinary bladder and large intes-
tine are almost the only ones which find an exit from the body in this
way. A minute quantity of albuminous matter is exhaled in a vola-
tile form with the breath, and a little also, in all probability, from the
cutaneous surface. But the entire quantity so discharged bears an
insignificant proportion to that which is daily introduced with the food.
The albuminous substances, accordingly, are decomposed in the interior
of the body. They are transformed by the process of destructive assi-
milation, and their elements are finally eliminated and discharged under
other forms of combination.

CHAPTER Y.

COLORING MATTERS.

THERE are found, in various parts of the animal body, a number of
substances which are distinguished by imparting to the tissues and
fluids a distinct and characteristic coloration. Notwithstanding the
evident physiological importance of these substances, and the striking
character of their optical properties, they have proved in many re-
spects more difficult of study than the other proximate principles ;
and with regard to several of them our knowledge is still very imper-
fect. In some instances this is partly due to the comparatively small
quantity in which they occur, in others to the extreme readiness with
which they are decomposed or altered in the process of separation. In
some cases it has been found difficult to decide whether a variation of
tint be due to the different proportions of one or more different color-
ing matters or to the varying degrees of concentration of a single one.

The coloring matters are all nitrogenous compounds, but differ in
essential particulars from the albuminous substances. Those which
have been most fully examined are known to be crystallizable ; and it is
possible that all of them might be obtained in a crystalline form, could
they be completely separated without decomposition. The most abun-
dant of all, and that which possesses the most important physiological
properties, is the red coloring matter of the blood. It appears to be
analogous in many respects to the green matter of the leaves and leaf-
like organs in the vegetable world. Each of these two coloring matters
is the most abundant and widely diffused in its own kingdom, and is
distinguished by the identity of its characters in many different species
of animals and plants respectively ; and while the red coloring matter
of the blood, on the one hand, is the agent by which oxygen is absorbed
and distributed in the animal body, on the other, it is the green coloring
matter of plants by which carbonic acid and water are decomposed and
oxygen set free in the act of vegetation. It is believed by many ob-
servers that all the coloring matters of the animal body, at least in man
and the vertebrate animals, are derived by transformation from the
coloring matter of the blood ; and although we have no complete experi-
mental evidence that this is true in all cases, yet it is evident that these
substances have a close physiological relation with each other, perhaps
as distinct and real as that which exists between the various members
of the albuminous or saccharine groups.

The organic coloring matters may be conveniently removed from
liquids containing them by the action of animal charcoal; that is,
(94)

HEMOGLOBINE.

95

Fig. 19.

carbon derived from the imperfect combustion of animal substances.
Burned bones are generally employed for this purpose, their combustion
having been carried on with a scanty supply of air, so that while the
hydrogen, nitrogen, and oxygen are driven off in the form of gaseous
combinations, the carbon remains behind. If a fluid containing either
of the coloring matters be mixed with a sufficient quantity of this char-
coal and filtered, the filtered fluid will pass through colorless. Albu-
minous substances are also retained upon the filter when treated with
animal charcoal ; while glucose and other crystallizable and saline mat-
ters pass through freely in solution.

The animal coloring matters most distinctly recognized are those of
the blood, the blackish-brown solid tissues, the bile, and the urine.

Hemoglobine, C900H960N154Fe,S30179.

This is the coloring matter of the red globules of the blood, the most
abundant and important of all the substances belonging to this group.
It constitutes much the largest proportion of the solid ingredients of
the blood-globules, amounting in all probability to from 25 to 30 per
cent, of their weight in the
fresh condition. It is also
found, in much smaller quan-
tity, in the substance of the
muscular tissue, of which it
forms the coloring principle.
It crystallizes in well marked
forms, which vary somewhat
in different species of ani-
mals; but are all, so far as
accurately known, either
rhombic or hexagonal tables
or prisms. It is soluble in
water, in very dilute alcohol,
and in dilute solutions of
albumen, of the alkalies and
their carbonates, and of so-
dium and ammonium phos-
phates. It is insoluble in
strong alcohol, in ether, and

in the volatile and fatty oils. In almost every condition it is readily
decomposed. According to Preyer,1 crystals which have been thoroughly
dried at a temperature below the freezing point become, after a time,
decomposed, and lose their color and solubility, even at ordinary tem-
peratures. A watery solution of hemoglobine kept at any temperature
above 0° (32° F.) becomes altered in the course of twenty-four hours,
and if heated to 64° (147° F.) it is at once decomposed.

HEMOGLOBINE CRYSTALS; from human blood.
(Funke.)

1 Die Blutkrystalle. Jena, 1871, p. 58.

96

COLORING MATTERS.

HEMOGLOBINE CRYSTALS; from dog-faced
baboon. (Preyer.)

Hemoglobine, both crystallized and in watery solution, has the clear
bright red color of arterial blood. It is distinguished beyond all other

known ingredients of the

Fig. 20. body, by its capacity for ab-

sorbing oxygen, which it
retains in the form of a loose
combination. According to
the average result of various
experiments one gramme of
hemoglobine in watery solu-
tion will absorb 1.27 cubic
centimetres of oxygen. The
oxygen thus absorbed is
again given off under the in-
fluence of diminished pres-
sure, heat, or the continued
displacing action of hydro-
gen or nitrogen' gas. The
coloring matter is accord-
ingly known under two dif-
ferent forms, namely, that
of " oxidized" hemoglobine,

containing an excess of loosely combined oxygen, and that of " reduced"
hemoglobine, in which the surplus oxygen has been removed. The color
of hemoglobine varies according to these two conditions, being bright
red in the oxidized form, and dark purple when deoxidized. The
presence of hemoglobine in either one of these two conditions is the
cause of the color of arterial and venous blood.

A marked feature in the chemical constitution of hemoglobine is that
it contains iron. This fact is the more important because it is the only
' substance in the animal body, excepting hair, which contains iron in
any considerable amount, and because iron is also an indispensable
requisite for the formation of the green coloring matter of plants.
Experiment has shown that without the presence of iron vegetation
cannot go on ; and there is every reason to believe that iron is equally
essential to the constitution of the animal coloring matter, and thus
indirectly to the general nutrition of the animal body. It is present
in hemoglobine, in all probability, not in the form of a distinct oxide,
but directly combined, like sulphur, with the carbon, hydrogen, nitro-
gen, and oxygen which form the remainder of its substance.

One thousand parts of hemoglobine contain 4.2 parts of iron ; and,
according to the average results obtained by different observers, healthy
human blood contains, per thousand parts, 123.4 parts of hemoglobine,
and 0.52 part of iron. This would give, for a man weighing 65 kilo-
j grammes, 2.82 grammes of iron, as contained in the blood of the whole
body.

The iron of the hemoglobine passes out of the body by the bile and

MELANINE. 97

the urine, both of which contain slight traces of its presence. It is also
contained in the hair, where it forms sometimes as much as 7 per cent,
of the incombustible ingredients. It is supplied to the body in ample
abundance by ordinary food, in which it is always present in appre-
ciable amount. Green vegetables of course contain it, as an ingre-
dient of their coloring matter. Since hemoglobine exists to some
extent in muscular tissue, it will be present in a more or less altered
form, but still containing iron, in most kinds of animal food. Accord-
ing to the analyses of Moleschott, 500 grammes of beef (about one
pound avoirdupois) will contain 0.035 gramme of iron; and iron is
also found in even larger proportion in rye, barley, oats, wheat, peas,
and especially in strawberries. As the quantity of this substance daily
discharged in the urine and with the bile is so small, we must regard
the greater portion of that which passes through the system as used
in the growth of the hair ; and a very moderate amount contained in
the food must be sufficient for the daily requirements of nutrition.

Melanine.

In all the dark-colored tissues of the body, in the choroid coat of
the eyeball, the rete Malpighi of the skin in the black and brown races
and in all individuals of dark complexion, in the hair, and in the
substance of melanotic tumors, there exists a coloring matter known
as melanine. When isolated or when collected in compact masses, it is
of a very dark blackish-brown color ; but by its mixture, in different
proportions, with other colorless or ruddy semitransparent elements of
the tissues, it may produce all the varying grades of hue, from light
yellowish-brown to an almost absolute black. It is deposited in the
substance of the animal cells in the form of minute granules, and is
usually more abundant in the immediate neighborhood of the nucleus,
when one is present, than near the edges of the cell.

Melanine has not yet been obtained in a perfect crystalline form, and
its chemical characters are not completely determined. It is known,
however, to be a nitrogenous substance. As the average result of vari-
ous analyses collected by Hoppe-Seyler,1 it contains, freed from ashes,
the following proportions, by weight, of carbon, hydrogen, nitrogen, and
oxygen.

COMPOSITION OF MELANINE.

Carbon 54.39

Hydrogen " 5.08

Nitrogen 11.17

Oxygen 29.36

100.00
According to Kiiline2 repeated observations show that it also con-

1 Handbuch der Physiologisch- und Pathologisch-Chemischen Analyse. Berlin,
1870, p. 177.

2 Lehrbuch der Physiologischen Chemie. Leipzig, 1868, pp. 365, 442.

98 COLORING MATTERS.

tains iron, which has been found in the proportion of 2.5 parts per
thousand in the incombustible residue.

Melanine is insoluble in water, alcohol, ether, and solutions of the
organic and mineral acids. Boiling solutions of potassium hydrate
dissolve it without change of color, but its color is destroyed by chlo-
rine. It is regarded as derived from the coloring matter of the blood,
but there is no positive evidence of this, further than the fact that it
contains iron, and that it forms the coloring matter of the hair, in
which most of the iron of the blood-globules is probably deposited.

Bilirubine, C16HI8N203,

The red or orange-red coloring matter of the bile. This substance
has been designated, by different writers, under the various names of
Biliphaein, Bilifulvine, Hematoidine, and Cholepyrrhine. It is formed
in the substance of the liver, and may be extracted from the liver-
cells in a pure form. From these it is taken up by the biliary
ducts and mingled with the other ingredients of the bile. It is crystal-
lizable, soluble in chloroform, less so in alcohol, and slightly soluble
in ether. It is readily soluble also in alkaline liquids, but quite insolu-
ble in pure water. In the crystallized form its color is red; in the
amorphous condition, orange ; and in solution, reddish-brown or yellow,
according to the degree of concentration. According to Hoppe-Seyler,
it gives a perceptible yellow color when viewed in a layer of 1.5 centi-
metre's thickness, even if dissolved in 500,000 times its weight of fluid.

Solutions of bilirubine exhibit a well-marked reaction with nitroso-
nitric acid, which is known as " Gmelin's bile test." If to such a solu-
tion we add a small quantity of nitric acid, in which nitrous acid is also
present, a series of colors is produced in the following order : green,
blue, violet, red, and finally a dingy yellow. These colors are produced
by transformation of the bilirubine, and represent successive degrees
of its oxidation by nitric acid. The reaction is a very sensitive one,
and, according to Hoppe-Seyler, will produce a visible result in solu-
tions containing only one part in 70,000.

Bilirubine is generally regarded as derived from hemoglobine. The
reasons for this opinion are: First, its reddish color, similar, in some
degree, to that of diluted blood. Secondly, it has been found in various
parts of the body, in old bloody extravasations, evidently produced
from an alteration of the blood upon the spot. When found under
these circumstances, it was formerly known as hematoidine. Thirdly,
if hemoglobine, in the living animal, be withdrawn from the blood-
globules, and made to assume a liquid form by alternately freezing
and thawing a portion of freshly drawn blood, and then re-injected
into the bloodvessels, this operation is followed by a discharge of bili-
rubine with the urine. If hemoglobine, however, be normally trans-
formed into bilirubine, its iron and sulphur must enter into some other
combination, as neither of these substances exists in the coloring matter

BILIVERDINE. — UROCHROME. 99

of the bile. Bilirubine, if exposed to the atmospheric air in alkaline
solution, becomes oxidized and assumes a green color, being converted
into another closely related substance, namely, biliverdine.

Biliverdine, C16H20N205.

In addition to bilirubine, the bile contains also a green coloring
matter, namely, biliverdine; and its varying tint in different specimens
depends on the different proportions in which the two substances are
present. In many species of animals, as in the ox, sheep, rabbit, and
vegetable feeders generally, the bile presents a strong green or greenish
color, due to the comparative abundance of biliverdine. Biliverdine
is insoluble in water, ether, and chloroform, readily soluble in dilute
alkaline solutions and in alcohol. It is also soluble in glacial acetic
acid, and is deposited from the evaporated solution in the form of an
imperfect crystallization. It is often found in human gall-stones, and
in the dog is abundantly deposited along the edges of the placenta.

There is every reason to believe that biliverdine is formed from bili-
rubine by a process of oxidation, the elements of water entering at the
same time into combination. The nature of this change is shown by
the following formula:

Bilirubine. Biliverdine.

C16H18N203 + H20 + 0 = C16H.20N205.

The prompt conversion of the color of ruddy or reddish-brown bile
into green by the action of various oxidizing agents, or even by ex-
posure to the air, and the evident chemical relationship between the
two substances, leave no doubt that this is the mode in which bili-
verdine originates in the animal body. Both bilirubine and biliverdine
are discharged with the bile into the alimentary canal, but they become
undistinguishable toward the lower end of the small intestine. Beyond
that point they are replaced by the brown coloring matter of the feces,
and are finally discharged from the body under this form.

Urochrome.

The coloring matter of the urine has been repeatedly studied by
competent and laborious observers, but thus far with only partial suc-
cess. The substances which have been extracted from the urine by
various methods, and which have been regarded as representing, more
or less exactly, its natural coloring principle, are known by the dif-
ferent names of Urochrome, Urosine, Urosacine, Hemaphaeine, Uro-
hematine, Uroxanthine, Urobiline, and Hydrobilirubine. They are all
probably modifications of the same substance, variously altered by dif-
ferent methods of extraction, or obtained in different grades of purity-
The fresh, normal urine has a light yellowish or amber color, while
specimens of unusually high specific gravity, and particularly specimens
of febrile urine, often exhibit a distinct reddish hue. Normal urine,
which, when fresh, is only amber-colored, will often, by exposure to
the air, acquire a jiftge? tff iec£^ The substance obtained by Thudi-

100 COLORING MATTERS.

chum,1 and called by him urochrome, is precipitable from the urine by
various metallic salts. It has not yet been produced in a crystalline
form. It is soluble in water and in ether, but only slightly soluble
in alcohol. Its watery solution has a yellowish color, which, on stand-
ing, becomes red. Urohematine (Harley) is nitrogenous in composition,
and contains iron.2 It is insoluble in pure water, but soluble in the
fresh urine, as well as in ether, chloroform, and alcohol. The sub-
stance termed Urobiline (Jaffe) was so named because supposed to be
derived from the coloring matters of the bile. It is soluble in alcohol,
ether, and chloroform. Its solutions have a brownish-yellow color,
and, by dilution, become first yellow, and lastly faint rosy-red. It was
found by Jaffe5 to be present in nearly every instance (45 cases) in
healthy human urine, where it was recognized, after partial extraction
and purification, by its peculiar optical (spectroscopic) properties.
The same observer, however, found that fresh urine, not subjected to
chemical manipulation, would often present no indication of urobiline.
Such urine, if secluded from the atmosphere, would remain light-
colored, and free from this substance ; but if exposed to the air for from
two to twelve hours, would become darker in hue, and at the same time
would show, by the spectroscope, signs of the presence of urobiline.

It is evident, therefore, that the urine contains a coloring matter
which gives to it in the fresh condition its well known amber tint.
This substance is liable to be changed under the influence of oxidation,
and to assume in that condition a more or less distinct red color.
Such a modification certainly takes place outside the body, and it is
possible that it may also occur within the system, giving rise to the
varying proportions of red in the color of the urine in different
healthy and diseased conditions.

Beside the above named substances, there are two other bodies of suf-
ficient interest in general physiology to be enumerated in connection
with those already described.

Lnteine.

This substance, as its name indicates, is of a strongly marked yellow
color. It is extracted from the yolk of eggs, and from the tissue of the
corpus luteum. It exists also, according to Thudichum,4 in the grains
of Indian corn, in certain berries and roots, and in the yellow stamens
and petals of a large number of flowering plants. It is crystallizable,
soluble in alcohol, ether, .chloroform, and the fatty oils, but insoluble in
water. It is readily decomposed and decolorized by sunshine ; and by
the action of nitric acid it is first turned blue, and afterward decolorized.

1 British Medical Journal, London, Nov. 5, 1864.

2 Harley, The Urine and its Derangements. Philadelphia, 1872, p. 97.

3 Archiv fur Pathologische Anatomic und Physiologic, 1869, vol. xlvii.
p. 405.

4 Centralblatt fur'die'Me.lictnische W'hsFfosch'afttfn', 78f&; JK 2.

CHLOROPHYLLS. 101

Its color is also changed to blue or green by other strong acids, but it
is not affected by dilute solutions of the alkalies. It has not yet been
obtained in sufficient quantity for complete analysis.

Chlorophylle,

This is the green coloring matter of plants. It is more widely dif-
fused than any other coloring matter in the vegetable world, and it
apparently constitutes exclusively the coloring principle of all the green
parts of the higher plants without exception. Its exact chemical con-
stitution has not been fully determined, but it is considered to be a
nitrogenous substance, and Mulder has given it the formula C9H(JN04.
It is certain that iron is essential to its production, as plants artificially
cultivated without the access of this substance, grow up in a blanched
or chlorotic condition ; and their green color may afterward be restored
by the supply of moisture containing a ferruginous salt.1

Chlorophylle is of the first importance in vegetable physiology, as it
is under the influence of this substance, together with that of the solar
light, that the inorganic ingredients of the soil and the atmosphere are
deoxidized and combined in the form of an organic carbo-hydrate. The
process of vegetation proper, that is, the production and accumula-
tion of organic material in the form of starch, sugar, cellulose, woody
fibre, and the substance of various vegetable tissues, is inseparably
dependent on the presence and action of Chlorophylle. At the same
time, in order to produce this effect, the Chlorophylle must constitute a
part of the living vegetable cell ; for the coloring matter alone, if ex-
tracted from the chlorophylle-holding cells, and placed under all other
conditions, such as the access of air, sunlight, warmth, and moisture,
known to be essential to the work of production, is found to be incapable
of forming organic matter out of water and carbonic acid. Its func-
tion, therefore, is not that of a simple chemical reagent, but that of an
active constituent of the living vegetable organism.

Chlorophylle is produced, in the interior of the vegetable cell, some-
times as a uniformly diffused mass. Usually, however, it is deposited
in the form of distinct rounded grains, frequently arranged in definite
figures or patterns in the cavity of the cell. It may be extracted by the
action of alcohol or of ether, and retains its green color in solutions of
these substances. It disappears previously to the shedding of the leaves,
when they cease to perform the act of vegetation, and is usually replaced
by a few grains of red or yellowish color.

1 Mayer, Lehrbuch der Agrikultur-Chemie, Band i. pp. 51, 265.

CHAPTER VI.

CRYSTALLIZABLE NITROGENOUS MATTERS.

THE fifth and last group of proximate principles consists of a
number of colorless substances which, like the albuminous matters,
contain nitrogen, but which differ from them in being readily crystal-
lizable. Many of them are evidently derived from the albuminous
ingredients of the body by retrograde metamorphosis, being dis-
charged from the system as products of excretion. Others do not
exhibit this character, and are found only in the permanent tissues or
the internal fluids of the body. Several of them are of comparatively
recent discovery, and, although undoubtedly of importance in the con-
stitution of the body, are still somewhat obscure in their physiological
relations.

Lecithine, C44H90NP09,

From Af'xt^oj, the yolk of egg, in which substance it was first discovered.
Lecithine was for some time described under the name of phosphorized
fat, owing to the circumstance that one of the products of its de-
composition is phosphoglyceric acid (C3H9P06). It is not, however,
a fatty substance, since it contains nitrogen, and in other respects
differs from the fats. As mingled or combined with other animal mat-
ters, it has also been known by the name of " protagon." Lecithine is
of very wide distribution in both the animal and vegetable kingdoms,
occurring in the cereal grains and the leguminous seeds, and, according
to Hoppe-Seyler, in the cellular juices of a variety of plants. It is
found in the blood, both in the plasma and the globules, in the bile, the
spermatic fluid, the yolk of egg, and particularly in the tissues of the
brain, spinal cord, and nerves. In the plasma of the blood, it is in the
proportion of 0.4 part per thousand, and in the fresh substance of the
calf's brain, according to the analyses of Petrowsky,1 in the proportion
of 31 parts per thousand. Taking into account the watery ingredients
of the brain, lecithine is about equally abundant in the white and gray
substance ; but of the solid matters alone, it constitutes a little less than
10 per cent, in the white substance, and rather more than It per cent,
in the gray substance.

Lecithine obtained from either of these sources, if treated with water,
swells up into a pasty mass and gives origin to the remarkable appearances
under the microscope known as "myeline forms;" that is, a great

1 Archiv fur die gesammte Physiologie, 1873, Band vii. p. 101.
(102)

CRYSTALL1ZABLE NITROGENOUS MATTERS. 103

variety of mucilaginous or oily looking drops and filaments, of double
contour, which exude from the edges of the mass, and remain separate
and insoluble ; resembling the microscopic forms produced under simi-
lar circumstances from the "myeline," or medullary layer of nerve
fibres. It is readily soluble in alcohol, less so in ether, and is also solu-
ble to some extent in chloroform and the fatty oils. It is readily
decomposed on standing, either in solution or in a state of watery
imbibition, acquiring an acid reaction. Decomposition is also effected
by the action of acids or alkalies. By boiling with baryta water it
suffers a characteristic alteration, giving rise to the production of two
new bodies; namely, a nitrogenous alkaline substance and phospho-
gly eerie acid.

Lecithine has a special importance, not only as an abundant ingre-
dient of the nervous tissue, but also as being the only organic combina-
tion in the body containing phosphorus. Considering the number of
vegetable and animal articles of food in which it is an ingredient, it is
evident that a considerable quantity must be introduced with the nutri-
ment into the system and assimilated by the tissues, particularly by
those of the nerves and nervous centres. But as no known organic
combination of phosphorus is discharged with the excretions, this sub-
stance must pass out of the body as part of the phosphates which
appear in the urine and the perspiration. On this account, together
with the known fact of the constant consumption of oxygen by the
animal body, it is believed that the phosphorus, introduced as an ingre-
dient of organic materials, is converted by oxidation in the system
into phosphoric acid, and thus appears finally under the form of phos-
phatic salts.

Cerebrine, C17H33N03.

As its name indicates, this is an ingredient of the brain and nerves,
the only healthy constituents of the body in which it is known to exist.
Although this substance has not been obtained in a crystalline form,
it is placed among the members of this group because it resembles
them in the general features of its chemical composition, particularly in
its small proportion of nitrogen, and also in certain of its reactions,
which are entirely dissimilar to those of an albuminous matter.

Cerebrine is insoluble in water, but if moistened swells up slowly
into a pasty mass. It is insoluble in ether and in cold alcohol.

It is readily soluble in boiling absolute alcohol, from which it is
again deposited on cooling. Boiling with baryta water decomposes it
very slowly and incompletely, and does not produce phosphoglyceric
acid, by which means it may be distinguished from lecithine. If
strongly heated in the air, it turns brown, melts, and finally burns with
a bright flame.

It is much more abundant in the white than in the gray substance of
the brain, forming, according to Petrowsky, in the solid ingredients of
the white substance 9.5 per cent., in those of the gray substance but

104: CRYSTALLIZABLE NITROGENOUS MATTERS.

little more than 0.5 per cent. It is, therefore, undoubtedly a constitu-
ent of the medullary layer of nerve fibres.

Leucine, C6H13N0.2,

So called from the glistening white color of its crystals. It is found
in the tissue of the spleen, the thymus, thyroid, lymphatic, submaxillary,
and parotid glands, the pancreas and pancreatic juice, the brain, liver,
kidneys, and supra-renal capsules. In all these situations it exists in
comparatively small quantity, but its exact proportions have not been
determined. ' It has not yet been found in the blood in a state of health,
and has only been met with in the urine in certain cases of disease.
According to Hoppe-Seyler it is one of the products of putrefactive
decomposition of albuminous and gelatinous substances. When pure,
it crystallizes in thin white laminae, in which form it is readily solu-
ble in water, less so in alcohol, and insoluble in ether. Heated
slowly to 170° (338° F.) it volatilizes unchanged; above this point it
is decomposed ; two of the products of its decomposition being carbonic
acid and ammonia. But little is known with regard to the normal
origin or physiological destination of this substance, its importance
being only indicated by the number and variety of the situations in
which it is found.

Sodium Glycocholate, C26H42N06Na.

This is one of the characteristic ingredients of the bile, where it
sometimes forms, according to the observations of Jacobsen, nearly 49
per cent, of the dry residue. It is also found in the tissue of the liver
and in the fluids of the upper part of the intestinal canal, into which
it is discharged with the bile ; but it does not exist in the blood or in
the other animal fluids.

It is a saHne body, consisting of a nitrogenous organic acid, glyco-
cholic acid (C26H43N06) in combination with sodium. Glycocholic acid
is so called because by boiling with solutions of potassium hydrate or
baryta water, or by continued boiling with dilute hydrochloric or
sulphuric acids, it is decomposed with the production of two new
bodies, namely, glycine (C2H6N02), a nitrogenous neutral substance,
and cholic acid (C24H4005), a non-nitrogenous organic acid, so called
because peculiar to the bile. This change takes place with the assump-
tion, by the glycocholic acid, of the elements of water, as follows :

Glycocholic acid. Glycine. Cholic acid.

C26H43N06 + H20 = C2H5N02 + C24H4005.

The two bodies thus formed do not, therefore, pre-exist in the organic
acid of the bile, but are produced, by the addition of other elements,
at the time of its decomposition.

Sodium glycocholate is a neutral, crystallizable substance, very
soluble in water and in alcohol, and insoluble in ether. It is accord-
ingly extracted from the bile by the following process : The bile is first
evaporated to dry ness over the water-bath, the dry residue extracted

CRYSTALLIZABLE NITROGENOUS MATTERS.

105

Fig. 21.

SODIUM GLYOOOHOI.ATI! FROM OX-BILB,

after two days' crystallization. At the lower
part of the figure the crystals are melting into
drops, from evaporation of the ether and absorp-
tion of moisture.

with absolute alcohol, the alcoholic solution decolorized with animal
charcoal, and then mixed with from 8 to 10 times its volume of ether.
A whitish precipitate is thrown
down which soon collects into
little drops and masses, of a
consistency like that of Canada
balsam, whence the biliary salts
have been sometimes termed the
" resinous" matters of the bile.
In the course of 24 hours,
sometimes only after four or
five days, the sodium glyco-
cholate crystallizes abundantly
in the form of hemispherical or
star-shaped masses of fine ra-
diating acicular crystals. These
crystals may be preserved in-
definitely in the mixture of al-
cohol and ether ; but if the mix-
ture be poured off, the cold
produced by evaporation causes
a condensation of atmospheric
moisture and a rapid melting

and solution of the crystals, which may be seen under the microscope
liquefying into transparent, rounded,, oleaginous-looking drops. The
solubility of these drops in water and their insolubility in ether will
readily distinguish them from oil globules, which they closely resemble
in their optical properties. Sodium glycocholate may be precipitated
from its watery solution by both the neutral and tribasic lead acetates.
Its alcoholic solution rotates the plane of polarization toward the right
25°.T.

Sodium Taurocholate, C26H44NS07Na.

This is a substance similar in many of its properties to the last, and,
like it, a peculiar ingredient of the bile. Its organic acid, taurocholic
acid (C26H43NS07), is distinguished by containing an atom of sul-
phur, owing perhaps to its having been derived from the albuminous
matters. If so, glycocholic acid will represent a product of further
oxidation, under which sulphur, hydrogen, and oxygen are given up in
such proportions that the products of elimination are sulphuric acid and
water, as follows :

Taurocholic acid. Glycocholic acid.

C26H45NS07 - S(HaO) = C26H43N06.

By boiling with dilute acids or alkalies, or even in water, taurocholic acid
is decomposed with the formation of two other bodies, namely, taurine
(C2H.NSO.S), a neutral nitrogenous substance, containing all the sulphur,
so called because first discovered in bullock's bile, and cholic acid

8

106

CRYSTALLIZABLE NITROGENOUS MATTERS.

Fig. 22.

(C24H4005), the same body produced by a similar process from glyco-
cholic acid. The change here also takes place with the assumption
of the elements of water, as follows :

Taurocholic acid. Taurine. Cholic acid.

C26H45NS07 + H20 = C2H7NS03 + C24H4005-
Sodium taurocholate, like the preceding biliary
salt, is soluble in water and in alcohol, and insoluble
in ether. It is extracted from the bile by a similar
process to that already described, and, after precipita-
tion by ether, crystallizes in slender needles, much
like those of the glycocholate. It may be distin-
guished, however, and separated from the last-named
substance, when in company with it, by its reaction
toward the salts of lead. It is not precipitated from
its watery solution by the neutral, but only by the
tribasic acetate. If a watery solution, therefore, con-
taining both salts be precipitated by neutral lead ace-
tate, the filtered fluid will contain the sodium tauro-
cholate alone. In alcoholic solution it rotates the
plane of polarization toward the right 24°.5.

The two biliary salts are associated in the bile in
varying proportions. Generally the glycocholate may
be said to preponderate in the bile of the ruminant
animals, taurocholate in that of the carmvora. In
dog's and cat's bile, the taurocholate exists alone. In
human bile it appears that both substances may be
present, sometimes one of them being the more abun-
dant, sometimes the other ; according to some writers the taurocholate
existing alone or in larger proportion (Gorup-Besanez, Hoppe-Seyler,
Robin, Hardy), according to others the gtycocholate (Bischoff, Lossen,
RankeJ. In the observations of Jacobsen,1 on a case of biliary fistula
in man, the glycocholate was shown to be a constant ingredient, while
the taurocholate was either absent, or, if present, varied in quantity.
We have also found human bile to contain the glycocholate without
the presence of taurocholate.

The biliary salts are formed in the glandular tissue of the liver and
discharged with the bile. According to the observations of Ranke on
a man with biliary fistula, the average quantity of the organic acids of
the bile thus produced, by a man weighing 65 kilogrammes, would be a
little over 15 grammes per day. They are not discharged with the feces,
but are changed in the intestine, and, probably, reabsorbed under another
form by the blood.

Creatine, C4H9N302, from x^, flesh.

This is a neutral crystallizable substance, which exists very generally
in the muscular tissue, both voluntary and involuntary, of man and

SODIUM TAU-
ROCHOLATE, from
alcoholic extract of
dog's bile, crystalliz-
ing at the bottom of
a test-tube.

Kevue des Sciences Medicales, 1874, vol. iii. p. 85.

CRYSTALLIZABLE NITROGENOUS MATTERS.

107

CREATINE, crystallized from hot water.
(Lehmann.)

animals; its proportion in the human muscles being, according to
Neubauer,1 about two parts per thousand. It has also been found
in minute quantity in the blood,
the brain, and the kidneys. It is
soluble in cold, very readily in hot
water, slightly soluble in alcohol,
insoluble in ether. From its watery
solution it crystallizes in the form
of transparent, colorless, rhombic
prisms of firm consistency. It is
decomposed by a temperature of
100° (2120 p.). By boiling in acid
solutions, or by long-continued
boiling in water, it is transformed
into another closely related sub-
stance, namely, creatinine. If boil-
ed with baryta water it produces,
among other substances, urea, car-
bonic acid, and ammonia. Creatine
is regarded as a product of metamorphosis of the albuminous matters,
especially of those existing in muscular tissue. It does not appear in
the urine, but undergoes further transformation in the interior of the
body, probably into the following substance.

Creatinine, C4H.N30,

Is known to exist, with certainty, only in the urine. Although it has
been occasionally found by some observers in the muscles, according to
Neubauer it is not a normal ingredient of the tissue, but is produced
during the process of extraction,
under the continued influence of
heat and moisture, from the previ-
ously existing creatine. C reatinine
is soluble in water and in alcohol,
but only slightly soluble in ether.
It crystallizes in colorless glitter-
ing prisms. In solutions it has a
strong alkaline reaction, decom-
poses the combinations of am-
monia, and forms with various
acids neutral salts.

The relation between these two
bodies is such that by different
chemical processes they may be
artificially converted into each

,, T J.U • A. *• it i -i CREATININE, crystallized from hot water.

other. In the interior of the body (Lehmann.)

Fig. 24.

1 Neubauer und Vogel, Analyze des Harns, 1872, p. 20.

108 CKYSTALLIZABLE NITROGENOUS MATTERS.

the change which takes place is undoubtedly the conversion of creatine
into creatinine, since the former is that which exists normally in the
muscles, while the latter is an ingredient of the urine. In this change
the elements of water are eliminated as follows :

Creatine. Creatinine.

C4H9N302 — H20 = C4H7N30.

Thus creatine represents an intermediate stage of the products of meta-
morphosis, which finally appear in the urine under the form of creatinine.
According to the observations of Neubauer, the quantity of creatinine
discharged by a healthy man, under ordinary diet, is about 1 gramme
per day.

Urea, CH4N20.

This is one of the most important and well known substances of its
class, as it is the principal solid ingredient of the urine, and the main
product of the decomposition of nitrogenous matters in the body. It is
most abundantly found in the urine, where it is present on the average,
in man, in the proportion of 26 parts per thousand ; while in the blood
it is only in the proportion of 0.16 part per thousand. As it makes its
appearance in the blood, it is constantly drained away by the kidneys,
and thus accumulates in larger proportion in the urine. This is further
shown by the comparative analyses of Picard, who found, in the dog,
the proportion of urea in the blood of the renal arteries to be 0.36 per
thousand, in the renal veins 0.18 per thousand. Urea has also been
found in minute quantity in the lymph, the aqueous and vitreous humors
of the eye, the crystalline lens, and the perspiration.

Urea is a colorless, neutral substance, abundantly soluble in water
and in boiling alcohol, less so in cold alcohol, nearly insoluble in ether.
It crystallizes in four-sided prisms, often with blunt pyramidal ends,
which are decomposed on being heated above 120° (248° F.). Its pure
watery solution may be kept without change at ordinary temperatures ;
but by long continued boiling, or by a short boiling in the presence of
alkalies, it is decomposed with the production of ammonium carbonate.
If heated with water in an hermetically sealed tube to 180° (356° F.),
it undergoes the same alteration. This change takes place with the
assumption of the elements of water, as follows :

Urea. Ammonium carbonate.

CH4N20 + HA « (NH4)2C03.

Urea has been produced artificially from albuminous matter, by
placing the latter in contact with potassium permanganate in watery
solution, and subjecting it to a heat of 60° to 80° (14(P to 176Q F.).
This reaction, first established by Bdchamp,1 has been confirmed by
Hitter,2 in whose experiments 30 grammes of albumen furnished 0.09
gramme of urea, and the same quantity of fibrine, 0.0 T gramme;

1 Coraptes Kendus de I'AcadSmie des Sciences, Paris, 1870, tome Ixx. p. 866.

2 Comptes Rendus, 1871, Ixxiii. p. 1219.

CRYSTALLIZABLE NITROGENOUS MATTERS,

109

while from 30 grammes of gluten, in an average of three experiments,
there was obtained 0.21 gramme of urea. According to Bechamp,
this

Fig. 25.

UREA, prepared from urine, and crystallized
by slow evaporation. (Lehmann.)

is not a process of simple
oxidation, but an oxidation with
decomposition, in which various
other substances are produced from
the albuminous matter at the same
time with urea. The quantity of
urea excreted by a healthy man is
about 35 grammes per day. This
amount varies, of course, with the
size of the body, the average daily
proportion of urea to the weight
of the whole body being 0.5 per
thousand parts. Lehmann, in ex-
periments on his own person, found
the average daily quantity to be
32.5 grammes. Bischoff, by simi-
lar experiments, found it to be 35
grammes. Prof. William A. Ham-
mond, whose weight was 90 kilogrammes, found it to be 43 grammes.
Prof. John C. Draper, whose weight was 66 kilogrammes, found it
26.5 grammes.

It has been shown by Prof. John C. Draper,1 and confirmed by other
observers, that there is a diurnal variation in the normal quantity of
urea. A smaller quantity is produced during the night than during
the day ; and this difference exists even in patients who are confined to
the bed during the whole twenty-four hours, as in the case of a man
under treatment for fracture of the leg. This is probably owing to the
greater activity, during the waking hours, of both the mental and di-
gestive functions. More urea is produced in the latter half than in the
earlier half of the day ; and the greatest quantity is discharged during
the four hours from 6j to 10^ P. M.

The quantity of excreted urea represents almost completely the
amount of decomposition in the nitrogenous organic ingredients of the
body ; since it is the only nitrogenous substance discharged in consider-
able quantity by the excretions. A comparison of the entire amount
of nitrogen contained in the daily food with that discharged from the
body in various forms shows that fully 85 per cent, of that introduced
reappears as an ingredient of the urea ; the remaining 15 per cent, being
contained in the uric and hippuric acids and creatinine of the urine, and
in the nitrogenous matters of the feces.

All observers are agreed that the quantity of urea excreted varies in
proportion to the amount of nitrogenous matters contained in the food.

1 New York Journal of Medicine, March, 1856.

110 CRYSTALLIZABLE NITROGENOUS MATTERS.

Lehmann found,1 in experiments on his own person, that the daily
amount of urea was increased by a diet of animal food, diminished by
one of vegetable food, and reduced to its minimum by a diet consisting
exclusively of non-nitrogenous matters, such as starch, sugar, and fat.
The comparative results were as follows :

Kind of diet. Daily quantity of urea.

Mixed 32.5 grammes.

Animal 53.2 "

Vegetable 22.5 "

Non-nitrogenous ....... 15.4 "

It also appears from the observations of Mahomed2 that the influence
of a change of diet in this respect is manifested very rapidly ; twenty-
four hours of a non-nitrogenous diet being sufficient to reduce the excre-
tion of urea 50 per cent., while it is again restored to its ordinary
standard within three or four hours after the use of animal food.

Urea, however, does not depend exclusively upon the direct trans-
formation of the nitrogenous matters of the daily food, but is also, in
part at least, derived from the metamorphosis of the more permanent
constituents of the body ; since it continues to be discharged, though
in diminished quantity, when no food is taken. Lehmann found as
much urea in the urine after twenty -four hours of abstinence from all
food, as after a diet of non-nitrogenous matters. In the dog, when
subjected to entire abstinence, the urea is reduced in three or four days
to nearly one-third its former quantity, but is still present in about the
same proportion at the end of seven days. In the experiments of Dr.
Parkes on a man subjected to a purely non-nitrogenous diet, the daily
excretion of urea fell on the second day to 12 grammes, but afterward
remained nearly uniform, at rather more .than half that quantity, and on
the fifth day still amounted to 7 grammes. Urea has also been found
by Lassaigne in the urine of man after continued abstinence from food
for fourteen days.

The quantity of urea has been found by Lehmann,3 Prof. A. Flint, Jr.,4
Parkes,5 and Yogel6 to be increased during or after unusual muscular
exertion. Other observers (Fick and Wislicenus, Yoit, Ranke) have
found no perceptible variation owing to this cause. The same discrep-
ancy exists between different writers in regard to creatinine. It is
possible that the details of the process by which the albuminous matters
during decomposition give rise to the formation of urea are not }^et
fully known to us. But it is a matter of common experience, both for
man and animals, that continued and laborious muscular activity

1 Physiological Chemistry. Sydenham edition. London, 1853, vol. ii. p. 450.

2 Pavy on Food and Dietetics. Philadelphia edition, 1874, pp. 79-81.

3 Physiological Chemistry. Sydenham edition, vol. ii. p. 452.

4 New York Medical Journal, June, 1871.

5 Proceedings of the Royal Society, March 2d, 1871, p. 357.

6 Neubauer und Yogel, Analyse des "Earns,, 1872, p. 338.

CRYSTALLIZABLE NITROGENOUS MATTERS. Ill

requires a corresponding supply of nitrogenous food ; and the final
result of the internal metamorphosis of such substances is mainly repre-
sented by the excretion of urea.

Sodium Urate, C5H3N403Na.

As its name indicates, this is a saline body, consisting of a nitro-
genous organic acid, namety, uric acid (C5H4N403), in union with so-
dium. A portion of it is also in combination with potassium, but the
sodium salt is in much the greater quantity of the two. The urates
are found normally only in the urine, where they exist in the proportion
of about 1.45 parts per thousand. The entire quantity of uric acid
excreted by a healthy, full-grown man, is about 0.1 gramme per day.
It is, therefore, very much less abundant than urea; and, according
to the researches of J. Ranke, the proportion between them is very con-
stant, the relative daily quantity of the two substances in the same
individual being nearly always —

Uric acid . . . . . 1 part.
Urea 45 parts.

Uric acid is a colorless, crystallizable substance, only very slightly
soluble in either cold or hot water, quite insoluble in alcohol and in
ether. It is much less easily decomposed than urea, remaining for a
long time unchanged under all ordinary conditions. If treated with
concentrated sulphuric acid it is decomposed, with the production of
ammonia and carbonic acid. If boiled with dilute nitric acid, it dis-
solves with a yellow color and abundant liberation of gas-bubbles;
and, on evaporation, the solution leaves a brilliant red stain, which is
changed to purple by the addition of a drop of ammonia water. This
is known as the " murexide test" for uric acid or the urates.

Uric acid, like urea, is formed within the body by the metamorphosis
of nitrogenous organic substances. It is most abundant under the use
of animal food, and diminished by a vegetable diet, and is reduced to a
minimum, though it does not entirely disappear, during complete absti-
nence. It is this substance which indirectly, in great measure, causes
the acid reaction of the urine. It is nowhere present normally in a free
form, being by itself exceedingly insoluble ; but simultaneously with
its production it unites with part of the alkaline bases of the phosphates,
thus becoming mainly sodium urate, which is soluble and neutral in
reaction, and giving rise to sodium biphosphate, which communicates
to the urine its acid reaction.

Sodium Hippurate, C9H8N03Na.

This is also a saline body, formed by the union of sodium with a
nitrogenous organic acid, namely, hippuric acid, C9H9N03, so called
because it was first discovered in the urine of the horse. It is com-
paratively abundant in the urine of most herbivorous animals, especially
the horse, ox, sheep, goat, elephant, camel, and rabbit; while it is

112 CRYSTALLIZABLE NITROGENOUS MATTERS.

absent, or nearly so, in that of the carnivorous animals. In human
urine, under an ordinary mixed diet, it is constantly present, amount-
ing to about 0.35 gramme per day, or about one-half the quantity of
uric acid. It increases, however, perceptibly under a vegetable diet,
and diminishes or disappears altogether under the exclusive use of ani-
mal food. It thus alternates in quantity, under these circumstances,
with uric acid. In the urine of the horse, which normally contains
hippuric acid, after continued abstinence from food, this substance
ceases to appear, and uric acid takes its place. Herbivorous animals,
when deprived of food, are placed in the condition of carnivora, since
the ingredients of the urine must then be derived from the metamor-
phosis of their own substance. In the calf, while living upon the milk
of its dam, the urine contains uric acid ; after the animal is weaned and
begins to live upon vegetable food, the uric acid disappears, and the
urine contains salts of hippuric acid.

CHAPTEE VII.

FOOD.

UNDER the term " food" are included all substances, both solid and
liquid, necessary to sustain the process of nutrition. The first act of
this process is the appropriation from without of the materials which
enter into the composition of the living frame, or of others which may
be converted into them in the interior of the body. Like the tissues
and the fluids, therefore, the food contains various ingredients, both
organic and inorganic ; and the first important fact to be noted with
regard to them is that no single class of substances, by itself, is suffi-
cient to sustain life, but that several must be supplied, in due propor-
tion, in order to maintain the body in a healthy condition.

Inorganic Ingredients of the Food.

It is well known that inorganic substances, although they afford the
necessary materials for vegetation, are not sufficient for the nourish-
ment of animals, which depend for their support upon elements already
combined in the organic form. Nevertheless, it is equally true that the
inorganic matters are also essential to animal life, and require to be sup-
plied in sufficient quantity to keep up the natural proportion in which
they exist in the various solids and fluids. As we have found it to
be a general characteristic of these substances, that they are exempt
from alteration in the interior of the body, but are absorbed, deposited,
and expelled unchanged, each one, as a rule, requires to be present
under its own form, and in sufficient quantity in the food. This is
especially true of water and sodium chloride, both of which enter and
leave the system in abundant daily quantity; and of the calcareous
salts, which during the growth and ossification of the skeleton are
deposited in large proportion in the osseous tissue. The alkaline car-
bonates, phosphates, and sulphates are partly formed within the system
during the metamorphosis or decomposition of organic substances ; but
the elements of which they are composed must of course enter the
body in some form, in order to enable these changes to be accomplished.

Since water enters into the composition of every part of the body,
it is important as an ingredient of the food. In man, it is probably the
most important substance to be supplied with constancy and regularity,
and the system suffers more rapidly when entirely deprived of fluids,
than when the supply of solid food only is withdrawn. A man may
pass eight or ten hours without solid food, and suffer little or no
inconvenience ; but if deprived of water for the same length of time,

(113)

114 FOOD.

he becomes exhausted, and feels the deficiency in a marked degree.
Magendie found, in his experiments on dogs subjected to inanition,1 that
if the animals were supplied with water alone they lived six, eight, and
even ten days longer than if deprived at the same time of both
solid and liquid food. Sodium chloride, also, is usually added to the
food in considerable quantity, and requires to be supplied as a condi-
ment with tolerable regularity ; while the remaining inorganic materials,
such as the calcareous salts, and the alkaline phosphates and sulphates,
occur naturally in sufficient quantity in most of the articles used as
food.

The entire quantity of mineral substances discharged daily by a
healthy adult, by both the urine and perspiration, averages as follows :

QUANTITY OF MINERAL MATTERS DISCHARGED PER DAY.

Sodium and potassium chlorides 15.0 grammes.

Calcareous and magnesian phosphates .... 1.0 "
Sodium and potassium phosphates . , . 4.5 "

Sodium and potassium sulphates 4.0 "

24.5 "

According to the average dietaries for adults in full health collected
by Dr. Playfair2 about 20 grammes of mineral matter are daily intro-
duced with the food. The remainder is to be accounted for by the
phosphates and sulphates formed within the system as above described.

Non-Nitrogenous Organic Ingredients of the Pood.

These substances, so far as they enter into the composition of the
food, are divided into the two natural groups already mentioned —
namely, the carbohydrates, including starch and sugar, and the fats,
including all the varieties of oleaginous matter. Since starch is always
converted into glucose in the digestive process, these two substances
have the same value and significance as nutritive materials. As the
carbohydrates are to be found as a general rule only in vegetable pro-
ducts, they do not constitute a part of the food of carnivorous animals.
It is true that glucose exists in the milk even of the carnivora during
lactation, and is consequently supplied as a nutritive material to the
young animal during the early portion of its growth. But this supply
ceases as soon as the period of lactation is finished ; and the fact of the
secretion of sugar by the mammary gland, as well as that of its produc-
tion in the liver, shows that in the carnivorous animal the carbohydrates
requisite for the process of nutrition may originate within the body from
other organic substances. This does not apply, however, to the vege-
table feeders or to man. The carnivora have no desire for vegetable
food, while the herbivora live upon it exclusively, and in man there is
a natural craving for it, which is almost universal. It may be dis-

1 Comptes Rendus de l'Acad£mie des Sciences. Paris, tome xiii. p. 256.

2 London Chemical News, May 12, 1865.

FOOD. 115

pensed with for a few days, but not indefinitely. The experiment has
often been tried, in the treatment of diabetes, of confining the patient
to a strictly animal diet. It has been invariably found that, if this regi-
men be continued for some weeks, the desire for vegetable food becomes
so imperative that the plan of treatment is unavoidably abandoned.

A similar question has arisen with regard to the oleaginous matters.
Are these substances indispensable as ingredients of the food, or may
they be replaced by other proximate principles, such as starch or sugar ?
It has already been seen, from the experiments of Boussingault and
others, that a certain amount of fat is produced in the body over and
above that which is taken with the food ; and it appears also that a
regimen abounding in saccharine substances is favorable to the produc-
tion of fat. It is altogether probable, therefore, that the materials for
the production of fat may be derived, under these circumstances, either
directly or indirectly from saccharine matters. But saccharine matters
alone are not sufficient. Dumas and Milne-Edwards1 found that bees,
fed on pure sugar, soon cease to work, and sometimes perish in con-
siderable numbers ; but if fed with honey, which contains some waxy
and other matters beside the sugar, the}r thrive upon it ; and produce,
in a given time, a much larger quantity of fat than was contained in
the whole supply of food.

The same thing was established by Boussingault with regard to
starchy matters. He found that in fattening pigs, though the quantity
of fat accumulated by the animal considerably exceeded that contained
in the food, yet fat must enter to some extent into the composition of
the food in order to maintain the animal in good condition ; for pigs,
fed on boiled potatoes alone (an article abounding in starch but nearly
destitute of oily matter), fattened slowly and with difficulty ; while
those fed on potatoes mixed with a greasy fluid fattened readily, and
accumulated much more fat than was contained in the food.

The apparent discrepancy between these facts may be easily explained,
when we recollect that, in order that an animal become fattened, it must
be supplied not only with the materials of the fat itself, but also with
everything else necessary to maintain the body in a healthy condition.
Oleaginous matter is one of these necessary substances. The fats taken
in with the food are not simply introduced into the body and deposited
unchanged. On the contrary, they are altered and used up in the pro-
cess of digestion and nutrition ; while the fats which appear as con-
stituents of the tissues are, in great part, of new formation, and are
produced from materials derived, perhaps, from a variety of sources.

It is certain, then, that either one or the other of these two groups of
substances, saccharine or oleaginous, must enter into the composition
of the food ; and furthermore, that, though oily matter may sometimes
be produced in the body from the sugars, it is also necessary for perfect
nutrition that fat be supplied, under its own form, with the food. For

1 Annales de Chimie et de Physique, 3d series, tome xiv. p. 400.

116 FOOD.

man it is natural to have them both associated in the alimentary ma-
terials. They occur together in most vegetable substances, and there is
a natural desire for them both, as elements of the food.

They are not, however, when alone, or even associated with each
other, sufficient for the nutrition of the animal body. Magendie found
that dogs, fed exclusively on starch or sugar, perished after a short
time with symptoms of profound disturbance of the nutritive functions.
An exclusive diet of butter or lard had a similar effect. The animal
became exceedingly debilitated, though without much emaciation; and
after death, all the internal organs and tissues were found infiltrated
with oil. Boussingault1 performed a similar experiment, with a like
result, upon a duck, which was kept upon an exclusive regimen of butter.
"The duck received 90 to 100 grammes of butter every day. At the
end of three weeks it died of inanition. The butter oozed from every
part of its body. The feathers looked as though they had been steeped
in melted butter, and the body exhaled an unwholesome odor like that
of butyric acid."

Lehinann was led to the same result by experiments performed upon
himself for the purpose of ascertaining the effect produced on the urine
by different kinds of food.2 This observer confined himself first to a
purely animal diet for three weeks, afterward to a purely vegetable one
for sixteen days, without any marked inconvenience. He then put him-
self upon a regimen consisting entirely of non-nitrogenous substances,
starch, sugar, gum, and oil, but was only able to continue this diet for
two, or at most for three days, owing to the disturbance of the general
health which supervened. The unpleasant symptoms, however, imme-
diately disappeared on his return to an ordinary mixed diet. In some
instances a restricted diet of this kind can be borne for a longer time.
Dr. Parkes3 kept two soldiers upon non-nitrogenous food alone for five
consecutive days without their exhibiting serious signs of physical ex-
haustion. Prof. Wm. A. Hammond,4 in experiments performed upon
himself, was enabled to live for ten days on a diet of boiled starch and
water. After the third day, however, the general health began to
deteriorate, and became much disturbed before the termination of the
experiment. The prominent symptoms were debility, headache, pyrosis,
and palpitation. After the starchy diet was abandoned, it required
some days to restore the health to its usual condition.

Nitrogenous Ingredients of the Food.

The nitrogenous or albuminous nutritive principles enter so largely
into the constitution of the animal tissues and fluids, that their import-
ance, as elements of the food, is easily understood. No food can be

1 Chimie Agricole. Paris, 1854, p. 166.

2 Journal fur praktische Chemie, Band xxvii. p. 257.

3 Proceedings of the Koyal Society of London, March 2d, 1871.

4 Experimental Eesearches, being the Prize Essay of the American Medical
Association for 1857.

FOOD. 117

long nutritious, unless a certain proportion of these substances be
present in it. Since they are so abundant as ingredients of the body,
their absence from the food is felt more speedily than that of any other
substance except water. They have, therefore, sometimes received the
name of " nutritious substances," in contradistinction to those of the
second class, which contain no nitrogen, and which are found to be
insufficient for the support of life. The albuminous substances, however,
when taken alone, are no more capable of supporting life indefinitely
than the others. It was found in the experiments of the French
" Gelatine Commission"1 that animals fed on pure fibrine and albumen,
as well as those fed on gelatine, become, after a short time, much
enfeebled, refuse the food offered to them, or take it with reluctance,
and finally die of inanition. This result has been explained by sup-
posing that these substances, when taken alone, excite after a time
such disgust that they are either no longer taken, or if taken are not
digested. But this disgust is simply an indication that the substances
used are insufficient and finally useless as articles of food, and that the
system demands other materials for its nourishment. It is well de-
scribed by Magendie, in the report of the commission above alluded
to, while detailing his investigations on the nutritive qualities of gela-
tine. " The result," he says, " of these first trials was that pure gelatine
was not to the taste of the dogs experimented on. Some of them suf-
fered the pangs of hunger with the gelatine within their reach, and would
not touch it ; others tasted of it, but would not eat ; others still de-
voured a certain quantity once or twice, and then obstinately refused to
make any further use of it."

In one instance, Magendie succeeded in inducing a dog to take a
considerable quantity of pure fibrine daily throughout the whole course
of the experiment ; but notwithstanding this, the animal became ema-
ciated, and died at last with the symptoms of inanition.

It is evident, therefore, that no single proximate principle, nor even
any one class alone, can be sufficient for nutrition. The albuminous
substances are first in importance because they constitute the largest
part of the mass of the body ; and exhaustion follows more rapidly
when they are withheld than when the animal is deprived of other kinds
of alimentary matter. But starchy and oleaginous substances are also
requisite ; and the body feels the want of them sooner or later, though
it may be plentifully supplied with albuminous food. Finally, the inor-
ganic saline matters, though in smaller quantity, are also necessary to
the continued maintenance of life. In order that the animal tissues and
fluids remain healthy, and take their proper part in the functions of
life, they must be supplied with all the ingredients necessary to their
constitution ; and a man may be starved to death at last by depriving
him of sodium chloride or lime phosphate as surely, though not so
rapidly, as if he were deprived of albumen or oil.

1 Comptes Rendus de l'Acad6mie des Sciences. Paris, 1841, torn. xiii. p. 267.

118 FOOD.

Composition of Different Articles of Food.

In the most valuable and nutritious kinds of food, which have been
adopted by the universal and instinctive choice of man, the first three
classes of proximate principles are all more or less abundantly repre-
sented. In all there exists naturally a certain proportion of saline
matter; and water and sodium chloride are generally taken in addition.

Milk. — In milk, the first food supplied to the infant, and largely
employed in various culinary preparations, all the important groups of
nutritive substances are present. It is a white, opaque fluid, consisting,
1st, of a serous portion, which contains albuminous matters, sugar, and
mineral salts in solution, and, 2d, of fatty globules suspended in the
watery liquid. It is this mixture of oleaginous particles with a serous
fluid which gives to the milk its opacity and its white color. Its rich-
ness in fatty matter may therefore be estimated from these physical
qualities. The ingredients in cow's milk are present in the following
proportions, according to Payen :

COMPOSITION OF Cow's MILK IN 1000 PARTS.

Water 864

Nitrogenous matter (caseine and albumen) .... 43

Sugar of milk . 52

Fat 37

Mineral salts 4

1000

Cow's milk resembles human milk in its general characters, but con-
tains a larger proportion of solid ingredients, especially of the nitro-
genous and saccharine matters, fat being present in nearly the same
amount in each. Sheep and goat's milk is richer in both nitrogenous
and fatty matters ; while the milk of the ass and the mare contains a
greater abundance of sugar, but is comparatively poor in nitrogenous
matter and fat. The nitrogenous matter of milk consists almost entirely
of caseine, associated with a very small proportion of albumen. Owing
to the relative quantity of these two substances, milk does not solidify
on boiling, but merely covers itself with a thin pellicle of coagulated
albumen, the caseine remaining liquid. The addition of any acid, how-
ever, such as acetic or tartaric acid, will precipitate the caseine and
curdle the milk. If milk be allowed to remain exposed to the air at a
moderately warm temperature, it curdles spontaneously, owing to the
development of lactic acid, due to a transformation of its sugar ; and
the same change will sometimes occur instantaneously from electric
disturbance, during a thunder storm.

The caseine of milk, artificially coagulated by the action of rennet,
constitutes cheese. Rennet is the dried contents and mucous membrane
of the stomach of the calf, the animal being killed and the stomach
taken out while digestion is in full activity and the gastric fluids abun-
dantly secreted. A faintly acidulated infusion of this substance even in
small quantity, added to fresh milk at the temperature of 30° (86° F.)

FOOD.

119

produces complete coagulation in fifteen or twenty minutes. The coagu-
lum is drained from the watery serum or " whey," and afterward pressed
into the form of cheese. The variety in consistency and flavor of differ-
ent cheeses depends mainly on the proportion of fatty matter retained in
the coagulum, and upon certain slow changes, in the nature of fermen-
tations, which go on in it subsequently.

The fatty matter of milk is suspended in the serous portion under the
form of minute spheroidal masses. These little masses or " milk-glob-
ules" are not quite fluid at ordinary temperatures, but have a semi-solid
consistency owing to their containing a considerable proportion of pal-
mitine. The fat globules, separated by churning from the other ingre-
dients of the milk, and made to unite into a coherent mass, constitute
butter. This substance, accordingly, represents simply the oleaginous
ingredients of the milk ; and when purified from the watery portions
entangled with it, consists mainly of palmitine and oleine, together
with a small proportion of peculiar odoriferous and flavoring ingredi-
ents, the principal of which has received the name of " butyrine." These
substances are usually mingled in the following proportions :

Palmitine 68 parts.

Oleine 30 "

Butyrine and other flavoring matters . . . 2 "

100

When well prepared and in good condition, butter constitutes one of
the most valuable and easily assimilated forms of oleaginous food. If
contaminated with the remains of the nitrogenous matter of the milk,
its fatty ingredients after a time become decomposed with the develop-
ment of volatile fatty acids ; in which condition the butter is said to be
" rancid," and is no longer fit for food.

Bread. — The cereal grains resemble each other more or less in their
constitution, all of them containing starch, nitrogenous matter, dextrine
or sugar, fat, and mineral salts in various proportions. Wheat is dis-
tinguished from the remainder in containing a considerably larger quan-
tity of nitrogenous matter as compared with the other ingredients, and
in the peculiarly adhesive or fibrinous quality of this substance, which
has received accordingly the name of " gluten." The different grains
in common use for food have when dry the following average compo-
sition, according to Payen.

COMPOSITION OF THE CEREAL GRAINS.

Nitrogenous
matter.

Starch.

Dextrine,
etc.

Fat.

Cellulose.

Mineral
salts.

Wheat ....

18.00

66.80

7.50

2.10

3.10

2.50

Eye

12 50

64 65

Udfl

O OK

310

o £n

Barley ....

12.96

66.43

10.00

2.76

4.75

3.10

Oats ....

14.39

60.59

9.25

5.50

7.06

3.25

Indian corn . .

12.50

67.55

4.00

8.80

5.90

1.25

Rice ....

7.55

88.65

1.00

0.80

1.10

0.90

120 FOOD.

Thus, of the different grains, that of oats contains, next to wheat, the
largest proportion of nitrogenous matters ; but it also contains a con-
siderable abundance of cellulose, or indigestible vegetable tissue, which
interferes with its nutritive quality as human food. Indian corn is
especially rich in fatty ingredients, while rice consists mainly of starch,
and is the poorest of all in both nitrogenous and fatty ingredients.

Wheat is more valuable than the other cereal grains for the purpose
of making bread, not only on account of its larger proportion of albu-
minous matter, but also on account of the peculiar glutinous quality of
this ingredient, already mentioned.

In preparing the wheat, the grains are first cleansed from husks and
adherent foreign material, ground into meal, and the finer and whiter
portions derived from the interior of the grain separated by sifting
and bolting from the coarser external parts, or bran. Thus purified, the
flour consists of starch, gluten, diastase, dextrine, a little fat, sometimes
a trace of sugar, mineral salts, and about 15 per cent, of water, which is
never fully expelled by ordinary drying. For making into bread, the
flour is mixed with about one-half its weight of water, and kneaded into
a flexible dough of uniform consistency. The next process is the fer-
mentation of the dough. For this purpose a little yeast is incorporated
with it, and the mixture allowed to remain for a few hours at a tem-
perature of about 25° (77° F.). During this time the sugar originally
present in the flour, and that produced from the starch and dextrine by
the action of the diastase, passes into fermentation under the influence
of the yeast, and is transformed into alcohol and carbonic acid. The
alcohol is dissipated by evaporation ; but the carbonic acid, which is
generated in small gas-bubbles, is entangled by the tenacious gluten of
the flour, and the dough is thus puffed up into a spongy, reticulated
mass. When the fermentation of the dough is completed, it is placed in
ovens, and baked at a temperature of 210° (about 40(PF.). The effect
of this heat is to cook the glutinous part of the dough, communicating
to it an agreeable flavor, and at the same time solidifying it ; so that
the substance of the baked loaf, when cut open, retains its spongy and
reticulated texture. It is thus made easy of mastication, and readily
permeable by the saliva and other digestive fluids. The spongy texture
acquired by bread is the main object of its fermentation, although an
agreeable flavor is also developed by the process, which does not exist
in unfermented bread. The interior of the loaf, in baking, does not rise
above 100° (212° F.); the exterior, which is subjected to a higher tem-
perature, becomes covered with a crust formed of partially torrefied
starch or dextrine, and caramelized sugar. The interior of the loaf also
usually retains a little glucose, which is not all destroyed in the process
of fermentation. A considerable portion of the water which was mixed
with the flour remains permanently united with its organic ingredients ;
so that 100 parts of flour will usually yield, after baking, 130 parts, by
weight, of bread.

FOOD. 121

Wheaten bread, prepared in this way, has the following average com-
position :

COMPOSITION OF WHEATEN BREAD.

Starchy matters (starch, dextrine, glucose) . ... 56.7

Albuminous matter (gluten, etc.) 7.0

Fatty matter . . 1.3

Mineral matter (calcareous, magnesian, and alkaline salts) . . 1.0

Water 340

100.0

Thus, while bread contains an abundance of albuminous and starchy
matter, it is deficient in fat ; and instinct accordingy leads us to take
with it butter, fat bacon, or some other form of oleaginous food.

The good quality of bread, aside from that of the flour of which it is
made, depends mainly on the success of the process of fermentation. If
this be incomplete, the bread is heavy, and not sufficiently reticulated
in texture. If it be allowed to go on beyond the proper time, it passes
into an acid fermentation, and develops a sour taste. If properly
conducted, the bread is uniformly light and spongy, and has no -acid
reaction.

Meat. — The muscular flesh of various animals affords an exceedingly
valuable and nutritious food, of which beef, mutton, and venison hold
the highest place. The muscular fibre itself consists almost exclusively^
of nitrogenous matters, but in point of fact the flesh used for food is
always accompanied with more or less adipose tissue, and even when
freed from visible fat, there is always, according to Payen and Pavy,
more or less oleaginous matter entangled with the muscular fibres. In
various kinds of meat, and even in meat from different parts of the
same animal, the proportion of fat will vary considerably ; but it was
found by Pavy, in one of the best and most commonly used portions of
beef, to amount to about 5 per cent, of the whole.

COMPOSITION OF BEEF FLESH.

Water 77.5

Albuminous matter 16.0

Fat 5.0

Mineral salts .......... 1.5

100.0

The mineral matters consist of alkaline chlorides and phosphates, with
phosphates of lime and magnesia.

In the cooking of meat by roasting or broiling, the external parts are
exposed to a rapid heat of 120° or 130° (260° F.) by which their albu-
minous parts are coagulated, their coloring matter turned brown, and a
characteristic flavor developed. The interior, which does not rise above
65° (1500 F.) remains red and juicy, its fluids being protected from,
evaporation by the coagulation of the outer portions. In boiling, where
the meat is cooked by contact with the boiling water, none of it rises.
9

122 FOOD

above the temperature of 100° (212° F.) ; but this may penetrate
throughout the whole substance of the meat, producing a uniform
decolorization. Notwithstanding the coagulation of the albuminous
liquids by boiling, the fibrous connective tissues are gelatinized, and
the muscular flesh thus partially softened and disintegrated. On the
whole, the effect of cooking upon meat is to increase the consistency
of its albuminous ingredients, its principal benefit being the attractive
flavor which is developed by the aid of heat, and no doubt an increased
digestibility from the same cause. By either method, meat loses in
cooking from 25 to 30 per cent, of its weight, principally by the escape
of water and liquefied fat.

Eggs. — The eggs of various animals are used for food, as those of the
common fowl, the duck, goose, turkey, seafowl, turtles, and the roe of
many kinds of fish. Those of the common fowl, which are the most
abundantly used, may be considered as representing the general quali-
ties of this article of nourishment. They consist of the globular "• yolk,"
surrounded by a layer of albumen or " white." The composition of
these two portions is nearly the same, excepting that the yolk contains
a larger proportion of solids and particularly of fatty matter which gives
to it its yellow color and rich flavor. A comparative analysis of the
yolk and white is as follows :

COMPOSITION OF THE FOWL'S EGG.

Yolk. White.

Albuminous matter 16.0 20.4

Fat 30.7

Mineral salts 1.3 1.6

Water 52.0 78.0

100.0 100.0

The mineral matters consist mainly of the sodium and potassium
chlorides, potassium sulphate, and lime and magnesium phosphates.
Of the entire contents of the egg, exclusive of the shell, the yolk consti-
tutes one-third, and the white two-thirds. Cooking produces but little
effect upon eggs except to coagulate their albuminous matters, since
these are comparatively but little susceptible of developing any marked
flavor by the action of heat.

Vegetables. — Of the different vegetables used as food, some are valu-
able for their solid starchy and albuminous ingredients, others mainly
for their saccharine and watery juices. The former are nutritious in
the ordinary sense of the word, though much less so than bread or ani-
mal food ; the latter are useful for supplying certain materials contained
in the fresh vegetable juices which are essential to the continued main-
tenance of health. The most important of the first group are repre-
sented by the potato and the leguminous seeds. The tuber of the potato
abounds in starch, but is poor in other nutritive ingredients.

FOOD. 123

COMPOSITION OF THE POTATO.
Starch ......... 20.0

Albuminous matter ....... 2.5

Sugar and gum . . . • • • .1.1
Fatty matter ..... . - .0.1

Cellulose ......... 1-0

Mineral and vegetable salts ..... 1-3

Water .........

100.0

The leguminous seeds, on the other hand, contain an abundance of
albuminous matter, similar in character to the caseine of milk, and
called u legumine."

COMPOSITION OF WHITE BEANS.
Starch ......... 55.7

Albuminous matter ....... 25.5

Fatty matter . . . . . . .2.8

Cellulose ...... ... 2.9

Mineral salts ...... . .3.2

Water ......... 9-9

100.0

The composition of dried peas is very similar to the above, the
starchy matters only being present in rather larger, the albuminous
ingredients in rather smaller proportion. Notwithstanding the abund-
ance of nitrogenous matter in leguminous seeds, its quality is inferior
to that contained in the cereal grains. Peas and beans also have a
texture which renders them comparatively difficult of digestion, and
requires long boiling to fit them for use as food. The same is true of
many juicy and saccharine roots, such as beets and parsnips, which
appear to have a comparatively soft consistency, but which nevertheless
need prolonged boiling. The object and effect of the cooking process
in vegetables generally is to disintegrate and soften their texture, and
particularly, by the aid of heat and moisture, to bring their starchy
ingredients into the hydrated condition. Raw starch is nearly or quite
indigestible by man, and if taken into the stomach under that form will
often pass unchanged from the bowels ; but when thoroughly hydrated
it is easily acted on and transformed into glucose by the digestive fluids.
It is for this reason that starchy vegetables require more thorough cook-
ing to render them digestible than most kinds of animal food.

Beside the more solid kinds of vegetable food, many of the pulpy and
succulent fruits and herbaceous substances are valuable as an addition
to the nutritive regimen — celery, lettuce, parsley, spinach, with all the
sweet fruits and melons, are used with advantage either in the raw or
cooked form. They introduce into the system a large number of salts
of the vegetable acids, such as malates, tartrates, and citrates, the
privation of which for a long time is one of the inducing causes of

124 FOOD.

scurvy. The green parts of vegetables are no doubt also useful by
furnishing to the system a supply of iron contained in their chlorophylle.
From what has been said above, it will be seen that the nutritious
character of any substance, or its value as an article of food, does not
depend simply upon its containing either one of the alimentary substances
in large quantity; but upon its containing them mingled together in
such proportion as is requisite for the healthy nutrition of the body.
What these proportions are cannot be determined from simple chemical
analysis, nor from any other data than those derived from observation
and experiment.

Requisite Quantity of Food and of its Different Ingredients,
The entire quantity of food required per day varies with the circum-
stances of the individual, such as the size and weight of the body, the
comparative development of the muscular and other systems, the tem-
perature, and especially the amount of physical activity. More food is
required, on the average, in cold than in warm weather, more by persons
of a muscular than by those of an adipose or phlegmatic constitution,
more in a condition of active exertion than in one of comparative repose.
Even the proportion of different classes of proximate principles required
for nutrition varies to a considerable extent according to special condi-
tions. When the individual is in a perfectly healthy condition, and so
situated that he can supply himself at will with any kind of nourishment
desired, the natural demands of the appetite afford the surest criterion
for both the quantity and quality of the food to be used. But not
infrequently provision must be made in advance for supplies destined
to last over a considerable period, as in the case of military or exploring
expeditions, or for the inmates of hospitals or asylums where the diet
must be regulated to a great extent upon a uniform plan. It therefore
becomes important to know both the quantity and kind of food necessary
for the support of life.

The standard adopted for this estimate is that of a healthy adult
man, employed in active but not exhausting occupation. The amount
requisite will be found to vary in either direction from this standard,
according to the circumstances above mentioned. The average require-
ments as given by different authors do not vary materially from each
other in any essential particular. According to our own observations,
a man in full health, taking active exercise in the open air, and restricted
to a diet of bread, fresh meat, and butter, with water and coffee for drink,
consumes the following quantities per day :

QUANTITY OF FOOD REQUIRED PER DAT.

Meat 453 grammes.

Bread 540

Butter or fat 100 "

Water . 1530

This represents the requisite daily quantity of food and the propor-
tions of its different kinds, when composed of such articles as are most

FOOD. 125

completely nutritious, and of the most uniform composition. For the
continued maintenance of health and strength in a working condition,
other articles, such as fresh vegetables, sugar, milk, fruit, etc., should
be mingled with the above, in a variety of proportions ; but there is no
doubt that bread and fresh meat, with a certain quantity of fat, will
prove sufficient for the wants of the system, for a longer time than any
other single articles of food.

Such a diet also affords the best means of ascertaining the absolute
and relative quantities of the different proximate principles required for
food. If we take the average composition of meat and bread, and esti-
mate the quantities of their solid albuminous, starchy, and saline ingre-
dients, together with the water contained in both solid and liquid food,
we find that the daily ration is composed nearly as follows :

Albuminous matter 130 grammes.

Starch and sugar 300 "

Fat 100 "

Mineral salts 20 "

Water . .' 2000 "

Of the mineral salts, nearly eight grammes are naturally contained in
the substances used for food and drink ; the remainder consists of sodium
chloride, artificially added to the food, or used in its preparation.

The proportion in which the albuminous and the non-nitrogenous
principles should be mingled in the food is of considerable importance,
and this proportion has been determined within very accurate limits.
In making such an estimate it is necessary to include the carbohydrates
(starch and sugar) and the fats under the same head ; but the fats are
properly regarded by all writers as having a different alimentary value
from the carbohydrates. This depends upon the well-known fact that
the final result of the transformation in the living body of all the non-
nitrogenous substances is carbonic acid and water, thus representing a
process of oxidation, the necessary oxygen being introduced with the
inspired air. But the capacity for oxidation of the fats is greater than
that of the carbohydrates, as shown by the relative proportion by weight
of their constituent elements.

. . . f C 72 C 44.47

The composition, by weight, 1 „ , . » « ** TT /

of starch (C6H1005) is } * 80 "' " P ' 04936

162 100.00

Here the oxygen is already present in sufficient proportion to saturate
all the hydrogen by the formation of water; while the 44.47 parts of
carbon will unite with 118.58 parts of oxygen to form carbonic acid.

On the other hand, if we take palmitine as representing the average
constitution of the fats, we have —

The composition, by weight, ( ° 612 C 75'93

offat(C51H9806)is {* 99* -, in 100 parts, H 12.15

806 100.00

126 FOOD.

Here the oxygen is present in much diminished proportion ; and, for
complete oxidation of the fat, to form carbonic acid and water, the 75.93
parts of carbon will require 202.48 parts of oxygen, and the 12.15 parts
of hydrogen will need 85.28 additional, over and above the 11.92 parts
of oxygen already present. Thus the quantities of oxygen appropriated
during complete oxidation, by starch and fat respectively, are as
follows :

QUANTITY OP OXYGEN REQUIRED FOR THE COMPLETE OXIDATION OF

100 parts of starch 118.58

" " " fat 287.76

A fatty substance, therefore, has a capacity for the production of car-
bonic acid and water, by oxidation, about 2.4 times greater than that of
starch. In estimating, accordingly, the requisite quantity of all the non-
nitrogenous matters taken together, the fat is calculated as starch upon
this basis ; one part of fat, by weight, being reckoned as equal to 2.4
parts of starch. This quantity, added to that of the carbohydrates in
the food, is sometimes called the " starch-equivalent" of the non-nitro-
genous matters.

If we ascertain the amount of solid albuminous and non-nitrogenous
matter contained in the daily food of an ordinary nutritious diet of
mixed quality, we find that the non-nitrogenous matters, reckoned as
starch, amount to four or five times as much as the albuminous ingredi-
ents. A comparison of our own observations with the estimates and
diet tables of Moleschott, Payen, and Playfair, all of which correspond in
the main with each other, gives the following as the average daily
quantity of these two classes of proximate principles in the food.

Albuminous matter ...... 130 grammes.

Non-nitrogenous matter, as starch .... 600 "

Thus albuminous matter constitutes rather less than one-fifth of the
entire food, for a healthy adult in active occupation ; and its quantity
is to that of the non-nitrogenous matters as 1 to 4.62.

This proportion varies to some extent with the age and condition of
the individual. In human milk, which at first forms the exclusive food
of the young infant, according to the average analyses of Simon, Yernois,
and Becquerel, as given by Milne Edwards, the albuminous ingredients
are to the non-nitrogenous matters reckoned as carbohydrates in the
proportion of 1 to 2.95. In cow's milk, upon which the young calf is
sustained, the proportion is as 1 to 3.27 ; while in green grass and hay,
upon which the adult animal feeds, it is as 1 to 11.70 and 1 to 9.28 re-
spectively. The larger proportion of albuminous matter in the food at
this early age is evidently connected with the growth which is then
taking place. As the nitrogenous principles constitute much the larger
part of the solid organic matters contained in the body, the steady in-
crease in weight during the growing period demands a corresponding
supply of these substances in the food.

There is also evidence that the requisite proportion of nitrogenous

FOOD. 127

principles varies in the adult with the amount of physical activity. A
condition of bare subsistence may be maintained upon a diet in which
the albuminous substances are in smaller, and the non-nitrogenous
matters in larger proportion ; but when the system is habitually called
upon for a greater amount of muscular exertion, the proportion of
albuminous matters in the food must be increased. This is a well-known
fact in regard to horses and working cattle generally. In a state of
comparative inactivity they may be supported mainly upon grass or
hay, in which the proportion of nitrogenous to non-nitrogenous matter
is not more than 1 to 9.28 ; but when employed in active labor they
require a liberal supply of oats, in which the proportion is as 1 to 1.13.
In Dr. Play fair's diet tables, which were collected with great care from
a variety of sources, including those of prisons and infirmaries, those of
the American and European armies during peace and in active service,
and of certain hard-working laborers, the increase of albuminous matter
with increased labor is a marked feature. While in a bare subsistence
diet the proportion of albuminous to non-nitrogenous matter is as 1 to
5.87, in that of active laborers it is as 1 to 4.34. The following table
will show the relative increase of the two kinds of food under different
conditions of exercise, as calculated from Dr. Play fair's data.

KELATIVE INCREASE, UNDER DIFFERENT CONDITIONS, OF ALBUMINOUS AND NON-
NITROGENOUS MATTERS IN THE FOOD.

Albuminous Non-nitrogenous
matter. matter.

Bare subsistence diet . . . .100 100

Full diet with moderate exercise . . 180 161

Diet of active laborer .... 232 171

Diet of hard-worked laborer . . .242 189

As these diet tables were adopted by the various civil and military
authorities as the result of long experience in the practical adaptation
of food to the amount of work performed, they may be regarded as
expressing with great approximation to certainty the physiological re-
quirements under different conditions. They are corroborated by the
variation in diet adopted in the convict establishments of Great Britain,
as given by Pavy.1 In the change from " Light-labor Diet" to " Hard-
labor Diet," while the non-nitrogenous food is increased only 13.37 per
cent., the albuminous food is increased 16.15 per cent.

It is evident, therefore, that increased physical exertion requires a
greater proportional increase in the albuminous than in the non-nitro-
genous ingredients of the food.

It is also a matter of interest to determine the quantity, source, and
destination of the different chemical elements entering into the composi-
tion of the food. Taking the average chemical composition of albumin-
ous matters and fat, and that of the carbohydrates, we find that a man
under ordinary full diet takes into his system daily the constituents of
the food, in round numbers, as follows :

1 On Food and Dietetics. Philadelphia edition, 1874, p. 433.

128 FOOD.

DAILY CONSUMPTION IN THE FOOD.

O H O N S

Albuminous matter, 130 grammes, containing 70 10 29 20 1
Starch . . 300 " 134 18 144

Fat . . . 100 " " 76 12 12

280 40 185

Of these elementary bodies, carbon and nitrogen are considered
especially important as constituents of the food, carbon as forming
the most abundant and characteristic ingredient of all organic combi-
nations, and nitrogen, as the distinguishing element of albuminous
substances. Of these two, accordingly, the system requires daily, to
be supported in an active condition, about 20 grammes of nitrogen and
about 280 grammes of carbon. This fact alone makes it evident that a
mixed diet of animal and vegetable food is the most available for man.
Meat contains, according to the analyses of Pay en, 3 per cent, of nitrogen
and 11 per cent, of carbon. Consequently, if the diet were composed
exclusively of this food, the necessary quantity of nitrogen would be
supplied by 666 grammes of meat ; but in order to obtain the required
carbon, 2545 grammes would need to be consumed, thus involving a
great waste of its nitrogenous matter. On the other hand, bread, the
most nutritious of all vegetable substances, contains only 1 per cent, of
nitrogen and 30 per cent, of carbon. Therefore, if this were the only
food used, 933 grammes would be sufficient to supply all the carbon ;
but, in order to obtain the due amount of nitrogen, it would be neces-
sary to consume 2000 grammes. A mixture, accordingly, of the two
kinds of food, in which nitrogenous and hydrocarbonaceous matters
respectively preponderate, is best adapted to supply the wants of the
system without unnecessary expenditure of material.

The changes undergone in the body, and the final destination of the
ingredients of the food, vary for different kinds. The carbohydrates no
doubt, after serving the purposes for which they are intended in the
animal economy, are finally expelled under the form of carbonic acid
and water. The action of the oxygen, introduced with the inspired air,
produces this result by uniting with the carbon of the organic body,
while its own hydrogen and oxygen, already present in the relative
quantities to produce water, are liberated under that form. This result
is expressed by the following formula :

Starch. Carbonic acid. Water.

C6H1005 + 012 = C6012 + H1005.

Thus the change undergone by starch and allied substances in the
animal body, where they are consumed, is precisely the reverse of that
taking place in plants during the act of vegetation, by which they are
produced.

For the fats the change is a similar one, their only final products, so
far as we know, being carbonic acid and water. In this process, how-
ever, the fats require, as already mentioned, a greater supply of extra-

FOOD. 129

neous oxygen, since, beside their larger proportion of carbon, they also
contain hydrogen which requires further oxidation, in order to form
water. The change thus undergone by fatty substances may be ex-
pressed as follows :

Fat. Carbonic acid. "Water.

C5iH9806 + 0145 = C510102 + H980,9.

In the case of the albuminous matters the process is a different one.
These substances contain an element, namely, nitrogen, which does not
appear in the carbonic acid and watery vapor of the expired breath,
but forms a distinguishing constituent of the crystallizable matters of
the urine. Of these matters, urea is by far the most abundant, and, as
already mentioned, fully five-sixths of the nitrogen taken in with the
food reappears as an ingredient of urea, while the remainder is included
in the creatinine and uric and hippuric acids of the urine, and in the
excrementitious substance of the feces.

There is evidence, however, that the nitrogenous matters also take
part in the formation of carbonic acid ; that is, although all their nitro-
gen is discharged under the form of urea and other similar combina-
tions in the urine and feces, all their carbon does not appear in these
excretions, and must pass out by some other channel. While, as we
have seen, 130 grammes of albuminous matter are taken daily with the
food, containing 70 grammes of carbon, only 35 grammes of urea are
discharged during the same time, containing 7 grammes of carbon ; and,
according to the most accurate analyses,1 not more than 23 grammes
are discharged daily by both the urine and feces together. This leaves
unaccounted for about 47 grammes of carbon, or two-thirds of the
original quantity, which must pass out from the body under some other
form of combination. The same thing is true, to a considerable extent,
of the hydrogen of these substances, of which 10 grammes are intro-
duced daily as an ingredient of the albuminous matters of the food,
while not more than 5 or 6 grammes are discharged in organic combi-
nations with the urine and feces. The albuminous matters, therefore,
not only give rise to the elimination of urea, but also contribute to the
production of carbonic acid and water.

The manner in which this takes place is probably by the separation
of some of the elements of albumen combined as urea, after which the
remainder are left behind as a non-nitrogenous substance. If we adopt,
for the constitution of an albuminous body, exclusive of its sulphur,
the formula C72H112N18O23, and take away from it all the nitrogen in the
form of urea, a substance will remain analogous in composition to a
fat, th us-

Albumen ..... C-2 H112 N18 023
9 Urea (CH4N20) . . . . C H36 N18 09

1 Kanke, Grundziige der Physiologic des Menschen. Leipzig, 1872, p. 298.

130 FOOD.

The remaining substance nuiy then undergo complete oxidation
without the further production of any nitrogenous compound. This
double result of the decomposition of the albuminous substances, to-
gether with the fact that we take habitually between four and five
times as much non-nitrogenous as nitrogenous matter in the food, will
explain the great preponderance in quantity of carbonic acid as an
excretion over urea. For while the average daily quantity of urea
discharged is only 35 grammes, the carbonic acid exhaled with the
breath amounts to from 700 to 800 grammes per day ; the entire quan-
tity of the carbonic acid produced being, by weight, fully twenty times
as great as that of the urea. Urea is a nitrogenous substance sepa-
rated by decomposition from the albuminous ingredients of the system ;
while carbonic acid represents the combination of its remaining elements
with the abundant oxygen introduced by the breath.

The quantities of the various substances taken in with the food and
discharged with the excretions are liable to many variations from the
changing condition of the individual. If the body be increasing in
weight, the substances introduced will be greater in quantity than those
discharged ; if it be diminishing, the material discharged will be more
than that introduced. Even in the healthy adult, where the body does
not sensibly gain or lose weight for long intervals, observation has
shown that there are frequent fluctuations of small extent, and that the
income for any single day rarely counterbalances exactly the outgo for
the same period. Consequently the quantities given in the preceding
tables cannot be taken as furnishing, in any case, a uniform and
invariable standard, but only as showing what, upon the whole, are the
relative proportions of the different ingredients entering into the com-
position of the food and of the bodily frame. And although for many
of them we are not yet able to ascertain their quantities with sufficient
accuracy for determining all the changes which they undergo in the
system, yet there is no doubt of the main result produced by the internal
transformation of the ingredients of the food. We have certain nutri-
tious substances introduced on the one hand, and certain excrementitious
products discharged on the other, which may be expressed as follows :

INTRODUCED WITH THE FOOD. DISCHARGED WITH THE EXCRETIONS.

Albuminous matter. Urea.

Fat. Carbonic acid.

Carbohydrates. Water.

This represents the decomposition and metamorphosis of the organic
substances proper ; while the mineral ingredients of the food, as a rule,
pass through the system unchanged.

CHAPTEE VIII.

DIGESTION.

DIGESTION is the process by which the food is reduced to a form in
which it can be absorbed from the intestinal canal, and taken up by the
bloodvessels. This process does not occur in vegetables, which are
dependent for their nutrition upon materials which are supplied to them
in a form already fitted for absorption.

Carbonic acid, ammonium carbonate, and ammonium nitrate exist in
a gaseous form in the atmosphere, or are brought down in solution by
the rain, and penetrate the soil to the roots of the growing plants ; while
many of the mineral salts, as sulphates, nitrates, and carbonates, are
also present in the soil in a soluble condition. Thus they require no
alteration before being taken up by the tissues of the plant. The only
known exception to this is in the case of materials composed of the
earthy carbonates and phosphates, which are insoluble or nearly so in
water, but which are known to be corroded and rendered soluble by the
acid juices of the plant-roots in contact with them. As a general rule,
the substances requisite for vegetation are directly absorbed from the
exterior in their original condition. But with animals and man the
case is different. They cannot subsist upon inorganic substances only,
but require for their support materials which have already been organ-
ized, and which have previously constituted a part of animal or vegetable
bodies. Their food is almost invariably solid or semi-solid when taken,
and insoluble in water. Meat, bread, fruits, vegetables, and the like, are
all taken into the stomach in a solid and insoluble condition ; and even
substances naturally fluid, such as milk, albumen, white of egg, are nearly
always, in the human species, more or less solidified by the process of
cooking, before being taken into the stomach.

In animals, accordingly, the food requires to undergo a process of
digestion or liquefaction, before it can be absorbed. In all cases, the
general characters of this process are the same. It consists essentially
in the food being received into a canal, running through the body from
mouth to anus, called the " alimentary canal," in which it comes in con-
tact with certain digestive fluids, which act upon it in such a way as to
liquefy and dissolve it. These fluids are secreted by the mucous mem-
brane of the alimentary canal, and by certain glandular organs situated
in its neighborhood. The food consists, as we have seen, of a mixture
of various substances, having different physical and chemical properties ;
and the several digestive fluids are also different from each other, each

(131 )

132

DIGESTION.

Fig. 26.

one of them exerting a peculiar action, which is more or less confined
to particular species of food. As the food passes through the alimentary
canal from above downward, those parts of it which become liquefied
are successively removed by absorption, and taken up by the vessels ;
while the remaining portions, consisting of the indigestible matter, to-
gether with the refuse of the intestinal secretions, gradually acquire a
firmer consistency owing to the absorption of
the fluids, and are finally discharged from the
intestine under the form of feces.

In different species of animals, the differ-
ence in their habits, in the constitution of their
tissues, and in the character of their food, is
accompanied with a corresponding variation
in the anatomy of the digestive apparatus, and
the character of the secreted fluids. As a
general rule, the digestive apparatus of herb-
ivorous animals is more complex than that of
the carnivora ; since, in vegetable substances,
the nutritious matters are often present in a
comparatively solid and unmanageable form, as,
for example, in raw starch and the cereal grains,
and are nearly always entangled among vege-
table cells and fibres of an indigestible character.
In those instances 'where the nutriment consists
mostly of grass, leaves, twigs, and roots, the
digestible matters bear only a small proportion
to the entire quantity ; and a large mass of food
must therefore be taken, in order that the re-
quisite amount of nutritious material may be
extracted from it. In such cases, accordingly,
the alimentary canal is large and long ; and is
divided into many compartments, in which dif-
ferent processes of disintegration, transforma-
tion, and solution are carried on.

In the common fowl, for instance (Fig. 26),
the food, consisting mostly of grains, or of in-
sects with hard, coriaceous integument, first
passes down the oesophagus (a) into a diverti-
culum or pouch (6) termed the crop. Here it
remains for a time mingled with a watery secre-
tion in which the grains are macerated and
softened. The food is then carried farther down
until it reaches a second dilatation (c)^ the pro-
ventriculus, or secreting stomach. The mucous membrane here is thick
and glandular, and is provided with numerous secreting follicles. From
them an acid fluid is poured out, by which the food is subjected to
further changes. It next passes into the gizzard (d), or triturating

ALIMENTARY CANAL
OF FOWL. — a. (Esophagus.
b. Crop. c. Proventriculus,
or secreting stomach, d. Giz-
zard, or triturating stomach.
e. Intestine. /. Two long
caecal tubes which open into
the intestine a short distance
ahove its termination.

DIGESTION.

133

stomach, a cavity inclosed by thick muscular walls, and lined with a
tough and horny epithelium. Here it is subjected to the crushing and
grinding action of the muscular parietes, assisted by grains of sand and
gravel, which the fowl instinctively swallows with the food, by which it
is so triturated and disintegrated, that it is reduced to a uniform pulp,
upon which the digestive fluids can effectually operate. The mass then
passes into the intestine (<?), where it meets with the intestinal juices,
which complete the process of solution ; and from the intestinal cavity
it is finally absorbed in a liquid form, by the vessels of the mucous
membrane.

In the ox, the sheep, the camel, the deer, and all ruminating animals,
there are four distinct stomachs, each lined with mucous membrane of
a different structure, and adapted

to perform a different part in the Fig-. 27.

digestive process. (Fig. 27.) The
first two, situated side by side at
the lower extremity of the oesoph-
agus (a), consist of the rumen or
paunch (6), a large sac, itself par-
tially divided by incomplete par-
titions, and lined by a mucous
membrane thickly set with long
prominences or villi ; and the
reticulum (c) or second stomach,
so called from the intersecting
folds or ridges of its mucous
membrane, which give it a reticu-
lated or honey-combed appear-
ance. Into these two stomachs
the food is received when first
swallowed by the animal in feed-
ing or browsing, and remains
there for some time, especially in the capacious rumen, slowly macerated
and softened by the action of the warmth and watery fluids, but not
undergoing any marked chemical action. When the animal has finished
browsing, and the process of rumination commences, the food is regur-
gitated into the mouth by an inverted action of the muscular walls of
the paunch and oesophagus, and slowly masticated. It then descends
again along the oesophagus ; but the lateral opening which communicates
with the first two stomachs is now closed by muscular action, and' the
oesophagus, thus converted into a tubular canal, conducts the masticated
food into a third stomach, the omasus or "psalterium" (d), in which the
mucous membrane is arranged in thin longitudinal folds, lying parallel
with each other, like the leaves of a book, thus increasing considerably
its extent of surface. The exit from this cavity leads directly into the
abomasus or "rennet" (e), the true digestive stomach, in which the
mucous membrane is soft, thick, and glandular, and in which an acid

COMPOUND STOMACH OP Ox.— a. CEsopha-
gua. 6. Rumen, or first stomach, c. Reticulum,
or second, d. Omasus, or third, e. Abomasus,
or fourth. /. Duodenum. (Rymer Jones.)

134

DIGESTION.

Fig. 28.

solvent fluid is secreted. Then follows the intestinal canal with its
various divisions and variations.

In the carnivora the alimentary canal is shorter and narrower than in
the preceding, and presents fewer complexities. The food upon which

these animals subsist is softer
than that of the herbivora, and
less encumbered with indigest-
ible matter; so that the process
of its solution requires a less
extensive apparatus.

In the human species, the
food is naturally of a mixed
character, containing both ani-
mal and vegetable substances.
But, notwithstanding this dif-
ference in the kind of nourish-
ment, the digestive apparatus
in man resembles closely that
of the carnivora. For the
vegetable matters which we
take as food are, in the first
place, artificially separated, to
a great extent, from indigesti-
ble impurities ; and secondly,
they are so softened by the
process of cooking as to be-
come nearly or quite as di-
gestible as animal substances.
In the human species the
process of digestion, though
simpler than in the herbivora,
is still somewhat complex.
The alimentary canal is di-
vided into different compart-
ments or cavities, which com-
municate with each other by
narrow orifices. At its com-
mencement (Fig. 28) we find
the cavity of the mouth, which
is guarded at its posterior ex-
tremity by the muscular valve
of the isthmus of the fauces.
Through the pharynx and
oesophagus (a), it communi-
cates with the second compart-
ment, or the stomach (6), a flask-shaped dilatation, guarded at its cardiac
and pyloric orifices by circular bands of muscular fibres. Then follows

HUMAN ALIMENTARY CANAL. — a. (Esoph-
agus, b. Stomach, c. Cardiac orifice, d. Pylorus.
e. Small intestine. /. Biliary duct. 0. Pancreatic
duct. h. Ascending colon, i. Transverse colon.
;. Descending colon, k. Rectum.

DIGESTION. 135

the small intestine (e), different parts of which, owing to the vary-
ing structure of their mucous membrane, have received the different
names of duodenum, jejunum, and ileum. In the duodenum are situated
the orifices of the biliary and pancreatic ducts (f, g). Finally comes
the large intestine (h, i,j, &), separated from the smaller by the ileo-caecal
valve, and terminating, at its lower extremity, by the anus, at which is
situated a double sphincter, for the purpose of guarding its orifice.
Everywhere the alimentary canal is composed of a mucous membrane
and a muscular coat, with a layer of submucous connective tissue between
the two. The muscular coat is composed of a double layer of longitudinal
and transverse fibres, by the alternate contraction and relaxation of which
the food is carried through the canal from above downward, and the
arrangement of which varies indifferent portions of the alimentary tract.
The mucous membrane presents, also, a different structure, and has dif-
ferent properties in different parts. That of the mouth and oesophagus
is smooth, with a hard, white, tessellated epithelium, which, however,
terminates abruptly at the cardiac orifice of the stomach. The mucous
membrane of the gastric cavity is soft and glandular, covered with a
transparent, columnar epithelium, and thrown into minute folds or pro-
jections on its free surface, which are sometimes reticulated with each
other. In the small intestine it presents larger transverse folds known
as the " valvulse conniventes," is covered upon its free surface with
thickly set villosities of various forms, and contains throughout an
abundance of tubular follicles. Finally, in the large intestine the mu-
cous membrane is smooth and shining, free from villosities, and pro-
vided with a glandular apparatus different in structure and function
from that of the preceding parts.

The digestive secretions, also, vary in these different regions. In its
passage from above downward, the food meets with at least five dif-
ferent secreted fluids, namely, the saliva, in the cavity of the mouth:
the gastric juice in the stomach; and the intestinal juice, with the pan-
creatic juice and the bile, discharged into the cavity of the small intes-
tine. These fluids are themselves, in some instances, of complex nature,
resulting from the mingled secretions of several different associated
glands, or of the various parts of a single mucous membrane. To a
certain extent, the special action of each digestive fluid upon the food
has been investigated ; and it is found that certain of the secretions
have a distinct and peculiar influence upon special ingredients of the
food. As the result of the successive action of the digestive fluids,
modified, perhaps, by the effect of their combined operation, the sub-
stances composing the alimentary mass are gradually reduced to a fluid
condition, in which they are fit for absorption by the vessels of the
intestinal mucous membrane.

The action which is exerted upon the food by the digestive fluids is
not that of a simple chemical solution. It is a transformation, by
which the ingredients of the food are altered in character at the same

136 DIGESTION.

time that they undergo the process of liquefaction. The active agent
in producing this change is in every instance an albuminoid or nitro-
genous matter, which forms the most important ingredient in the
digestive fluid; and which, by coming in contact with the food, exerts
upon it a peculiar action, transforming its ingredients into new sub-
stances. It is these newly-formed materials which are finally absorbed
by the vessels and mingled with the general current of the circulation.
In the human species the first process to which the food is subjected is
that of mastication, while it is at the same time mingled with the saliva
in the cavity of the mouth.

Mastication.

Mastication consists in the cutting and trituration of the food by the
teeth, by which it is reduced to a state of minute subdivision. The
process is entirely a mechanical one, and is necessary in order to pre-
pare the food for the subsequent action of the digestive fluids. As
this action is chemical in its nature, it will be exerted more promptly
and efficiently if the food be finely divided than if brought in con-
tact with the digestive fluids in a solid mass. This is necessarily
the case when a solid body is subjected to the action of a solvent
fluid ; since, by being broken up into minute particles, it offers a larger
surface to the contact of the fluid, and is more readily attacked and
dissolved by it.

In the structure of the teeth, and their physiological action, there are
certain marked differences, corresponding with the habits of the animal

and the kind of food upon which it subsists.
In fish and serpents, in which the food is swal-
lowed entire, and in which the process of
digestion, accordingly, is comparatively slow,
the teeth are simply organs of prehension.
They have generally the form of sharp, curved
spines, with their points set backward, and

SKITLL OF RATTLESNAKE. , . , . ,

(Achiiie Richard.) arranged in a double or triple row about

the edges of the jaws, and sometimes cover-
ing the mucous surfaces of the mouth, tongue, and palate. They serve
merely to retain the prey, and prevent its escape, after it has been
seized by the animal. In the carnivorous quadrupeds, there are three
different kinds of teeth, adapted to different purposes. (Fig. 30.)
First, the incisors, twelve in number, situated at the anterior part of
the jaw, six in the superior, and six in the inferior maxilla, of flat-
tened form, and placed with their thin edges running from side to side.
The incisors, as their name indicates, are adapted for dividing the food
by a cutting motion, like that of a pair of shears. Behind them come
the canine teeth, or tusks, one on each side of the upper and under jaw.
These are long, curved, conical, and pointed ; and are used as weapons
of offence, and for laying hold of and retaining the prey. Lastly, the

MASTICATION.

137

Fig. 30.

molars, eight or more in number on
each side, are larger and broader than
the incisors, and provided with serrated
edges, each presenting several sharp
points, arranged generally in a direc-
tion parallel with the line of the jaw.
In these animals, mastication is very
imperfect, since the food is not ground
up, but only pierced and mangled by
the action of the teeth before being
swallowed into the stomach. In the
herbivora, on the other hand, whose
food is more easily obtained, but is
generally more hard and resisting in

texture, the teeth are adapted especially for mastication. In the rumi-
nating animals generally, the canine teeth are wanting, and the incisors
are present only in the lower jaw. In the horse and allied species,
the incisors are present in both upper and lower jaws (Fig. 31), and
are used simply for cutting off the herbage upon which the animal feeds.

Fig. 31.

OF POLAR BKAR. Anterior
view ; showing incisors and canines.

SKULL OF THE HORSE.

The canine teeth are absent in the female, and only slightly developed
in the male, and the real process of mastication is performed altogether
by the molars. These are large and thick (Fig. 32), and present a broad,
flat surface, diversified by variously folded and projecting ridges of
enamel, with shallow grooves between them. By
the lateral rubbing motion of the roughened sur-
faces against each other, the food is effectually com-
minuted and reduced to a pulpy mass.

In the gnawing animals, rats, mice, squirrels, rab-
bits, and hares, the incisor teeth are developed to a
remarkable extent, presenting two chisel-like edges
opposed to each other in the upper and lower jaws,
and growing from permanently vascular roots ; so
that their waste from mechanical attrition is con-
10

Fig. 32.

MOLARTOOTH OF

THK HORSE. Grind-
ing surface.

138

DIGESTION.

stantly repaired, and the animal is able to penetrate the hardest sub-
stances.

In the human subject, the teeth combine the characters of those of the
carnivora and the herbivora. (Fig. 33.) The incisors (a), four in num-
ber in each jaw, have, as in other instances, a cutting edge running from
side to side. The canines (6), which are situated immediately behind
the former, are much less prominent and pointed than in the carnivora,
and differ less in form from the incisors on the one hand, and the

first molars on the other.
The molars (c, d) are
thick and strong, and have
comparatively flat surfaces,
like those of the herbivora ;
but instead of presenting
curvilinear ridges, are
covered with more or less
conical eminences, like
those of the carnivora. In
the human subject, there-
fore, the teeth are evidently
adapted for a mixed diet,
consisting of both animal
and vegetable food. Mas-
tication is here as perfect
as in the herbivora, though
less prolonged and labo-
rious ; for the vegetable substances used by man, as already remarked,
are previously separated to a great extent from their impurities, and
softened by cooking; so that they do not require, for their masti-
cation, so extensive and powerful a triturating apparatus. Finally,
animal substances are more completely masticated in the human subject
than in the carnivora, and their digestion is accordingly completed with
greater rapidity.

We can easily estimate, from the facts above stated, the importance,
to the digestive process, of a thorough preliminary mastication. If the
food be hastily swallowed in undivided masses, it must remain a long
time undissolved in the stomach, where it will become a source of irri-
tation and disturbance ; but if reduced beforehand, by mastication, to a
state of minute subdivision, it is readily attacked by the digestive fluids,
and becomes speedily and completely liquefied.

HUMAN TERTH— UPPER JAW.— a. Incisors, b. Ca-
nines, c. Anterior molars, d. Posterior molars.

The Saliva and its Action upon the Food.

The saliva is a compound fluid, derived from the secretion of four
different glandular organs — namely, the parotid, submaxillary, and sub-
lingual glands, and the muciparous glandules of the cavity of the mouth.
All these glands resemble each other in the essential points of their

THE SALIVA.

189

structure, their substance being composed of dis-
tinct irregularly spherical or ovoidal masses,
more or less flattened into a polygonal form by
mutual compression. The separate divisions or
lobules are connected with corresponding ter-
minal branches of the salivary duct, which pene-
trate into their interior, and there divide into
smaller tubes each one of which finally termi-
nates in a rounded sac called the glandular
follicle or alveolus. The appearance presented
upon an injection of such a lobule is as if the
follicles were arranged in clusters, like grapes,
around the ends of the smaller salivary tubes.
(Fig. 34.) A more complete examination has
shown, however, that the follicles are simply

the rounded extremities of tubular or sac-like offshoots from the
salivary tube ; and that it is the windings and prolongations of the
tube itself which constitutes the secreting follicles of the gland. The
follicles themselves are in general about 50 mmm. in diameter, and
are lined with the glandular epithelium cells, which cover their in-
ternal surface and nearly fill their cavity ; so that there is frequently
to be seen only a comparatively small space toward the central part
of the follicle, containing a transparent fluid, produced by the secreting

Fig. 35.

LOBUI.B OF PAROTID
GLAND of newly-born in-
fant, injected with mercury.
(Wagner.)

Two SALIVARY TUBES FROM THE LOBULE OF A MTTCIPAROUS GLAND, entering
the main duct. — a. Duct of the lobule, b. Salivary tube, c. Follicles, on one Bide, as they
appear in situ. d. Follicles separated from each other, showing the windings and offshoots
of the salivary tube. (Kulliker.)

action of the cells. The glandular cells, which are arranged in a
single layer, are finely granular bodies, about 15 mmm. in diameter.,
each one provided with an oval nucleus, situated toward the external
part of the follicle. The cells are closely packed together, and are of
various polygonal forms.

The salivary tubes or ducts, outside the follicles, unite into larger and
larger branches, until they reach the principal excretory duct of the gland.
They are lined with a layer of cells which vary in form from those of
the follicles, being elongated and cylindrical, and provided with a nucleus
which is situated about their middle portion. It is very probable that
the epithelium of the salivary ducts, as well as that of the follicles, takes

140

DIGESTION.

part in the process of secretion ; since Pfliiger has found that in sec-
tions of the gland, examined immediately after being taken out of the

Fig. 36.

GLANDULAR FOLLICLES AND CELLS; from the subm axillary gland of the dog.

(Heidenhain.)

body, transparent drops of fluid may be seen exuding from the ends of
the cylindrical epithelium cells into the cavity of the duct. The follicles

Fig. 37.

SECTION OF THE SUBMAXILLARY GLAND FROM THE DOG.— a. Salivary duct,
with cylindrical epithelium and central cavity. 6. Follicle, with glandular epithelium and
central cavity. (Kolliker.)

and lobules are surrounded with a delicate layer of connective tissue, in
which are distributed the capillary bloodvessels, which supply to the
gland the materials for its secretion.

THE SALIVA.

141

Physical and Chemical Properties of the Saliva — Human saliva,
obtained directly from the cavity of the mouth, is a colorless, slightly
viscid, and alkaline fluid, with a specific gravity of 1.005. When first
discharged, it is frothy and opaline, holding in suspension minute whitish
flocculi. On being allowed to stand for some hours in a cylindrical glass
vessel, an opaque, whitish de-
posit collects at the bottom,
while the supernatant fluid be-
comes clear. The deposit, when
examined by the microscope
(Fig. 38), is seen to consist of
abundant epithelium scales
from the internal surface of
the mouth, detached by me-
chanical attrition, minute,
roundish, granular, nucleated
cells, apparently epithelium
from the mucous follicles, a
certain amount of granular
matter, and a few oil-globules.
The supernatant fluid has a
faint bluish tinge, and becomes
slightly opalescent by boiling,
or by the addition of nitric
acid. Alcohol in excess causes the precipitation of abundant whitish
flocculi.

According to the analyses of Bidder and Schmidt, the composition
of the saliva is as follows :

BTTCCAL AND GLANDULAR EPITHELIUM,
with Granular Matter and Oil-globules; deposited
as sediment from human saliva.

COMPOSITION OF THE SALIVA.

995.16

Albuminous matter 1.34

Potassium sulphocyanide 0.06

Calcareous, magnesian, and alkaline phosphates . . 0.98

Sodium and potassium chlorides 0.84

Mixture of epithelium 1.62

1000.00

It will be seen that the saliva is one of the least concentrated of the
digestive secretions, containing but a very small quantity of organic
matter, and by no means a large proportion of mineral salts ; its watery
ingredient being by far the most abundant, as compared with the other
animal fluids. The albuminous matter of the saliva consists of a small
quantity of albumen, coagulable by the ordinary means ; more or less
mucosine, which gives to the fluid its slightly viscid character; and
ptyaline, a substance peculiar to the saliva, which is not coagulated,
like albumen, by nitric acid or potassium ferrocyanide, but is precipi-

142 DIGESTION.

tated both by a boiling temperature and by alcohol in excess. Some
of these reagents, accordingly, precipitate all the albuminous matters
of the saliva, while others produce coagulation of only a part of them.
The sodium sulphocyanide of the saliva may be detected by adding to
the secretion a small quantity of a solution of iron chloride, when the
characteristic red color of iron sulphocyanide is produced. A similar
red .color is also produced by the action of the ferric salts upon
me conic acid, or the meconates ; but the two substances may be dis-
tinguished from each other by the fact that the red color caused by the
presence of a sulphocyanide is destroyed by the addition of either gold
chloride or mercurial bichloride, neither of which affects the tint pro-
duced by meconic acid. The presence of a combination of sulphocy-
anogen in human saliva is almost constant, and we have never failed to
find it in the freshly collected secretion by the iron-chloride test.
Yierordt1 has calculated the amount of potassium sulphocyanide in
saliva by measuring the absorption of light in the green and blue por-
tions of the spectrum of the red fluid produced on the addition of iron
chloride; and has found it, in an average of six observations, to be 0.16
parts per thousand.

The saliva, like various other animal fluids, has the property of con-
verting hydrated starch into glucose if mingled with it at or about a
temperature of 38° (100° F.). The change is not confined to precisely
this temperature, but will go on, with diminished rapidity, both above
and below it, if the degree of cold or warmth be not too great. It is
entirely suspended, however, at or near the freezing point, and is per-
manently arrested by the temperature of boiling water. It depends, in
the saliva, upon the presence of pty aline, which acts in this respect like
the "diastase" of certain vegetable substances. Like other similar
matters which exert a so-called " catalytic" action, it will produce its
effect only within certain limits of temperature, and is most efficient at
about the warmth of the living body. It is affected differently, how-
ever, by the action of cold and that of heat ; for while a freezing tem-
perature only suspends it for the time being, and allows it to recommence
when moderate warmth is again applied, a boiling temperature at once
•coagulates the pty aline and destroys its catalytic property. Saliva,
therefore, which has been boiled for a few instants and allowed to cool,
is found to have permanently lost its power of transforming starch
into sugar.

This action of human saliva on hj^d rated starch takes place sometimes
with great rapidity. Traces of glucose may often be detected in the
mixture in one minute after the two substances have been brought in
contact ; and we have even found that starch paste, introduced into the
cavity of the mouth, if already at the temperature of 38°, will yield
traces of sugar at the end of half a minute. The rapidity, however, with

1 Anwendung des Spectralapparates zur Photometric der Absorptionsspectren.
Tubingen, 1873, p. 147.

THE SALIVA. 143

which this action is manifested, varies very much, as formerly noticed
by Lehmann, at different times ; and it is frequently impossible, even
with the mixture kept steadily at the temperature of 38°, to find any
evidence of sugar under five, ten, or fifteen minutes. This difference
depends probably upon the varying constitution of the saliva itself.

Notwithstanding the rapidity with which glucose begins to show itself
in a mixture of saliva with boiled starch, this action is not a very ener-
getic one ; that is, only a very small quantity of the starch is converted
into glucose within a given time, the greater portion remaining un-
changed. This is proved by the fact that such a mixture will show
the characteristic reaction of starch with iodine long after Fehlmg'a
test has shown the existence of traces of glucose. If a weak solu-
tion of boiled starch, made in the proportion of 3 parts of starch to
100 parts of water, be mixed with one-third of its volume of fresh human
saliva and placed in the water-bath at the temperature of 38°, it will
often give, in one minute, a prompt sugar -reaction with Fehling's test ;
but it also contains, at the same time, an abundance of unaltered starch.
Even at the end of an hour, according to our own observations, the starch
is far from being entirely converted, as the mixture will still give a strong
purple-blue color on the addition of iodine. The same persistence of
starch in considerable proportion may be seen when the mixture is
retained in the mouth itself. If a thin paste of hydrated starch, con-
taining no traces of sugar, be taken into the mouth and thoroughly
mixed with the buccal secretions, it will often, as above mentioned,
begin to show the reaction of glucose in half a minute ; but some of the
starchy matter still remains, and will continue to manifest its character-
istic reaction with iodine for fifteen or twenty minutes, or even for half
an hour.

The secretions produced by the different salivary glands vary some-
what in their physical properties, especially in the degree of their vis-
cidity, depending mainly upon the quantity of mucosine present. The
parotid saliva is obtained in a state of purity from the dog by exposing
the duct of Steno where it crosses the masseter muscle, and introducing
into it, through an artificial opening, a silver canula. The secretion
then runs directly from its external orifice, without being mixed with
that of the other salivary glands. It is clear, limpid, and watery, and
without the slightest viscidity. The submaxillary saliva is obtained in
a similar manner, by inserting a canula into Wharton's duct. It dif-
fers from the parotid secretion, so far as its physical properties are
concerned, chiefly in possessing a well marked viscidity. The sublingual
saliva is also colorless and transparent, and possesses a greater degree of
viscidity than that from the submaxillary. The secretion of the muci-
parous glandules, which forms properly a part of the saliva, is obtained
b}^ placing a ligature simultaneously on Wharton's and Steno's ducts,
and on that of the sublingual gland, so as to shut out from the mouth
all the glandular salivary secretions, and then collecting the fluid se-
creted by the buccal mucous membrane. This fluid is very scanty, and

144 DIGESTION.

much more viscid than either of the other secretions ; so much so, that
it cannot be poured out in drops when received in a glass vessel, but
adheres strongly to the surface of the glass. All the salivary secretions
are alkaline in reaction.

We have obtained the parotid saliva of the human subject in a state
of purity by introducing directly into the orifice of Steno's duct a
silver canula a little over one millimetre in diameter. The other ex-
tremity of the canula projects from the mouth between the lips, and
the saliva is collected as it runs from the open orifice. This method
gives results much more valuable than observations made on salivary
fistulae and the like, since the secretion is obtained under perfectly
healthy conditions, and unmixed with other animal fluids.

The result of many different observations, conducted in the manner
above described, is that the human parotid saliva, like that of the dog,
is colorless, watery, and distinctly alkaline in reaction. It differs from
the mixed saliva of the mouth, in being perfectly clear, without tur-
bidity or opalescence. Its flow is scanty while the cheeks and jaws
remain at rest ; but as soon as the movements of mastication are excited
by the introduction of food, it runs in much greater abundance. We
have collected, in this way, from the parotid duct of one side only, in a
healthy man, 31.1 grammes of saliva in the course of twenty minutes ;
and in seven successive observations, made on different days, comprising
in all three hours and nine minutes, we have collected a little over 194
grammes.

The parotid saliva obtained in this way has been analyzed by Prof.
Maurice Perkins, with the following result :

COMPOSITION OF HUMAN PAROTID SALIVA.

Water 983.308

Organic matter precipitable by alcohol .... 7.352
Substance destructible by heat, but not precipitated by alcohol 4.810

Sodium sulphocyanide 0.330

Lime phosphate 0.240

Potassium chloride 0.900

Sodium chloride and carbonate . 3.060

1000.000

Prof. Perkins found, in accordance with our own observations, that
the fresh parotid saliva, when treated with iron chloride, showed no
evidences of sulphocyanogen ; but after the organic matters had been
precipitated by alcohol, the filtered fluid was found to contain an appre-
ciable quantity of sulphocyanide.

The parotid saliva, accordingly, differs from the mixed saliva of the
mouth in containing some substance which masks the reaction of sul-
phocyanogen. If the parotid saliva and that from the mouth be drawn
from the same person within the same hour, the addition of iron chloride
will produce a distinct red color in the latter, while no such change
takes place in the former. And yet the parotid saliva itself contains a

THE SALIVA. 145

sulphocyanide which may be detected, as we have seen, after the organic
matters have been precipitated by alcohol.

Both the parotid saliva and that from the submaxillary gland in the
human subject contain ptyaline, but they differ considerably, as in the
case of the lower animals, in their degree of viscidity.

Mode of Secretion of the Saliva.— The different salivary glands vary
in the quantity of fluid secreted by them and in the different influences
which excite them to activity. As shown by Bernard, the parotid
saliva is most abundantly poured out under the stimulus of anything
which excites the movement of the jaws, as in the mastication of dry
substances, or continuous speaking ; while that of the submaxillary is
especially increased by the introduction of substances which excite the I
sense of taste. According to the same experiments, the secretion of the
sublingual glands in the dog is particularly excited at the moment of
deglutition, and aids, together with that of the muciparous glandules, in
lubricating the surface of the mouth and fauces, and in facilitating the
passage of the masticated food through the oesophagus. Colin, in expe-
rimenting upon the horse and the ox,1 found also that the parotid saliva
in these animals is abundantly excited by the movements of mastication,
but not by the simple contact of sapid substances with the mucous mem-
brane of the mouth ; while, on the other hand, the secretion of the sub-
maxillary saliva is considerably increased by introduction into the mouth
of substances having a marked taste. Both the parotid and submaxillary
secretions are abundant while the animal is feeding, their quantity being
proportional to the rapidity of mastication and the sapid quality of the
alimentary substances. They are both either suspended or very much
diminished during abstinence. In the ruminants, however, the sublingual
saliva, like the submaxillary, is excited by sapid substances ; it is also
secreted continuously while the animal is feeding, and not simply at the
moment of deglutition. It continues to be secreted during abstinence,
and contributes to the supply of fluid by which the surfaces are kept in
a moist condition.

Another fact observed by Colin which indicates the different nervous
influences by which the salivary glands are controlled, is that in the
ruminant animals while feeding both the parotid and submaxillary
glands furnish an abundant supply of saliva ; but during the process of
rumination, although the parotid glands are in full secretion, discharging
frequently as much as 900 grammes of saliva in a quarter of an hour,
the submaxillary glands are entirely inactive or produce only an insig-
nificant quantity of fluid. Colin has also found that in the horse and ass,
as well as in the ox and other ruminating animals, the parotid glands of
the two opposite sides, during mastication, are never in active secretion
at the same time; but that they alternate with each other, one remain-
ing quiescent while the other is active, and vice versa. In these animals
mastication is said to be unilateral, that is, when the animal commences

Physiologie compare des Animaux Domestiques. Paris, 1854, tome i. p. 468.

146 DIGESTION.

feeding or ruminating, the food is triturated for fifteen minutes or more
by the molars of one side only. It is then changed to the opposite side ;
and for the next fifteen minutes mastication is performed by the molars
of that side only. It is then changed back again, and so on alternately,
so that the direction of the lateral movements of the jaw may be reversed
many times during the course of a meal. By establishing a salivary
fistula simultaneously on each side, it is found that the flow of saliva
corresponds with the direction of the masticatory movement. When
the animal masticates on the right side, it is the right parotid which
secretes actively, while but little saliva is supplied by the left ; when
mastication is on the left side, the left parotid pours out an abundance
of fluid, while the right is nearly inactive.

We have observed a similar alternation in the flow of parotid saliva
in the human subject, when mastication is changed from side to side.
In an experiment of this kind, the tube being inserted into the parotid
duct of the left side, the quantity of saliva discharged during twenty
minutes, while mastication was performed mainly on the opposite side
of the mouth, was 8.26 grammes ; while the quantity during the same
period, mastication being on the same side of the mouth, was 24.25
grammes — being nearly three times as much in the latter case as in the
former.

Daily Quantity of the Saliva. — Owing to the physiological variations
in the rapidity of secretion of the saliva, and also to the fact that it is
not excited in the same way by artificial stimulus as by the presence of
food, it is somewhat difficult to ascertain with exactness its total daily
quantity. The first attempts to do so were made upon patients affected
with fistula of the parotid duct, and the amounts collected were so small
as to lead to the conclusion that the entire quantity secreted by all the
glands was not more than ten or twelve ounces, or about 350 grammes
per day. As in these cases, however, the subjects of experiment were
not in a healthy condition, and as the proportion in quantity between the
parotid saliva and that secreted by the remaining glands must necessarily
be a matter of conjecture, the above calculation could hardly be regarded
as correct. Bidder and Schmidt,1 from the results of direct observation,
were led to make a higher estimate. One of these observers, in experi-
menting upon himself, collected from the mouth in one hour, without
using any artificial stimulus, 97 grammes of saliva; and calculates,
therefore, the amount secreted daily, making an allowance of seven
hours for sleep, as not far from 1620 grammes.

On repeating this experiment we have not been able to collect from
the mouth, without artificial stimulus, more than 36 grammes of saliva
per hour. This quantity, however, may be greatly increased by the
introduction into the mouth of any smooth unirritating substance,
as glass beads or the like ; and during the mastication of food, the
saliva is poured out in very much greater abundance. The sight and

1 Yerdauungssaefte und Stoffwechsel. Leipzig, 1852, p. 1

THE SALIVA. 147

odor of nutritious food, when the appetite is excited, will stimulate
to a remarkable degree the flow of saliva; and, as it is often expressed,
" bring the water into the mouth." Any estimate, therefore, of the total
quantity of saliva, based on the amount secreted in the intervals of mas-
tication, would be imperfect. We may make a tolerably accurate calcu-
lation, by ascertaining how much is really secreted during a meal, over
and above that which is produced at other times. We have found, by
experiments performed for this purpose, that wheaten bread gains during
complete mastication 55 per cent, of its weight of saliva ; and that fresh
cooked meat gains, under the same circumstances, 48 per cent, of its
weight. We have already seen that the daily allowance of these two
substances, for a man in full health and activity, is about 540 grammes
of bread and 450 grammes of meat. The quantity of saliva, accordingly,
employed in the mastication of these two substances is, for the bread
29 1 grammes, and for the meat 216 grammes. If we now calculate the
quantity secreted between meals as continuing for twenty-two hours at
the rate of 36 grammes per hour, we have :

Saliva required for the mastication of bread = 297 grammes.

'• " " " meat = 216 "

" secreted in intervals of meals = 792 "

Total quantity per day, a little over 1300 "

Physiological Action of the Saliva. — The principal function of the
saliva is undoubtedly to moisten the food and provide in this way for its
further solution, and especially to assist in mastication, by which the
food is converted into a pultaceous mass. This is mainly accomplished
by the watery ingredients of the secretion, while the albuminous matters
contained in it not only aid in giving to the masticated food the requi-
site consistency, but also act by lubricating its surface, and facilitating
its deglutition. This is evident from the fact that the principal trouble
which results from absence or deficiency of the saliva is a difficulty in
the mechanical processes of mastication and swallowing. Food which
is hard and dry, like crusts or crackers, cannot be masticated and
swallowed with readiness, unless moistened by some fluid. If the
saliva be prevented from entering the cavity of the mouth, its loss
does not interfere directly with the chemical changes of the food in
digestion, but only with its physical preparation. This is the result
of direct experiments performed by various observers. Bidder and
Schmidt,1 after tying Steno's duct, together with the common duct of
the submaxillary and sublingual glands on both sides in the dog,
found that the immediate effect of such an operation was " a remark-
able diminution of the fluids which exude upon the surfaces of the
mouth ; so that these surfaces retained their natural moisture only so
long as the mouth was closed, and readily became dry on exposure to
the air. Accordingly, deglutition became evidently difficult and labo-

1 Verdauungssaefte und Stoffwechsel, p. 3.

148 DIGESTION.

rious, not only for dry food, like bread, but even for that of a tolerably
moist consistency, like fresh meat. The animals also became very
thirsty, and were constantly ready to drink."

Bernard1 also found that the only marked effect of cutting off the flow
of saliva from the mouth was a difficulty in the mechanical processes of
mastication and deglutition. He first administered to a horse 500
grammes of oats, in order to ascertain the rapidity with which mastica-
tion would naturally be accomplished. The above quantity of grain was
thoroughly masticated and swallowed at the end of nine minutes. An
opening had been previously made in the esophagus at the lower part
of the neck, so that none of the food reached the stomach ; but each
mouthful, as it passed down the oesophagus, was received at the cesopha-
geal opening and examined by the experimenter. The parotid duct on
each side of the face was then divided, and another similar quantity of
oats given to the animal. Mastication and deglutition were both found
to be immediately retarded. The alimentary masses passed down the
03sophagus at longer intervals, and their interior was no longer moist
and pasty, as before, but dry and brittle. Finally, at the end of twenty-
five minutes, the animal had succeeded in masticating and swallowing
only about three-quarters of the quantity which he had previously dis-
posed of in nine minutes.

It appears from the experiments of Magendie, Bernard, and Las-
saigne, on horses and cows, that the quantity of saliva absorbed by
the food during mastication is in direct proportion to its hardness and
dryness, but has no particular relation to its chemical qualities. These
experiments were performed as follows : The oesophagus was opened at
the lower part of the neck, and a ligature placed upon it, between the
wound and the stomach. The animal was then supplied with a pre-
viously weighed quantity of food, and this, as it passed out by the oeso-
phageal opening, was received into appropriate vessels and again
weighed. The difference in weight, before and after swallowing, indi-
cated the quantity of saliva absorbed by the food. The following table
gives the results of some of Lassaigne's experiments, performed upon a
horse.

Kind of Food employed. Quantity of Saliva absorbed.

For 100 parts of hay 400 parts.

barley meal 186 "

oats 113 "

green stalks and leaves . . 49 "

It is evident from the above facts, that the quantity of saliva pro-
duced has not so much to do with the chemical character of the food
as with its physical condition. When the food is dry and hard, and
requires much mastication, the saliva is secreted in abundance; when it
is soft and moist, a smaller quantity of the secretion is poured out ; and
finally, when the food is taken in a fluid form, as soup or milk, or
reduced to powder and moistened artificially with a large quantity of

1 Leqons de Physiologic Experimental. Paris, 1856, p. 146.

THE SALIVA. 149

water, it is not mixed at all with saliva, but passes at once into the
cavity of the stomach.

A difference of opinion exists among various authors as to whether
the transforming power of the saliva upon starch be also an essential
part of its physiological action. If the digestion of the food took place
in the cavity of the mouth, or if it were retained there for any consider-
able time, there would be no doubt in this respect. But in reality the
food is in only momentary passage though the mouth, remaining there
merely long enough to allow for mastication. We have already seen
that this time is too short to complete the conversion into glucose
of even the small quantity of starch contained in a dilute solution,
much more so the abundant semi-solid starchy matters of bread or
vegetables. There can be no question whatever that in point of fact,
the starchy elements of the food are not digested or transformed to any
considerable extent while in the cavity of the mouth. They are swal-
lowed into the stomach with by far their greater portion still unchanged.
Some observers (Schiff, F. G. Smith, Flint, Kanke, Brunton) believe
that the transforming action of the saliva, which is commenced in the
mouth, may continue subsequently in the stomach in presence of the
gastric juice. Others (Bernard, Robin, Colin) assert that the action
of the saliva on starch is arrested by the gastric juice, and, as a matter
of fact, does not go on in the stomach. This discrepancy no doubt
depends partly upon differences in the mode of experimentation ; some
writers contenting themselves with testing the effect of dilute acids only
on the saliva, others using the gastric juice itself. The proportion in
which the two secretions are mingled also makes a difference in the
result, and the properties of either one may vary somewhat according
to the time at which it is collected. Our own observations lead to
the conclusion that gastric juice certainly interferes with the chemical
action of saliva, usually to a very marked degree, when mingled with it
in equal volumes. If we take fresh unfiltered human saliva, which is
shown by a preliminary experiment to be capable of producing a prompt
sugar-reaction in a solution of boiled starch at the end of one minute,
mix it with an equal volume of freshly collected gastric juice from the
dog, then add the starch-solution, and place the mixture in the .water-
bath at the temperature of 38° (100°F.)5 there is no sugar-reaction
whatever at the end of five minutes, and only an imperfect one in
half an hour; while at the end of an hour there may be distinct
reduction by Fehling's test.1 But if three volumes of gastric juice
be added for one volume of saliva, the mixture gives no indication of
sugar even at the end of an hour. As all observations tend to show
that the gastric juice is naturally secreted in much larger quantity than
the saliva, these proportions undoubtedly indicate, more nearly than

1 In these examinations the fluid mixture is always treated with animal char-
coal previously to applying Fehling's test; otherwise the albuminous matter of the
secretions would interfere with its certainty.

150 DIGESTION.

the former, the relative quantities in which the two secretions are
present in the stomach during ordinary digestion.

Experiments upon the lower animals, provided with gastric fistulse,
show furthermore that in them starch is not, in point of fact, converted
into sugar in the stomach. In the dog, the horse, the sheep, and the
ox, according to Bernard, Schiff, and Colin, the action of saliva upon
hydrated starch is distinct, though less rapid than that of the human
subject. In the gnawing animals generally it is present, and in the
guinea pig, according to Schiff, is more decided than in man. But
if a dog, with a gastric fistula, be fed with a mixture of meat and
boiled starch, and portions of the fluid contents of the stomach with-
drawn afterward through the fistula, the starch is easily recognizable
by its reaction with iodine for ten, fifteen, and twenty minutes after-
ward. In forty-five minutes it is diminished in quantity, and in one
hour has usually disappeared ; but no sugar is to be detected at any
time. Sometimes the starch disappears more rapidly than this ; but at
no time, according to our observations, is there any indication of the
presence of sugar in the gastric fluids. Bernard1 has shown the same
want of transformation in the dog's stomach after swallowing a mix-
ture of hydrated starch with ordinary food. Briicke,2 in dogs fed with
starch paste, found in the stomach more or less unchanged starch, and
either no sugar or only traces of it, after the lapse of from one to five
hours. This does not depend upon any want of power in dogs to digest
hydrated starch, since this substance is converted into glucose in these
animals with great promptitude on arriving in the duodenum, by the
influence of the pancreatic and intestinal juices.

It is also an important consideration, in this respect, that the saliva
exerts its transforming power only upon starch which has been cooked
or hydrated. All observers agree that it is nearly or quite without
action upon raw starch, which remains unchanged in contact with it at
all temperatures. But in the herbivorous animals, where the salivary
glands are at least as fully developed and the saliva as abundant as
in man, the starchy elements of the food are habitually taken in
the raw state. Even in the ruminating animals, where the food is
retained, for some time after the first mastication, in the paunch,
unmixed with gastric juice, it does not undergo there the sugar-
conversion. Prof. Francis G. Smith, in a series of experiments upon
Alexis St. Martin, affected with a gastric fistula, in 1856,3 withdrew
the contents of the stomach two and a half hours after bread had been
masticated and swallowed; and in the mixed fluids so obtained, he
detected at the end of that time unchanged starch, both by the micro-
scope and by the iodine test. Glucose was also found in the fluid, but,
as bread nearly always contains glucose, it is uncertain how much,

1 SScre'tions Digestives. Paris, 1856, p. 159.

2 Jahresberichte der Anatomie und Physiologie. Leipzig, 1873, p. 467.

3 Philadelphia Medical Examiner, July and September, 1856.

THE SALIVA. 151

if any, had been produced by transformation of the starch. Colin1
has found the farinaceous matter of oats and of starchy roots recogniz-
able by its iodine reaction, after these substances had remained in the
first stomach of the ox, mixed with saliva, for twenty-four hours. The
same observer introduced into the interior of the paunch, through a
fistula, small muslin bags containing uncooked potato starch, which
were found in the same cavity, still full of unaltered starch, at the end
of twenty and twenty-two hours. It is worth remembering furthermore
that the salivary glands and their secretion are also abundantly devel-
oped in the carnivora, whose food never in the natural condition con-
tains starch as an ingredient.

It appears evident, therefore, that the chemical action of the saliva in
the lower animals forms no part of the natural process of digestion ;
and that in man it is insignificant in amount, and quite subordinate to
that of other digestive fluids. In both animals and man, however, and
in the carnivora as well as in the herbivora, its physical properties are
important in accomplishing the processes of mastication and degluti-
tion.

Mastication is aided and controlled in great measure by the sen-
sibilities of touch and taste, residing in the surface of the tongue and
other parts of the mucous membrane. The sense of taste notifies us
of the alimentary qualities of the food taken into the mouth, and
its sapid qualities must be fully brought out by the comminution and
moistening of the food before mastication is complete. The taste itself
depends, for one of its essential conditions, upon a sufficient supply of
saliva, and this is by no means an unimportant function of the secretion.
No substance can produce an impression upon the nerves of taste unless
it be in a fluid form and capable of absorption by the mucous membrane.
The saliva produces this effect upon the soluble ingredients of the food,
and brings them in contact with the papillae of the tongue in sufficient
quantity to produce a gustatory sensation.

The general sensibility of the tongue, which is highly developed,
also enables this organ to appreciate the physical condition of the food
and how far it is prepared for deglutition. At the same time its mus-
cular apparatus provides for its movement in every direction. When
the alimentary material is finally reduced, by mastication and mixture
with the saliva, to a sufficiently pasty and homogeneous condition, the
softened mass is collected from every part of the mouth by the move-
ments of the tongue and brought together upon its upper surface. It
is then pressed backward by the muscular force of the organ, and car-
ried through the fauces into the pharynx and upper part of the oesopha-
gus. Here it passes beyond the control of the will. It is then grasped
by the muscular fibres of the oesophagus, and by the continuous and rapid
peristaltic action of this canal is carried downward into the stomach.

1 Physiologic compare des Animaux Domestiques. Paris, 1854, tome i. p. 603.

152

DIGESTION.

The Gastric Juice and Stomach Digestion,

The stomach has long been recognized as the organ in which the
most important part of the digestive process is inaugurated, and in
which the essential chemical modifications of the alimentary matters first
take place. Its action consists in the production of a special digestive
fluid, the gastric juice, furnished by the glandular apparatus of its
mucous membrane.

The gastric mucous membrane presents certain variations, both in its
general appearance and its intimate structure, in different portions of
the stomach. It is red in the cardiac and middle portion, paler in the
cardiac portion. It increases also in thickness from the cardia toward
the pylorus ; being, according to the measurements of Kolliker, about
half a millimetre thick in the cardiac portion, one millimetre in the
middle, and one and a half to two millimetres near the pylorus. Its
free surface is everywhere more or less uneven and marked with minute
ridges or eminences. In the cardiac portion (Fig. 39) these ridges are
reticulated with each other, so as to include between them polygonal
interspaces, each of which is encircled by a network of capillary blood-
vessels. In the pyloric portion Fig. 40) the eminences are more distinct

Fig. 39.

Fig. 40.

Free surface of GASTRIC Mucous MEM- Free surface of GASTRIC Mucous MEM-
BRANE, viewed from above; from Pig's BRANE, viewed in vertical section; from
Stomach, Cardiac portion. Moderately mag- Pig's Stomach, Pyloric portion. More highly
nified. magnified.

from each other, pointed in form, about one-tenth of a millimetre in
height, and generally flattened from side to side. In the human subject
these villus-like projections have even been found extending over the
whole surface of the gastric mucous membrane. Each one contains a
capillary bloodvessel, which returns upon itself in a loop at the extremity
of the projection, and communicates freely with adjacent vessels.

The entire thickness of the mucous membrane of the stomach consists
of glandular follicles or tubules, some of which are simple in structure,

THE GASTRIC JUICE AND STOMACH DIGESTION. 153

while others are compound or branched. Another distinction between
the follicles is that some of them are lined throughout with cylindrical
epithelium cells, not very different from those on the free surface of the
mucous membrane, while others contain also larger cells of a rounded
form, which give to the follicles a peculiar aspect. Both simple and
branched follicles may be found, presenting both these two kinds of epi-
thelium ; but as a general rule, the simple tubular follicles are distin-
guished by their lining of cylindrical epithelium, while the compound or
branched follicles more especially contain the larger cells of glandular
epithelium.

In the pyloric portion of the stomach, the follicles with cylindrical
epithelium preponderate, or in some instances are present exclusively.
In the dog, according to the observations of Ebstein, and in man, ac-
cording to Kb'lliker, the mucous membrane in the immediate proximity
of the pylorus, for a zone of considerable width, contains follicles of this
kind only. They present the same essential characters in man and in
different species of animals. They are nearly straight or slightly tor-
tuous tubules, y1^ of a millimetre in diameter, lined with cylindrical
epithelium cells, and terminating in blind extremities at the under sur-
face of the mucous membrane (Fig. 41). In their lower half they are

Fig. 41.

Fig. 42.

Mucous MEMBRANE OF PIG'S STO-
MACH, from Pyloric portion; vertical sec-
tion; showing tubular follicles, and, at o, a
closed follicle. Moderately magnified.

TUBULAR FOLLICLES, from Pyloric
portion of Pig's Stomach, showing their
coecal extremities and epithelial lining. At
a, the torn end of a follicle, showing its
cavity. More highly magnified.

often slightly branched, one or more lateral diverticula passing off from
the principal tubule, and forming a little mass or lobule of glandular
tubes. At their upper extremities they open on the free surface of the
mucous membrane, in the interspaces between the projecting folds or
villi. The cylindrical epithelium cells, which cover the general surface
of the gastric mucous membrane, extend downward into the cavity of
11

154

DIGESTION.

the follicles and reach even to their blind extremities (Fig. 42) ; only in
the interior of the follicles they are shorter, less transparent, and more
glandular in appearance than on the free surface of the mucous mem-
brane.

In the cardiac portion of the stomach the superficial part of the
mucous membrane contains wide depressions or tubes, lined with large
cylindrical epithelium cells. These tubes, at a short distance below
the surface, are joined each by two or more tubular follicles, lined with
small glandular epithelium cells, and terminating below, like the pre-
ceding, in rounded extremities (Fig. 43).

Fig. 43.

Fig. 44.

GASTRIC FOLLICLES, from Pig's Sto-
mach, Cardiac portion. At a, two follicles
joining a larger tube ; 6, portion of a tube
seen endwise ; c, its centra/I cavity.

G-ASTRIO FOLLICLES, with large gland-
ular cells ; from middle portion of Pig's
Stomach.

In the mucous membrane of both the fundus and middle portion of
the stomach, but especially in the middle portion, there are follicles
which are distinguished by containing, in addition to the cylindrical or
small glandular epithelium cells, larger spheroidal cells of peculiar
aspect. As already mentioned, these follicles are usually compound,
but they are also met with of a simple tubular form. The spherical
cells which they contain are usually most abundant in their lower
portions, but are often more distinctly defined in the middle part of the
follicle. These cells are rounded in form, about 20 mmm. in diameter,
finely granular, and provided with well-marked oval nuclei. They nearly
fill the cavity of the follicle, and also project laterally from its external
surface, giving to it from this cause an extremely characteristic varicose
or irregularly tumefied appearance (Fig. 44). In the compound follicles
of the cardiac portion of the human stomach (Fig. 45), the spherical cells
are found more or less abundantly throughout their deeper and middle

THE GASTRIC JUICE AND STOMACH DIGESTION. 155

Fig. 45.

parts, up to the point where they join the wider tube leading to the
surface.

These spheroidal cells have been designated by the name of " pepsine
cells," and the glandular follicles con-
taining them as " peptic glands," from
a supposition that they are exclusively
concerned in the production of the
essential organic ingredient of the gas-
tric juice. Opinions, however, are
divided upon this point. The follicles
in question contain both the so-called
"pepsine cells" and the smaller cells
of glandular epithelium ; the two kinds
of cells being found associated in the
same follicles over a large portion of
the stomach. It is only in the pyloric
region that the follicles contain cells
of the smaller variety alone. It is
acknowledged by all that by the action
of glycerine a substance having the
properties of pepsine may be extracted
from the middle or cardiac portions of
the gastric mucous membrane, and not
from the pyloric portion. But Ebstein
has shown1, that, if two digestive fluids
be prepared by macerating the gastric
mucous membrane in water acidulated
with hydrochloric acid, using for one
the pyloric portion and for the other the
middle portion, both of these fluids pos-
sess under similar conditions, digestive properties which are the same in
kind, and differ only in degree. The principal distinction between the
two kinds of cells, according to the same observer, is that the substance
of the cylindrical cells becomes cloudy and shrivelled by the action of
acids generally ; while that of the spheroidal cells is thus affected only
by mineral acids, acetic acid, on the contrary, causing them to become
swollen and transparent. From this it is concluded that the smaller
cells contain a substance like mucosine, while the larger consist of
materials more closely resembling albumen.

It cannot therefore be said with certainty, that either the larger cells
or the follicles containing them produce exclusively either the pepsine
or the acid of the gastric juice. No doubt the follicles in different por-
tions of the stomach differ from each other more or less, in function as
well as in appearance ; but it is not yet possible to determine the exact
nature of the differences between them. By the combined action of all

COMPOUND GASTRIC FOLLICLE,
from the Cardiac portion of human
stomach. 1. Excretory tube, leading
to the surface. 2. Tubular follicles,
containing spheroidal cells. (Kolliker.)

1 Archiv fur Mikroskopische Anatomie, 1870, vi. p. 515.

156 DIGESTION.

parts of the glandular apparatus is produced the characteristic secretion
of the gastric juice.

Physical Qualities and Composition of the Gastric Juice. — The earliest
decisive investigations in regard to the existence and properties of the
gastric juice were those made by Dr. Beaumont, of the United States
Army, in the case of Alexis St. Martin, a Canadian boatman, who was
affected with a permanent gastric fistula, the result of an accidental gun-
shot wound. The musket, which was loaded with buckshot at the time
of the accident, was discharged, at the distance of a few feet from St.
Martin's body, in such a manner as to tear away the integument at the
lower part of the left chest, open the pleural cavity, and penetrate,
through the lateral portion of the diaphragm, into the great pouch of the
stomach. After the integument and the pleural and peritoneal surfaces
had united and cicatrized, there remained a permanent opening about two
centimetres in diameter leading into the left extremity of the stomach,
which was usually closed by a circular valve of protruding mucous
membrane. This valve could be readily depressed at any time, so as to
open the fistula and allow the contents of the stomach to be extracted
for examination.

Dr. Beaumont experimented upon this person at various intervals
from the year 1825 to 1832.1 He established during the course of his
examinations the following important facts : First, that the active agent
in digestion is an .acid fluid, secreted by the walls of the stomach;
secondly, that this fluid is poured out by the glandular walls of the
organ only during digestion, and under the stimulus of the food ; and
finally, that it will exert its solvent action upon the food outside the
body as well as in the stomach, if kept in glass phials upon a sand-bath
at the temperature of 38° (100° F.). He made also a variety of other
interesting investigations as to the effect of various kinds of stimulus on
the secretion of the stomach, the rapidity with which the process of
digestion takes place, and the comparative digestibility of various kinds
of food.

The same person, with his gastric fistula unchanged, after an interval
of twenty-four years, came under the observation of Prof. Francis G.
Smith, of the University of Pennsylvania, who again made a series of
important experiments of a similar nature, confirming and extending
those of Dr. Beaumont ; and another case, in a young and otherwise
healthy woman, the result of a local inflammation and abscess, happened
in Germany in 1854, and was investigated by Prof. C. Schmidt.

Since Dr. Beaumont's time similar experiments have been frequently
performed by means of gastric fistulae artificially established upon the
lower animals, especially upon the dog, which has been found most
convenient for this purpose ; the result of examinations conducted by
this and other methods being that the gastric juice presents the same
essential characters in man and in the carnivorous and herbivorous

1 Experiments and Observations upon the Gastric Juice. Boston, 1834.

THE GASTKIC JUICE AND STOMACH DIGESTION. 157

animals. The simplest and most effectual mode of establishing a gas-
tric fistula in the dog is the following : A longitudinal incision, about
six centimetres in length, is made through the abdominal parietes in the
median line, over the great curvature of the stomach. The anterior wall
of the organ is then to be seized with a pair of hooked forceps, drawn
out at the external wound, and opened with the point of a bistoury. A
short silver canula from one to two centimetres in diameter, armed at
each extremity with a narrow projecting rim or flange, is inserted into
the wound in the stomach, the edges of which are fastened round the
tube with a ligature in order to prevent the escape of the gastric fluids
into the peritoneal cavity. The stomach is then returned to its place in
the abdomen, and the canula allowed to remain with its external flange
resting upon the edges of the wound in the abdominal integuments,
which are to be drawn together by sutures. The animal may be kept
perfectly quiet, during the operation, by the administration of ether
or chloroform. In a few days the ligatures come away, the wounded
peritoneal surfaces unite with each other, and the canula is retained in
a permanent gastric fistula ; being prevented by its flaring extremities
both from falling out of the abdomen and from being accidentally
pushed into the stomach. It is closed externally by a cork, which may
be withdrawn at pleasure, and the contents of the stomach thus obtained
for examination.

Experiments conducted in this manner confirm, in the main, the results
obtained by Dr. Beaumont. Their results are even, in some respects,
more satisfactory than those obtained from the human subject ; since
animals are more completely under the control of the experimenter, and
all sources of deception or mistake are thereby avoided, while the inves-
tigation is, at the same time, facilitated by the simple character of the
food administered.

The gastric juice obtained by this method is a clear, colorless, or
faintly amber-colored fluid, of a perfectly watery consistency and a dis-
tinctly acid reaction. Its specific gravity does not vary much from
1010. It becomes slightly opalescent on boiling.

The following is the composition of the gastric juice of the dog,
based upon a comparison of various analyses by Lehmann, Blondlot,
Otto, Bidder and Schmidt.

COMPOSITION OF GASTRIC JUICE.

Water .......... 975.00

Free acid 4.78

Pepsine 15.00

Sodium chloride 1.70

Potassium " 1.08

Calcium " 0.20

Ammonium "........ 0.65

Lime phosphate 1.48

Magnesium "........ 0.06

Iron " 0.05

1000 00

158 DIGESTION.

Prof. C. Schmidt1 found the gastric juice of the human subject similar
in constitution to the above, except that it contained a larger propor-
tion of water and a considerably smaller proportion botli of free acid
and pepsine, as well as of solid ingredients generally. From our own
repeated observations upon the dog, there is no doubt that both the
quantity and density of the gastric juice vary, within certain limits, in
different individuals even of the same species — the proportion of solid
ingredients being less when the secretion is more abundant, and greater
when the secretion is in small quantity.

The most striking physical property of the gastric juice is its acid
reaction, which is always strongly marked, and by which it is distin-
guished from all the other digestive secretions and internal fluids of the
body. This property, as indicated in the foregoing table, depends upon
the presence in the secretion of a free acid. Notwithstanding the
numerous investigations which have been directed to this point, it is
still uncertain whether the reaction of the gastric juice be due to free
hydrochloric or free lactic acid ; each of these two substances having
been found by different observers. Those who attribute the reaction of
the gastric juice to hydrochloric acid (Prout, Dunglison, Enderlin,
Bidder and Schmidt) depend upon its being obtainable by distillation,
and more especially upon a quantitative determination of all the alka-
line and earthy bases contained in the secretion, and an estimate of
the amount of hydrochloric acid necessary to saturate these bases ; the
hydrochloric acid, actually obtainable, being found to be more than
sufficient to unite with the above bases in neutral combination. On the
other hand, various experimenters (Lehmann, Leuret, Lassaigne, Francis
G. Smith, Bernard and Barreswil) have not only found evidences of
the presence of free lactic acid in the gastric juice, but some of them
have also shown3 that during distillation the concentrated lactic acid
would set free hydrochloric acid by decomposition of the alkaline chlo-
rides, although none were originally present in the fluid. They also
point out that the addition of a small quantity of oxalic acid to the
gastric juice produces a precipitate of lime oxalate, while no such pre-
cipitation will take place in a fluid containing two parts per thousand
of free hydrochloric acid. It is certain, however, that either of these
acids may replace that which naturally exists in the gastric juice with-
out essentially impairing its digestive properties.

The remaining important ingredient of the gastric juice is its albu-
minoid matter, known under the name of pepsine. This substance is
not precipitated by either the organic or the mineral acids, but is thrown
down by the action of heat and by alcohol in excess. It may also be
precipitated, like ptyaline, from its watery solution acidulated with
dilute phosphoric acid, by the addition of lime water ; the precipitated
lime phosphate bringing down the pepsine entangled with it. Pepsine

1 Annalen der Chemie und Pharmacie, 1854, p. 42.

2 Bernard. Le<;ons de Physiologic Exp6rimentale. Paris, 1856, p. 396.

THE GASTRIC JUICE AND STOMACH DIGESTION. 159

is not affected in the same way, however, by all the agents which cause
its coagulation. After precipitation by alcohol or by lime phosphate, it
is unchanged in its chemical qualities, and may be again dissolved in
water without losing any of its original digestive properties ; but when
coagulated by boiling, it is permanently altered and cannot again be
brought into an active condition.

Pepsine may also bek precipitated from the gastric juice by contact
with the bile. If ten to fifteen drops of dog's bile be added to 10 cubic
centimetres of fresh gastric juice from the same animal, a complete pre-
cipitation takes place ; so that the whole of the biliary coloring matter
is thrown down as a deposit and the filtered fluid is found to have lost
its digestive power although it still retains an acid reaction. This ex-
plains the disturbing effect upon digestion produced by a regurgitation
of bile through the pylorus into the stomach.

Pepsine may be extracted from the fresh mucous membrane of the
stomach by cutting it into small pieces and macerating it for some hours
with distilled water. The filtered fluid, acidulated with dilute hydro-
chloric acid until it presents a similar grade of acid reaction to that of
the fresh gastric juice, is found to possess the peculiar digestive proper-
ties of the natural secretion.

These digestive properties depend accordingly upon the presence of
both the pepsine and the free acid. They are not exhibited by a dilute
acid alone, nor by a solution of pepsine which is neutral or alkaline in
reaction. The pepsine, which acts in some unexplained manner, like
other so called " catalytic" bodies, requires, as a special condition of its
activity, the presence of a free acid. Accordingly, the fluids of the sto-
mach, even though they contain pepsine, will not act upon the food unless
they have also an acid reaction. If the fresh gastric juice be neutralized
by the addition of an alkali, it loses its digestive properties as soon as
the point of neutralization is reached; but these properties may be
restored by again acidulating the fluid. For this purpose, either lactic
or hydrochloric acids may be used, both of which yield very active
digestive fluids with pepsine. Dilute sulphuric, nitric, and acetic acids,
on the other hand, according to Lehmann,1 produce a mixture of only
slight digestive power ; while phosphoric, oxalic, and tartaric acids are
nearly inert in this respect. If the gastric juice, again, be subjected to
a boiling temperature, it is found to have lost its digestive properties
owing to the chemical alteration of its pepsine, notwithstanding its acid
reaction may remain the same as before.

The characteristic property of the fresh gastric juice, as well as of
acidulated solutions of pepsine, is that it has the power of digesting and
dissolving substances of an albuminous nature. This is best shown by
suspending in gastric juice pieces of coagulated fibrine and keeping
the fluid at the temperature of 38° (100° F.). The fibrine rapidly swells

1 Physiological Chemistry. Cavendish Society edition. London, 1853, vol. ii.
p. 58.

160 DIGESTION.

up, becomes transparent and gelatinous, and after a time dissolves.
The same effect is produced, though more slowly, upon hard-boiled white
of egg. The solid caseine of cheese is liquefied and the oleaginous
particles set free. This action is in every case more or less dependent
upon the temperature. It is entirely suspended at or near the freezing
point, but becomes more and more active with the increase of warmth,
and is most energetic from 35° to 40° (about 100° P.). Above that
point its activity again diminishes, and at a boiling temperature it is
entirely destroyed. It is owing to the influence of temperature that
digestion is more slowly performed in the cold-blooded reptiles than in
the warm-blooded birds and quadrupeds. This difference has been
shown by Schiff,1 who made acidulated infusions of the stomachs of two
serpents, and placed in each the same measured quantity of coagulated
albumen ; one of the infusions being allowed to remain at a temperature
varying from 10° to 11° (50° to 62° F.), the other being introduced, in a
closed glass tube, into the stomach of a living dog. The second was
found to have digested in six hours as much albumen as the first at the
end of three weeks.

The changes produced in solid albuminous matters during digestion
by gastric juice are as follows: The first effect is a swelling and gela-
tinization of the substance under the influence of the free acid. This
will take place by the action of a dilute acid alone, and with the aid of
continuous warmth a part of the substance will after a time even be
dissolved. This solution, however, is not a true digestion of the albu-
minous body. It has merely been modified in such a way as to be
soluble in an acidulated liquid, and it may be again precipitated by
neutralizing the solution by means of an alkali or an alkaline carbonate.
This modification of the albuminous matter, however, by the action of
the free acid, seems to be an essential preliminary in the digestive act.
If it be allowed to go on farther, the influence of the pepsine produces
a more important change, by which the original substance is converted
into albuminose. In this form it is no longer precipitable by neutral-
ization of the fluid, and has consequently become soluble in water. It
is not coagulable by boiling, either in a neutral, acid, or alkaline liquid ;
and it is not precipitable by nitric acid or by potassium ferrocyanide,
although it may still be thrown down by alcohol in excess. It has thus
become essentially altered in its chemical relations.

An equally or even more important change has also taken place in
its physical characters ; that is, it has acquired the property of diffusi-
bility. The other liquid albuminous matters, as albumen, caseine,
mucosine, and the like, do not pass through parchment paper or the sub-
stance of an animal membrane ; or they pass, if at all, very slowly and
in small quantity. Even pepsine is retained in this way almost com-
pletely by such a membrane. Albuminose, on the contrary, diffuses
itself with great readiness through membranous partitions, and can be

1 Lecons sur la Physiologic de la Digestion. Paris, 1867, tome ii. p. 19.

THE GASTRIC JUICE AND STOMACH DIGESTION. 161

detected by its ordinary reactions in the external liquids. It is thus
suited for absorption by the mucous membrane of the alimentary canal.

All the albuminous matters, without exception, which are susceptible
of digestion, whether of animal or vegetable origin, are finally converted
by the action of the gastric juice into albuminose. They therefore lose
their original distinctive properties, and, when fully prepared for absorp-
tion into the bloodvessels, are all reduced to the condition of a single
substance.

A further very remarkable peculiarity of the gastric juice is its apti-
tude for resisting putrefaction. While other animal fluids, as the saliva,
the bile, the pancreatic juice, mucus and blood, enter into putrefaction
with great readiness, the gastric juice remains when exposed to the air
at ordinary temperatures for many months without developing any
putrescent odor or losing its characteristic properties. It becomes
somewhat darker in color, and after a time deposits a brownish sediment
upon the bottom of the vessel, but it still retains its acid reaction and
its power of digesting albuminous matters. Gastric juice will even
arrest putrefactive changes when they have already begun in organic
substances ; and consequently putrefaction does not go on in the living
stomach. Dr. Beaumont preserved some fragments of meat unaltered for
a month in gastric juice, while other portions of the same substances,
kept in saliva, were putrefied in ten days. Spallanzain found in the
stomach of a viper the body of a lizard which had remained there for
sixteen days without undergoing any putrefactive alteration ; and similar
observations have been made by other physiologists.

Mode of Secretion of the Gastric Juice. — As a rule, the gastric juice
is not a constant but an occasional secretion, being poured out only when
food is taken into the stomach. Dr. Beaumont found it to be entirely
absent during the intervals of digestion, the stomach containing at that
time no acid watery fluid, but only a little neutral or alkaline mucus.
He was able to obtain a sufficient quantity of gastric juice for examina-
tion, by gently irritating the mucous membrane with a gum-elastic
catheter, or the end of a glass rod, and by collecting the secretion as it
ran in drops from the fistula; and on the introduction of food he found
'that the mucous membrane became turgid and reddened, a clear acid fluid
collected everywhere in drops underneath the layer of mucus lining the
walls of the stomach, and was soon poured out abundantly into its
cavity. Prof. F. G. Smith, in his subsequent observations upon Alexis
St. Martin, also found the fluids obtained from the empty stomach
invariably neutral in reaction ; while during digestion, whatever might
be the nature of the food, they were always acid. Other observers, in
experimenting upon the dog, have found more or less acid reaction
always present at the surface of the mucous membrane. According to
our own observations, the irritability of the gastric mucous membrane,
and the readiness with which the flow of gastric juice may be excited,
varies considerably in different animals, even in those belonging to the
same species. In experimenting with gastric fistulas on different dogs,

162 DIGESTION.

for example, we have found in one instance, like Dr. Beaumont, that the
gastric j uice was always entirely absent in the intervals of digestion ;
the mucous membrane then presenting invariably either a neutral or
slightly alkaline reaction. In this animal, which was a perfectly healthy
one, the secretion could not be excited by any artificial means, such as
glass rods, metallic catheters, and the like ; but only by the natural
stimulus of ingested food. Tough and indigestible pieces of tendon,
introduced through the fistula, were expelled again in a few minutes, one
after the other, without exciting the flow of a single drop of acid fluid ;
while pieces of fresh meat, introduced in the same way, produced at
once an abundant supply. Jn other instances, on the contrary, the
introduction of metallic catheters or glass rods into the empty stomach
has produced a scanty flow of gastric juice ; and in experimenting upon
dogs that have been kept without food during various periods of time
and then killed by section of the medulla oblongata, we have usually,
though not always, found the gastric mucous membrane to present a
distinctly acid reaction, even after an abstinence of six, seven, or eight
days. There is at no time, however, under these circumstances, any
considerable amount of fluid present in the stomach ; but only sufficient
to moisten the gastric mucous membrane, and give it an acid reaction.

The gastric juice which is obtained by irritating the stomach with a
metallic catheter is clear, perfectly colorless, and acid in reaction. A
sufficient quantity of it cannot be obtained by this method for any
extended experiments; and for that purpose, the animal should be fed,
after a fast of twenty-four hours, with fresh lean meat, a little hardened
by short boiling, in order to coagulate the fluids of the muscular tissue,
and prevent their mixing with the gastric secretion. No effect is usually
apparent within the first five minutes after the introduction of the food.
At the end of that time the gastric juice begins to flow ; at first slowly,
and in drops. It is at first perfectly colorless, but soon acquires a
slight amber tinge. It then begins to flow more freely, usually in drops,
but often running for a few seconds in a continuous stream. In this
way, from 60 to 75 cubic centimetres may be collected in the course of
fifteen minutes. Afterward it becomes somewhat turbid with the debris
of the food, which has begun to be disintegrated ; but from this it may
be readity separated by filtration. After three hours, it continues to
run freely, but has become very much thickened, and even grumous in
consistency, from the abundant admixture of alimentary debris. In six
hours after the commencement of digestion it runs less freely, and in
eight hours has become very scanty, though it continues to preserve the
same physical appearances as before. It ceases to flow altogether in
from nine to twelve hours, according to the quantity of food taken.
For purposes of examination, the fluid drawn during the first fifteen
minutes after feeding should be collected, and at once separated by
filtration from accidental impurities. Obtained in this way it repre-
sents, as closely as possible, the normal constitution of the gastric juice
as secreted by the stomach during the digestive process.

THE GASTRIC JUICE AND STOMACH DIGESTION. 163

Both the essential constituents of the gastric juice, namely, the pep-
sine and the free acid, are produced by the glandular mucous membrane
of the stomach. It would appear, however, that the mode of their
production is somewhat different. Pepsine is an albuminoid substance
formed by the nutritive process in the glands themselves. It probably
accumulates in the intervals of digestion, and may therefore be extracted
from the substance of the mucous membrane in the manner already de-
scribed. On the other hand, the free acid appears in quantity only at
the time of digestion, and is poured out with the watery constituents
of the secretion. There is evidence, however, that the acid is not imme-
diately formed by the glandular cells, but is produced by a subsequent,
though very rapid, change after the fluid has been secreted. The acid
reaction of the gastric fluids is never strongly pronounced in the deeper
and middle parts of the mucous membrane, but only upon its free sur-
face. This was shown by Bernard,1 who injected into the jugular vein
of a rabbit two successive solutions, one of iron lactate, the other of
potassium ferrocyanide. These two salts would remain unaltered in
neutral or alkaline fluids, but in the presence of a free acid would unite
to form Prussian blue (iron ferrocyanide). On killing the animal three-
quarters of an hour afterward, no blue coloration was found anywhere
excepting in the stomach ; and in this organ it was confined to the free
surface of the mucous membrane, not being perceptible in the substance
of the glands. As the two salts must have both exuded from the blood-
vessels of the mucous membrane, it is evident that it was only at or
near its upper surface that they met with a sufficient quantity of free
acid to cause their combination. According to Dr. Lauder Brunton,2
moreover, a horizontal section through the lower part of the gastric
glands of the pigeon, if tested by litmus paper, will be found to have a
neutral or extremely weak acid reaction, while the inner surface of the
stomach presents a strongly marked acidity. At the same time, the
deeper parts of the mucous membrane contain pepsine in sufficient
quantity to form a digestive fluid, if extracted and acidulated in the
usual way. Finally, the free acid continues to be formed during a certain
time after death; for it has been found that if the fresh gastric mucous
membrane of a rabbit or a pig be cut in small pieces and washed with
distilled water until all trace of acidity is removed, it will again acquire
an acid reaction after being left to itself for some hours. The materials
of the free acid of the gastric juice are therefore furnished during life
by the alkaline fluids of the circulating blood ; but the acid itself origi-
nates subsequently by some change taking place in the products of
exudation.

Self-digestion of the Stomach after Death. — Notwithstanding that the
gastric juice has the power, at the temperature of the living body, of
digesting all soft tissues composed of albuminous matter, yet owing to

1 Liquides de TOrganisme. Paris, 1859, torn. ii. p. 375.

2 Handbook for the Physiological Laboratory. Philadelphia, 1873, p. 491.

164 DIGESTION.

the mode of its production it does not attack the walls of the stomach
itself. As the pepsine alone accumulates in any considerable quantity
in the gastric follicles, while the acid ingredient appears abundantly only
at the time of digestion, no dissolving action can be manifested while
the organ is empty of food. It has already been seen, furthermore, that
during the active secretion of the gastric juice, its free acid is formed by
some modification in the exuded fluids, so that it is distinctly perceptible
only in the fluids on the free surface and in the cavity of the stomach.
In the substance of the mucous membrane, the acid fluid, even if ab-
sorbed, could not exert its solvent action, since it must be at once neu-
tralized by the alkaline plasma of the circulating blood.

Even after death the gastric mucous membrane usually remains nearly
intact, because, as a general rule, digestion has been at least partially
suspended during the last hours of life, and the stomach accordingly
contains little or no gastric juice. Still it is rare, in the human subject,
to make an examination of the body twenty-four or thirty-six hours
after death, without finding the mucous membrane in the great pouch
of the stomach more or less softened and altered in its appearance from
this cause. Sometimes, when death takes place suddenly, by violence
or accident, in a healthy person, soon after the ingestion of food,
and when the body has been protected against rapid cooling, the accu-
mulated gastric juice acts powerfully upon the walls of the stomach as
well as upon the food which it contains. Owing to the stoppage of
the circulation, the local alkalescence of the fluids is no longer main-
tained, and the increasing quantity of free acid at last preponderates
over the blood remaining in the capillary vessels. The mucous mem-
brane becomes imbibed with an active digestive fluid, and in the course
of ten or twelve hours may be thoroughly softened and disintegrated,
exposing the submucous layer of connective tissue; and occasionally all
the coats of the organ have been found destroyed, with a perforation
leading into the peritoneal cavity. These changes show that, after death,
the gastric juice, if present in sufficient quantity, may dissolve the coats
of the stomach without difficulty ; while during life, the changes of nutri-
tion going on in the tissues protect them from its influence, and effectu-
ally preserve their integrity.

Daily Quantity of the Gastric Juice. — The quantity of gastric juice,
secreted during a given time, like that of the saliva, varies very much
according to the condition of the secreting organ. In many instances,
as we have already seen, it is entirely absent during the intervals of
digestion, and is poured out in abundance under the stimulus of recently
introduced food. An exact estimate of the normal daily quantity is
difficult for several reasons. First, it is evident that if the secretion be
excited by artificial irritation of the gastric mucous membrane with in-
soluble glass or metallic substances, its quantity is not so abundant as
when produced by the stimulus of natural food. Secondly, if excited
by the introduction of food, a part of it is almost necessarily absorbed
by the alimentary material, and consequently cannot be collected for

THE GASTRIC JUICE AND STOMACH DIGESTION. 165

measurement ; and thirdly, if we measure the quantity obtainable by
either of these means during a short period, it does not follow that it
would continue to be secreted at the same rate during the remainder of
the twenty-four hours, because the rapidity of its production is so much
influenced by the condition of the digestive process. Neither can we
draw from an animal with a stomach fistula all the gastric juice which
will flow during twenty-four hours, and consider that as representing
the normal daily quantity ; because we should then be drawing away a
quantity of secreted fluid which in the natural condition is retained in
the alimentary canal and reabsorbed by the bloodvessels. Its supply
would therefore be necessarily diminished by the continuous loss of
fluids from the system. Notwithstanding these difficulties, however, a
sufficient number of facts have been observed to show that the usual
daily secretion of the gastric juice is undoubtedly far more abundant
than that of the other digestive fluids. Dr. Beaumont was able to ob-
tain from the stomach of St. Martin, simply by the introduction of a
gum-elastic catheter, 44 grammes of gastric juice in the course of fifteen
minutes. We have often collected from a medium-sized dog, under the
stimulus of commencing digestion, from 60 to 75 grammes in the same
time. Bidder and Schmidt found that, in a dog weighing about 15.5
kilogrammes, they were able to obtain, by separate experiments, con-
suming in all twelve hours, 793 grammes of gastric juice. If these
separate experiments, therefore, as is probable, indicate the average
rate of its production at diflerents parts of the day, the entire quantity
for twenty-four hours, in an animal of that size, would be 1586 grammes ;
or about 100 grammes for every kilogramme in weight of the body
of the animal. By applying this calculation to a man of ordinary size
the authors estimate the average daily quantity of gastric juice in
the human subject as about 6500 grammes. It is, however, quite
unsafe to estimate the quantity of this secretion as necessarily in pro-
portion to the weight of the body. It is probably more strictly in
proportion to the quantity of food which it is its function to digest ; and
the dog habitually consumes a much larger quantity of animal food, in
proportion to his size, than a man. Schmidt, in the series of observa-
tions already quoted,1 performed upon a woman with accidental gastric
fistula, whose weight was only 53 kilogrammes, obtained, as the mean
result of several observations, 580 grammes of gastric juice from the
fistula in the course of an hour. In this case, however, the secretion
was much poorer in its characteristic ingredients than that usually
obtained from the dog, and was also much inferior in digestive power.

Another method which has been adopted for estimating the quantity
of the gastric juice is to ascertain the amount capable of digesting the
quantity of albuminous food required per day. According to the experi-
ments of Lehmann,2 one gramme of coagulated albumen, calculated as

1 Annalen der Chemie und Pharmacie, 1854, Band xcii. p. 42.

2 Physiological Chemistry. London, 1853, vol. ii. p. 53.

166 DIGESTION.

dry, requires for its solution 20 grammes of gastric juice. As the aver-
age daily consumption of albuminous matter in man is 130 grammes,
this would accordingly require in him the secretion of 2600 grammes
of gastric juice per day. Our own observations on the digestibility of
fresh meat make the daily requirement still higher. A weighed quantity
of fresh lean meat, containing 18 per cent, of water and 22 per cent, of
solid ingredients, was cut into small pieces, and digested for ten hours,
with frequent agitation, in a measured quantity of fresh gastric juice at
the temperature of 38° (100° F.). At the end of that time, the liquefied
portions were filtered away, the residue evaporated to dryness, and the
quantity of fresh meat remaining undissolved thus calculated from the
percentage of its solid ingredients. In this way it was found that one
gramme of meat had been liquefied by 13.5 grammes of the digestive
fluid; and accordingly the 453 grammes of meat consumed by a man
in twenty-four hours would require for complete solution a little over
6000 grammes of gastric juice. This agrees very nearly with the esti-
mate of Bidder and Schmidt given above. If the gastric juice were the
only digestive fluid which acts on the food, we could rely fully 011 the
foregoing estimate. But below the stomach other secretions also take
part in the digestive process ; and it is possible that some of them,
especially the pancreatic juice, have also a certain amount of action
upon albuminous matters, and may facilitate considerably their solu-
tion in the intestine. For the partial solution of meat, the disintegra-
tion of its fibres, and its reduction to a soft, grumous, liquid or semi-
liquid consistency, Dr. Beaumont found a much smaller quantity of
gastric juice to be sufficient. In one experiment 1 gramme of cooked
meat was completely disintegrated in this way by 2.5 grammes, and in
another by 1.83 grammes of gastric juice. Its entire solution would of
course have required a larger quantity.

These data are accordingly insufficient for determining the precise
quantity of the secretion required for the digestive process. But if we
allow sufficient weight to all the observations on this subject, it is evi-
dent that the gastric juice is very abundant ; and it would not be an
extravagant calculation to estimate its quantity as at least 3000 grammes
per clay.

Physiological Action of the Gastric Juice. — From the properties of
the gastric juice already ascertained, it is seen to have an energetic
action upon the albuminous ingredients of the food. As but few of the
alimentary substances, however, habitually taken by either man or
animals, consist solely of albuminous matter, the changes which they
actully undergo in the stomach become a subject for further investi-
gation.

The first effect of the introduction of food into the stomach, according
to all observers, is an increased vascularity of its mucous membrane, a
slight elevation of its temperature, and the immediate exudation, in
more or less abundant quantity, of its acid secretion. At the same
time the stimulus of the ingested food excites the peristaltic movement

THE GASTRIC JUICE AND STOMACH DIGESTION. 167

of the stomach, which is accomplished by the alternate contraction and
relaxation of the longitudinal and circular fibres of its muscular coat.
The motion is minutely described by Dr. Beaumont, who examined it,
both by watching the movements of the food through the gastric fistula,
and also by introducing into the stomach the bulb and stem of a ther-
mometer. According to his observations, when the food first passes
into the stomach, and the secretion of the gastric juice commences, the
muscular coat, which was before quiescent, is excited and begins to
contract actively. The contraction takes place in such a manner that
the food, after entering the cardiac orifice of the stomach, is first car-
ried to the left into the great pouch of the organ, thence downward and
along the great curvature to the pyloric portion. At a short distance
from the pylorus, Dr. B. often found a circular constriction of the gastric
parietes, by which the bulb of the thermometer was gently grasped and
drawn toward the pylorus, at the same time giving a twisting motion
to the stem of the instrument, by which it was rotated in his fingers.
In a moment or two, this constriction was relaxed, and the bulb of
the thermometer again released and carried, together with the food,
along the small curvature of the organ to its cardiac extremity. This
circuit was repeated so long as any food remained in the stomach ;
but, as the liquefied portions were successively removed toward the end
of digestion, it became less active, and at last ceased altogether when
the stomach had become completely empty, and the organ returned to
its ordinary quiescent condition.

It is easy to observe the muscular action of the stomach during diges-
tion in the dog, by the assistance of a gastric fistula, artificially estab-
lished. If a metallic catheter be introduced through the fistula when
the stomach is empty, it must usually be held carefully in place, or it
will fall out by its own weight. But immediately upon the introduction
of food, it can be felt that the catheter is grasped and retained with
some force, by the contraction of the muscular coat. A twisting or
rotatory motion of its extremity may also be frequently observed, similar
to that described by Dr. Beaumont. This peristaltic action of the
stomach, however, is a gentle one, and not at all active or violent in
character. We have never seen, in opening the abdomen, any such
energetic or extensive contractions of the stomach, even when full of
food, as may be easily excited in the small intestine by the mere con-
tact of the atmosphere, or by pinching with the blades of a forceps.
This difference in activity between the peristaltic movement of the
stomach and that of the intestine corresponds to the difference in its
object and result. In the intestine the peristaltic action carries the
semifluid contents of the alimentary canal continuously from above
downward ; in the stomach it produces a kneading effect upon the mas-
ticated food, and mixes it intimately with the gastric juice. This action
of the stomach, accordingly, though quite gentle, is sufficient to pro-
duce a constant churning movement of the food, by which it is carried
back and forward to every part of the stomach, and incorporated with

168 DIGESTION.

the gastric juice, which is at the same time poured out by the mucous
membrane ; so that the digestive fluid is made to penetrate equally
every part of the alimentary mass, and the digestion of all its albu-
minous ingredients goes on simultaneously. This movement of the
stomach is one which cannot be completely imitated in experiments on
artificial digestion with gastric juice in test-tubes ; and consequently the
process, under these circumstances, is never so rapid as when it takes
place in the interior of the stomach.

The result of the action of the gastric juice, thus incorporated in the
stomach with the alimentary matters, is that they are disintegrated by
the softening and liquefaction of their albuminous ingredients. Bread
consists mainly of hydrated starch, entangled and incorporated with
the semi-solid gluten. By digestion in the stomach, the gluten is di-
gested and liquefied by its conversion into albuminose, the starch being
thus set free, and the whole reduced to a diffluent condition. The same
effect can be seen when bread is subjected to the action of gastric juice
in a test-tube, the gluten passing into the condition of liquid albuminose,
while a deposit of unaltered starch settles at the bottom. Cheese, con-
sisting of coagulated caseine and milk globules, undergoes an analogous
change. Its caseine is liquefied by digestion, while its liberated fat
globules rise to the upper part of the fluid, forming a creamy-looking
layer upon its surface.

Adipose tissue is very readily disintegrated by the liquefaction of its
connective tissue, which is formed of albuminous matter, while the fatty
matter escapes in the form of oil drops, floating upon the surface of
the other contents of the stomach. Dr. Beaumont always found free
fat, in the form of oil globules, thus extricated from the fatty tissues
soon after they had been introduced into the stomach with the food ;
and it is easy to verify this observation, either by artificial digestion of
adipose tissue in gastric juice, or by opening the stomach of an animal
soon after the administration of food containing fat.

The digestion of muscular flesh is also at first a process of disintegra-
tion. The connective tissue intervening between the fibrous bundles
yields to the action of the gastric juice, and the fibres themselves thus
become separated from each other, and form a gruelly mixture of minute
and almost microscopic threads and fragments. The substance of the
muscular fibres then also begins to become altered — they break up into
shorter fragments, and, when examined by the microscope, are found to
have lost the distinctness of their transverse striations. If the food
have been thoroughly masticated before being taken into the stomach,
this change goes on rapidly and uniformly throughout the mass. If,
as in the dog, the meat be swallowed without much mastication, or if
portions be suspended in a test tube containing gastric juice, the action
progresses regularly from without inward. The external parts of the
muscular tissue are first softened and decolorized, and become covered
with a grayish layer, of grumous consistency, containing the isolated
and partially destroj^ed fragments of muscular fibre. As these por-

THE GASTKIC JUICE AND STOMACH DIGESTION. 169

tions are removed by the peristaltic movements of the stomach, the
digestive action extends to the parts underneath, and so on until the
whole has been reduced to a uniform mixture, of a thickish gruelly con-
sistency, in which the distinctive elements of the tissue are no longer
recognizable by the eye, and in which the remnants of the muscular
fibres can only be detected by the microscope. It, is this apparently
homogeneous, pultaceousor gruelly semi-fluid material that was formerly
designated by the name of "Chyme." It is evidently nothing more
than a mixture of the disintegrated remnants of the digested tissues,
portions of which have been completely liquefied while others are not
yet reduced to a state of solution.

When milk is taken into the stomach in a fresh condition, its caseine
is at first coagulated, afterward dissolved. The preliminary coagula-
tion, which is due to the action of the pepsine and dilute acid, takes
place very rapidly. Dr. Beaumont found that milk could be withdrawn
in a coagulated condition in fifteen minutes after its introduction into
the stomach ; and that if the mixture were kept at the temperature of
38° (100° F.), the coagula were again liquefied in the course of eight
hours. The coagulation of milk, thus produced by its first contact
with the gastric juice is, however, no obstacle to its subsequent diges-
tion. The caseine does not form a solid uniform clot, but is thrown
down in the form of minute flocculi, of soft consistency, which are
constantly bathed by the digestive fluids, and at the temperature of the
living body undergo readily the conversion into albuminose. As it is
this chemical change which constitutes the real process of digestion,
the preliminary coagulation of the caseine does not interfere with its
accomplishment. Milk, furthermore, as used by adults, is to a large
extent incorporated, in the coagulated form, with other solid or semi-
solid articles of food.

The substance of vegetable tissues, as a rule, is digested in a similar
manner to that described above. The albuminous matters are dissolved
out, leaving the starchy or oleaginous ingredients in a free condition,
but chemically unchanged. As these tissues generally contain a much
smaller proportion of albuminous matter than most kinds of animal
food, their disintegration is the main result of the changes which they
undergo in the stomach.

The gastric juice, together with the disintegrated debris of the food,
after commencing its action in the stomach, passes into the upper part
of the intestine. This can be seen readily in the dog by killing the
animal after feeding, and examining the contents of the intestine. We
have observed the same thing by establishing, in the dog, an artificial
duodenal fistula, by means of an operation similar to that for producing
a permanent fistula of the stomach. A silver tube, armed at each
end with narrow projecting flanges, is introduced into the lower part
of the duodenum, and the wound allowed to heal, after which the
contents of the intestine may be withdrawn at will, and subjected to
examination at different periods during digestion.
12

170 DIGESTION.

By examining in this wa}T, from time to time, the intestinal fluids, it
becomes manifest that the action of the gastric juice, in the digestion
of albuminous substances, is not confined to the stomach, but con-
tinues after the food has passed into the intestine. About half an
hour after the ingestion of a meal, the gastric juice begins to pass into
the duodenum, where it may be recognized by its strongly-marked
acidity, and by its peculiar action, already described, in interfering with
Trommer's test for glucose. It has accordingly already dissolved some
of the ingredients of the food, and contains a certain quantity of
albuminose in solution. It soon afterward, as it continues to pass
into the duodenum, becomes mingled with the debris of muscular
fibres, fat vesicles, and oil drops ; substances which are easily recog-
nizable under the microscope, and which produce a grayish turbidity
in the fluid withdrawn from the fistula. By the continuous passage,
in this way, of the alimentary material, mixed with gastric juice,
through the pylorus into the intestine, the stomach becomes gradually
cleared of its contents. According to Dr. Beaumont the time required
for the entire disappearance of food from the stomach varies from one
hour to five hours and a half, according to the quality and quantity of
the material used. In the experiments of Prof. Francis G. Smith upon
the same subject, food seldom remained in the stomach more than two
hours after its introduction. Three hours is probably sufficient, as a
rule, for the completion of stomach digestion, in the human subject,
when the food is in moderate quantity and has been properly prepared
by cooking and mastication. In the carnivorous animals generally,
where the food is swallowed in fragments of some size, the process is
longer; and in the dog a moderate meal of fresh uncooked meat
requires from nine to twelve hours for its complete liquefaction and
disappearance from the stomach.

The gastric juice, after having accomplished its work in the digestion
of the food, is reabsorbed from the alimentary canal and taken up by
the bloodvessels. It thus forms a vehicle for the dissolved nutritious
materials, and again enters the circulation with the alimentary substances
which it holds in solution. It is in this way that the system is enabled
to furnish so abundant a secretion without being exhausted by drainage.
The reabsorption of the gastric juice goes on simultaneously with its
secretion during the continuance of the digestive act; and the fluids
which the blood loses by one process are incessantly restored to it by
the other. An abundant supply, therefore, of the secretion may be
poured out during the digestion of a meal, at an expense to the
blood, at any one time, of only a small quantity of fluid. The simplest
investigation shows that the gastric juice does not accumulate in the
stomach to any considerable amount during digestion ; but that it is
gradually secreted so long as any food remains undissolved ; each por-
tion, as it is digested, being disposed of by reabsorption, together
with its solvent fluid. There is accordingly, during digestion, a con-
tinuous circulation of the digestive fluids from the bloodvessels to

PANCREATIC JUICE AND ITS ACTION UPON FOOD. 171

the alimentary canal, and from the alimentary canal back again to the
bloodvessels.

That this circulation really takes place is shown by the following
facts : First, if a dog be killed some hours after feeding, there is never
more than a very small quantity of fluid found in the stomach, just suf-
ficient to smear over and penetrate the half digested pieces of meat ; and
secondly, in the living animal, gastric juice, drawn from the fistula five
or six hours after digestion has been going on, contains little or no more
albuminous matter in solution than that extracted fifteen to thiity
minutes after the introduction of food. It has evidently been freshly
secreted ; and, in order to obtain gastric juice saturated with alimentary
matter, it must be artificially digested with food in test-tubes, where
this constant absorption and renovation cannot take place.

The secretion of the gastric juice is much influenced by nervous condi-
tions. It was noticed by Dr. Beaumont, in his experiments upon St.
Martin, that irritation of the temper, and other moral causes, would fre-
quently diminish or altogether suspend the supply of the gastric fluids.
Any febrile action in the system, or any unusual fatigue, was liable to
exert a similar effect. Every one is aware how readily any mental dis-
turbance, such as anxiety, anger, or vexation, will take away the appe-
tite and interfere with digestion. ' Any nervous impression of this kind,
occurring at the commencement of digestion, seems moreover to pro-
duce some change which has a lasting effect upon the process ; for it is
often noticed that when any anno3rance, hurry, or anxiety occurs soon
after the food has been taken, though it may last only for a few moments,
the digestive process is not only liable to be suspended for the time,
but to be permanently disturbed during the entire day. In order that
digestion, therefore, may go on properly in the stomach, food must be
taken only when the appetite demands it ; it should be thoroughly
masticated at the outset ; and, finally, both mind and body, particularly
during the commencement of the process, should be free from any-
unusual or disagreeable excitement.

The Pancreatic Juice and its Action upon the Food.

The pancreas, which is a lobulated gland, similar in its general struc-
ture to the salivary glands, lies across the upper part of the abdo-
men in such a manner that its larger or right-hand extremity is in
contact with the duodenum. It is traversed in its longitudinal direction
by its main excretory duct, which receives, as it passes from left to right,
the lateral branches coming from the glandular lobules, and finally, in
the human subject, opens into the cavity of the duodenum, closely
adjacent to the situation of the common biliary duct, at about ten centi-
metres below the pyloric orifice of the stomach. Its secretion thus
enters the intestine, and mingles with the substances undergoing diges-
tion, almost immediately after they have passed from the stomach into
the duodenum.

The arrangement of the gland and its duct is similar to the above, in

172 DIGESTION.

its essential particulars, in most of the lower animals. In the dog and
cat, there are two ducts opening into the intestine, one of them in juxta-
position with the orifice of the biliaiy duct, the other from one to three
centimetres farther down. The lower of these ducts is usually, though

Fig. 46.

PORTION OF HUMAN PANCREAS AND DUODENUM.— a. Cavity of duodenum, b. Orifice
of the pancreatic duct. c. Orifice of lower pancreatic duct. (Bernard.)

not always, the larger of the two, and they generally communicate
with each other by a transverse branch, in the substance of the gland,
before opening into the intestine. Even in the human subject, as shown
by Bernard, Kolliker, and Sappey, there is often a smaller accessory duct
opening into the intestine, sometimes above and sometimes below the
situation of the principal one. The most marked peculiarity in the
arrangement of the parts is seen in the rabbit, where the pancreatic duct
is single, but opens into the intestine at a distance of from 30 to 40
centimetres below the orifice of the biliary duct.

The pancreatic juice has been obtained in many instances from the
living animal by opening the abdomen during the act of digestion, and
inserting a silver canula into the principal pancreatic duct, immediately
before its entrance into the intestine. The canula being secured in its
position by a ligature placed round the duct, the parts are returned
into the abdominal cavity, and the external wound closed with sutures,
leaving the open extremity of the canula projecting between its edges.
The secretion is thus diverted from the intestine, and may be collected
for examination as it flows from the canula. This operation has been
done most frequently upon the dog, but also upon the rabbit, the ox,

PANCREATIC JUICE AND ITS ACTION UPON FOOD. 173

the sheep, the goat, the pig, and the goose. The secretion has also been
obtained from the horse, by opening the duodenum and inserting the
canula into the natural orifice of the pancreatic duct.

Under these circumstances, the fistula produced is only a temporary
one; since the ligature soon cuts its way through the duct by ulcera-
tion, when the canula falls out and the wound closes spontaneously,
the natural communication of the duct with the intestine being at the
same time re-established. Even in the ox, Colin found that the canula
became displaced within six or eight days after the operation ; and in
the dog, according to Bernard, the same thing happens at the end of
two or three days. Furthermore, the pancreas being very sensitive to
external irritation, its secretion is liable to become altered in character
during the inflammatory process, and it is therefore to be collected for
examination only within the first twenty-four hours after the insertion
of the canula.

A permanent pancreatic fistula has been successfully established by
Ludwig and Bernstein, by making an incision in the side of the pan-
creatic duct near the intestine, introducing into the orifice thus made a
leaden wire extending a short distance each way, toward the gland and
toward the duodenum, and provided with an arm projecting at right
angles from its middle, which is allowed to protrude from the external
wound. After the healing of the parts, the fistula is thus kept perma-
nently open by the wire, which lies somewhat loosely in the cavity of the
duct and allows the secretion to escape by its side. The objection to
the plan is that, as the secretion passes by a narrow fistulous passage,
it may be mingled with unnatural secretions.

Physical Character and Composition of the Pancreatic Juice. The

pancreatic juice obtained from the dog within the first day after the
introduction of the canula, and while digestion is going on, is a clear
colorless fluid, with a distinctly alkaline reaction. It has a well marked
viscidity, somewhat like that of the serum of blood, or uncoagulated
white of egg, and differs strongly in this respect from the watery con-
sistency of the gastric juice. It coagulates completely by the applica-
tion of a boiling temperature, often solidifying into a uniform jelly-like
mass. It also gelatinizes partially on being cooled down to the zero
point (320 F.). According to the analyses of Schmidt,1 it has the fol-
lowing composition :

COMPOSITION OF PANCREATIC JUICE.

Water 900.76

Pancreatine 90.44

Sodium chloride . . . 7.35

Potassium chloride 0.02

Lime phosphate 0.41

Magnesium phosphate 0.12

Soda, lime, and magnesia, in combination with the pancreatine . 0.90

100000
1 Annaleu der Chemie und Pharmacie, 1854, xcii. p. 33.

174 DIGESTION".

The most important ingredient of the pancreatic juice is its animal
matter, known as pancreatine. It is this substance which gives to the
fluid its tenacious or viscid character, and, in the secretion obtained by
the above method, it amounts to over ten per cent, of the whole,
being more abundant than all the other solids taken together. It is
also considerably more abundant, in proportion, than the albuminous
ingredient of any other of the digestive fluids. It is coagulable by
heat, by nitric acid, by alcohol, and also by magnesium sulphate added
in excess. In this last particular it differs from albumen, which is not
affected by magnesium sulphate. Another peculiarity, in which it
resembles pepsine, is that after being precipitated by alcohol, it may
be again dissolved in water, retaining all • its original properties. By
some observers it is considered as a mixture of several substances
which differ from each other in their chemical relations ; but, taken as
a whole, it forms a strongly marked distinguishing ingredient of the
pancreatic juice.

When drawn from the canula several days after its introduction, or
obtained by means of a permanent fistula, the secretion is usually more
abundant, but poorer in its organic constituents. Schmidt found that
in the dog, immediately after the operation, the pancreatic juice was
of a thick, tenacious consistency, containing an abundance of solid
ingredients, consisting principally of organic matter ; while that ob-
tained from a permanent fistula was comparatively thin and watery,
containing only from 1.5 to 3.6 per cent, of solids, of which not more
than two-thirds consisted of organic matter. Other observers have
met with the same difference. The fluid obtained soon after the intro-
duction of the canula, during the period of digestion, probably repre-
sents most fully the normal secretion.

The organic matter of pancreatic juice, like that of the other
digestive secretions, may be extracted from the substance of the gland-
ular tissue. For this purpose the pancreas is taken out from the dog
or pig, killed while digestion is going on, a few hours after the inges-
tion of food, cut into small pieces, or ground to a pulp with sand,
and allowed to macerate for two hours in water at 25° (77° F.). The
filtered fluid contains a substance nearly or quite identical in its pro-
perties with that contained in the pancreatic juice itself. It may also
be obtained, in a form better adapted for permanent use, by placing the
freshly divided pancreas for twenty-four hours in absolute alcohol, then
separating it from the alcohol, and macerating it for several days in
glycerine, which is afterward filtered. The glycerine extracts the or-
ganic matter of the glandular tissue, and preserves it without alteration.
It may be precipitated at any time from the glycerine solution by the
addition of strong alcohol, and afterward dissolved in water. It thus
forms a watery extract of the pancreas.

Physiological Properties of the Pancreatic Juice — This secretion
has certain well marked characters which indicate that its action is of

PANCREATIC JUICE AND ITS ACTION UPON FOOD. 175

great importance in the digestive process, although the precise limits
of its operation are not yet fully determined.

In the first place, the pancreatic juice has the power of transforming
starch into sugar. This action takes place with great rapidity at the
temperature of the living body. According to Hardy,1 it is much more
prompt as well as more complete than the corresponding change
produced by saliva, being at the temperature of 40° (104° F.) almost
instantaneous; and, while the transforming action of saliva is very
partial, much of the starch remaining unchanged, that of the pancreatic
juice appears to convert the whole of it into glucose. Kroeger found2
that one gramme of fresh pancreatic juice, at the temperature of 35°
(95° F.), transformed into sugar, within thirty minutes, 4.67 grammes
of starch ; while, according to our own observations, if one gramme of
fresh human saliva be mixed at 38° (lOQOF.), with a watery solution
containing less than 0.1 gramme of boiled starch, though the sugar re-
action becomes manifest in one minute, a large portion of the starch
is still unchanged at the end of an hour. It is certain that hydrated
starch, although it may be recognized for a long time in the stomach
by its iodine reaction, disappears completely as soon as it enters the
upper part of the duodenum. According to Ranke,3 pancreatic juice
causes the transformation not only of hydrated, but also of raw starch;
a property which was found by Bouchardat and Sandras to be very
energetic in the secretion of the common fowl, if aided by a slight ele-
vation of temperature.

The organic matter of the pancreatic juice, which produces this
change, is coagulable by a boiling temperature, and after its solution
has once been boiled, it is inactive in regard to starchy matters. It is
produced in the substance of the gland, probably by the transformation
of some previousl}7" formed material, since it has been found by Liver-
sidge,4 that after it lias been completely extracted from the chopped
glandular tissue by treatment with glycerine, if the inactive residue be
transferred to a filter, and allowed to remain exposed to the air for five
or six hours, it is regenerated, and may be again extracted by the addi-
tion of water or glycerine. This is undoubtedly due to a real reproduc-
tion of the active organic substance, and is not the result of a putrefac-
tive change, since the same observer found that a watery extract of the
pancreas, which had once been deprived of its action on starch by boil-
ing, never regained this property at any stage of subsequent decompo-
sition.

Secondly, the pancreatic juice has the power of emulsifying the fats.
This is perhaps its most marked and peculiar property, by which it is

1 Chimie Biologique. Paris, 1871, p. 152.

2 Cited in Milne Edwards, LeQons sur la Physiologic. Paris, 1862, tome vii.
p. 68.

3 Physiologic des Menschens. Leipzig, 1872, p. 271.

4 Studies from the Physiological Laboratory of the University of Cambridge,
Part I. Cambridge, 1873, p. 49.

176 DIGESTION.

especially distinguished from the other digestive secretions. If a fluid
fatty substance, such as olive oil or melted butter, be shaken up in a
test-tube with the saliva, the gastric juice, the bile, or any of the
excreted fluids, it suffers no change in its physical characters. It is
partially broken up by the mechanical agitation, but, on being allowed
to remain at rest, the oil globules run together and soon collect in a
distinct layer upon the surface of the liquid. If, on the contrary, the'
same experiment be tried with fresh pancreatic juice, the oil is instantly
broken up into a state of fine subdivision, producing a uniformly white,
opaque, milky looking fluid. The emulsion thus formed is permanent,
the microscopic fat granules being held in suspension by the organic
matter of the secretion, and thus prevented from uniting into visible oil
drops. If the proportion of oily matter be considerable, a part of it may
rise to the surface as a creamy layer, and if it be in excess, the super-
fluous portion will also rise to the upper part of the liquid ; but the
remainder will continue indefinitely in the emulsioned condition, dis-
seminated uniformly through the fluid mixture.

The emulsifying property of the pancreatic juice is very active, when
the secretion exhibits its normal characters. Bernard found that the
freshly extracted j uice formed a complete emulsion at 38° (100° F.) with
olive oil, butter, suet, or lard, when mixed with either of these substances
in the proportion of one gramme of oleaginous matter to two grammes
of pancreatic juice. The emulsion thus produced retained its physical
appearance unchanged, although allowed to remain at the above tempe-
rature for fifteen or eighteen hours.

The power of the pancreatic juice to emulsify oils, though facilitated
by its alkaline reaction, does not depend upon the free alkali, but is
mainly due to the action of its organic matter. This is indicated by the
fact that other animal fluids which are also alkaline do not have the
same power in a corresponding degree ; and Bernard has shown that the
pancreatic juice, after being neutralized by a dilute acid, still retains its
property of acting upon the fats.

The property of emulsifying oily matters, first shown to exist in the
pancreatic juice of the dog, has been found by Colin in that of the
horse, the ass, the ox, the sheep, and the pig; and by Bernard has been
found fully developed in that of the goose. According to Colin, its
intensity, in these different animals, is proportional to the quantity of
albuminous matter contained in the secretion ; one part of oil requiring,
for complete emulsion, from two to three parts of pancreatic juice
when its albuminous ingredient is abundant, and four, five, or six parts
when the proportion of this substance is diminished.

There is every evidence that the emulsifying action of the pancreatic
juice is of the first importance in the digestion of fatty substances.
These substances are not affected by contact with gastric juice outside
the body ; and examination shows that they are not digested .in the
stomach, but are unchanged in their essential character so long as they
remain in the gastric cavity. They are merely melted by the warmth

PANCKEATIC JUICE AND ITS ACTION UPON FOOD. 177

of the organ, and set free by the solution of the vesicles, fibres, or capil-
lary tubes in which they are contained, or among which they are
entangled ; and they are still readily discernible, floating in larger or
smaller drops on the surface of the semi-fluid alimentary mass. Very
soon, however, after its entrance into the intestine, the oily portion of
the food loses its characteristic appearance, and is converted into a
white, opaque emulsion, which is gradually absorbed. This emulsion
is termed the chyle, and is always found in the small intestine during
the digestion of fat, entangled among the valvulse conniventes, and
adhering to the surface of the villi. The digestion of fatty substances
accordingly consists mainly in their emulsion, by which they are con-
verted into chyle and made ready for absorption. This change begins
to take place in the duodenum, immediately below the orifice of the
pancreatic duct. But as the pancreatic and biliary ducts in most ani-
mals open into the intestine in company or in close juxtaposition with
each other, it might, from this circumstance alone, be doubtful whether
the two secretions have not an equal share in producing the effect. Ber-
nard first removed the doubt by examining the products of digestion in
the rabbit. In this animal, the biliary duct opens, in the usual manner,
just below the pylorus, while the pancreatic duct, as stated above, com-
municates separately with the intestine 30 or 40 centimetres farther
down ; so that there is here a considerable extent of the small intestine
already containing bile, but into which the pancreatic juice has not
yet been discharged. Bernard fed these animals with substances con-
taining oil, or injected melted butter into the stomach ; and, on killing
them afterward, found that there was no chyle in the intestine between
the openings of the biliary and pancreatic ducts, but that it was abun-
dant immediately below the orifice of the latter. Above this point, also,
he found the lacteals empty or transparent, while below it they were
full of white, opaque chyle. These experiments, which were confirmed
by Prof. Samuel Jackson,1 fully demonstrate that the emulsifying action
of the pancreatic juice upon oily matters is exerted within the body
during digestion, and is the direct agent in the production of chyle in
the intestine.

Thirdly, the pancreatic juice at the temperature of the living body
gradually dissolves coagulated albuminous matters. This property of
the secretion, first recognized by Bernard and Corvisart, has been alter-
nately confirmed and denied by various subsequent observers. Among
those who found in the pancreatic juice more or less power of this kind,
some stated it to be only present when the fluid was acidulated (Meissner),
while others maintained that it could only be exerted in presence of an
alkaline reaction (Wundt) ; and the information obtained in regard to
the process has been generally much less distinct and satisfactory than
that relating to the other properties of the secretion. The most definite

1 American Journal of the Medical Sciences. Philadelphia, October, 1854.

178 DIGESTION.

and valuable observations on this subject are those of Kiihne,1 who ex-
perimented both with the pancreatic juice of the dog, and also with infu-
sions of the glandular tissue. He found that the fresh viscid secretion
could, in from half an hour to three hours, effect the solution of coagulated
fibrine and albumen, without any modification of its alkaline reaction,
and without giving rise to signs of putrefaction ; the albuminous mat-
ters, thus dissolved, being changed into a substance not coagulable by
boiling and readily diffusible through parchment paper. The product of
this action accordingly resembles that obtained from a similar digestion
with the pepsine of gastric j nice.

In his experiments with the glandular tissue, Kiiline placed the finely
divided gland in warm water together with a weighed quantity of the
substance to be experimented on ; allowing the infusion of the pancreas
and the digestion of the albuminous matter to proceed simultaneously.
He found that when employing for this purpose a dog's pancreas of from
50 to 60 grammes weight, 400 grammes of boiled and pressed fibrine,
after remaining in the infusion at 40° to 45° (104° to 113° F.) for from
three to six hours, were reduced to an insignificant residue, the reaction
of the mass continuing throughout faintly alkaline.

The details of this process, however, are different in some respects
from those of digestion in gastric juice. If bits of coagulated fibrine
be placed in gastric juice, or an acidulated solution of pepsine, they first
swell up and become transparent under the influence of the free acid;
and this action is preliminary to their subsequent solution and transfor-
mation into albuminose. But in an infusion of the pancreas, according
to Kiihne, the pieces of fibrine do not become at all swollen or altered
in transparency, even when considerably softened and near the point
of solution. They are, however, essentially modified in their physical
and chemical properties. Boiled fibrine, by itself, is but slowly affected
by dilute acids or alkalies, and is nearly or quite insoluble in a ten per
cent, solution of hydrochloric acid; but after remaining for a time in
an infusion of the pancreas, a part of it is found to be almost instantly
soluble in a solution of hydrochloric acid of one part per thousand.

It is evident, accordingly, that the organic matter of the pancreatic
juice may exert a transforming action on the albuminous matters, some-
what analogous to that of the pepsine of gastric juice. How far this
action takes place in the natural process of digestion has not been
demonstrated by direct observation, but it is possible that the two
secretions may be in some degree complementary to each other. In the
gastric juice, we have an abundant fluid with an acid reaction, and with
a small proportion of organic substance ; in the pancreatic juice a com-
paratively scanty secretion, but with a much larger proportion of organic
matter, capable of exerting a transforming power on the albuminous
ingredients of the food. While the gastric juice acts alone in the
stomach, softening and disintegrating the food, and actually dissolving

1 Archiv fur Pathologische Anatomie und Physiologie, 1867, xxxix. p. 130.

PANCREATIC JUICE AND ITS ACTION UPON FOOD. 179

a part of it ; in the intestine the two secretions may act together, to
complete the liquefaction of the alimentary materials.

Mode of Secretion and Daily Quantity of the Pancreatic Juice. —
If examined in the living animal by means of a canula introduced into
its excretory duct, it is found that the action of the pancreas is by no
means the same at different times. If there be no food in the stomach or
intestine, or if the process of digestion be arrested from any cause, no
fluid whatever is discharged from the canula. If digestion be going on,
the pancreatic juice soon begins to run from the orifice of the tube, at
first slowly and in successive drops. Sometimes the drops follow each
other with rapidity for a few moments, and then an interval occurs
during which the secretion seems entirely suspended. After a time it
recommences, and continues to exhibit similar fluctuations during the
whole course of the experiment. Its flow, however, is at all times
scanty, as compared with that of the gastric juice. We have never
been able to collect, in a good sized dog, more than 75 grammes in the
course of three hours, and usually the quantity was much less than this.
Colin found a great variation in the animals upon which he experimented,
the quantity being from two and a half to thirty times as abundant at
one period as at another. In the bullock, the largest quantity obtained
was 342 grammes per hour while the animal was engaged in rumination.

The entire quantity of pancreatic juice secreted per day cannot be
determined with precision, but it is evidently moderate in amount, as
compared with the other digestive fluids. In the ox, cow, and horse,
Colin found the average quantity nearly the same, corresponding to
about 0.58 gramme per hour for every kilogramme of the animal's
weight. Schmidt, in his experiments upon the dog, found it, in recently
established fistulae, not more than 0.2 gramme per kilogramme per hour.
In the most successful instances, we have found it in the dog, as much
as 1.25 grammes per kilogramme per hour during active digestion, but
much less than this in the intervals. If we take, as the average of these
estimates, 0.5 gramme per hour for every kilogramme of bodily weight,
it would give for a man of medium size about 800 grammes as the entire
quantity of pancreatic juice secreted per day.

The condition of the pancreas varies at different periods corresponding
with the activity of its secretion. In the intervals of digestion it is
comparatively pallid and dense ; during digestion it becomes turgid and
vascular, its ruddy color showing the increased quantity of blood circu-
lating in its vessels. According to most observers, the substance which
is efficient in the solution of albuminous matters can only be extracted
from the pancreas at this time, during the height of its vascularity and
digestive action, which, in the dog, is from five to seven hours after the
ingestion of food. When the process of digestion is terminated, its
vascularity again diminishes, and the organ returns to its quiescent
condition. This periodical excitement during the period of functional
activity, though well marked in the pancreas, is not peculiar to it, but
may also be seen in the mucous membrane of the stomach and the small

180

DIGESTION.

intestine. It probably exists, more or less fully developed, in all the
organs taking part in the digestive process.

The Intestinal Juice and Digestion in the Intestine.
The secretory apparatus of the small intestine consists of two sets of
glandular organs, namely, first, Brunner's glands, which are compound
or lobulated, and confined to the upper part of the duodenum, forming
a sort of collar round the intestine for a distance of several centimetres
from the pylorus ; and, secondly, the follicles of Lieberkuhn, which are
simple tubular glandules, occupying the substance of the mucous mem-
brane for the whole length of the small intestine. ^

Fig. 47.

LONOITTJDINALSKCTION OF WALL OF DUODENUM IN THE DOG; showing the sub-
mucous layer of Brunner's Glands, a. Mucous membrane, b. Layer of submucous connective
tissue, in which the glands are situated, c. Muscular coat. d. Peritoneal coat. e. Brunner's
glands, with their ducts opening upon the free surface of the mucous membrane. (Bernard.)

Brunner's glands, or the duodenal glandules as they are sometimes
called, are situated in the submucous layer of connective tissue in this
part of the intestine. They are spherical, or, when thickly set, irregu-
larly flattened or polygonal in shape from mutual pressure, and from ^
to 1 millimetre in diameter.

Fig. 48.

Fig. 49.

Entire BRUNNER'S GLAND, from human intestine.
(Frey.)

Portion of one of BRUNNER'S
GLANDS, from human intestine.

In their structure, the glands are similar to the lobulated glandules
of the mouth, being composed of rounded follicles clustered about a
central branching excretory duct. Each follicle is about TV of a milli-
metre in diameter, and consists of a delicate membranous wall, lined

INTESTINAL JUICE AND DIGESTION IN INTESTINE. 181

with cells of glandular epithelium, showing small but distinctly marked
nuclei. The follicles collected round each terminal branch of the main
duct are bound together by a thin layer of connective tissue, and covered
with a plexus of capillary bloodvessels.

The follicles of Lieberkiihn, which are much more numerous than the
preceding, are not situated in the submucous connective tissue, but
occupy the entire thickness of the mucous membrane, forming, like the
gastric follicles in the mucous membrane of the stomach, the greater part
of its substance. They are

simple, nearly straight tubules, Fl£- 50-

from y1^ to TV of a millimetre
in diameter, lined throughout
with cylindrical epithelium,
opening by their orifices upon
the free surface of the intes-
tinal mucous membrane and
terminating below by rounded
extremities. They are so
thickly set that in many places
there appears to be no space
left between them, except that
occupied by the capillary
bloodvessels which encircle
them in every direction.

The fluid produced by the

mucous membrane of the small testine of Dog.

intestine consists of a mixture

of the secretions of these two sets of glands. But as, owing to the situa-
tion of Brunner's glands, it has been found impossible to obtain their
secretion unmixed with other fluids, and as it is evidently much less
abundant than that produced in the remainder of the intestine, the
secretion of the follicles of Lieberkiihn is regarded as the main con-
stituent of the intestinal juice. It is by no means easy to obtain this
fluid in a pure form and in normal condition. There is no single excre-
tory duct, like that of the pancreas, into which a canula might be
inserted ; and a fistulous opening made in the intestine itself would of
course yield a mixture of all the secretions discharged into its cavity.
If these should be shut off by a ligature permanently applied above
the fistula, the disturbance of the digestive process would be so great,
that the experiment could hardly be expected to give a valuable result.

Nevertheless, attempts have been made, ~by various methods, ' to
obtain the intestinal juice in condition sufficiently pure for examination.
Bidder and Schmidt first tied the biliary and pancreatic ducts, and then
established an intestinal fistula below, from which they extracted the
fluids accumulated in the cavity of the gut. Frerichs operated by
opening the abdomen, taking out a loop of intestine, emptying it so
far as possible by gentle pressure, isolating its cavity by the application

FOLLICLES OF

from Small In-

182

DIGESTION.

of two ligatures 15 or 20 centimetres apart, and returning the whole
into the abdominal cavity. After a few hours the animal was killed,
and the fluid, which had collected in the isolated portion of intestine,
taken out and examined. Colin adopted a similar method, but with
greater precautions, in the horse. In one of these animals, while diges-

Fig. 51.

LOOP OF SMALL INTESTINE, from the horse, isolated by compressors, for obtaining
intestinal juice. (Colin.)

tion was in full activity, he took out, through an opening in the left
flank, a loop of small intestine, which he isolated by two compressors,
made of flat wooden or metallic strips, enveloped by a ribbon of velvet,
and fastened by screws in such a way that the inner surfaces of the
intestine might be retained in close contact, without bruising or lacerat-
ing their tissues. The compressors being applied at a distance of from
one to twro metres apart after the included portion of intestine had
been emptied by gentle pressure, the whole was returned into the abdo-
men, the external wound closed by sutures and the animal killed at the
end of half an hour.

On the average, 100 grammes of fluid had accumulated within this
time. It was clear, with a slightly yellowish or amber tint, alkaline in
reaction, and with a specific gravity of 1010. According to the analysis
of Lassaigne, it was composed as follows :

INTESTINAL JUICE AND DIGESTION IN INTESTINE. 183

COMPOSITION OF INTESTINAL JUICE FROM THE HORSE.

Water 981.0

Albuminous matter 4.5

Sodium chloride
Potassium chloride i

Sodium phosphate
Sodium carbonate

1000.0

Thiry separated a portion of the small intestine from the remainder
by two transverse sections, leaving the mesentery and vessels of the
isolated portion uninjured, and then united by sutures the divided ends
of the remaining portions, so as to re-establish the continuity of the intes-
tine, but with a portion of it, 10 or 15 centimetres long, left out. Of
this isolated portion, still nourished by its vessels, he closed one end
by sutures, so as to make of it a blind extremity, while the other he
fastened to the edges of the external wound in such a way as to make
of it a permanent fistula. When all the parts had healed, and natural
digestion was re-established, he collected the fluid discharged from the
open end of the isolated portion of intestine. This operation has been
repeated by other observers. The objection to it is that the isolated por-
tion of intestine, after being for some weeks precluded from taking part
in the process of digestion, becomes partially atrophied, and cannot
be relied on as furnishing a secretion similar to the normal intestinal
juice. The results obtained vary, some of them indicating that the
secretion converts starch into sugar and has a dissolving action on
coagulated albuminous matters, others that these properties are some-
times absent or but slightly developed.

On the whole, the method adopted by Frerichs and Colin, with its
various modifications, seems to be the best and has furnished the most
uniform results. Colin found that the fluid obtained in this way has the
power of slowly transforming hydrated starch into sugar, and of emul-
sioning fatty matters with considerable energy. One part of olive oil,
treated with five or six parts of intestinal juice, was transformed into a
homogeneous mixture of a white color; and oil injected into the isolated
portion of intestine, in the living animal, was found, after an hour, re-
duced to the condition of whitish homogeneous flakes.

Bernard obtained from a healthy dog which had been without food
for twelve days, by an opening in the intestine 60 centimetres below the
pylorus, a transparent, amber colored, alkaline fluid, which coagulated
by heat, emulsioned oily matters distinctly though not strongly, and
effected the transformation of hydrated starch. A small quantity of
melted lard having been injected into the lower part of the intestine
and a ligature placed above, at the end of an hour and a half the lower
part of the intestine was found turgid, with emulsioned fat in its cavity,
and its chyliferous vessels filled with opaque chyle.

It appears accordingly that the intestinal juice, so far as ascertained

184 DIGESTION.

by direct observation, is a comparatively scanty, alkaline fluid, contain-
ing an albuminous ingredient capable of coagulation by heat. It exerts
an action upon starchy and fatty matters similar to that of the pancreatic
juice, but less energetic in operation. Its action upon albuminous
matters is less distinct, and has sometimes been found to be absent or
feebly developed. It is undoubtedly of importance as accessory to the
other digestive secretions, but the precise mode and extent of its opera-
tion have not yet been determined.

In the process of intestinal digestion a number of different actions
are going on at the same time. The materials of the food, disinte-
grated and partly dissolved in the stomach, pass through the pylorus
into the intestine still mingled with a notable quantity of gastric juice,
and are there subjected to the action of the remaining digestive secre-
tions. Hydrated starch, set free by the solution of the albuminous
matters with which it was associated, rapidly undergoes the conver-
sion into glucose, and the saccharine fluid so produced is promptly ab-
sorbed. If a dog be fed with a mixture of meat and boiled starch,
although this conversion does not begin until the fluids enter the duo-
denum, we have found, in some instances, that at the end of three-
quarters of an hour all traces of both starch and sugar had disappeared
from both stomach and intestine. Raw starch in the lower animals is
digested more slowly but in a similar manner. Bouchardat and Sandras,
in examining the alimentary canal of the rabbit when fed with potato,
found the grains of starch only slightly changed in the stomach, but in
the small intestine they were altered, corroded, and more or less dis-
solved in proportion as they had descended the intestinal canal, while in
the rectum only feeble traces of them remained.

All observers agree that cane sugar undergoes the transformation
into glucose by contact with the intestinal juices. This conversion
may be slowly effected by the action of gastric juice alone. If one
part of cane sugar be dissolved in 20 parts of dog's gastric juice, and
kept at 38° (lOtPF.) the mixture will give traces of glucose at the end
of two hours, and in three hours its quantity is considerable. It cannot
be shown, however, that the gastric juice exerts this effect on sugar dur-
ing ordinary digestion. If pure cane sugar be given to a dog with a
gastric fistula while digestion of meat is going on, it disappears in from
two to three hours, without any glucose being detected in the fluids
withdrawn from the stomach. It is, therefore, either directly absorbed
under the form of cane sugar, or passes, little by little, into the duode-
num, where the intestinal fluids convert it into glucose.

Fatty matters, which are simply melted in the stomach, or set free by
the liquefaction of the tissues which contain them, on entering the intes-
tine begin to be emulsified by the pancreatic and intestinal juices. This
process continues throughout the small intestine, together with the com-
plete solution of muscular flesh which has been disintegrated by stomach
digestion. If a dog, with a permanent duodenal fistula, be examined
during the digestion of animal food, the fluid drawn from the fistula

INTESTINAL JUICE AND DIGESTION IN INTESTINE. 185

Fig. 52.

within the first hour contains gastric juice, and is turbid with the rem-
nants of disintegrated muscular tissue, mixed with fat vesicles and oil
drops. This turbid mixture grows constantly thicker and more gruelly
in consistency from the second to the tenth or the twelfth hour ; after
which the discharge of fluid from this part of the intestine becomes less
abundant, and finally ceases almost completely, as digestion comes to
an end.

The gradual alteration in the ingredients of the food may also be
seen by killing the animal while digestion is going on, and examining
the contents of the alimentary
canal. If the food consisted of
muscular flesh and adipose tis-
sue, the stomach contains (Fig.
52) masses of softened meat,
smeared over with gastric juice,
and also a moderate quantity
of a grayish grumous fluid with
an acid reaction. This fluid
contains muscular fibres, iso-
lated from each other and more
or less reduced to imperfect
fragments. The fat vesicles of
the solid adipose tissue of beef
are but little altered, and there
are only a few free oil globules
to be seen floating in the mixed
fluids in the cavity of the
stomach. In the duodenum
the muscular fibres are further
disintegrated (Fig. 53). They

become much broken up, pale, and transparent, but can still be recog-
nized, under the microscope, by their characteristic granular markings
and striations. The fat vesicles also begin to become altered in the
duodenum. The solid granular fat of beef and similar kinds of meat
becomes liquefied and emulsioned ; and appears under the form of free
oil drops and fatty molecules ; while the fat vesicle itself is partially
emptied, and becomes more or less collapsed and shrivelled. In the
middle and lower parts of the intestine (Figs. 54 and 55) these changes
continue. The muscular fibres become constantly more and more dis-
integrated, and a large quantity of granular debris is produced, which
is at last also dissolved. The fat also progressively disappears, and the
vesicles may be seen in the lower part of the intestine, collapsed and
empty.

In this way the digestion of the different ingredients of the food goes
on in a continuous manner, from the stomach throughout the entire
length of the small intestine. At the same time, it results in the pro-
duction of three different substances, namely : 1st. Albuminose, produced
13

CONTENTS OF STOMACH DURING DIGES-
TION OF MEAT, from the Dog. — a. Fat Vesicle,
filled with opaque, solid, granular fat. b, b. Bits
of partially disintegrated muscular fibre, c. Oil
globules.

186

DIGESTION.

by the digestion of albuminous matters ; 2d. A chylous fluid, from the
emulsion of the fats ; and 3d. Glucose, produced by the transformation

Fig. 53.

Fig. 54.

FROM DUODENUM OF DOG, DURING
DIGESTION OP MEAT.— a. Fat vesicle,
with its contents diminishing. The vesicle
is beginning to shrivel and the fat breaking
up. 6, 6. Disintegrated muscular fibre, c, c.
Oil globules.

FROM MIDDLE OF SMALL INTESTINE.
— a, a. Fat vesicles, nearly emptied of their
contents.

of starch. These substances are then ready to be taken up into the cir-
culation : and as the mingled ingredients of the intestinal contents pass

successively downward through

Fig. 55. the intestine, the products of di-

gestion, together with the diges-
tive secretions themselves, are
gradually absorbed by the vessels
of the mucous membrane, and
carried away by the current of the
circulation.

The Large Intestine and its
Contents.

The mucous membrane of the
large intestine is abundantly pro-
vided with tubular glandules
which are not essentially differ-
ent, in their anatomical charac-
ters, from the follicles of Lieber-
ktihn. Their secretion, however,
appears to be comparatively

scanty, at least in the watery and albuminous ingredients which are
present in the other intestinal juices. According to Ranke, fistulous
openings in the large intestine do not yield any notable quantity of

FROM LAST QUARTER OF SMALL IN-
TESTINE.— a, a. Fat vesicles, quite empty and
shrivelled.

THE LARGE INTESTINE AND ITS CONTENTS. 187

fluid ; and if a loop of the gut itself be isolated by ligatures, an accumu-
lation of mucus-like matter is the only result. In the rabbit, however,
after ligature of the vermiform appendix, Funke obtained, at the end of
from two to four hours, a quantity of a turbid alkaline secretion, with
which the appendix had become filled. This fluid was without action
upon coagulated albumen ; but it transformed starch into sugar, and
also decomposed the sugar, with production of lactic and butyric acids.
The same change was produced upon starch introduced into the cavity
of the appendix.1 This accounts for the acid reaction sometimes found
in the caecum of herbivorous animals, from the decomposition of undi-
gested starch, although the mucous surface of the large intestine is
constantly alkaline.

As the remnants of the alimentary mass pass the situation of the
ileo-csecal valve and enter the large intestine, they begin to acquire a
more pasty consistency and a peculiar repulsive odor. Both these
changes become more marked in the middle and lower part of the gut,
until all the superfluous fluids have disappeared, and the consistency
and odor of the feces are fully developed. This odor is not a putrefac-
tive one, but is characteristic of the contents of the large intestine. Its
source may be either a peculiar transformation of some of the ingre-
dients of the food, or an excretory action of the mucous membrane of
the intestine. It is probably in great part the result of an excretion,
since in different kinds of animals, whatever be the nature of their food,
the feces have usually a distinct odor characteristic of the species.

The average daily quantity of the feces in the human subject is 150
grammes, of which about 75 per cent, is water, and 25 per cent, solid
residue. They consist, first, of the undigested remnants of the food ;
and, secondly, of the excreted materials from the alimentary canal.
The undigested substances derived from the food are mainly animal or
vegetable tissues, which, from their constitution, are incapable of diges-
tion. These are elastic fibres, or bits of elastic tissue, which nearly
always pass the intestine unchanged ; shreds of tendon or fascia, not
sufficiently softened by cooking ; horny epidermic tissues, both animal
and vegetable ; and the spiral tubes and ducts of vegetable substances.
The excreted materials of internal origin are the mucus of the large
intestine, and probably also the volatile substances which produce the
fecal odor. The coloring matters of the bile are present in a more or
less altered form.

The mineral salts contained in the feces amount to a little over one-
tenth of the solid ingredients. They are, for the most part, the same
with those common to the animal fluids in general, but are mingled in
different proportions ; only about 4 per cent, consisting of the soluble
chlorides and sulphates, while fully 80 per cent, are composed of lime
and magnesium phosphates. They are regarded as mainly derived from

1 Kanke, Physiologic des Menschen. Leipzig, 1872, p. 297.

188 DIGESTION.

the unabsorbed mineral ingredients of the food, and partly from the
saline matters of the intestinal secretions.

Beside the above, the feces contain two crystallizable matters of
organic origin, which, though not present in large quantity, are of
importance from their chemical characters and the mode of their pro-
duction ; namely, excretine and stercorine.

Excretine. — This was discovered and described by Dr. W. Marcet,1
as an ingredient of human feces, though it does not occur in those of
the lower animals, either carnivorous or herbivorous. It is a neutral or
faintly alkaline crystallizable substance, insoluble in water, but soluble
in ether and hot alcohol. It crystallizes in radiated groups of four-
sided prismatic needles. It fuses at 96° (204° F.)? and burns at a higher
temperature. It is non-nitrogenous, and consists of carbon, hydrogen,
oxygen, and sulphur, in the following proportions: —

It is thought to be present mostly in a free state, but partly in union
with certain organic acids, as a saline compound.

Stercorine. — This substance was discovered by Prof. A. Flint, Jr.,
both in human feces and in those of the dog, and was obtained by him
in proportions varying from O.Ot to 0.3 per cent, of the entire fecal
mass. It is most abundant in the feces of the human subject, where its
average quantity is estimated by its discoverer as about 0.65 gramme
per day. It is insoluble in water, soluble in ether and in boiling alco-
hol, neutral in reaction, and, like excretine, crystallizes in the form of
radiating needles. It differs from excretine, however, in having a much
lower fusion point, becoming liquefied at 36° (96°. 8 F.). It is regarded
as produced by transformation in the intestine from the cholesterine of
the bile.2

1 Philosophical Transactions. London, 1857, p. 410.

2 American Journal of the Medical Sciences. Philadelphia, October, 1862.

CHAPTEE IX.

Fig. 56.

ABSORPTION.

THE mucous membrane of the small intestine, beside containing the
glandular follicles already described, is provided with a special appa-
ratus for the process of absorption. This apparatus consists of innu-
merable minute eminences or prolongations of its substance, so closely
set over its free surface that they give to it a characteristic velvety appear-
ance. These are the so-called villosities or villi of the small intestine.
They are found throughout this part of the alimentary canal, from the
pylorus to the free border of the ileo-csecal valve, most abundant in the
duodenum and jejunum, rather less so in theileum, but in general in the
proportion of from 20 to 40 to the square millimetre. In the upper
part of the intestine they are flattened, laminated, or leaf-like in form,
becoming cylindrical and filamentous in the middle and lower portions.
In the human subject they are about one-half a millimetre in length.

Each villus consists of a mass of tissue continuous with that of the
mucous membrane beneath. It is covered
with a uniform layer of nucleated, finely
granular cylindrical epithelium cells, closely
united with each other by their lateral sur-
faces, and presenting at their outermost por-
tion a thin layer which is more transparent
than the rest of their substance, and is
marked, according to Kolliker, Frey, and
other observers, by fine vertical striations.
The villus is penetrated from below by blood-
vessels supplied from a terminal twig of the
mesenteric artery, which form by their fre-
quent division and inosculation an exceed-
ingly abundant capillary network, almost
immediately beneath the epithelial layer.
At its base they reunite to form a venous
branch, which is one of the commencing
rootlets of the mesenteric vein.

In the deeper part of the villus, and lying
nearly in its longitudinal axis, there is also
the commencement of a lymphatic vessej,
which, after its emergence from the base of
the organ, joins the general system of the
abdominal lymphatic or lacteal vessels. The
lymphatic vessel is usually single in the fili-

AN IHTESTTTTAL YlLLUS.

— a. Layer of cylindrical epithe-
lium, with its external trans-
parent striated portion, b b.
Bloodvessels entering and leav-
ing the villus. c. Lymphatic
vessel occupying its central
axis. (Leydig.)

(189)

190

ABSORPTION.

Fig. 57.

form or cylindrical villi, sometimes double or even triple in those of a
more flattened form. It has exceedingly thin walls, consisting only of
a single layer of flattened epithelium cells.

Closed Follicles of the Small Intestine — In addition to the secreting
glandules and villi, the intestine presents, throughout its extent, two

sets of glandular looking organs, known
as the glandules solitariae and the
glandular agminatae. The first of these,
or the solitary glandules, are found in
the upper part of the intestine, scattered
at intervals over its surface, as minute
whitish points. Farther down they
begin to occur in clusters of several to-
gether, and in the lower part of the
jejunum and in the ileum they consti-
tute rounded or elongated oval patches,
from 1J to 5 centimetres in length,
known by the name of "Peyer's patches."
These patches are always situated op-
posite the attachment of the mesentery,
and with their long diameter parallel to
the axis of the intestine.

The structure of the solitary gland-
ules and of those forming Peyer's
patches is the same. The only differ-
ference between them is that in one case
the follicles are distributed separately over the surface of the intestine,
while in the other they are collected into distinct groups.

Each follicle is a rounded or

Fig. 58. ovoid body, from one-half to two

millimetres in diameter, situated
partly in the thickness of the
mucous membrane, and partly
below. It consists of an ex-
ternal investing capsule, closed
on all sides, from the inner sur-
face of which slender anastomos-
ing filaments pass through the
substance of the organ, forming
a delicate scaffolding or frame-
work of minute fibres. In the
interstices between these fibres
there is a small quantity of fluid,
together with an abundance of

O

OF THE CLOSED FOLLICLES OP PET- lymph corpuscles, or faintly

ER'S PATCHES, from Small Intestine of Pig, ffranular cells about 13 mmm.
showing the bloodvessels in its interior. Magni- .

fled 60 diameters. in diameter. The follicle is also

FK visit's PATCH of
glandules from the ileum.

nominated
(Boehm.)

ABSORPTION. 191

penetrated by capillary bloodvessels, which pass through its investing
capsule from without, inosculate freely with each other in its interior,
and return upon themselves in loops near its centre.

The follicles have a close relation with the lymphatics of the intestine.
The lymphatic vessels coming from the villosities form a plexus in the
substance of the mucous membrane from which branches pass to the
follicles and ramify upon their surface, forming another close plexus upon
their investing capsule. The lymphatic vessels, however, do not pene-
trate into the interior of the follicles, which are occupied by blood-
vessels alone Owing to the analogy in structure between these
bodies and portions of the lymphatic glands, as well as to the fact that
the lacteals coming from the neighborhood of Peyer's patches are
more numerous than from other points of the intestine, the closed folli- ,
cles are generally regarded as belonging to the system of the lym- i--
phatic glands. They constitute the simplest form of these glands,
situated in or immediately beneath the intestinal mucous membrane.
They furnish no fluid secretion to the intestinal cavity, but are con-
nected in some way with the preparation or elaboration of the absorbed
materials.

Mechanism of Absorption by the Villi. — The villi are the active
agents in the process of absorption. The entire extent of the mucous
membrane of the small intestine, including the valvulse conniventes, is
estimated at about 6000 square centimetres of surface ; and as the
number of the villi is, on the average, not less than 30 to the square
millimetre, there must be at least from fifteen to twenty millions of them
in the whole length of the small intestine. By their great abundance,
accordingly, as well as by their projecting form, they multiply the ex-
tent of surface over which the digested fluids come in contact with the
intestinal mucous membrane, and increase, to a corresponding degree,
the energy with which absorption takes place* They hang out into the
nutritious, semi-fluid mass contained in the intestinal cavity, as the
roots of a tree penetrate the soil ; and they imbibe the liquefied portions
of the food with a rapidity which is in direct proportion to their extent
of surface and the activity of the circulation.

The process of absorption is also hastened by the peristaltic move-
ments of the intestine. The muscular layer here, as in other parts of
the alimentary canal, is double, consisting of both circular and longitu- I/
dinal fibres. The action of these fibres maybe readily seen by pinching
the exposed intestine with the blades of a forceps. A contraction takes
place at the spot irritated, by which the intestine is reduced in diame-
ter, its cavity partially obliterated, and its contents forced onward into
the succeeding portion of the alimentary canal. The local contraction
then propagates itself to the neighboring parts, while the portion
originally contracted becomes relaxed ; so that a slow, continuous,
creeping motion of the intestine is produced, by successive waves of
contraction and relaxation, which follow each other from above down-
ward. At the same time, the longitudinal fibres have a similar alter-

192

ABSORPTION.

Fig. 59.

nating action, drawing the narrowed portions of intestine up and down,
as they successively enter into contraction or become relaxed in the
intervals. The effect of the whole is to produce a peculiar, writhing,
worm-like, or " vermicular" motion, among the different coils of intes-
tine. During life, the vermicular or peristaltic motion of the intestine
is excited by the presence of food undergoing digestion. By its action,
the substances which pass from the stomach into the duodenum are
steadily carried from above downward, so as to traverse the entire
length of the small intestine, and to come in contact successively with
the whole extent of its mucous membrane. During this passage the
absorption of the digested food is constantly going on. Its liquefied
portions are taken up by the villi of the mucous membrane, and succes-
sively disappear; so that, at the termination of the small intestine,
there remains only the undigested portion of the food, together with
the refuse of the intestinal secretions. These pass through the ileo-
csecal orifice into the large intestine, and there become reduced to the
condition of feces.

The digested fluids taken up from the intestine are first absorbed by
the epithelial cells covering the surface of the villi, and are thence

transmitted to the deeper por-
tions of their tissue. This pas-
sage of the products of diges-
tion through the substance of
the epithelial cells is difficult
of demonstration for perfectly
homogeneous liquids, but it
may be distinctly seen in the
case of the fatty matters of the
chyle. As already described,
the oleaginous matters of the
food are emulsified by diges-
tion, forming in the intestine a
white milky fluid, termed the
" chyle," which is entangled in
the folds of the mucous mem-
brane, and adheres to the sur-
face of the villi. In chyle
which is drawn either from the

lacteal vessels or the thoracic duct, the fatty matter still presents itself
in the same condition, and retains all the chemical properties of oil.
Examined by the microscope, it is seen to exist under the form of fine
granules and molecules, varying in size from 2.5 mmm. downward,
which present the ordinary appearances of oil in a state of minute sub-
division. The chyle, therefore, does not represent the entire product of
the digestive process, but consists of the fatty substances, suspended by
emulsion in a serous fluid.

The emulsioned oil has accordingly passed from the cavity of the

CHYLE PROM COMMENCEMENT OF THORACIC
DUCT, from the Dog.

ABSORPTION.

193

intestine into that of the lacteal vessels. Its transmission is facilitated
by the alkaline condition of the blood and of the intestinal juices. Oil
by itself is a non-diffusible substance; that is, it is incapable of
passing through an animal membrane by endosmosis. If a fluid con-
taining oil be placed on one side of an animal membrane, and pure
water on the other, the water will readily penetrate the substance of
the membrane, while the oily particles cannot be made to pass under
any ordinary pressure. Though this be true, however, for pure water,
it is not true for slightly alkaline fluids like the serum of blood or the
lymph. This has been demonstrated by the experiments of Matteucci,
in which he made an emulsion with an alkaline fluid containing 4.3
parts per thousand of potassium hydrate. Such a solution has no per-
ceptible alkaline taste, and its action on reddened litmus paper is about
equal to that of the lymph and chyle. If this emulsion were placed in
an endosmometer, together with a watery alkaline solution of similar,
strength, it was found that the oily particles penetrated the animal
membrane without much difficulty, and mingled with the fluid on the
opposite side. Endosmosis will thus take place with a fatty emulsion,
provided the fluids used in the experiment be slightly alkaline in re-
action.

The fatty molecules of the chyle, accordingly, are taken up by the
layer of epithelium cells covering the surface of the villi, and their
passage into and through the epithelial layer produces a marked altera-
tion in the physical appearance of the cells composing it. In the inter-
vals of digestion these cells are nearly transparent and homogeneous-

60.

Fig. 61.

INTESTINAL EPITHELIUM; from the
Dog, while fasting.

INTESTINAL EPITHELIUM; from the Dog,
during the digestion of fat.

looking, presenting under the microscope only the appearance of a very
fine and delicate granulation. (Fig. 60.) But if examined during the
digestion and absorption of fatty matters, their substance is seen to be

194 ABSORPTION.

crowded with oily particles, taken up by absorption from the intestinal
cavity. (Fig. 61.) The oily matter then passes onward, penetrating
deeper into the substance of the villus, until it is at last received by the
capillary vessels in its interior.

Absorption by the Bloodvessels. — The final absorption of the digested
fluids is accomplished mainly by the bloodvessels of the intestinal villi.
Their situation, their numbers, and the rapid movement of the blood
through these channels, are all circumstances especially favorable for
the performance of this function. The capillary plexus of each villus
is situated in the most superficial part of its substance, almost immedi-
ately beneath the epithelium cells which cover its surface, so that the
absorbed fluids, after passing through the epithelial layer, come at once
in contact with the capillaries of the vascular network. The exten-
sion of absorbing surface, from the repeated division and inosculation
of these vessels, and the constant renovation of the fluids which they
contain, by the movement of the circulation, provide for their constant
activity, and drain away the absorbed fluids from the substance of the
villus as fast as they are taken up by its exposed surface.

Fig. 62.

CAPILLARY BLOODVESSELS OF THE INTESTINAL VILLI; from the Mouse.

(KOlliker )

The activity of the bloodvessels in the process of absorption is also
a matter of direct observation. Abundant experiments have demon-
strated, not only that soluble substances introduced into the intestine
may be soon afterward detected in the blood of the portal vein, but
that absorption takes place more rapidly and abundantly by the blood-
vessels than by the lacteals. This was first shown by Magendie,1 who
found that the absorption of poisonous substances would take place, in
the living animal, both from the cavity of the intestine and from the
tissues of the lower extremity, notwithstanding that all communication
through the lacteals and lymphatics was cut off, and the passage by the

1 Journal de Physiologic. Paris, 1825, tome i. p. 18.

ABSORPTION. 195

bloodvessels alone remained. These results were afterward corroborated
by Panizza, who succeeded in detecting the substance which had been
absorbed in the venous blood returning from the part. This observer
opened the abdomen of a horse, and drew out a fold of the small intes-
tine, about 20 centimetres in length (Fig. 63, a, a), which he included

Fig. 63.

PANIZZA'S EXPERIMENT. — aa. Intestine, b. Point of ligature of mesenteric vein.
c. Opening in intestine for introduction of poison, d. Opening in mesenteric vein behind the
ligature.

between two ligatures. A ligature was then placed (at 6) upon the
mesenteric vein receiving the blood from this portion of intestine; and,
in order that the circulation might not be interrupted, an opening was
made (at d) in the vein behind the ligature, so that the blood brought
by the mesenteric artery, after circulating in the intestinal capillaries,
passed out at the opening, and was collected in a vessel for examination.
Hydrocyanic acid was then introduced into the intestine by an opening
at c, and almost immediately afterward its presence was detected in the
venous blood flowing from the orifice at d. The animal, however, was
not poisoned, since the acid was prevented from gaining an entrance
into the general circulation by the ligature at 6.

Panizza afterward varied this experiment in the following manner:
Instead of tying the mesenteric vein, he simply compressed it. Then,
hydrocyanic acid being introduced into the intestine, as above, no effect
was produced on the animal, so long as compression was maintained
upon the vein. But as soon as the blood was again allowed to pass
through the vessels, symptoms of general poisoning became manifest.
Lastly, in a third experiment, the same observer removed all the nerves
a'nd lacteal vessels supplying the intestinal fold, leaving the blood-
vessels alone untouched. Hydrocyanic acid, now being introduced into
the intestine, found an entrance at once into the general circulation, and

\

196 ABSORPTION.

the animal was immediately poisoned. The bloodvessels, therefore, are
not only capable of absorbing fluids from the intestine, but take them
up even more rapidly than the lacteals.

The entrance of digested materials into the bloodvessels of the intes-
tine is readily demonstrated in a similar way. After the digestion of
food containing a mixture of albuminous and starchy ingredients, both
sugar and albuminose are to be met with in the blood of the mesenteric
and portal veins. Digested and emulsioned fatty matters may also be
distinctly followed, in their passage through the same channels, by the
turbid and chylous aspect which they communicate to the portal blood.
It is easy to see that the blood of the portal system, in the carnivorous
animals during digestion, contains fatty matter in a state of minute
subdivision, similar in appearance to that found in the chyle and in the
substance of the villi, often so abundant as to communicate a turbid
appearance to the serum after coagulation; and various observers
(Lehmann, Schultz, Simon), in examining the blood from different parts
of the body, have also found the blood of the portal system consider-
ably richer in fat than that of the arteries or of other veins, particularly
while intestinal digestion is going on with activity.

Absorption by the Lacteals. — The absorption of digested materials,
but more particularly of the fatty matters, is also accomplished by the
lymphatics or lacteals of the small intestine. These, however, do not
form a distinct class of vessels by themselves, but are simply a part of
the great system of lymphatic or absorbent vessels, which are to be
found everywhere in the integuments of the head, the parietes of the
trunk, the upper and lower extremities, and in the glandular and mus-
cular organs and mucous membranes throughout the body. Originat-
ing in the tissues of the above mentioned parts, they pass from the
periphery toward the centre, their branches converging and uniting with
each other like those of the veins, and passing, at various points in
their course, through certain glandular-looking bodies, known as the
lymphatic glands.

The fluid generally contained in these vessels is called the " lymph."
It is a colorless or slightly yellowish transparent liquid, which is ab-
sorbed by the lymphatic vessels from the tissues in which they originate.
So far as regards its composition, it is known to contain, beside water
and saline matters, a small quantity of fibrine and albumen. Its ingre-
dients are evidently derived from, the metamorphosis of the tissues, and
are returned to the centre of the circulation to be eliminated by excretion,
or to undergo some new transforming process, the details of which are
not as yet fully understood.

The lymphatic vessels of the intestine originate, as we have seen, in
the substance of the villi, where they commence by longitudinal spaces
lined with flattened epithelium cells, becoming provided, at a short dis-
tance from their origin, with thin, transparent, elastic coats, like those
of the capillary bloodvessels. After leaving the base of the villi they
become part of the lymphatic plexus, from which the main branches pass

ABSORPTION. 197

inward, between the layers of the mesentery, from the intestine toward
the posterior part of the abdomen. During their course through the
mesentery, they inosculate with each other by transverse branches, and
pass in succession through several ranges of mesenteric glands, which
have the same structure with those already mentioned, and which are
accordingly the lymphatic glands of the abdominal cavity. On arriving
near the attached portion of the mesentery, on the right side of the
abdomen, at about the level of the second lumbar vertebra, they terminate
iii a saccular dilatation, known as the " receptaculum chyli." From
this point the thoracic duct passes upward through the cavity of the
chest, crossing obliquely from the right to the left of the median line,
and finally discharges its contents into the left subclavian vein, at its
junction with the jugular of the same side.

In the intervals of digestion the fluid contained in the lymphatic
vessels is the same in appearance throughout the body. Its colorless
and transparent character, together with the small size of the lymphatics
themselves, and the thinness and delicacy of their coats, make these
vessels nearly or quite invisible to the unaided eye. But during the
digestion and absorption of food the elements of the chyle are taken up
by the lymphatics of the small intestine, which are distended with a
milky fluid, and thus become visible as an abundant network of opaque
white filaments, ramifying in the intestinal walls, converging from the
intestine to the receptaculum chyli, and contrasting strongly with the
ruddy and semi-transparent color of the neighboring tissues. If, when
in this condition, one of them be opened with the point of a scalpel, it
discharges a chylous liquid, which is easily seen to be the same in
character with that contained in the cavity of the intestine itself, namely,
an emulsion of fatty molecules and granulations. Owing to the appear-
ance thus given to the vessels themselves, and to the milky fluid which
they contain, they have received the name of the lacteals, or lactiferous
vessels of the abdomen.

The presence of chyle in the lacteals is, therefore, not a constant, but
only a periodical phenomenon. The fatty substances constituting the
chyle begin to be absorbed during the process of digestion, as soon as
they have been disintegrated and emulsioned by the action of the intes-
tinal fluids. As digestion proceeds, they accumulate in larger quantity,
and gradually fill the whole lacteal system, giving to its vessels the
characteristic aspect above described. But as digestion and absorption
from the intestinal cavity come to an end, the milky fluid disappears
from the lymphatics, and they resume their former transparent and
colorless appearance.

The lacteals accordingly are nothing more than the lymphatics of the
small intestine, which, in addition to the transparent and colorless
lymph which they usually contain, have absorbed a fluid rich in fat
derived from the process of digestion. While this process is going on,
they are distinguished from the lymphatics elsewhere by the milky
character of their contents, which accumulate in the receptaculum chyli,

198

ABSOKPTION.

Fiff. 64.

and may be followed thence through the thoracic duct, to the point
where it terminates in the left subclaviaii vein.

It was owing to the opacity and visibility of the lacteals during diges-
tion that these vessels were discovered in 1622 by Asellius, who first
saw them on opening the abdomen of a dog, a few hours after the inges-
tion of food. The discovery of the general system of lymphatic vessels

was made subsequently by Hud-
beck and Bartholin, in 1651 and
1653, and was consequent upon
the previous observations on
the lacteals of the abdomen.

That the white color of the
chyle during digestion is really
due to the presence of fatty sub-
stances absorbed from the intes-
tine, is shown by the fact that
the intensity of this color is in
proportion to the quantity of
fat contained in the food. It
is generally less marked in her-
bivorous than in carnivorous
animals. According to the- ob-
servations of Tiedemann and
Gmelin, in a dog fed with fatty
matters the lacteals are abund-
antly filled with an opaque white
fluid, while in the same animal
fed with starchy matters alone,
the chyle is pale and but slightly
opaline ; and finally Bernard has
shown that if, in a dog after
several days fasting, a little
ether, containing fat in solution,
be injected into the stomach,
without the introduction of any
other food, at the end of a few
hours the lacteals are found
fully distended with milky chyle,
precisely similar in appearance
to that obtained during ordinary
digestion.

Passage of Absorbed Materials into the Circulation.— The products
of digestion, which are taken up by the bloodvessels and lymphatics of
the intestine, pass by two different routes into the general circulation.
The blood of the portal system, containing albuminose, sugar, and
molecular fat, is carried at once to the liver, where it traverses the
capillary vessels of this organ before reaching the vena cava and the

LACTEALS AND LYMPHATICS, during
digestion.

ABSORPTION.

right side of the heart. The chyle, on the other hand, containing also
a large proportion of fatty ingredients, passes by the thoracic duct
directly to the left subclavian vein and is there mingled with the return-
ing current of the venous blood. But all these substances, after entering
the circulation and coming in contact with the organic ingredients of
the blood, are modified in such a way as no longer to be recognizable
under their original form. This change takes place very rapidly with
the albuminose and the sugar, both of which are taken up in greatest
proportion by the bloodvessels and are carried at once through the
hepatic capillaries. The albuminose passes, in all probability, into the
condition of ordinary albumen, while the sugar rapidly becomes decom-
posed, or transformed, and loses its characteristic properties ; so that,
on arriving at the entrance of the general circulation, both these newly
absorbed ingredients have become already assimilated to those which
previously existed in the blood. The fatty matters also, which reach
the blood on the right side of the heart both by the portal and hepatic
veins, and by the thoracic duct and subclavian vein, undergo a trans-
formation while passing through the lungs by which their distinctive
characters are destroyed, and they are no longer visible as oleaginous
molecules. This alteration is so complete, during the early part of
digestion, or when the proportion of fat in the food is small, that all the
oleaginous matter disappears in the lungs and none of it is to be de-
tected in the blood of the general circulation.

But as digestion proceeds, especially when the food has been abun-
dant in oleaginous substances, an increasing quantity of fatty matter
finds its way, by these two passages, into the blood ; and a time at last
arrives when the whole of the fat so introduced is not destroyed during
its passage through the lungs. Its absorption taking place at this time
more rapidly than its decomposition, it begins to appear, in moderate
quantity, in the blood of the general circulation ; and, lastly, when the
intestinal absorption is at its point of greatest activity, it is found in
considerable abundance throughout the entire vascular system. At this
period, some hours after the ingestion of food rich in oleaginous matters,
the blood, not only of the portal vein, but also of the general circula-
tion, everywhere contains a superabundance of fat, derived from the
digestive process. If blood be then drawn from the veins or the arteries
in any part of the body, it will present the peculiar appearance known as
that of "chylous" or " milky" blood. On the separation of the clot the
serum is turbid ; and after a few hours of repose, the fatty substances
which it contains rise to the top and cover its surface with a partially
opaque and creamy-looking pellicle. This appearance has been occa-
sionally observed in the blood of the human subject, particularly in
cases of apoplexy occurring after a full meal. It is a purely normal /
phenomenon, and depends simply on the rapid absorption, at certain
periods during the digestive process, of oleaginous substances from the
intestine. It can be observed in the dog at any time by feeding him with

200 ABSORPTION.

fat meat, and drawing blood, seven or eight hours afterward, from the
carotid artery or the jugular vein.

This state of things continues for a varying length of time, according
to the amount of oleaginous matters contained in the food. When
digestion is terminated, and the fat ceases to be introduced in unusual
quantity into the circulation, its transformation and decomposition con-
tinuing to take place in the blood, it disappears gradually from the
veins, arteries, and capillaries of the general system ; and, finally, when
the whole of it has been disposed of by the nutritive process, the serum
again becomes transparent, and the blood returns to its ordinary condi-
tion.

In this manner the nutritive elements of the food, prepared for ab-
sorption by the digestive process, are taken up into the circulation under
the different forms of albuminose, sugar, and chyle, and accumulate as
such, at. certain times, in the blood. But these conditions are tempo-
rary and transitional. The nutritive materials soon pass by transfor-
mation into other forms, and become assimilated to the pre-existing
elements of the circulating fluid. In this way they accomplish finally
the object of digestion, and replenish the blood by a supply of new
materials from without.

CHAPTEE X.

THE BILE.

THE first peculiarity of the liver, as compared with other secreting
organs, is that it is supplied with blood at the same time from two dif-'
lerent sources ; namely, from the hepatic artery and the portal vein.
The ramifications of the hepatic artery are especially distributed to the
walls of the hepatic ducts, to those of the portal vein, to the capsule of
Glisson, and to the peritoneal covering of the organ ; while those of the
portal vein pass in a peculiar manner into the glandular parenchyma,
and after traversing its substance as a capillary plexus become continu-
ous with the rootlets of the hepatic vein. Beside arterial blood, accord-
ingly, which it receives in common with the other abdominal organs,
in moderate quantity, it is supplied with an abundance of venous blood,
collected by the portal system from the stomach, the spleenr the pancreas
and the intestinal canal.

Secondly, the liver is distinguished by its large size. While the
weight of all the salivary glands taken together, in the human species,
is but little over 100 grammes, and that of the pancreas about 75
grammes, the liver forms a compact vascular and glandular organ,
weighing nearly or quite 1600 grammes, and occupying a considerable
portion of the abdominal cavity.

Lastly, the liver is peculiar in its texture, and differs so much in this
respect from the other secretory organs, as to require a special descrip-
tion. As in other instances, the secreting apparatus consists essentially
of glandular cells and capillary bloodvessels, with the ducts which col-
lect and transport the secreted fluid ; but these elements, instead of
being arranged as elsewhere in distinct groups of tubular or rounded
follicles, are closely united with each other, forming on all sides a con-
tinuous mass by their mutual contact and adhesion.

The substance of the liver, in man and in the quadrupeds generally,
is divided into pentagonal or hexagonal masses or islets, about 1.5 milli-
metre in diameter, which are known by the name of the hepatic lobules.
These lobules, however, are not distinctly separated from each other,
but are simply made visible by the relative arrangement of the afferent
and efferent bloodvessels. Each lobule is embraced upon its external
surface by the terminal branches of the portal vein, which ramify be-
tween the lobules lying adjacent to each other. These vessels are
accordingly known as the interlobular veins. From the side of the
interlobular vein, minute vessels pass into the substance of the lobule,
and there form by their division and inosculation an abundant capillary
14 ( 201 )

202

THE BILE.

plexus, the vessels of which have a general convergent direction from
the periphery toward the centre. At the middle part of the lobule they
unite to form the commencement of an efferent vessel which, from its

central or interior posi-

Fig. 65. tion, is termed the intra-

lobular vein. This root-
let continues its course
until it joins one of the
smaller branches of the
hepatic vein. Each lobule
may therefore be con-
sidered as a more or less
ovoid, cylindrical or pris-
matic mass, resting upon
a branch of the hepatic
vein, and attached to this
vessel by its own intra-
lobular vein, which passes
through its axis and re-
ceives the blood collected
from its capillary vessels ;
while it is encircled by
terminal branches of the
portal vein supplying the
blood for its interior cir-
culation.

Beside its capillary bloodvessels, the mass of the lobule is made up
mostly of glandular cells. These cells are generally of a five- or six-

HEPATIC LOBULE, in transverse section, showing
the distribution of its bloodvessels. — a, a. Interlobular
veins, b. Intralobular vein, c, c, c. Plexus of Capillary
bloodvessels in the substance of the lobule, d, d. Twigs
of inteilobular vein, passing to adjacent lobules.

Fig. 66.

GLANDULAR HEPATIC CELLS. From the
human liver.

sided prismatic form, often with
one or two of their borders ex-
cavated by curvilinear furrows
at the points where they are in
contact with a capillary blood-
vessel. They are, on the aver-
age, 22 mmm. in diameter, of a
finely granular aspect, usually,
in the human subject, containing
one or more minute fat globules,
and provided with a well-marked
round or oval nucleolated nu-
cleus. The cells are every-
where in contact with each
other by their plane surfaces,
and each one is also in direct
relation at several points with
a capillary bloodvessel. Thus

THE BILE.

203

the union of these two elements is intimate and complete throughout
the substance of the hepatic lobule.

There is an equally close connection between the glandular substance
of the liver and the biliary ducts. The main hepatic duct, which with
its ramifications accompanies the divisions of the portal vein, breaks up
into branches which finally reach the interlobular spaces. The biliary
ducts in the human liver which have a larger diameter than about 200
mmm. are lined with cells of cylindrical epithelium ; while in those
which are below 100 mmm. in diameter, the form of the cells changes
gradually to that of pavement epithelium. The biliary ducts which
occupy the interlobular spaces are of the smaller variety, being not
more than 50 mmm. in diameter, and are lined accordingly with pave-
ment epithelium. They break up into communicating branches which
cover the surface of the lobule with a plexus of biliary canaliculi.

Fig. 67.

FINER BILIARY CANALS AND BILIARY DTTCTS, from the frog's liver.— a. Small
biliary duct, with its lining of epithelium cells. 6, c. Terminal branches of the minute bili-
ary canals, surrounded by glandular cells, d. Transverse communicating branch between
two biliary canals, e, e. Sheath of glandular secreting cells, surrounding the biliary canals.
/. Section of capillary bloodvessel. (Eberth.)

From this superficial plexus the finest biliary tubes penetrate into the
substance of the lobule and there inosculate with each other between
the glandular secreting cells. In the liver of the amphibia (frogs and
water-lizards), as shown by the investigations of Hering and Eberth, the
Itimate structure of the secreting apparatus is not essentially different
from that of other lobulated glands. The smaller biliary ducts, lined
with pavement epithelium, give off minute branches which communicate
with each other more or less abundantly and are themselves in contact
everywhere with the large glandular cells ; each terminal branch being

204

THE BILE.

Fig. 68.

surrounded by a single sheath of such glandular cells, which stand in
place of the epithelial lining of a tube or follicle.

In the liver of the warm-blooded quadrupeds, the texture of the organ
is more compact, the glandular cells and capillary bloodvessels more
closely united, and especially the finest biliary passages in the substance
of the lobule are more abundant and inosculate more frequently with
each other. From the plexus of biliary canaliculi upon the surface of
the lobule, already described, branches of much smaller size penetrate
into its interior, and these inosculate so abundantly by transverse com-
munications that they encircle each glandular cell in the meshes formed
by their network. These interior communicating passages are the capil-
lary bile-ducts. They are much smaller than the capillary bloodvessels,
being in the rabbit's liver, according to Kolliker, not more than 2 mmm.
in diameter, regularly cylindrical in form, and without any perceptible
dilatations at the points of inosculation. They embrace the glandular
cells in such a way that they are always situated at the greatest possible
distance, that is, half the diameter of a cell, from the nearest capillary
bloodvessel ; the bloodvessels running along the borders or angular
edges of the prismatic cells (Kolliker), while the capillary bile-ducts
pass along the middle of their plane surfaces. Thus, the two sets of

canals, namely, capillary blood-
vessels and bile-ducts, form a
double series of inosculating
passages embracing the gland-
ular cells, the meshes of which
are always directed nearly or
quite at right angles to each
other.

The intralobular capillary bile
ducts, above described, as de-
monstrated by injections, have
been regarded by some authori-
ties as artificially produced by
the accidental extravasation of
the injection fluid and its infiltra-
tion between the glandular cells.
But the existence of these ducts
as a natural formation has been
corroborated by too many ob-
servers to leave it a matter of
doubt, especially considering the
regular and uniform arrange-
ment under which they present themselves. Their situation is also
against the hypothesis of their artificial origin, since they are not placed
at the angular borders of the glandular cells, where an extravasated
fluid would naturally find its way, but run along the middle of their
plane surfaces where they lie in close contact with each other ; and.

SECTION OP PART ov A

L.OBULE PROM THE RABBIT'S LlVER.—

a, 0,0. Nucleated glandular cells. b,b,b. Capil-
lary bile-ducts passing between the adjacent
cells. c,c,c. Sections of capillary bloodvessels.
(Genth.)

THE BILE. 205

finally, Kolliker has found that the capillary bile ducts in the liver of
the rabbit may become visible in their usual positions in thin sections
hardened in alcohol, where no injection has been practised. They are,
therefore, to be regarded as the finest commencing ramifications of the
biliary canals, which receive the secreted fluids directly from the sub-
stance of the glandular cells.

Physical and Chemical Characters of the Bile. — The bile is distin-
guished from all the other secretions discharged into the alimentary
canal principally by the fact that it does not contain any albuminous
ingredient analogous to those of the saliva, the gastric, pancreatic, or
intestinal juices ; its most important constituents being nitrogenous
crystallizable substances, together with cholesterine and coloring mat-
ters. Bile taken from the gall-bladder contains, it is true, a certain
amount of mucus, which gives it more or less of a ropy and viscid charac-
ter; but this mucus is secreted by the gall-bladder itself, and bile taken
from the gall-ducts in the substance of the organ is always perfectly
fluid and watery in consistency. Furthermore, the gall-bladder is by
no means constantly present, even in the higher animals, being absent,
according to Wagner, in the horse, the camel, most of the pach^dermata
and several of the gnawing animals, and at the same time present in
many closely allied species. The bile accordingly, in its essential in-
gredients, differs in a marked degree from the digestive secretions
proper.

The bile, as it comes from the gall-bladder, is a clear, more or less
tenacious and ropy fluid, neutral in reaction, with a faint and rather
indefinite animal odor. If it be shaken up with air, or if air be blown
into it through a narrow tube, it easily foams up into a frothy mixture
which remains for a long time on the surface of the fluid. This property
of frothing upon agitation with air does not depend upon the mucus which
it contains, but upon the biliary salts proper, namely, the sodium glyco-
cholate and taurocholate ; since these salts iu a pure watery solution
exhibit the same property.

Its specific gravity is rather high, as compared with that of the other
secretions. In ox-bile, we have found it to be 1024, in pig's bile 1030
to 1036. The specific gravity of human bile, according to Robin, is
from 1020 to 1026 ; according to Jacobsen, in bile from a biliary fistula,
but little over 1010. We have found it, in bile taken from the gall-
bladder, 1018.

Its color varies, in different species of animals, from a reddish-orange
to a nearly pure green, and in different instances presents all the inter-
mediate tints of golden-yellow, reddish-brown, olive-brown, olive, yel-
lowish-green, and bronze-green. It may be described in general terms as
a greenish-bronze, with sometimes more or less of an orange tint.
Human bile from a biliary fistula was found by Jacobsen to be of a
clear yellowish bronze-green; that taken from the gall-bladder after
death is usually of a dark golden-brown. Dog's bile is of a brownish-
olive or bronze color; pig's bile of a reddish-orange or reddish-brown;

206 THE BILE.

and sheep and ox-bile of a greenish-olive, or more frequently of a pure
green. As a general rule, the bile of the herbivorous animals is more
decidedly green in hue, that of the carnivora and omnivora orange or
brown. All these differences may be referred to two main classes of
tints, corresponding with two different coloring matters; in one of which
the predominating color is red or reddish-brown, dependent on biliru-
bine, while in the other it is green owing to the presence of biliverdinc.
As the proportion of these two substances varies in any given specimen,
it will exhib^ a corresponding color of the pure or mingled tints.

The color of the bile is also modified by oxidizing agents, which pro-
duce a green hue in bile which was originally olive or brown, and
increase the intensity of the green tint when this color is already pre-
sent. If brown or olive-colored bile be exposed to the air for a short
time, its surface becomes green by contact with the atmosphere. The
same change may be instantly produced by adding to the bile a few
drops of a watery solution of iodine ; and a little nitric acid acts with
great energy, developing a bright grass-green hue. These changes
depend upon the oxidation of the bilirubine, and its consequent con-
version into biliverdine.

The green color of bile also disappears rapidly when excluded from
all sources of oxidation. If ox-bile, of a pure green or olive-green hue,
be inclosed in a perfectly full and securely stoppered vessel, so as to be
entirely protected from the air, it gradually loses its green color and
becomes of a dull yellow. This change progresses from the external
parts of the liquid toward its centre, until at the end of twelve, twenty-
four, or thirty-six hours the whole of it has become of a light yellow or
yellowish-brown. In this condition the green hue may be again restored
by the addition of iodine, or by exposing the bile in thin layers to the
air. The green color of the bile accordingly appears to be dependent
on continued oxidation.

The bile presents, in addition, certain remarkable optical properties
which distinguish it from other animal fluids.

In the first place, it is dichroic ; that is, it has two different colors
by transmitted light, according to the thickness of its mass. If ox-bile,
which is of a pure transparent green by ordinary daylight in layers of
two or three centimetres, be viewed by strong sunlight in a thickness
of five or six centimetres, it is red. In this respect it resembles a solu-
tion of chlorophylle, which presents the contrast of the same two colors
in a very marked manner.

Secondly, the bile is fluorescent? that is, it becomes faintly luminous

1 This property, so called from fluor spar, in which it was first observed, is
shown by various transparent substances, when illuminated by solar light, or by
that of certain parts of the spectrum. Thus a solution of quinine sulphate, which
is perfectly colorless by ordinary diffused daylight, becomes blue at any spot where
the sun's rays are concentrated upon it by a lens ; and it exhibits a distinct lumi-
nosity in both the violet and ultra-violet parts of the spectrum.

THE BILE. 207

with a color of its own, when viewed by the more refrangible rays of
the solar spectrum. If a specimen of bile, of a clear greenish color, be
placed in the track of either the violet or blue rays of the solar spec-
trum, it becomes visible with a light yellowish-green tint. In the green
it is more yellowish ; and in the yellow it has a distinct tinge of red ;
while in the red ray its fluorescence is hardly perceptible. Thus in all
parts of the spectrum where it exhibits this property, it emits a light
of less refrangibility than that of the ray by which it is illuminated.
The property of fluorescence is also manifested, to a remarkable degree,
by solutions of chlorophylle, which, although of a clear green color by
diffused daylight, are of a pure red, when viewed by either the violet,
blue, green, or yellow rays of the spectrum.

The fluorescence of bile, however, does not depend altogether upon
its coloring matter, but is due mainly to the presence of the biliary salts,
since it is exhibited in an equal degree by watery or alcoholic solutions
of sodium taurocholate and glycocholate ; the only difference being that
the color of these solutions by the violet and blue rays is nearly pure
yellow instead of yellowish-green.

Thirdly, the spectrum of bile is distinguished by certain peculiar
characters and absorption bands, dependent upon its coloring matter.1
All the more refrangible rays are absorbed with great intensity, so that
the visible spectrum is very short, terminating usually within the limits
of the green, about midway between the lines E and F. A portion of
the green, accordingly, and the whole of the blue, indigo, and violet are
completely absorbed, even when the bile 'is viewed in a layer only one
centimetre in thickness. In dog's and pig's bile the spectrum some-
times terminates in the first half of the green, at or just beyond the
situation of the line E ; and in human bile even within this point, about
the commencement of the green part of the spectrum.

Another peculiarity of the spectrum of bile is that its light does not
fade away gradually toward the more refrangible portions, as is the ^
case with most other colored fluids, but it terminates suddenly, so that
the light is cut off abruptly at the situations above mentioned, thus
making a strong contrast with the complete darkness immediately
beyond its limits. This peculiarity is perceptible in bile of all shades
of green, olive, yellow, or reddish-brown.

1 If any colored fluid be placed before the slit of a spectroscope, so that the
light which passes through it is afterward dispersed by the prism of the instru-
ment, to form a spectrum, it is found that it absorbs the light of the different
colors with different degrees of intensity. When the absorption of light in any
particular part of the spectrum is so strong as to cause at that spot a decided
dimness in comparison with the neighboring regions, it is called an " absorption
band," and is characteristic of the fluid which produces it. The situation of an
absorption band is usually indicated by reference to Frauenhofer's lines of the
solar spectrum, known as A, B, C, D. E, F, G, and H.

208 THE BILE.

The spectrum of bile shows furthermore three absorption bands, situ-

. / ated in the red, the orange, and the yellow.

V The first is a dark and strongly marked band in the red, at the situa-
tion of the line C, but extending usually a considerable distance to the
left toward B. Its width varies with the thickness of the layer of fluid
examined, but when this is increased beyond a certain limit the whole
of the red disappears, so that the absorption of light at this spot is no
longer visible as a distinct band with red on each side of it. The band
itself rarely reaches the situation of the line B, and seldom or never
passes beyond it without extinguishing at the same time all the red
light of the spectrum. In layers of two or three centimetres' thickness
it is quite dark, often almost black, while the red on each side of it is
still very brilliant.

Asa rule, the intensity of the absorption band at C is in proportion to

L the preponderance of green in the color of the bile. Though easily seen,

I in comparatively thin layers, in specimens of a pure green or a decided
greenish-olive color, it is less perceptible in specimens of a yellowish,
yellowish-brown, or olive-brown tint. But if a specimen of reddish or
yellowish-brown bile, which does not show the band distinctly, be turned
green by the addition of a few drops of an iodine solution, the band at
C at once becomes visible, often to a very marked degree.

Fig. 69.

A BC D

Red Or. Yel. Green Blue Inditfo Violet

,

SPECTRUM OF G-KEEN (SHEEP'S) BILE.

It would appear from this that the band at C in the spectrum of bile
is probably due to the presence of its green rather than its red coloring
matter. As the bilirubine is well known to be converted by oxidizing
agents into biliverdine, and as this change is accompanied by the
appearance of the C band when it was not previously visible, it is evi-
dent that the band in question belongs to the green coloring matter.
At the same time it is occasionally to be seen in the spectrum of dog's
bile which is olive-brown or even brownish-yellow in hue ; its intensity
in these cases being much increased by turning the bile of a decided
green with iodine.

The absorption band at C is a normal characteristic of the bile, and is
not dependent on post-mortem changes in the secretion. We have seen
it distinctly marked in the spectrum of perfectly fresh sheep's bile,

THE BILE. 209

examined within fifteen minutes after the animal was killed and the gall-
bladder taken out of the abdomen.

The two other absorption bands of bile are exceedingly faint in com-
parison with the first, and much less constant in their occurrence. One
of them, very dim and ill-defined, is situated at the junction of the orange
and yellow, immediately to the left of the line D, occupying about the
last third of the space between C and D. The remaining band is much
narrower than either of the others, but a little more distinctly defined
than the second. It is situated at about one-third the distance between
D and E. The last two absorption bands are more frequently visible in
sheep's bile than in that of other animals ; but all three may be some-
times seen in a watery solution of desiccated ox-bile which has been
kept, in the form of a dry powder, for several years.

Lastly, the spectrum of bile exhibits a remarkable diminution in
intensity of the orange and yellow colors. As the second absorption
band is situated at the junction of these colors, it will account for a
part of this diminution; but the light of the spectrum is also remark-
ably dim in the space between the second and third absorption bands, £^
where, in the normal spectrum, it is at the brightest. This is the
place naturally occupied by pure yellow, but in the great majority of
cases, in the spectrum of bile, there is no pure yellow perceptible, and
but little or no orange. The situation of these two colors is encroached
upon by the red and green respectively ; and in not a few instances, as
the spectrum terminates before the commencement of the blue, the only
colors really perceptible in it are red and green^ The line C in the
normal spectrum is situated at the junction of the red and orange, and
yet the principal absorption band at this point, when viewed in the
spectrum of bile, nearly always appears to be situated entirely in the
red, owing to this color taking the place of the orange on the right of
the line C. This peculiarity in the spectrum of bile shows itself, whether
the color of the specimen be greenish or yellowish-brown.

If a tolerably thick layer of bile be placed before the spectroscope,
and the slit of the instrument gradually opened, the first light which
appears in the spectrum is a green light, in the latter half of the space
between D and E. On continuing to increase the size of the opening,
if the bile be deeply colored, the next to appear is a red light, at the
extreme end of the spectrum between A and B ; in less concentrated
specimens the red light may show itself simultaneously on both sides of
the absorption band at C. Afterward the green light extends further
toward the left until the spectrum is complete.

The spectrum of bile, in its most important feature, namely, the ab-
sorption band at C, presents a remarkable similarity to that of chloro-
phylle. The band at C is identical in the two spectra so far as regards
its position and general appearance ; the only perceptible difference
being that in an alcoholic solution of chlorophylle its edges are more
sharply defined than is usually the case in the spectrum of bile. In
other respects, however, the spectrum of chlorophylle differs from that

210

THE BILE.

of bile, since it has three additional absorption bands less distinct than
at C, but sufficiently well marked and differently situated from those of
bile. One of these additional bands is placed at about three-quarters
the distance from C to D, another a little to the left of E, and a third,

Fig. 70.

SPECTRUM OP CHLOROPHYLLS iff ALCOHOLIC SOLUTION.

wider than the others, but very faint and ill-defined, about midway
between E and F. In the spectrum of chloroplrylle, also, notwithstand-
ing the strong absorption of light at the situation of the principal
bands, the yellow of the spectrum appears in its proper place and with
nearly its natural hue. An additional distinction of chlorophylle, as
compared with that of bile, is that its light does not terminate abruptly,
, but fades more or less gradually toward the refrangible end.

The bile exhibits a peculiar reaction when treated with nitric acid,
owing to the effect upon its coloring matter. If a moderate quantity
of dilute nitric acid be added to fresh bile and the mixture shaken up,
the whole becomes of a bright grass-green, the first color produced by
oxidation of the bilirubine and biliverdine. But if the bile be brought
in contact, in a cylindrical glass vessel, with a layer of strong nitric
acid, especially if it contain a trace of nitrous acid, and allowed to
remain without agitation, a series of colored rings are produced at the
surface of contact of the two liquids, following each other in a definite
order, from the bile to the nitric acid, as green, blue, violet, red, and
yellow. These colors represent successive stages of oxidation and
, final destruction of the biliary coloring matter. The test is known as
s " Gmelin's bile test," and may be applied to other animal fluids in which
bilirubine or its derivatives are supposed to be present.

Composition of the Bile. — In its immediate composition the bile is
especially destinguished by the presence of the two peculiar biliary salts,
namely, sodium glycocholate and sodium taurocholate, which have been
described in Chapter VI., under their appropriate heads. It is evidently
these substances which give to the secretion its most important charac-
ters. They vary in relative quantity in the bile of different animals,
and perhaps also in that of the same species at different times. They
are produced, like the coloring matters, in the substance of the liver
itself, while other ingredients of the secretion, such as the various inin-

...

THE BILE. 211

eral salts, fatty matters and cholesterine, occur in other parts of the
system, and are supplied to the liver, ready formed, in the blood. In
the inferior animals, bile can be obtained, for purposes of analysis, in a
state of freshness and purity, from the gall-bladder of the recently
slaughtered animal ; but in man it is usually more or less altered in
character by remaining in the gall-bladder for some hours after death.
It was obtained in a case of accidental biliary fistula in the human sub-
ject by Jacobsen, who found that the entire solid ingredients amounted
to about 22.5 parts per thousand ; a little over one-third consisting of
mineral salts, the remaining two-thirds of organic matters. Sodium
glycocholate was invariably present, the taurocholate being less con-
stant; and the fluid always contained both bilirubine and biliverdine.
The proportions of all the different ingredients, according to the results
of his analyses, were as follows : —

COMPOSITION OF HUMAN BILE, ACCORDING TO THE ANALYSES OF JACOBSEN.

Water . . . .... . 977.40

C Sodium glycocholate 9.94

Cholesterine . . . . . 0.54

Organic I Free fats . .... 0.10

matters ' Sodium palmitate and stearate . . . 1.36

Lecithine 0.04

Other organic matters .... 2.26

Sodium chloride ..... 5.45

Potassium chloride ..... 0.28

Sodium Phosphate 1.33

Lime phosphate ..... 0.37

Sodium carbonate ... 0.93

1000.00

In ox-bile, as shown by the previous analyses of Berzelius, Frerichs,
and Lehmann, the proportion of both mineral and organic ingredients
may be very much greater than the above, the biliary salts themselves
amounting to 90 parts per thousand. According to Robin1 they may
exist, even in human bile, in the proportion of 56 to 106 per thousand
parts.

Tests for the Biliary Salts. — In testing for the existence of bile in
other animal fluids, a distinction must be made between those reactions
which indicate only the presence of the coloring matters, and those
which are appropriate for the detection of the biliary salts proper. The
optical properties of bilirubine and biliverdine, already described, and
especially the colors produced by the action of nitric acid, constitute a
test for these coloring matters alone. They do not indicate the presence
of the most essential ingredients of the secretion, which may be con-
tained in an animal fluid unaccompanied by the coloring matters, or, on
the other hand, may be absent where the coloring matters are to be

1 Lecjons sur les Humeurs. Paris, 1874, p. 656.

212 THE BILE.

found in appreciable quantity. Other tests are therefore necessary in
investigations for the biliary salts proper.

The ordinary characters of the biliary salts are that they are soluble
in water and in absolute alcohol, and insoluble in ether ; and that they
will gradually crystallize in the form of radiating needles, if precipitated
from their alcoholic solution by the addition of ether in excess. Fur-
thermore, they are both precipitable from their watery solutions by the
tribasic lead acetate, while the sodium glycocholate is also precipitable
by the neutral acetate of the same metal.

Pettenkofer's Test. — The biliary salts accordingly, when in consider-
able quantity, may be recognized by the above-named properties ; but
when present in smaller proportions they are to be detected by the
reaction known as *' Pettenkofer'ls test." This consists in the production
of a red color, changing to a purple or violet, on the addition of cane
sugar and sulphuric acid. The test is applied in the following way :
One part of^cjine sugar is dissolved in four parts of water. Of this
saccharine liquid, one drop is added to each cubic centimetre of the solu-
tion of biliary salts. The sugar should not be used in larger quantity,
because it might in that case give a perceptible brown tinge under the
action of sulphuric acid and heat. The admixture of the sugar pro-
duces no visible change in the solution of biliary salts. On adding a
few drops of pure sulphuric acid, the biliary acids are decomposed, form-
ing cholic acid. If the biliary salts were originally present in the solu-
tion in a proportion of not more than one part in 500, the fluid remains
clear ; if in larger quantity, the cholic acid is precipitated, forming a
whitish turbidity. This turbidity is again cleared up on the continued
addition of sulphuric acid ; and in the course of a few minutes, a cherry-
red color appears, which rapidly changes to a violet, and subsequently,
if the biliary salts be present in the proportion of one part in 500, or
over, to a deep rich purple. In very dilute solutions, the violet or purple
color may not be distinctly visible before the end of an hour.

The precautions necessary to observe in using this test are as follows :
First, the liquid to be examined should be free from other organic sub-
stances, particularly albuminous and coloring matters, which might
themselves cause discoloration of the mixture. For this purpose, the
suspected fluid should always be first evaporated to dryness, the dry
residue extracted with absolute alcohol, the alcoholic solution decolorized,
if necessary, with animal charcoal, then precipitated with ether in excess,
and the ether precipitate finally dissolved in water. This gives a clear,
colorless solution, free from other organic contamination. Secondly,
as the liquid becomes heated by the liberal admixture of sulphuric acid
with the watery solution, its temperature should not be allowed to rise
above 70° (158°F.) nor to fall much below this point. The test-tube
may therefore be cooled by occasionally moistening it in cold water.
Thirdly, the addition of the sulphuric acid should be made slowly, and
should be stopped as soon as a red tint begins to show itself, the mix-

THE BILE. 213

ture being allowed to remain at rest until the violet and purple colors
are developed.

There are various other substances which yield a red, violet, or purple
color, when treated with sugar and sulphuric acid. Among these are
oleine, oleic acid, ethereal oil, amyl-alcohol, albuminous matters and the
salts of morphine and codeine. Albumen of the blood, white of egg,
and the opium alkaloids in the proportion of ten parts per thousand, if
treated with Pettenkofer's test, all produce a color un distinguishable
from that obtained with the biliary salts. These substances, however,
with the exception of morphine, may all be excluded by previously
treating the fluid as above described ; namely, evaporating to dryness,
extracting with alcohol, precipitating with ether, and dissolving the
precipitate in water. The salts of morphine might still remain, as they
are soluble both in water and in alcohol, and may be precipitated by
ether from their alcoholic solution. This substance, however, is very
unlikely to be present in an extract of the animal fluids, especially in
the proportion of ten parts per thousand.

Pettenkofer's test is a very delicate one for either or both of the
biliary salts. A watery solution of pure sodium glycocholate, made in
the proportion of 1 part to 2000, yields, at the end of fifteen minutes, a
clear violet pink color, if the test be applied with care ; and a solution
of sodium taurocholate, in the proportion of 1 part to 3000, will give a
similar color at the end of an hour. The general characters of the test
are the same in both cases, as the reaction is really produced by cholic
acid, derived from the decomposition of either the glycocholic or tauro-
cholic acid of the original biliary salts.

Fig. 71.

SPECTBUM OF PETTENKOFER'S TEST, with the Biliary Salts in watery solution.

The spectrum of Pettenkofer's test presents certain characters which
may be of service in distinguishing it from the reactions produced by
other organic substances. Jf either or both of the biliary salts, dis-
solved in water, be treated with sugar and sulphuric acid until a violet
or purple color is produced, and the colored fluid then placed before the
slit of the spectroscope, its spectrum shows a wide and dark absorption
band at E, extending usually from midway between D and E to a
quarter part the distance between E and F, the central parts of the

214

THE BILE.

band being darker than the edges. Beyond the absorption band, the
light of the spectrum is dim, fading gradually and terminating some-
where about the line G.

When the purple color produced by Pettenkofer's test with the biliary
salts is very pronounced, it is usually found that the fluid is altogether
too opaque for spectroscopic examination, even in a layer of only one
centimetre. But if it be diluted with water, it becomes turbid, owing
to a re-precipitation of cholic acid, and the purple color disappears.
This difficulty, however, may be obviated by using a solution of the
biliary salts which is sufficiently dilute in the first instance. If sodium
glycocholate be dissolved in water, in the proportion of 1 part to 500, and
the solution treated with Pettenkofer's test, it gives in a few moments
a clear violet-pink color, which afterward becomes a rich purple. This
fluid is so opaque that, when placed before the slit of the spectroscope
in a layer of one centimetre, it extinguishes completely everything but
the red ; and yet it may be diluted with water without showing any tur-
bidity or losing its color. A watery solution of this strength is amply
sufficient to exhibit the reaction of Pettenkofer's test and the spectro-
scopic appearances belonging to it. If any solution, therefore, of the
biliary salts should prove, on trial, too opaque for spectroscopic exam-
ination when treated by Pettenkofer's test, another portion of it may be
diluted, before applying the test, until it is reduced to about the
strength of 1 part to 500. Even when a strongly colored purple fluid
has been rendered turbid and decolorized by the addition of water, its
transparency and color may be again restored by the addition of sul-
phuric acid ; but this method is less convenient than the former.

Fig. 72.

SPECTKUM OF PETTENKOFEK'S TEST, with the Biliary Salts in alcoholic solution.

If Pettenkofer's test be applied to the biliary salts in alcoholic solu-
tion, its spectrum is modified. There are now two absorption bands
instead of one. The first is situated at E, and is identical with that
obtained in a watery solution of the same salts. The second is at F,
and usually rather narrower and fainter than the first, although some-
times the two bands are of equal intensity.

The pink or purplish -red fluid, produced by Pettenkofer's test with

THE BILE.

215

both codeine and morphine, has a spectrum very similar to that of the
biliary salts. If the ruddy color of the fluid be strongly pronounced,
its spectrum, even when viewed in a layer of one centimetre, is very
short, terminating completely about midway between D and E, or even
before that point, showing the red and yellow clear and bright, but very
little of the green. If diluted with water, the mixture is not rendered
turbid, but its color is very much reduced, being soon changed to a
faint amber or often to a light apple-green, while the former peculiari-
ties of the spectrum disappear. The best way is to place the fluid
before the slit of the spectroscope in a layer of two centimetres before
its color is fully developed, and while it is still of a light pink. The
color then gradually becomes more pronounced, and, when it has at-
tained the proper degree of strength, the spectrum exhibits a certain
though ill-defined absorption-band at E. Beyond the band, the whole
spectrum is very dim, and terminates gradually between F and G.

The distinction between the spectrum of Pettenkofer's test with
biliary salts and that with the opium alkaloids is, that in the former
case the absorption-band at E is very marked and distinct, and often
quite black, when viewed in a layer of two centimetres' thickness, while
in the latter it is always dim and very ill-defined. With the biliary
salts, also, the fluid may frequently be diluted with its own or even
twice its volume of water, and the absorption-band still remain plainly
visible; but with morphine or codeine a very moderate dilution rapidly
destroys the character of the spectrum and causes the absorption-bar. d
to disappear.

Fig. 73.

SPECTRUM OF PETTENKOFEB'S TEST, with albumen.

The violet-colored fluid produced by Pettenkofer's test with albumen
has a well-marked and peculiar spectrum, easily distinguishable from
that belonging to the biliary salts. If tolerably dense, it requires to be
diluted with water for spectroscopic examination, and afterward cleared
up by the further addition of sulphuric acid. The spectrum then shows
a single absorption-band, extending from somewhere about the line E
to the line F, and occupying the intermediate space. In concentrated
specimens it may begin considerably to the left of E, and extend thence
to F. If the albuminous liquid be more dilute, it may reach only from

216 THE BILE.

a short distance beyond E to F. It is, therefore, always limited on the
right by the line F, but extends farther toward E and D, according to
the degree of concentration of the liquid. Its edsres are not very well
defined, but are more distinct when the band is narrow than when it is
wide. Beyond the band, the refrangible portion of the spectrum is
quite dim.

Mode of Secretion of the Bile. — It is a matter of importance, in
regard to the bile, as well as the other intestinal fluids, to ascertain
whether it be a constant secretion, like the urine and perspiration, or
whether it be intermittent, like the gastric juice, and discharged only
during the digestive process. Bidder and Schmidt have investigated
this point in the following manner : They operated by tying the common
bile-duct, and then opening the fundus of the gall-bladder, so as to pro-
duce a biliary fistula, by which the whole of the bile was drawn off.
By doing this operation, and collecting and weighing the fluid discharged
at different periods, they came to the conclusion that the flow of bile
begins to increase within two and a half hours after the introduction of
food into the stomach, but that it does not reach its maximum of activity
till the end of twelve or fifteen hours. Other observers, however, have
obtained different results. Arnold,1 for example, found the quantity to
be largest soon after meals, decreasing again after the fourth hour.
Kolliker and Miiller,3 again found it largest between the sixth and
eighth hours. It appears, accordingly, that the bile is not an intermittent
but a constant secretion ; and that the quantity produced varies with
the condition of the digestive process, being, according to the majority
of observers, most abundant some time after the digestion and absorp-
tion of food have commenced in the intestinal canal.

Discharge of Bile into the Intestinal Canal. — As, in those animals
which have been the subject of experiment, the liver is provided with a
gall-bladder, in which the secretion may be partially accumulated after
its production, and from which it may find its way at regular or irregular
intervals into the alimentary canal, it becomes important to ascertain
by other means at what time and in what quantity it is really discharged
into the intestine. In order to determine this point, we have performed
the following series of experiments on dogs. The animals were kept
confined, and killed at various periods after feeding, sometimes by the
inoculation of woorara, sometimes by hydroc}ranic acid, but most fre-
quently by section of the medulla oblongata. The contents of the
intestine were then collected and examined. In all instances, the bile
was also taken from the gall-bladder and treated in the same way, for
purposes of comparison. The intestinal contents always presented some
peculiarities of appearance when treated with alcohol and ether, owing
probably to the presence of other substances than the bile ; but they
always gave evidence of the presence of biliary matters as well. The

1 Cited in the American Journal of the Medical Sciences, April, 1856.
8 Ibid., April, 1857.

THE BILE.

217

CRYSTALLINE AND EKSINOUS BILIARY
SUBSTANCES; from Small Intestine of Dog,
after two days fasting.

biliary substances could almost Fig. 74.

always be recognized by the
microscope in the ether preci-
pitate of the alcoholic solution ;
both as a resinous matter,
under the form of rounded,
oily-looking drops (Fig. 74),
and also under the form of
crystalline groups, generally
presenting the appearance of
double bundles of slender,
radiating, slightly curved or
wavy, needle-shaped crystals.
These substances, dissolved in
water, gave a purple color with
sugar and sulphuric acid.
These experiments were tried
after the animals had been kept
for one, two, three, five, six,

seven, eight, and twelve days without food. The result showed that,
in all these instances, bile was present in the small intestine. The bile,
therefore, is not only constantly secreted by the liver in the intervals
of digestion, as well as during that
process, but it also continues to be
discharged into the intestine for
many days after the animal has
been deprived of food.

But the quantity of bile passing
into the intestine within a given
time is greatest soon after the com-
mencement of digestion. Our own
experiments bearing on this point
were performed on dogs, by mak-
ing a permanent duodenal fistula,
on the same plan as that used for
gastric fistulse (Fig. 75). An inci-
sion was made through the abdomi-
nal walls, a short distance to the
right of the median line, the floating
portion of the duodenum drawn up
toward the external wound, opened
by a longitudinal incision, and a
silver tube, armed at each end with
a narrow projecting flange, inserted
into it by one extremity, about
fourteen centimetres below the
pylorus, and seven centimetres
15

Fig. 75.

DUODENAL FISTULA — a. Stomach. 6.
Duodenum, c, c, c. Pancreas ; its two ducts
are seen opening into the duodenum, one
near the orifice of the biliary duct, d, the
other a short distance lower down. e. Silver
tube passing through the abdominal walls
and opening into the duodenum.

218

THE BILE.

below the orifice of the lower pancreatic duct. The other extremity of
the tube was left projecting from the external opening in the abdo-
minal parietes, the parts secured by sutures, and the wound allowed to
heal. After cicatrization was complete, and the animal had entirely
recovered his healthy condition and appetite, the intestinal fluids
were drawn off at various intervals after feeding, and their contents
examined. This operation, which is rather more difficult than that of
making a permanent gastric fistula, is nevertheless exceedingly useful
when it succeeds, since it enables us to study the actual time and rate
of the biliary discharge into the upper part of the intestinal canal.

In order to ascertain the absolute quantity of bile discharged into the
intestine, and its variations during digestion, the duodenal fluids were
drawn off, for fifteen minutes at a time, at various periods after feeding,
collected, weighed, and examined separately, as follows : each separate
quantity was evaporated to dryness, its dry residue extracted with
absolute alcohol, the alcoholic solution precipitated with ether, and the
ether-precipitate, regarded as representing the amount of biliary salts
present, dried, weighed, and then treated with Pettenkofer's test, in
order to determine, as nearly as possible, their degree of purity or ad-:
mixture. The result of these experiments is given in the following
table. At the eighteenth hour so small a quantity of fluid was obtained
that the amount of its biliary ingredients was not ascertained. It
reacted perfectly, however, with Pettenkofer's test, showing that bile
was really present.

DISCHARGE OF INTESTINAL AND BILIARY FLUIDS FROM DUODENAL FISTULA IN A
DOG WEIGHING 16.5 KILOGRAMMES.

Time after feed-
ing.

Quantity of fluid
in 15 minutes.

Dry residue of the
same.

Quantity of bili-
ary salts.

Proportion of bili-
ary salts in the
dry residue.

Immediately.
1 hour.

(Grammes.)
41.467
128.936

(Grammes.)
2.138
6.803

(Grammes.)
0.648
0.259

(Per cent.)
30
3

3 hours.

50.537

3.887

0.259

7

6

48.594

4.729

0.227

5

9

55.721

5.053

0.291

6

12

21.057

1.490

0.243

16

15

22.482

1.166

0.259

22

18

—

—

21

24.880

0.712

0.064

9

24

10.561

0.615

0.210

34

25

9.783

0.324

0.194

60

From this it appears that the bile passes into the duodenum in by far
the largest quantity immediately after feeding. This is undoubtedly
due to a contraction of the gall-bladder and a discharge of the surplus
bile accumulated in it during the interval of digestion. It is a matter
of common observation that the gall-bladder, in animals killed after a
day or two of fasting, is distended with an unusual quantity of thick
and dark-looking bile ; while in those killed immediately or soon after

THE BILE. 219

feeding, it is comparatively collapsed and empty. This evacuation of
the gall-bladder, excited by the ingestion of food, causes a sudden flow
of bile into the duodenum. After that time, its discharge remains pretty
constant ; not varying much, in a dog of sixteen and a half kilogrammes'
weight, from 256 milligrammes of the biliary salts every fifteen minutes,
or a little over one gramme per hour. In a man of ordinary size (65
kilogrammes), if the quantity of bile were increased in proportion, this
would amount to 8.667 grammes of solid biliary matter per hour dis-
charged into the intestine during the greater part of the digestive process.

Daily Quantity of the Bile. — The first experiments of value upon this
point were those of Bidder and Schmidt, published in 1852.1 They were
performed upon dogs, cats, sheep, and rabbits, in the following manner :
The abdomen was opened, and a ligature placed upon the common
biliary duct, so as to prevent the bile finding its way into the intestine.
An opening was then made in the fundus of the gall-bladder, by which
the bile was discharged externally. The bile, so discharged, was received
into previously weighed vessels, and its quantity accurately determined.
Each observation usually occupied about two hours, during which period
the temporary fluctuations occasionally observable in the quantity of
bile discharged were mutually corrected, so far as the entire result was
concerned. The animal was then killed, weighed, and carefully ex-
amined, in order to make sure that the biliary duct had been securely
tied, and that no inflammatory alteration had taken place in the ab-
dominal organs. The observations were made at different periods after
the last meal, so as to determine the influence exerted by the digestive
process upon the rapidity of the secretion. The average quantity of
bile for twenty-four hours was then calculated from a comparison of the
above results ; and the quantity of its solid ingredients was also ascer-
tained in each instance by evaporating a portion of the bile in the water
bath, and weighing the dry residue.

Bidder and Schmidt found in this way that the daily quantity of bile
varied considerably in different species of animals. It was much greater
in the herbivorous animals used for experiment than in the carnivora.
The results obtained by these observers were as follows :

For every kilogramme of the entire bodily weight of the animal, there
is secreted, in twenty-four hours,

Fresh bile. Dry residue.

In the cat . . . 14.537 grammes. 0.816 grammes.
" dog . . . 19.956 " 0.985

" sheep . . . 25.372 " 1.340

" rabbit . . . 136.556 " 2.464

According to the later researches of Schiff,2 these estimates are cer-
tainly not beyond the truth, since he obtained considerably larger
quantities in the dog, by simply establishing an open fistula of the gall-

Verdauungssaefte und Stoffwechsel. Leipzig, 1852.

Archiv fur die Gesammte Physiologie. Bonn, 1870, Band iii. p. 598.

220 THE BILE.

bladder, without tying the common biliary duct. While the average
quantity obtained in Bidder and Schmidt's experiments on the dog was
0.832 grammes of fresh bile per hour for every kilogramme of bodily
weight, in those of Schiff it was 1.3 to 3.2 grammes per kilogramme per
hour.

Since in the human subject the processes of digestion and nutrition
resemble those of the carnivora, rather than those of the herbivora, the
former should be selected to serve as a term of comparison in estimating
the probable daily quantity of the bile in man. If we apply accordingly
to the human subject the average of the results obtained by Bidder and
Schmidt from the cat and dog, the entire quantity of bile, for a man
weighing 65 kilogrammes, would be a little over 1 100 grammes per day.
Ranke1 obtained from direct observation a result not essentially different
from this. He collected at various times the bile discharged in a case
of biliary fistula in a man weighing only 47 kilogrammes, and found the
average quantity for twenty-four hours to be 652 grammes; the max-
imum quantity for the same period being .945 grammes. In a man of
65 kilogrammes' weight this would correspond, for the average, to 902
grammes, and for the maximum to 1307 grammes. The entire quantity
of bile, therefore, for a man of medium size, is evidently not far from
1000 grammes per day. This contains about 30 grammes of solid ingre-
dients.

Decomposition of the Biliary Matters in the Intestine. — Observers
generally are agreed that the biliary salts, though constantly poured
into the upper part of the intestinal canal, are not discharged with the
feces. Although traces of them are sometimes to be found in the evacua-
tions, they are always very far from representing the total quantity pro-
duced by the liver, and as a general rule they disappear altogether in
their passage through the intestine. This may be readily demonstrated
by experiments upon dogs, which are conducted in the following man-
ner. The animals are to be fed with fresh meat, and then killed at
various intervals after the meals, the abdomen opened, ligatures placed
upon the intestine at various points, and the contents of its upper,
middle, and lower portions collected and examined separately. The
results thus obtained show that, under ordinary circumstances, the bile,
which is quite abundant in the duodenum and upper part of the small
intestine, diminishes in quantity from above downward, and is not to be
found in the large intestine. The entire quantity of the intestinal con-
tents also diminishes and their consistency increases, as we approach
the ileo-csecal valve ; and at the same time their color changes from a
light yellow to a dark bronze or blackish-green, which is always strongly
pronounced in the last quarter of the small intestine.

If the contents of the small and large intestine be furthermore evapo-
rated to dryness, extracted with absolute alcohol, and the alcoholic solu-
tions precipitated with ether, the quantity of ether-precipitate being

1 Grundziige der Physiologie des Menschen. Leipzig, 1872, p. 284.

THE BILE. 221

regarded as representing approximately that of the biliary substances
proper, the result shows that the quantity of ether-precipitate is, both
positively and relatively, very much less in the large intestine than in
the small. Its proportion to the entire solid contents is only one-fifth
or one-sixth as great in the large intestine as it is in the small. But
even this inconsiderable quantity, found in the contents of the -large
intestine, does not consist of biliary matters ; for, the watery solutions
being treated with sugar and sulphuric acid, those from both the upper
and lower portions of the small intestine always give Pettenkofer's reac-
tion perfectly in less than a minute and a half; while in that from the
large intestine no red or purple color is usually produced, even at the
end of three hours.

The small intestine consequently contains, at all times, substances
presenting the usual reactions of the biliary ingredients ; while in the
contents of the large intestine no such substances can be recognized by
Pettenkofer's test.

It is not possible to say, however, what is the precise nature of the
changes undergone by the biliary salts in the intestinal canal. The sup-
posed decomposition of these salts by contact with the acid secretions
of the alimentary canal, and the separation of the glycine, taurine, and
cholic acid of their organic ingredients, with their subsequent transfor-
mations, are all more or less hypothetical, and without sufficient basis of
experimental evidence. The biliary matters in the intestine pass, by
decomposition or metamorphosis, into the condition of other unknown
substances which do not respond to Pettenkofer's test.

Physiological Function and Destination of the Bile. — The physio-
logical function of the bile is still very obscure. With regard to its
action in the digestive process, we may say that nothing whatever is yet
known which can account for' the constant presence of so important and
peculiar a secretion. By itself, in experiments on artificial digestion, it
does not exhibit any direct action upon either of the principal alimentary
substances, of such a definite character as those which belong to the gas-
tric, pancreatic, and intestinal juices ; its action being limited to simple
solution of a certain proportion of oily matter, and to a feeble and incon-
stant transforming power upon hydrated starch. Two other actions have
also been attributed to it, from certain properties which observation
shows it to possess ; namely, first, that of exciting the secretions and
peristaltic movement of the intestine and thus serving as a natural
cathartic, and secondly, that of facilitating the absorption of oily matters
by the intestinal mucous membrane. But although the bile is found, when
applied to the muscular coat of the intestine, to excite its contraction,
and similar effects are thought to have been seen even in the villi, yet
the alimentary canal is known to be naturally excited to action by the
ingestion of food, or its downward passage from other parts ; and there
is nothing to show that the intestine, below the orifice of the biliary
duct, should require any peculiar or exceptional stimulus for the excite-
ment of its normal actions. It is true, in the second place, that the bile

222 THE BILE.

has been shown, by direct experiment, to facilitate the passage of oily
matters by osmosis through closed organic membranes or parchment
paper ; that is, oily matters will pass through these membranes more
readily when they are moistened with bile, than when simply wetted
with water ; and it is upon these experiments that the supposed func-
tion of the bile, in effecting the absorption of oil in the intestine, has
been based. But the villi of the intestine are not simply membranes
moistened with water. They are penetrated throughout by alkaline and
albuminous fluids, their bloodvessels contain an abundance of organic
material in the liquid form, and the fatty emulsion formed by the pan-
creatic juice is itself fully adapted for absorption by the villi. There
seems to be no good reason for assigning to the physical properties of
the bile, in this respect, any special importance for the absorption of
fatty substances.

An action of quite the opposite nature has also been attributed to the
bile, namely that of precipitating the half-digested ingredients of the
food from their solution in the gastric juice. But there is reason to
believe that this also rests upon an error, and that there is no such
antagonism between the bile and the gastric juice in the intestine as
when they are mingled together in a test-tube.

It has already been stated (page 159) that the bile precipitates by con-
tact with the gastric juice. If one or two drops of dog's bile be added
to as many cubic centimetres of fresh gastric juice from the same ani-
mal, a copious yellowish-white precipitate falls down, containing the
whole of the coloring matter of the bile which has been added ; and if
the mixture be then filtered, the filtered fluid passes through quite color-
less. The gastric juice, however, still retains its acid reaction. This
precipitation depends upon the presence of the biliary substances proper,
namely, the sodium glycocholate and taurocholate ; for if the bile be
evaporated to dryness and the biliary substances extracted by alcohol
and precipitated by ether in the usual manner, their watery solution will
precipitate with gastric juice, in the same way as fresh bile would do.

Although the biliary matters, however, precipitate by contact with
fresh gastric juice, they do not do so with gastric juice which holds albu-
minose in solution. We have invariably found that if the gastric juice
be digested for several hours at the proper temperature with boiled
white of egg, the filtered fluid, which contains an abundance of albu-
minose, will no longer give the slightest precipitate on the addition of
bile or of a watery solution of the biliary substances, even in very large
amount. The gastric juice and the bile, therefore, are not finally incom-
patible with each other in the digestive process, notwithstanding the
reaction which takes place between them when artificially mingled.

Although, however, the bile cannot be shown to exert any direct
action in the digestion of the food, similar to that of the other intestinal
fluids, yet there is evidence that it takes part, in the intestine, in some
process which is important, and even, in the long run, essential to life.
This is shown by the fact that if the bile be permanently diverted from

THE BILE. 223

the cavity of the intestine by closure of the common bile-duct, and
evacuated by a fistula of the gall-bladder, the animals which are the
subjects of the operation gradually emaciate, and die with general
symptoms of disordered nutrition.

This experiment has been successfully performed at least ten times by
Schwann, Bidder and Schmidt,1 Bernard,2 and Prof. A. Flint, Jr.,3 the
animals surviving the immediate effects of the operation, the biliary
fistula remaining open, and the common bile-duct, as shown by subse-
quent post-mortem examination, being permanently closed so that none
of the bile could have found its way into the intestine. The general
results were alike in these cases. The animals died with the signs of
inanition, usually between 30 and 40 days after the operation ; although
in one instance death occured at the end of the seventh day, and in
another not until the eightieth. The average length of life, in all the
cases taken together, was 36 days. The symptoms were constant and
progressive emaciation, which proceeded to such a degree that nearly
every trace of fat disappeared from the body. The loss of flesh amounted,
in one case, to more than two-fifths, and in another to nearly one-half
the entire weight of the animal. There was also sometimes a falling off
of the hair, and an unusually disagreeable, putrescent odor in the feces
and in the breath. Notwithstanding this, the appetite remained good.
Digestion was not essentially interfered with, and none of the food was
discharged with the feces ; but there was, in the cases of Bidder and
Schmidt, much rumbling and gurgling in the intestines, and abundant
discharge of flatus, more strongly marked in one instance than in the
other. There was no pain ; and death took place, at last, without any
violent symptoms, but by a simple and gradual failure of the vital
powers.

It appears therefore that the bile is not simply an excrementitious fluid
destined to be eliminated from the system ; but that, after being secreted
and discharged by the liver, it must pass into and through the small
intestine, in order to maintain the continuous and healthy nutrition of
the body. We have already seen, furthermore, that its most essential
ingredients, namely, the biliary salts, disappear during their passage
through the alimentary canal, and are not to be found in the fecal
evacuations. This may be accounted for in two different ways. Either
the biliary salts, while in the intestine, may become altered and insolu-
ble, so as to lose their reaction with Pettenkofer's test, and be finally
evacuated with the feces under this insoluble form; or, on the other
hand, they may be reabsorbed from the alimentary canal and thus re-enter
the circulation as ingredients of the blood.

The conclusion generally adopted by physiologists is that they are
reabsorbed. The most positive evidence on this point is that derived

1 Yerdauungssaefte und Stoffwechsel. Leipzig, 1852, p. 103.

2 Liquides de 1'Organisme. Paris, 1859, torn. ii. p. 199.

3 Physiology of Man. New York, 1867, p. 369.

224 THE BILE.

from the experiments of Bidder and Schmidt on the quantity of sulphur
contained in the feces of the dog, as compared with that in the tauro-
cholic acid of his biliary salts. The significance of these experiments
depends upon the fact that the biliary salts themselves, being compound
bodies, might be so altered by decomposition in the intestine as to lose
their characteristic reactions, and yet their separated materials might
remain ; but as sulphur, on the other hand, is a chemical element, not
decomposable by any known means, it must be capable of detection, if
present, by ultimate analysis. The dog was selected as the subject of
experiment, for the reason that the bile in this animal contains so large
a proportion of the sodium taurocholate, of which sulphur is a constituent
part.

The results obtained by Bidder and Schmidt1 showed that the quantity
of sulphur evacuated in the feces was much less than that discharged
into the intestine with the bile.

These observers collected and analyzed all the feces passed, during
five days, by a healthy dog, weighing 8 kilogrammes. The entire fecal
mass during this period weighed 97.716 grammes,

("Water 56.642 grammes.

I Solid residue .... 41.074 "

97.716
The solid residue was composed as follows : —

Neutral fat, soluble in ether . . 2.832 grammes.

Fat, with traces of biliary matter . 4.991 "

Alcohol extract, with biliary matter 3.816 containing 0.070 of sulphur.

Substances not of a biliary nature

extracted by muriatic acid and

hot alcohol .... 9.641 containing 0.085 of sulphur.

0.155

Fatty acids with oxide of iron . 6.377
Residue consisting of hair, sand, etc. 13.417

41.074

As it has already been shown (page 219) that the dog secretes, during
24 hours, 0.985 gramme of solid biliary matter for every kilogramme
of bodily weight, the entire quantity of biliary matter secreted in five
days by the above animal, weighing 8 kilogrammes, must have been
39.4 grammes, or nearly as much as the whole weight of the dried feces.
But furthermore, the natural proportion of sulphur in dog's bile, derived
from the sodium taurocholate, is 6 per cent, of the dry residue. The
39.4 grammes of dry bile, secreted during five days, contained, there-
fore, 2.364 grammes of sulphur. But the entire quantity of sulphur,
existing in any form in the feces, was 0.385 gramme ; and of this only
0.155 gramme could have been the product of biliary matters — the re-

1 Yerdauungssaefte und Stoffwechsel. Leipzig, 1852, p. 217

THE BILE. 225

mainder being derived from the hairs which are always contained in
abundance in the feces of the dog. That is, not more than one-fifteenth
part of the sulphur originally present in the bile could be detected in
the feces. It must, accordingly, have been reabsorbed from the intestine.

A still further corroboration of the reabsorption of the biliary materials
from the intestinal canal is furnished by the very careful and ingenious
experiments of Schiff,1 performed in a different manner. This observer
found that, in animals provided with a gall-bladder, less pressure is re-
quired to make a fluid pass from the hepatic duct into the cavity of the
gall-bladder than to force it through the common duct into the intes-
tine. Unless, therefore, the pressure under which the bile is secreted be
increased, either by distension or by muscular contraction, it passes into
the gall-bladder more readily than into the intestine ; and a fistula of the
fundus of the gall-bladder, if kept freely open, will be of itself sufficient
to discharge all, or nearly all, the secreted bile, without any considerable
portion of it reaching the intestine. He demonstrated furthermore that
this was really the fact by establishing at the same time, in the same
animal, a fistula of the gall-bladder and one of the duodenum. So long
as the cystic fistula remained open, either no biliary matters, or only
insignificant traces of them, could be detected in the fluids drawn from
the duodenum.

The advantage, for certain purposes, of this method of operating,
over that in which the common duct is also tied and obliterated, is that
by the last operation the bile is permanently shut off from the intestine,
in consequence of which the animal soon passes into an abnormal and
enfeebled condition. One of the earliest results of this unhealthy state
is a diminution in the daily quantity of bile secreted. On the other
hand, by Schiff 's method, so long as the cystic fistula is closed, the bile
continues to pass through the common duct into the intestine, thus
maintaining the animal in a healthy condition. At any time, however,
by opening the cystic fistula and emptying the gall-bladder, the rate at
which the bile is secreted may be observed with facility. It has already
been mentioned that larger quantities of bile were usually obtained by
this than by the older method.

The observations of Schiff show that by leaving open the cystic fistula,
and thus practically diverting all the bile from the intestine, its rate of
secretion by the liver is at once diminished, so that even at the end of
twenty-four hours, if the influence of digestion be eliminated, it is already
reduced to a minimum, and this minimum continues afterward with only
insignificant fluctuations. On the other hand, if, in the same animal,
the fistula be kept closed for some hours, the quantity of bile soon rises
to its normal standard.

The same observer experimented upon the dog with similar results
by making a duodenal fistula, through which he introduced a canula into
the orifice of the common bile-duct. This canula had a lateral opening

1 Archiv fiir die Gesammte Physiologic. Bonn, 1870, p. 598.

226 THE BILE.

near its inner end, which might be left open or kept closed by shifting
the position of an inner tube fitting closely in the canula. Thus the bile
might be at will either discharged externally from the orifice of the
canula, or allowed to pass into the duodenum by its lateral opening. It
was found that, after being discharged externally for even two or three
hours previously to the examination, its rate of secretion was much less
than if it had been allowed to pass into the intestine. The results
obtained, in a dog weighing 12 kilogrammes, were as follows:

CUBIC CENTIMETRES OF BILE OBTAINED IN TEN MINUTES AFTER HAVING BEEN,
FROM Two TO THREE HOURS,

Evacuated externally. Discharged into the duodenum.

2.2 6.0

2.3 5.4
2.1 5.6
2.0 6.2

1.8 6.5

1.9 5.7

Average . . 2.05 5.90

Thus the quantity of bile secreted, when it has been allowed to follow
its natural course into the duodenum, is nearly three times as great as
when it has been evacuated through the external fistula. It does not
necessarily follow from this that it is again directly used for secretion
by the liver, since this process may be influenced by a variety of sec-
ondary conditions ; but it is difficult to avoid the conclusion that its
ingredients are absorbed from the intestinal cavity, and supply in some
way the materials for continued secretion.

Before their reabsorption, however, the biliary salts undergo certain
alterations in the alimentary canal, so that when finally taken up by the
bloodvessels, they have already assumed a different form; otherwise
they could be detected in the blood of the portal vein. But such re-
searches have constantly led to a negative result. Our own experiments
on this point were performed on dogs, by examining the portal blood
obtained at different periods after feeding. The animals were killed by
section of the medulla oblongata, a ligature immediately placed on the
portal vein, while the circulation was still active, and the requisite
quantity of blood collected by opening the vein. The blood was some-
times immediately evaporated to dryness by the water-bath. Sometimes
it was coagulated by boiling in a porcelain capsule over a spirit lamp,
with water and an excess of sodium sulphate, and the filtered watery
solution afterward examined. But most frequently the blood, after
being collected from the vein, was coagulated by the gradual addition
of three times its volume of alcohol, stirring the mixture constantly, so
as to make the coagulation gradual and uniform. It was then filtered,
the moist mass remaining on the filter subjected to strong pressure in a
linen bag, by a porcelain press, and the fluid thus obtained added to that
previously filtered , The entire spirituous solution was then evaporated

THE BILE. 227

to dryness, the dry residue extracted with absolute alcohol, and the
alcoholic solution treated as usual to discover the presence of biliary
matters. In every instance, blood was taken at the same time from the
jugular vein, or the abdominal vena cava, and treated in the same way
for purposes of comparison.

We have examined the blood, in this way, one, four, six, nine, eleven
and a half, twelve, and twenty hours after feeding. The result shows
that in the venous blood, both of the portal vein and of the general circu-
lation, there exists a substance soluble in water and in absolute alcohol,
and precipitable by ether from its alcoholic solution. This substance
is often considerably more abundant in the portal blood than in that
taken from the general venous system. It adheres closely to the sides
of the glass vessel after precipitation, so that it is always difficult, and
often impossible, to obtain enough of it, mixed with ether, for micro-
scopic examination. It dissolves, also, like the biliary substances, with
great readiness in water ; but in no instance have we ever been able
to obtain from it such a reaction with Pettenkofer's test, as would
indicate the presence of bile. This is not because the reaction is
masked by any other ingredient of the blood ; for if, at the same time, a
little bile be added to blood taken from the abdominal vena cava, in the
proportion of one drop of bile to seven or eight cubic centimetres of
blood, and the two specimens treated alike, the ether-precipitate may
be considerably more abundant in the case of the portal blood ; and yet
that from the blood of the vena cava, dissolved in water, will give Pet-
tenkofer's reaction for bile perfectly, while that of the portal blood will
give no such reaction.

Notwithstanding the evidence, therefore, that the biliary matters are
absorbed by the portal blood, they cannot be recognized there by Pet-
tenkofer's test. They must accordingly have passed through such
changes, in the intestine, previously to their absorption, that they can
no longer give the ordinary reaction of the biliary salts. We cannot
say precisely what these changes are, but they are undoubtedly depen-
dent upon the action of the intestinal juices, and are therefore more rapid
while the process of digestion is going on. This is probably the ex-
planation of the fact that the bile, though a continuous secretion, is dis-
charged into the alimentary canal in greatest abundance immediately
after the ingestion of food ; since it is not so much needed to assist the
intestinal juices in the process of digestion, as to be itself acted on by
them and converted into other materials.

The bile, accordingly, is a secretion which has not yet accomplished
its function when it is discharged from the liver and poured into the
intestine. While in the cavity of the alimentary canal, in contact with
its glandular surface, and mingled with the intestinal juices, its ingre-
dients lose their original character and pass into the form of new com-
binations. These substances again enter the circulation by absorption
from the intestinal cavity, and are carried away by the blood, to com-
plete their function in some other part of the body.

CHAPTEE XI.

PRODUCTION OF GLYCOGEN AND GLUCOSE IN THE

LIVER.

IP the liver of a carnivorous or herbivorous animal, after twenty-four
hours' fasting, be taken from the body immediately after death, finely
divided, and boiled for a few moments in water with animal charcoal or
an excess of sodium sulphate, to eliminate the albuminous and coloring
matters, the filtered fluid will be nearly clear, or show only a moder-
ately opaline tinge. But if the same thing be done within a few hours
after the ingestion of animal or vegetable food, the watery decoction of
the liver tissue will be strongly opalescent, being rendered turbid by
the presence in considerable quantity of a matter which communicates
to the solution a partial turbidity. This matter is glycogen, which is
contained, in greater or smaller quantity, in the liver extract under these
two conditions.

This substance, first discovered by Bernard, has so strong an analogy,
in its composition and properties, with the ordinary amylaceous matter
of vegetable tissues, that it is often spoken of as "animal starch." It
is, when purified, a non-nitrogenous body, having the formula C6H1005.
It is accordingly a carbohydrate, and indentical with starch in its ulti-
mate chemical composition.

It is obtained from the liver by first cutting the organ into small
pieces and immediately coagulating them by a short immersion in boil-
ing water. This is for the purpose of prevening the partial transforma-
tion of the glycogen which would otherwise take place, under the influ-
ence of a moderate temperature, by contact with the albuminous matters
present in the liver. These albuminous matters having been once
coagulated by the preliminary boiling, the glycogen can afterward be
extracted at leisure. The liver tissue is then ground to pulp in a
mortar and boiled continuously for half an hour with a small quantity
of water, just sufficient to keep the mixture fluid, in order to obtain a
decoction as concentrated as possible. The decoction is then treated
with animal charcoal, to remove the coloring matters, and filtered. The
solution is distinctly opaline, and if allowed to fall into a vessel of strong
alcohol, the glycogen, which is insoluble in this fluid, is precipitated in the
form of a white deposit. This deposit is still contaminated by a little
glucose, and by a certain quantity of biliary salts and other nitrogenous
matters. The glucose and biliary salts are removed by repeatedly
washing the precipitate with alcohol. The deposit is then boiled for
a quarter of an hour with a concentrated solution of potassium hydrate,
( 228 )

GLYCOGEN AND GLUCOSE IN THE LIVER. 229

which dissolves the albuminous matters, but does not affect the gly-
cogen. After being separated by filtration it is again dissolved in
water, the traces of alkali removed by the addition of a little acetic
acid, and the glycogen then precipitated anew, in a pure form, by
alcohol in excess. It is then dried and may be kept in the form of a
white pulverulent mass, which retains its properties for an indefinite
time.

Glycogen thus prepared is soluble in water, its solution having an
opalescent tinge. Treated with iodine, it gives a violet color, inter-
mediate between the blue reaction of starch and the red of dextrine.
It does not reduce the copper salts in Trommer's test, nor give rise to
fermentation with yeast ; but it is converted into dextrine and glucose
by all those agencies which have a similar effect upon starch — namely,
prolonged boiling with dilute mineral acids, the contact of vegetable
diastase, of saliva, the pancreatic juice, and the serum of blood at a
moderately warm temperature. If allowed to remain in the liver after
death, a part of it suffers transformation into glucose by contact with
the fluids of the hepatic tissue.

Origin and Mode of Formation of Glycogen. — As this substance is
present in the liver tissue of both carnivorous and herbivorous animals,
it may be derived from the materials of either kind of food. In the
carnivora, at least, there is evidence that it is supplied from nitrogenous
materials, by the nutritive changes which they undergo in the substance
of the liver. Under some circumstances a material resembling glycogen,
or identical with it, may be present in the muscles of the herbivora.
Bernard has found it in the muscular tissue in rabbits, and especially in
pigeons, when fed upon the cereal grains, and in horses kept upon oats
and barley; but in all these animals it disappears when the food is
changed, or after some days' fasting. Lnchsinger1 has also found it to
be absent from the muscles of the rabbit after several days' fasting, but
to continue more persistently in the pectoral muscles of the fowl under
similar conditions.

It is accordingly not a constant but only an occasional ingredient of
muscular flesh, and when present is usually found in very small quan-
tity. Poggiale,2 in very many experiments instituted for this purpose
by a Commission of the French Academy of Sciences, found glycogen
present in ordinary butcher's meat only once. We have also found it
to be absent from the fresh meat of the bullock's heart, when examined
in the manner described above. Nevertheless, in dogs fed exclusively
for eight clays upon this food, glycogen may be abundant in the liver,
while it does not exist in the other internal organs, as the spleen, lungs,
and kidneys.

The production of glycogen from nitrogenous substances is also
shown, according to Bernard, by the fact that it makes its appearance

1 Archiv fur die Gesammte Physiologie, 1873. Band viii. p. 290.

2 Journal de la Physiologie. Paris, 1858, p. 558.

230 PRODUCTION OF

in the bodies of maggots during the course of their development,
although neither the eggs from which they are hatched, nor the putrefy-
ing meat upon which they feed, contain any appreciable traces of this
substance.

Glycogen is produced, however, in especial abundance in the liver,
after the ingestion of starchy and saccharine food. Bernard1 found the
decoction of the liver tissue in the dog, after feeding for two days with
bread and starch paste, very turbid and milky in appearance. Subse-
quent experiments by the same observer2 have shown that a starchy
diet augments notably the quantity of glycogen existing in the liver.
This fact was first demonstrated in a special manner by the observations
of Pavy,3 who, by comparative experiments upon dogs fed with animal
and vegetable food, found that the influence of the latter was to increase
very decidedly the weight of the whole liver, and also the pencentage
of glycogen which it contained. The same effect was produced by a
diet of animal food with sugar in addition. The following table gives
the average results of three series of observations by Pavy :

AVERAGE PRODUCTION OF GLYCOGEN, IN DOGS, UNDER DIET OF ANIMAL AND
VEGETABLE FOOD.

Diet for "Weight of liver, Glycogen in the

several days in percentage of fresh liver,

previously. bodily weight. per cent.

Tripe 3.03 7.19

Tripe and sugar . . . 6.42 14.50

Meal, bread, potatoes . . 6.06 17.23

Experiments on the rabbit also showed that in this animal both the
weight of the liver and its percentage in glycogen are much diminished
by several days' fasting, but are maintained at the maximum standard,
for a time at least, by a diet consisting exclusively of the carbohydrates.
The average results were as follows :

AVERAGE PRODUCTION OF GLYCOGEN IN RABBITS, TN THE FASTING CONDITION AND
WHEN FED ON CARBOHYDRATES.

Diet for Absolute weight Glycogen in the

three days of liver fresh liver

previously. (grammes). (per cent.).

No food 34.02 1.35

Starch and sugar . . . 73.71 16.15

The quantity of glycogen found in the liver by Pavy is considerably
greater than that obtained by subsequent observers under similar cir-
cumstances, and is attributed to his having employed an imperfect
method of purification ; but the principal fact of the increase of glycogen
under the use of the carbohydrates has been confirmed by several other

1 LeQons de Physiologic Experimentale. Paris, 1855, p. 159.

2 Revue des Sciences Medicales. Paris, 1874, torn. iii. p. 34.

3 On the Nature and Treatment of Diabetes. London, 1862.

GLYCOGEN AND GLUCOSE IN THE LIVER. 231

experimenters. Dock found, in his experiments on the rabbit,1 that after
from 3 to 5 days' fasting the glycogen in the entire liver was reduced
to a very minute quantity, or more frequently was entirely absent.
But if, in this condition, a solution of glucose were introduced into the
stomach through a catheter, and the animal killed from 19 to 24 hours
afterward, the quantity of glycogen contained in the liver amounted to
from 0.650 to 1.243 grammes. After even t days' fasting, followed by
an injection of glucose into the stomach, so short a time as four hours
was sufficient to produce an abundance of glycogen in the liver. The
deposit of this substance accordingly takes place so rapidly after the
ingestion of this kind of food, that no doubt can remain of its being
directly produced from the materials of the saccharine or starchy sub-
stances.

Tscherinow showed, by his observations on fowls,2 both the production
of glycogen from animal food, and also its more abundant deposit under
a vegetable diet. He found that, in this species, two days7 fasting was
sufficient to reduce the quantity of glycogen to a minimum. After
being subjected to a preliminary fast of this duration, the fowls were
fed for two or three days with different kinds of food, and then killed
and examined. The average results were as follows :

PRODUCTION OF GLYCOGEN IN FOWLS UNDER DIFFERENT KINDS OF DIET.
Diet previous to the Glycogen in the fresh

experiment. liver, per cent.

Fasting, 2 days 0.57

Lean meat, 2 to 4 days ....... 1.40

Barley, 2 days 5.41

Kice, 2 days 7.21

Fibrine and sugar, 2 to 3 days 10.20

It appears furthermore from the experiments of Weiss and Luch-
singer3 that a similar increase of glycogen will take place in the liver
after the ingestion of glycerine (C3H8O3), a substance closely related in
chemical composition to the carbohydrates, but not under the use of fat
or of the alkaline tartrates or lactates.

There is accordingly every reason for the belief that the carbohydrates,
when taken in with the food, are at once transported to the liver by the
portal circulation, and there fixed in its substance under the form of
glycogen. It makes no difference, in this respect, whether these sub-
stances be taken as starch or as sugar ; since starchy matters are always
transformed into glucose by the process of digestion, to be afterward
absorbed by the bloodvessels of the intestine. It is under the form of
glucose, therefore, that they all enter the portal circulation and thus
reach the tissue of the liver. The process of the conversion of this sub-

1 Archiv fur die Gesammte Physiologic. Bonn, 1872, Band v. 571.

2 Archiv fur Pathologische Anatomic und Physiologic, 1869, Band xlvii. p. 102.

3 Archiv flir die Gesammte Physiologic, 1873, Band viii. p. 290.

232 PRODUCTION OF

stance into glycogen is a dehydration; that is, the separation from it
of the elements of water, as follows :

Glucose. Water. Glycogen.

C6H1206 - H20 = CCH1005.

It is not possible to say in what manner or by what influence this
change takes place ; but it is one of the simplest actions manifested by
organic substances, and is known to occur, as well as the opposite change
of hydration, in many of the phenomena of both animal and vegetable
nutrition. The formation of glycogen from albuminous materials is a
more complicated process, and is necessarily accompanied by the appear-
ance of another secondary product containing nitrogen ; but we have no
certain knowledge as to what this substance may be, or whether there
may not be several new compounds formed at the same time.

Transformation of Glycogen into Sugar. — One of the most marked
characters of glycogen, as extracted from the liver tissue, is its ready
convertibility into glucose by contact with certain organic matters con-
tained in the secretions and in the blood. This change takes place
partially in the liver itself; and the consequence is that in a state of
health the tissue of the organ always contains glucose as well as gly-
cogen. In fact, the existence and production of sugar in the liver was
a discovery anterior to that of glycogen, having been demonstrated b}'
Bernard1 in 1848. The experiments of this observer, the most important
of which have been repeatedly confirmed by others, show that the glu-
cose found in the liver of both carnivorous and herbivorous animals has
an internal origin, and that it first makes its appearance in the hepatic
tissue itself.

If a dog, cat, or other carnivorous animal, be fed for several days
exclusively upon meat and then killed, the liver alone of all the internal
organs is found to contain glucose. For this purpose, a portion of the
organ should be cut into small pieces, reduced to a pulp by grinding in
a mortar with a little water, and the mixture coagulated by boiling with
an excess of sodium sulphate. The filtered fluid will then reduce the
oxide of copper, with great readiness, on the application of Trommer's
test. A decoction of the same tissue, mixed with a little yeast, will
also give rise to fermentation, producing alcohol and carbonic acid, as
is usual with saccharine solutions. On the contrary, the tissues of
the spleen, the kidneys, the lungs, and the muscles, treated in the same
way, give no indication of sugar, and do not reduce the salts of copper.
Every other organ in the body, as well as the blood of the portal vein
by which the liver is supplied, may be destitute of sugar, while the liver
always contains it, provided the animal be healthy.

The presence of sugar in the liver is common to all species of animals,
so far as yet known. Bernard found it invariably in monkeys, dogs,
cats, rabbits, the horse, the ox, the goat, the sheep, in birds, in reptiles,

1 Comptes Rendus de 1'Academie des Sciences. Paris, 1850, tome xxxi. p. 571.

GLYCOGEN AND GLUCOSE IN THE LIVER. 233

and in most kinds of fish. ' It was only in two species of fish, namely, the
eel and the ray (Muraena anguilla and Eaia batis), that he sometimes
failed to discover it ; but the failure in these instances was apparently
owing to the commencing putrescence of the tissue, by which the sugar
had probably been destroyed. In the fresh liver of the human subject,
examined after death from accidental violence, sugar was found to be
present in the proportion of 1.10 to 2.14 per cent, of the entire weight
of the organ.

The following list shows the average percentage of sugar present in
the healthy liver of man and different species of animals, according to
the examinations of Bernard :

PERCENTAGE OF GLUCOSE IN THE LIVER.

In man . . . 1.68 In ox . . . . 2.30

" monkey . . . 2.15 " horse . . . 4.08

« dog . . . . 1.69 " goat .... 3.89

" cat . . . . 1-94 " birds .... 1.49

" rabbit . . . 1.94 " reptiles . . . 1.04

" sheep . . . 2.00 " fish . . . . 1.45

The glucose thus found in the liver originates by transformation of
the glycogen of the hepatic tissue. As glycogen diminishes in quantity
or disappears altogether by continued fasting, and is again produced
from the ingestion of animal food, the glucose which is derived from it
exhibits similar fluctuations. In the carnivorous animals, sugar is pre-
sent in the liver, although no carbohydrates have been given with the
food for an indefinite time. Bernard kept a dog under observation
for three months upon an exclusive diet of boiled calves' heads, and
another for eight months upon scalded tripe. At the end of that
time the liver in each case contained the usual quantity of glucose.
We have also found that in the dog, after an exclusive diet for eight
days of the fresh meat of the bullock's heart, the liver contains both
glycogen and sugar, while neither of these substances exists in the
blood of the portal vein. The diminution of glucose by fasting, and its
reappearance under the influence of animal food, were shown by Ber-
nard in the following way : Nine rats, taken in the sewers beneath the
College of France, were used for experiment. Three of them were at
once killed and their livers found to be highly saccharine. The remainder
were then kept without food for four days. At the end of that time
three of them were killed, and their livers, upon examination, found to
be nearly destitute of sugar, only slight traces being discovered, too
small for quantitative determination. The glucose which existed, ac-'
cordingly, in the livers of these animals at the time of their capture,
had disappeared during their four days' period of fast. The remaining
three were then supplied with a meal of raw beef, and when killed, six
hours afterward, their livers contained an abundance of sugar.

The most distinct proof that the saccharine matter of the liver origi-
16

234 PRODUCTION OF

nates in the tissue of the organ itself, by transformation of the glycogen,
is that it continues to be formed for a certain length of time after death,
provided the liver "contain glycogen. This fact also was first shown by
Bernard,1 and is easily verified. If the liver of a healthy dog be taken
out of the body immediately after death, and injected with water by the
portal vein, the watery injection which escapes by the hepatic vein, after
traversing the liver-tissue, will be found to contain sugar. But, as the
injection is continued, the quantity of glucose extracted by it from the
liver grows constantly less, until, in from half an hour to an hour, it is
completely exhausted, and at the end of this time neither the injected
fluid nor the hepatic tissue contains any trace of glucose. If such a
liver be kept in a moderately warm place for some hours it will again
be found abundantly saccharine. The glucose may be again exhausted
by a fresh injection and again reproduced, until all the glycogen has
been transformed or until the changes of decomposition begin to be
established. The glycogen itself, being less soluble than the sugar,
remains behind after such an injection, and produces a new supply of
glucose by a new transformation.

Immediately after death, accordingly, if the liver be allowed to remain
saturated with its natural organic juices, the transformation of its gly-
cogen takes place at first with considerable rapidity ; approximating, no
doubt, the rate at which this transformation takes place during life.
Within the first hour, according to our own observations in the dog,
the glucose in the liver tissue is increased to between 4.81 and 5.66
times its original amount. After this the change goes on more slowly,
its rate diminishing with the lapse of time, so that at the end of twelve
hours the sugar may have increased to not more than 5.73 times its
former quantity. The following table gives the results of three ex-
periments in this direction.

PROPORTION OF GLUCOSE IN THE LIVER OF THE DOG, AT DIFFERENT PERIODS AFTER

DEATH.

No. 1.

No. 2.

No. 3.

In the tables of Bernard (page 234), the results are drawn mostly from
livers examined some time after death, and according^ represent, not

1 Gazette Hebdomadaire. Paris, 5 Octobre, 1855.

At the end of

Per thousand parts.

810

15 minutes .

..... 792

1 hour

10.260

3.850

6 hours

11.458

4 seconds .

2.675

11.888

4 hours

13.361

12 hours • .

. 15.351

GLYCOGEN AND GLUCOSE IN THE LIVER. 235

only the glucose present in the organ at the moment of death, but also
that which accumulates afterward. The proportion found in the dog at
the end of twelve hours corresponds very closely in both tables.

It has been doubted by some observers (Pavy, Meissner, Hitter,
SchifF), whether glucose be really produced in the liver during life ; its
presence in the liver tissue, in ordinary examinations, being attributed
entirely to a post-mortem production by transformation of the glycogen.
It is true, as these experimenters have found, that if a small portion of
the liver substance be cut out from the body of the living animal and
instantly plunged into a freezing mixture, boiling water, or strong
alcohol, so as to arrest the transformation of the glycogen, its subse-
quent examination may not show the presence of glucose by Trom-
mer's test, as applied in the usual way. Professor Flint, Jr.,1 by ope-
rating in this way with boiling water, found in two instances, where
the time employed in the extraction and coagulation of the liver sub-
stance was respectively 28 seconds and 22 seconds, there was no marked
or certain evidence of sugar. In another instance, where the time em-
ployed was only 10 seconds, the liver extract presented no trace of
sugar whatever; and yet the blood of the hepatic vein, obtained within
a minute after the first operation, showed a well-marked saccharine reac-
tion by the copper test. We have also found, that under similar con-
ditions, the liver tissue may yield no reduction by the copper test at the
end of 17 or of 22 seconds, though it is distinct in 50 seconds after its
extraction from the living body. Harley,2 by killing the animal by
section of the medulla oblongata, immediately placing a portion of the
liver in a freezing mixture and afterward slicing it directly into boiling
acidulated water, has shown that glucose may be demonstrated to exist
in the organ within 20 seconds after the death of the animal.

But the failure to demonstrate the presence of glucose, even within
the shortest time after the extraction of the liver, is only owing to the
use of too small a quantity of the liver tissue and an imperfect purifica-
tion of its watery extract. If these sources of error be avoided, glucose
will always be found in the liver at the instant of its extraction, or as
soon afterward as the necessary test can be applied. In order to demon-
strate this, a portion of the liver is to be taken out of the abdomen of
the living animal by an instantaneous incision, reduced to a pulpy mass
by passing it between two fluted rollers, and at once dropped into a
vessel of boiling water or of strong alcohol. By this means all further
change of the glycogen is arrested, and the time which elapses between
the extraction of the liver substance and its immersion in the coagulating
liquid may be reduced to a very few seconds. A watery extract is finally
to be made of the liver substance, which must be completely purified by
the repeated use of animal charcoal until it is absolutely transparent

1 New York Medical Journal, January, 1869.

2 Proceedings of the Royal Society of London, vol. x. p. 289.

236

PRODUCTION OF

and colorless 1 after which it is tested for glucose l)y the use of Fehling's
solution.

We have experimented, in the manner above described, upon twenty
dogs. In four of the cases, the method employed was that by boiling
water ; in the remaining sixteen cases, that by alcohol. The animals
were examined four, eight, twelve, and twenty-four hours after feeding ;
the food consisting always of the fresh or cooked meat of the bullock's
heart. The longest time which elapsed from the separation of the liver
to its immersion in alcohol or boiling water was thirteen seconds ;
the shortest time was three seconds. The average time was six and a
quarter seconds. In every instance the final watery solution gave a
distinct and perfectly unmistakable sugar reaction by the copper test.
In one-half the cases, the presence of sugar alone was determined by
this method ; in the remainder, its proportion to one thousand parts of
the liver tissue was also ascertained.

The following is a list of these experiments, with their results :

GLUCOSE FOUND IN THE LIVER OF THE DOG IMMEDIATELY AFTER ITS EXTRACTION.

Experiment.

Time after
feeding.

Time consumed in
taking out liver.

Process
of treatment.

Proportion of glucose
per thousand parts.

No. 1

4 hours

13 seconds

Alcohol

Glucose

No. 2

4 hours

7 seconds

No. 3

4 hours

10 seconds

<

No. 4

4 hours

4 seconds

«

No. 5

8 hours

7 seconds

i

No. 6

8 hours

6 seconds

<

No. 7

4 hours

5 seconds

Boiling Water

No. 8

12 hours

6 seconds

11 ' U

No. 9

12 hours

8 seconds

« («

No. 10

12 hours

5 seconds

" "

No. 11

4 hours

9 seconds

Alcohol

• 2.093

No. 12

4 hours

5 seconds

0.804

No. 13

8 hours

7 seconds

1.750

No. 14

8 hours

3 seconds

1.510

No. 15

12 hours

5 seconds

1.810

No. 16

12 hours

5 seconds

4.175

No. 17

12 hours

7 seconds

1.830

No. 18

12 hours

3 seconds

4.375

No. 19

24 hours

5 seconds

3.850

No. 20

24 hours

4 seconds

2.675

It appears from these results, that when the requisite precautions are
adopted, glucose is found in the liver at the earliest period at which it
is possible to examine the organ after its separation from the body of
the living animal ; the average quantity of sugar existing in the liver
tissue, at this time, being at least two and a half parts per thousand.
The exact proportion of sugar thus present in the liver at the instant
of death, or within a few seconds afterward, varies from 0.804 to 4.375

1 All the necessary details of this process are given in the New York Medical
Journal for July, 1871.

GLYCOGEN AND GLUCOSE IN THE LIVER. 237

parts per thousand. These variations appear to depend upon individual
differences in the animals employed for experiment ; in the same man-
ner as other ingredients of the tissues and fluids are founcl to vary,
within physiological limits, in different individuals.

As sugar is found, under some circumstances, in minute quantity in
the blood of the general circulation, there might be room for doubt
whether the glucose, present in the liver at the moment of death, be not
due to the arterial blood with which the organ is supplied, rather than
an ingredient of the hepatic tissue. This, however, is not the case, as
is shown by examining, at the same time with the liver or immediately
afterward, some other abdominal organ equally well supplied with arte-
rial blood. In the experiments above described, the spleen in three
cases was taken out within ten minutes after the excision of the
liver, treated in the same manner by the alcohol process, and examined
for glucose with the following result:

PROPORTION OF GLUCOSE PER THOUSAND PARTS.
At the end of In the

Exp. No. 14. | 3 seconds Liver . .

( 10 minutes ; Spleen .

Exp. No. I9.l5seconds ^er • •

1 10 minutes '. Spleen . . 0.

Exp.No.20.{ 4seconds ^yer • • 2'675

(30 minutes .... Spleen . . 0.

It is evident, accordingly, that the liver sugar does not belong to the
arterial blood with which the organ is supplied, but is a normal ingre-
dient of the hepatic tissue.

The sugar formed in tho liver is similar in most of its properties to
the glucose derived from other sources. Its solution readily reduces
the salts of copper in Trommer's or Fehling's test, and is colored brown
when boiled with a solution of caustic alkali. It rapidly enters into
fermentation if mixed with yeast and kept at a temperature of from 21°
to 38° (700 to 1000 F.). It is distinguished from other varieties of sugar,
according to Bernard,1 by the readiness with which it becomes decom-
posed in the blood — since cane sugar, if injected into the circulation of
a living animal, passes through the system without sensible decomposi-
tion, and is discharged unchanged with the urine; sugar of milk, and
glucose prepared artificially from starch, if injected in moderate quan-
tity, are decomposed in the blood, but if introduced in greater abund-
ance, make their appearance also in the urine ; while a solution of liver-
sugar, though injected in much larger quantity than either of the others,
may disappear altogether in the circulation, without passing off by the
kidneys.

Absorption and final Disappearance of the Liver-sugar. — The glu-
cose produced in the liver by transformation of the glycogen does not

1 Lemons de Physiologic Experimental. Paris, 1855, p. 213.

238

PKODUCTION OF

remain at the place of its formation. It is constantly absorbed by the
blood traversing the capillaries of the organ, and carried away in the
current of the circulation. This is shown by the fact that not only the
liver tissue, but also the blood of the hepatic vein contains glucose in
appreciable quantity, although it may not exist in the portal blood by
•which the organ is supplied. As the blood accordingly, before its en-
trance into the liver, in these cases, is destitute of sugar, and yet con-
tains this substance after its passage through the organ, it must acquire
its saccharine ingredients by the absorption of glucose in the liver
itself. Bernard has shown1 that if two specimens, of portal and hepatic
blood, be taken from the same dog, when in a fasting condition or after
an exclusive diet of animal food, the former will show no trace of sugar,
while the latter will be distinctly saccharine. Lehmamr has obtained
similar results by experimenting upon both dogs and horses. In these
animals, nourished with vegetable matters, glucose was found in the
blood of the portal vein, though often in very small quantities. In
dogs, when under a diet of animal food, the portal blood contained no
glucose, while this substance was present in the blood of the hepatic
vein. The following table gives the results of Lehmann's experiments :

QUANTITY OF GLUCOSE IN THE BLOOD OF THE HEPATIC VEIN. AS COMPARED WITH

THAT OF THE PORTAL

Species
of animal.

,

Regimen previous to the
experiment.

Proportion of glucose per thousand parts
in the blood of the

Portal vein.

Hepatic vein.

. Dog

«

Fasting for two days

tt tt tt

0
0

7.640
6.380

H

a it tt

0

8.040

tt

Meat

0

8.140

»

(4

0

7.990

tt

U

0

9.460

It
It

Boiled potatoes

it tt

Traces

9.810
8.540

Horse

Bran, hay, and straw

0.550
0.052

8.950
6.350

Glucose, accordingly, although constantly produced in the liver, does
not accumulate in the organ during life, owing to its being absorbed
by the blood, and carried away nearly as rapidly as it is formed. It is
only after death, when the circulation has come to an end and the trans-
formation of glycogen still goes on for a time, that the proportion of
glucose in the liver tissue becomes notably increased. The circulation
of blood through the organ, so. long as it continues, acts like an artificial
watery injection of the hepatic vessels, and extracts from its substance
the sugar which has been produced at the expense of the glycogen.

1 Lecjons de Physiologic Bxperimentale. Paris, 1855, p. 265, 469.

2 Comptes Kendus de 1* Academie des Sciences. Paris, 1855. Tome xi. p. 585.

GLYCOGEN AND GLUCOSE IN THE LIVER. 239

Unless, therefore, a new supply of food be taken, all the glycogen of the
liver, as shown by experiments cited above, becomes after a time ex-
hausted ; having gradually undergone the saccharine transformation and
absorption by the bloodvessels.

Owing to these processes going on in the hepatic tissue, the blood
beyond the liver, that is, the blood in the hepatic vein, the inferior vena
cava above the diaphragm, and the right side of the heart, contains
traces of glucose. The proportion of sugar in the blood, however, con-
stantly diminishes as it recedes from the point of its origin, since the
saccharine blood coming from the liver is diluted with that of the inferior
vena cava, and this mixture again with that of the superior vena cava,
before reaching the right cavities of the heart. Beyond -the pulmonary
circulation, under ordinary circumstances, it has disappeared altogether,
so that no sugar is to be found, as a rule, in the blood of the general
circulation.

The changes, therefore, which take place in the liver, so far as regards
the carbohydrates, consist, first, in a deposit of glycogen, derived from
the ingredients of the blood. This glycogen acts as a reserve material,
which is afterward used for the purposes of nutrition. The vegetable
starch and sugar of the food, after digestion, are absorbed under the
form of glucose and taken up by the vessels of the portal system. This
glucose does not at once enter the general circulation, but on reaching
the liver undergoes, for the most part, a conversion and deposit as
glycogen, or animal starch. It then gradually again passes into the
form of glucose by a secondary transformation, and in this form is
carried away by the hepatic blood, to be finally decomposed or assimi-
lated in some unknown manner for the maintenance of the vital phe-
nomena. The final product of its metamorphosis or destruction in the
animal body is undoubtedly carbonic acid and the elements of water ;
but how far this is accomplished by direct oxidation, or what other
intermediate changes may occur in the act of nutrition, cannot as yet be
determined with certainty.

Similar successive transformations of the starchy and saccharine
carbohydrates are already known to take place in vegetables. In the
growing plant, under various conditions, the starch, first formed in the
green leaves, passes into the condition of a saccharine fluid to be trans-
ported into organs of reserve, such as tuberous roots, grains, and fruits,
where it is again deposited as starch ; and from these it is subsequently
taken up at the requisite time as glucose, and carried by the vascular
channels into the growing organs for its final destruction or assimila-
tion.1 Starch and sugar, therefore, in animals as well as in vegetables,
are to be regarded as two different forms of the same nutritive substance,
one of which is in the condition of temporary deposit, the other in that
of solution and activity.

1 Mayer, Lehrbuch der Agrikultur Chemie. Heidelberg, 1871, Band i. pp. 76,

78, 81.

240 PRODUCTION OF

Accumulation of Glucose in the Blood, and its discharge by the Urine.
— The sugar formed from the glycogen of the liver, and discharged little
by little into the circulation, is not usually recognizable at a distance
from the organ, owing to the changes which it undergoes in the blood.
But under certain conditions its quantity, or the rapidity of its dis-
charge by the liver, may be increased ; so that, its decomposition no
longer keeping pace with its production, it is diffused to a greater dis-
tance from the point of its origin. Bernard has observed this to take
place, in an appreciable degree, during ordinary digestion. In this pro-
cess, the circulation through the liver being increased in intensity, after
a time the glucose derived from its substance may become perceptible
in small quantity beyond the lungs, and traces of it may appear in the
arterial blood. At the same time its alteration continues to be effected,
so that the venous blood, after passing through the capillaries of the
general system, is no longer saccharine. This condition lasts but for a
short time. As the digestive process comes to an end, and the hepatic
circulation returns to its ordinary standard of activity, the glucose
which it supplies to the blood is again reduced to such a proportion, that
it disappears altogether from the vascular system beyond the right side
of the heart.

If, however, from any cause, the quantity of glucose in the blood of
the general circulation be increased beyond a certain proportion, it then
fails to be completely decomposed or assimilated, and a part of it is dis-
charged by the kidneys. Under these circumstances the urine becomes
saccharine, and the animal is placed in a condition of diabetes. The
proportion of glucose which the blood must contain, in order that it may
be discharged by the kidneys, lias been determined in several instances.
Yon Becker found1 that in rabbits, if glucose be present in the blood in
the proportion of 5 parts per thousand, it passes off by the urine, where
it may be distinctly recognized by the copper test ; but if less abundant
than this, the indications of its presence in the urine are faint and un-
certain. Bernard ascertained,2 by injecting in the same animal a solu-
tion of glucose into the veins, that in general a condition of diabetes
was produced when glucose was injected in larger quantity than one part
per thousand of the entire bodily weight. The appearance of glucose in
the urine is therefore dependent upon the proportion in which it exists
in the blood. If its quantity be below a certain point, it is all decom-
posed by contact with the ingredients of the blood ; if it be above this
point, some of it escapes this change and is then eliminated as an in-
gredient of the urine. According to the experiments of Von Becker, a
solution of glucose, injected into the jugular vein of the rabbit in suffi-
cient quantity, may cause the appearance of sugar in the urine in less
than three hours ; but at the end of from six to seven hours the whole

1 Zeitschrift fiir Wissenschaftliche Zoologie, Band v. p. 176.

2 LeQons sur les Liquides de 1'Organisme. Paris, 1859, tome ii. p. 73.

GLYCOGEN AND GLUCOSE IN THE LIVER. 241

of it may be eliminated, so that it is no longer to be found as an ingre-
dient of the excretions.

There are a variety of circumstances which may so increase the pro-
portion of glucose in the blood as to cause a saccharine condition of the
urine.

I. One of these causes is an unusually abundant and rapid absorption
of sugar from the intestine. The sugar taken in with the food, or pro-
duced in the intestine by the transformation of starch, is usually changed
into glycogen by the hepatic tissue, and is afterward only slowly recon-
verted into glucose and discharged under this form into the blood. But
where a very large quantity of sugar is suddenly absorbed by the blood-
vessels of the intestine and at once carried by the portal vein to the
liver, the tissue of the organ is not capable of immediately converting
the whole of it into glycogen. Thus a portion of the sugar taken up
in this way passes through the hepatic circulation unchanged, and, reach-
ing the general circulation in unusual quantity, is accordingly discharged
with the urine. Yon Becker observed that when concentrated solutions
of glucose are introduced in abundance into the intestinal canal of the
rabbit, it may appear subsequently in the urine. Bernard has also found
that, in the rabbit after one or two days' fasting, if sugar in large amount
be injected into the stomach, the urine becomes diabetic; and that the
same result may follow, if the animal, in a similar fasting condition, be
made to eat a considerable quantity of carrots, which are highly saccha-
rine. The same thing has been observed by Bernard in the human sub-
ject, in consequence of taking a large supply of sugar in solution when
the stomach has been empty for several hours. This result is produced,
however, only when a much greater abundance of sugar is present in
the intestine than occurs in ordinary digestion, and depends upon the
excessive quantity absorbed within a given time.

II. A diabetic condition may also be induced by anything which
hastens the circulation of blood through the liver, or increases its supply
of blood. Many observers have met with this result, as produced by a
variety of causes. Bernard has found that in dogs the blood of the
venous system generally may present traces of glucose after the abdo-
men of the animal has been subjected to pressure or manipulation over
the region of the liver, and after any continued struggles or convulsive
muscular action, by which the abdominal organs are forcibly compressed
In the same animal, according to the experiments of Harley, the injec-
tion of weak solutions of ammonia or of ether into the portal vein may
be followed by a saccharine condition of the urine. This condition has
also been seen in the human subject after a bruise received upon the
right hypochondriac region. The resistance of an animal to the inhala-
tion of ether and the subsequent muscular relaxation, general paralysis
from a fracture of the skull with cerebral hemorrhage, and the action of
woorara, or the South American arrow-poison, which also causes complete
muscular paralysis, are all known to be. sometimes followed by the ap-

242 GLYCOGEN AND GLUCOSE IN THE LIVER.

pearance of sugar in the urine. Schiff1 has even found that in various
animals, by simply compressing the abdominal aorta for ten minutes, or
by tying the principal bloodvessels of one limb, he has induced, for the
time, a condition of diabetes. These diiferent causes may all operate
by accelerating the hepatic circulation as well as that of the abdominal
organs generally.

III. A saccharine condition of the blood and urine may also be in-
duced by puncture of the medulla oblongata in the floor of the fourth
vertricle. This remarkable fact, which was first discovered by Bernard,2
may be demonstrated in both carnivorous and herbivorous animals. It
is best shown in the rabbit by introducing a narrow chisel-shaped
instrument, with the cutting edge directed transversely, through the
back part of the skull and the cerebellum, so that it shall pierce the pos-
terior part of the medulla exactly in the median line, without passing
completely through its substance. Glucose appears in the urine after
from one to two hours and continues to be present for two or three days.
The immediate effect of this operation, according to the direct observa-
tions of Bernard, is to increase the activity of the abdominal and
hepatic circulation. It is not due to a direct influence conveyed by the
pneumogastric nerve, since the result follows, as usual, although the
pneumogastric nerves may have been divided, and neither division nor
irritation of these nerves produces a similar effect. When successfully
performed, the operation causes no serious disturbance of the vital
functions, and the animal recovers after a few days without suffering
permanent injury.

In all the instances above mentioned, the appearance of sugar in the
urine is only temporary, depending upon an occasional disturbance of
the circulation. When in the human subject this condition becomes
permanent, it constitutes the disease known as Diabetes mellitus. In
this affection, which is generally progressive and fatal, the urine is
increased in quantity, of greater specific gravity than natural, and
continuously charged with sugar, sometimes in excessive abundance.
Fluctuations are observable in the quantity of glucose discharged at
different periods of the digestive process, but it may continue to appear,
even when no starchy or saccharine matter is taken with the food.

1 Journal de 1' Anatomic et de la Physioloerie. Paris. 1866. No. iv. p. 365.

2 LeQons de Physiologie Experimeutale. Paris, 1855, p. 290.

CHAPTEE XII.

THE BLOOD.

THE blood, in its natural condition, while circulating in the vessels,
is a thick opaque fluid, varying in different parts of the body from a
brilliant scarlet to a dark purple or nearly black color. It has a slightly
alkaline reaction, and a specific gravity of 1055. It consists, first, of a
nearly colorless, transparent, alkaline fluid, termd ihQ plasma, containing
water, fibrine, albumen, and salts, in a fluid condition; and, secondly, of
a large number of distinct cells, or corpuscles, the blood-globules, swim-
ming freely in the liquid plasma. The globules form about 40 per cent.,
and the plasma about 60 per cent., by volume, of the entire mass. The
specific gravity of the two ingredients is somewhat different. That of
the plasma is about 1030 ; that of the globules, 1088. Their relative
quantities by weight are therefore more nearly equal to each other than
when estimated by volume; the exact proportions, according to Robin,
being nearly 45 per cent, of globules and 55 per cent, of plasma.

Notwithstanding the difference in specific gravity between the blood-
globules and the plasma, the natural movement of the blood in the
vessels keeps them thoroughly mingled ; and even when the blood is
allowed to remain at rest in a glass jar, the globules subside only very
slowly and imperfectly. Thus the globules, disseminated uniformly
throughout the plasma, give to the entire mass of the blood an opaque
aspect and a deep red color.

The globules of the blood are of two kinds, namely, red and white;
of these the red are by far the most numerous.

Red Globules of the Blood.

The red globules of human blood are so abundant that, in the thinnest
layer under the microscope, they appear crowded together in such profu-
sion as to cover or touch each other in every direction. According to
the estimates of Welcker and Vierordt about 5 millions of them are con-
tained in each cubic millimetre of blood. On account of their quantity
therefore, as well as their peculiar properties, it is evident that they
form a most important constituent of the circulating fluid.

Physical Properties of the Red Globules.— The red globules of hu-
man blood present, under the microscope, a perfectly circular outline
and a smooth exterior. According to the most recent and careful mea-
surements of various observers, they have, on the average, a transverse
diameter of from 7.50 to 7.75 mmm. Their size varies more or less,
but this variation is not very marked for the greater number of the

(243)

THE BLOOD.

Fig. 76.

HUMAN BLOOD-GLOBULES. — a, Red glob-
ules, seen flatwise, b. Red globules, seen edge-
wise, c. White globule.

globules , and, according to the observations of Schmidt, over 90 per
cent, of those contained in a single specimen have the same dimensions.
The smallest size observed is 4.50 mmm. (Harting), and the largest 9.3

mmm.; while their average di-
ameter, as found in different
individuals, varies from 6.70 to
8,20 mmm.

The form of the red globule
is that of a spheroid, very much
flattened on its opposite sur-
faces, somewhat like a thick
piece of money with rounded
edges. The globule accordingly,
if seen flatwise, presents a com-
paratively broad surface and a
circular outline (Fig. 76, o);
but if it be made to roil over,
it will present itself edgewise
during its rotation, and assume
the flattened form indicated
at b. The thickness of the
globule, seen in this position,
is about one-fifth of its transverse diameter. When the globules are
examined lying upon their broad surfaces, it can be seen that these

surfaces are not exactly flat,
but that there is on each side a
slight central depression, so that
the rounded edges of the blood-
globule are evidently thicker
than its middle portion. This
inequality produces a remarka-
ble optical effect. The substance
of which the blood-globule is
composed refracts light more
strongly than the fluid plasma.
Therefore, when examined with
the microscope by transmitted
light, the thick edges of the
globules act as double convex
lenses, and concentrate the light
above the level of the fluid,,
Consequently, if the object-glass
be carried upward by the ad-
justing screw of the microscope, and lifted away from the stage, so that
the blood-globules fall beyond its focus, their edges will appear brighter.
But the central portion of each globule, being excavated on both sides,
acts as a double concave lens, and disperses the light from a point be-

Fig. 77.

RED GLOBULES OF THE BLOOD, seen a little
beyond the focus of the microscope.

RED GLOBULES OF THE BLOOD.

245

Fig. 78.

low the level of the fluid. It thus becomes brighter as the object-
glass is carried downward, and the object falls within its focus. An
alternating appearance of the
blood-globules may, therefore,
be produced by viewing them
first beyond and then within the
focus of the instrument. When
beyond the focus, the globules
will be seen with a bright rim
and a dark centre (Fig. 77).
When within it, they will appear
with a dark rim and a bright
centre. (Fig. 78.)

Within a minute after being
placed under the microscope,
the blood-globules, after a fluc-
tuating movement of short du-
ration, often arrange themselves
in slightly curved rows or chains,
in which they adhere to each
other by their flat surfaces, presenting an appearance which has been
aptly compared with that of rolls of coin. This is probably owing to
the coagulation of the blood,
which takes place very rapidly
when spread out in thin layers
and in contact with glass sur-
faces ; and which, by compress-
ing the globules, forces them
into such a position that they
occupy the least possible space.

The color of the blood-glob-
ules, when viewed by transmit-
ted light and in a thin layer, is
a light amber or pale yellow.
It is deep red when seen by re-
flected light, or in thick layers.
The blood-globules have a con-
sistency which is very nearly
fluid They are exceedingly

a .. . °~ RED GLOBULES OP THE BLOOD, adhering

flexible, and easily elongated, together, like roils of coin,

bent, or distorted by pressure

in passing through the narrow currents of fluid which often establish
themselves in a drop of blood under microscopic examination ; but re-
gain their original shape as soon as the pressure is taken off.

So far as immediate observation can show, the red globules of the
blood, in man and the mammalians, are homogeneous in structure. The
most careful examination fails to show, with any certainty, the evidence

THE SAME, seen a little within the focus.

Fijr. 79.

246

THE BLOCD.

Fig. 80.

RED GLOBULES OP THE BLOOD, shrunken,
with their margins crenated.

of an external envelope, distinct from the parts contained within it ;
and although some microscopists of high authority (Kolliker, Richard-
son) continue to regard the existence of such a cell-membrane as proba-
ble, it is not generally admitted, and cannot be directly demonstrated.

Each globule appears to con-
sist of a mass of organic sub-
stance, presenting the same
color, consistency, and compo-
sition throughout.

The appearance of the blood-
globules is altered by various
physical and chemical reagents-
If a drop of blood, when placed
under the microscope, be not
protected from evaporation, the
globules near the edges of the
preparation often diminish in
size, becoming shrivelled and
crenated, presenting an appear-
ance as if minute granules were
projecting from their surfaces ;
an effect apparently produced
by the loss of a part of their

watery ingredients. This distortion of the globules sometimes takes
place with great rapidity, and care is requisite not to confound a change
produced by external physical causes with morbid alteration of the in-
gredients of the blood. According to the observations of Kolliker, this,
as well as certain other abnormal forms presented by the blood-globules,
is never to be seen in the blood while circulating in the vessels.

If water, on the other hand, be added to the blood, so as to dilute the
plasma, the red globules absorb it by imbibition, lose the central con-
cavity of their flat surfaces, assume the spherical form, and become
paler. If a larger quantity of water be added, it may dissolve out com-
pletely the coloring matter, leaving the globules as pale, colorless circles,
which are almost invisible on account of their tenuity. They may still,
however, be brought into view by the addition of an iodine solution,
which stains them of a yellowish color. If the water added to the
blood be moderate in quantity, just sufficient to be taken up by imbibi-
tion by the globules, but not to extract their coloring matter, a special
change in their form is exhibited. The edges of the globules, being
thicker than the central portions, and absorbing water more abun-
dantly, become turgid, and encroach gradually upon the central part.
(Fig. 81.) It is very common to see the central depression, under these
circumstances, disappear on one side before it is lost on the other, so
that the globule, as it swells up, curls over toward one side, and
assumes a peculiar cup-shaped form. (Fig. 81, a, a.) This figure may
often be seen in blood-globules after soaking for some time in the urine,

RED GLOBULES OF THE BLOOD,

247

Fig. 81.

RED GLOBULES OF THK BLOOD, after the
imbibition of water.

or other animal fluids of less density than the plasma of the blood.
Dilute acetic acid, added to the blood, instantly extracts the coloring
matter of the red globules, reducing them to the condition of pale and
nearly invisible colorless bodies.
After the action of water,
however, these colorless cells
remain for a long time, and are
dissolved very slowly in com-
parison with the coloring mat-
ter.

Dilute alkaline solutions, on
the contrary, dissolve readity
the whole substance of the
blood-globules. A solution of
potassium hydrate, in the pro-
portion of ten per cent., acts
most rapidly in this manner.
Solutions of soda and ammonia
have a similar effect, although
less promptly than the preced-
ing-
Solutions of sodium glycocholate or taurocholate, in any grade of
concentration, or of the fresh bile itself, as shown by Kiihne, have also
the property of dissolving completely the red globules of the blood.

Composition of the Red Globules. — The red globules are composed of
an albuminous and a coloring matter, together with mineral salts and a
certain proportion of water. According to Lehmann, the water of the
red globules amounts to 688 per thousand parts, and a little over 8
parts per thousand consist of mineral salts, namely, sodium and potas-
sium chlorides, phosphates, and sulphates, together with lime and mag-
nesium phosphates.

By far the most important ingredient of the red globules is undoubt-
edly their coloring matter, or hemoglobine, the main characters of which
have been described in Chapter Y. According to the estimates of
Preyer,1 founded upon the observed quantity of iron as an ingredient,
the average proportion of hemoglobine in healthy human blood is 12.34
per cent. As the globules themselves constitute 45 per cent of the
whole blood, the quantity of hemoglobine in each blood globule is
about 27 per cent, of its entire mass, or 86 per cent, of its solid ingre-
dients. It is, accordingly, as regards its quantity, the principal substance
of which the globules are composed.

In the fresh globule, the hemoglobine is united with another substance
which is colorless and undoubtedly albuminous in its nature, and which
forms a substratum for the other ingredients of the globules. This
colorless matter is less soluble in water than the hemoglobine, and it is

Die Blutkrystalle, Jena, 1871, p. 117.

218

THE BLOOD.

owing to this fact, already mentioned, that when water is added to
the blood in sufficient quantity, the hemoglobine may be entirely ex-
tracted from the globules in a state of solution, leaving behind the
colorless substratum, much reduced in volume, but still remaining
undissolved for a considerable time. The exact physical condition of
the hemoglobine in the blood-globule and its mode of union with the
colorless substratum are not positively known. Preyer calculates that
the water of the blood-globule is quite insufficient in quantity to hold in
solution, by itself, the hemoglobine which is present ; and, according to
the same observer, it cannot exist in the blood-globules in a solid form,
since the crystals of hemoglobine are always doubly refracting, while
the fresh globules themselves are never so. So far as we can judge, the
two substances are united uniformly throughout the mass, in a condition
of thick or tenacious semi-fluidity ; but the hemoglobine is more easily
affected by various artificial dissolving agents, and by this means may be
extracted from the mass of the globule.

Hemoglobine is remarkable for the avidity with which it absorbs
oxygen whenever, either as constituent of the blood-globules or in the
form of solution, it is brought in contact with this gas or with atmo-
spheric air. The brilliant red color presented by its solutions depends
upon the quantity of oxygen present ; for if this substance be exhausted
by means of the air-pump, the application of heat, or the displacing
action of an indifferent gas, the clear scarlet hue of the solution dis-
appears and is replaced by a dull red or purple color.

Solutions of pure hemoglobine, as well as the blood-globules them-
selves, or diluted mixtures of blood and water, in the aerated condition,
exhibit a well-marked and peculiar spectrum. This spectrum is dis-
tinguished by the existence of two absorption bands between the lines
D and E, and situated, the one in the yellow, the other at the commence-
ment of the green. The first of these absorption bands is comparatively

Pig. 82.

BC D

Red Or. Yel. Green Blue

Violet

SPECTRUM OF HEMOOLOBINE, in Aerated Blood.

narrow, well defined, and dark, and is placed at about one-fifth the dis-
tance from D to E. The second is double the width of the first, but is
less dark, and not so well defined ; it occupies nearly the last half of
the space between D and E. Beyond the second band the light of the

RED GLOBULES OF THE BLOOD. 249

spectrum gradually diminishes, and ceases altogether about the termina-
tion of the blue, midway between F and G.

If the solution or mixture be much concentrated, or be viewed in a
very deep layer, it is too opaque for spectroscopic examination, and
may shut off all the light of the spectrum except a little of the red and
orange; if it be too dilute, it will fail to exhibit the distinguishing
characters of hemoglobine. A solution of a certain grade of strength,
which allows an abundance of light to pass through, and is yet sufficient
to cause its marked absorption at particular points of the spectrum, is
to be used for examination. With pure hemoglobine, according to
Preyer, a solution of about 1.5 parts per thousand gives the most marked
results. With fresh blood, if one volume of the defibrinated blood be
diluted with one hundred volumes of water, and the mixture viewed in
a layer of one centimetre, all the characteristic traits of the spectrum
will be distinctly shown.

The spectroscopic characters above described form a very delicate
test for the coloring matter of blood. According to Preyer, with a
solution of pure hemoglobine in water, of 4 parts per ten thousand, the
absorption bands may still be seen, though the second one is very faint.
Fresh dog's blood, if diluted with 1000 parts of water and viewed in a
layer of 3 centimetres' thickness, will show a spectrum in which both
absorption bands are distinctly perceptible though not very strong. If
diluted with 10,000 parts of water and viewed in a layer of 4.5 centi-
metres, the first band is still visible, though very faint ; the second is
entirely imperceptible.

These characters are also of value in showing that hemoglobine, as
extracted in the crystalline form, is identical with the normal coloring
matter of the fresh globules. A solution of crystallized hemoglobine
gives the same spectrum with solutions of fresh blood or with the dried
globules. EA^en the blood while still circulating in the vessels may be
made to exhibit the same appearances. If a spectroscope eye-piece with
two prisms be attached to the body of a microscope in such a way that
two spectra may be seen in the field, one above another, one of them
formed by the light coming through the body of the instrument, the
other by that coming through a lateral opening in the eye-piece ; and if
the mesentery of a living frog be placed before the objective of the micro-
scope, while a solution of human blood is placed at the lateral opening,
it will be seen that the absorption bands in the two spectra are the same,
and exactly correspond with each other.

In all the above cases the blood which yields the characteristic spec-
trum already described is in the aerated condition. Even if venous blood
be taken for examination, the process of extracting it and placing it in
a suitable vessel for examination brings it in contact with the atmosphere
and thus restores it to the condition of arterial blood. In the mesentery
of the living frog, when extracted from the abdomen and spread out
under the microscope, the free access of air to the peritoneal surface
constantly supplies the circulating blood with oxygen ; and accordingly
17

250 THE BLOOD.

no marked difference, either of color or of spectroscopic characters, is
to be seen between the blood in the arteries and capillaries, and that in
the veins. But if by any means the blood or a solution of hemoglobine
be deprived of its oxygen, and examined in that condition, it at once
shows a decided change both in color and spectroscopic appearances.

This reduction or deoxidation of the coloring matter of the blood may
be effected in either of two ways, namely, first, by the addition of deoxi-
dizing agents, and secondly by keeping the blood for a time excluded
from the access of air. According to the experiments of Stokes, the
addition of iron protosulphate to fresh blood reduces the hemoglobine,
and changes its color from bright red to dark purple ; the scarlet color
being again restored by agitating the blood with oxygen or atmospheric
air. Other observers have accomplished the reduction of the hemoglo-
bine by continued treatment of the blood or its solutions with a stream
of carbonic acid. The second method, however, is more easily applied.
If a solution of fresh blood, of a bright scarlet color, which yields a
spectrum with the absorption bands of aerated hemoglobine fully devel-
oped, be inclosed in a securely stoppered test-tube, the whole of which
it completely fills, and be kept in this condition secluded from the air
for twenty-four or forty-eight hours, the hemoglobine at the end of that
time will have lost its oxygen which has entered into other combinations.
If now placed before the spectroscope, the solution will show a spectrum
in which the two absorption bands above described have disappeared,
and which shows in place of them a single wide and comparatively ill-
defined band covering about three-quarters of the distance from D to E,
and extending usually toward the red a little beyond the situation of
the line I). The darkest part of this absorption band occupies exactly
the space which intervened between the two former bands.

Fig. 83.

SPECTRUM OF REDUCED HEMOGLOBIXE.

If the solution be now shaken up for a few instants with atmospheric
air. its bright color is at once restored, and at the same time the single
absorption band of reduced hemoglobine disappears, and is replaced by
the two normal bands of oxidized or aerated blood. These changes
may be repeated until the blood begins to show the effect of putrefaction.

Red Globules of the Blood in different Classes of Animals. — In all
vertebrate animals the blood contains red globules, of which the color-

RED GLOBULES OF THE BLOOD. 251

ing matter is identical with that in the human species. Even in Am-
phioxus, a kind of fish of very low grade of organization, which was
long regarded as exceptional in this respect, the existence of faintly
colored globules has been demonstrated of late years. That th'e coloring
matter of these globules consists of hemoglobine has been demonstrated
in such different animals as the dog, fox, cat, horse, sheep, pig, lion,
cougar, baboon, bat, hedge-hog, rat, guinea-pig, squirrel, mole, goose,
pigeon, lark, owl, crow, lizard, python, tortoise, frog, carp, perch, her-
ring, and pike. It has been discovered, in all, in 22 species of mam-
malians, 7 birds, 5 reptiles, and 12 fish; and has been found to exist in
every species of vertebrate animal which has been examined for that
purpose. Even in several invertebrate species where the blood is of a
red color, although it exhibits no distinct globules, it has been found to
contain hemoglobine in a state of solution. Preyer found that the red
circulating fluid of the earthworm, when examined by the spectroscope,
yielded a spectrum with two absorption bands identical with those of
human hemoglobine. It has also been discovered in the blood of the
pond-snail, the horse-leech, and the fresh-water shrimp.

But although in all these cases the red globules contain the same
coloring matter, they present, in different animals, variations of form,
size, and structure, which are more or less characteristic of the different
classes, families, and species, to which they belong.

In the mammalians, or warm-blooded quadrupeds, the red globules
of the blood have without exception the same homogeneous structure as
in man. They have also invariably the same disk-like figure, with a
circular outline, except in the species belonging to the family of the
camelidse (camel, dromedary, lama), where the disks have an oval form.
The size of the red globules in the mammalians varies much in extreme
cases; the smallest known being those of the Java musk-deer, an animal
not larger than a rabbit, which have a diameter of 2.50 mmm., while the
largest are those of the elephant, which measure 9.20 mmm. The rela-
tive size of the globules, however, in different species, does not con-
stantly correspond with that of the animal itself; since those of the cat
are larger than those of the sheep, and those of the rabbit larger than
either. The following list gives the size of the red globules in various
species of mammalians, according to the measurements of Gulliver and
Welcker:

DIAMETER OF THE CIRCULAR RED GLOBULES OF MAMMALIANS,

in micro-millimetres.

• . . 7.35 Horse .... 5.43

f>og . 7.30 Sheep .... 5.00

Wolf .... 6.94 Red deer . . . 5.00

Rabbit . . . 6.90 Goat .... 4.10

Cat .... 6.50 Elephant . . . 9.20

Fox .... 6.10 Two-toed sloth . . 8.93

Ox .... 5.95 Java musk deer . 2.50

252

THE BLOOD

In animals where the red globules are of comparatively smaller size
they are proportionally more numerous. It is estimated by Kolliker that
the entire volume or mass of all the red globules together, in any deter-
minate quantity of blood, does not vary much in different species ; and
that accordingly, in blood containing the smaller and more abundant
globules, the extent of their surface, and probably their functional
activity, is greater than where they are larger and less numerous. This
will apply also to the inferior groups of vertebrate animals, in which the
globules are often very much larger and at the same time less abundant
than in man.

In the birds, reptiles, and fish, comprising all the oviparous verte-
brata, as well as some which are viviparous, the red globules are distin-
guished by two very marked characters of shape and structure : namely,
an oval form and the presence of a granular, colorless nucleus. The
only known exception is in two species of fish belonging to the family
of the Lampreys, in which the globules have a circular outline; but here
also they are provided with a nucleus, and accordingly readily distin-
guishable from the circular globules of mammalia.

It is among the Batrachians, or naked reptiles, that the red globules
present the largest size and exhibit most distinctly their structural
character. They are of a regularly oval form, their short diameter

being between one-half and
three-quarters the long one, a
little thicker toward the edges
and thinner in the middle ; the
round or oval nucleus project-
ing slightly from the lateral
surface at its central portion
In their reactions toward dif-
ferent physical and chemical
agents, they resemble the red
blood-globules of mammalians.
In the frog, the red globules
have a long diameter of 22
mmm., or nearly three times
that of the human globules ; in
Proteus anguinus, the blind
water-lizard of the Carniola
grottoes, 58 mmm. ; in Meno-
branchns, an allied species inhabiting the northern lakes of the United
States, 62.5 mmm. ; and in Amphiuma tridactylum, the great water-
lizard of Louisiana, according to Dr. Riddell, the red globules are one-
third larger than in Proteus, or about 77 mmm. The following list
gives the size of different globules of the oval form.

BLOOD-OLOBULKS OF FROG. — a. Blood-glo
bule seen edgewise, b. White globule.

BED GLOBULES OF THE BLOOD. 253

LONG DlAMKTEK OF THE OVAL RED GLOBULES OF BlRDS, REPTILES, AND FlSH,

in micro-millimetres.

Pigeon .... 147 Frog ...... 22.0

Fowl . . . . . 12.1 Triton 29.3

Duck 12.9 Menobranchus . . . 62.5

Tortoise .... 20.0 Carp 13.1

Lizard .... 16.4 Sturgeon .... 13.4

Alligator 19.2 Perch 12.0

Diagnosis of Blood, and the distinction between Human Blood and that
of Animals. — It is often of consequence to recognize the existence of
blood in various animal fluids in physiological experiments, and it some-
times becomes important in medico-legal investigations. For this
purpose, in the fresh fluids, nothing can be more satisfactory than
spectroscopic examination ; a very small quantity of hemoglobine, as
already shown, being sufficient to yield a spectrum with the character-
istic absorption bands. There is a further advantage in this method,
namely, that it will enable us to detect the presence of blood in fluids
where the red globules have been dissolved and the coloring matter
reduced to a fluid condition. The washings of a blood spot or stain
may therefore show the spectrum of hemoglobine, although they may
not contain any red globules perceptible by the microscope. This, how-
ever, only shows the presence of the coloring matter of blood, and thus
allows us to distinguish blood from other colored fluids ; it does not
enable us to make a distinction between the blood of man and that of
animals, since the hemoglobine is the same in all.

But by microscopic examination of the red globules, either when
fresh or after having been dried and again moistened, we can often dis-
tinguish the blood of an inferior animal from that of the human subject.
According to the observations of Prof. J. G, Richardson,1 a fragment of
a blood spot, weighing less than r-|^ of a milligramme, which had been
kept in the dried condition for five years, when decolorized with a weak
watery solution (0.15 per cent.) of sodium chloride, and afterward tinted
with a solution of aniline, exhibited the blood-globules in such a condi-
tion that their size could be accurately measured.

If a blood stain, accordingly, which in a watery solution gives the
common spectrum of hemoglobine, be found to contain oval nucleated
globules, this would show it to be the blood of a bird, reptile, or fish ;
and the oval form alone would show that it is not human blood. The
question, therefore, whether a particular specimen be composed of human
blood may often be. decided with certainty in the negative by microscopic
examination. But if the specimen contain circular globules, without
nuclei, it will be impossible to say positively, in any instance, that they
belong to human blood, and not to that of some animal, such as the ape
or the dog, whose red globules nearly approach the human in size. In
most of the domesticated quadrupeds, the globules are smaller than in

1 Monthly Microscopical Journal. London, September 1, 1874, p. 140.

THE BLOOD.

human blood; but in both the sloth and the elephant, they are larger.
If it were only required to decide whether a given specimen of fresh
blood belonged to man or to the musk deer, for example, or even to the
goat, no doubt the difference in size of the globules would be sufficient
to determine the question.

But within nearer limits of resemblance it would be doubtful, because
the size of the red globules varies to some extent in each kind of blood ;
and in order to be certain that a particular specimen were human blood,
it would be necessary to show that the smallest of its globules were
larger than the largest of those belonging to the animal in question, or
vice versa. The limits of this variation have been tolerably well defined
for human blood, but not sufficiently so for many of the lower animals
to make an absolute distinction possible.

In the examination of stains or blood spots, the difficulty is increased
by the fact that the drying and subsequent moistening of the globules
introduces another element of uncertainty as to their exact original size.

Physiological Function of the Bed Globules. — There is no doubt that
the red globules of blood serve mainly as the carriers of oxygen. The
extreme readiness with which they absorb this substance from the
atmosphere or from any other gaseous mixture containing it, their im-
mediate change of color depending upon the supply or withdrawal of
oxygen, corresponding with the change of color in the blood as it tra-
verses the lungs or the capillaries of the general circulation, all indicate
that they have a special relation to the introduction and distribution of
oxygen in the living body. As a general rule, in those animals where
the red globules are of large size and few in number, the activity of the
vital functions is below the average ; while in the species where they are
smaller and more numerous, the processes of respiration, circulation,
nutrition, and movement are increased in rapidity to a similar degree.
The strongly marked physical and chemical characters of the red glo-
bules correspond with their importance in the functions of vitality.

White Globules of the Blood.

Beside the red globules above described, the blood contains a certain
number of other cellular bodies, which differ from the former in several
important particulars. These are the white or colorless corpuscles. As
their name implies, they are destitute of red or other coloring matter,
but under many circumstances present under the microscope a glistening
appearance, and when collected in large quantity may give to the fluid
or clot which contains them a whitish hue. They are much less abun-
dant than the red globules, the average proportion in healthy human
blood being one white globule to 300 red. They are nearly spherical
in form, and measure, on the average, 11 mmm. in diameter. They are
accordingly, in human blood, distinctly larger than the red globules.
(Fig. 76, c.) As regards their structure, they consist of a soft, some-
what viscid, colorless, finely granular substance, containing in its
interior one, two, or three ovoid nuclei. They are less yielding and

WHITE GLOBULES OF THE BLOOD.

255

Fig. 85.

slippery than the red globules, and have a tendency to adhere more
readily to the surfaces with which they are in contact ; so that if a
small quantity of a watery fluid be added to the drop of blood under
examination, the red globules will be hurried away by the currents pro-
duced, while the white globules lag behind, and, if the irrigation be con-
tinued, may finally be left alone in the field of the microscope. Their
transparency is such that, when slowly rolling over with the current,
the granules in their interior may often be perceived to rotate past
each other, above and below, with the motion of the globule. The
nuclei are sometimes visible in the perfectly fresh globule, but may
always be brought into view by the addition of pure water or of dilute
acetic acid. The action of these fluids is to cause a slight swelling of
the globule and to increase the
transparency of its substance,
by which the nuclei become
perceptible as sharply defined
ovoid or vesicular bodies in or
near the central part of the
mass. By the prolonged ac-
tion of acetic acid, a portion
of the cell substance becomes
condensed about the nuclei in
various irregular forms, while
the remainder appears as a per-
fectly transparent and homo-
geneous material, surrounded
by a very delicate circular out-
line. The final effect of both
water and acetic acid is to dis-
integrate the white globules
and cause their disappearance. Dilute alkalies dissolve them with great
readiness.

Amoeboid Movements of the White #Zo6u/es.— These movements are
so called from their resemblance to the motions of Amoeba, a minute
gelatinous creature, of very simple organization, living in fresh-water
pools and ditches. They are never to be seen while the blood is circu-
lating in a normal manner within the bloodvessels, where the white
globules always present their natural rounded form and uniformly
granular appearance. But within a short time after the blood has been
withdrawn from the vessels, provided it be maintained at or near the
normal temperature of the animal, the white globules may be seen to
alter their shape in a very remarkable way. The first indication of the
change is that a certain portion of the rounded outline of the globule
becomes faint and irregular, its substance at this point flattening out
and extending itself into one or more transparent and homogeneous
looking prolongations. These prolongations are alternately protruded
and retracted, sometimes extending into long filamentous processes,

WHITK GLOBULES OP THE BLOOD; altered
by dilute acetic acid.

256 THE BLOOD.

sometimes into shorter expansions with rounded ends. Variations in
the form of the globule are thus produced which succeed each other with
different degrees of rapidity according to circumstances. In man and
the warm-blooded animals, the blood under examination requires to be
kept at about the normal temperature of the body, in order that these
appearances may be exhibited; but in the cold-blooded animals they
may be shown at the ordinary temperature of the air.

Fig. 86.

CHANGES IN FORM OF A SINGLE WHITE GLOBULE of the blood of the Newt (Triton
millepunctatus) occurring in an interval of seven minutes, and within half an hour after its
extraction from the living body.

Besides showing these changes of form, the white globules of the
blood may sometimes be seen, by a similar mechanism, to move from
place to place. In these cases, the globule first sends out the pale pro-
longations of its substance as above described. The granulations of the
remaining portion are then propelled, by a kind of flowing movement,
into the prolongations, which thus become granular, and at the same
time assume a more rounded form. The remaining portion is subse-
quently drawn after and into the part previously expanded ; and by a
continuance of this process the whole mass makes a slow progression
from one point to another in the field of the microscope.

These movements are accomplished, like those of the amoeba, by alter-
nate local contractions and relaxations of the substance of the globule.
In Amoeba princeps the movement of progression may take place at the
rate of 73 micro-millimetres per minute, and in some forms of gelatinous
animalcules is occasionally so active that it may be followed continuously
by the eye. But in the white globules of the blood it is much more
slowly performed, and, like that of the hour hand of a clock, is to be
distinguished only by noting their change of position after a certain
interval of time. The white globules of the frog, when upon the free
surface of the mesentery, may be seen to move at a rate, as measured
by the micrometer, of 13 micro-millimetres per minute ; and similar
granular corpuscles, in the meshes of the connective tissue of the mesen-
tery itself, may progress at the rate of 3.5 micro-millimetres in the same
time. Certain changeable cells in the tissue of the frog's cornea, which
are regarded by some observers as identical in character with the white
globules of the blood, may change their position in the substance of the
cornea at the rate of 2.5 micro-millimetres per minute.

The amoeboid movements of the white globules of the blood are also
sometimes to be seen in the interior of the capillary bloodvessels or

PLASMA OF THE BLOOD. 257

small veins, when imprisoned in a stagnant portion of the blood-plasma.
But if the circulation be re-established, and the globules again move
with the blood current, they cease to be distorted, and resume their
original rounded form.

The precise physiological properties and functions of the white cor-
puscles cannot be determined so distinctly as in the case of the red
globules. Their great inferiority in number shows that they are less
important for the immediate continuance of the vital operations ; and
the same thing may be inferred from their want of strongly marked spe-
cific characters. For while the red globules of the blood vary in ap-
pearance to a marked degree in different classes and orders of animals,
the white globules present nearly the same general features of size, form,
and structure throughout the series of vertebrate animals.

Plasma of the Blood.

The plasma of the blood is the transparent, colorless, homogeneous
liquid, in which the blood-globules are held in suspension. It consists
of water, holding in solution various mineral salts, and of certain albu-
minous matters, which are distinguished by their modes of coagulation,
the principal of which are known as fibrine and albumen.

Ths plasma of the blood, according to the estimates of Lehmann and
Robin, has, on the average, the following constitution :

COMPOSITION OF THE BLOOD-PLASMA.

Water 902.00

Albumen .......... 75.00

Fibrine 3.00

Fatty matters 2.50

Crystallizable nitrogenous matters 4.00

Other organic ingredients . 5.00

Sodium chloride

Potassium chloride

Sodium carbonate

Sodium and potassium sulphates

Sodium and potassium phosphates

Lime and magnesium phosphates j

Mineral salts 8.50

1000.00

The above ingredients are all intimately mingled in the blood-plasma,
in a fluid form, by mutual solution ; but they may be separated from
each other for examination by appropriate means. The two ingredients
which on account of their nature and properties have received the
greatest attention, are the fibrine and the albumen.

The fibrine cannot be obtained for examination under the form in
which it naturally exists in the blood, since it is only to be separated
from the other albuminous ingredients by undergoing the process of
coagulation. Notwithstanding that this substance, or the material from
which it is derived, is present in the blood in so small a quantity as
three parts per thousand, it is evidently an important element in the

258

THE BLOOD.

Fig. 87.

constitution of the circulating fluid, since it is upon its power of spon-
taneous solidification that the coagulability of the entire blood depends.
This process takes place, under all ordinary conditions, soon after the
blood has been withdrawn from the circulation ; and the fibrine may be
obtained in a state of tolerable purity by continuously stirring freshly-
drawn blood with glass rods or a bundle of twigs. When coagulation
occurs, the fibrine solidifies in the form of thin layers adherent to the
surface of the rods or twigs. It at first contains, entangled with' it,
some of the red globules of the blood with their coloring matter ; but
these, as well as other foreign substances, may be removed by subjecting
the mass for a few hours to the action of running water. The fibrine
then presents itself under the form of nearly white threads and flakes,
having a semi-solid consistency and a considerable degree of elasticity.
Coagulated fibrine, if examined in thin layers, is seen to have a fibroid
or filamentous texture. The filaments of which it is composed are

colorless and elastic, and when
isolated are seen to be exceed-
ingly minute, being not more
than 0.5 mmm. in diameter.
They are partly so placed as to
lie parallel with each other, and
this is probably their arrange-
ment throughout the undis-
turbed fibrinous laj^er; but
when torn up for microscopic
examination, its filaments are
seen to be in many spots inter-
laced with each other in a kind
of irregular network. On the
addition of dilute acetic acid
the filaments become swollen,
transparent, and fused into a
homogeneous mass, but do not
dissolve. They are often in-
terspersed with minute granules, which render their outlines more or less
obscure.

Once coagulated, fibrine is insoluble in water and can only be again
liquefied by the action of an alkaline or strongly saline solution, by pro-
longed boiling at a very high temperature, or by digesting with gastric
juice or an acidulated solution of pepsine. These agents, however, pro-
duce a permanent alteration in the properties of the fibrine, and after
being subjected to their influence it is no longer the same substance as
before.

The quantity of fibrine which may be extracted from the blood varies
in different parts of the body. According to most observers, venous
blood in general yields less fibrine than arterial blood. A portion of it
therefore disappears in passing through the capillary circulation. In

COAGULATED FIBRINE, showing its flbrillatod
condition.

PLASMA OF THE BLOOD. 259

the liver and the kidneys this disappearance is so complete that no
fibrine is to be obtained, as a general rule, from the blood of the renal
or the hepatic veins. On this account, also, the blood in the large veins
near the heart is more deficient in fibrine than in those at a distance ;
since the venous blood coming from the general circulation, and con-
taining a moderate quantity of fibrine, is mingled, on approaching the
heart, with that of the renal and hepatic veins, in which the coagulating
material is entirely absent.

The albumen of the plasma is undoubtedly the most important of its
ingredients in regard to the process of nutrition, since it is by far the
most abundant of the albuminous matters present. It coagulates at
once on being heated to 72° (162° F.), or by contact with alcohol, the
mineral acids, or their metallic salts, or with potassium ferrocyanide in
an acidulated solution. It exists naturally in the plasma in a fluid form
by reason of its union with the water. The greater part of the water
of the plasma being united with the albumen, when this latter substance
coagulates, the water remains in combination with it, and assumes at
the same time the solid form. If the plasma of the blood, accordingly,
after removal of the fibrine, be exposed to a boiling temperature, it
solidifies almost completely, so that only a few drops of water can be
drained away from the coagulated mass. The earthy phosphates are
also retained by the solidified albuminous mass.

The substance existing in the blood plasma, however, and designated
as albumen, appears to consist really of two different ingredients, of
which one is about double the quantity of the other. Both of them are
coagulable by heat ; and on this account the whole albuminous ingredient
of the plasma solidifies when exposed to a boiling temperature. But one
of them is coagulable also by magnesium sulphate added in excess.
This substance is termed metalbumen, and is present in the plasma in
the proportion of about 22 parts per thousand. It may be separated
from the remainder by filtering the plasma through magnesium sulphate,
which retains the metalbumen in a coagulated form and allows the
remaining liquid to pass through. The second substance, which has
passed through the filter, and which is coagulable by heat but not by
magnesium sulphate, is albumen proper. It has been called " serine"
by Denis and Robin, to indicate that it is the kind of albumen present
in blood-serum. It exists in the plasma in the proportion of about 53
parts per thousand, being accordingly rather more than twice as abun-
dant as the metalbumen. It is not known whether these two substances
are mutually convertible, or if so, which of them is produced by trans-
formation of the other.

A certain quantity of albuminose is also to be found in the blood,
probably derived from the products of digestion. Its quantity, accord-
ing to Robin, varies from 1 to 4 parts per thousand. As it is absorbed
from the intestine during digestion, and neither accumulates in the
blood nor appears in any of the excretions, it is no cloubt transformed
into some other substance after being taken into the blood.

260 THE BLOOD.

ThQ fatty matters exist in the blood mostly in a saponified form, ex-
cepting soon after the digestion of food rich in fat. At that period, the
emulsioned fat finds its way into the blood, and circulates for a time
unchanged. Afterward it disappears as free fat, but remains partly in
the saponified condition.

The saline substances of the plasma are principally sodium and potas-
sium chlorides, phosphates, and sulphates, together with lime and mag-
nesium phosphates. Of these the sodium chloride is the most abundant,
constituting nearly 40 per cent, of all the mineral ingredients. The
sodium and potassium phosphates are of great importance in providing
for the alkalescence of the blood plasma, a property which is essential
to the performance of the functions of nutrition and even to the im-
mediate continuance of life ; since it is the alkaline condition of the
plasma which enables it to absorb from the various tissues the car-
bonic acid produced in their substance and return it to the centre of the
circulation, for elimination by the lungs. The sodium and potassium
carbonates also take part in the production of this alkalescence, and in
the herbivorous animals are its principal cause; while in the carnivora
the alkaline phosphates alone are to be found in the plasma in appre-
ciable quantity. In the human subject, under the use of an ordinary
mixed animal and vegetable diet, both the alkaline phosphates and car-
bonates are present in varying proportions.

The earthy phosphates of the plasma, which are by themselves in-
soluble in alkaline or neutral fluids, are held in solution in the blood by
union with its albuminous ingredients.

Coagulation of the Blood.

A few moments after the blood has been withdrawn from the vessels,
a remarkable phenomenon presents itself, namely, its coagulation or
clotting. This process commences at nearly the same time throughout
the whole mass of the blood, which becomes first somewhat diminished
in fluidity, so that it will not run over the edge of the vessel, when
slightly inclined ; while its surface may be gently depressed with the
end of the finger or a glass rod. It then becomes rapidly thicker, and
at last solidifies into a uniformly red, opaque, consistent, gelatinous
mass, which takes the form of the vessel in which the blood was received.
The process usually commences, in man, in about fifteen minutes after
the blood has been drawn, and is completed in about twenty minutes.

The coagulation of the blood is dependent upon the presence of its
fibrine. This fact may be demonstrated in various ways. In the first
place, if freshly drawn frog's blood be mixed with a solution of sugar,
of the strength of one-half per cent., and placed upon a filter, the blood-
globules will be retained upon the filter, while a transparent colorless
liquid passes through, which after a time coagulates like fresh blood.
Secondly, if horse's blood, which coagulates more slowly than that of
most other warm-blooded animals, be drawn from the veins into a cylin-
drical glass vessel and allowed to remain at rest, by the time coagulation

COAGULATION OF THE BLOOD.

261

Fig. 88.

takes place the blood-globules have subsided from the upper part of the
fluid, leaving a layer at the surface which is colorless and partly trans-
parent, but which is as firmly coagulated as the rest. Thirdty, if horse's
blood be freshly drawn into such a vessel, surrounded by a freezing
mixture and kept at the temperature of 0° (32° F.), coagulation is for
the time altogether suspended, and the globules sink toward the bottom,
leaving a transparent colorless fluid above. If this colorless fluid be
removed by decantation, and allowed to rise in temperature a few de-
grees, it coagulates firmly like fresh blood.

These facts show that the blood-globules take no direct part in the
process of coagulation; and that, when present, they are simply en-
tangled mechanically in the solidifying clot.

Finally, if the freshly drawn blood of man, or of any of the warm-
blooded animals, be briskly stirred with a bundle of twigs or glass rods,
the fibrine coagulates in comparatively small mass upon the surface of the
foreign bodies ; and the red globules which it entangles may be removed
by washing, without changing in any way its essential characters.

It is the fibrine, therefore, which, by its own coagulation, induces the
solidification of the entire blood. As it is uniformly distributed before-
hand throughout the blood, when coagulation
takes place the minute filaments which make
their appearance in it entangle in their meshes
the globules and the albuminous fluids of the
plasma. A very small quantity of fibrine,
therefore, is sufficient to include in its solidifi-
cation all the fluid and semi-fluid ingredients
which were before mingled with it, and to
convert the whole into a voluminous, trem-
bling, jelly-like mass of coagulated blood.

As soon as the coagulum has fairly formed,
it begins to contract, increasing somewhat in
consistency as it diminishes in size. By
means of this contraction the albuminous liquids begin to be pressed
out from th^e meshes in which they were entangled. A few isolated
drops first appear on the surface of the clot,
which soon increase in size and also become
more numerous. After a time they enlarge so
much as to come in contact with each other
at various points, when they coalesce, extend-
ing in all directions as the exudation increases,
until the whole surface of the clot is covered
with a thin layer of fluid. The clot at first ad-
heres pretty strongly to the sides of the vessel
into which the blood was drawn; but as its
contraction goes on, its edges are separated,

and the fluid continues to exude between it and showing the clot contracted
the sides of the vessel. This process continues

Bowl of recently OOAGTT-
LATKD BLOOD, showing the
whole mass uniformly solidi-
fied.

Fig. 89.

262 THE BLOOD..

for ten or twelve hours ; the clot growing constantly smaller and firmer,
and the expressed fluid more abundant

The globules, owing to their greater consistency, do not escape with
the albuminous fluids, but remain entangled in the fibrinous coagulum.
At the end of ten or twelve hours the whole of the blood has usually
separated into two parts, namely, the clot, which is a red, opaque, semi-
solid mass, consisting of the fibrine and the blood-globules ; and the
serum, which is a transparent, nearly colorless fluid, containing the
water, albumen, and saline matters of the plasma.

The change of the blood in coagulation may be expressed as follows :

Before coagulation the blood consists of

f Fibrine,

1st. GLOBULES ; and 2d. PLASMA — containing . . \ en'

I

Salts.
After coagulation it is separated into

1st. CLOT, containing \ . f an and 2d. SERUM, containing j Water
lW°buleS; '

Salts.

Conditions favoring or retarding Coagulation. — The coagulation of
the blood is influenced by various physical conditions. In the first
place it is suspended by a freezing temperature. If the blood be drawn
into a narrow vessel surrounded by a freezing mixture, so that the whole
of it is rapidly cooled down to 0° (32QF.)t coagulation does not occur,
and the blood remains fluid indefinitely, so long as the temperature is
not allowed to rise above this point. A variety of other changes, such
as fermentation, putrefaction, and many chemical combinations or de-
compositions, are also prevented, as it is well known, by special condi-
tions of temperature.

Secondly, the coagulation of the blood is prevented by certain of the
neutral salts. If fresh blood be allowed to mingle with a concentrated
watery solution of sodium sulphate, no coagulation takes place. This
is not because the coagulable material has been decomposed or chemi-
cally altered ; because if the mixture be diluted with six or seven times
its volume of water, so as to reduce the concentration of the saline solu-
tion, the fibrine solidifies in a few moments in the usual manner.

Coagulation of the blood may also be hastened or retarded by varia-
tions in the manner of its withdrawal from the veins, or in the surfaces
with which it afterward comes in contact. If drawn rapidly from a
large orifice, it remains fluid for a comparatively long time ; if slowly,
from a narrow orifice, it coagulates quickly. The shape of the vessel
into which the blood is received, and the condition of its internal sur-
face, also exert an influence. The greater the extent of surface over
which the blood comes in contact with the vessel, the more is its coagu-
lation hastened. If the blood be allowed to flow into a tall, narrow,
cylindrical vessel, or into a shallow plate, it coagulates more rapidly

COAGULATION OF THE BLOOD. 263

than if received into a hemispherical bowl, in which the extent of sur-
face is less, in proportion to the quantity of blood which it contains.
For the same reason, coagulation takes place more rapidly in a vessel
with a roughened internal surface than in one which is smooth ; and
blood coagulates most rapidly when spread out in thin layers, or entan-
gled among the fibres of cloth or sponges. Hemorrhage, accordingly,
continues longer from an incised wound than from a lacerated one ; be-
cause the blood, in flowing over the ragged edges of lacerated tissues,
solidifies upon them, and thus blocks up the wound.

In all cases there is an inverse relation between the rapidity of coagu-
lation and the firmness of the clot. When coagulation takes place slowly,
the clot afterward becomes small and dense, and the serum is abundant-
When it is rapid, there is but little contraction of the coagulum, an im-
perfect separation of the serum, and the clot remains large, soft, and
gelatinous.

The blood coagulates also in the interior of the vessels after stoppage
of the circulation. Under these circumstances coagulation takes place
less rapidly than if the blood were wholly withdrawn from the body.
In man, as a general rule, the blood is found coagulated in the cavities
of the heart and large vessels in from twelve to twenty -four hours after
death. In the lower animals, coagulation occurs earlier than this,
namely, from four to ten hours after death.

Coagulation of the blood takes place also in the interior of the body,
during life, from local arrest or impediment of the circulation. Thus, if
blood be accidentally extravasated into the connective tissue, the sub-
stance of the brain or spinal cord, or a serous cavity, it coagulates after
a short time, and forms a clot which takes the shape of the cavity occu-
pied by it. If a ligature be placed upon an artery in the living subject,
the blood which stagnates above the ligatured spot coagulates as it
would do if removed from the circulation. The clot extends from the
ligature backward to the situation of the next collateral branch, that is,
to the point at which the movement of the circulation still continues.
In an Arterial aneurism, during life, the blood in the dilated portion of
the artery, which is sufficiently removed from the centre of the current,
gradually coagulates upon the inner surface of the sac. In these cases,
as well within as outside the body, and during life as well as after
death, the stoppage or retardation of the circulatory movement induces,
after a time, the coagulation of the blood.

It is asserted, however, by some observers, that simple stoppage of
the circulation during life will not induce coagulation, unless the inner
membrane of the bloodvessels be wounded or irritated. According to
Burdon Sanderson, if blood be imprisoned in the jugular vein of the
living rabbit by carefully compressing the vessel at two points between
transverse needles, so arranged as not to wound or bruise the vascular
coats, it will remain fluid in this situation for two clays ; while if ordi-
nary ligatures be placed immediately around the vessel, a coagulum is
formed in the isolated portion of the vein.

264: THE BLOOD.

The coagulation of fibrine is not a commencement of -organization.
It is simply the passage of an albuminous ingredient of the blood from
its normal fluid condition to a state of solidity. The coagulable ingre-
dient of the blood, when solidified, has lost its natural properties as a
constituent of the liquid plasma, and cannot afterward be restored to
its original condition. The clot, therefore, when once formed, even in
the interior of the system, as in cases of ligature, apoplexy, or extrava-
sation, becomes a foreign body, and is reabsorbed by the neighboring
parts during convalescence. At first the clot is comparatively volumi-
nous, soft, and of a deep red color. Its more fluid parts are then reab-
sorbed, and the clot becomes smaller and denser. The red coloring
matter gradually diminishes as absorption goes on, and finally altogether
disappears. The time required for complete reabsorption varies from a
few days to several months, according to the size of the clot and the
situation in which extravasation has taken place.

Nature of the Process of Coagulation. — The difficulty in fully under-
standing the nature of coagulation depends upon the fact that the blood
naturally continues fluid under all ordinary conditions while circulating
in the vessels, but coagulates inevitably within a few minutes after its
removal. Properly speaking, the fibrine which we obtain at the time of
coagulation, either by itself or as forming a part of the clot, does not
pre-exist in the blood with the same constitution and properties, other-
wise it would coagulate within the vessels during life. It must be de-
rived from some ingredient of the blood, which, on being withdrawn from
the current of the circulation, suffers a change by which it becomes
spontaneously coagulable. It is not easy to understand what this
change may be, or what are the immediate influences which produce it.

There are two theories in existence as to the nature of coagulation.
According to one of them (Denis), the coagulable fibrine is produced by
the spontaneous decomposition of a liquid substance pre-existing in the
blood. This substance is termed plasmine, and is thought to be present
in the plasma of the blood in the proportion of 25 parts per thousand.
When withdrawn from the circulation it decomposes or separates into
two new substances. One of these is fibrine (3 parts per thousand),
which immediately coagulates ; the other is metalbumen (22 parts per
thousand), which remains fluid. The basis of this theory is, that if
fresh blood be drawn into a concentrated solution of sodium sulphate,
as above stated, no coagulation takes place. But if sodium chloride in
powder be added to this mixture in the proportion of ten per cent., it
precipitates a white pasty substance, which is thrown down because it
is insoluble in a sodium chloride solution of that strength. This sub-
stance, the so-called " plasmine," represents 25 parts per thousand of
the original plasma. After its separation it may be readily dissolved
again by the addition of water; but in a few moments its solution coagu-
lates, yielding 3 parts of a solid matter like ordinary fibrine, and 22
parts of a liquid substance having the properties of metalbumen. The
albumen proper of the blood remains behind in the sodium sulphate

COAGULATION OF THE BLOOD. 265

solution, not having been precipitated by the addition of sodium chlo-
ride.

According to the other theory (Schmidt), the coagulable fibrine is
produced by the union of two previously existing substances, neither
of which is coagulable by itself. One of these is termed fibrino-plastic
matter, because it has the property of inducing coagulation in a liquid
containing the other material. This second material is named fibri-
nogen, being considered as more directly the generator of the coagulable
fibrine. The plasma of the blood is supposed to contain both these
substances, but in very different quantities ; the fibrino-plastic matter
being abundant, the fibrinogen comparatively scanty. When the fibri-
nogen, accordingly, has all been converted into fibrine and has coag-
ulated, a surplus of fibrino-plastic matter still remains in the serum,
and may be used to induce coagulation in other liquids which would not
coagulate of themselves. This last fact forms the basis of the theory.
If the clear serum from coagulated blood be added, at the temperature
of the living body, to filtered hydrocele fluid, after some minutes the
mixture coagulates into a transparent gelatinous mass, which afterward
exudes a colorless serum. Both fibrino-plastic matter and fibrinogen
are obtained from the liquids containing them, by dilution with water
and by passing though them for a considerable time a continuous stream
of carbonic acid. Fibrinogen is also precipitable by the addition of
sodium chloride to the point of saturation.

This theory not having been found sufficient to account for all the
phenomena of coagulation, its author has modified it1 by supposing that,
while fibrino-plastic matter and fibrinogen by their combination furnish
the material of the coagulable fibrine, they need, in order to effect their
union, the influence of a third substance, which does not itself form any
part of the fibrine, but which acts as a ferment to excite the combina-
tion of the two others. A fluid accordingly may contain both fibrino-
plastic matter and fibrinogen, and yet will not coagulate unless the
ferment be also present. The ferment is supposed to be generated in
the blood only after its withdrawal from the vessels ; and this accounts
for its fluid condition while the circulation is going on.

Neither of the foregoing explanations rests upon complete demonstra-
tion. The plasmine of Denis may be, from the first, a mixture of two
different substances, both of which are precipitable by sodium chloride
from the sodium sulphate solution ; and the union of the twro fibrine
generators of Schmidt, under the influence of a " ferment," still leaves
it quite unknown how or by what causes this ferment is generated when
the blood coagulates after removal from the vessels. The only thing
which seems absolutely certain is that a substance exists in the blood
in small quantity which becomes coagulable by a spontaneous change
soon after it is withdrawn from the influences of the circulation.

If we endeavor to explain why this change and the consequent coagu-

1 Archiv fur die Gesammte Physiologic, 1872, Band vi. p 413.
18

266 THE BLOOD.

lation of the blood do not occur normally in the bloodvessels during life,
the most important facts bearing on this point are that the blood of the
renal and hepatic veins yields no fibrine, or much less than arterial blood.
The substance which causes coagulation, therefore, is decomposed and
disappears from the blood while passing through the liver and the kidneys.
This is established by the observations of Simon, Lehmann, and Brown-
Sequard. While an abundance of fibrine may be obtained from either
arterial or portal blood, none or only feeble traces of it are to be found
in that of the hepatic or the renal veins. This substance, being con-
stantly eliminated from the blood in this way by the liver and kidneys, is
necessarily produced afresh elsewhere at the same time, since its quan-
tity in the blood remains unchanged ; and the new material thus formed
is also rapidly altered by a continuation of the same process. -By
calculating approximately the quantity of blood contained in the whole
body and that passing daily through the liver and kidneys, it appears
that a quantity of fibrine equal to that in the entire blood must be de-
stroyed and reproduced several times over in the course of a single day.
Thus the fibrine which appears in a specimen of blood drawn from the
vessels at any one time, and which causes its coagulation, is derived
from a substance of very recent formation ; and, if allowed to remain in
the bloodvessels, it would have disappeared by metamorphosis before
arriving at the stage of coagulation.

Usefulness of Fibrine and of its property of Coagulation. — Although
the fibrine of the blood, from its small quantity and the general charac- t
ter of its properties, does not seem to take a direct part in the more
essential phenomena of nutrition, it is still a very important ingredient
of the circulating fluid. Upon the presence of this substance depends
the process by which nature effects the arrest of hemorrhage from
divided or ruptured bloodvessels. Whenever a wound is accidentally
made in vascular tissues, the blood at first flows freely from the external
orifice. But a portion of the blood coagulates upon the edges of the
wound, and after a time the successive deposits of cogulated fibrine
become sufficient to effectually close the opening and prevent further
loss of blood. The proper treatment for wounds of moderate size, in
which only the veins and capillaries, or small arteries, have been divided,
is simply to apply compression and to keep the edges of the wound in
contact continuously for fifteen or twenty minutes. By this time the
thin layer of blood between the wounded surfaces, thus kept at rest, has
coagulated, and the hemorrhage does not reappear when the artificial
compression is removed. If a larger artery be opened, the force with
which the blood is expelled prevents local coagulation, or is sufficient
to detach the coagula after they are formed. In such cases accordingly
the surgeon places a ligature upon the wounded artery itself, and in this
way effectually controls the hemorrhage. But even in this instance the
ligature is only a means of applying compression for a longer time, and
is still temporary, as it must come away again when it ulcerates through
the coats of the vessel. The immediate and essential means of stopping

COAGULATION OF THE BLOOD. 267

the flow of blood, even in a ligatured artery, is the coagulum which
forms within the vessel behind the ligature; and which, by the time the
ligature is detached by ulceration, has become sufficiently firm and adhe-
rent to resist the impulse of the blood.

The importance of fibrine in this respect is shown by the difficulties
which follow in cases where it is deficient. In some instances of the
ligature of large arteries, in patients much exhausted by injury or by
previous loss of blood, the surgeon finds that when the ligature comes
awajr the bleeding begins again, no internal clot having been formed ;
and a second ligature, applied above the situation of the former one, is
again followed by secondary hemorrhage. In certain persons also there
appears to be a congenital deficiency of the coagulating ingredient of
the blood, a peculiarity sometimes observed in several members of the
same family ; and in these cases, any slight accidental wound, or tri-
vial surgical operation, may be followed by long-continued or even fatal
hemorrhage.

Entire Quantity of Blood in the Body. — The estimation of the whole
mass of the blood in the living body is surrounded with many difficul-
ties. The first and simplest method adopted for this purpose was by
suddenly dividing all the vessels of the neck in the living animal and
collecting all the blood which escaped. This method, however, was
found to be quite faulty, since the flow of blood ceases, in such an
experiment, not because the whole of it has been discharged, but because
coagula have formed about the orifices of the divided vessels and because
the force of the heart's action is no longer sufficient to overcome the
obstruction. A certain quantity of blood, therefore, always remains in
the body after death by hemorrhage ; and this quantity, as shown by
subsequent experiments, may even amount to over 25 per cent, of the
whole mass of blood. The animal therefore dies before he has lost quite
three-fourths of the circulating fluid.

-Other methods have been adopted by various experimenters, none of
which are absolutely free from all possible sources of error. The best
is that by which, after all the blood is discharged which can be made
to escape spontaneously from divided vessels, the circulatory system
is immediately injected with water or a weak saline solution, until the
fluid of injection, after traversing the vascular channels, returns nearly
or quite colorless. The quantity of blood which it has thus washed out
of the vessels is then ascertained, either by a comparison of its color
with that of a watery dilution of blood of known strength, or by com-
paring the quantity of its solid ingredients with that of a similar watery
dilution.

The most accurate of these processes is that employed by Steinberg,1
who, after bleeding the animal to death, injected the aorta with a watery
solution of sodium chloride, of the strength of one-half per cent., until
the fluid of injection returned colorless. The whole of the fluid which

1 Archiv fur die Gesammte Physiologic, 1873, Band vii. p. 101.

268 THE BLOOD.

had been used for injection being then mingled, a small quantity of it
was taken, and the proportion of hemoglobine contained in it determined
by the spectroscopic test as follows : Equal quantities of pure blood were
placed in two similar test-tubes, and diluted, one of them with pure
water, the other with the fluid of injection, until each of them, placed
before the slit of the spectroscope, just allowed the green light of the
spectrum to become visible. From the relative quantities of the two
liquids which must be added to produce this result, the amount of
hemoglobine, and consequently of blood, extracted by the injection could
be readily calculated. This quantity, added to that which had escaped
spontaneously from the vessels, gave the entire amount of blood, as
follows :

QUANTITY OF BLOOD, IN VARIOUS ANIMALS, AS COMPARED WITH THE WEIGHT OF THE

WHOLE BODY.

In Dogs, from 8.00 to 8.93 per cent.

" Cats, " 8.40 " 9.61

" Guinea-pigs, " 8.13 " 8.33
" Babbits, " 7.50 " 8.13

There is evidence, however, that the quantity of blood varies naturally,
in the same animal^ according to the condition of the system at large,
and especially according to that of the digestive process. Steinberg
found that in the cat, while fasting, the percentage of blood was reduced
from 8.40 to 5.61 per cent. Bernard1 has observed that if two animals
of the same weight, one of which is in full digestion while the other is
fasting, be suddenly decapitated, the quantity of blood discharged from
the former is much greater than that from the latter. He has also
shown that, in a rabbit during digestion, twice as much blood can be
withdrawn without causing death, as in one of the same weight but
in the fasting condition. The volume of the blood, therefore, contained
in the body, fluctuates, within certain limits, with the alternate intro-
duction of nutritious matter by digestion and its expenditure during
the interval of fasting.

The most satisfactory determination of the quantity of blood in the
human subject is that by Weber and Lehmann.2 These observers
operated upon two criminals who suffered death by decapitation ; the
methods and results being essentially the same in both cases. In one
of them the body weighed before decapitation 60.14 kilogrammes ; and
the blood which escaped from the vessels at the time of decapitation
amounted to 5540 grammes. In order to estimate the quantity of blood
which remained in the vessels, the experimenters injected the arteries
of the head and trunk with water until it returned from the veins of a
pale red or yellow color, collected the fluid thus returned, and ascer-
tained how much solid matter it held in solution. This, amounted to

1 LeQons sur les Liquides de TOrganisme. Paris, 1859, tome i. p. 419.

2 Physiological Chemistry, Cavendish edition. London, 1853, vol. ii. p. 269.

COAGULATION OF THE BLOOD. 269

37.24 grammes, corresponding to 1980 grammes of blood. The result
of the experiment is therefore as follows :

Blood which escaped from the vessels .... 5540 grammes,
remained in the body .... 1980 ''

Whole quantity of blood in the living body, 7520 "

The blood, accordingly, in these cases amounted .to 12.54 percent, of
the entire bodily weight ; and the body of a healthy man, weighing 65
kilogrammes (143 pounds avoirdupois) will contain on the average 8127
grammes (18 pounds) of blood.

CHAPTEE XIII.

RESPIRATION.

THE most constant and striking phenomenon presented by living
organisms, both animal and vegetable, is the absorption of oxygen. A
supply of this substance, either in the gaseous form as a constituent
part of the atmospheric air, or dissolved in water or other liquids, is
indispensably requisite for the maintenance of life and the manifestation
of vital phenomena. Oxygen exists diffused everywhere over the sur-
face of the earth, forming rather more than one-fifth part of the volume
of the atmosphere, and it is dissolved in greater or less abundance in
the water of springs, rivers, lakes, and seas. Animals and plants, ac-
cordingly, whether living in the air or in the water, are surrounded by
media in which this substance is constantly present. Even parasitic
organisms, inhabiting the interior of other living bodies, and the foetus
during the period of its intra-uterine development, though not imme-
diately in contact with oxygen, are supplied with nutritious fluids which
have themselves been exposed to its influence. The function of respi-
ration consists in the process by which oxygen penetrates the substance
of living organisms, together with the changes which accompany and
follow its introduction.

Respiration in Vegetables. — In regard to the phenomena of respira-
tion in vegetables, a distinction is to be made between respiration proper
and the absorption of gaseous matter for the production of organic
material. It is well known that all green plants, under the influence
of the solar light, have the power of absorbing carbonic acid and water,
and of partially deoxidizing these substances, to form, with their re-
maining elements, starch, cellulose, and fat. The oxygen thus sepa-
rated from its inorganic combinations is exhaled by the plant in a free
form ; while, as a result of the process, an accumulation of organic ma-
terial takes place in the vegetable fabric, which increases in substance,
and may afterward serve for the nutrition of animal bodies. This ac-
cordingly is not a process of respiration, but one of organic production.
It is peculiar to vegetables, animals having no power to produce organic
material, and therefore depending upon vegetables for their supply of food.

Animals, on the other hand, consume the organic material thus pro-
duced, at the same time absorbing oxygen and exhaling carbonic acid
and water. In this respect there is an opposition between the actions
of animal and vegetable life, by which they stand in a complementary
relation to each other. Vegetables produce organic matter by a process
of deoxidation ; animals consume it with the phenomena of oxidation.
(270)

ORGANS OF RESPIRATION. 27i

But this apparent opposition between the phenomena of animal and
vegetable life only exists because plants have the special power of pro-
ducing organic matter, by which they become the source of nourish-
ment for the entire living creation. The organic substances so pro-
duced do not immediately take part in the more active phenomena even
of vegetable life. They are, on the contrary, deposited in a more or less
quiescent form, and constitute a reserve material, to be afterward trans-
formed and assimilated by the plant, or consumed by herbivorous ani-
mals. In vegetables, as well as in animals, a true respiration also takes
place, which is marked in both instances by the absorption of oxygen.
The deoxidizing process, by which organic matter is produced, occurs
only in green vegetables, and under the influence of the solar light ;
while the absorption of oxygen is a constant phenomenon, taking place
in both green and colorless plants, and in darkness as well as in the
light.

The more active phenomena of vegetation, moreover, are immediately
dependent upon the absorption of oxygen, and cannot go on without it.
When the starch which has been stored up in the seed becomes liquefied
and converted into sugar, and the process of germination and growth
begins, the absorption of oxygen is necessary to its continuance. This
is seen not only in germinating seeds, but also in expanding leaf and
flower buds, all of which organs consume in a short period several times
their volume of oxygen. The processes of germination, growth, and
flowering, as well as the intra-cellular movement of the vegetable plasma,
the motions of the sensitive-plant in response to stimulus, and the pe-
riodical movements of the leaves in certain other vegetable species, all
cease in an atmosphere deprived of oxygen.1 The function of respira-
tion is accordingly a universal one, and essential to all forms of vital
activity.

Organs of Respiration.

The process of respiration takes place very actively in the mamma-
lians and birds, less so in reptiles and fishes ; and in these different
classes the organs by which it is accomplished vary in size and struc-
ture according to the activity of the function itself. Its necessary con-
ditions everywhere are that the circulating fluid should be exposed in
some way to the influence of the atmospheric air or of an aerated fluid.
The respiratory apparatus, accordingly, consists essentially of a moist
and permeable animal membrane, termed the respiratory membrane,
with bloodvessels on one side of it, and air or an aerated fluid on the
other. The blood and the air, consequently, do not come in direct con-
tact with each other, but absorption and exhalation take place through
the respiratory membrane which lies between.

1 Mayer, Lehrbuch der Agrikultur-Chemie. Heidelberg, 1871, Band i. pp.
91-95.

272

RESPIRATION.

90-

In most aquatic animals, the respiratory organs have the form of
gills or branchiae; that is, filamentous prolongations of some part of the
integument or mucous membranes, which contain an abundant supply
of bloodvessels, and which hang out freely into the surrounding water.
In many kinds of amphibious reptiles, as, for example, in Menobranchus

(Fig. 90), there are upon each
side of the neck feathery tufts or
prolongations from the mucous
membrane of the pharynx, which
pass out through lateral fissures
in the neck. Each filament con-
sists of a thin fold of mucous
membrane, containing in its in-
terior a network of minute blood-
vessels. The venous blood, as it

enters the filament, is exposed to
HEAD AND G-ILLS OF MENOBRANCHUS.

the influence of the surrounding

water, and is thus converted into arterial blood. The apparatus is
further supplied with a cartilaginous framework and a set of muscles,
by which the gills are kept in motion, and constantly brought into con-
tact with fresh portions of the aerated fluid.

In terrestrial and air-breathing animals, the respiratory apparatus is
situated internally. In salamanders and newts, for example, which,
though partly aquatic in their habits, are air-breathing animals, the
lungs are cylindrical sacs, running nearly the entire length of the body,
commencing anteriorly by a communication with the pharynx, and ter-
minating by rounded extremities at the posterior part of the abdomen.
These air-sacs have a smooth internal surface ; and
the blood which circulates through their vessels is
arterialized by exposure to the air contained in their
cavities. The air is forced into the lungs by a kind
of swallowing movement, and is after a time regur-
gitated and discharged, to make room for a fresh
supply.

In frogs, turtles, and serpents, the cavity of the
lung, instead of being simple, is divided by incom-
plete partitions into a number of smaller cavities or
" cells." The cells all communicate with the central
pulmonary cavity ; and the partitions, which join
each other at various angles, are composed of thin,
projecting vascular folds of the lining membrane.
(Fig. 91.) By this arrangement, the extent of sur-
face presented to the air by the pulmonary membrane is increased, and
the arterialization of the blood takes place with a corresponding degree
of rapidity.

In man, and in the warm-blooded quadrupeds, the lungs are constructed
on a plan essentially similar to the above, but which differs from it in

Fig. 91.

Li TING OF FROG,

cut open, showing its
internal surface.

ORGANS OF RESPIRATION. 273

the greater extent to which the pulmonary cavity is subdivided. The
respiratory apparatus in man (Fig. 92) commences with the larynx,
which communicates with the pharynx at the upper part of the neck.

Fig. 92.

HUMAN LARYNX, TRACHEA, BRONCHI, AND LUNGS; showing the ramification of
the bronchi, and the division of the lungs into lobules.

Then follows the trachea, a membranous tube with cartilaginous rings,
which, upon its entrance into the chest, divides into the right and left
bronchi. These divide successively into secondary and tertiary bronchi ;
the subdivision continuing, while the bronchial tubes grow smaller and
more numerous, and separate constantly from each other. As they
diminish in size, the tubes grow more delicate in structure, and the car-
tilaginous rings and plates disappear from their walls. They are finally
reduced, according to Kolliker, to the size of 0.3 millimetre in diameter ;
and are composed only of a thin mucous membrane, lined with pave-
ment epithelium, resting upon an elastic fibrous layer. They are then
known as the " ultimate bronchial tubes."

Each ultimate bronchial tube terminates in a pyramidal division or
islet of the pulmonary tissue, about 2 millimetres in diameter, which is
termed a " pulmonary lobule." Each lobule may be considered as rep-
resenting the entire frog's lung in miniature. It consists of a vascular
membrane in the form of a pyramidal sac, the cavity of which is divided
into secondary compartments by thin septa or partitions which project
from its internal surface. These secondary cavities are the " pulmonary

274 RESPIRATION.

vesicles." They have, according to Kolliker, an average diameter of
about 0.25 millimetre ; but owing to the elasticity of their walls, each
vesicle is capable of dilating to double or triple its former size, and
returning to its original dimensions when the distending force is re-
moved. There is every reason to believe that during life they are alter-
nately enlarged and diminished in size, as the lungs are filled and emptied
with the movements of respiration.

Fig. 93. Fig. 94.

SINGLE LOBULE OF HUMVN LUNO. NKTWOKK OF CAPILLARY BLOOD-
— a. Ultimate bronchial tube. b. Cavity of VESSELS in the Pulmonary Vesicles of the
lobule. c,c,c. Pulmonary vesicles. Horse. (Frey.)

Each pulmonary vesicle is covered upon its exterior with a 'close net-
work of capillary bloodvessels, which penetrate into the septa between it
and the adjacent cavities, and which are thus exposed on both sides to
the influence of the atmospheric air. In the walls of the vesicles, and
also in the interspaces between the lobules, there is an abundance of
elastic tissue, which gives to the pulmonary structure its property of
resiliency. The thin layer of pavement epithelium lining the ultimate
bronchial tubes extends into the cavities of the lobules and vesicles,
forming, according to the observations of Kolliker, a continuous invest-
ment of their internal surface.

The abundant involution of the respiratory membrane, effected by the
subdivision of the bronchial tubes and the multiplication of the vascular
septa between the vesicles, existing in the lungs of man and the mam-
malians, evidently increases to an extraordinary degree the functional
activity of the organs of respiration. The entire extent of the respira-
tory surface in the human lungs has been estimated at 130 square
metres, which is probably not an exaggeration. The blood, accordingly,
in the pulmonary capillaries, distributed in thin layers over so large a
surface, in immediate proximity to the air in the cavity of the vesicles,
is placed under the most favorable conditions for its rapid and complete
arterialization.

MOVEMENTS OF KESP1RATION.

275

Movements of Respiration.

The air which is contained in the pulmonary lobules and vesicles,
being used for the purpose of arterializing the blood, becomes rapidly
vitiated in the process of respiration, and requires accordingly to be as
rapidly expelled and replaced by a fresh supply. This exchange or
renovation of the air is effected by alternate movements of the chest, of
expansion and collapse, which follow each other in regular succession,
and which are known as the " movement of inspiration," and the " move-
ment of expiration."

Movement of Inspiration. — The expansion of the chest is effected by
two sets of muscles, namely, the diaphragm and the intercostals.
While the diaphragm is relaxed, it has the form of a vaulted partition,
the edges of which are attached to the inferior extremity of the sternum,
the inferior costal cartilages, the borders of
the lower ribs and the bodies of the lumbar
vertebrae, while its convexity rises into the
cavity of the chest, as high as the level of
the fifth rib. When the fibres of the dia-
phragm contract, their curvature is neces-
sarily diminished; and they approximate a
straight line, in proportion to the extent of
their contraction. Consequently, the entire
convexity of the diaphragm is diminished in
the same proportion, and it descends to-
ward the abdomen, enlarging the cavity of
the chest from above downward. At the
same time the intercostal muscles enlarge it
in a lateral direction. For the ribs, articu-
lated behind with the bodies of the vertebrae,
and attached to the sternum by the flexible
and elastic costal cartilages, are so arranged
that, in a position of rest, their convexities
look obliquely outward and downward.
When the movement of inspiration is about
to commence, the first rib is fixed by the
contraction of the scaleni muscles, and, the
intercostal muscles then contracting simul-
taneously, the ribs are drawn upward. In
this movement, as each rib rotates upon its
articulations with the spinal column at one
extremity and with the sternum at the
other, its convexity is necessarily carried
outward at the same time that it is drawn
upward, and the parietes of the chest are
expanded laterally. The sternum rises slightly with the same move-
ment, and enlarges to some extent the antero-posterior diameter of the

DIAGRAM ILLUSTRATING
THE RESPIRATORY MOVE-
MENTS.—a. Cavity of the chest.
6. Diaphragm. The dark out-
lines show the figure of the chest
when, collapsed ; the dotted lines
show the same when expanded.

276 RESPIRATION.

thorax. By the simultaneous action of the diaphragm which descends,
and of the intercostal muscles which lift the ribs and the sternum, the
cavity of the chest is expanded in every direction, and the air passes
inward, through the trachea and bronchial tubes, by the force of aspira-
tion.

The action of these two sets of respiratory muscles is indicated exter-
nally by two different motions, visible to the eye; namely, an expansion
of the chest, due to the action of the intercostals, and a protrusion of
the abdomen, caused by the descent of the diaphragm. In children, as
well as in the adult male, in the ordinary quiescent condition, the dia-
phragm performs most of the work in the act of inspiration ; and the
movements of the abdomen are the only ones which are especially
marked. Any muscular exertion, however, produces an increased expan-
sion of the chest ; and the movement of the ribs, accordingly, becomes
more plainly visible after walking or running. In the female the move-
ments of the chest, and particularly of its upper half, are habitually
more prominent than those caused by the action of the diaphragm;
and this difference in the mechanism of respiration is a characteristic
mark of the two sexes.

In certain abnormal conditions the activity of either the intercostal
muscles or the diaphragm may be separately suspended, leaving the
entire work of respiration to be performed by the remaining set of
muscles. If the intercostal muscles be paralyzed, by disease or injury
of the spinal cord in the lower cervical or upper dorsal region, the
thorax remains quiescent in respiration, while the protrusion of the
abdomen is increased in extent to a corresponding degree. This mode
of breathing is called abdominal respiration.

In cases of peritonitis, on the other hand, or any local inflammation
within the abdominal cavity, the movements of the diaphragm are some-
times restrained, owing to the pain which they excite in the inflamed sur-
faces. This is known as thoracic respiration ; since the expansion of
the chest becomes more active than usual, and is the only visible move-
ment performed.

Movement of Expiration. — After the movement of inspiration is
accomplished and the lungs have been filled with air, the diaphragm
and intercostal muscles relax, and a movement of expiration takes place,
by which the chest is partially emptied, and a portion of the air con-
tained in the pulmonar}'' cavity is expelled. While the movement of
inspiration, however, is an active one, accomplished by means of mus-
cular contraction, that of expiration is a passive one, resulting from a
combination of several forces. The principal one of these forces is the
elastic reaction of the lungs themselves, due to the numerous fibres of
elastic tissue which enter into the structure of the walls of the pul-
monary vesicles and smaller bronchial tubes, and are disseminated gene-
rally between the lobules. The existence of this elastic force in the
pulmonary tissue is readily demonstrated by removing the lungs from
the chest of a recently killed animal, distending them by artificial

MOVEMENTS OF RESPIRATION. 277

insufflation through a tube inserted into the trachea, and then relieving
them from pressure. They at once react with sufficient power to expel
the larger portion of the air which had been forced into their cavities.
The same elasticity being constantly present during life, the air is sub-
jected to its pressure, and is consequently expelled as soon as the mus-
cles of inspiration cease to act. Other organs, however, aid in the
same process. The costal cartilages, which are also elastic, having
been twisted slightly out of position by the elevation of the ribs, resume
their original form, and, drawing the ribs down again, thus serve to com-
press the sides of the chest. Lastly, the abdominal organs, which have
been displaced by the descent of the diaphragm, are forced backward
by the elasticity of the abdominal walls and of their own fibrous attach-
ments, carrying the relaxed diaphragm before them. By the constant
recurrence of these alternating movements of inspiration and expiration,
fresh portions of air are incessantly introduced into and expelled from
the chest.

All the air, however, contained in the lungs, is not changed at each
movement of respiration. On the contrary, a considerable quantity
remains in the pulmonary cavity after the most complete expiration ;
and even when the lungs have been removed from the chest, they still
contain a certain amount of air, which cannot be entirely displaced by
any violence short of disintegrating the pulmonary tissue. It is evi-
dent, therefore, that only a comparatively small portion of the air in
the lungs passes in and out with each respiratory movement ; and it
will require several successive respirations before it can be entirely
changed. The proportion existing between the air which is changed at
each respiration and the entire quantity contained in the chest varies
considerably with the different conditions of the respiratory function ;
but the average results obtained by different observers show that, in
general, the volume of the inspired and expired air is from 10 to 13 per
cent, of that contained in the whole of the pulmonary cavity. Thus it
will require from eight to ten respirations to renovate completely the
air in the lungs.

Respiratory Movements of the Glottis. — Beside the movements of
expansion and collapse already described, belonging to the chest, there
are similar movements of respiration which take place in the larynx.
If the respiratory passages be examined in the state of collapse in which
they are usually found after death, it will be observed that the opening
of the glottis is smaller in calibre than the cavity of the trachea below.
The glottis presents the appearance of a narrow chink, while the passage
for the inspired air widens in the lower part of the larynx, and in the
trachea constitutes a spacious tube, nearly cylindrical in shape, and over
12 millimetres in diameter. We have found that in the human subject
the space included between the vocal chords has an area, on the aver-
age, of only one square centimetre ; while the calibre of the trachea in
the middle of its length is 2.81 square centimetres. This disproportion,
which is so evident after death, does not exist during life. While

278

RESPIKATION.

respiration is going on, there is a regular movement of the vocal chords,
synchronous with the inspiratory and expiratory movements of the
chest, by which the size of the glottis is alternately enlarged and dimin-
ished. At inspiration, the glottis opens and allows the air to pass freely

Fig. 96.

HUMAN LARVNX, viewed from above
in its ordinary post-mortem condition.— a.
Vocal chords, b. Thyroid cartilage, c, c.
Arytenoid cartilages. o. Opening of the
glottis.

The same, with the glottis opened by sepa-
ration of the vocal chords. — a. Vocal chords.
b. Thyroid cartilage, c, c. Arytenoid carti-
lages, o. Opening of the glottis.

Fig. 98.

into the trachea ; at expiration it collapses, and the air is driven out
from below. These movements are the " respiratory movements of the
glottis." They correspond in every respect with those of the chest, and
are excited or retarded by similar causes. Whenever the general move-
ments of respiration are hurried, those of the glottis become accelerated

at the same time ; and when the movements
of the chest are slower or fainter than
usual, those of the glottis are diminished
in the same proportion.

In the respiratory motions of the glottis,
as in those of the chest, the movement of
inspiration is an active one, and that of ex-
piration passive. In inspiration, the glottis
is opened by contraction of the posterior
crico-arytenoid muscles. These muscles
originate from the posterior surface of the
cricoid cartilage, near the median line ; and
their fibres, running upward and outward,
are inserted into the external angles of the
arytenoid cartilages. By the contraction
of these muscles, during the movement of
HUMAN LARYNX, POSTERIOR inspiration, the arytenoid cartilages are

VIEW.— a. Thyroid cartilage, b. ,. . * .. . ,.

Epiglottis, c, c. Arytenoid carti- rotated upon their articulations, so that
lages. d. Cricoid cartilage, e, e. their anterior extremities are carried out-
Posterior crico-arytenoid muscles. , . , . t •, i

/. Trachea, ward, and the vocal chords stretched and

MOVEMENTS OF RESPIRATION. 279

separated from each other. In this way, the orifice of the glottis may
be nearly doubled in size, being increased from 0.94 to 1.69 square cen-
timetre.

At the time of expiration, the posterior crico-arytenoid muscles are
relaxed, and the elasticity of the vocal chords brings them back to their
former position.

The motions of respiration consist, therefore, of two sets of move-
ments, namely, those of the chest and those of the glottis. These move-
ments, in the natural condition, correspond with each other both in time
and intensity. It is at the same time and by the same nervous influence,
that the chest expands to inhale the air, while the glottis opens to admit
it ; and in expiration, the muscles of both chest and glottis are relaxed,
while the elasticity of the tissues restores the parts to their original
condition.

Rapidity of the Movements of Respiration. — The movements of res-
piration in the human subject follow each other in general with great
regularity, and, according to the results obtained from the most exten-
sive and varied observations, are performed on the average with a
rapidity of 20 inspirations per minute. This rate varies considerably
under the influence of different conditions, one of the most important of
which is age. It is well known that respiration, as a rule, is more rapid
in young children than in the adult, and Quetelet has found, as the
average of a large number of observations, that in the newly born infant
the rate is 44 per minute, and at the age of 5 years 26 per minute ; be-
coming reduced to the standard rapidity of 20 per minute between the
ages of fifteen and twenty years. Even in the adult, a condition of rest
or activity readily influences the number of respirations ; as, according
to the same observer, they are less frequent during sleep than in the
waking condition. Even a difference in position has been found to have
a perceptible effect, the number of respirations being, in the same indi-
vidual, 19 per minute while lying down, and 22 per minute when standing
up.1 Any especial muscular activity, as the rapid motion of walking
or running, at once increases the frequency of respiration, which returns
to its ordinary regularity soon after the exertion has ceased.

In all cases the movements of respiration are involuntary in character,
and even their acceleration or diminution is regulated by influences
beyond our control. It is possible for a short time to increase or retard
the rate of respiration, within certain limits, by voluntary effort ; but
this cannot be done continuously. If we intentionally arrest or diminish
the respiratory movements, after a short interval the nervous impulse
becomes too strong to be controlled, and the movements necessarily
resume their regular frequency. If on the other hand we endeavor to
breathe much more rapidly than twenty times per minute, the exertion
soon becomes too fatiguing to be continued, and the rate of movement
returns to its normal standard. The movements of respiration, accord-

1 Milne-Edwards, Legons sur la Physiologic. Paris, 1857, tome ii. p. 483.

280 RESPIRATION.

ingly, as they are actually performed, in infancy and childhood, during
sleep, and for the greater part of the waking condition, when the atten-
tion is not directed to them, are purely automatic in character, like the
pulsations of the heart, and do not require the expenditure of an}T
voluntary exertion.

Quantity of Air used in Respiration. — Like all the quantitative esti-
mates connected with respiration, that of the volume of air habitually
inspired and expired with the breath, varies considerably as given by
different observers. The differences incident to the different individuals
subjected to observation, and to the conditions of rest or activity, pre-
vent our arriving at an absolutely invariable standard. The average
result, however, which most nearly conforms to the truth, as derived
from several of the most trustworthy experimenters, as well as from
our own observations, is that which gives the amount of air taken into
and expelled from the lungs with each inspiration and expiration as 320
cubic centimetres. It is certain that this estimate is not above the
reality. If we take, accordingly, eighteen respirations per minute as
the mean rapidity between the sleeping and waking hours, this would
amount to 5760 cubic centimetres of inspired air per minute, 345,600
per hour, and 8,294,400 cubic centimetres, or 8294.4 litres per day. But
as the breathing is increased, both in rapidity and extent, by every
muscular exertion, the entire quantity of air daily used in respiration is
not less than 10,000 litres, or a little over 350 cubic feet.

The quantity of air daily used in respiration is sometimes employed
as a basis for calculating the air-space necessary to allow for each in-
mate of a hospital or school-room. This estimate alone, however, can
never give sufficient data for the purpose. The successful ventilation
of a room depends not so much on the quantity of air which it contains
at any one time as upon the quantity of fresh air introduced, and of
vitiated air expelled, within a certain period. The air of a small room
which is thoroughly ventilated may be amply sufficient for respiration,
while that of a large room, if allowed to remain stagnant, will gradually
become unfit for use. A large air-space, in any occupied apartment,
will render ventilation more easy of accomplishment by ordinarj-
methods, because the air will not be so rapidly vitiated by the same
number of persons as if it were in smaller volume ; but the air must
still be changed with a rapidity proportionate to that of its contamina-
tion, in order to maintain the apartment in a wholesome condition.

Changes in the Air by Respiration.

The atmospheric air, as it is drawn into the cavity of the lungs, is a
mixture of oxygen and nitrogen in the proportion, by volume, of about
21 parts of oxj^gen to 79 parts of nitrogen. It also contains about .05
per cent, of carbonic acid, a varying quantity of watery vapor, and
some traces of ammonia. The last named ingredients, so far as animal
respiration is concerned, are quite insignificant in comparison with the
oxygen and nitrogen which form the principal part of its mass.

CHANGES IN THE AIR BY RESPIRATION. 281

If collected and examined, after passing through the lungs, the air is
found to have become altered in the following particulars: first, it has
lost oxygen; secondly, it has gained carbonic acid; and thirdly, it has
absorbed the vapor of water. The most important of these changes are
its diminution in oxygen and its increase in carbonic acid.

Diminution of Oxygen. — According to the researches of Valentin,
Yierordt, Regnault, and Reiset, the air loses during respiration, on an
average, five per cent, of its volume of oxygen. At each inspiration,
therefore, about 16 cubic centimetres of oxygen are removed from the
air and absorbed by the blood ; and, as we have seen that the daily
quantity of air used in respiration is about 10,000 litres, the entire quan-
tity of oxygen thus consumed in twenty-four hours is not less than 500
litres. This is, by weight, 715 grammes, or rather more than one pound
and a half avoirdupois.

In consequence of this diminution in oxygen, air which has once been
breathed is less capable, both of supporting combustion and of serving
for respiration, than before. If an animal be confined in a limited space,
the air becomes poorer in oxygen as respiration goes on ; and when its
proportion has been reduced to a certain point, the animal dies by suf-
focation, because the substance which is essential to life is no longer
present in sufficient quantity. Different kinds of animals are affected in
different degrees of intensity by a given diminution in the proportion of
atmospheric oxygen. Cold-blooded animals, in which respiration is
naturally a comparatively slow process, may continue to breathe when
only a very small quantity of oxygen is present ; and it has been found
that electrical fishes, as well as slugs and snails, may continue respira-
tion until they have completely exhausted the oxygen in the water or
the air in which they are confined. But in species where the respira-
tion and circulation are carried on with activity, as in birds, in quad-
rupeds, and in man, a partial reduction of the oxygen is sufficient to
cause death. If the carbonic acid exhaled be absorbed by an alkaline
solution, so that the purity of the air be maintained, it is found that
a sparrow dies in an hour when its proportion of oxygen has been
gradually reduced to 15 per cent. ; and a mouse dies in five minutes
when the oxygen is reduced to 10 per cent.;1 the remainder of the air
in both cases consisting of nitrogen. In man, also, asphyxia is almost
immediately produced when the proportion of oxygen has fallen to 10
per cent.

As a candle flame is also extinguished in an atmosphere deprived of
oxygen, this is sometimes employed as a test to determine whether it
be safe to enter an atmosphere the composition of which is doubtful.
In bread-rooms and beer-vats, where the process of fermentation has
been going on, in old wells which have been for a long time closed, or
in any newly opened underground cavity or passage, the atmosphere is
frequently so poor in oxygen that suffocation would at once follow if

1 Milne-Edwards, Lec.ons sur la Physiologie. Paris, 1857, tome ii. p, 638.
19

282 RESPIRATION.

they were to be entered without precaution. A lighted candle is accord-
ingly first let down into the suspected cavity, and if a sufficient quantity
of oxygen be present, it continues to burn ; if not, it is immediately
extinguished.

This test is the more valuable, because it is found that the proportion
of oxygen necessary to support the combustion of a candle is a little
greater than that required for the immediate continuance of respiration.
A candle is extinguished when the air contains only It per cent, of its
volume of oxygen, while a little less than this may still serve a short
time for respiration. According to Milne-Edwards, a man may still
keep up respiration in an atmosphere which is insufficient to support
combustion ; and we have repeatedly seen pigeons continue to breathe,
though with difficulty, in air in which a candle flame was immediately
extinguished.

Although, however, an atmosphere containing from 10 to IT per cent,
of oxygen is not immediately fatal to man by suffocation, it is still unfit
for continued breathing. The deficiency is not sufficient to stop respira-
tion at once, but after a time its deleterious effects become manifest,
and increase in intensity with each repetition. A complete renewal of
the deteriorated atmosphere is essential to the perfect performance of
the respiratory process.

The absorption of oxygen by different species of animals varies
according to their general state of functional activity ; and this differ-
ence may be manifested even between species belonging to the same
class. Thus it has been found that in the sparrow the amount of
oxygen absorbed, in proportion to the weight of the body, is ten times
as great as in the common fowl ; and in a carp the quantity consumed
in the course of an hour would hardly be sufficient for the respiration
of a pigeon for a single minute.

In the same individual, also, a temporary increase of muscular activity
augments in a marked degree the absorption of oxygen by the lungs.
In the human subject it was found by Lavoisier and Seguin that a man,
who in the ordinary quiescent condition absorbed a little over 19,000
cubic centimetres of oxygen per hour, consumed nearly 13,000 cubic
centimetres of the same gas during fifteen minutes of active muscular
exercise ; the rapidity of absorption being thus increased to more than
2J times its former rate. On the other hand, the same process is dimin-
ished in activity during sleep ; and in the hibernating animals, and in
insects which undergo transformation, at the time of their most pro-
found lethargy is reduced to a mere vestige as compared with its usual
activity. Spallanzani observed that in insects the amount of oxygen
consumed in a given time by the chrysalis was far less than that ab-
sorbed before or afterward by the caterpillar or the butterfly ; and in
the experiments of Kegnault and Reiset upon the marmot, at the com-
mencement of the cold season, the consumption of oxygen by this
animal was about 500 cubic centimetres per hour for every kilogramme

CHANGES IN THE AIR BY RESPIRATION. 283

of bodily weight, while after hibernation was fully established it was
reduced to 26 cubic centimetres per kilogramme per hour.

The absorption of oxygen, accordingly, in the process of respiration,
is directly associated, so far as regards its rapidity and amount, with the
physiological activity of the living organism.

Increase of Carbonic Acid. — The expired air usually contains, in
man, about 4 per cent, of its volume of carbonic acid, which it has ab-
sorbed in its passage through the lungs. Rather less than 13 cubic
centimetres of this gas are accordingly given off with each ordinary
expiration ; and as we have found that 10,000 litres of air are habitually
inhaled and discharged during twenty-four hours, this will give 400
litres of carbonic acid as the amount expired per day. This quantity
is, by weight, 186 grammes, or rather less than one pound and three-
quarters avoirdupois.

The rate of exhalation of carbonic acid by respiration varies in the
same manner and according to the same conditions as the absorption
of oxygen. In a general way it may be said, as the result of many
trustworthy observations, both in animals and man, that the quantity
of carbonic acid exhaled during a given time, in proportion to the weight
of the body, is increased by muscular exertion or by any physiological
activity of the system, and is diminished by quietude, during sleep, and
in a state of inanition.

These facts have been established more particularly for the human
subject, in a special series of investigations by Prof. Scharling,1 who
found that the quantity of carbonic acid exhaled was greater during
digestion than in the fasting condition. It was greater in the waking
state than during sleep ; and in a state of activity than in one of repose.
It was diminished by fatigue, and ~by most conditions which interfere
with perfect health.

It is also known that in man the habitual rate of exhalation varies
according to age, sex, constitution, and development. These variations
were very fully investigated by Andral and Gavarret, who found them
to be very marked in different individuals, notwithstanding that the
experiments were made at the same period of the day, and with the
subject as nearly as possible in the same condition. Thus they found
that the quantity of carbonic acid exhaled per hour in five different per-
sons was as follows :

QUANTITY OP CARBONIC ACID PER HOUR.
In subject No. 1 ...... 19,770 cubic centimetres.

" 2 15,888 "

" 3 , . . . . . 20,475 "

" 4 20,475 "

11 5 26,060 "

With regard to the difference produced by age, it was found that from
the period of eight years up to puberty the quantity of carbonic acid

1 Annales de Chimie et de Physique. Paris, 1843, tome viii. p. 490.

284 KESPIRATION.

increases constantly with the age. Thus a boy of eight years exhales,
on the average, 9238 cubic centimetres per hour ; while a boy of fifteen
years exhales 16,168 cubic centimetres in the same time. Boys exhale
during this period more carbonic acid than girls of the same age. In
males this augmentation of the quantity of carbonic acid continues
till the twenty-fifth or thirtieth year, when it reaches, on the average,
22,899 cubic centimetres per hour. Its quantity then remains stationary
for ten or fifteen years ; then diminishes slightly from the fortieth to
the sixtieth year ; and after sixty years diminishes in a marked degree,
so that it may fall as low as IT, 000 cubic centimetres. In one superan-
nuated person, 102 years of age, Andral and Gavarret found the hourly
quantity of carbonic acid to be less than 11,000 cubic centimetres.

In women, the increase of carbonic acid 'ceases at the period of
puberty; and its production then remains constant until the cessation
of menstruation, about the fortieth or forty-fifth year. At that time it
increases again until after fifty years, when it subsequently diminishes
with the approach of old age, as in men. Pregnancy, occurring at any
time in the above period, produces a temporary increase in the quantity
of carbonic acid.

The strength of the constitution, and particularly the development of
the muscular system, was found to have a great influence in this respect.
The largest production of carbonic acid observed was in a young man,
26 years of age, whose frame presented a remarkably vigorous and
athletic development, and who exhaled 26,060 cubic centimetres per
hour. On the other hand, an unusually large skeleton, or an abundant
deposit of adipose tissue, is not accompanied by any similar increase of
the carbonic acid.

Andral and Gavarret sum up the results of their investigation as
follows :

1. The quantity of carbonic acid exhaled from the lungs in a given
time varies with the age, the sex, and the constitution of the subject.

2. In the male, as well as in the female, the quantity of carbonic acid
varies according to age.

3. During all periods of life, the male and female may be distinguished
by the different quantities of carbonic acid exhaled in a given time.
Other things being equal, the male exhales a larger quantity than the
female. This difference is particularly marked between the ages of 16
and 40 years, during which period the male usually exhales twice as
much carbonic acid as the female.

4. In the male, the quantity of carbonic acid increases constantly from
eight to thirty years ; and the rate of this increase undergoes a rapid
augmentation at the period of puberty. Beyond forty years the exha-
lation of carbonic acid begins to decrease, and its diminution is more
marked as the individual approaches extreme old age, so that near the
termination of life, the quantity of carbonic acid produced may be no
greater than at the age of ten years.

5. In the female, the exhalation of carbonic acid increases according

CHANGES IN THE AIR BY RESPIRATION. 285

to the same law as in the male, from the age of eight years until puberty.
But at the period of puberty, at the appearance of menstruation, the
exhalation ceases to increase ; and it afterward remains stationary so
long as the menstrual periods recur with regularity. At the cessation
of the menses, the quantity of carbonic acid increases in a notable
manner ; then it decreases again, as in the male, toward old age.

6. During the whole period of pregnancy, the exhalation of carbonic
acid rises, for the time, to the same standard as in women whose menses
have ceased.

7. In both sexes, and at all ages, the quantity of carbonic acid is
greater, as the constitution is stronger and the muscular system more
fully developed.

The process of respiration is not altogether confined to the lungs,
but the discharge of carbonic acid takes place also, to a slight extent,
both by the urine and the perspiration. Morin1 has found that the
urine always contains gases in solution, of which carbonic acid is con-
siderably the most abundant. The mean result of fifteen observations
showed that urine excreted during the night contains about 1.96 per
cent, of its volume of carbonic acid. During the day the quantity of
this gas contained in the urine varied considerably, according to the
condition of muscular repose or activity.; since after remaining quiet for
an hour or two, it was only 1.19 per cent, of the volume of the urine,
while after continued exertion for the same space of time, not only was
the urine augmented in quantity, but the proportion of carbonic acid
contained in it was nearly doubled, amounting to 2.29 per cent, of its
volume.

An equal or even greater activity of gaseous exhalation takes place
by the skin. It has been found, by inclosing one of the limbs in an air-
tight case, that the air in which it is confined loses oxygen and gains
carbonic acid. From an experiment of this sort, Prof. Scharling esti-
mated that the carbonic acid given off from the whole cutaneous surface,
in man, is from one-sixtieth to one-thirtieth of that discharged during
the same period from the lungs. In the more recent and complete obser-
vations of Aubert upon this subject, the whole body without clothing
was confined in an air-tight case, leaving only the head exposed. A
continuous ventilation of the space was kept up during the course
of the experiment with air free from carbonic acid, while the carbonic
acid exhaled from the surface of the body was absorbed by baryta-
water. Each observation lasted for two hours, and the average result
obtained was that, for the entire day of twenty-four hours, 198 cubic
centimetres of carbonic acid were exhaled from the skin ; a quantity
representing rather less than 0.5 per cent, of that given off by the lungs
in the same time.

In the amphibious reptiles, as frogs, newts, and salamanders, which

1 Recherches sur les Gaz libres de 1'Uriue. Journal de Pbarmacie et de Chinrie.
Paris, 1864, tome xlv. p. 396.

286 RESPIRATION.

breathe by lungs, and yet can remain under water for a considerable
time, the thin, moist, and flexible integument takes a still more active
part in the process of respiration. The skin in these animals is covered,
not with dry cuticle, but with a delicate layer of epithelium. It accord-
ingly presents all the conditions necessary for the accomplishment of
respiration ; and while the animal remains beneath the surface of the
water, though the lungs are in a state of comparative inactivity, the
exhalation and absorption of gases continue to take place through the
skin, and respiration goes on without interruption.

Relation between the Oxygen absorbed in respiration and the Car-
bonic Acid given off. — It has been seen that, in the human subject, with
each respiration, on the average, 16 cubic centimetres of oxygen are
taken into the system by absorption, and 13 cubic centimetres of car-
bonic acid given off. As the oxygen thus taken in weighs rather less
than .023 gramme, while the carbonic acid discharged weighs .025
gramme, it is evident that the gross result of the process is a loss of
weight to the system, and this loss of substance by continued respira-
tion amounts on the average to a little over 70 grammes per day. This
is one of the most important facts connected with the plvysiology of
respiration. It shows that this function is carried on at the expense of
the substance of the animal body, since the oxygen and carbon dis-
charged under the form of carbonic acid, weigh more than the oxygen
which is absorbed in a free state. This difference in quantity must
accordingly be supplied in some way by the ingredients of the food;
and if this be withheld, the progress of respiration alone will be suffi-
cient to diminish gradually the weight of the body, and to bring it to a
state of more or less complete emaciation.

If we endeavor to ascertain what becomes of the oxygen itself, it is
found that the quantity of this gas which disappears from the inspired
air is not entirely replaced in the carbonic acid exhaled ; that is, there
is less oxygen in the carbonic acid which is returned to the air by expi-
ration than has been lost by it during inspiration.

The proportion of ox}-gen which disappears in the interior of the
body, over and above that returned in the breath under the form of
carbonic acid, varies in different kinds of animals. In the herbivora it
is about 10 per cent, of the whole amount of oxygen inspired; in the
carnivora, 20 or 25 per cent.; and even in the same animal, the propor-
tion of oxygen absorbed, to that of carbonic acid exhaled, varies accord-
ing to the kind of food upon which he subsists. In clogs, while fed on
meat, according to the experiments of Regnault and Reiset,1 25 per
cent, of the inspired oxygen disappeared in the body of the animal ;
but when fed on starchy substances, all but 8 per cent, reappeared in
the expired carbonic acid. Under some circumstances, a difference may
show itself in the opposite direction ; that is, more oxygen may be con-
tained in the carbonic acid exhaled than is absorbed in a free state from

1 Annales de Chimie et de Physique, tome xxvi. p. 428.

CHANGES IN THE AIR BY RESPIRATION. 287

the atmosphere. In some of the experiments of Regnault and Reiset,1
where rabbits and fowls had been led exclusively upon bread and grain,
the proportion of oxygen in the expired carbonic acid was 101 or 102
per cent, of that taken in by respiration ; and even in the human sub-
ject, according to the observations of Doyere, the quantity of oxygen
eliminated by the breath as carbonic acid, may be considerably greater
than that absorbed. But, as a general rule, it is the reverse ; the quan-
tity of oxygen which is not to be accounted for in the expired carbonic
acid being habitually greater in the carnivorous animals than in the
Jierbivora.

These facts have been established by direct observation, and without
any reference to the supposed manner in which the internal changes of
respiration take place. Nevertheless, they are susceptible of so ready
an explanation that there can be little doubt as to their significance.
The simplest case for examination would be that of an herbivorous ani-
mal living exclusively upon the carbo-hydrates, as starch or sugar.
Since these substances, as their name implies, already contain hydrogen
and oxygen in the proportions to form water, any further oxidation
which they undergo must result in the production of carbonic acid ;
and in this case exactly the same quantity of oxygen as that taken in
must necessarily be returned to the atmosphere as a constituent of the
carbonic acid exhaled ; the remainder of the substance being separated
from its combinations in the form of water. This process is represented
in the following formula :

Starch. Carbonic acid. Water.

C6H100- + 012 = CG012 + H1005.

In an animal supported upon this food, therefore, the whole of the
oxygen taken in by respiration would reappear in the expired carbonic
acid. But in an animal feeding also upon fatty substances, the propor-
tions would be changed. As these matters no longer contain oxj^gen
in the requisite quantity to form water with the hydrogen present, more
oxygen must be taken in with the breath than is sufficient to unite with
the carbon under the form of carbonic acid ; and consequently a portion
of it will disappear from the gaseous products of respiration. The
change in this instance is as follows :

Oleine. Carbonic acid. Water.

Cor^oA H- 0160 = C3701U + H104052.

In effecting, therefore, the complete disappearance of a fatty sub-
stance, 160 parts of oxygen will be absorbed, and only 114 parts re-
turned in the form of carbonic acid. This will also take place where
albuminous matters are used as food, since it is known that all the
nitrogen of these substances is expelled from the body under the form
of urea ; and after the separation of urea from albumen, a body must be
left which is analogous in composition to fat ; that is, which contains

1 Annales de Chimie et de Physique, tome xxvi. pp. 409-451.

288

RESPIRATION.

less oxjrgen than would be required to convert all its hydrogen into
water.

It is no doubt for these reasons that, in herbivorous animals, feeding
largely on the carbohydrates, the quantity of oxygen exhaled in the
carbonic acid should be nearly equal to that taken in with the breath ;
while in the carnivora, which consume only fats and albuminous matters,
a larger proportion of oxygen should disappear from the products of
respiration.

Finally, some kinds of vegetable food, as fruits and green tissues,
contain certain substances in which the oxygen is more than sufficient
to form water with the hydrogen present. Such are the salts of vegeta-
ble acids, like oxalic, citric, gallic, malic, and tartaric acid. The result
of the internal consumption of tartaric acid, for example, would be as
follows •

Tartaric acid.

Carbonic acid.

= c,o8 4-

Water.

H603.

In this instance more oxygen will be exhaled, in the carbonic acid
produced, than was absorbed from the atmosphere; because a super-
abundance already existed in the material used as food.

The relative proportions of oxygen and carbonic acid, absorbed and
expired in respiration, will therefore vary, as has been well shown by
Mayer,1 not only with the nature of the food, but also according to the
transformations, in the interior of the living organism, of one nutritive
substance into another, as of a carbohydrate into a fat, or of either into
an organic acid. In the fermentation of a saccharine solution there is
even an elimination of carbonic acid without the absorption of any
oxygen whatever ; this process being one, not of direct oxidation, but
of the rearrangement of the elements already present in the sugar, a
portion of them being exhaled as carbonic acid, while the rest remain
behind in the form of alcohol.

In the animal body the function of respiration consists, first in the
absorption of oxygen, and secondly in the exhalation of carbonic acid.
It is evidently, therefore, so far as its consequences are concerned, an
act of oxidation. But the elements of the food are in no case subjected
to immediate oxidation. They are digested in the alimentary canal and
taken up into the circulating fluid under other forms of organic com-
bination. These undergo still further transformations, both in the blood
and in the tissues, passing through a series of successive metamorphoses,
until they finally leave the body, principally under the forms of urea,
carbonic acid, and water. Oxidation, accordingly ? as it occurs in the
living body, is not so much the immediate process as the result of the
vital operations, and is very different from the direct combustion of
hydrocarbonaceous matters in the atmosphere.

Exhalation of Watery Vapor in Respiration. — The watery vapor,
exhaled with the breath, is given off by the pulmonary mucous mem-

1 Lehrbuch der Agrikultur-Chemie. Heidelberg, 1871, p. 101.

CHANGES IN THE AIR BY RESPIRATION. 289

brane, by which it is absorbed from the blood. At ordinary tempera-
tures it is transparent and invisible ; but in cold weather it becomes
partly condensed on leaving the lungs, and appears under the form of a
cloudy vapor in the breath. According to the researches of Valentin,
the average quantity of water exhaled from the lungs is about 500
grammes per day.

The exhalation of watery vapor by the lungs is a purely physical
process, dependent upon the moist and permeable structure of the pul-
monary mucous membrane and the volatility of the watery fluid, by
which it necessarily becomes vaporized under the requisite conditions
of temperature at the ordinary pressure of the atmosphere. Any moist
animal membrane, after death as well as during life, loses water by
evaporation and thus becomes gradually desiccated. Experiments upon
recently killed frogs have shown that the spontaneous desiccation goes
on rapidly at first, and afterward more slowly, as the proportion of water
contained in the tissues becomes diminished. In the lungs of a warm-
blooded animal during life all the requisite conditions are present for
rapid and continuous evaporation, namely, a moderately elevated tem-
perature, a constant renewal of atmospheric air by the movements of
respiration, and a continuous supply of fresh moisture to the pulmonary
membrane by the blood circulating in its vessels. The quantity of
watery vapor exhaled by the lungs in a given time is therefore increased
or diminished by corresponding changes in the rapidity of respiration,
by greater dryness or humidity of the atmosphere, and by increase or
diminution of the pulmonary circulation.

In some species of animals, as in the dog, where the integument is
comparatively destitute of perspiratory glands, the pulmonary trans-
piration becomes much more active ; and it is not uncommon to see
these animals, in hot weather, lying at rest with their tongues protruded,
and the movements of respiration doubled or trebled in frequency, for
the purpose of increasing the watery exhalation from the lungs.

In the human subject the precise physiological value of the pulmonary
transpiration is not known. Though subject to fluctuations according
to variation in the physical conditions above mentioned, it is a continu-
ous process, and even at ordinary temperatures the expired breath
directed upon a polished glass or metallic surface will always produce
an immediate dimness by the condensation of its watery vapor. It is
very possible that the vapor thus exhaled, beside being complementary
to the perspiration by the skin, may serve as a vehicle for the discharge
of certain other substances from the pulmonary cavity. •

Exhalation of Organic Matter by the Breath. — Beside carbonic acid
and water, the expired air also contains a small amount of an organic
ingredient, which communicates a faint but perceptible odor to the
breath. This substance is discharged in the vaporous form, probably
entangled in the watery vapor exhaled by respiration. Under ordinary
circumstances it is present in so small a quantity as to be hardly notice-
able ; but if a large number of persons be confined in a small apartment

290 RESPIRATION.

x

with insufficient ventilation, the organic matter accumulates in the
atmosphere, and after a few hours its odor becomes exceedingly offen-
sive. According to Carpenter, if the fluid condensed from the expired
air be kept in a closed vessel at ordinary temperatures, a putrescent
odor is after a time exhaled, which could only come from some organic
substance in a state of decomposition.

When perfectly fresh and in the healthy condition, the organic in-
gredient of the expired breath is not offensive and appears to have no
unwholesome qualities. It is only when accumulated in undue quantity,
and allowed to stagnate in the atmosphere, that its disagreeable properties
become manifest. It appears to be distinct in character for each species
of animal, and it is liable to be absorbed and retained for a time by any
porous material, as wood, rough plaster, or woven fabrics. It is easy
to distinguish by its odor the breath of cattle from that of sheep or
swine, and the odor remains perceptible in any small inclosure or trans-
portation-car in which these animals have been recently confined. The
organic ingredient of the expired air which communicates these quali-
ties to the breath has not been isolated in sufficient quantity to deter-
mine its exact composition.

Vitiation of the Air by Continued Respiration. — From what has pre-
ceded it is seen that the air, after being exhaled from the lungs, has
become altered in its constitution by diminution of its oxygen and the
addition of certain other materials derived from the breath. Under
ordinary conditions, this deteriorated air is at once diffused in the sur-
rounding atmosphere, rising to a higher level on account of its increased
temperature, and being readily dispersed by the aerial currents which
are always more or less in motion ; so that a fresh supply of air, with
its normal constitution, is taken into the lungs with each successive
inspiration. But when breathing is carried on in a confined space, the
air necessarily becomes vitiated ; and this effect is produced with rapidity
in proportion to the small extent of the air space and the number of
men or animals confined in it.

This vitiation of the atmosphere by respiration is accordingly the
result of several different changes taking place at the same time, and its
effects are a combination of those due to all these alterations.

So far as regards immediate danger to life, the diminution of oxygen
is no doubt the most important change in the vitiated air, when carried
to a sufficient extent. We have already seen that for man and the
mammalians, the air is completely irrespirable when its proportion of
oxygen is diminished to 10 per cent. In these experiments, however,
the carbonic acid exhaled was removed, as fast as produced, by the
action of an alkaline solution, so that the air was retained in a state of
purity except for its loss of oxygen. In the experiments of Leblanc, a
dog and a pigeon, breathing in a confined space, were both reduced to
extremities when the air still contained 16 per cent, of oxygen but was
also contaminated with 30 per cent, of carbonic acid. The different

CHANGES IN THE AIR BY RESPIRATION. 291

modifications of the atmosphere in respiration, therefore, react upon
each other and combine to produce a common result.

The second element in the vitiation of the respired air is that due to
the presence of carbonic acid. The effect of this gas, as produced by
respiration, cannot be ascertained from that of an atmosphere consisting
of carbonic acid alone. A man or an animal, introduced suddenly into
an atmosphere of pure carbonic acid, as sometimes happens in beer-vats
and old wells, dies at once by suffocation. But this result is not due to
the influence of carbonic acid. It is simply the consequence of the
absence of oxygen ; and death would take place as promptly, in the
warm-blooded animals, by exposure to an atmosphere of pure nitrogen
or any other indifferent gas. It may be said that, as a general rule, for
birds and small mammalians, the atmosphere becomes incapable of
supporting life when, in addition to its normal proportion of oxygen, it
contains 20 per cent, of its volume of carbonic acid ; that is, five times
as much as is present, in man, in the expired breath. But Regnault
and Reiset found that dogs and rabbits could continue to breathe with-
out difficulty in an atmosphere containing even 23 per cent of carbonic
acid, provided its proportion of oxygen were at the same time increased
to 30 or 40 per cent. Thus a part at least of the influence of carbonic
acid, when present exclusively or in large quantity in the atmosphere,
is evidently due to its physical action in excluding or interfering with
the absorption of oxygen.

When pure carbonic acid is gradually mingled with atmospheric
air, its immediate effects are not so fatal as they have sometimes been
represented. If a pigeon be confined in a glass receiver with a wide
open mouth, and carbonic acid be introduced through a tube placed just
within the edge of the vessel, so that it will not completely displace the
air but gradually mingle with it, its effect is to produce a rapid and
laborious respiration, gradually increasing in intensity ; and in a few
moments the pigeon falls in a state of complete insensibility. But if
the glass receiver be removed and fresh air allowed access, the insen-
sibility rapidly passes off, and in a few moments longer the animal is
again breathing in a natural manner, without having suffered any per-
ceptible permanent injury. The effect of carbonic acid alone, thus
mingled with the atmosphere, is very similar to that of an anaesthetic
vapor, like ether or chloroform, with the addition of strong symptoms
of dyspnoea.

There is evidence that in man the immediate effects of carbonic acid
in respiration are of a similar nature. From personal experiments upon
this subject we have found that the inhalation of pure carbonic acid
from a gasometer is at first extremely difficult, owing to the stimulant
effect of the gas upon the mucous membrane of the larynx, which pro-
duces a spasmodic stricture of the glottis. If the gas, however, be
allowed to remain in contact with the mucous membrane for a short
time, this effect passes off, the glottis may be gently opened, and the
carbonic acid drawn into the lungs, by a full, deep inspiration, to the

292 RESPIRATION.

amount of from 800 to 1200 cubic centimetres. At first it produces in
the chest only a sensation of warmth and moderate stimulus. But at
the end of two or three seconds there comes on very suddenly a sense
of extreme dyspnoea, with rapid and laborious respiration, accompanied
immediately by dimness of vision, slight confusion of mind, and partial
insensibility, all of which are soon terminated, as respiration returns to
its normal condition, leaving only a feeling of quietude and tendency to
sleep.

Notwithstanding, however, the intense feeling of dyspnoea produced
by such an inhalation of pure carbonic acid, the external signs of actual
suffocation are very slight, and bear no proportion to the severity of
the sensations. They are confined to a little suffusion of the face with
partial lividity of the lips ; and the pulse is but little if at all affected.

A mixture of carbonic acid and atmospheric air in equal volumes pro-
duces a perceptible feeling of warmth and pungency at the glottis, but
may still be readily drawn into the lungs. After two or three deep
inspirations, the strong sense of want of air, and the access of rapid and
laborious respiration, come on as before. The dyspnoea, suffusion of
the face, and lividity are all less marked than after breathing pure
carbonic acid, but the subsequent condition of quiescence and partial
anaesthesia is more decided and of longer continuance.

A mixture of one volume of carbonic acid with three volumes of
atmospheric air may be inspired without difficulty, producing a rather
agreeable sensation by contact with the lungs. After about 3000 cubic
centimetres have been inhaled in successive inspirations, a sense of
dyspnoea comes on, which however is not particularly increased by con-
tinuing the inspiration of the mixture to 6000 cubic centimetres. The
nervous symptoms produced are moderate in degree, but similar to the
preceding.

On the other hand, pure nitrogen has no taste or odor, nor does it
have any stimulating effect on the mucous membrane. It may be inspired
from the gasometer to the amount of 6000 cubic centimetres, without
producing any sense of dyspnoea, or any perceptible effect on the nervous
system.

These results indicate that the presence of carbonic acid in the lungs
acts as a stimulus to respiration by causing a sense of the want of air ;
and that furthermore its principal toxic effect, when in abnormal quan-
tity, is that of producing more or less insensibility or anaesthesia. The
sense of drowsiness and inattention experienced by an audience in an
imperfectly ventilated lecture-room or theatre is probabry due to this
cause, especially as the burning gas-lights are at the same time contribu-
ting to the formation of carbonic acid. The temporary nature of these
sensations, and their immediate relief on coming into the open air, are
matters of common observation.

The third element in the vitiation of air by the breath is the accumu-
lation of its organic vapor. This is the least understood, but probably
the most deleterious ingredient of the atmosphere produced by respira-

CHANGES IN THE BLOOD BY RESPIRATION. 293

tion in a crowded and ill-ventilated apartment. It is this which causes
the offensive odor and the sense of oppression on entering any confined
space, where too great a number of persons have remained for a time
without sufficient renewal of the air. It is most marked when such con-
tinued respiration and neglect of ventilation have been going on over
night, as in a crowded dormitory or sleeping-car; since the organic
emanations have then had time not only to accumulate but also to pass
into a state of incipient decomposition. They are then in the condition
in which they belong to the class of animal poisons ; and there is reason
to believe that, once introduced into the system, they may cause dis-
turbances which last for a considerable time. It is certain that the con-
tagion of many febrile diseases, as scarlatina, meases, and smallpox, is
communicated through the air by the products of respiration ; and the
normal organic exhalations of the pulmonary mucous membrane, when
altered by concentration, the accumulation of moisture, and an elevated
temperature, are undoubtedly capable of producing morbid effects of an
analogous kind.

All the above causes of vitiation of the atmosphere in respiration,
notwithstanding the differences in their nature and effects, are to be
obviated by the same means ; that is, a sufficient renewal of the air by
ventilation.

Changes in the Blood by Respiration.

The blood as it circulates in the arterial system has a bright scarlet
color; but as it passes through the capillaries it gradually becomes
darker, and on arriving in the veins it is deep purple, or in some situ-
ations nearly black. There are, therefore, two kinds of blood in the
body ; arterial blood, which is of a bright color, and venous blood, which
is dark. The dark-colored venous blood, which has been thus altered
by passing through the capillaries, is incapable, in this state, of supply-
ing the organs with their healthy stimulus and nutrition, and has lost its^
value as a circulating fluid. It is accordingly returned to the heart by
the veins, and is thence sent, through the pulmonary artery, to the lungs.
In passing through the pulmonary circulation it reassumes its scarlet
hue, and is again converted into arterial blood. Thus the most striking
physical effect produced upon the blood by respiration is its change of
color from venous to arterial.

This change is accomplished by the influence of the air in the pulmo-
nary cavities. For if defibrinated venous blood, recently drawn from
the veins of the living animal, be shaken up in a glass vessel with
atmospheric air, it at once changes its color and acquires the bright hue
of arterial blood. If injected through the vessels of the lungs them-
selves after removal from the body, the lungs being filled with air, the
same change takes place. If a dog be rendered insensible by a narcotic
injection or other similar means, the thorax opened, and artificial re-
spiration kept up by the nozzle of a bellows inserted into the trachea,
the dark venous blood can be seen in the great veins and in the right

294 EESPIRATION.

auricle of the heart, while that returning from the lungs to the left
auricle is bright red. But if artificial respiration be stopped, the circu-
lation through the lungs continuing, the blood soon ceases to be arteri-
alized in the pulmonary capillaries, and returns to the left auricle of a
dark venous hue. On recommencing artificial respiration, arterialization
of the blood is again produced, and its red color is restored in the pul-
monary yeins and the left cavities of the heart.

At the same time, in passing through the pulmonary circulation, the
blood undergoes a change in its gaseous constituents, the converse of
that which is produced in the air ; that is, it absorbs oxygen and exhales
carbonic acid.

Passage of Oxygen into the Blood in Respiration. — The oxygen which
is absorbed from the air in the lungs is taken up by the blood circulating
in the pulmonary capillaries. It does not at once enter into intimate
chemical union with other elementary substances, but is still in the form
of solution or of such loose combination that it may be removed from
the blood by means of the air-pump, by a current of hydrogen or nitro-
gen, and especially by the action of carbonic oxide (CO), which expels
it completely. According to a large number of observations which have
been made on this point, its quantity, in the fresh arterial blood of the
dog, may vary from a little over 10 per cent, to 22 per cent, of the
volume of the blood ; the average in the experiments of Schoeffer and
Ludwig1 being about 15 per cent.

Nearly the whole of the oxygen is taken up by the blood-globules;
the hemogiobine of which has been shown to possess so remarkable a
power of absorption for this gas that one gramme of hemogiobine in
solution will absorb more than one cubic centimetre of oxygen. Ac-
cording to the experiments of Magnus, while the blood contains more
than twice as much oxygen as water could hold in solution at the same
temperature, the serum alone has no more solvent power for this gas
'than pure water ; and on the other hand, defibrinated blood, that is, the
serum and globules mingled, dissolves as much oxygen as the fresh blood
itself. Pfliiger also found, as the average of six observations on the arte-
rial blood of the dog, that the oxygen contained in the entire blood was,
by volume, 15.6 per cent., while in the serum alone he found only 0.2 per
cent. According to the same observer, the arterial blood in the carotids
contains nearly though not quite all the oxygen it is capable of holding in
solution ; since a specimen of dog's blood drawn directly from the artery
already contained 18.8 per cent, of oxygen, and after being shaken up
with atmospheric air contained rather less than 20 per cent. The blood,
therefore, either does not become fully saturated with oxygen in passing
through the lungs, or else a little of this gas has already passed into
some other form of combination on reaching the carotid arteries.

The color of the blood depends solely on the presence or absence of
oxygen, not on that of carbonic acid. Yenous blood, shaken up with

1 Archiv fur die Gesammte Physiologic, 1868, Band 1, p. 279.

CHANGES IN THE BLOOD BY RESPIRATION. 295

oxygen or atmospheric air, at once assumes the arterial tint, although
its carbonic acid may remain. According to Pfliiger's experiments, if
defibrinated dog's blood be placed in two flasks, and shaken up, one with
pure oxygen, the other with a mixture of oxygen and carbonic acid, both
specimens will present the same bright color ; both of them being found
on analysis to contain nearly the same quantities of oxygen, while their
proportions of carbonic acid are very different. Also the recently drawn
blood of these animals, after they have been made to breathe either pure
oxygen, or oxygen and carbonic acid mingled, is of the same color in
each instance ; the percentage of oxygen which it contains being the
same, but that of carbonic acid being different in the two cases.

It is the oxygen, therefore, which, on being taken up by the blood-
globules, changes their color from dark purple to bright red. It passes
off with the arterial blood in this condition, and is then distributed to
the capillary circulation. Here, as the blood comes in contact with the
tissues, its oxygen in great measure disappears, and its color is again
changed from arterial to venous.

The loss of oxj^gen by the blood, in traversing the capillaries, is due
to its transfer from the blood-globules to the substance of the tissues.
Nearly all the tissues, in fact, exert an absorbent power upon oxygen,
when exposed to this gas or to atmospheric air containing it. The ex-
periments of Paul Bert1 have shown that the following tissues, extracted
from the body of the recently killed dog and exposed to the contact of
atmospheric air in closed vessels, absorb oxygen, with different degrees
of intensity, in the following order, namely : muscles, brain, kidneys,
spleen, testicle, and pounded bones. Of these the muscles are the most
active, absorbing 50 cubic centimetres of oxygen for every 100 grammes
of muscular tissue; while the bones absorb only a little over Jt cubic
centimetres for the same weight of substance.

The tissues have even a greater absorbent power for oxygen than the
blood-globules themselves. This is shown by the experiments of Spal-
lanzani, and still more completely by those of Bert. In these experi-
ments, three equal portions of recently drawn defibrinated dog's blood
are placed in test-tubes, a piece of fresh muscular tissue from the same
animal being introduced into one of them, a portion of the spleen-tissue
into another, while the third is left to itself. After a time it is found
that the solid tissues have abstracted oxygen from the blood with which
they are in contact, so that in these two specimens the blood, on
analysis, contains less oxygen than in the third specimen, which has
remained by itself. The result obtained by Bert was as follows :

QUANTITY OF OXYGEN BY VOLUME REMAINING IN

Blood left to itself 18 per cent.

Blood containing spleen tissue . . 12 "

Blood containing muscular tissue 6 "

1 Lecjons sur la Physiologic compare de la Respiration. Paris, 1870, p. 46.

296 RESPIKATION.

Finally, successive analyses of the blood, as it passes from the arte-
rial into the venous system, shows that it loses oxygen in proportion as
it has been subjected to the influence of the capillary circulation. Ber-
nard1 found that the blood of the same dog, from different parts of the
circulatory system, 3delded, by the action of carbonic oxide, the follow-
ing quantities of oxygen :

QUANTITY OP OXYGEN BY VOLUME IN

Arterial blood 18.93 per cent.

Yenous blood from right side of heart . . . 9.93 ';
Yenous blood from hepatic veins .... 2.80 "

The average quantity of oxygen existing in venous blood generally is
8 per cent. ; that is, it is reduced about one-half from its proportion in
arterial blood.

Thus the blood-globules serve as carriers of oxygen from the lungs
where it is absorbed, to the tissues where it is consumed ; and the first
object of respiration is to supply oxygen to the blood, in order that the
blood may supply it to the tissues.

Exhalation of Carbonic Acid by the Blood. — The venous blood, as it
returns to the right side of the heart, is already charged with carbonic
acid to such an extent that a portion of this gas is exhaled through the
pulmonary membrane, and discharged with the breath. Its absolute
quantity in the blood has not been determined with the same accuracy
as that of the oxygen. Carbonic oxide, which is so efficient for the
extraction of oxygen from the blood, displaces only a portion of its
carbonic acid ; and in the experiments of Bernard, the maximum quan-
tity of carbonic acid obtained from venous blood by this means was
only about 6.5 per cent, by volume. A much larger proportion may be
extracted by the mercurial air-pump, amounting on the average, in the
experiments of Ludwig, to about 28 per cent, for arterial blood, and
about 31 per cent, for venous blood. But a large part of the carbonic-
acid obtainable in this way does not exist in a free form in the blood,
but in a state of combination with the alkaline phosphates and carbon-
ates of the plasma; since it is known that a wratery solution of sodium
bicarbonate will lose a portion of its carbonic acid, and become reduced
to the condition of a carbonate by being subjected to the influence of a
vacuum, or even by agitation with pure hydrogen at the temperature
of the ~body. Lehmann found2 that after the expulsion from ox's blood
of all the carbonic acid removable by the air-pump and a current of
hydrogen, there still remained 0.1628 per cent, of sodium carbonate,
with wThich a certain quantity of the carbonic acid previously given off
must have been united in the form of bicarbonate.

It is estimated by Bert, according to the experiments of Fernet, that
a portion of the carbonic acid of the blood is in simple solution and a

1 Liquides de 1'Organisme. Paris, 1859, tome i. p. 394.

2 Physiological Chemistry, Cavendish edition. London, 1854, vol. i. p. 438.

CHANGES IN THE BLOOD BY RESPIRATION. 297

portion combined with the alkaline salts ; the blood, when artificially
saturated with this gas, containing about three-fifths in a state of solu-
tion and about two-fifths in a state of combination. We do not know,
however, what this proportion is in the venous blood as it exists in the
living body ; and the large amount of carbonic acid removable by the
action of a vacuum does not represent that which is capable of being
exhaled from the blood through the pulmonary membrane. This quan-
tity is very much smaller. We know that, on the average, 13 cubic
ceniirnetres of carbonic acid are discharged from the lungs in man with
each expiration ; and during this interval, judging from the capacity
of the left auricle and the frequency of its pulsations, there can hardly
be less than 400 cubic centimetres of blood passing through the pulmo-
nary circulation. This would give only a little over 3 per cent, as the
volume of carbonic acid discharged from a given quantity of blood in
respiration. The average results obtained by extraction with the mer-
curial air-pump, in the experiments of Ludwig, give this quantity as
the actual difference between venous and arterial blood, as follows :

AVERAGE QUANTITY OF CARBONIC ACID REMOVABLE BY THE AIR-PUMP, FROM

Venous blood 31.27 per cent.

Arterial blood 27.99 "

Difference 3.28

All the different modes of analysis, whether by carbonic oxide, other
indifferent gases, or the air-pump, though differing in the quantity of
gas extracted, show that there is less carbonic acid in arterial than in
venous blood, and accordingly that this gas is exhaled from the circu-
lating fluid during its passage through the lungs.

Unlike the oxygen, the carbonic acid of the blood is principally con-
tained in the plasma^ and not in the blood globules ; since the capacity
of absorption for this gas is not essentially different for the serum and
for the entire blood.

Source of the Carbonic Acid of the Blood — The source of the car-
bonic acid of the blood, as well as the destination of its oxygen, is in
the tissues themselves. From the experiments of various observers it
is found that every organized tissue, in the recent condition, has the
power of absorbing oxygen and exhaling carbonic acid. G. Liebig,
for example, showed that frogs' muscles, recently prepared and com-
pletely freed from blood, will continue to absorb oxygen and discharge
carbonic acid. Similar experiments with other tissues have led to the
same result. It is in the substance of the tissues, accordingly, that the
oxygen becomes fixed and assimilated, and that the carbonic acid takes
its origin. These two phenomena, however, are not immediately de-
pendent upon each other. This is shown by the fact that animals and
fresh animal tissues will continue to exhale carbonic acid in an atmo-
sphere of hydrogen or of nitrogen, or even when placed in a vacuum.
Marchand found that frogs would live for from half an hour to an hour
20

298 RESPIRATION.

in pure hydrogen gas ; and that during this time they exhaled even
more carbonic acid than in atmospheric air, owing probably to the
superior displacing power of hydrogen for carbonic acid. For while
1000 grammes' weight of frogs exhaled about 0.071 gramme of carbonic
acid per hour in atmospheric air, they exhaled during the same time in
pure hydrogen as much as 0.263 gramme. The same observer found
that frogs would recover on the admission of air after remaining for
about half an hour in a nearly complete vacuum ; and that if they were
killed by total abstraction of the air, 1000 grammes' weight of the ani-
mals were found to have eliminated 0.600 gramme of carbonic acid.
Similar facts were previously observed by Spallanzani ; and Paul Bert
found that while a certain quantity of fresh muscular tissue, in atmo-
spheric air, exhaled in a given time 30 cubic centimetres of carbonic acid,
the same quantity, in pure hydrogen, exhaled 23 cubic centimetres during
the same time. He even found that the exhalation of carbonic acid
would continue to go on, in an atmosphere of nitrogen, from muscular
tissue which had previously been subjected for a quarter of an hour to
the action of a vacuum.1

It is furthermore evident that in this process of internal respiration
by the tissues, as in the external phenomena of respiration by the lungs,
the quantities of oxygen absorbed and of carbonic acid exhaled do not
always bear the same relation to each other. This is shown by the ex-
periments of Paul Bert on the gases absorbed and discharged by the
different tissues of the dog in contact with atmospheric air, where in
some instances the volume of carbonic acid produced was greater, and
in others less than that of the oxygen consumed ; the proportions of
the two varying considerably in each case.

The following list gives the result of a series of these experiments :

QUANTITY OP 0 AND C0a ABSORBED AND EXHALED DURING 24 HOURS,

IN CUBIC CENTIMETRES.
By 100 grammes of Oxygen absorbed. Carbonic acid exhaled.

Muscle 50.8 56.8

Brain 45.8 42.8

Kidneys 37.0 15.6

Spleen 27.3 15.4

Testicles 18.3 27.5

Pounded bones .... 17.2 8.1

The production of carbonic acid by the tissues is not, therefore, di-
rectly connected with the absorption of oxygen. The precise chemical
action by which carbonic acid originates in the solid organs is unknown ;
but it is probably by some mode of decomposition in which a portion
of the carbon and oxygen present in the tissues separate from their
previous combinations in this form, while the remaining elements at the
same time unite to produce other substances of different composition.

The process of respiration consists, accordingly, in an interchange of

1 LeQons sur la Physiologic comparee de la Kespiration. Paris, 1870, p. 49.

CHANGES IN THE BLOOD BY RESPIRATION. 299

gases between the blood and the lungs. The blood coming to the lungs
comparatively poor in oxygen and charged with carbonic acid, the for-
mer gas is absorbed from the air in the pulmonary vesicles, while the
latter is discharged at the same time, to be exhaled with the breath.
These changes, however, are neither of them complete, but only partial,
both for the air and for the blood. The expired air is never deprived
of the whole of its oxygen, and contains only about 4 per cent, of its
volume of carbonic acid. On the other hand, the venous blood coming
to the lungs still contains a moderate percentage of oxygen ; and a cer-
tain quantity of carbonic acid is also present in arterial blood. It is
only the proportion of -these gases which is changed in respiration, the
carbonic acid of the blood being diminished, and its oxygen increased,
by its passage through the pulmonary circulation.

The office of the respiratory apparatus is therefore to afford ingress
and egress to the two substances which enter and leave the body in
the gaseous form. These two substances have no immediate relation
with each other, excepting as to the organ by which they are absorbed
and exhaled. They represent the beginning and the end of a series of
internal combinations and decompositions, which are among the most
essential of the changes contributing to the maintenance of life.

CHAPTER XIV.

ANIMAL HEAT.

ONE of the characteristic properties of living creatures is that of
maintaining, more or less constantly, a standard temperature, notwith-
standing the external changes of heat or cold to which they are sub-
jected. If a bar of iron or a vessel of water be heated to a temperature
above that of the external air, and then left to itself, it will at once
begin to lose heat by radiation and conduction ; and this loss of heat
will continue until, after a certain time, the temperature of the heated
body has been reduced to that of the surrounding atmosphere. It then
remains stationary at this point, unless the atmosphere should become
warmer or cooler ; in which case a similar change takes place in the
inorganic body, its temperature remaining constant or varying with
that of the surrounding medium.

With man and many animals the case is strikingly different. If a
thermometer be introduced into the stomach or rectum of a dog, or
placed under the tongue of the human subject, it will indicate a tem-
perature of from 37° to 38° (about 100° F.),1 whether the surrounding
atmosphere at the time be warm or cool. This internal temperature of
the body is sensibly the same in summer and in winter. Although the
external air may be at the freezing point, the internal parts of the body,
in a condition of health, will indicate their usual standard of warmth
when examined by the thermometer; and even in ordinary summer
weather the temperature of the air is, for the most part, many degrees
below that of the living body. As the body, however, by exposure to
such an atmosphere must be constantly losing heat by radiation and
conduction, like any inorganic mass, and yet maintains a standard tem-
perature, it is plain that a certain amount of heat must be generated in
its interior, sufficient to compensate for the external loss. The internal
-heat, so produced, is known by the name of vital or animal heat.

Thus it is by its own internal heat that the body is warmed. The
clothing used by man, and the fur, wool, or feathers by which the
bodies of animals are protected, have, of course, no warmth in them-
selves ; they simply prevent the body from losing heat too rapidly and
thus becoming cooled down below its normal standard. Even the fur-
naces and fires of a dwelling house only serve in a similar way to
moderate the cooling influence of the air ; for the atmosphere, even in

•

1 To convert any given number of degrees of the Centigrade scale into the
corresponding value for the Fahrenheit scale, multiply by 1.8 and add 32 to the
product.

(300)

ANIMAL HEAT. 301

the warmest apartment, never rises to the heat of the living body, which
is still the only source of its own vital temperature.

Differences of Temperature in Different Classes of Animals. — The
intensity of the production of internal heat varies in different classes
of animals. As a rule, it is most active in birds, whose temperature is
in general 45°. In the mammalians it is 37° to 40°; in man about
ST. 5. As in these two classes the internal organs and the blood are
nearly always much above the temperature of the air or of the surface
of the skin, and accordingly feel warm to the touch, they are called the
"warm-blooded animals." In reptiles and fish, on the other hand, the
production of heat is much less rapid, and preponderates so little over
that of the air or water which they inhabit, that no marked difference is
perceptible on cursory examination ; and as their internal organs have
a lower temperature than our own integument, and consequently feel
cool to the touch, they are called the "cold-blooded animals." This
difference, however, is only one in degree and not in kind. Reptiles
and fish also generate heat within their bodies, which may be measured
by the thermometer. The temperature of frogs, serpents, tortoises,
water-lizards, and fish has thus been found to be from 1.7° to 4.5°
above that of the surrounding air or water.

In the invertebrate animals, as insects and the like, the heat produced
is still less easily perceptible because, from the great extent of the sur-
face presented by their bodies in proportion to their mass, the warmth
is more rapidly dissipated. But when many of them are collected in a
small air-space, or when they are in a state of activity, it is still distin-
guishable by thermometric measurement. The temperature of the butter-
fly after active motion has been found to be from 2.77° to 5° above that
of the air; that of the humble-bee from 1.5° to 5.5° higher than the
exterior. According to the experiments of Newport, the interior of a
hive of bees may have a temperature of 9° when the external atmos-
phere is at 1.4°, even while the insects are quiet ; but if they be excited
to activity by tapping on the outside of the hive, it may rise to 38.8°.
Thus, while the insects are at rest, the thermometer indicates a very
moderate temperature ; but if kept in rapid motion in a confined space,
they may generate a sufficient amount of heat to produce a sensible
elevation in the course of a few minutes.

The production of heat is not confined to animal organisms, but takes
place also in vegetables. Here, however, it is still more rapidly dissi-
pated than in insects, owing to the great extent of surface presented
by the ramifications and foliage, and to the abundant evaporation of
moisture from the leaves, by which the heat generated is in great
measure consumed without becoming perceptible by the ordinary ther-
mometer. If this loss of heat from the plant be diminished by keeping
the air charged with watery vapor and thus preventing evaporation, the
elevation of temperature becomes sensible and may be measured. Du-
trochet1 first demonstrated, by the use of the thermo-electric needle, that

1 Annales des Sciences naturelles. Paris, 2me S6rie, tome xii. p. 277.

302 ANIMAL HEAT.

nearly all parts of a living plant, such as the green stems, the leaves,
the buds, and even the roots and fruit, generate a certain amount of
heat; the maximum temperature thus detected being about 0.28° above
that of the surrounding atmosphere. Subsequent observations have
shown that in certain periods of vegetative activity, as in the processes
of germination and flowering, the development of heat is much more
rapid. In the malting of barley, when a considerable quantity of the
germinating grain is piled in a mass, its elevation of temperature may
be readily distinguished, both by the hand and the thermometer. The
most striking example of heat-production in flowers is presented by
those of the Aracese (Calla, Indian turnip, Sweet flag) at the time of
fecundation,1 which in warm weather ma}^ show a temperature of 4°,
5°, or even 10° above that of the surrounding air.

The generation of heat is accordingly a phenomenon common to all
living organisms, whether animal or vegetable. When the mass of the
organized body is large in proportion to its extent of surface, the heat
thus produced is readily distinguishable both by the touch and by the
thermometer. When rapidly dissipated by increased extent of surface,
and especially by the evaporation of moisture, it is less easily detected,
but it exists in each case. In birds and mammalians it is more active
than in reptiles and fish ; and even in different species of animals belong-
ing to the same class, it is usually found that the normal temperature
of the body, like the other physiological phenomena, differs slightly,
according to the special organization of the animal and the general
activity of its functions.

Quantity of Heat in the Living Body. — The quantity of heat produced
in the body within a given time is best measured by the increase of
temperature which it will produce in a certain volume of water. Prof.
John C. Draper2 found that the human body, having a volume of about
85 litres (3 cubic feet) and a weight of 81.65 kilogrammes (180 pounds
avoirdupois), by remaining at rest in the bath for one hour, could raise
the temperature of 212 kilogrammes of water 1.1 1° ; which he estimates,
assuming the specific heat of the body to be about the same with that
of water, would be capable of warming the body itself 2.11°. But as
the temperature of the body, in the observation quoted, was lowered
0.55° while in the bath, the heat actually generated would be capable
of warming the body itself, or an equal volume of water, 2.22°. This
would be equivalent to 188.7 heat units,3 produced by the human body
in the course of one hour, or 2.31 heat units for every kilogramme of
bodily weight.

The experiments of Senator4 on the heat-producing power in dogs

1 Sachs, Traite de Botanique. Paris, 1874, p. 847.

2 American Journal of Science and Arts. New Haven, 1872, vol. ii. p. 445.

3 A heat unit is the quantity of heat required to raise the temperature of one
kilogramme of water from 0° to 1° of the centigrade scale.

4 Archiv fur Anatomic, Physiologic, und Wissenschaftliche Medicin. Leipzig,
1872.

ANIMAL HEAT. 303

were performed with much accuracy. The animals were inclosed in a
copper cage, through which ventilation was kept up at a known rate,
the temperature of the incoming and outgoing volumes of air being noted
at intervals of ten minutes. The cage containing the animal was sur-
rounded by a known volume of water, at from 26.5° to 29°, and the
whole apparatus inclosed in an outer case made as nonconducting as
possible ; the quantity of heat actually lost from it by external cooling
being determined by preliminary observations. The internal tempera-
ture of the animal having been taken, he was introduced into the cage
and allowed to remain there a certain time. The heat produced within
this time was mainly ascertained by the increase of temperature in the
water surrounding the cage, the result being corrected by that of the
air used for ventilation, as well as by the variation in temperature of the
animal himself, and the loss from the apparatus by external cooling.
By this method the experimenter found, as the average result of five
observations, that a dog of 5.392 kilogrammes' weight, at rest and in
the fasting condition, produced in one hour 12.63 heat units; that is,
2.34 heat units for every kilogramme of bodily weight. According to
these experiments, the heat-producing power in the dog and that in the
human subject are nearly the same; while that of the dog is rather the
more active of the two.

Normal Variations of Temperature in the Living Body. — The tem-
perature of the body is not the same in its different regions, but increases
for a certain distance, from the exterior toward the central parts. This
is because the living body is subjected to a constant loss of heat from
the surface, like any other solid substance of higher temperature than
the surrounding air. Consequently the integument and the parts im-
mediately subjacent to it, being more exposed to this cooling influence
than the internal organs, have habitually a temperature slightly below
that of the body in general. Accordingly, whenever the external air
rises to the neighborhood of 3t° or 3f.5° it feels uncomfortably warm ;
because, although this is exactly the normal temperature of the blood
and the internal organs, it is considerably above that of the skin, which
is readily sensitive to variations of cold or warmth. The cooling influ-
ence of the external atmosphere upon the skin is considerably moderated
by the movement of the circulation ; since the warmer blood coming
from the internal parts constantly supplies the integument with fresh
quantities of heat and thus tends to compensate for its external loss.

Notwithstanding this compensation, however, the difference in tem-
perature between the external and internal parts of the body is always
perceptible during health. If the bulb of a thermometer be held for
some minutes between the folds of skin in the palm of the hand, it will
stand at 36.4° ; in the axilla, at 36.6° ; under the tongue, it will reach
37.2°; in the rectum, 31.5°; and Dr. Beaumont found, in the case of
Alexis St. Martin, that the thermometer, introduced into the stomach
through the gastric fistula, often indicated a temperature of 31.8°. It
is evident therefore that, in order to ascertain the real internal tempera-

304 ANIMAL HEAT.

ture of the body, the bulb of the thermometer should be inserted so
deeply as to pass beyond the superficial zone affected by the process of
external cooling. Even when placed beneath the tongue it is in contact
with parts which are themselves slightly cooled by the passage of the
air in inspiration and expiration, and accordingly does not reach the
maximum temperature of the body. To accomplish this, it must be in-
serted into the abdominal cavity or the rectum, so deeply that a further
introduction produces no increase in the indicated temperature. This
is the method usually adopted in physiological observations.

Beside the differences observable from the above cause between the
superficial and the deep-seated parts, there is a real variation within
narrow limits of the internal temperature of the body, according to dif-
ferent physiological conditions. Jiirgensen has shown1 that in the human
subject there is a diurnal variation, the temperature during the day
being a little higher than at night, even when both periods are passed
in complete repose. A series of observations upon the same individual
in a state of rest gave the following averages :

TEMPEKATURE OF THE HUMAN BODY WHEN AT REST.
By day. By night.

37.34° 36.91°

The difference between the two averages amounts to 0.43°. There
are also temporary variations of small extent during each of the above
periods ; the greatest variation during the day being 0.21° ; that during
the night 0.15°.

The temperature of the body is also increased by muscular activity.
It is a matter of common observation, both in man and animals, that
temporary exertion produces an increase of bodily warmth. Jurgensen
observed in the same individual that while during a day of absolute
rest the maximum temperature attained was 37.7°, under the influence
of exercise it reached 38.8°. A much more striking difference, corre-
sponding with muscular repose or activity, has already been mentioned
as observable in insects.

The animal temperature is furthermore increased or diminished by a
condition of digestion or abstinence. This was indicated in several
instances by the observations of Jurgensen upon man, but is shown in
a very marked degree by those of Senator upon the dog, in which the
average production of heat was sensibly diminished by continued fast-
ing and increased by the digestion of food. The following table shows
the quantity of heat produced by the same animal, in the conditions of
abstinence and digestion.

QUANTITY OF HEAT PRODUCED BY THE DOG IN ONE HOUR.
After two days' fasting .... 10.90 heat units.
After one day's fasting .... 12.63
Fed one hour previously .... 18.87

1 Die Korperwarme des gesundcn Menscben. Leipzig, 1873.

MODE OF PRODUCTION OF ANIMAL HEAT. 305

As the production of heat in the body can only take place by the con-
sumption or change of combination of its ingredients, it is evident that
in continued abstinence from food, the materials susceptible of this
change must be constantly diminishing in quantity ; and the animal
temperature accordingly, like other vital phenomena, becomes depressed
from a deficiency in the sources of its supply.

Mode of Production of Animal Heat.

In all instances, so far as observation has gone, the production of
heat in living organisms is in proportion to the activity of the internal
changes going on in the body. These changes are more especially and
constantly indicated by the absorption of oxygen and the exhalation
of carbonic acid in respiration. Even in the vegetable kingdom, it is
demonstrated by the researches of physiological botanists that the ab-
sorption of oxygen in plants is always accompanied both by the pro-
duction of carbonic acid and by the evolution of heat ; and the quantity
of heat produced is greatest at the time when those processes are going
on which, like germination and flowering, are accompanied by the most
active absorption and exhalation of oxygen and carbonic acid respec-
tively.

The same thing is manifest in the different classes of the animal king-
dom. Birds and mammalians, where respiration is most active, have
also the highest temperature; while in reptiles and fish the respiratory
process is more sluggish, and the production of heat at the same time
less abundant. A very close connection between the two phenomena is
observable in hibernating animals, in which, during the winter sleep,
respiration becomes comparatively inactive and the bodily temperature
is also reduced to a very low standard. In the observations of Horvath1
on the respiration of marmots, he found that these animals during cold
weather are plunged in a profound stupor in which the movements of
respiration are exceedingly infrequent and sometimes hardly perceptible.
At certain intervals the animals awake for a short time, after which
they again return to the state of insensibility. Horvath found that the
internal temperature of the marmot, when awake, was from 35° to 37°;
while, in the hibernating condition, it was reduced to 10°, 9°, or even
to 2°, according to that of the surrounding air. On awakening, the tem-
perature of the body rapidly rises. In one animal, the internal tempera-
ture during sleep was from 9° to 10° ; but on awakening it rose at the
end of an hour to 12°, in two hours to 17°, and in two hours and a half
to 32°. Respiration also becomes increased in activity to a similar
degree. A marmot weighing 153 grammes produced, while in the
comatose condition, 0.015 gramme of carbonic acid per hour; and two
days afterward, when awake, produced 0.513 gramme in the same time,
that is, more than thirty times as much as when in the state of hiberna-
tion.

1 Revue des Sciences Medicales. Paris, 1873, tome i. p. 59.

306 ANIMAL HEAT.

These and similar facts point to so close a relation between the
intensity of respiration and that of heat-production, that the one of
these processes may be taken, in general terms, as the measure of the
other ; particularly as respiration consists in the absorption of oxygen
and the exhalation of carbonic acid, and as we know that the oxidation
of carbonaceous matters, outside the body, is one of the readiest means
for the production of heat.

This connection, however, is not an immediate one, nor can we con-
sider the production of heat in the living body as a result of simple
oxidation. We have already seen in the preceding chapter that the
formation of carbonic acid is not due to direct oxidation, since it will
go on in the tissues without the immediate presence of oxygen. Re-
spiration is essential to all the phenomena of animal life, and may be
taken as the criterion of vital activity in general. The production of
heat is one of these phenomena, and, like the rest, increases or dimin-
ishes in intensity with that of respiration ; but it cannot be said to
depend upon respiration in any peculiar or exclusive manner.

The Evolution of Heat and the Products of Eespiration not strictly
proportional. — Furthermore, notwithstanding the general relation in
activity between the two functions, if an accurate comparison be made
between the quantity of heat produced, under different circumstances,
and that of oxygen absorbed or of carbonic acid exhaled, they are
found not to correspond exactly with each other. In the experiments
of Senator on the bodily temperature in dogs, it was shown that the
evolution of heat and the production of carbonic acid do not follow the
same rate of increase. They are both augmented during digestion, but
the production of carbonic acid never in the same degree with that of
heat. An examination of the averages obtained in three series of obser-
tions gives the following result :

„ XT , ( Fasting .
Dog No. 1 { In d]gestioi

QUANTITIES OF HEAT AND OF CARBONIC ACID PRODUCED BY THE DOG IN ONE HOUR.

Condition Carbonic acid in Proportion

of the animal. grammes. Heat units. between the two.

. . 3.455 12.630 1 to 3.65

ion . . . 5.013 18.875 1 to 3.76

( Fasting .... 4405 16.500 1 to 3.72

Dog No. 2 j In digestion m t m 4837 19 390 1 to 4.01

f Fasting .... 3.154 16.880 1 to 5.35

Dog No. 3 1 In digestion , m 3,846 21.960 1 to 5.71

Thus the proportion of carbonic acid formed to the heat produced is
different in the three animals when compared with each other in the
same condition ; and it also varies in each animal under the different
conditions of fasting and digestion.

In the experiments of the same observer on the effect exerted by arti-
ficial cooling on the animal body, he found that under the influence of a
low temperature the actual production of heat in dogs was never in-
creased, but was usually perceptibly diminished; while that of carbonic
acid was generally somewhat increased and never diminished.

MODE OF PRODUCTION OF ANIMAL HEAT. 307

It is evident, accordingly, that the evolution of heat in the living
animal is due to other causes than those which result in the immediate
production of carbonic acid. Even outside the body a notable elevation
of temperature may be produced by the hydration of quicklime, the
mixture of alcohol and water, or of sulphuric acid and water, as well
as other chemical or physical actions in which direct oxidation does not
take part. Many analogous changes may take place in the process of
internal nutrition, from which a part, at least, of the animal heat origin-
ates in the living body.

Local Production of Heat in the Organs and Tissues — Although
the living body, as a whole, presents a certain standard temperature,
the production of heat takes place separately in each organ and tissue
by the changes of nutrition which go on in its substance. This is
shown by the fact that each separate organ has a special temperature
of its own, which increases or diminishes according to its condition of
activity or repose. A very considerable quantity of heat is thus pro-
duced in the substance of the muscles. The experiments of Becquerel
and Breschet on the brachialis, in man, showed the temperature of this
muscle in repose to be 36.5° ; while, after repeated and energetic flexion,
it was from 37° to 37.5°. Bernard,1 by placing thermo-electric needles
in the two gastrocnemii muscles of the dog, after section of the spinal
cord to prevent voluntary movements, found the temperature of the
muscles on the two sides to be sensibly equal ; but on producing con-
traction by galvanizing one of the sciatic nerves, the temperature of
the muscle on that side rose from 0.1° to 0.2°, at the same time that
the venous blood of the muscle became darker in hue. Since the
muscles constitute so large a part of the mass of the body, it is easy to
understand how continuous muscular exertion should, after a time,
produce a general elevation of temperature. In the muscles, during
contraction, the increase in warmth is always accompanied by a greater
consumption of oxygen, and consequently by a darker color of the
venous blood.

Heat is also produced in the glandular organs when in active secre-
tion, as shown by comparing the temperature of the arterial blood enter-
ing with that of the venous blood leaving the glandular tissue. Under
these circumstances the venous blood coming from the gland is warmer
than the arterial blood with which it is supplied. According to the
observations of Bernard upon the submaxillary gland of the dog, while
the gland is in repose, the circulation through its tissue is slow, its
venous blood scanty and very dark-colored, and the oxygen of the arte-
rial blood is reduced, in traversing the organ, to 40 per cent, of its
original quantity ; but when the gland is excited to active secretion, its
circulation is increased in rapidity, its venous blood is more abundant
and of a brighter color, its oxygen being only reduced to 61 per cent,
of that contained in the arteries. At the same time its temperature

1 Revue Scientifique. Paris, 1871, No. I., p. 1064.

308

ANIMAL HEAT.

rises, notwithstanding the consumption of oxy gen is less than in the
condition of glandular repose.

A similar elevation of temperature is shown by the blood while tra-
versing the capillary circulation of the intestine and of the liver. The
following tables give the results of two series of observations by Ber-,
nard on the temperature of the blood entering and leaving these two
organs in the dog:

TEMPERATURE OF THE BLOOD IN THE
Aorta. Portal Vein.

36.8° 38.8°

40.3° 40.7°

39.40 39.5°

Portal Vein. Hepatic Vein.
40.2° 40.6°

40.6° 40.9°

40.7° 40.9°

Thus the blood of the hepatic vein, after traversing two successive
capillary circulations, is warmer than that drawn from any other part
of the body.

Even in the kidneys, when the secretion of urine is actively going on,
there is a rise of temperature in the blood of the renal veins. At the
same time, as in the submaxillary glands, the circulation is increased in
activitjr, the venous blood leaves the organ of a bright red color, and its
proportion of oxygen, according to Bernard, is only reduced to 88 per
cent, of that contained in the arteries, while in the condition of glandular
repose it is reduced to 33 per cent.

The production of heat, therefore, is accomplished in the different
organs of the body with different degrees of intensity according to the
special nature of the act of nutrition in each one. In the muscles it is
accompanied by an increased consumption of oxygen and a deeper
coloration of the venous blood ; in the salivary glands and the kidneys
by a diminished consumption of oxygen and a less complete change in
the color of the blood. The blood coming from each organ has a higher
temperature in proportion to the activity of heat-production in the
organ itself; and thus the temperature of the venous blood varies in
different parts of the circulatory system, while that of the arterial blood
is everywhere sensibly the same.

Cooling of the Blood in its Passage through the Lungs and Skin. —
While in the other internal organs the blood is warmed during its pass-
age through the capillary vessels, in the lungs its temperature is slightly
diminished. This fact, which has been alternately asserted and denied,
owing to the difficulties of exact observation without introducing other
causes of a change of temperature, has been abundantly confirmed by the
more recent observations of Bering, Bernard, Heidenhain and Korner,
and Strieker and Albert. That of Hering was made upon a young calf,
otherwise in good condition, but presenting the malformation of ectopia

MODE OF PRODUCTION OF ANIMAL HEAT. 309

eorclis, by which the heart was withdrawn from the immediate contact
of other organs, and in which case the blood of the right ventricle had
a temperature of 39.37°, that of the left ventricle 38.75°. Heidenhain
and Korner,1 in 94 observations on the dog, partly with the use of thermo-
electric needles and partly with the mercurial thermometer, found the
temperature of the blood on the two sides of the heart equal in only
one instance. In all the others, it was higher on the right side than on
the left, by 0.1° to 0.6°. Bernard,2 who first demonstrated this differ-
ence by the mercurial thermometer, has shown it also by the use of
thermo-electric needles, introduced into the right and left ventricles of
the dog's heart, through the jugular vein and carotid artery respectively ;
always finding the blood in the right ventricle warmer than that in the
left. According to these observations, the difference in temperature may
amount in the fasting animal to 0.174°, during digestion to 0.232°.
Although during digestion the temperature of the blood generally is
higher than in the fasting condition, the difference between the two
sides of the heart continues to show itself in the same direction.

The diminution in temperature of the blood while passing through the
lungs is usually attributed to the physical influence of the cooler air in
the pulmonary cavities and to that of the vaporization of watery fluid.
As the air expelled by respiration is warmer than when introduced into
the lungs, it must withdraw a certain amount of heat from the internal
parts ; and as it contains, furthermore, watery vapor disengaged from the
lungs, the vaporization of this fluid must also reduce the temperature of
the respiratory organs. Whether the cooling influence of these causes
is more or less than sufficient to account fully for the difference in the
blood on the two sides of the heart has not been determined. It is pos-
sible that heat is also produced in the lungs, as in the other internal
organs ; but that the wrhole of it, and a little more, is consumed by the
influence of the air upon the pulmonary membrane. It is evident, how-
ever, that physical conditions exist in the lungs which must cause the
disappearance of more or less sensible heat ; and it is certain that the
blood, in point of fact, diminishes slightly in temperature while passing
through the pulmonary circulation.

In the cutaneous circulation the same physical causes exist for a cool-
ing effect on the blood as in the lungs ; namely, the contact of the skin
with the cooler air, and the vaporization of the watery fluid supplied by
perspiration. It is for this reason, as already mentioned, that the super-
ficial parts of the body have a normal temperature somewhat below that
of the interior ; and accordingly the blood, after passing through the
vessels of the integument, returns to the centre with its temperature
slightly diminished. There is every reason to believe that the tissues
of the skin and subjacent parts evolve a certain amount of heat by their
own nutritive changes ; but the heat thus produced, as in the case of the

1 Archiv fur die Gesammte Physiologie. Bonn, 1871, Band iv. p. 558.

2 Eevue Scientifique. Paris, 1871, No. 1, p. 946.

310 ANIMAL HEAT.

lungs, being rather more than counterbalanced by that lost from the
surface, the total effect upon the circulating fluid is a lowering of its
temperature. The amount of warmth thus lost will vary with the degree
of external cold and other conditions of the atmosphere which influence
the rapidity of the abstraction of heat.

Local Elevation of Temperature by increased Circulation. — If the
circulation be increased in any part of the external integument, the
immediate effect produced is a local rise of temperature. This was first
shown by Bernard in his experiments upon division of the sympathetic
nerve on one side of the neck. If this operation be performed upon the
rabbit, the consequence is a relaxation of the bloodvessels in the cor-
responding side of the head, an increased vascularity of the parts, most
readily seen in the semi-transparent tissues of the ear, and a higher
temperature, readily perceptible both by the touch and the thermometer.
In a rabbit, after section of the sympathetic nerve upon the right side
of the neck, the temperature of the corresponding ear, as indicated by
the thermometer, was increased from 25° to 32°; and the difference
between the two sides is usually more marked as the external air is
colder. Since the superficial parts of the body are habitually cooler
than the internal on account of their exposure to the air, and as they
are constantly supplied with warm blood from the interior, their actual
temperature will be increased in proportion to the amount of blood cir-
culating through their vessels. The local rise of temperature in these
instances is a passive one, the exposed tissues being warmed at the
expense of the blood coming from the internal organs. No more heat
is actually produced in the body than usual, and the cooling effect of the
air upon the whole system is unchanged ; but it is less perceptible in
the part subjected to experiment, because it receives a larger quantity
of heat from the interior owing to the increased volume of blood passing
through it in a given time.

This influence of the circulation upon the temperature of the external
parts has been shown by Dr. Wier Mitchell1 by observations upon the
human subject. If the hand and arm be held for some moments above
the head, emptied as fully as possible of blood, and a tourniquet then
applied to the arm in such a way as to check the circulation, the tem-
perature of the hand falls 0.55°. If, on the contrary, the circulation be
left unimpeded, and a freezing mixture applied to the elbow, sufficient
to chill the ulnar nerve, when sensation has become entirely abolished
the temperature of the corresponding hand rises from 1.10° to 2.20°.
But if the arm be first emptied of blood as before, the tourniquet applied,
and the ulnar nerve then chilled to insensibility, the temperature of the
hand no longer rises, but falls, as in the former experiment, 0.55°.

In the internal or glandular organs, on the other hand, when ex-
cited to functional activity, the rise of temperature is an active one,
taking place in the substance of the gland itself; since the blood

1 Archives of Scientific and Practical Medicine. New York, 1873, vol. i. p. 354.

REGULATION OF THE ANIMAL TEMPERATURE. 311

passing through these organs becomes warmer instead of cooler, and
receives heat from the changes taking place in the glandular tissue.

Equalization of Temperature by the Circulation. — As the production
of heat is a local process in each separate organ or tissue, varying in
intensity with the nature of the nutritive changes in different parts, the
blood, as we have seen, acquires a higher temperature in some organs
than in others ; and in the lungs and skin its heat actually diminishes
instead of increasing. If it remained at rest, these differences of tem-
perature would no doubt be more marked than they are at present. But
as the blood is in constant motion, passing from the circumference to
the centre, and being again distributed from the centre to the circum-
ference, the effect of this movement of circulation is to equalize to a
considerable degree the temperature of different parts of the body. The
venous blood coming from the general integument with a diminished
temperature is mingled with that of the muscular system, which has
become warmed during its capillary circulation. The blood of the
hepatic veins, which is the warmest of all, joins the current of the inferior
vena cava, returning from the pelvic organs and the inferior extremities.
This is again mingled, at its entrance into the right cavities of the heart,
with the slightly cooler column of blood descending from the head and
upper extremities by the superior vena cava. The whole volume of the
blood then passes through the lungs, with the effect of still further
moderating its temperature ; and the arterial blood is then distributed
to the various parts of the body, to gain warmth in some of them and to
lose it in others, and again mingled after a few seconds at the centre
of the circulation. Thus the superabundant heat of certain organs,
where its production is most active, is constantly transferred to others
by the moving column of the blood ; and a certain equilibrium or standard
of temperature is thus established for the body as a whole. It is found,
by the observations of Jurgensen, that this standard temperature for
the human body, as measured in the rectum, varies within very narrow
limits, from day to night, and even at successive periods of each division
of the twenty-four hours. These normal fluctuations are no doubt owing
to the greater or less activity, at different times, of different internal
organs ; the total amount of heat produced being increased or dimin-
ished with the preponderating influence of organs in which it is more or
less rapidly generated.

Regulation of the Animal Temperature.

A certain temperature is .not only the result of the vital actions; it is
also necessary to their accomplishment. Even in the vegetable king-
dom this temperature, which varies within moderate limits in different
kinds of plants, is requisite for all the phenomena of growth and vitality.
A seed sown in the most productive soil does not germinate until it
feels the influence of the necessary warmth ; and its germination is also
impossible if it be exposed to a heat which is too intense. The degrees
both of heat and cold which favor or arrest the functions of vegetation

312 ANIMAL HEAT.

have been in many instances accurately determined. According to the
experiments of Sachs, the limits of germination for wheat and barley
are between 5° and 38°, and for Indian corn between 9° and 42°. The
irritability and periodic movements of the sensitive-plant do not show
themselves unless the temperature of the surrounding air be above 15°.
In air at 48° to 50°, on the other hand, the leaflets become rigid in a
few moments, though they may afterward recover if the temperature be
moderated; while a heat of 52° permanently destroys their vitality.
Thus no vegetative function can come into activity, unless the tempera-,
ture of the plant reaches a certain degree above the freezing point ; and
it ceases, furthermore, if the temperature rise above another determinate
degree, which cannot for any considerable time exceed 50°. Within
these two limits, also, every vegetable function has a special tempera-
ture at which it is most active; diminishing in intensity both above
and below this point.

Observation shows that the same is true of the animal functions.
Each species of animal has a definite bodily temperature, and this tem-
perature cannot be raised or lowered beyond certain limits without
arresting the phenomena of life. Mammalians, whose normal tempera-
ture is from 37° to 40°, become insensible and soon die, when cooled
down to 18° or 20°, which is the natural standard for reptiles and fish;
while a frog is soon killed by being kept in water at 38°. On the other
hand, mammalians die when their blood and internal organs are heated
up to 45°, which is precisely the normal temperature of birds; and
birds themselves are fatally affected when their internal temperature is
raised to 48° or 50°. In every case the vital functions are seriously
disturbed by a very moderate change in the actual temperature of the
bodily organs ; and in the mammalians, as a general rule, death follows
when this change amounts to an elevation of 6° or 7°, or to a depres-
sion of 20°.

In the human subject, in febrile affections, the rise of temperature, as
measured in the axilla, yields a very accurate criterion of the gravity of
the disease. An increase of this temperature from 36.6° to 37.5° or 38°
indicates a mild form of the malady; but an increase to 40° or 40.5°
shows that the attack is severe. Above 40.5° it is a symptom of great
danger; and when the temperature rises to 42.5° or 43° a fatal result is
almost inevitable.1

Effects of Lowering the Temperature of the Animal Body. — If a
warm-blooded animal be exposed to cold in such a way as to abstract
the internal heat faster than it can be produced, the effect is a general
and continuous depression of the vital functions. After a short period
of pain in the more exposed and sensitive parts, the skin becomes
insensible, the muscles lose their contractile energy, the movements of
respiration diminish in frequency, and the nervous system becomes more
and more inactive. In the human subject a marked sluggishness of

1 Flint, Principles and Practice of Medicine. Philadelphia, 1868, p. 109.

REGULATION OF THE ANIMAL TEMPERATURE. 313

mind and a disposition to sleep have been observed as among the symp-
toms of long continued and dangerous exposure to unusually low tem-
peratures.

The local effects of cold upon the nervous tissues in man have been
shown by the experiments of Dr. Weir Mitchell,1 in chilling the ulnar
nerve at the elbow by the application of a freezing mixture. This at
first produces pain in the hand, subsequently followed by loss of sensi-
bility and motive power in the parts corresponding with the distribu-
tion of the nerve.

The general effects of a lowered temperature result from its combined
influence upon all the separate organs and tissues. According to the
observations of Bernard, if the body of a rabbit or a guinea-pig be sur-
rounded by snow or ice so as to prevent spontaneous motion and to
cause a continuous abstraction of heat, the temperature, as taken in
the rectum, gradually falls from 38° to 30°, 25°, 20°, and 18°. When
the depression of the bodily temperature has reached this point, the
animal is insensible and paralyzed, and the respiration feeble and infre-
quent. The heat-producing power is also lost, so that if the animal be
withdrawn from the cooling mixture and kept in the air at 10° or 12°,
the temperature of the body continues steadily to diminish, and death
takes place after a short time.

But when in this condition of depression and insensibility, although
most of the vital actions are suspended, and the animal has lost the
power of maintaining his own temperature, if he be supplied with arti-
ficial warmth up to a certain point, he may regain his vitality, and the
processes of life be again put in operation. The respiration, which
was reduced to a minimum by the continued action of cold, becomes
increased in rapidity as the body is artificially warmed, and the func-
tions of the nervous and muscular systems are also finally restored.

A striking example of the temporary suspension of the bodily func-
tions by cold is presented by the hibernating animals, as marmots and
some species of squirrels, which pass into a condition of torpor during
the winter, becoming insensible, unconscious, and immovable, while
at the same time respiration is nearly imperceptible, and the bodily
temperature sinks to 10°, 8°, or even 2°. Life, however, is not abol-
ished but only held in abeyance ; and with the return of spring all the
functions resume their activity. A hibernating animal is accordingly
somewhat in the condition of a seed, which remains in the ground over
winter, with its vitality dormant, but ready to come into action when
supplied with the requisite degree of warmth.

Effects of Elevating the Temperature of the Animal Body. — If the
temperature of the body, in a living animal, be artificially raised some
degrees above the normal standard, the effects are quite different from
those produced by cold. In the experiments of Bernard, the animals,
both birds and mammalians, were inclosed in a cage with heated air ;

1 Injuries of Nerves and their Consequences. Philadelphia, 1872, p. 59.
21

314 ANIMAL HEAT.

the air being sometimes dry and sometimes loaded with moisture, but
renewed by due ventilation. The primary effects were increased fre-
quencjr of respiration and an appearance of discomfort and agitation ;
and finally death took place usually with convulsive movements, some-
times accompanied by an audible cry. The fatal result was more rapidly
produced in birds than in mammalia. Thus, a rabbit placed in the cage
with dry air at 65°, died in twenty minutes; and a bird, in air at the
same temperature, died in four minutes. This difference is no doubt
partly due to the greater activity of the circulation in birds, by which
external heat is more rapidly transferred to the internal organs ; since
the same observer found that of two rabbits, one living and one dead,
placed in the warm cage at 100°, the internal temperature of the living
animal became sensibly raised sooner than that of the dead one. In a
medium of high temperature, therefore, a fatal amount of heat reaches
the internal organs more rapidly by means of the circulation than by
simple conduction through the solid tissues.

After death from exposure to too warm an atmosphere, the internal
temperature is found to be 5° or 6° above the normal standard; the
heart is motionless ; both the muscles and the nerves are insensible to
the stimulus of galvanism ; and lastly, cadaveric rigidity is established
with unusual promptitude. In many instances the blood is found dark-
colored in the arterial as well as in the venous system ; but this is a
post-mortem change, since observation shows that the arterial blood
continues red so long as life lasts, while its oxygen disappears and its
color darkens with great rapidity after the stoppage of respiration. The
appearances indicate that an unnaturally high temperature produces
death by hastening, in an undue degree, the chemical changes taking
place in the tissues and fluids, in such a manner that their vitality is
rapidly exhausted and can no longer be maintained by the usual pro-
cesses of nutrition.

Resistance of the Living Body to Low External Temperature. — Since
an actual depression of the temperature of the body is followed by such
serious results, and as, in point of fact, its temperature is maintained in
health at the normal standard, notwithstanding exposure to varying
degrees of cold, it is evident that the living organism possesses the
power of increased production of internal heat, to compensate for the
greater loss without. In the experiments of Senator on the abstraction
of warmth, by confining dogs in close cages surrounded by a cold me-
dium, it was found that the total amount of heat produced by the ani-
mal was not increased. But in these cases the animals were placed
under conditions by which their natural movements were prevented,
and the results obtained were due to simple cooling of the body, with-
out the action of compensating causes. In the natural, unconfined con-
dition, the effect is different. It is a matter of common observation,
that the influence of moderate external cold, if not too long continued,
produces a sense of warmth and increased vigor, instead of depression.
The atmosphere of a winter's day, or a cold shower bath, acts as a

REGULATION OF THE ANIMAL TEMPERATURE. 815

stimulant to vital processes ; and, even although the exposed parts of
the skin may be reduced considerably below their normal temperature,
the body, as a whole, does not experience a loss of warmth, but main-
tains its natural condition of vitality. It is certain that under these
circumstances more heat than usual must be produced from the influ-
ence of external cold.

The mode in which this result is accomplished has not been deter-
mined with precision by experimental means. It is plain that the
nervous system has its share in the mechanism of the process, perhaps
by directly stimulating the molecular changes which produce the evolu-
tion of animal heat. There are, however, two sources of heat supply,
which evidently play an important part in maintaining the temperature
of the body when exposed to cold.

The first of these is muscular activity. It has been shown that the
muscles produce a considerable quantity of heat in their own tissue, and
that this quantity is increased by the contraction of the muscular fibres.
The total production of heat, therefore, for the whole body, must be
considerably augmented when all the voluntary muscles are thrown into
a condition of unusual functional activity. Experience shows that this
is, in fact, one of the requisite conditions of resistance to cold. The
stimulus of the cool air upon the skin excites the desire for active move-
ment, and muscular exercise produces a compensating quantity of
internal heat. But if the body be exposed to even moderate winter
weather without voluntary motion, it must either be protected by an
unusual quantity of clothing, or it will soon feel the depressing effect
of a loss of its animal heat.

Secondly, the increased production of warmth, when required, is pro-
vided for by an increased supply of food. The materials for the chemical
changes requisite for heat-production are supplied directly by the tissues
or the blood, but primarily, of course, from the ingredients of the food.
Even a recent ingestion of food, as shown in the experiments of Senator,
increases perceptibly the amount of heat generated, in the dog, within
a given time ; and for longer periods, the influence of an ample or a
scanty supply is abundantly manifest. In animals which are scantily
fed or ill nourished, the capacity for resistance to cold is much less than
in those which are in good condition and which have received a suffi-
cient quantity of food. The immediate effect of a moderate exposure
to cold in the healthy condition, is to increase the appetite. A larger
quantity of food is habitually taken during the winter than during the
summer season; and among the inhabitants of northern and arctic
regions, the daily consumption of food is much greater than in the
temperate and tropical climates.

It is not necessary to assume that the food, thus required for main-
taining a greater heat-production, is directly employed to furnish the
necessary warmth by its consumption. The heat is no doubt generated
from the activity of all the nutritive changes in the different tissues of
the body, and these changes are enabled to continue indefinitely only by

316 ANIMAL HEAT.

a supply of food sufficiently ample to provide for the material demands
of the animal system.

Resistance of the Living Body to High External Temperature. — It
has been seen that, in the human subject and the warm-blooded animals
generally, an actual rise in the bodily temperature of 6° or 7° is certainly
fatal ; and yet the body may be exposed, as shown by repeated observa-
tions, to much higher degrees of heat without any injurious result.
According to Dr. Carpenter, the temperature of the air, in many parts
of the tropical zone, often rises, during a large portion of the year, to
43.3°, and in some regions of India is occasionally above 50°; while it
is well known that the air of manufactory dr3ring-rooms and of the
Turkish bath may be easily endured at a heat of considerably more than
45°. Either of these temperatures would be fatal to man, if they indi-
cated the actual warmth of the internal organs. The body therefore
must either possess some means of diminishing its own production of
heat, or else of neutralizing, to a certain extent, temperatures which are
higher than that of the normal standard.

The most direct and simplest means of moderating the temperature
of the body is that by the cutaneous perspiration. This fluid, derived
from the perspiratory glands of the skin, is a clear, colorless, watery
secretion, with a distinctly acid reaction, and a specific gravity of 1003
or 1004. Its constitution is as follows :

COMPOSITION OF THE CUTANEOUS PERSPIRATION.

Water

Sodium chloride

Potassium chloride ........

Sodium and potassium sulphates .....

Salts of organic acids

1000.00

It is accordingly a fluid of very simple composition, containing more
than 99^ per cent, of water, and more than half its solid ingredients
consisting of the inorganic alkaline chlorides. There are also present
in the perspiration traces of an organic substance similar to albumen,
and a free volatile acid, which gives to the fluid its acid reaction and
odor.

The perspiration is a constant secretion. In a condition of repose or
of moderate bodily activity, it is exuded in so gradual a manner that it
is at once carried off by evaporation, and has received the name, under
these circumstances, of the insensible transpiration. The entire quantity
of fluid discharged in this way, according to the observations of Lavoi-
sier and Seguin, amounts on the average to 900 grammes per day. In
addition to this, about 500 grammes are discharged from the lungs,
making 1400 grammes of daily exhalation from the whole body. The
vaporization of this quantity of water will consume 750 heat units; or

REGULATION OF THE ANIMAL TEMPERATURE. 317

about one-fifth of all the heat produced in the body during twenty-four
hours.

The cutaneous secretion may be greatly increased by temporary causes.
An elevated temperature or unusual muscular exertion, will increase the
circulation through the skin and largely augment the amount of fluid
discharged. It then exudes more rapidly than it can be carried off by
evaporation, and collects upon the skin as a visible moisture, whence it
is known as the sensible perspiration. The amount of perspiration dis-
charged during violent exercise has been known to rise as high as 350
or 380 grammes per hour ; and Dr. Southwood Smith1 found that the
laborers employed in heated gas-works sometimes lost, by both cutane-
ous and pulmonary exhalation, nearly 1600 grammes in the course of an
hour. The evaporation of this increased quantity of fluid consumes a
large portion of the caloric derived from the heated atmosphere, and
thus prevents an undue rise in the temperature of the bodily organs.

It is possible that certain influences transmitted through the nerves
may also have the power of controlling directly the molecular activity
of the tissues, and may thus diminish the amount of internal heat at
the source of its production ; but the experimental evidence of this
action is yet incomplete, and its mode of operation comparatively
obscure.

The production of heat in the animal body and the regulation of its
temperature, by which it is maintained at or near a normal standard,
are two of the most important phenomena presented by the living organ-
ism. They are the result of an associated series of vital actions, and
at the same time essential conditions for the continuance of life.

1 Philosophy of Health. London, 1838, chap. xiii.

CHAPTER XV.

THE CIRCULATION.

THE blood is a nutritious fluid, holding in solution the ingredients
necessary for the formation of the tissues. In all the higher animals
and in man, the structure of the body is compound, consisting of various
organs, with widely different functions, situated in different parts of the
frame. In the intestine the process of digestion is accomplished, and
the prepared ingredients of the food are thence absorbed into the blood-
vessels, by which they are transported to distant parts. In the lungs
the blood absorbs oxygen, which is afterward appropriated by the
tissues ; and the carbonic acid produced in the tissues is finally exhaled
from the lungs. In the liver, the kidneys, and the skin, other substances
are produced or eliminated, and these local processes are all necessary
to the preservation of the general organization. The circulating fluid
is therefore a means of transportation, by which substances produced in
particular organs are dispersed throughout the body, or by which sub-
stances produced in the tissues generally are conveyed to particular
organs, in order to be eliminated.

The circulatory apparatus consists of four different parts, namely, 1st.
The heart ; a hollow, muscular organ, which propels the blood. 2d. The
arteries ; a series of branching tubes, which convey it from the heart to
different parts of the body. 3d. The capillaries ; a network of inoscu-
lating tubules, interwoven with the substance of the tissues, which bring
the blood into intimate contact with their component parts ; and 4th.
The veins ; a set of converging vessels, destined to collect the blood
from the capillaries, and return it to the heart. In each of these different
parts of the circulatory apparatus, the movement of the blood is peculiar
and dependent on special conditions.

The Heart.

The structure of the heart and of the adjacent vessels varies in dif-
ferent classes of animals, owing to the different arrangement of the
respiratory organs.

In man and the mammalians the process of respiration is not only
much more active than in cold-blooded animals, but the lungs are also
the only special organs of aeration. The whole of the blood, accord-
ingly, after returning from the general system, passes through the
lungs before it is again distributed to the system. It thus traverses in
succession the general circulation for the whole body, and the special
circulation for the lungs. The mammalian heart (Fig. 99), consists of
(318)

THE HEART.

319

Fig. 99.

a right auricle and ventricle (a, 6), receiving the blood from the vena

cava (i), and driving it to the lungs; and a left auricle and ventricle

(/, g) receiving the blood from

the lungs and propelling it out-

ward through the arterial sys-

tem.

In the mammalian heart, the
different parts of the organ pre-
sent certain peculiarities and bear
certain relations to each other,
which influence its action and
movements. The heart itself is
suspended somewhat freely in
the cavity of the chest, attached
to the spinal column mainly by
the great bloodvessels passing
through the superior and pos-
terior mediastinum. It is of a
more or less conical form ; its base,
situated upon the median line,

being directed upward and back-

,,.,., . , ,

Ward, While its apex points down-

ward, forward, and to the left,
, , , ,, . ,.

surrounded by the pericardium,

but capable of a certain degree

of lateral and rotatory motion. The auricles, which have a smaller

capacity and thinner walls than the ventricles, are situated at the upper

and posterior part of the organ (Figs. 100 and 101); while the ventri-

CIRCULATION IN MAMMALIANS.— a.
Right auricle. b. Right ventricle, c. Pulmon-
ary artery, d. Lungs, e. Pulmonary vein.
/. Left auricle, cr. Left ventricle, h. Aorta.

< Vena cava>

Fig. 100.

Fig. 101.

HUMAN HEART, anterior view.—
a. Right ventricle. 6. Left ventricle.
c. Right auricle, d. Left auricle, e.
Pulmonary artery, /. Aorta.

HUMAN HEART, posterior view. —
a. Right ventricle. 6. Left ventricle.
c. Right auricle, d. Left auricle.

cles occupy its anterior and lower portions. The two ventricles, more-
over, are not situated on the same plane. The right ventricle occupies

320 THE CIRCULATION.

a position somewhat in front and above that of the left ; so that in an
anterior view of the heart the greater portion of the left ventricle is con-
cealed by the right (Fig. 100), and in a posterior view the greater por-
tion of the right ventricle is concealed by the left (Fig. 101) ; while in
both positions the apex of the heart is constituted altogether by the
point of the left ventricle.

The different cavities of the heart and of the adjacent bloodvessels on
each side, though continuous with each other, are partially separated by
certain constrictions. The orifices by which they communicate are
known by the names of the auricular, auriculo-ventricular, and aortic
and pulmonary orifices ; the auricular orifices being the passages from
the venae eavse and pulmonary veins into the right and left auricles ; the
auriculo-ventricular orifices leading from the auricles into the ventricles ;
and the aortic and pulmonary orifices leading from the ventricles into
the aorta and pulmonary artery respectively.

The auriculo-ventricular, aortic, and pulmonary orifices are furnished
with valves, which allow the blood to pass readily from the auricles to
the ventricles, and from the ventricles to the arteries, but shut back in
such a manner as to prevent its return in the opposite direction. The
course of the blood through the heart is, therefore, as follows (Fig. 102) :

Fig. 102.

RIGHT AURICLE AND VENTRICLE; Auriculo-ventricular Valves open, Arterial

Valves closed.

From the vena cava it passes into the right auricle ; and from the right
auricle into the right ventricle. On the contraction of the right ventri-
cle, the tricuspid valves shut back, preventing its return into the auricle
(Fig. 103) ; and it is thus driven through the pulmonary artery to the
lungs. Returning from the lungs, it enters the left auricle, thence
passes into the left ventricle, from which it is finally delivered into the
aorta, and distributed throughout the body. The two streams of blood,

THE HEART.

321

arterial and venous, in their passage through the heart, follow a course
which is, in each case, curvilinear and more or less spiral in direction ;

Fig. 103.

RIGHT AURICLE AND VENTRICLE; Auriculo-ventricular Valves closed, Arterial

Valves open.

the axes of the currents crossing each other in the right and left cavi-
ties of the organ respectively (Fig. 104). The venous blood, received

Fig. 104.

COURSE OP BLOOD THROUGH THE HEAKT. — a, a. Vena cava, superior and inferior.
b. Right ventricle, c. Pulmonary artery, d. Pulmonary vein. e. Left ventricle. /.Aorta.

by the right auricle from the two venae cavae, passes downward and
forward from the auricle into the ventricle. In the body of the right

322 THE CIRCULATION.

ventricle it turns upon itself and then follows a direction from below
upward, from right to left and from before backward, through that part
of the right ventricle tying in front of the heart and termed the " conus
arteriosus," to the commencement of the pulmonary artery. On return-
ing from the lungs to the left auricle, it passes from above downward
into the cavity of the left ventricle, when it makes a turn like that upon
the right side and is directed again from below upward and from left to
right, behind the situation of the conus arteriosus, and crossing it at an
acute angle, to the commencement of the aorta. The aorta itself, though
its point of origin is placed somewhat posteriorly to that of the pulmo-
nary artery, soon comes more to the front in its arched portion, while
the pulmonary artery runs almost directly backward. Thus the two
blood-currents may be said to twist spirally round each other in their
course through the corresponding auricles and ventricles.

The movement of the blood through the cardiac cavities is not a con- <
tinuous and steady flow, but is accomplished by alternate contractions '
and relaxations of the muscular walls of the heart ; by which successive
portions of blood are delivered from the auricles into the ventricles, and
thence discharged into the arteries. Each one of these successive actions
is called a beat or pulsation of the heart. The cardiac pulsations are
accompanied by certain physical phenomena dependent upon the struc-
ture of the heart and its mode of action.

Sourtds, Movements, and Impulse of the Heart. — The sounds of the
heart are two in number. They can be heard by applying the ear over
the cardiac region, when they are found to be quite different from each
other in position, tone, and duration. They are distinguished as the
first and second sounds of the heart. The first sound is heard with the
greatest intensity over the anterior surface of the heart, and particularly
at the situation of the apex beat, over the fifth rib and the fifth inter-
costal space. It is comparatively long, dull, and smothered in tone,
and occupies one-half the entire duration of a beat. It corresponds in
time with the impulse of the heart in the precordial region, and with the
stroke of the large arteries in the immediate vicinity of the chest. The
second sound follows almost immediately upon the first. It is heard
most distinctly at the situation of the aortic and pulmonary valves,
namely, over the sternum at the level of the third costal cartilage. It
is short and distinct, and occupies only about one-quarter of the whole
time of a pulsation. It is followed by an equal interval of silence ; after
which the first sound again recurs. The whole time of a cardiac pulsa-
tion may be divided into four quarters, of which the first two are occu-
pied by the first sound, the third by the second sound, and the fourth
by an interval of silence, as follows :

KELATIVE TIME AND DURATION OF THE HEART-SOUNDS.

r 1st quarter )

I 2d „ j First sound.

Cardiac pulsation \ _

3d Second sound.

1 4th " Interval of silence.

THE HEART. 323

The cause of the second sound is universally admitted to be the sudden
closure and tension of the aortic and pulmonary valves. This fact is
established by the following proofs : 1st. The sound is heard with per-
fect distinctness, as mentioned above, directly over the situation of these
valves at the base of the heart ; 2d. The further we recede in any direc-
tion from this point, the fainter becomes the sound ; and 3d, in experi-
ments upon the living animal, b}' different observers, it has been found
that if a curved needle be introduced into the base of the large vessels,
so as to hook back the semilunar valves, the second sound disappears,
and remains absent until the valve is again liberated. The valves con-
sist of fibrous sheets, covered with a layer of endocardial epithelium.
They have the form of semilunar festoons, the free edge of which is
directed from the cavity of the ventricle, while the attached edge is
fastened to the inner surface of the base of the artery. While the blood
is passing from the ventricle to the artery, the valves are thrown for-
ward and relaxed ; but when the artery reacts upon its contents they
shut back, and their fibres, becoming suddenly tense, yield a clear,
characteristic, snapping sound. The character of this valvular sound
may be closely imitated by snapping a piece of tape or ribbon (Fig. 105),

Fig. 105.

alternately loosening and extending it, while firmly held between the
fingers of the two hands. A short piece of ribbon by this sudden tension
will give out a sharp and distinct sound ; a longer one will yield a sound
which is more dull and prolonged.

The first sound of the heart contains two elements, which are mingled
in different proportions according to the point at which it is heard. One
of these elements is comparatively dull in tone, and when heard over
the apex or front of the heart communicates its character to the whole
of the first sound. It is variously attributed to the muscular contrac-
tion of the cardiac fibres and to the movement of the surface of the
heart against the inner walls of the chest. The remaining element of
the first sound is valvular in character, and is caused by the tension of
the auriclo-ventricular valves at the time of the ventricular pulsation.
It gradually predominates over the other, at points further removed
from the apex of the heart, toward the left border of the organ and the

324 THE CIRCULATION.

left nipple ; and still further to the left it is heard alone, the first sound
at this situation being purely valvular, like the second.1

The movements of the heart ma}' be observed in the dog, or other
warm-blooded quadruped, by opening the cavity of the chest by a longi-
tudinal incision through the sternum, and separating the costal cartilages,
on each side, at their junction with the ribs; artificial respiration being
maintained by the nozzle of a bellows inserted in the trachea. The
animal may be partially narcotized by a preliminary subcutaneous in-
jection of morphine, after which complete etherization is produced and
continued with great facility. The operation of opening the chest and
exposing the thoracic organs increases the rapidity of the heart's move-
ments and diminishes their force ; but its action is not otherwise
changed, and the circulation will continue for several hours, provided
artificial respiration be maintained with regularity.

When exposed to view under these conditions, the movements of the
mammalian heart are at once seen to be complicated to such a degree
that close examination is requisite to distinguish their different elements.
The most obvious appearance at first presented is the rapid succession
of two alternating conditions, namely a condition of rest and a condi-
tion of movement. Furthermore, if the heart be touched or gently
grasped between the fingers, it becomes evident that the two states of
rest and movement are accompanied by corresponding changes in the
consistency of the organ. At the time of rest it is comparatively soft
and yielding to the touch ; at the time of its movement, it becomesxhard
and tense. Inspection alone cannot determine which of these two states
corresponds with the entrance of the blood into the ventricles and which
with its exit ; in other words, which represents muscular relaxation and
which the contraction of the heart. Different observers, while watching
the movements of the same heart in the living animal, will often be led
to opposite conclusions in this respect. The only method of directly
determining the point is that first adopted by Harvey, in his observa-
tions upon the heart, which formed the basis of the discovery of the
circulation of the blood. If we insert through the walls of the left
ventricle a silver canula from one to two millimetres in diameter, so as
to pierce its cavity, the blood is forcibly projected from its orifice at the
time of the tension of the cardiac walls, while its flow is suspended in
the intervals of repose.

Thus the two states of relaxation and tension of the heart correspond
with the relaxation and contraction of its muscular fibres. Like mus-
cular tissue elsewhere, that of the heart during relaxation is compara-
tively soft to the touch ; when the ventricles contract upon their contents
and forcibly expel the blood, they become tense and firm, by the sudden
rigidity of their fibres. By this means the two opposite conditions of
the diastole and systole of the ventricles may be recognized with cer-
tainty, and connected with the other corresponding phenomena of the

1 Flint, Treatise on Diseases of the Heart. Philadelphia, 1870, pp. 61-62.

THE HEART.

325

heart's action. At the time of their diastole, the blood enters the
cavity of the ventricles through the auricular orifice ; at the time of
their systole it is expelled into the arterial trunks.

Simultaneously with the hardening and contraction of the ventricles
the apex of the heart moves slighly from left to right, and rotates at
the same time upon its own axis in a similar direction. This movement
was also observed by Harvey, who describes it as follows:1 —

" And if any one," he says, u bearing these things in mind, will care-
fully watch the motions of the heart in the body of the living animal,
he will perceive not only all the particulars I have mentioned, namely,
the heart becoming erect and making one continuous motion with its
auricles ; but, further, a certain obscure undulation and lateral inclina-
tion in the direction of the axis of the right ventricle, the organ twisting
itself slightly in performing its work."

Both these movements, of lateral inclination and rotation, result from
the spiral arrangement of the muscular fibres on the exterior of the

heart. The most superficial of these fibres
Fig. 106. start from the base of the organ and pass

toward its apex, following an obliquely
spiral course over its anterior surface, from
above downward and from right to left.
The contraction of this superficial portion

Fig. 107.

BULLOCK'S HEAKT, anterior
view, showing the superficial mus-
cular fibres.

CONVERGING SPIRAL FIBRES AT THE APKX
OP THE HEART. The direction of the arrows indi-
cates that of the rotating movement of the heart at
the time of the ventricular systole.

of the muscular fibres accordingly tilts the apex of the heart in a slight
degree bodily from left to right. As the fibres, however, reach the point
of the heart they curl round its axis, change their direction, and disap-
pear from sight, becoming deep seated and passing upward along the
septum and internal surface of the ventricle, to a termination finally in
the columnse carneae and the fibrous border of the auriculo-ventricular
ring. They thus form, exactly at the apex of the heart, a kind of whorl
or vortex, of spiral muscular fibres easily distinguishable when the organ
is in active motion. Any muscular fibre arranged in this direction

Works of William Harvey, M.D., Sydenham Edition. London, 1847, p. 32.

THE CIRCULATION.

necessarily tends, at the moment of its contraction, to straighten or
untwist the spiral. At the time of the ventricular contraction, there-
fore, the apex of the heart rotates upon its axis, from left to right ante-
riorly and from right to left posteriorly. This twisting movement at
the apex is very perceptible at each pulsation of the heart when exposed
in the living animal.

The impulse of the heart is a stroke, more or less forcible, of the
apex of the organ against the walls of the chest, taking place at the
time of the ventricular systole. This impulse is readily perceptible
externally, as a general rule, both to the eye and to the touch. In the
human subject, when in the erect position, it is located in the fifth inter-
costal space, midway between the left edge of the sternum and a line
drawn perpendicularly through the left nipple ; while in the supine posi-
tion of the body, the heart subsides, in a measure, from the anterior part
of the chest, so that its external impulse may become for the time very
faint, or may even disappear altogether.

This alternate recession and advance of the apex of the heart, corre-
sponding with its relaxation and contraction, is visible in the organ when
exposed by opening the walls of the chest. According to the descrip-
tion given by Harvey, at the time of its motion " 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." If we allow the end of the
finger to rest lightly upon the apex of the exposed heart, the protrusion
of this part of the organ at the time of the ventricular systole is dis-
tinctly felt, lifting the finger at each beat with a somewhat forcible
impulse ; and if a light rider of white paper be placed upon the apex, it
is also seen to be thrown forward and backward at each alternate con-
traction and relaxation of the heart.

The immediate cause of the protrusion of the heart's apex at the time
of the ventricular systole has been variously regarded, first as an actual
elongation of the ventricle, and secondly, as a forward movement of the
whole heart, due to a recoil from the blood expelled from it under pres-
sure, or to a reaction of the distended arteries at its base. Galen, who
was the first to study the action of the heart by inspection in the living
animal, found the transverse diameter of the organ increased during
relaxation and its length diminished, while during the systole its width
was diminished and its length increased.1 Of subsequent observers,
some believed the heart to be lengthened, others that it was shortened at
the time of the ventricular systole. Nearly all the more recent physio-
logical writers of eminence (Longet, Carpenter, Flint, Ranke, Burdon-
Sanderson) are of the opinion that the ventricles when contracting
diminish in size in every direction, that the apex of the organ approaches
the base, but that the whole heart is thrown forward by the impulse of
recoil above mentioned. Prof. Flint2 cut out the heart suddenly from

1 Galen, De Usu Partium, vi. 8.

2 Physiology of Man. New York, 1866, p. 189.

THE HEART. 327

the dog, and, fastening it upon a table by needles passed through its base,
found the ventricles shortened in contraction ; and obtained the same
result, in another experiment, by pinning the heart, in the chest of the
living animal, to a thin board placed underneath. On the other hand,
Drs. Pennock and Moore, who performed a series of very careful experi-
ments upon the action of the heart in sheep, calves, and horses,1 observed
an elongation of the organ at the time of the ventricular systole. They
operated by stunning the animals with a blow upon the head, opening
the chest, and keeping up artificial respiration, and they were able to
measure the extent of elongation by means of a shoemaker's rule applied
to the heart.

In our own observations on this point, many times repeated, we have
always seen reason to believe that the heart actually elongates in the
ventricular systole, and that it is not simply thrown forward by an im-
pulse of recoil. The appearances presented, when viewing the front of
the mammalian heart, as it lies in its natural position in the chest, are
somewhat complicated. The anterior surface of the organ is mainly
occupied by the right ventricle and especially by that portion of it
known as the conus arteriosus. This is in reality a vaulted channel
running obliquely over the front of the heart, from right to left and from
below upward, toward the origin of the pulmonary artery. Its muscular
fibres, on the other hand, run directly across it and at right angles to
the axis of its cavity, namely, from right to left and from above down-
ward, constituting the most superficial fibres of the heart in this situa-
tion. At the time of ventricular systole, these fibres contract across the
line of the conus arteriosus, become thickened and more prominent and
approximate the base of the heart and the lower -border of the conus
arteriosus toward each other.

But the right ventricle constitutes a comparatively small portion of
the heart. The greater part of its mass is formed by the thick walls of
the left ventricle, which occupies a posterior position, and is not fully
seen in a front view of the organ. If the heart be tilted up and viewed
from its posterior surface, at every contraction its sides will be seen to
approximate and its point to elongate ; in other words, its transverse
diameter diminishes, while its longitudinal diameter increases. Its base
may be firmly held by the fingers placed upon the large vessels, -while
this change of form of the organ is observed. Even in an anterior view,
with the whole heart securely held in this position, according to our
observations, the apex, at each systole, will rise toward an ivory rod
placed horizontally above it, and will recede in the same degree at each
diastole.

If this be true, the explanation of the ventricular elongation is readily
found in the arrangement of the muscular fibres of the left ventricle.
The left ventricle preponderates so much in mass over the other parts of
the organ, that its changes of figure determine those of the entire heart.

1 Philadelphia Medical Examiner, 1839, No. 44.

328

THE CIRCULATION.

Fig. 108.

TRANSVERSE SECTION OF THE
BULLOCK'S HEART IN THE STATE
OP CADAVERIC RIGIDITY. — a. Cav-
ity of the Left Ventricle, b. Cavity of
the Right Ventricle.

Fig. 109.

A transverse section of the heart, in its contracted condition, shows the
relative volume of the muscular walls of the right and left ventricles,

and the difference in form of the two
cavities.

The left ventricle forms a thick
muscular tube, with its cavity nearly
in the centre of the cardiac mass ;
while the right ventricle has the ap-
pearance of a comparatively incon-
siderable layer of fibres, attached to
the lateral surface of the organ, and
enclosing a cavity of a more linear
and flattened form.

The surperficial cardiac fibres, which
make the visible part of the wall of
the right ventricle, run obliquely from
right to left and from above down-
ward, toward the heart's apex; but the more deeply seated layers,
belonging to the left ventricle, take more and more a horizontal or
circular course, being wrappped round the ven-
tricle, almost like those of the small intestine.
Whenever these muscular fibres contract, they
must, of course, swell in the direction of their
thickness ; and the effect produced by this simul-
taneous swelling of all the circular fibres is to
increase the longitudinal diameter of the ven-
tricle, at the same time that its sides are drawn
together and its calibre diminished. In the sys-
tole of the ventricle, accordingly, its muscular
fibres contract upon its contents, like the fingers
of a closed hand, and the blood is expelled from
its cavity very much as the fluids of the intestinal
canal are forced onward by the contracting cir-
cular fibres of the muscular coat.

fihythm of the Heart's Action. — The succession of phenomena in the
heart's action is peculiar and somewhat complicated. Each pulsation
is made up of a double series of contractions and relaxations. The two
auricles contract together, and afterward the two ventricles ; and in
each case the contraction is immediately followed by a relaxation. The
auricular contraction is short and feeble, and occupies the first part of
the time of a pulsation. The ventricular contraction is longer and more
powerful, and occupies the latter part of the same period. Following
the ventricular contraction there comes a short interval of repose, after
which the auricular contraction again recurs. The auricular and ven-
tricular contractions, however, do not alternate distinctly with each
other, like the strokes of the two pistons in a double forcing-pump. On
the contrary, they are connected and continuous. The contraction,

LEFT VENTRICLE OF
BULLOCK'S HEART,
showing its deep fibres.

THE HEAKT. 329

which commences at the auricle, is immediately propagated to the ven-
tricle, and runs rapidly from the base of the heart to its apex, very
much in the manner of a peristaltic motion, excepting that it is more
sudden and vigorous. This part of the heart's action is described by
Harvey in very graphic terms, evidently drawn from direct study of the
phenomena in the living animal.

"• First of all," he says, "the auricle contracts, and in the course of its
contraction throws the blood (which it contains in ample quantity as
the head of the veins, the storehouse and cistern of the blood) into the
ventricle, which being filled, the heart raises itself straightway, makes
all its fibres tense, contracts the ventricles, and performs a beat, b}'
which beat it immediately sends the blood, supplied to it by the auricle,
into the arteries ; the right ventricle sending its charge into the lungs
by the vessel which is called vena arteriosa, but which, in structure and
function, and all things else, is an artery ; the left ventricle sending its
charge into the aorta, and through this by the arteries to the body at
large.

" These two motions, one of the ventricles, another of the auricles,
take place consecutively, but in such a manner that there is a kind of
harmony or rhythm preserved between them, the two concurring in
such wise that but one motion is apparent, especially in the warmer
blooded animals, in which the movements in question are rapid. Nor
is this for any other reason than it is in a piece of machinery, in which,
though one wheel gives motion to another, yet all the wheels seem to
move simultaneous^ ; or in that mechanical contrivance which is
adapted to fire-arms, where, the trigger being touched, down comes the
flint, strikes against the steel, elicits a spark, which falling among the
powder, it is ignited, upon which the flame extends, enters the barrel,
causes the explosion, propels the ball, and the mark is attained ; all of
which incidents, by reason of the celerity with which they happen, seem
to take place in the twinkling of an eye."

The above description indicates precisely the manner in which the
contraction of the ventricle follows successively and yet continuously
upon that of the auricle. The contraction begins, as already stated, at
the auricle. Thence it runs immediately forward to the apex of the
heaVt. The entire ventricle contracts vigorously, its walls harden, its
apex protrudes, strikes against the walls of the chest, and twists from
left to right, the auriculo-ventricular valves shut back, the first sound
is produced, and the blood is driven into the aorta and pulmonary artery.
These phenomena occupy about one-half the time of pulsation. Then
the ventricle is relaxed, and a short period of repose ensues. During
this period the blood flows from the large veins into the auricle, and
through the auriculo-ventricular orifice into the ventricle; filling the
ventricle, by a kind of passive dilatation, about two-thirds or three-
quarters full. Then the auricle contracts with a quick motion, forces
the last drop of blood into the ventricle, distending it to its full capa-
22

330 THE CIRCULATION.

city ; and lastly the ventricular contraction takes place, driving the blood
into the large arteries. These movements continue to alternate with
each other, and form, by their recurrence, the successive cardiac pul-
sations.

ft*

The Arterial Circulation.

The arteries are a series of branching tubes, which commence with
the aorta and ramify throughout the body, distributing the blood to the
various vascular organs. They consist of three principal coats, namely,
an inner coat, composed of thin elastic laminae lined with a single layer
of narrow, elongated and flattened epithelium cells ; a middle coat, com-
posed of elastic tissue and imstriped muscular fibres, running trans-
versely, or in a circular direction, round the calibre of the vessel; and
an external coat, consisting mainly of a more or less condensed layer
of connective tissue. The principal anatomical distinction between the
larger and the smaller arteries is in the structure of their middle coat.
In the smaller arteries this coat is composed exclusively of muscular
fibres, arranged in one or several layers. In arteries of medium size
the middle coat contains both muscular and elastic tissue; while in
those of the largest calibre it consists of elastic tissue alone. The
large arteries, accordingly, possess a remarkable degree of elasticity and
but little contractility; while the smaller are contractile, and less dis-
tinctly elastic.

Movement of the Blood through the Arterial System. — The movement
of the blood through the arteries is due to the muscular force of the
heart and the impulse derived from the ventricular systole. The arte-
rial system, which is an extensive ramification of tubular canals, may
be regarded as a great vascular cavity, subdivided from within outward
by the successive branching of its vessels, but communicating freely
with the heart and aorta at one extremity, and with the capillary plexus
at the other, and filled everywhere with the circulating fluid. At the
time of the heart's contraction, the muscular walls of the ventricle close
in upon its cavity ; and as the auriculo-ventricular valves at the same
time shut back and prevent regurgitation, the blood is forced out from
the ventricle through the aortic orifice. As the ventricle relaxes it is
again filled with blood from the auricle, and delivers it, as before, by
a new contraction, into the arteries. It is by these impulses, recurring
at short intervals, that the entire blood moves in a direction from the
heart outward through the arterial system.

Distension of the Arteries by the HearVs Action; Arterial Pulse. — At
each ventricular systole a charge of blood is driven into the arteries,
distending their walls by the pressure of the additional quantity of fluid
introduced into their cavities. When the ventricle afterward relaxes,
this active distending force is suspended ; and the elastic arterial walls,
reacting upon their contents, would drive the blood back into the heart
were it not for the closure of the semilunar valves, which shut together

THE AUTERIAL CI RCUL ATTON. 331

and prevent any movement in a backward direction. The blood is thus
urged onward, under the pressure of the arterial elasticity, into the
capillary system. When the arteries have become partially emptied,
and have returned to their previous dimensions, they are again dis-
tended by another contraction of the heart. In this manner a succes-
sion of expansions is produced, which can be felt throughout the body
wherever the arterial ramifications penetrate. This phenomenon is
known by the name of the arterial pulse.

Since each arterial expansion is produced by a ventricular systole,
the pulse, as felt in any superficial artery, is a convenient guide for
ascertaining the frequency and regularity of the heart's action. The
radial artery at the wrist, owing to its easily accessible situation, is
mainly employed for this purpose. Any increase or diminution in the
frequency of the heart's action is accompanied by a similar change in
the arterial pulsations ; and alterations in the force or regularity of the
cardiac movements are also indicated by corresponding modifications
of the pulse at the wrist.

The average frequency of the pulse in the human subject is, for the
adult male in a state of quiescence, 70 beats per minute. This rate
may be more or less accelerated by any muscular exertion. Even the
difference of muscular effort between the positions of standing, sitting,
and lying down, will make a normal difference in the pulse of from 8 to
10 beats per minute. Age has a very marked influence on the rapidity
of the pulse ; it being found, as a rule, more rapid the younger the sub-
ject of observation. According to Dr. Carpenter, the pulse of the
foetus, before birth, is about 140, and that of the newly-born infant 130.
During the first, second, and third years it gradually falls to 100; by
the fourteenth year to 80 ; and is only reduced to the adult standard
by the twenty-first year. At every age, mental excitement may pro-
duce a temporary acceleration of the pulse, varying in degree with the
peculiarities of the individual.

As a general rule, the rapidity of the heart's action is in inverse ratio
to its force ; that is, a slow pulse, within physiological limits, is a strong
one ; a rapid pulse is a feeble one. This is readily noticeable in ex-
periments upon the lower animals, where the force of the heart's action
may be measured by the arterial impulse ; and where an increase in the
frequency of the cardiac pulsations is almost invariably accompanied
by a diminution in their strength. The same thing is true in cases of
increased frequency of the heart's action from morbid causes ; the pulse
in febrile or chronic affections becoming weaker as it growls more rapid.
An excessive rapidity of the pulse is an indication of great danger ;
and, in the adult male, a continuous pulse of 160 per minute is almost
invariably a fatal symptom.

Increased Curvature of the Arteries in Pulsation. — When the blood
is driven by the ventricular systole into the arteries, these vessels are
not only distended laterally, but are elongated as well as widened,

332

THE CIRCULATION.

Elongation and
increased curvature
of an ARTERY IN
PULSATION.

Fi«r. 110. becoming enlarged in every direction. Especially

in arteries having a distinctly curved or serpen-
tine course, this elongation and increase of curva-
ture may be observed at the time of each pulsa-
tion. It is perceptible, for instance, in emaciated
persons, in the temporal artery, or even in the ra-
dial at the wrist, and may readily be seen in the
mesenteric arteries in the abdomen of the living
animal. At every contraction of the heart, the
curves of the vessel on each side become more
strongly pronounced. In the case of the radial or
other artery, running over a bony surface, the vessel
may even partially rise out of its bed at each pulsa-
tion. In old persons the arterial curvatures become
permanently enlarged from frequent distension ; and
all the arteries tend to assume, with the advance of
age, a more serpentine and spiral course.
Time of the Arterial Pulse. — The shock of an arterial pulsation, as
perceived by the finger, varies a little in time, according to its distance
from the centre of the circulation. If we place one finger upon the
chest over the apex of the heart, and another over the carotid artery at
the middle of the neck, we can distinguish little or no difference in time
between the two impulses ; the distension of the carotid being sensibly
simultaneous with the heart's contraction. But if the second finger be
placed upon the temporal artery, instead of the carotid, there is a per-
ceptible interval between the two beats. The impulse of the temporal
artery is felt to be a little later than that of the heart. The pulse of the
radial artery at the wrist also appears to be a little later than that of
the carotid, and that of the posterior tibial at the ankle joint a little
later than that of the radial. The greater the distance from the heart
at which the artery is examined, the later is the pulsation perceived by
the finger laid upon the vessel.

But it has been conclusively shown that this difference in time of the
arterial pulsations, in different parts of the body, is rather relative than
absolute. The impulse is communicated at the same instant to all parts
of the arterial system ; but the apparent difference between them, in this
respect, depends upon the fact, that, although all the arteries begin to
be distended at the same moment, yet those nearest the heart are ex-
panded suddenly, while for those at a distance the distension takes place
more gradually. The impulse given to the finger marks the condition
of maximum distension of the vessel ; and this condition occurs at a
later period, according to the distance of the artery from the heart.

The contraction of the left ventricle is a brisk and sudden motion.
The blood driven into the arterial system, meeting with a certain amount
of resistance from that already filling the vessels, does not instantly
displace a quantity equal to its own mass, but a certain proportion of
its force is used in expanding the distensible walls of the vessels. In

THE ARTERIAL CIRCULATION. 333

the immediate neighborhood, therefore, the expansion of the arteries is
sudden and momentary, like the contraction of the heart itself. But
this expansion requires for its completion a certain expenditure, both
of force and time ; so that at a little distance farther on, the vessel is
distended neither to the same degree nor with the same rapidity. At
the more distant point the arterial impulse is less powerful and arrives
more slowly at its maximum.

On the other hand, when the heart becomes relaxed, the artery in its
immediate neighborhood reacts upon the blood by its own elasticity ;
and as it meets with no other resistance than that of the blood in the
smaller vessels beyond, it drives a portion of its own blood into them,
and thus supplies to these vessels a certain degree of distending force
even in the intervals of the heart's action. Thus the difference in size
of the carotid artery, at the two periods of the heart's contraction and
relaxation, is ve^ marked ; for the degree of its distension is great
when the heart contracts, and its own reaction afterward empties it of
blood to a considerable extent. But in the small branches of the radial
or the ulnar artery, there is less distension at the time of the cardiac
impulse, because this force has been partly expended in overcoming the
elasticity of the larger vessels ; and there is less emptying of the vessel
afterward, because it is still kept partially filled by the reaction of the
aorta and its larger branches.

These facts have been illustrated by Marey,1 by attaching to the pipe
of a small forcing pump, worked by alternate strokes of the piston, a
long elastic tube open at its farther extremity. At different points
upon this tube are placed small movable levers, which are raised by the
distension of the tube whenever water is driven into it by the forcing
pump. Each lever carries upon its extremity a small pencil, which
marks upon a strip of paper, moving with uniform rapidity, the lines
produced by its alternate elevation and depression. By these curves
both the extent and rapidity of distension of different parts of the elastic
tube are accurately registered. The curves thus produced are as follows :

Fig. 111.

CURVES OF PULSATION IN AN ELASTIC TUBE. — 1. Near the distending force
2. At a distance from it. 3. Still farther removed.

From these experiments it is shown that the distension produced by
the stroke of the forcing pump begins at the same moment throughout

1 Journal de la Physiologie. Paris, Avril, 1859

334 THE CIRCULATION.

the entire length of the tube, and that the whole time of a pulsation is
everywhere of equal duration. But near the commencement of the tube,
the expansion is wide and sudden, and occupies only a sixth part of the
entire pulsation, while all the rest is taken up by a slow reaction. At
more remote points the period of expansion becomes longer and that of
collapse shorter ; until finally, at a certain distance, the amount of ex-
pansion is reduced one-half, and at the same time the two periods are
completely equalized.

Automatic Registration of the Arterial Pulse; the Sphygmograph. —
The frequency and characters of the arterial pulse may be permanently
recorded by the use of a movable lever capable of registering its own
oscillations, and so arranged that it may be applied to any of the super-
ficial arteries in the living body. This instrument, which was first made
practically serviceable by the improvements of Marey, is the sphygmo-
graph. It consists of a small ivory plate, which is gently pressed upon
the artery by means of a fine spring, and which thus rises and falls with
each expansion and collapse of the arterial tube. The motion of the
plate is communicated to a vertical metallic rod touching the under sur-
face of the registering lever near its attached extremity. The oscillating
extremity of the lever, when the instrument is in operation, thus follows
the movements of the ivory plate, and registers faithfully upon the strip
of paper, the frequency and form of the arterial pulsations.

The advantage of this instrument is, first, that the length of the lever
magnifies to the eye the extent of the arterial oscillations, and thus
enables us to perceive movements too delicate to be distinguished by
the touch alone ; and, secondly, that, each part of a pulsation being
permanently registered upon paper, the most evanescent changes in the
form of the artery may be afterward studied at leisure and compared
with each other.

By the use of the sphygmograph it is shown, that, while there is a
general resemblance in the form of pulsation of different arteries, nearly
every vessel to which the instrument can be applied presents certain
peculiarities dependent on its size, position, and distance from the
heart. In the radial artery at the wrist, each pulsation consists of a

Fi>. 112.

TKACE 01- THE K ADI AL PULSE, taken by the Sphygmograph.

sudden expansion of the vessel, indicated by a rapid upward movement
of the lever, making, in the trace, a straight, nearly A^ertical line. This
is followed by a gradual descent corresponding with the collapse of the
artery, until it reaches the lowest point of the trace, when the move-
ment of ascension again takes place, and so on alternately. The line
of descent, however, is not straight, like that of ascension, but is marked

THE ARTERIAL CIRCULATION.

335

by one, arid sometimes by two or even three slight undulations, indi-
cating a corresponding variation in the tension of the artery during its
period of collapse.

The undulations in the line of descent, in the sphygmograph tracing,
are due to an oscillation in the mass of the blood, subsequent to the
impulse of the heart, and during the reaction of the arterial system.
Marey has shown, by a series of well-conducted experiments,1 that
similar oscillations are produced when any incompressible liquid is
driven by a sudden impulse into an elastic tube; and that they are indi-
cated by a similar movement of the index of the sphygmograph. When
the heart's impulse is moderate, and the tension of the arterial system
fully developed, the undulations in the descending line of the pulse are
only slightly perceptible ; but when the heart's impulse is more rapid,
and the arterial tension diminished, the undulations become more
marked. Marey found that he could procure upon his own person
traces of different form, in this respect, by simply increasing the tem-
perature of the body by the addition of warmer clothing. The following
are three traces of the radial pulse obtained in this way, by increasing
the quantity of clothing at intervals of twenty minutes.

Fig. 11 3.

Fi?. 114.

Fig. 115.

VARIATIONS OF THE KADIAL PULSE, under the influence of increased temperature.

(Marey.)

Dicrotic Pulse. — In certain conditions, accompanied by rapid pulsa-
tion of the heart with greatly diminished arterial tension, the rebound
or oscillation of the artery becomes so marked, in proportion to the
original impulse, that it is easily perceived by the finger, and thus the
pulse is apparently reduplicated; that is, there are two pulsations of
the artery for each. contraction of the heart, namely, one due to the
original impulse, and another due to the oscillation of the blood in the

1 Physiologic Medicale de la Circulation du Sang. Paris, 1863, p. 266.

836

THE CIRCULATION.

feebly distended artery. This is the dicrotic pulse, which is often
present in diseases of a typhoid character.

116.

DICROTIC PULJSK OF TYPHOID PNEUMONIA. (Marey.)
Fig. 117.

DICROTIC PULSE OF TYPHOID FEVER (Marey.)

It is evident that the dicrotic character of the pulse is not, in reality,
peculiar to diseased conditions, since the sphygmograph shows that it
exists more or less perfectly in a state of health ; only it is too slight
in degree to be appreciated by the finger.

Koschlakoff1 has succeeded in verifying the results obtained from
the sphygmograph, and in demonstrating the mechanism of the dicrotic
pulse. He shows that if a liquid be driven by a rapid impulse through
an elastic tube, connected with two separate pressure gauges, one
situated near the point of entrance of the liquid, the other near its point
of exit, the liquid will rise in the first gauge before the increased pres-
sure reaches the second ; that it then falls while the second is rising,
and again rises while the second falls ; showing an alternate increase
and diminution of pressure in the two extremities of the elastic tube.
This alternation continues until the pressure is equalized, or until the
tube is again distended by a new impulse.

Pulsating Movement of the Blood in the Arterial System. — Owing to
the alternate contraction and relaxation of the heart, the blood passes
through the arteries in a series of impulses ; and the hemorrhage from
a wounded artery is distinguished from venous or capillary hemorrhage
by the fact that the blood flows in successive jets, as well as more
rapidly and abundantly. If a slender canula be introduced through the
walls of the left ventricle, in the exposed heart of a living animal, the
flow of blood from its external orifice is seen to be completely intermit-
tent. A strong jet takes place at each ventricular contraction, and at each
relaxation the flow is interrupted. If a puncture be made, however, in
any of the large arteries near the heart, the flow of blood through the
opening is no longer intermittent, but continuous ; only it is much
stronger at the time of the ventricular contraction, and diminishes,
though it does not entirely cease, at the time of relaxation. If the
blood were driven through rigid and unyielding tubes, its flow would

1 In Lorain Etudes de MSdecine Clinique. Paris, 1870, p 75

THE ARTERIAL CIRCULATION. 337

be everywhere intermittent ; and it would be delivered from an orifice
situated at any point, in perfectly interrupted jets. But the arteries
are yielding and elastic ; and this elasticity moderates the force of the
separate arterial pulsations, and partially fuses them with each other.
The effect of this is to produce, in the larger and medium-sized arteries,
a movement of the blood which is increased in rapidity and volume at
each cardiac impulse, and diminished in the interval of relaxation.

Equalization of the Blood-current in the peripheral parts of the
Arterial System. — It has already been shown that the distensible and
elastic properties of the arterial walls have the effect of making the flow
of blood more continuous than it would be if subjected only to the
intermitting action of the heart. A part of the force of each cardiac
pulsation is absorbed for the time in the distension of the artery ; and
this force is again returned in the form of an impulse to the blood at
the following interval, by the elastic reaction of the vessel. The farther
from the heart the blood recedes, the greater becomes the influence of
the intervening arteries ; and thus the remittent or pulsating character
of the arterial current, which is strongly pronounced in the vicinity of
the heart, becomes gradually diminished during its passage through the
vessels, until in the smaller arteries, like the labials, it is hardly percep-
tible to the unaided eye.

The physical influence of an elastic medium, in equalizing the force
of an interrupted current, may be shown by forcing water from a
syringe alternately through two tubes, one of India rubber, the other of
glass or metal. Whatever be the length of the inelastic tube, the water
thrown into one extremity will be delivered from the other in distinct
jets, corresponding with the strokes of the piston : but if the metallic
tube be replaced by one of India rubber of sufficient length, the elas-
ticity of this substance merges the separate impulses into each other,
and the water is discharged from the farther extremity in a continuous
stream.

The elasticity of the arteries never entirely equalizes the force of the
separate pulsations, since a pulsating character can be seen in the flow
of the blood through even the smallest arteries, if examined under the
microscope ; but this pulsating character diminishes from the heart out-
ward, and the current becomes much more continuous in the smaller
vessels than in the larger arteries or in those of medium size.

The Arterial Pressure. — The arterial circulation, as shown by the
above facts, is not an entirely simple phenomenon, but is the combined
result of two different physical forces. It is due, first, to the intermit-
ting action of the heart, by which the blood is driven in successive im-
pulses from within outward ; and, secondly, to the elasticity of the entire
arterial system, by which it is subjected to a continuous pressure.

If an}- one of the larger or medium sized arteries be divided, in the
living animal, and a glass tube of the same diameter securely fixed in
its open orifice and held in the vertical position, the blood will at once
rise in the tube to a height of five and a half or six feet, and will con-

338 THE CIRCULATION.

tinue to oscillate at or about this level. The height of the column of
fluid, thus supported outside the body, indicates the degree of pressure
to which the blood is subjected in the interior of the vessels. This
pressure, due to the reaction of the entire arterial system, is known as
the arterial pressure.

The arterial pressure is best measured by connecting the open arteiy,
by a flexible tube, with a small reservoir of mercury, provided with a
narrow upright glass tube, open at its upper extremity. When the
mercury in the receiver is exposed to the pressure of the arterial blood,
it rises in the upright tube to a corresponding height.

This pressure averages, in the dog and other animals of similar size,
150 millimetres of mercury.

When such an instrument is connected with the carotid artery, the
level of the mercury in the upright tube, while indicating on the whole
an average pressure, exhibits two series of oscillations ; showing that
the degree of the blood-pressure is constantly changing, owing to two
different causes. One of these oscillations is synchronous with the move-
ments of respiration. At every inspiration, the level of the mercury
falls somewhat, with every expiration it rises. As the movement of in-
spiration consists in an expansion of the cavity of the chest, its effect is
to diminish the support afforded the heart and great bloodvessels, and of
course to lower in a similar degree the tension of the whole arterial
system. At the moment of expiration, on the other hand, the thoracic
parietes return to their former position, and the pressure upon the heart
and the arteries in the chest is re-established. These changes are indi-
cated by corresponding slow fluctuations in the arterial pressure and in
the height of the mercurial column. The oscillations of the mercury
due to respiration, however, are not at all uniform, but vary according
to the condition of the respiratory movements. When respiration is
active and somewhat labored, the oscillations may reach the extent of
30 millimetres ; when it is very quiet, as in an animal deeply etherized,
they may diminish so far as to be nearly or quite imperceptible.

The other series of oscillations is a more constant one and is clue to
the cardiac pulsations. It consists of comparatively rapid undulations
of the mercurial column, simultaneous with the movements of the heart.
At every contraction of the ventricle, the mercury rises from 12 to 15
millimetres, and at every relaxation it falls to its previous level. Thus
the instrument becomes a measure, not only for the constant pressure
of the arteries, but also for the intermitting pressure of the heart ; and
on that account it has received the name of the cardiometer. It is seen,
accordingly, that each contraction of the heart is superior in force to
the resistance of the arteries by nearly one-tenth ; and the arterial system
is, therefore, kept filled by successive cardiac pulsations, and the arterial
tension maintained, notwithstanding that the blood is constantly being
discharged from the arteries into the capillary circulation.

Velocity of the Arterial Current. — The rapidity with which the blood
moves in the arterial tubes is much greater than in any other part of the

THE ARTERIAL CIRCULATION.

339

vascular system. Its exact rate varies somewhat according to the
situation of the vessel and the period of the pulsation. Its velocity is
greatest in the immediate neighborhood of the heart, and diminishes as
the blood recedes from the centre of the circulation. The successive
division of the aorta and its primary branches into smaller and smaller
ramifications increases the extent of surface of the arterial walls with
which the blood comes in contact. The adhesion produced by this con-
tact, as well as the mechanical obstacle arising from the frequent division
of the vessels and the separation of the streams, contributes to retard
the current, which accordingly becomes perceptibly slower in the small
arteries than in those of larger or medium size. In the smallest arte-
ries, as examined by the microscope in the transparent tissues, the par-
tial adhesion of the blood to the vascular wall, and the greater rapidity
of its flow in the axis of the vessel are readily perceptible. The con-
sistency of the circulating fluid, however, and the smoothness of the
internal surface of the arteries, are such that this obstacle to the move-
ment of the blood has only a very partial influence in retarding its flow;
and even in the smallest arteries it is so rapid, when seen under the
microscope, that the shape of the separate blood-globules cannot be dis-
tinguished, but only a mingled current shootin'g forward with increased
velocity at each cardiac pulsation.

The average rapidity of the blood stream in the larger arteries, in
dogs, horses, and calves, was determined by Yolkmann, as 30 centi-
metres per second. The most exact experiments on this point are
those of Chauveau.1 He experimented by introducing into the carotid
artery of the horse a brass
tube with thin walls, about five
centimetres long and eight
or nine millimetres in diame-
ter. The tube was introduced
through a longitudinal incision
in the walls of the exposed
vessel, and secured in position
by a ligature near each ex-
tremity ; so that the arterial
current would pass, without
serious obstruction, through
the brass tube forming, for the
time, a part of the arterial
walls. In the side of the tube
was a small opening, three
millimetres long by one and
a half millimetre wide, closed
by an elastic membrane pro-
perly secured so as to prevent the escape of the blood. Through the
centre of the elastic membrane there was passed a very light metallic

1 Journal de la Physiologic, Paris, Octobre, 1860, p. 695.

w~^ -v%- A--"

V

CHAUVEAU'S INSTRUMENT, for measuring
the rapidity of the arterial current.— a. Brass tube,
introduced into the calibre of the artery, b. Index-
needle passing through the elastic membrane in
the side of the brass tube, and moving by the im-
pulse of the blood-current, c. Graduated scale,
for measuring the extent of the oscillations of
the needle.

34:0 THE CIRCULATION.

needle, the inner extremity of which, somewhat flattened in shape, pro-
jected into the interior of the vessel, and received the impulse of the
arterial blood ; while the outer portion, prolonged into a slender index,
marked upon a semicircular graduated scale the oscillations of the
inner extremity, and consequently the varying rapidity of the arterial
current. The actual velocity, indicated by any given oscillation of the
needle, was ascertained beforehand by attaching the apparatus to an
elastic tube and passing through it a stream of warm water of known
rapidity.

Chauveau found, by these experiments, that the details of the circu-
latory movement differ somewhat in the larger arteries near the heart
from those in the smaller branches farther removed.

a. In the carotid artery, at the instant of the systole of the heart, the
blood is suddenly put in motion with a high degree of rapidity, amount-
ing on the average to a little over fifty centimetres per second.

At the termination of the systole, and immediately before the closure
of the aortic valves, the movement of the blood decreases considerably,
and may even, for the time, be completely arrested.

At the instant of closure of the aortic valves, the circulation receives
a new impulse, and the blood again moves forward with a velocity of
rather more than 20 centimetres per second.

Subsequently, the rapidity of the current diminishes gradually during
the period of the heart's inaction, until, at the end of this period and
just before a new systole, it is reduced, on the average, to 15 centi-
metres per second.

b. In the smaller arterial branches, such as the facial, the movement
of the arterial current is more uniform. It is less rapid at the moment
of the heart's systole; and on the other hand, it is always more active
during the period of ventricular repose.

The secondary impulse, following the closure of the aortic valves, is
much less perceptible than in the larger arteries, and may even be alto-
gether absent.

The Venous Circulation.

The veins are composed, like the arteries, of three coats ; an inner,
middle, and exterior. They differ from the arteries in containing a
much smaller quantity of muscular and elastic fibres, and a larger pro-
portion of condensed connective tissue. They are consequently more
flaccid and compressible than the arteries, and less elastic and contrac-
tile. They are furthermore distinguished, throughout the limbs, neck,
and external portions of the head and trunk, by being provided with
valves, arranged in the form of festoons, and so placed as to allow the
blood to pass readily from the periphery toward the heart, while they
prevent its reflux in the opposite direction.

Although the walls of the veins are thinner and less elastic than those
of the arteries, yet their capacity for resistance to pressure is equal, or
even superior, to that of the arteries. Milne Edwards has collected the

THE VENOUS CIRCULATION. 341

results of various experiments, which show that the veins will some-
times resist a pressure which is sufficient to rupture the walls of the
arteries.1 In one instance the jugular vein supported, without breaking,
a pressure equal to a column of water 148 feet in height ; and in another,
the iliac vein of a sheep resisted a pressure of more than four atmos-
pheres. The portal vein was found capable of resisting a pressure of
six atmospheres ; and in one case, in which the aorta of a sheep was
ruptured by a pressure of 12 kilogrammes, the vena cava of the same
animal supported a pressure equal to 80 kilogrammes.

This property of the veins is to be attributed to the abundance of
white fibrous tissue in their composition ; the same tissue which forms
nearly the whole of the tendons and fasciae, and which is distinguished
by its density and unyielding nature.

The elasticity of the veins, on the other hand, is much less than that
of the arteries. When filled with blood, they enlarge to a certain size ;
and when cut across and emptied, their sides simply collapse and remain
in contact with each other.

Another peculiarity of the venous system consists in its numerous
independent and communicating channels.

In injected preparations, two, three, or more veins are often to be
seen coming, together, from the same region of the body, and presenting
frequent transverse communications. The deep veins accompanying the
brachial artery inosculate freely with each other, and also with the
superficial veins of the arm. In the veins coming from the head, the
external jugulars communicate with the thyroid veins, the anterior
jugular, and the brachial veins. The external and internal jugulars
commuicate with each other, and the two thyroid veins also form an
abundant plexus in front of the trachea.

Thus the blood, coming from the extremities toward the heart, flows,
not in a single channel, but in several; and as these channels communi-
cate freely with each other, the blood passes most abundantly some-
times through one of them, and sometimes through another.

Movement of the Blood through the Venous System. — The flow of
blood through the veins is less powerful and regular than that through
the arteries. It depends on the combined action of three different physi-
cal forces.

I. The most constant and important of these forces is the pressure
of the blood from the capillary circulation. The blood moves from the
arteries into and through the capillary vessels, under an impulse derived
originally from the contractions of the heart, and converted by the elas-
ticity of the arterial walls into a more or less steady and uniform pres-
sure. This pressure is not entirely exhausted in carrying the blood
through the narrow channels of the capillary system ; and it accord-
ingly emerges from these vessels and enters the commencement of the
veins with a certain amount of force sufficient to fill the venous rootlets

1 Legons sur la Physiologie. Paris, 1859, tome iv. p. 301.

oi2 THE CIRCULATION.

and to pass thence into the larger branches and trunks of the venous
system. As the veins converge from the periphery toward the centre,
and unite into branches of larger calibre, the resistance afforded by
contact of the circulating fluid with their inner surfaces constantly
diminishes from without inward; and every contraction of the right
ventricle, accompanied by the closure of the tricuspid valve, expels a
certain quantity of venous blood, and thus relieves the returning current
from the obstacle of its accumulation. As the pressure of the blood
from the capillaries continues uniform, and as the resistance to it is
incessantly neutralized by the action of the right ventricle, it forms
the most simple and effective cause for the movement of the blood
through the venous channels.

II. The flow of the blood through the veins is also aided in great
measure by the contraction of the voluntary muscles. The veins which
convey the blood through the limbs, and the parietes of the head and
trunk, lie among voluntary muscles which are more or less constantly
in a state of alternate contraction and relaxation. At every contraction
these muscles become swollen laterally, and thus compress the veins
situated between them. The blood, expelled from the vein by this pres-
sure, cannot regurgitate toward the capillaries, owing to the venous
valves, which shut back and prevent its reflux. It is accordingly forced
onward toward the heart ; and when the muscle relaxes and the vein is
liberated from pressure, it is again filled from behind, and the circula-
tion goes on as before.

Fig. 119. Fig. 120.

VEIN with valves open. VEIN with valves closed; stream of blood

passing off by a lateral channel.

This force is very efficient in maintaining the venous circulation ;
since the voluntary muscles are more or less active in every position of
the body, and the veins are thus alternately subjected to compression
and relaxation. The entire voluntary muscular system acts in this way
by communicating to the venous current indirect impulses of frequent

THE CAPILLARY CIRCULATION. 343

repetition, which, combined with the action of the valves, urge the blood
from the periphery toward the heart.

III. A third cause, which is more or less active in promoting the
movement of the venous blood, is the force 'of aspiration exerted by
the thorax. When the chest expands by the lifting of the ribs and the
descent of the diaphragm, this movement tends to diminish the pressure
upon its contents, and consequently to draw into the thoracic cavity any
fluids which can gain access to it. The expanded cavity is principally
filled by the atmospheric air, which passes in through the trachea to fill
the bronchial tubes and the pulmonary vesicles. But the blood in the
neighboring parts of the venous system is solicited at the same time,
though to a less degree, in a similar direction. This force of aspiration,
like the respiratory movements themselves, is gentle and uniform in
character. Its influence extends indirectly throughout the venous sys-
tem, each expansion of the chest causing an increased flow of blood from
the extra- to the intra- thoracic veins, while the former are filled up from
behind as fast as they are emptied in front.

Eapidity of the Venous Circulation — With regard to the velocity of
the venous current, no direct results have been obtained by experiment.
Owing to the flaccidity of the veins, and the readiness with which the
flow of blood through them is disturbed, it is not possible to determine
this point, in the same manner as it has been determined for the arteries.
The only calculation which has been made in this respect is based upon
a comparison of the total capacity of the arterial and venous systems.
As the same blood which passes outward through the arteries returns
inward through the veins, the rapidity of its flow in each direction must
be in inverse proportion to the capacity of the two systems. The ca-
pacity of the entire venous system, when distended by injection, is about
twice as great as that of the entire arterial system. During life, how-
ever, the venous system is at no time so completely filled with blood as
is the case with the arteries; and, making allowance for this difference,
it may be estimated that the entire quantity of venous blood is to the
entire quantity of arterial blood nearly as three to two. The velocity
of the venous blood, as compared with that of the arterial, is therefore
as two to three ; and if we regard the average rapidity of the arterial
current, according to Yolkmann's experiments, as 30 centimetres per
second, this would give the movement of blood in the large veins as
about 20 centimetres per second. This calculation, however, is alto-
gether an approximative one ; since the venous circulation varies,
according to many different circumstances, in different parts of the
body. 'It may nevertheless be considered as expressing with sufficient
accuracy the general relative velocity of the arterial and venous currents
in corresponding parts of their course.

The Capillary Circulation,

The capillary bloodvessels are minute inosculating tubes, which per-
meate the vascular organs in various directions, and bring the blood into

344

THE CIRCULATION.

Fig. 121.

indirect contact with the substance of the tissues. They are continuous
with the terminal ramifications of the arteries on the one hand, and with
the commencing rootlets of the veins on the other. They vary some-
what in size in the different organs and tissues, their average diameter
in the human subject being about 10 mmm., or T^ of a millimetre. The
largest capillaries, according to Kolliker, in the glands and the osseous
tissue, may reach the diameter of 15 mmm. ; while the smallest, in the
muscles, the nerves, and the retina, are 4.5 mmm., that is, almost exactly
the size of the smallest of the red globules of the blood.

As the arterial ramifications approach the confines of the capillary
system they diminish gradually in size, and lose first their external
coat of connective tissue. Their middle coat at the same time becomes
reduced to a single layer of fusiform muscular fibres, which become
in turn less numerous, and lastly disappear altogether. The vascular
canal is thus finally composed only of a single tunic continuous with
the internal coat of the arterial ramifications.

The capillary bloodvessel, examined in its recent condition, as ex-
tracted from any soft vascular tissue, appears to consist of a simple,

nearly homogeneous tubular mem-
brane, provided with flattened oval
nuclei placed at more or less regular
distances from each other, and pro-
jecting slightly into the cavity of the
vessel.

It has been found, however, that if
a capillary bloodvessel be treated with
a weak solution of silver nitrate, its
inner surface becomes marked off into
regular spaces, each of which includes
a nucleus ; indicating that its appa-
rently homogeneous tunic is com-
posed of flattened epithelium-like
cells, united with each other at their
adjacent edges by an intervening
cement. It is this thin layer of in-
tervening substance which becomes
darkened by the action of the silver

nitrate and thus brings into view the outlines of the cells forming the
vascular wall.

The form of the cells constituting the vascular membrane varies in
different regions and in capillaries of different calibre. According to
Kolliker, in the smallest capillary bloodvessels, measuring from 4.5
to 7 mmm. in diameter, the cells are narrow, elongated, and fusiform,
as in Fig. 122; often curled from side to side, so as to form each a
half cylinder, two of them joining at their edges to complete the
capillary tube, and alternating longitudinally, the pointed extremity of
one cell being intercalated between those of the two following cells. In

AKTERY, with its muscular
tunic (a) breaking up into capillaries.
From the pia mater.

THE CAPILLARY CIRCULATION.

345

the larger capillaries, of 8 to 13 mmm. in diameter, where the calibre of
the vessel is surrounded by three or four cells placed side by side, they
are shorter and wider in form, like those of ordinary pavement epithe-
lium. The arrangement of these microscopic forms in the wall of the

Fig. 122.

CAPILLARY BLOODVESSEL, from the tail of the tadpole; showing the outlines of
its epithelium-like cells, rendered visible by the action of silver nitrate. (KOlliker.)

capillary bloodvessels has given rise to the opinion, entertained by some
histologists, that the vascular system is to be regarded as a series of
intercellular canals, provided, in different regions, with varying addi-
tional layers of muscular, elastic, and connective tissue.

The capillary bloodvessels ure further distinguished from both arteries
and veins by their frequent inosculation. The arteries constantly divide
and subdivide, as they pass from within outward, while the veins as
constantly unite with each other, to form larger and less numerous
branches and trunks, as they converge from the periphery toward the
centre ; and although the arteries always present inosculations in certain
regions, and the veins more frequently still, this feature is, nevertheless,
a secondary or incidental one in both vascular systems. The arteries
are essentially diverging tubes to distribute the blood from within out-
ward ; the veins are converging channels to collect and transport it from
without inward.

The capillaries, on the other hand, are mainly characterized by their
constant and repeated intercommunication. They are vascular canals
which penetrate the solid organs and tissues, uniting with each other at
23

346

THE CIKCULATION.

Fig. 123.

CAPILLARY PLEXUS, from the web of the
frog's foot.

short intervals, in such a manner as to form an interlacing network or
plexus of minute bloodvessels, known as the capillary plexus. The

vessels forming this plexus vary
somewhat in size, abundance,
and arrangement in different
parts of the body. In every
vascular organ and tissue there
are certain spaces or islets, in-
closed on all sides by capilla-
ries, but into the interior of
which these vessels do not pene-
trate. Such islets or intervas-
cular spaces must therefore ob-
tain their nourishment by the
exudation and absorption of the
fluid ingredients of the blood
through the capillary walls and
the substance of the intervening
tissue.

The special arrangement of

the capillary bloodvessels, and the form and size of the meshes of their
network, are, in general, characteristic of each separate organ or tissue.
In the muscles, the meshes are in the form of long parallelograms, cor-
responding with that of the muscular fibres ; in the mucous membranes
of the stomach and large intestine, they are hexagonal, or irregularly
circular, inclosing the orifices of the secreting follicles ; in the papillae
of the tongue and skin, and in the placental tufts, the capillaries form
twisted vascular loops ; in the glomeruli of the kidneys, convoluted
coils ; in the connective tissue, irregularly shaped figures, correspond-
ing in direction with the fibrous bundles of the tissue.

The capillary bloodvessels are the most abundant, and interlaced in
the finest network, in those organs to which the blood is distributed for
other purposes than for local nutrition; as for that of aeration, secre-
tion, or absorption. One of the closest of all the capillary networks is
that of the lungs, in which the diameter of the spaces separating the
r bloodvessels, in the walls of the pulmonary vesicles, is sometimes a little
greater and sometimes a little less than that of the capillaries them-
selves. In the glandular tissue of the liver, the spaces separating the
adjacent vessels are only a little wider than the capillaries forming the
intra-lobular network. In the nerves, the serous membranes, and the
tendons, on the other hand, the capillary vessels are less closely inter-
woven ; and in the adipose tissue they form wide, open meshes, em-
bracing the exterior of the separate fat vesicles.

Movement of the Blood in the Capillary Vessels. — The motion of the
blood in the capillaries may be studied by examining, under the micro-
scope, any transparent tissue of a sufficient degree of vascularity. The
frog is the most convenient animal for this purpose, owing to the readi-

THE CAPILLARY CIRCULATION.

347

ness with which the circulation may be maintained even in the internal
organs, exposed at ordinary temperatures. In order to secure immo-
bility, the medulla oblongata may first be broken up by a strong needle
introduced through the cranium, or the voluntary muscles may be para-
lyzed by the subcutaneous injection of six drops of a filtered watery
solution of woorara, made in the proportion of one part to five hundred.
The whole body, with the exception of the part used for observation,
should be enveloped in a light linen or cotton bandage, kept moistened
to prevent desiccation of the surface. The tongue, or the web of one
foot, may be stretched over a glass side, and placed under the lens of
the instrument. To examine the pulmonary circulation, an opening
should be made in one side just behind the anterior limb, and the
lung moderately inflated through the glottis, until it protrudes through
the external wound. For the mesenteric circulation, an incision should
be made in the left flank of a male frog, a loop of intestine carefully
drawn out of the abdomen, and the mesentery allowed to rest upon a
circular glass plate, 12 millimetres in diameter, and 6 millimetres in
thickness, cemented upon a large glass plate, by which the body of the
animal is supported. Under favorable circumstances the circulation
will go on in either of these organs for several hours.

When the circulation is examined in this manner, the smaller arte-
ries, the capillary vessels, and the minute veins are often -visible under
the microscope in the same
region. The blood can be
seen entering the field by
the smaller arteries, shooting
through them with great ra-
pidity in successive impulses,
and flowing off by the veins
at a somewhat slower rate.
In the capillaries, the circula-
tion is considerably less rapid
than in either the arteries or
the veins. It is also perfectly
steady and uninterrupted in
its flow. The blood moves
through its vascular channels
in a uniform current, without
their exhibiting any appear-
ance of contraction or dilata-
tion. Another marked peculiarity of the capillary circulation is that
it has no definite direction. Its numerous streams pass indifferently
above and below each other, at right angles to each other's course, or
even in opposite directions ; so that the blood, while in the capillaries,
circulates everywhere among the tissues, in such a manner as to be
distributed to all parts of their substance.

The motion of the red and white globules is also peculiar, and shows

CAPILLARY CIRCULATION in web of frog's foot.

THE CIRCULATION.

distinctly the difference in their physical properties. In the larger ves-
sels the red globules are carried along in close column, in the central
part of the stream; while near the edges of the vessel there is a trans-
parent space occupied only by clear plasma, in which no red globules
are to be seen. In the smaller vessels the globules pass two by two, or
follow each other in single file. The flexibility and semi-fluid consist-
ency of the red globules are very apparent from the readiness with
which they become folded up, bent or twisted, and with which they
glide through minute branches of communication, smaller in diameter
than themselves. The white globules, on the other hand, move more
slowly through the vessels. They drag along the external portions of
the current, and are sometimes temporarily arrested, adhering for a few
seconds to the internal surface of the vessel. Whenever the current is
obstructed or retarded, the white globules accumulate in the affected
portion, and become more numerous there in proportion to the red.

It is during the capillary circulation that the blood serves for the
nutrition of the vascular organs. Its fluid portions transude through
the walls of the vessels, and are absorbed by the tissues in the propor-
tions requisite for their nourishment, or for the products of secretion ;
while its albuminous ingredients are also transformed into new materials,
characteristic of the different tissues and fluids. In this way are pro-
duced the myosine of the muscles, the collagen of the bones, tendons,
and ligaments, the ptyaline of the saliva, and the pepsine of the gastric
juice ; and in the lungs, the exchange of oxygen and carbonic acid takes
place in the capillary vessels. The blood in the capillary circulation
thus furnishes, directly or indirectly, the materials of nutrition for the
entire body.

Physical Cause of the Capillary Circulation. — The physical condi-
tions which influence the movement of the blood in the capillaries are
somewhat different from those of the arterial and venous circulations.
By the successive division of the arteries from the heart outward, the
movement of pulsation is to a great extent equalized in the smaller
arterial branches. But as these vessels reach the confines of the capillary
system, they suddenly break up into a terminal ramification of still
smaller and more numerous vessels, and so lose themselves at last in
the capillary network. By this final increase of the vascular surface,
the equalization of the heart's action is completed. There is no longer
any pulsating character in the force which acts upon the circulating
fluid ; and the blood moves through the capillary vessels under a con-
tinuous and uniform pressure.

This pressure is sufficient to cause the blood to pass with considerable
rapidity through the capillary plexus, into the commencement of the
veins. This fact was first demonstrated by Sharpey,1 who employed an
injecting syringe with a double nozzle, one extremity of which was con-

1 Todd and Bowman, Physiological Anatomy and Physiology of Man, vol. ii.
p. 350.

THE CAPILLARY CIRCULATION. 349

nectcd with a mercurial gauge, while the other was inserted into the
artery of a recently killed animal. When the syringe, filled with defi-
brinated blood, was fixed in this position, the defibrinated blood would
press with equal force upon the mercury in the gauge and upon the fluid
in the bloodvessels ; and thus the height of the mercurial column indi-
cated the amount of pressure required to force the defibrinated blood
through the capillaries of the animal, and to make it return by the cor-
responding vein. In this way Prof. Sharpey found that, when the free
end of the injecting tube was attached to the mesenteric artery of the
dog, a pressure of 90 millimetres of mercury caused the blood to pass
through the capillaries of the intestine and of the liver ; and that under
a pressure of 130 millimetres, it flowed in a full stream from the divided
extremity of the vena cava.

We have obtained similar results by experimenting upon the vessels
of the lower extremity. A full grown, healthy dog was killed, and one
of the lower extremities immediately injected with defibrinated blood,
by the femoral artery, in order to prevent coagulation in the smaller
vessels. A syringe with a double flexible nozzle was then filled with
defibrinated blood, and one extremity of its injecting tube attached to
the femoral artery, the other to the mouthpiece of a cardiometer. By
making the injection, it was then found that the defibrinated blood was
returned from the femoral vein in a continuous stream under a pressure
of 120 millimetres, and that it was discharged very freely under a pres-
sure of 130 millimetres.

Since the arterial pressure upon the blood during life is equal to 150
millimetres of mercury, it is evident that this pressure is sufficient to
propel the blood through the capillary circulation.

Furthermore, the blood is not altogether relieved from the influence
of elasticity, after leaving the arteries. For the capillaries themselves
have a certain degree of elasticity, and are surrounded, in addition, by
the tissues of the organs in which they are distributed ; many of which,
such as the lungs, spleen, skin, lobulated glands, and mucous membranes,
contain elastic fibres more or less abundantly disseminated through their
substance. The effect of this physical property, in the vessels and the
neighboring parts, may be exhibited in artificial injections of one of the
lower limbs through the femoral artery, or of the liver through the
portal vein. If, while the parts are distended by the fluid passing
through their vessels, the injecting force be suddenly arrested, the move-
ment of the current does not at once cease, but the fluid of injection
continues to escape for several seconds from the femoral or hepatic vein,
owing to the continuous pressure exerted from behind. The elasticity
of the surrounding tissues, therefore, supplements, that of the minute
bloodvessels, and aids in producing a uniform movement of the capillary
circulation.

Velocity of the Blood in the Capillary Vessels. — The motion of the
blood in the capillary vessels is much less rapid than in either the
arteries or the veins. It may be measured, with a tolerable approach

350 THE CIRCULATION.

to accuracy, during the microscopic examination of transparent and
vascular tissues. The results obtained in this way by different observers
(Valentin, Weber, and Volkrnann), show that the rate of movement of
the blood through the capillaries is rather less than one millimetre per
second ; or about 5 centimetres per minute. Since the rapidity of the
current must be in inverse ratio to the entire calibre of the vessels
through which it moves, it appears that the united calibre of all the
capillaries must be not less than 300 times greater than that of the
arteries. It does not follow from this, however, that the whole quantity
of blood contained in the capillaries at any one time is so much greater
than that in the arteries ; since, although the united calibre of the capil-
laries is large, their length is very small. The effect of the anatomical
structure of the capillary system is to disseminate a comparatively small
quantity of blood over a very large space, so that the physiological
reactions necessary to nutrition take place with promptitude and energy.
Although the rate of movement of the blood in these vessels, accordingly,
is a slow one, yet as the distance to be passed over between the arteries
and veins is very small, the blood requires but a short time to traverse
the capillary system, and to commence its returning passage by the veins.

General Rapidity of the Circulation.

The rapidity with which the blood passes through the entire round
of the circulation has been demonstrated by Hering, Poisseuille, Mat-
teucci, and Vierordt in the following manner : A solution of potassium
ferrocyanide was injected into the right jugular vein of a horse, at the
same time that a ligature was placed upon the corresponding vein on
the left side, and an opening made in it above the ligature. The blood
flowing from the left jugular vein was then received in separate vessels,
which were changed every five seconds, and the contents afterward ex-
amined. It was thus found that the blood drawn from the first to the
twentieth second contained no traces of the ferrocyanide ; but that which
escaped from the vein at the end of from twenty to twenty-five seconds,
showed unmistakable evidence of the presence of the foreign salt. The
potassium ferrocyanide must, therefore, during this time, have passed
from the point of injection to the right side of the heart, thence to the
lungs and through the pulmonary circulation, to the left side of the
heart by the pulmonary veins, outward by the arteries to the capillary
circulation of the head and neck, and must have again commenced its
downward passage to the heart by the opposite jugular vein.

By extending these observations, it was found that the duration of
the circulatory movement varies to some extent in different species of
animals ; being, as a general rule longer in those of larger size. The
main result, as given by Milne Edwards,1 is as follows:

1 Leqons sur la Physiologic. Paris, 1859, tome iv. p. 364.

LOCAL VARIATIONS. 351

DURATION OF THE CIRCULATORY MOVEMENT.

In the Horse 28 seconds.

" Dog 15

" Goat 13 "

" Rabbit 7 "

These results are corroborated by subsequent investigations. In ex-
perimenting upon the dog, by injecting a solution of potassium ferrocy-
anide into the jugular vein, and immediately drawing blood from the
corresponding vein on the opposite side, we have found that the short
interval of time requisite for closing the first vein by ligature after
terminating the injection, and opening the second in such a manner as
to obtain a specimen of blood for examination, is sufficient to allow
of the passage of the ferrocyanide through the entire round of the cir-
culation. If we regard the duration of this movement in the human
subject as intermediate between that in the dog and the horse, making
allowance for the difference in size, this would give the time required
by the blood to make the circuit of the veins, arteries, and capillaries,
in man, as not far from 20 seconds.

Local Variations in the Capillary Circulation.

An important class of phenomena connected with this part of the
subject consists of the local variations in the capillary circulation.
These variations are often very marked, and show themselves in many
different parts of the body. The pallor or suffusion of the face under
mental emotion, the congestion of the mucous membranes during diges-
tion, and the local and denned redness of the skin produced by any
irritating application, are all instances of this sort. These changes are
due to the contraction or dilatation of the smaller arterial branches
which supply the part with blood, under the influence of nervous action.
The middle coat of these vessels is composed mainly of organic or
unstriped muscular fibres, arranged in a transversely circular direction,
which by their contraction diminish and by their relaxation enlarge
the calibre of the arterial tube. They regulate, accordingly, by this
means, the quantity of blood passing to the capillary system. When
contracted, they resist more strongly the impulsive force of the arterial
current, and admit the blood in smaller quantity. When dilated, they
allow a freer access to the capillaries and the blood passes in greater
abundance.

These changes are most distinctly manifested in the' periodical con-
gestion of the glandular organs. All the glands and mucous membranes
connected with the digestive apparatus enter into a state of unusual
vascular excitement at the time of secretion and digestion. This can
readily be seen, in the living animal, in the pancreas, and in the mucous
membranes of the stomach and small intestine ; the tissues of these
parts being visibly redder and more turgid during digestion and absorp-
tion than in the fasting condition.

A similar variation of the circulation has been particularly studied

352 THE CIRCULATION.

by Bernard1 in the submaxillary gland of the dog. During the ordinary
condition of glandular repose he found that it required sixty-five seconds
to obtain five cubic centimetres of blood from the submaxillary vein ;
but, when the gland was excited to functional activity, the same quan-
tity of blood was discharged by the vein in fifteen seconds. Thus the
volume of blood passing through the organ in a given time was more
than four times as great while the gland was in a state of active secre-
tion, as in a condition of repose.

The increased flow of blood, in a secreting gland, is accompanied also
by an important change in its appearance. During repose, the blood,
which enters the submaxillary gland from the arteries bright red, is
changed in its tissue from arterial to venous, and passes out by the
veins of a dark color. But when the secretion of the gland is excited,
either by galvanization of its nerve or by introducing vinegar into the
mouth of the animal, the blood is not only discharged in larger quantity,
but passes out red by the veins, so as hardly to be distinguished in
color from arterial blood. When the secretion of the gland is suspended,
the blood in its vein again becomes dark-colored as before. There is
little doubt that the same is true of most of the secreting glands, and
that the blood circulating in their capillaries is changed from red to blue
only during the period of functional repose ; while at the time of active
secretion it not only passes through the vessels in greater abundance,
but also retains its ruddy color in the veins.

This -is because, during the period of glandular repose, the blood per-
forms in its tissues the usual functions of nutrition. It therefore under-
goes the ordinary changes and becomes altered in color from arterial to
venous. But the period of active secretion is a period of congestion,
during which the blood passes in larger quantity, while its watery and
saline ingredients exude into the secretory ducts, bringing with them
the materials accumulated in the interval of repose. There is nothing
in this process to exhaust the oxygen of the blood or to change its
color from arterial to venous, and it therefore passes into the veins
comparatively unaltered.

A similar ruddy color of venous blood is to be seen in the renal veins,
where it is often nearly identical with that of arterial blood. The dif-
ference in hue between the renal veins and the neighboring muscular
veins or the vena cava, when exposed by opening the abdomen of the
living animal, is very marked, provided the kidneys be at the time in a
state of functional activity. The greater part of the blood traversing
these organs is changed only by the elimination of its urea and the
remaining ingredients of the urine, which exude into the excretory
tubules. The process of active local nutrition is here altogether sub-
servient to the discharge of organic materials already existing in the
blood; -and the loss of oxygen and alteration in color of the circulating
fluid are thus comparatively insignificant.

1 Leqons sur les Liquides de TOrganisme. Paris, 1859, tome ii. p. 272.

LOCAL VARIATIONS.

353

Fig. 125.

On the other hand, the venous blood coming from the muscular tissue
is very dark colored, especially if the muscles be in a state of active
contraction. As the muscles form so
large a part of the entire mass of the
body, their condition has a prepondera-
ting influence upon the color of the
venous blood in general. The greater
the activity of the muscular system, the
darker is the color of the blood return-
ing from the trunk and extremities.
When the muscles are in a state of re-
pose or paralysis, on the contrary, the
change is less marked ; and in the com-
plete relaxation produced by abundant
hemorrhage or by complete etherization,
the blood in the veins often approxi-
mates in color to that in the arteries.

Finally, in the lungs the reverse pro-
cess takes place. In these organs the
blood is supplied with a fresh quantity
of oxygen, to replace that which has
been consumed elsewhere ; and accord-
ingly it changes its color from dark
purple to bright red as it passes through
the pulmonary capillaries.

Both the physical and chemical phe-
nomena, therefore, of the circulation
vary at different times and in different
organs. The actions which go on
throughout the body, are varied in cha-
racter, and produce a similar difference
in the phenomena of the circulation.
The venous blood, consequently, has a
different composition as it returns from
different organs. In the parotid gland
it yields the ingredients of the saliva ;
in the kidneys those of the urine. In
the intestine it absorbs the nutritious
elements of the digested food ; and in
the liver it gives up substances destined
to produce the bile, while it absorbs
glucose from the hepatic tissue. In the
lungs it changes from blue to red, and
in the capillaries of the general system,
from red to blue ; and its temperature, also, varies in different veins,
according to the peculiar chemical and nutritive changes going on in the
organs from which they originate.

DIAGRAM OF THK CIRCULA-
TION.—1. Heart. 2. Lungs. 3. Head
and upper extremities. 4 Spleen. 6.
Intestine. 6. Kidney. 7. Lower ex-
tremities. 8. Liver.

CHAPTEE XVI.

THE LYMPHATIC SYSTEM.

IN addition to the connected series of canals by which the blood
passes in a continuous round through the arteries, capillaries, and veins,
there is also a system of vessels, leading only from the periphery toward
the centre, and discharging into the great veins near the heart the fluids
which have been absorbed in the solid tissues of the body. The fluid
contained in these vessels is nearly or quite colorless, especially in thin
layers, and from its transparent and watery appearance is called the
" lymph," and the vessels themselves constitute what is known as the
lymphatic system.

As the blood circulates through the capillaries under the influence of
the arterial pressure, certain of its ingredients transude through the vas-
cular walls and penetrate the interstices of the anatomical elements of
the tissues. An increased pressure upon the blood, either from arterial
congestion or from obstruction to the venous current, will increase the
amount of transudation, producing an cedematous condition of the part,
which is first perceptible in the loose connective tissue, but which may
afterward involve the more compact substance of the organs. In the
normal state of the circulation, this interstitial fluid, which is the real
source of nutrition for the solid parts, does not, however, stagnate in
contact with them, but is renewed by a continual change. As fresh sup-
plies need to be drawn from the circulating blood, the older portions are
removed by absorption and returned to the centre of the circulation by
the lymphatic vessels. Thus these vessels may be considered as com-
plementary in their function to the veins. The blood, containing the red
globules, requires to be rapidly and abundantly returned to the lungs by
the veins, in order to regain the oxygen necessary for its continued vital-
ity ; while the lymphatics collect more gradually the fluids which have
served for the slower process of nutrition and growth.

Anatomical Structure and Arrangement of the Lymphatic System.
In structure the lymphatics do not essentially differ from the blood-
vessels, their principal peculiarity being that their walls are more delicate
and transparent. This circumstance, together with the colorless nature
of their contents, renders them less easily recognizable by dissection.
Those of larger and medium size consist of three coats, similar, in
general characters, to the corresponding tunics of the bloodvessels.
According to the observations of Kolliker, the external coat alone is
distinguished from that of the veins by the possession of smooth mus-
(354)

STRUCTURE OF LYMPHATIC SYSTEM. 355

cular fibres which are arranged in a longitudinal and oblique direction ;
a character which is to be seen in lymphatics of 0.2 millimetre in diame-
ter and upward. Like the veins, they are provided with numerous
valves, opening toward the heart and closing toward the periphery, the
vessel often presenting a well-marked dilatation just within the situation
of the valves. The smallest lymphatics consist of only a single coat,
composed of flattened, epithelium-like, nucleated cells, which may be
brought into view, like those of the capillary bloodvessels, by the
staining action of a silver nitrate solution.

Origin and Course of the Lymphatic Vessels. — So far as the origin
of the lymphatics has been demonstrated by injections, these vessels
commence in the substance of the tissues by plexuses. They are more
abundant in organs which are fully supplied with bloodvessels, and are
absent in tissues where bloodvessels do not exist, such as those of the
cornea, the vitreous body, and the epithelial coverings of the skin and
mucous membranes. According to Yon Recklinghausen, the meshes
of the lymphatic plexus, as a general rule, are intercalated between
those of the capillary bloodvessels; so that the point of junction of two
or more lymphatics is always in the middle of the space surrounded by
the adjacent bloodvessels. Thus the lymphatic capillary is situated at
the greatest distance possible from the nearest capillary bloodvessels;
and in the trans udation of fluids from one to the other, the interven-
ing substance of the tissue will always be completely traversed by
the nutritious ingredients of the blood. In membranous expansions
presenting a free surface, as in the skin and mucous membranes, the
plexus of capillary bloodvessels is invariably nearer the surface, while
the lymphatics occupy a deeper plane beneath it. Even in the villi of
the small intestine, the network of bloodvessels is situated immediately
under the epithelial layer, and surrounds the lacteal vessel which is
placed in the central part of the villus.

Beside the lymphatic capillaries proper, certain irregularly shaped
spaces or canals, containing only a colorless or serous fluid, have been
found in organs consisting of condensed connective tissue, like the cen-
tral tendon of the diaphragm and muscular fasciae. They have been
demonstrated mainly by the process of treating the tissues with a solu-
tion of silver nitrate, which stains the solid portions of a dark color,
but leaves the capillary vessels and the serous canals uncolored. These
interstitial spaces or serous canaliculi have been regarded by some ob-
servers (Recklinghausen) as directly continuous with the lymphatic
capillaries, and as constituting the immediate sources of supply for the
lymph ; but this connection is not universally admitted. The serous
canaliculi are distinguished from the lymphatic capillaries by their
much smaller size, and by the fact that they do not possess, like the
latter, a lining of epithelial cells.

From their plexuses of origin the lymphatic vessels pass inward
toward the great channels and cavities of the body, uniting into larger
branches and trunks, and following generally the course of the prin-

356 THE LYMPHATIC SYSTEM.

cipal bloodvessels and nerves. Those of the lower extremities enter
the cavity of the abdomen, and join with the lymphatics of the abdo-
minal organs to form the commencement of the thoracic duct, which
ascends through the cavity of the chest, receiving branches from the
thoracic organs to the root of the neck, where it is joined by lymphatics
from the left side of the head and the left upper extremity, and ter-
minates in the left subclavian vein, at the point of its junction with the
left internal jugular. The lymphatics coming from the right side of
the head and neck, the right upper extremity, and a portion of the
thoracic organs, form a trunk of smaller size, the right lymphatic duct,
which terminates in the right subclavian vein at its junction with the
right internal jugular. Thus the lymph, collected from the vascular
tissues of the entire body, is mingled with the venous blood a short
distance before its arrival at the right side of the heart.

The Great Serous Cavities of the Body are Lymphatic Lacunae. —
It is well known that in the amphibious reptiles there are irregularly-
shaped spaces or lacunae, forming a part of the lymphatic system and
interposed between adjacent organs in various parts of the body. In
the mammalia the peritoneal and pleural cavities, and probably all the
principal serous sacs, are also in direct communication with the lym-
phatic vessels. This was first shown by Recklinghausen1 for the peri-
toneal cavity of the rabbit, which communicates by microscopic orifices
with the lymphatic vessels in the central tendon of the diaphragm.
These communications were demonstrated in two ways : First, on in-
jecting into the peritoneal cavity of the animal milk, or a watery fluid
holding in suspension minute granules of coloring matter, the lymphatic
vessels of the central tendon of the diaphragm were afterward found to
be filled with the white or colored injection. Secondly, the central tendon
of the diaphragm being carefully removed from the recently killed animal,
and a drop of milk placed upon its peritoneal surface, the milk globules
could be directly observed under the microscope, running in converging
currents to certain points on the surface of the tendon and there pene-
trating into its lymphatic vessels. The cavity of the pleura has also
been found by similar means to communicate with the lymphatic vessels
in its neighborhood. The serous cavities accordingly are either exten-
sive lacunae, forming in some regions the origin of the lymphatic vessels,
or else they are wide but shallow expansions of the cavity of the lym-
phatics, situated at various points in their course.

The Lymphatic Glands. — During the passage of the lymphatic vessels
from the periphery toward the centre, they are repeatedly interrupted by
ovoid, glandular-like bodies, of a pale reddish color and somewhat firm
consistency, varying in size from about two to twenty millimetres in
their long diameter. They do not exist in fish and reptiles, but are
always present in birds and mammalia. As a rule, several lymphatic
vessels reach these bodies, coming in a direction from the periphery ; and

1 Strieker's Manual of Histology, Buck's Edition. New York, 1872, p. 221.

STRUCTUKE OF LYMPHATIC SYSTEM.

357

several others leave them at another portion of their surface, passing
onward toward the centre of the circulation. The former are called the
u afferent," the latter the " efferent" lymphatic vessels. Owing to the
general gland ular-like aspect which they present to the eye, these bodies
are known as lymphatic " glands," although they possess no proper ex-
cretory duct, and whatever new materials are formed in their interior
must be carried away either by the veins or by the efferent lymphatic
vessels.

The lymphatic glands are situated upon the course of the lymphatic
vessels on the inside of the limbs at the flexures of the joints, in the
axilla and the groin, in the thoracic and abdominal cavities, along the
sides of the spinal column, in the mesentery, and in the sides and ante-
rior part of the neck.

Fig. 126.

LYMPHATIC VESSELS AHD GLANDS OF THE HEAD, NECK, AND THORAX.— 1.
Thoracic duct, at the point of its emergence from the chest. 2. The same duct, at its junction
with the left subclavian vein. (Mascagni.)

As regards the structure of the lymphatic glands they consist, First,
of an external fibrous envelope, which sends from its internal surface
prolongations in the form of septa and branching bands into the deeper
parts of the gland, so that the interior of the organ is divided into a

358

THE LYMPHATIC SYSTEM.

multitude of smaller spaces by the inosculations of this fibrous frame-
work. The bands constituting this framework are called the " trabeculse."
Secondly, in the interstices between the trabeculse there is situated the
pulpy substance of the gland. In the more external or cortical part of
the gland, the interspaces have a rounded or sac-like form, which gives
to this portion of the organ a granular aspect, while this appearance is
wanting in the deeper or medullary portion ; but in both situations the
glandular pulp has essentially the same microscopic texture. Thirdly,
the bloodvessels of the gland penetrate it from the outside, usually at a
depressed spot called the "hilum," and, after reaching the interior, break
up into a rich plexus of capillaries. These bloodvessels and their capil-
lary plexus follow distinct routes in the gland, in the middle of the
spaces between the trabeculse. The capillary bloodvessels are sur-
rounded and held in position by very fine branching fibres attached to
their external surface; and in the meshes of these fibres, as well as
between the bloodvessels, there are imbedded a great number of rounded,
granular, nucleated cells, about 9 mmm. in diameter, similar to the white
globules of the blood and of the lymph, and which in this situation
are known as "lymph globules." The presence of these granular cells,
fixed between and immediately around the capillary bloodvessels, gives
to the parts occupied by them a well-marked opaque appearance by
transmitted light ; and there are thus formed, in a thin section of the
gland, elongated, opaque tracts or cords, separated by intervening trans-
parent spaces, and communicating with each other at frequent intervals.

Fig. 127.

Fig. 128.

THIN SECTION OP A LYMPHATIC GLAND
FROM THE Ox.— o. Medullary cords, b. Lymph
paths, c. Trabeculae. (Kolliker.)

LONGITUDINAL SECTION through
the hilum of a mesenteric gland from
the ox, showing the commencement of
the efferent lymphatic vessels injected
from a puncture of the glandular sub-
stance.— a. Plexus of efferent vessels.
b. Lymph paths, c. Medullary cords.
d. Trabeculae. (K6lliker.)

These opaque and vascular tracts are called the medullary cords of the
lymphatic gland. They are the only vascular parts of the organ ; as
the capillary bloodvessels never pass beyond them into the intervening
transparent spaces. The transparent spaces, situated between the

TRANSUDATION THROUGH ANIMAL TISSUES. 359

medullary cords and immediately surrounding the trabeculae, constitute
the lymph-paths, or the channels by which the lymph traverses the glan-
dular substance from the afferent to the efferent vessels. The afferent
lymphatic vessels, according to the united testimony of more recent
observers, after ramifying upon the outer surface of the gland, penetrate
its fibrous envelope and become continuous with the transparent por-
tions of the glandular substance. This has been shown by injections of
the lymphatic gland from the afferent vessels ; and Kolliker has also
demonstrated a similar connection of the same channels with the efferent
vessels, by injecting these vessels from the substance of the gland.

The lymph-paths present a transparent appearance in thin sections of
the gland for the reason that the granular lymph-cells which they con-
tain are easily detached and removed by manipulation, while those of
the medullary cords are more firmly fixed in the fibrous mesh-work and
do not readily yield to a displacing force. It has been found b/Kolliker
that a watery or serous fluid, injected through the substance of the gland
under very moderate pressure, will also displace these cells and leave
the spaces which they occupied nearly clear. For these reasons it is
regarded as certain that the lighter spaces in the lymphatic glands are,
as their name indicates, the channels by which the lymph passes from
the afferent to the efferent vessels, and that the lymph-cells are detached
by this current from the place of their growth and carried onward
through the rest of the lymphatic system.

Translation and Absorption fcy the Animal Tissues.

During the passage of the blood through the capillary bloodvessels
a variety of actions take place by which some of its ingredients are
given up to the tissues by transudation and are at the same time replaced
by others derived by absorption from the adjacent parts. The lym-
phatic system of vessels, furthermore, is entirely filled by the absorption
of materials taken up from the surrounding tissues ; and the composi-
tion of the fluid which they contain depends upon the property, belong-
ing to animal membranes, of transmitting or absorbing certain fluid
substances in a peculiar way. This property is exhibited experiment-
ally in the following manner.

If a fresh animal membrane be firmly attached over the mouth of a
cylindrical glass tube, filled with pure water and immersed in solutions
of various substances, in such a manner that the membrane forms a
continuous diaphragm, having the water on one side and the solution
on the other, it is found that different substances penetrate the mem-
brane and pass through it to the water with very different degrees
of rapidity. As a general rule crystallizable substances, such as
mineral salts, glucose, urea, pass with facility ; while the non-crystal-
lizable organic matters, such as albumen, starch, gum, pass with com-
parative difficulty There are certain exceptions, however, to this rule.
Thus albumen, under ordinary circumstances, transudes slowly or not
at all through animal membranes ; while albuminose, which is also non-

360 THE LYMPHATIC SYSTEM.

crystallizable, passes very rapidly and abundantly. The distinction,
furthermore, between the two classes of substances is not a complete
one, since they may nearly all be made to transude in some degree by
increasing the pressure of the column of fluid upon the corresponding
side of the membrane ; but the difference between them is often very
great in this respect. According to the observations of Liebig,1 the
requisite pressure for different liquids, in passing through the same
membrane in a given time, is as follows :

COMPARATIVE PRESSURE HEQUIRED TO CAUSE TRANSUDATION THROUGH
OX-BLADDER.

Kind of liquid. Height of the mercurial column.

Water . . 324 millimetres.

Solution of salt 514

Oil 920 "

Aldbhol 1298 "

Owing to their varying degree of transmissibity through membranes
this property has even been employed for the purpose of separating
different substances from each other, when mingled together in the
liquid form. This process is termed Dialysis. Thus, if a solution
containing both gum and sugar be placed in contact with one side of
the membranous diaphragm, with pure water on the other, the sugar
alone will pass through, while the gum will be left behind. If a mix-
ture of albumen and sodium chloride be placed under the same con-
ditions, the salt will transude in a pure form leaving the albumen
by itself; both substances in this way being purified from each other
through the action of the membrane. By the same process it has been
found possible to extricate poisonous c^stallizable matters, such as
strychnine or arsenious acid, from their admixture with albuminous
substances in a state of sufficient purity to allow of their detection by
chemical tests. The tissues of an animal membrane, accordingly, may
in this way exercise a kind of elective affinity for various substances,
and produce a special composition in fluids which have transuded
through them.

Endosmosis and Exosmosis. — Beside the elimination of chemical
ingredients above described, the phenomena of trans udation often give
rise to a change in volume of the fluid on either side of the membranous
septum. When an animal membrane is interposed between two different
liquids which are imbibed and transmitted by it with different degrees
of facility, that which passes most readily will accumulate in larger
quantity on the opposite side of the membrane.

If we take, for example, a solution of salt and an equal volume of
distilled water, and inclose them in a glass tube with a fresh animal
membrane stretched between, the two liquids being in contact with
opposite sides of the membrane, after a time they will have become

1 Cited in Longet, Trait§ de Physiologie. Paris, 1861, tome i. p. 384.

TRANSUDATION THROUGH ANIMAL TISSUES. 361

mingled, to a certain extent, with each other. A part of the salt will
have passed into the distilled water, giving it a saline taste ; and a part
of the water will have passed into the saline solution, making it more
dilute than before. If the quantities of the two liquids, which have
become so transferred, be measured, it will be found that a comparatively
large quantity of water has passed into the saline solution, and a com-
paratively small quantity of the saline solution has passed out into the
water. That is, the water passes inward to the salt more rapidly than
the salt passes outward to the water. The consequence is, that the
saline solution is increased in volume, while the water is diminished.
The more abundant passage of the water, through the membrane to the
salt, is called endosmosis ; and the more scanty passage of the salt out-
ward to the water is called exosmosis.

The mode usually adopted for measuring the rapidity of endosmosis
is to take a glass vessel, shaped somewhat like an inverted funnel, wide
at the bottom and narrow at the top. The bottom of the vessel is
closed by a thin animal membrane, stretched tightly over its edge and
secured by a ligature. From the top of the vessel there rises a narrow
glass tube, open at its upper extremity. When the instrument is thus
prepared, it is filled with a saline or saccharine solution and placed in a
vessel of distilled water; so that the membrane, stretched across its
mouth, shall be in contact with pure water on one side and with the
interior solution on the other. The water then passes in through the
membrane, by endosmosis, faster than the ingredients of the solution
pass out. An accumulation consequently takes place inside the vessel,
and the level of the fluid rises in the upright tube. The height to which
the fluid thus rises in a given time is a measure of the intensity of the
endosmosis, and of its excess over exosmosis. By varying the consti-
tution of the two liquids, and the arrangement of the membrane, the
variations in endosmotic action under different conditions may be
readily ascertained. Such an instrument is called an endosmometer.

Physical Conditions influencing Endosmosis. — The conditions which
regulate the intensity and extent of endosmosis have been investigated
by Dutrochet, Graham, Yierordt, Matteucci, and Cima. The first of
these conditions is the freshness of the animal membrane. A mem-
brane that has been dried and moistened again, or one that has begun
to putrefy, will not produce its full effect. It is also found that if the
membrane be allowed to remain and macerate in the fluids, after the
column has risen to a certain height in the upright tube, it begins to
descend again when putrefaction commences, and the two liquids finally
sink to the same level.

The next condition is the extent of contact between the membrane
and the two liquids. The greater the extent of contact, the more rapid
is endosmosis. An endosmometer with a wide mouth will produce
more effect than with a narrow one, though the volume of liquid may
be the same in both instances. The action takes place in the substance
of the membrane, and is proportional to its extent of surface.
24

362 THE LYMPHATIC SYSTEM.

The nature of the membrane employed, and even its position in re-
gard to the two liquids, also influence the result. Different serous and
mucous membranes act with different degrees of force. The effect pro-
duced is not the same with the integument of different animals, nor with
membranous tissues taken from different parts of the body of the same
animal. This depends upon the fact that the power of absorption for
a given liquid is different in different tissues. Chevreuil investigated
this point by taking definite quantities of certain animal substances, and
immersing them in various liquids for twenty-four hours, at the end of
which time the substance was removed and weighed. Its increase in
weight showed the quantity of liquid which it had absorbed. The fol-
lowing table1 shows the result of these experiments :

COMPARATIVE POWER OF ABSORPTION IN DIFFERENT TISSUES.

100 Parts of Water. Saline Solution. Oil.

Cartilage, 1 f 231 parts. 125 parts.

Tendon, 178 " 114 « 8.6 parts.

Elastic ligament, I absorb in I 148 " 30 " 7.2 "

Cornea, f 24 hours, j 461 " 370 " 9.1 "

Cartilaginous ligament, 319 " 3.2 "

Dried fibrine, [301 " 151 "

The influence of the position of the membrane depends upon a similar
difference in the absorbing power of its two surfaces. With some
fluids, endosmosis is more rapid when the membrane has its mucous
surface in contact with the dense solution, and its dissected surface in
contact with the water. With other substances, the more favorable
position is the reverse. Matteucci found that, in using the mucous
membrane of the ox-bladder, with water and a solution of sugar, if the
mucous surface of the membrane were in contact with the saccharine
solution, the liquid rose in the endosmometer between 80 and 113 milli-
metres in two hours. But if the same surface were turned toward
the water, the rise of the column of fluid was only 63 or 12 millimetres
in the same time.

Another important circumstance is the constitution of the two liquids
and their relation to each other. As a general thing, if the liquids
employed be water and a saline solution, endosmosis is more active, the
more concentrated is the solution in the endosmometer ; that is, a larger
quantity of water will pass inward toward a dense solution than toward
one which is dilute. But the force of endosmosis varies with different
liquids, though they may be of the same density. Dutrochet measured
the force with which water passes through the mucous membrane of the
ox-bladder, into different solutions of the same density, with the follow-
ing result :3

1 In Longet, Trait6 de Physiologie. Paris, 1861, tome i. p. 383.

2 In Matteucci, On the Physical Phenomena of Living Beings. Pereira's
translation. Philadelphia, 1848, p. 48.

TRANSUDATION THROUGH ANIMAL TISSUES. 363

COMPARATIVE INTENSITY OF ENDOSMOSIS OF WATER TOWARD DIFFERENT LIQUIDS, AS
MEASURED BY THE RISE OF THE COLUMN IN THE ExDOSMOMETER.
Endosmosis of water toward Divisions of the Endosmometer tube.

Solution of gelatine ...... 3

" gum 5

" sugar . . . . . ]1
" albumen 12

The primary cause of this variation in the phenomena of endosmosis
is the different absorptive power possessed by an animal membrane or
tissue for different liquids. This is partly shown by the experiments
of Chevreuil, in which oily matters were usually absorbed less readily
than either water or saline solutions. Nearly all animal membranes
also absorb water more rapidly than a solution of salt. If a membrane,
partly dried, be placed in a saturated solution of sodium chloride, it
will absorb the water in so much larger proportion than the salt that a
part of the salt will be left behind and deposited in a crystalline form
on the surface of the membrane.

When an animal membrane, accordingly, is placed in contact with
two different liquids, it absorbs one of them more abundantly than
the other ; and if that which is absorbed in the greatest quantity is also
readily diffused into the liquid on the opposite side, a rapid endosmosis
will take place in that direction, and a slow exosmosis in the other.
Consequent!}', the least absorbable fluid increases in volume by the con-
stant admixture of that which is taken up more rapidly. There are
even some cases in which endosmosis takes place without being accom-
panied by exosmosis. This occurs when water and albumen are em-
ployed as the two liquids. For while water readily passes inward
through the animal membrane, the albumen does not pass out. If an
opening be made in the large end of a fowl's egg, so as to expose the
shell-membrane, and the whole be then immersed in a goblet of water,
endosmosis will take place freely from the water to the albumen, so as
to distend the shell-membrane and make it protrude, like a hernia, from
the opening in the shell. But the albumen does not pass outward
through the membrane, and the water in the goblet remains pure.
After a time the pressure from within, due to the accumulation of fluid,
becomes so great as to burst the shell-membrane, after which the two
fluids mix uniformly with each other.

But a substance like albumen, which will not pass out by exosmosis
toward pure water, may traverse a membrane which is in contact with
a solution of salt. This has been shown to be the case with the shell-
membrane of the fowl's egg, which, if immersed in a watery solution
containing from 3 to 4 per cent, of sodium chloride, will allow the escape
of a small proportion of albumen. Furthermore, if a mixed solution of
albumen and salt be placed in a dialysing apparatus, the salt alone will
at first pass outward leaving the albumen ; but after the exterior liquid
has become perceptibly saline, the albumen also begins to pass in appre-
ciable quantity.

UULU

864 THE LYMPHATIC SYSTEM.

For the same membrane and different solutions of the same substance,
the direction and intensity of transudation depend upon the strength of
the solutions. With endosmometers containing solutions of sugar or
salt, and immersed in pure water, as shown by Dutrochet, the stronger
the solution the more rapid is the endosmosis from without ; and if two
solutions of salt be employed, with a membranous septum between them,
endosmosis takes place from the weaker solution to the stronger, and is
proportional to the difference in their densities. Density, however, is
not always the condition which determines the direction of the current.
For although with saline or saccharine solutions the direction of endos-
mosis is from the lighter to the denser liquid, with alcohol and water it
takes place from the water to the alcohol ; that is, from the denser to the
lighter liquid. It is evident from these facts that the process of endos-
mosis does not depend principally upon the attraction of the two liquids
for each other, but upon the attraction of the animal membrane for the
two liquids. The membrane is not a passive filter through which the
liquids mingle, but is the active agent which determines their transu-
dation. The membrane has the power of absorbing liquids, and of
taking them up into its own substance. This property, belonging to
the membrane, depends upon the organic ingredients of which it is com-
posed ; and, with different animal substances, the rate of absorption is
different. The tissue of cartilage, for example, as shown by the experi-
ments of Chevreuil, will absorb more water, weight for weight, than that
of the tendons; and the tissue of the cornea will absorb nearly twice as
much as that of cartilage.

The continuance of endosmosis is much favored by renewal of the
two liquids. Since the accumulation of fluid on one side of the mem-
brane depends on the difference in composition of the liquids employed
and the consequent difference in their rate of absorption, when endos-
mosis has been for some time going on, and the two liquids have
approximated each other in composition, the activity of endosmosis
will be diminished in proportion. As the salt or sugar passes out-
ward to the water and the water inward to the solution in the endos-
mometer, the external liquid acquires a saline or saccharine ingredient,
and the interior solution becomes more dilute ; and when the two liquids
have thus arrived at the same or nearly the same composition, endos-
mosis must cease. But if the exterior liquid be constantly replaced by
a current of pure water, and the interior solution maintained at its
original strength by the addition of new ingredients, the process of
transudation will go on with undiminished activity until. the membrane
has lost its absorbent power. The effect of a constantly renewed cur-
rent in aiding endosmosis may be readily shown by filling the cleansed
intestine of a rabbit with water from a reservoir and then placing it in
a shallow glass vessel containing a dilute solution of hydrochloric acid.
If the water be allowed to flow through the intestine under pressure
from the reservoir, that which is discharged from its open extremity
will in a few seconds show the presence of hydrochloric acid by its

TRANSUDATION THROUGH ANIMAL TISSUES. 365

reaction with litmus. The acid in this case passes through the wall of
the intestine against the pressure of the current, which is of course
directed from within outward.

Endosmosis is also regulated, to a great degree, by temperature.
As a rule it is more active when the temperature is moderately
elevated. Dutrochet found that an endosmometer, containing a solu-
tion of gum, absorbed only one volume of water at a temperature of
0°, but absorbed three volumes at about 34°. Variations of tempera-
ture will sometimes even change the direction of the endosmosis alto-
gether, particularly with dilute solutions of hydrochloric acid. In the
experiments of Dutrochet, when the endosmometer was filled with dilute
hydrochloric acid and placed in distilled water at the temperature of
10°, endosmosis took place from the acid to the water, if the density of
the acid solution were less than 1.020 ; but from the water to the acid,
if its density were greater than this. On the other hand, at the tem-
perature of 22°, the current was from within outward when the density
of the said solution was below 1.003, and from without inward when it
was above that point.

Absorption and Transudation in the Tissues of the Living Body. —
In the experiments above detailed, performed with membranes and tis-
sues taken from the dead body, by which the phenomena of endosmosis
and exosmosis were first studied, the phenomena represent imperfectly
those which take place in the living organism. The property, belong-
ing to an animal membrane, of determining the absorption or transu-
dation of various liquids, depends upon its organic constitution and is
exercised in the greatest intensity during life. In the living body, all
the conditions requisite for the acts of endosmosis and exosmosis are
present in a higher degree than is possible in any artificial experiment.
The membranes and tissues are all perfectly fresh, and unaltered by
either desiccation or putrescence; the extent of absorbing surface is
indefinitely multiplied by the repeated ramification of the capillary
bloodvessels or the glandular tubes; the internal temperature of the
body is maintained at a point most favorable for the activity of endos-
mosis ; and finally the continuous movement of the blood and the lymph,
in theii respective vessels, supplies the ingredients for a constant renewal
of the process and at the same time removes the accumulation of the
transuded material.

In the living body, accordingly, the transudation of fluids is accom-
plished with great rapidity. It has been shown by Gosselin, that if a
watery solution of potassium iodide be dropped upon the cornea of a
living rabbit, the iodine passes into the cornea, aqueous humor, iris,
lens, sclerotic and vitreous body, in the course of eleven minutes ; and
that it will penetrate through the cornea into the aqueous humor in
three minutes, and into the substance of the cornea in a minute and a
half. In these experiments it is evident that the iodine actually passes
into the deeper portions of the eye by simple endosmosis, and is not

366 THE LYMPHATIC SYSTEM.

transported by the bloodvessels ; since no trace of it is to be found in
the tissues of the opposite eye, examined at the same time.

The same observer has shown that the active principle of belladonna
penetrates the tissues of the eyeball in a similar manner. He applied a
solution of atropine sulphate* to both eyes of two rabbits. Half an hour
afterward, the pupils were dilated. Three-quarters of an hour later, the
aqueous humor was collected by puncturing the cornea with a trocar ;
and this fluid, dropped upon the eye of a cat, produced dilatation and
immobility of the pupil in half an hour. These facts show that the
aqueous- humor of the affected eye actually contains atropine, which it
absorbs from without through the cornea, and which thus acts directly
upon the muscular fibres of the iris.

But in all vascular organs, the processes of endosmosis and exosmosis
are still further accelerated by two important conditions, namely, first,
the movement of the blood circulating in the vessels, and secondly, the
minute dissemination and distribution of these vessels through the
tissues.

If a solution of the extract of nux vomica be injected into the subcu-
taneous connective tissue of the hind leg of two rabbits, in one of which
the bloodvessels of the limb have been left free, while in the other they
have been previously tied, so as to stop the circulation of blood in the
part, in the first rabbit the poison will be absorbed and will produce
convulsions and death in the course of a few minutes ; but in the second
animal, owing to the stoppage of the local circulation, absorption will
be retarded, and the poison will find its way into the general circulation
so slowly, that its specific effects will show themselves only at a late
period, or even may not be produced at all.

The processes of exosmosis and endosmosis, therefore, in the living
body, are regulated by the same or similar conditions as in artificial
experiments ; but they take place with greater rapidity, owing to the
movement of the circulating blood, and the extent of contact existing
between the bloodvessels and adjacent tissues. Although the arterial
blood is everywhere the same in composition, yet its different ingredients
are imbibed in varying quantities by the different tissues. And the
proportion of each ingredient is determined, in each separate tissue, by
its special absorbing or endosmotic power.

Albumen, under ordinary conditions, is not endosmotic ; that is, it
will not pass by transudation through an animal membrane. For this
reason, the albumen of the blood, in the natural state of the circulation,
is not exuded from the secreting surfaces, but is retained within the
vascular system. But the degree of pressure to which a fluid is sub-
jected has an influence in determining its endosmotic action. If the
pressure upon the blood in the capillary vessels be increased, by ob-
struction to the venous current and backward congestion of the capil-
laries, then not only the saline and watery parts of the blood pass out
in larger quantities, but the albumen itself may transude and infiltrate
the neighboring parts. In this way albumen may make its appearance

THE LYMPH AND CHYLE. 367

in the urine, in consequence of obstruction to the renal circulation; and
local oedema or general anasarca may follow upon venous congestion in
particular regions, or upon general disturbance of the circulation.

The Lymph and Chyle,

The tymph is the fluid which, having been absorbed from the various
tissues and organs of the body, is carried through the system of lym-
phatic vessels towards the centre of the circulation and is finally dis-
charged, by the thoracic and right lymphatic ducts, into the great veins
near the heart. As the chyle is simply the fluid of the mesenteric lym-
phatics, which assumes an opaque white color during digestion owing
to the absorption of fat, it is properly studied at the same time with
the lymph in general. The lymph has been obtained, for the purpose
of examination, from the living animal, by introducing a silver canula of
proper size into the thoracic duct at the root of the neck, or into large
lymphatic trunks in other parts of the body. It was obtained by Rees
from the lacteals of the mesentery and from the lymphatics of the leg
in the ass, by Colin from the lacteals and thoracic duct of the ox, and
from the lymphatics of the neck in the horse. We have obtained it
from the thoracic duct both of the dog and the goat.

Physical Characters and Composition of the Lymph. — The lymph,
thus obtained from the thoracic duct in the intervals of digestion, is an
opalescent or nearly transparent, alkaline fluid, usually of a light amber
color, and having a specific gravity of 1022. Its analysis shows a close
resemblance in composition with the plasma of the blood. It contains
water, fibrine, albumen, fatty matters, and the usual saline substances
of the animal fluids. It is, however, decidedly poorer in albuminous
ingredients than the blood. The following is an analysis by Lassaigne,1
of the fluid obtained from the thoracic duct of the cow:

COMPOSITION OF THE LYMPH.

Water 964.0

Fibrine 0.9

Albumen 28.0

Fat 0.4

Sodiijm chloride 5.0

Sodium carbonate \

Sodium phosphate > 1.2

Sodium sulphate )

Lime phosphate .........' 0.5

1000.0

Owing to the fibrine contained as an ingredient in the lymph, this fluid
coagulates, like blood, within a few moments after its removal from the
lymphatic vessels in the living animal, forming a gelatinous mass which

1 In Colin, Physiologic comparee des Aiiimaux domestiques. Paris, 1856,
tome ii. p. 111.

368 THE LYMPHATIC SYSTEM.

is more or less colorless and transparent, or whitish and opaque, accord-
ing to the proportion of fatty matter present in the specimen. After
coagulation, it separates into a liquid serum and a solid clot, precisely
as in the case of blood.

It thus appears that both fibrine and albumen are either formed in the
interior of the lymphatic system, or transude to a certain extent from
the bloodvessels, even in the ordinary condition of the circulation. If
so, this transudation takes place in so small quantity that the albumi-
nous matters are all taken up by the lymphatic vessels, and do not
appear in the excreted fluids.

When lymph is drawn from the thoracic duct and allowed to coagu-
late, the clot after a few moments almost invariably assumes a decided
pink color, and on microscopic examination is found to contain a very
few red blood-globules. The presence of these globules is attributed by
some competent authorities (Kolliker, Robin) to the accidental rupture
of capillary bloodvessels and consequent introduction of their contents
into the lymphatic system ; but their occurrence is so constant that it
must be doubted whether they have altogether an accidental origin.
The pinkish color of the lymph under these circumstances is never per-
ceptible when it is first drawn from the vessels, but only after it has
been for a short time exposed to the air.

An important peculiarity in regard to the fluid of the lymphatic
system, especially in the carnivorous animals, is that it varies, both in
appearance and constitution, at different times. In the ruminating and
graminivorous animals, as the sheep, ox, goat, and horse, it is either
opalescent with a slight amber tinge, or nearly transparent and color-
less. In the carnivorous animals, as the dog and cat, it is also opaline
and amber colored in the intervals of digestion, but soon after feeding
becomes of a dense, opaque, milky white, and continues to present that
appearance until digestion and absorption are complete. It then regains
its original aspect, and remains opaline until digestion is again in pro-
gress.

The results of analysis show that this variation in the appearance of
the fluid of the thoracic duct during digestion, like that of the blood, is
due to the absorption of fatty matters from the intestine. Although
the chyle is richer than lymph in nearly all its solid ingredients, the
principal difference between the two consists in the proportion of fat,
which is nearly absent from the transparent or opaline lymph, but very
abundant in the white and opaque chyle. This is shown in the following
analysis by Dr. Rees,1 of lymph and chyle from the ass.

1 In Colin, Physiologic compare des Animaux domestique. Paris, 1856 tome
ii. p. 18.

THE LYMPH AND CHYLE. 369

COMPARATIVE ANALYSIS OF LYMPH AND CHYLE.

Lymph. Chyle.

Water 965.36 902.37

Albumen 12.00 35.16

Fibrine 1.20 3.70

Spirit extract 2.40 3.32

Water extract 13.19 12.33

Fat . traces 36.01

Saline matter ....... 5.85 7.11

1000.00 1000.00

When a canula, accordingly, is introduced into the thoracic duct at
various periods after feeding, the fluid discharged varies considerably,
both in appearance and quantity. In the dog, the fluid of the thoracic
duct is never quite transparent, but retains a marked opaline tinge even
so late as eighteen hours after feeding upon lean meat, and at least three
days and a half after the introduction of fat food. Soon after feeding, it
becomes whitish and opaque, and so remains while digestion and absorp-
tion are in progress. After the termination of this process it resumes
its former appearance, becoming light colored and opalescent in the car-
nivorous animals, and nearly colorless and transparent in the herbivora.

The Lymph Globules. — The lymph, whatever may be its other ingre-
dients, contains nearly always a greater or less abundance of rounded,
transparent, or finely granular nucleated cells, similar to the white glo-
bules of the blood, which are known as the " lymph-globules." They
vary in size from about 6 to 12 mmm. in diameter. By treatment with
dilute acetic acid they become pale and transparent; while partial desic-
cation, or the contact of a concentrated saline or saccharine solution,
gives them a shrivelled appearance with an irregular outline. Accord-
ing to the observations of Kolliker, the lymph-globules vary much, both
in number and in size, according to the part of the lymphatic system
from which the fluid is taken. In the smallest lymphatic vessels of the
mesentery capable of examination, they may even be altogether absent,
the lymph consisting of a perfectly homogeneous fluid, not holding
any anatomical forms in suspension ; and in the lymphatics where they
first begin to show themselves, they are few in number and of less than
the average size. After the lymph, however, has traversed one or two
ranges of lymphatic glands, the globules are larger and more numerous,
manj^ of them in the larger lymphatic trunks attaining the size of 12
mmm. in diameter. From this circumstance, as well as from the micro-
scopic texture of the glands themselves, it is concluded that the lymph-
globules originate, in great part, in the interior of the lymphatic glands,
and that they are brought thence by the current which traverses the
lymph-paths in the substance of these organs.

Movement of the Fluids in the Lymphatic System. — The movement
of the lymph in the lymphatic vessels diners from that of the blood, in
the important particular that its course is always in one direction,

370 THE LYMPHATIC SYSTEM.

namely, from the periphery toward the centre. The fluids taken up by
the lymphatic capillaries are collected into the larger branches and
trunks, and by them conducted from without inward toward the heart.

The physical cause of the continuous movement of the lymph is pri-
marily the force of endosmosis acting at the confines of the lymphatic
system. As the volume of fluid accumulates in an endosmometer, in
such a manner as to rise perceptibty in the upright tube, so the lymph
accumulates by the force of absorption in the lymphatic capillaries, and
thence fills the larger vessels of the system. It is evident that the
pressure of fluids in a particular direction, due to the force of endos-
mosis, may be very considerable, since it is sometimes sufficient, as
already shown, to burst the shell-membrane of a fowl's egg when placed
in contact with water. As this pressure, in the lymphatic system, is
always directed from without inward, and as the main lymphatic trunks
finally terminate in the veins, the result is a uniform movement of the
lymph, from the peripheral parts of the various organs and tissues
toward the centre of the circulation.

The movement of the lymph is also aided by several secondary causes.
As these vessels are provided with valves, even more abundantly than
the veins, the alternate contraction and relaxation of the voluntary
muscles in the limbs and trunk must facilitate considerably the passage
of their fluids in an inward direction. The action of the heart and arte-
ries also contributes indirectly to this result. As the thoracic duct
passes upward through the chest, it crosses the median line obliquely
from right to left, passing between the spinal column and the aorta ; so
that at each pulsation of the aorta it is compressed, and its contents
urged toward its upper extremity. This effect is often very visible when
a canula is inserted, in the living animal, into the thoracic duct at the
root of the neck. Under these circumstances we have frequently seen
the lymph projected from the extremity of the canula in a distinct jet
at each cardiac pulsation, owing to the momentary pressure from the
distended aorta.

Lastly, the thoracic movements of respiration take part in maintain-
ing the flow of lymph. At each inspiration the resistance in the inte-
rior of the chest is diminished, and the lymph passes more readily from
below into the thoracic duct; at each expiration the duct is subjected
to compression, and is thus emptied of its fluids in a direction toward
its junction with the veins. The influence of the respiratory move-
ments, in a reversed form, may often be seen in animals poisoned by
woorara, where artificial respiration is kept up through the trachea.
If, in such an animal, a canula be inserted into the thoracic duct at the
root of the neck, the flow of tymph from its open extremity is percep-
tibly increased at each forcible insufflation of the lung, since this pro-
duces more or less pressure upon the thoracic duct in the cavity of the
chest.

Of these different physical causes of the lymph-current, the first alone,
namely, the endosmotic action, is entirely uniform and continuous. The

THE LYMPH AND CHYLE. 371

others are all intermittent in their action, and depend for their effi-
ciency upon the existence of valves in the lymphatic vessels. In a
set of vessels provided with such valves, opening forward and shutting
backward, any force which alternately compresses and releases them
will necessarily cause the fluids which they contain to move in a definite
direction. The mechanical forces above enumerated are more or less
constantly active, and in point of fact exercise a considerable influence
in producing an incessant transportation of the lymph from the peri-
phery to the centre.

Total Daily Quantity of the Lymph and Chyle. — The quantity of
fluids discharged from the thoracic duct within a given time varies
according to the condition of abstinence or digestion. In the fasting
condition it is comparatively moderate, but becomes more abundant
soon after the commencement of digestion, to diminish again during
the later stages of the process. We have found, at various periods after
feeding, in the dog, the following quantities discharged per hour, for
every thousand parts of the bodily weight of the animal :

• HOURLY QUANTITIES OF LYMPH AND CHYLE IN THE DOG,
PER THOUSAND PARTS OF BODILY WEIGHT.

3| hours after feeding 2.45

7 2.20

13 ....... 0.99

18 1.15

18£ " ...... 1.99

It would thus appear that the hourly quantity of these fluids, after di-
minishing during the latter stages of digestion, increases again somewhat
about the eighteenth hour, though still considerably less abundant than
while digestion is in active progress. It is probable that this increase
at the two periods indicated is owing to two different causes. The fluid
obtained in greatest abundance in the dog, in from 3 to 1 hours after
feeding, is quite white and opaque, and its increase in quantity is evi-
dently due to the admixture of chyle absorbed from the intestine. That
obtained so late as the eighteenth hour is simply opaline, or more nearly
transparent, and is composed of lymph alone. The absorption of chyle,
therefore, takes place, of course, while digestion is in progress ; but the
most abundant production of lymph occurs some hours later, after the
materials of nutrition have reached and permeated the tissues themselves.

The entire daily quantity of lymph and chyle is found, by direct
observation, \o be much larger than would be anticipated. In two
experiments upon the horse, extending over a period of twelve hours
each, Colin1 obtained from the thoracic duct in this animal, on the
average, 893 grammes of fluid per hour, which would amount to rather
more than 20 kilogrammes per day. In the ruminating animals, accord-
ing to the same observer, the quantity is still greater. In an ordinary

1 Physiologies comparee des Animaux domestiques. Paris, 1856, tome ii. p. 106.

372 THE LYMPHATIC SYSTEM.

sized cow, the smallest quantity obtained, in an experiment extending
over a period of twelve hours, was 625 grammes in fifteen minutes ; that
is, 2500 grammes per hour, or 60 kilogrammes per day. In another
experiment with a young bull weighing 185 kilogrammes, he actually
withdrew from the thoracic duct in the course of twenty-four hours, 15
kilogrammes of lymph and chyle, representing a little more than 8 per
cent, of the entire bodily weight of the animal.

We have obtained similar results from experiments upon the dog and
goat. In a young kid weighing 6.36 kilogrammes, we have obtained
from the thoracic duct 122.5 grammes of lymph in three hours and a
half. This quantity represents 35 grammes per hour, and, if continued
throughout the day, would amount to 640 grammes, or fully 10 per
cent, of the entire bodily weight. In the dog the fluids discharged from
the thoracic duct are less abundant. The average of all the results
obtained by us, in this animal, at different periods after feeding, gives
very nearly four and a half per cent, of the bodily weight, as the total
daily quantity of lymph and chyle. This is substantially the same
result as that obtained by Colin in the horse ; and for a man weigh-
ing 65 kilogrammes, it would be equivalent to about 3000 grammes
of lymph and chyle per day. But this quantity represents both the
products of tymphatic transudation and those of intestinal absorption
taken together. An estimate of the total amount of the lymph alone
must be based upon the quantity of fluids passing through the thoracic
duct in the intervals of digestion, when no chyle is being taken up from
the alimentary canal. In the dog, as shown by the experiments quoted
above, the average quantity obtained, from the thirteenth to the eigh-
teenth or nineteenth hour after feeding, when intestinal absorption had
come to an end, was about 1.30 per thousand parts of the bodily weight ;
or, for the whole twenty-four hours, a little over 3 per cent, of the bodily
weight. For a man of medium size, this would give not far from 2000
grammes as the average daily quantity of lymph alone.

Internal Renovation of the Animal Fluids. — By the combined actions
of secretion, transudation, and reabsorption, a continual interchange or
renovation of the animal fluids takes place in the living body, which is
dependent for its materials upon the circulation of the blood, and which
may be considered as a kind of secondary circulation through the sub-
stance of the tissues. For all the digestive fluids, as well as the bile
discharged into the intestine, are reabsorbed in the natural process of
digestion and again enter the current of the circulation. These fluids,
therefore, pass and repass through the mucous membrane of the alimen-
tary canal and adjacent glands, becoming more or less altered in con-
stitution at each passage, but still serving to renovate alternately the
constitution of the blood and the ingredients of the digestive secretions.
The elements of the blood itself also transude in part from the capillary
vessels, and are again taken up from the tissues by the lymphatics,
to be finally restored to the venous blood, in the immediate neighbor-
hood of the heart.

THE LYMPH AND CHYLE. 373

The daily quantity of all the fluids thus transuded and reabsorbed
will serve to indicate the activity of endosmosis and exosmosis in the
living body. In the following table, the quantities are all estimated,
from preceding data, for a man of medium size.

TOTAL QUANTITY OF FLUIDS TRANSUDED AND REABSORBED
DURING TWENTY-FOUR HOURS.

Saliva 1300 grammes.

Gastric juice 3000

Pancreatic juice 800 "

Bile 1000

Lymph 2000

8100

Not less than 8000 grammes therefore of the animal fluids, a quan-
tity equal to that of the entire blood and amounting to more than 12
per cent, of the weight of the whole body, transude through the internal
membranes and are restored to the blood by reabsorption, in the course
of a single day. It is by this process that the natural constitution of
the parts, though constantly changing, is still maintained in its normal
condition, through the movement of the circulating fluids and the
renovation of their materials.

CHAPTEE XVII.

THE URINE.

THE urine is distinguished from all the other animal fluids by the fact
that it represents only the products of the waste or physiological disinte-
gration of the body. The living body, while in the active performance
of its functions, is the seat of various manifestations of force, such as
animal heat, sensibility, and motion, which are the indications of its
vitality. These manifestations of force, in the living organism, as well as
elsewhere, are only produced at the expense of its materials, and by their
change of state or metamorphosis in the internal process of nutrition.
It is accordingly an essential condition of the existence and activity of
the animal body that it should go through with an incessant transfor-
mation and renewal of its component parts. Every living being absorbs
more or less constantly certain nutritive materials from without, which
are modified by assimilation and converted into the natural ingredients
of its tissues. At the same time with this continuous process of growth
and supply, there goes on an equally continuous change, by which the
elements of the organized frame pass over into new forms of combi-
nation, destined to be expelled from the body as the products of its
disintegration.

Certain substances, therefore, are constantly making their appearance
in the animal tissues and fluids, which were not introduced with the food,
but which have been produced in their interior b}r the process of con-
tinued metamorphosis. These substances result from the new combina-
tions taking place in the organized frame. They are the forms under
which those materials present themselves which have once made part
of the animal tissues, but which have become altered by the incessant
changes characteristic of living beings, and which are consequently no
longer capable of exhibiting vital properties, or of aiding in the per-
formance of the vital functions. The process of the elimination and
removal of these materials is called excretion, and the materials them-
selves are known as the excrementitious substances.

These substances have peculiar characters by which they are distin-
guished from other ingredients of the living body. They are crystal-
lizable and for the most part soluble in water, at least in the form under
which they appear in the excreted fluids. They are formed in the blood
or in the substance of the tissues from which they are absorbed by
the blood, and are conveyed by the circulating fluid to the excretory
organs through which they are discharged. If their elimination from the
body be in any way arrested or impeded, their accumulation in the
system produces a disturbance of the vital functions, which is more or
(SU)

THE URINE. 375

less severe according to their special character and the rapidity of their
production. This poisonous influence is especially manifested in its
action upon the nervous system, causing an abnormal irritability, de-
rangement of the special senses, delirium, insensibility, coma, and death.
These effects are more particularly marked in the case of urea after
suppression of the urine ; a complete stoppage of the elimination of this
substance in the human subject usually producing a fatal result in three
or four days.

The excrementitious matters, however, are not to be considered as
poisonous, or even deleterious, in the quantities in which they normally
occur in the animal solids and fluids. On the contrary, they are the
natural products of the functional activity of the animal system, and
are, therefore, as essential to the continued manifestation of life as the
nutritious materials supplied by the food. It is only when the regular
course of their elimination is retarded that they interfere with the due
performance of the functions, by deranging the natural constitution of
the tissues.

A variety of excrementitious substances are produced in the body,
some of which are probably eliminated, in small proportion, with the
perspiration or with the feces. The carbonic acid, exhaled in large
quantity from the lungs, is to be regarded as belonging to this class,
since it is produced in the substance of the tissues and constantly
discharged by respiration. But the most important substances,
usually included under the head of excrementitious matters, are distin-
guished by the fact that they contain nitrogen as one of their ultimate
elements, and that they otherwise exhibit a remarkable analogy with
each other in their chemical composition. They accordingly form a
natural group of organic substances, resembling each other in their
origin, their constitution, and their physiological destination. They are
furthermore associated together by the circumstance that they are all
eliminated from the body by the urine, of which they form the essential
and characteristic ingredients.

The urine is therefore the only animal fluid which is solely an excre-
tion. It is a solution of the nitrogenous excrementitious matters of the
animal frame ; and by its abundance and composition it indicates the
activity of the healthy metamorphosis of the organic tissues and fluids.
Beside its nitrogenous ingredients, it contains also most of the mineral
salts which are discharged from the body ; and by the water which holds
these solid matters in solution it forms the channel for a large propor-
tion of the fluids passing daily through the system. Furthermore, acci-
dental or abnormal ingredients, introduced into the blood, almost
invariably find their way out of the system by the kidneys, and thus
appear as temporary ingredients of the urine. The constitution and
physiological variations of this fluid during health, and its alteration
in disease, are regulated by the corresponding changes of nutrition or
activity in the body at large. The urine is therefore one of the most
essential products of the animal system, and its formation is second
in importance only to the function of respiration.

376 THE URINE.

Physical Properties of the Urine.

The urine is a clear, amber-colored fluid, of a watery consistency, and
with a distinctly acid reaction. As a general rule, its transparency is so
nearly perfect that no appearance of turbidity is perceptible by ordinary
diffused daylight. It contains, however, a very small quantity of
mucus from the urinary bladder, which may be rendered visible as a
faint opalescence when a sunbeam is made to pass through it in a lateral
direction. If the urine be allowed to remain at rest for a few hours in
a cylindrical glass vessel, the mucus gradually subsides, forming a very
light cloudy mass at the bottom and leaving the supernatant fluid en-
tirely clear. The ingredients of the urine itself are all therefore in a
state of complete solution. While still warm and fresh, the urine has a
peculiar but not offensive odor, which disappears on cooling and may
be then restored by gentle heating. The average specific gravity of
healthy urine, in the adult, is from 1020 to 1025 ; and its daily quantity
is about 1200 cubic centimetres.

Variations of the Urine in Quantity, Acidity, and Specific Gravity.
— The urine does not present uniformly the same characters, but varies
normally from hour to hour, in each individual, at different periods of
the day. It is usually discharged from the bladder five or six times in
the twenty-four hours, and each specimen shows more or less variation
in its physical properties. This variation depends upon the changing
conditions of the body, as to rest, exercise, food, drink, sleeping, and
waking. In the same person, leading a uniform mode of life from day
to day, the diurnal variations of the urine follow each other with great
regularity ; although in different persons, whose habits are different, they
may not be altogether the same. Asa general rule, the urine which
collects in the bladder during the night and is first discharged in the
morning is strongly colored, of high specific gravity, and has a very
distinct acid reaction. That passed during the forenoon, on the other
hand, is pale and of comparatively low specific gravity ; often falling
so low as 1018 or even 1015. At the same time, its acidity diminishes
or even disappears altogether ; so that at this time in the day the urine
is frequently neutral or slightly alkaline. Toward noon, its density and
depth of color increase, and its acidity returns. All these properties
become more strongly marked during the afternoon and evening ; and
toward night the urine is again deeply colored and strongly acid, and
has a specific gravity of 1028 or 1030.

The following instances will serve to show the general characters of
this variation :

OBSERVATION FIRST. March 20th.

Urine of 1st discharge, acid, sp. gr. 1025.

" 2d '• alkaline, " 1015.

3d " neutral, " 1018.

" 4th " acid, " 1018.

" 5th " acid, " 1027

PHYSICAL PROPERTIES OF THE URINE. 377

OBSERVATION SECOND. March 2lst.
Urine of 1st discharge, acid, sp. §T. 1029.

- 2d " neutral, <; 1022.

- 3d " neutral, " 1025.
•• 4th - acid, " 1027.
" 5th " acid, " 1030.

These variations do not always follow a perfectly regular course, since
they are liable to temporary modification from accidental causes during
the day ; but their general tendency corresponds with that given above.

The acidity of the urine is also liable to vary from temporary causes,
owing to the introduction of organic substances with the food which
give rise to alkalescence in the animal fluids. The salts of the organic
acids, such as the lactates, acetates, malates, and tartrates, when taken
into the stomach and absorbed by the circulation, are replaced by
carbonates of the same bases, and appear under that form in the urine.
When these salts, or the fruits and vegetables which contain them, are
taken in large quantit}^ the urine becomes alkaline from the presence
of the carbonates. The use of summer fruits, therefore, though they
may have an acidulous taste, is followed by alkalescence of the urine.
The effect thus produced may be manifested in a very short time;
according to the observations of Lehmann, the urine sometimes becom-
ing alkaline within a quarter of an hour after taking a little over 15
grammes of sodium acetate.

It is evident, therefore, that when the specific gravity or the acidity
of the urine is to be tested, either in health or disease, it will not be
sufficient to rely upon the examination of a single specimen. The nor-
mal variations in specific gravity during the day do not usually exceed
the limits of 1015 as a minimum and 1030 as a maximum; but either
of these would be unnatural if continued during the whole twenty-four
hours. All the different specimens 'of urine passed during the day
should therefore be collected and examined together. The average
specific gravity thus obtained will represent the normal daily density
of the excretion.

The daily volume of the urine is also to be taken into account. The
total amount of solids discharged by the urine in health is from 50 to
60 grammes per day ; and this quantity of solid material is dissolved in
about 1200 cubic centimetres of water. This gives an average daily
quantity and an average specific gravity of the urine, as the measure of
the excretory process during twenty-four hours.

Both the quantity of the urine and its mean specific gravity are
liable to vary somewhat in different individuals, or even in the same
individual from day to day. Ordinarily, the water of the urine is more
than sufficient to hold all the solid matters in solution ; and its propor-
tion may therefore be diminished by temporary causes without the
production of turbidity or the formation of a deposit. Under such cir-
cumstances, the urine merely becomes deeper in color, and of higher
25

378 THE UEINE.

specific gravity. If a smaller quantity of water than usual be taken
into the system with the drink, or if the exhalation from the lungs and
skin, or the intestinal discharges, be increased, a smaller quantity of
water will necessarily pass off by the kidneys ; and the urine will be
diminished in quantity, while its specific gravity is increased. The
urine is sometimes reduced in this way to 500 or 600 cubic centimetres
per day, its specific gravity rising at the same time to 1030. On the
other hand, if the fluid ingesta be unusually abundant, or if the per-
spiration be diminished, the surplus quantity of water will pass off by
the kidneys ; so that the amount of urine in twenty- four hours may be
increased to 1350 or 1400 cubic centimetres, and its mean specific
gravity reduced at the same time to 1020 or even 1017. Under such
conditions, the total amount of solid matter discharged remains about
the same. These changes depend simply upon the fluctuating quantity
of water, which may pass off by the kidneys in larger or smaller quan-
tity, according to circumstances. In purely normal or physiological
variations of this nature, the entire quantity of the urine and its mean
specific gravity vary always in an inverse direction with regard to each
other ; the former increasing while the latter diminishes, and vice versa.
If, however, it be found that both the quantity and specific gravity of
the urine are increased or diminished at the same time, or if either one
be increased or diminished while the other remains stationary, such an
alteration will show an actual change in the total amount of solid ingre-
dients, and consequently an unnatural and pathological condition.

Ingredients of the Urine.

The chemical composition of the urine, as derived from the most
recent and numerous analyses, is as follows:

Nitrogenous

organic
substances.

Mineral salts.

COMPOSITION OF THE UKINE.

Water 950.00

Urea 26.20

Creatinine 0.87

Sodium and potassium urates . . . 1.45

Sodium and potassium hippurates . . 0.70

Sodium biphosphate ..... 0.40

Sodium and potassium phosphates . . 3.35

Lime and magnesium phosphates . . 0.83

Sodium and potassium chlorides . . 12.55

Sodium and potassium sulphates . . 3.30

Mucus and coloring matter . . . 0.35

1000.00

The constitution of the urine is not invariable, but changes more or
less at different periods of the day, according to the rapidity of excre-
tion of its different ingredients. The foregoing list, however, repre-
sents, in an approximate manner, its average composition for the entire
twenty-four hours.

INGREDIENTS OF THE URINE. 379

Urea. — This is the most important constituent of the urine, both in
regard to character and amount, forming more than one-half the entire
quantity of its solid ingredients, and over 80 per cent, of all those of an
organic nature. The most important fact known with regard to the
origin of urea is, that it is not formed in the kidneys, but pre-exists in
the blood in small proportion, and is drained away from the circulat-
ing fluid during its passage through the renal vessels. This was first
shown by the experiments of Prevost and Dumas,1 who, after extir-
pating the kidneys, or tying the renal arteries in the living animal,
found the quantity of urea in the blood increased in marked proportion,
owing to the arrest of its elimination by the kidneys. It has also been
found in the blood of the human subject in cases of renal disease,
sometimes in so large a proportion as 1.5 parts per thousand,2 or nearly
ten times its normal quantity. It has not been found, however, in suf-
ficient quantity in any of the solid tissues to indicate the immediate
source of its production. It is either formed in the blood itself, by
transformation of some previous nitrogenous combination, or it is ab-
sorbed by the blood too rapidly to be detected as an ingredient of the
solid tissues.

Urea is obtained most readily from the urine by first converting it
into the form of a nitrate. For this purpose the fresh urine is evapo-
rated over the water-bath until it is reduced to one-quarter of its original
volume. It is then filtered, and the filtered fluid mixed with an equal
quantity of nitric acid, which produces nitrate of urea. This salt, being
less soluble than urea, rapidly separates in the form of abundant crys-
talline scales. The c^stalline deposit is separated from the mother
liquor, mixed with water, and decomposed by the addition of barium
carbonate, which sets free the urea, with the formation of barium nitrate.
This process is continued so long as carbonic acid is given off;- after
which the whole is evaporated to dryness, and the dry residue extracted
with absolute alcohol, which dissolves out the urea. The alcoholic solu-
tion is then filtered and evaporated until the urea separates in a crys-
talline form.3

The quantity of urea in a given volume of urine is readily ascertained
by decomposing it, according to Davy's method, with a solution of so-
dium hypochlorite. A long and narrow graduated glass tube, open at
one extremity, and capable of holding about 50 cubic centimetres of
fluid, is filled to a little more than one-third its capacity with mercury,
upon which are poured 3 or 4 cubic centimetres of the urine to be ex-

1 Prevost and Dumas, Annales de Chimie et de Physique, 1823, tome xxiii.
p. 90 ; Segalas, Journal de Physiologie, tome ii. p. 354 ; Mitscherlich, Tiede-
mann. and Gmelin, Poggendorf's Annalen, band xxxi. p. 303 ; Cl. Bernard,
Liquides de 1'Organisme. Paris, 1859, tome ii., Deuxieme Legon.

2 In Milne Edwards, Legons sur la Physiologie. Paris, 1857, tome i. p. 298.

3 Hoppe-Seyler, Handbuch der Physiologisch- und Pathologisch-Chemischen
Analyse. Berlin, 1870, p. 120.

380 THE UKINE.

amined. The remainder of the tube is then filled with the sodium
hypochlorite solution, the mouth of the tube closed, the fluids well
mixed, and the tube then inverted in a shallow glass dish filled with a
saturated solution of sodium chloride. The mixture of urine and hypo-
chlorite solution remains in the tube ; and as the urea is decomposed,
its nitrogen is given off in the gaseous form and collects in the upper
closed end of the tube, where its volume may be read off on the scale,
after the action has ceased. Every cubic centimetre of nitrogen, thus
disengaged, represents 2.5 milligrammes of urea.

The conditions influencing the quantity of urea produced and dis-
charged in the healthy subject during twenty-four hours, are the size
and general development of the body, the nature of the food, and the
state of rest or activity. Like other products of the living organism,
its quantity is in proportion to the entire mass of the body. As a
general rule, its daily quantity, in man, is 0.5 per thousand parts of the
entire bodily weight ; and for a man of medium size it amounts to about
35 grammes per day. As it is a nitrogenous substance, resulting from
the final consumption of the albuminous elements of the system, its
proportion is greater under a diet of animal food, which is comparatively
rich in albuminous matters, than under one of vegetable food, in which
these substances are less abundant. Its daily quantity falls to a
minimum when the diet is exclusively confined to non-nitrogenous arti-
cles of food, namely, starch, sugar, and fat. It is still, however, pro-
duced and excreted under an exclusively non-nitrogenous diet, and even
when no food whatever is taken, so long as the animal functions con-
tinue to be performed.

The results obtained by nearly all experimenters led to the conclu-
sion that the quantity of urea excreted is especially increased by mus-
cular exertion , until a doubt was thrown upon this point by Tick and
Wislicenus in 1866. These observers ascended a mountain on foot,
the ascent occupying a little over eight hours ; during which time, and
for seventeen hours beforehand, they confined themselves to a diet of
non-nitrogenous food. They found the amount of urea discharged per
hour to be less, while engaged in ascending the mountain, than it was
before ; but it increased during the following night, after a meal of
animal food.

Subsequent observers have obtained various results. Dr. Parkes, in a
series of very careful and extended observations,1 found that the dis-
charge of urea was increased not during, but after, a period of muscular
work. This was shown even in a man confined for five days to a non-
nitrogenous diet, in whom the discharge of urea was not increased on
the day of unusual muscular effort, but on the following day was a little
more than doubled.

The observations of Prof. A. Flint, Jr., on the excretion of urea in
the case of the pedestrian Weston, have the important advantage of ex-

1 Proceedings of the Royal Society of London, vol. xvi. p. 48, and March 2,
1871.

INGKEDiENTS OF THE UEINE.

381

tending over comparatively long periods, both of exercise and rest, the
diet at the same time remaining unchanged in its general characters.

The pedestrian was under observation for fifteen days ; namely, five
days previous to the walk, five days during its continuance, and five
days immediately afterward. For the period preceding the walk, the
average exercise was about eight miles per day ; during the walk it was
nearly sixty-four miles per day, and for the period subsequent to the
walk, it was a little over two miles per day. The results obtained
during the three peri9ds showed, accordingly, the normal amount of
urea excreted by the pedestrian under ordinary conditions, the amount
discharged during an unusual and nearly continuous muscular exertion,
and the subsequent effects of the exertion on the general condition of
the system.

The nitrogenous ingredients of the food, during all three periods,
were also recorded, so that the influence of the food itself on the amount
of urea may be estimated at the same time with that of the muscular
exertion.

The following table gives the main result of these experiments, so
far as they are connected with the present subject :

Daily Quantity of

First Period.
Five days
before the walk.

Second Period.
Five days
during the walk.

Third Period.
Five days
after the walk.

Urea
Nitrogen in food
Nitrogen in urea .
Total nitrogen in urea and feces
Nitrogen in urea and feces per
100 parts of nitrogen in food

628.24 grains.
339.46 "
293.18 "
315.09 "

95.53

722.16 grains.
234.76 "
337.01 "
361.52 "

174.81

726.79 grains.
440.93 "
339.17 "
373.15 "

91.93

It is evident, therefore, that during the time of unusual muscular
exertion the daily quantity of urea was increased by nearly fifteen per
cent, over that of the previous ordinary condition, the nitrogenous ele-
ments of the food being at the same time considerably diminished ; and
that, during the period of exertion, the total quantity of nitrogen dis-
charged by the urea and feces combined was nearly seventy-five per
cent, greater than that introduced with the food, while in both the pre-
vious and subsequent periods it was from about four and a half to eight
per cent. less. During the period of exertion there was a loss of nearly
three and a half pounds of bodily weight, and an increase of similar
amount during the subsequent period of rest. The author fairly explains
the above loss of weight by the disintegration of muscular tissue; and
the subsequent increase, by a retention of nitrogenous constituents in
the body, to repair the waste thus produced.

"During the five days of the walk,1 Mr. Weston consumed in all
1173.80 grains of nitrogen in his food. During the same period he

New York Medical Journal, June, 1871, p. 669.

382 THE URINE.

eliminated 1807.60 grains of nitrogen, in the urine and feces. This
leaves 633.80 grains of nitrogen, over and above the nitrogen of the food,
which must be attributed to the waste of his tissues, and probably
almost exclusively to the waste of his muscular tissue. According to
the best authorities, lean meat uncooked, or muscular tissue, contains 3
per cent, of nitrogen. The loss of 633.80 grains of nitrogen would then
represent a loss of 21,121.00 grains, or 3.018 Ibs. of muscular tissue.
The actual loss of weight was 3.450 Ibs. This allows about 0.43 Ib. of
loss unaccounted for, which might be fat or water."

Creatinine. — This substance is perhaps next in physiological import-
ance to the urea, considering its analogy in chemical composition, but
is produced in much smaller quantity ; its total amount usually not ex-
ceeding 1 gramme per day. It has not been found in any of the solid
tissues ; but it is probably derived by transformation of the creatine of
the muscles, since it may be artificially produced from the latter by the
action of heat and dilute sulphuric acid. It is undoubtedly, like urea,
a product of the metamorphosis of the albuminous ingredients of the
body, from which it derives its nitrogenous element. But little is known
with regard to the conditions which increase or dimmish its production.

Sodium and Potassium Urates. — The urates are due to a combination
of the alkaline base with a nitrogenous mineral acid, belonging to the
same physiological class of excrernentitious matters as urea and creati-
nine. This substance is known to be, like urea, increased in quantity
by a nitrogenous, and decreased by a non-nitrogenous diet ; but its rela-
tions to muscular exercise and other temporary conditions are not fully
known. The urates are readily soluble in water, and are usually excreted
to the amount of about 1.75 gramme per day. The hippurates have, in
general, similar chemical and physiological relations to those of the
urates, excepting that they are more abundant under the use of a vege-
table diet, and disappear altogether when the food is exclusively of an
animal nature. In the human subject under an ordinary mixed diet,
they amount to about one-half the quantity of the urates.

The preceding ingredients of the urine are all associated in a single
physiological group, forming its nitrogenous excrementitious substances.
Beside them, it also contains a variety of inorganic or mineral constitu-
ents, derived from the waste of the animal tissues and fluids.

Acid Sodium Phosphate, or sodium biphosphate. — This is the ingre-
dient which gives to the urine its acid reaction to test-paper. It is
regarded as derived from the ordinary sodium phosphate of the blood
(Xa.2H P04) by the action of the uric acid produced in the system, which
unites with a part of its sodium, forming sodium urate, and leaving an
acid sodium phosphate (NaHQPOJ. The uric acid produced from the
decomposition of animal substances, although it does not itself appear
in a free form, is, therefore, indirectly the cause of the acid reaction of
the urine ; and this reaction will vary in intensity with the amount of
uric acid discharged.

INGREDIENTS OF THE URINE. 383

The Alkaline Phosphates, or ordinary phosphates of sodium and
potassium. — These are the soluble phosphates, which exist in the blood
as well as in the urine, and which, in solution, have a mild alkaline re-
action. Owing to their ready solubility, they never appear as a precipi-
tate, nor disturb in any way the transparency of the urine. It is under
the form of these salts that most of the phosphoric acid in combination
is discharged with the urine. According to Yogel, the excretion of
phosphoric acid by this channel is increased by the use of food contain-
ing soluble phosphates or substances capable of yielding phosphoric
acid by the changes which they undergo in the system. It is accord-
ingly more abundant under a diet of animal food, less so under a vege-
table regimen. Its discharge, however, does not depend exclusively
upon the ingredients of the daily food, since it continues, although in
diminished quantity, after long-continued abstinence from all food. Its
immediate origin is, therefore, wholly or partly from the constituents
of the body itself. The observations of Wood,1 as well as those of
Yogel and others, show also that there is a diurnal variation of con-
siderable regularity in the normal excretion of the salts of phosphoric
acid. Its hourly quantity is at a minimum during the forenoon, in-
creases in the latter part of the day after the principal meal, and reaches
a maximum in the evening or during the night, to diminish again on the
morning of the following day. It is under the form of phosphates that
the phosphorus contained in certain organic substances (lecithine) is
finally discharged from the system. The average quantity of the alka-
line phosphates discharged during health under an ordinary diet is a little
over four grammes per day.

The Earthy Phosphates, or the phosphates of lime and magnesium. —
The earthy phosphates are usually present in the urine in much smaller
quantity than the preceding. They are held in solution only by the acid
reaction of the urine, and when this is absent or very much diminished
they are thrown down as a light precipitate, consequently, the neutral
or faintly alkaline urine passed in the forenoon is often slightly turbid
with a deposit of the earthy phosphates, without, however, indicating
any abnormal increase in their amount. According to the extensive
and careful observations of Wood, the alkaline and earthy phosphates
differ from each other in the conditions which influence their excretion.
"While the alkaline phosphates of the urine are increased in amount
during continued mental application, the earthy phosphates are dimin-
ished, and the total quantity of both kinds is not materially altered.
The earthy phosphates, on the other hand, are increased by abstinence
from mental labor. Their average daily quantity under ordinary condi-
tions is about one gramme, or rather less than one-quarter that of the
earthy phosphates.

1 On the Influence of Mental Activity on the Excretion of Phosphoric Acid by
the Kidneys. Proceedings of the Connecticut Medical Society, 1869.

THE URINE.

Sodium and Potassium Chlorides. — The sodium chloride, which repre-
sents nearly the whole of these two salts, is also by far the most abundant
mineral ingredient in the urine, forming over one-half of its inorganic
constituents. It is derived in great measure from the sodium chlo-
ride taken with the food, and is increased or diminished in quantity
with the variation in the amount of common salt in the diet. Various
circumstances, however, influence its excretion at different periods of the
day. Its hourly discharge is habitually least "during the night, increases
in the forenoon and is greatest during the latter part of the day. Ac-
cording to Vogel,1 both mental and bodily exertion perceptibly increase
its excretion ; and even water, when taken in unusual abundance, by in-
creasing the activity of the kidneys, causes also a temporary augmen-
tation in the discharge of sodium chloride, which is subsequently followed
by a corresponding diminution. The average amount of the chlorides
discharged with the urine is about fifteen grammes per day.

Sodium and Potassium Sulphates. — The sulphates present in the
urine are derived partly from those which have been introduced, under
their own form, as ingredients of the food ; and observation has shown
that their quantity is increased by the medicinal administration of sul-
phuric acid or of sodium sulphate. The administration of sulphur or
the sulphurets produces a similar effect. The albuminous matters of
the system, furthermore, which contain sulphur as one of their con-
stituent elements, give rise, by their changes in the oxidizing process of
nutrition and excretion, to sulphuric acid and the sulphates ; since the
whole of their carbon, hydrogen, and nitrogen is finally discharged
under the form of water, carbonic acid, and urea, while the small
quantity of sulphur remaining appears as sulphuric acid in the sul-
phates. Consequently the excretion of sulphates, as shown by Vogel,
is increased by an abundant diet of animal food, and diminished under
a vegetable regimen. The sulphates are freely soluble and never appear
as a spontaneous precipitate in the urine. Their average quantity is
about 3.96 grammes per day.

Reactions of the Urine to Chemical Tests.

The reactions of the urine to a variety of ordinary tests form a ready
criterion for ascertaining its normal or abnormal constitution. The
more exact quantitative determination of its ingredients requires the
attention and skill of the professional chemist; but many of its im-
portant characters may be recognized by the use of simple means.

The Application of Heat. — If transparent healthy urine, of a dis-
tinctly acid reaction, be heated in a test-tube over a spirit lamp to the
boiling point, no change in its appearance is produced. If its acidity
be very slightly pronounced, on the other hand, it becomes turbid on
boiling, from a precipitation of its earthy phosphates. This is because
the earthy phosphates are less soluble in a hot than in a cold liquid;

1 Analyse des Hams. Wiesbaden, 1872, p. 350.

KEACTIONS OF UKINE TO CHEMICAL TESTS.

385

and the faintly acid reaction of the urine, which was enough to hold
them in solution at ordinary temperatures, is no longer sufficient after
the application' of heat, and the phosphates are accordingly thrown
down as a deposit. The precipitation from this cause is never very
abundant, and it is instantly cleared up again by the addition of a drop
of nitric acid, which restores the normal acidity of the urine. The tur-
bidity thus produced by boiling, from the precipitation of the earthy
phosphates, is not, therefore, usually due to an increased quantity of
these salts in the urine, but simply to a deficiency of its acid reaction.

Diseased urine may also become turbid on boiling, from the coagula-
tion of albumen. This is readily distinguished from a precipitation of
the earthy phosphates by two facts — namely, first, that it may take
place in urine which is distinctly acid ; and second, that the addition of
nitric acid, which redissolves the phosphatic precipitate, only increases
the turbidity which is due to albumen.

Acids. — The addition of the mineral acids to healthy urine produces
no immediate visible effect, beyond increasing its acidity and slightly
modifying its color. They, however, decompose its urates ; and the uric
acid thus set free is slowly deposited in the crystalline form. If nitric
or hydrochloric acid be added to fresh filtered urine, in the proportion
of about 2 per cent, by volume, and the mixture be allowed to remain
at rest for twenty-four or forty-eight hours, the sides and bottom of the
vessel become covered with a thinly scattered deposit of uric acid
crystals. These crystals have
usually the form of transparent
rhomboidal plates, or oval
laminaj with pointed extremi-
ties, and are generally tinged of
a yellowish hue by the coloring
matter of the urine. They are
frequently arranged in radiated
clusters, or small spheroidal
masses, presenting the appear-
ance of minute calculous con-
cretions, which vary much in
size and regularity, according
to the time occupied in their
formation.

The deposit of uric acid crys-
tals, thus formed in healthy
urine from the addition of a
mineral acid, is always scanty in amount, and only becomes visible as
a crystalline precipitate after several hours.

In rare cases, when the urine is loaded with an unusual proportion
of the urates, a few drops of nitric acid will produce at once a per-
ceptible turbidity, from the precipitation of abundant microscopic crys-

CRYSTALS OF URIC ACID; deposited from
urine, after the addition of nitric acid. "

386 THE URINE.

tals of uric acid. This deposit may be distinguished from albumen by
the appearance of the crystals under the microscope, and also by the
fact that, unlike albumen, it is not produced by the application of a
boiling temperature.

When the urine is scanty and concentrated, owing to temporary causes,
with a specific gravity of 1030 to 1035, but without any abnormal in-
gredient, if it be mixed with one-half its volume of nitric acid and
exposed to a low temperature, a crystallization of nitrate of urea will
often take place in the course of half an hour or an hour. This is
clue simply to the diminished proportion of water, which is still suffi-
cient to hold 'the urea in solution, but allows a separation of nitrate of
urea when this salt is formed by the addition of nitric acid. It never
takes place when the urine has its normal specific gravity of 1020 to
1025.

Alkalies. — The addition of a free alkali or an alkaline carbonate to
normal urine diminishes its acid reaction, and, as soon as the point of
saturation has been reached, produces a turbidity, owing to the pre-
cipitation of the earthy phosphates. These are the only ingredients of
the urine which are thrown down by the addition of an alkali, and a
free acid immediately restores its transparency.

Mineral Salts. — Solutions of barium chloride, barium nitrate, or the
tribasic lead acetate, when added to healthy urine, decompose its sul-
phates, and produce a dense precipitate of the corresponding metallic
salts. Solutions of silver nitrate produce a precipitate with the sodium
and potassium chlorides, forming silver chloride which is insoluble. The
tribasic lead acetate and silver nitrate also throw down mucus and
coloring matters.

Abnormal Ingredients of the Urine.

The abnormal ingredients which appear in the urine are either: 1st.
Foreign substances accidentally present in the blood, which are elimi-
nated by the kidneys, such as glucose, biliary matters, and medicinal
substances; or 2d. The albuminous constituents of the blood, which are
discharged with the urine owing to a disturbance of the renal circulation.

Glucose. — The presence of glucose in the urine is characteristic of
diabetes mellitus. In this disease the urine is generally increased in
quantity and at the same time of unusually high specific gravity, namely,
from 1035 to 1050. It is of a light, clear, amber or straw color, and
remarkably transparent ; so that it has the appearance of being dilute,
although it is in reality denser than usual, owing to the presence of
glucose in solution. The glucose is detected by the application of Trom-
mer's or Fehling's test, or by that of fermentation. For the latter pur-
pose a little yeast should be mixed with 15 or 20 times its volume of
water, and the mixture allowed to remain at rest in a cylindrical upright
glass vessel until the yeast globules have subsided in a dense homo-
geneous layer at the bottom. The supernatant fluid, containing the

ABNORMAL INGREDIENTS OF THE URINE.

387

Fig. 130.

soluble impurities of the yeast, is poured off, and a small quantity of
the moist yeast-deposit at the bottom is added to the urine under exami-
nation. The mixture is then placed
in a ferment-apparatus and kept at a
temperature of about 25° (77° F.), for
forty-eight hours, when the gaseous
products of fermentation will have
been completely disengaged. The
most convenient form of apparatus is
a test-tube of known capacity (Fig.
-130, a, 6), supported by a foot and
provided with an India-rubber stopper,
through which passes a narrow glass
tube (c), open at both ends ; its inner
portion reaching to the bottom of the
test-tube, where it is bent upward, to
prevent the escape of gas, its outer
portion being bent downward, to allow
the liquid expelled to drop freely from
its orifice. The test-tube may be
graduated in cubic centimetres from
above downward. The apparatus
being filled with saccharine urine,
when fermentation begins the disen-
gaged gas rises in bubbles to the
upper part of the test-tube and col-
lects there, while the urine is forced
out through the bent glass tube.
Every cubic centimetre of carbonic
acid produced corresponds to 0.26

milligrammes of sugar decomposed. A similar apparatus, containing
the same quantity of healthy urine and yeast, should be kept at the
same temperature for an equal time, as a comparative test; since a small
quantity of carbonic acid might be disengaged from the yeast itself,
owing to its imperfect purification. The difference between the two
cases is that in the yeast alone the disengagement of gas soon ceases ;
while in a saccharine solution the yeast-cells multiply indefinitely, and
carbonic acid continues to be produced until most of the sugar has been
decomposed. This method does not give the precise quantity of the
glucose contained in any single specimen, since some of the urine
escapes before its fermentation is fully completed ; but it is at the same
time the surest indication of the existence of sugar, and a ready means
of determining approximatively whether it be scanty or abundant in
amount.

The simplest method of ascertaining the quantity of glucose in a
given specimen of urine with sufficient accuracy for all clinical pur-

FERMENT-APPARATUS, contain-
ing saccharine urine in fermentation. — a.
Upper part of the test-tube containing
carbonic acid. 6. Lower part of the test-
tube containing the fermenting liquid, c.
Bent glass tube, to allow the escape of
liquid, d. Liquid which has been forced
out from the test-tube by the accumula-
tion of gas.

388 THE URINE.

poses is that of Dr. Roberts,1 which depends upon the loss of specific
gravity occasioned by the decomposition of the glucose in fermentation.
A portion of the urine is taken and its specific gravity ascertained at
the temperature of 25° (77° F.). A little yeast is then added and the
mixture kept at the same temperature until fermentation has ceased ;
when the specific gravity is again taken. The diminution in density
caused by the conversion of the glucose into alcohol and carbonic acid
is such that the loss of one degree in specific gravity indicates the dis-
appearance of 2.191 milligrammes of glucose for every cubic centimetre
of urine.

The glucose can be obtained directly from diabetic urine, according to
the method of Hoppe-Seyler, by evaporating the urine over the water-
bath to the consistency of a syrup, and allowing it to remain at rest for
some days or weeks until completely crystallized. The crystalline mass
is triturated and washed with a small quantity of cold alcohol, to re-
move tire- urea. The residue is then extracted with boiling alcohol, and
the alcoholic solution filtered while still hot, after which the glucose is
deposited in a crystalline form.

The glucose of diabetic urine is not formed in the kidneys, but pre-
exists in the blood, from which it is eliminated in the renal circulation.
If a solution of sugar be introduced in sufficient quantity directly into
the bloodvessels of the rabbit, or injected into the subcutaneous con-
nective tissue so as to be absorbed thence by the blood, it is soon
discharged by the kidneys. It has been shown by Bernard,2 that the
time within which sugar appears in the urine under these circum-
stances varies with the quantity injected and the rapidity of its absorp-
tion. If a solution of one gramme of glucose in 25 cubic centimetres of
water be injected under the skin of a rabbit weighing a little over one
kilogramme, it is entirely destroyed in the circulation, and does not pass
out with the urine. A dose of 1.5 gramme, however, injected in the
same way, appears in the urine at the end of two hours, 2 grammes in
an hour and a half, 2.5 grammes in an hour, and 12.5 grammes in fifteen
minutes. Whenever, accordingly, glucose accumulates in the circula-
tion beyond a certain quantity in proportion to the whole mass of the
blood, it is eliminated as a foreign substance, and appears as an in-
gredient of the urine.

Biliary Matters. — In some cases of jaundice, the coloring matter of
the bile passes into the urine in sufficient abundance to give to the fluid
a deep yellow or yellowish-brown tinge, so that it may even stain linen
or cotton fabrics, with which it comes in contact, of a similar color.
The saline biliary substances, namely, sodium glycocholate and tauro-
cholate, according to Lehmann, have also been detected in the urine.
In these instances, the biliary matters are reabsorbed from the hepatic
ducts and conveyed by the blood to the kidneys.

1 Urinary and Renal Diseases. Philadelphia edition, 1872, p. 198.

2 Leqons de Physiologic Expe>imentale. Glycog6nie. Paris, 1855, p. 216.

ABNORMAL INGREDIENTS OF THE URINE. 389

Potassium ferrocyanide, when introduced into the circulation, ap-
pears with great readiness in the urine ; and, according to the observa-
tions of Bernard, may begin to be eliminated within twenty minutes
after being injected into the duct of the submaxillary gland.

Iodine, in all its combinations, passes out by the same channel.
After the administration, in the healthy human subject, of 192 milli-
grammes of iodine, in the form of syrup of the iodide of iron, we have
found it to be present in the urine at the end of thirty minutes, and that it
continued to be discharged for nearly twenty-four hours. In the case of
two patients who had been taking potassium iodide, one of them for six
weeks, the other for two months, the urine still contained iodine at the
end of three days after the suspension of the medicine ; but at the end
of three days and a half it was no longer present. Even when iodine,
however, is taken in a free form, as in that of alcoholic solution, it
always passes out by the urine in combination. It cannot be detected,
accordingly, by the simple admixture of starch with the urine, but must
be set free by the addition of a drop or two of nitric acid, after which it
produces its characteristic blue color by union with the starch. The
same thing is true of the other animal fluids, such as the saliva and the
perspiration, by which iodine is also eliminated after its introduction
into the system.

Quinine, when taken as a remedy, has been detected in the urine.
Ether passes out of the circulation in the same way, and its odor may
sometimes be very perceptible in the urine, after having been inhaled
for the purpose of producing anaesthesia. The peculiar odors developed
in the urine after the use of Asparagus, and certain other vegetable sub-
stances, are produced by a transformation of their ingredients while
passing through the animal system.

Albumen. — Under ordinary conditions the albumen of the blood does
not pass out in any proportion from the renal vessels ; but whenever the
pressure in these vessels is increased beyond a certain point, owing to
congestion, compression of the renal veins by abdominal tumors, preg-
nancy, or altered nutrition of the kidneys in Bright's disease, the
albuminous ingredients of the blood transude through the capillaries
and make their appearance in the urine.

Albuminous urine is usually rather pale, and often somewhat opales-
cent from the admixture of exfoliated epithelium cells or of fibrinous
casts from the uriniferous tubules of the kidney. When this is the case,
it should be rendered transparent by filtration before applying the tests,
since the turbidity already existing might mask the reaction, if the
albumen were present in small proportion.

If the urine have an acid reaction, the application of heat produces a
turbidity which is more marked in proportion to the quantity of albu-
men which it contains In extreme cases the fluid may solidify, like
the serum of blood, before reaching the boiling point ; but the albumen
is more frequently thrown down in loose whitish flakes. When the

390 THE URINE.

turbidity produced by boiling is moderate in amount, it may resemble
that due to the precipitation of the earthy phosphates. It can, how-
ever, be distinguished by the addition of a drop of free acid, which at
once redissolves the earthy phosphates, while it does not affect a tur-
bidity caused by albumen. An albuminous precipitate, on the contrary,
however abundant, is redissolved by the addition of a caustic alkali.

If the urine be alkaline in reaction, boiling may not throw down the
albumen present, this substance being soluble in an alkali. Urine,
accordingly, which is suspected of being albuminous, should be first
rendered distinctly acid in reaction, if necessary, by the addition of a
small quantity of acetic acid.

Nitric acid, added to albuminous urine, produces a turbidity by
coagulation of the albumen. Alcohol, added to the urine in equal
volume, will have the same effect ; and a solution of potassium ferrocy-
anide, acidulated with acetic acid, will also produce coagulation. All
the above tests, if applied in succession, will leave no doubt as to the
presence or absence of albumen.

Deposits in the Urine.

The deposits which appear spontaneously in the urine consist either :
1st, of some of its normal ingredients, thrown down in consequence
of a disturbance in its relative composition; or 2d, of exudations
from the mucous membrane of the urinary passages, owing to a dis-
eased condition of the parts. Those belonging to the first class are the
earthy phosphates and the urates. The most common of those belong-
ing to the second are blood, mucus, and pus.

Deposits of the Earthy Phosphates, — These deposits are always of a
white color, and are seldom abundant. When the urine is first passed,
the phosphates are disseminated through its mass in the form of a light
cloudiness, which settles slowly to the bottom of the vessel. The
urine is alkaline or neutral in reaction, and is usually of less than the
average specific gravity. The precipitate is amorphous, presenting no
crystalline forms under the microscope. It is at once redissolved on
the addition of an acid, and presents all the chemical reactions which
have been described as belonging to the earthy phosphates. The alka-
line reaction of the urine, which gives rise to the appearance of this
deposit, may be due to a temporary diminution in the quantity of uric
acid produced in the system, or to an unusual formation of alkaline
carbonates from the use of fruits or vegetables containing salts of the
vegetable acids.

Deposits of the Urates. — The urates appear as a deposit when the
formation of uric acid in the system is unusually abundant in propor-
tion to the entire quantity of the urine, so that a portion of the urates
are no longer held in solution. The urine is nearly always concentrated,
highly colored, above the average specific gravity, and of a strongly
acid reaction. The deposit is sometimes nearly white, but usually it is
of a light pink or even red color, according to the degree of concentra-

DEPOSITS IN THE URINE.

391

tion of the urine from which it is deposited. If the urine be allowed to
settle in a white earthen or porcelain vessel, and then carefully poured
off, the more deeply colored deposits are left as a brick-red stain upon
the inner surface of the vessel, forming what is known as the " brick-
dust" sediment.

Deposits of the urates are easily recognized by two special characters,
namely : First, they never appear while the urine is still warm, but only
after it has cooled ; the urine, when first passed, being always perfectly
clear, and becoming turbid on repose, more or less rapidly according to
the rate of cooling. Secondly, the urine, after cooling, however turbid,
if heated in a test-tube, becomes clear again, usually before reaching
the boiling point. Both these characters depend upon the solubility
of the urates at high temperatures.

In rare cases, when a specimen of urine is turbid with the urates and
also contains albumen, a double effect may be produced by the applica-
tion of heat. When such a specimen is first heated, it is cleared up,
owing to the solution of the urates ; but, on approaching the boiling
point, it again becomes turbid from precipitation of the albumen.

The urates are also soluble in the caustic alkalies, so that the ad-
dition of a few drops of a solution of sodium or potassium hydrate
redissolves the precipitate. The addition of a free acid decomposes it,
with the formation of a soluble salt, and the separation of uric acid which
afterward crystallizes, as when thrown down in the same manner
from normal urine. But the volume of the uric acid thus produced is
so much smaller than that of the urates previously disseminated through
the urine, that the immediate apparent effect is that of simple solution
of the precipitate. A deposit
of the urates is accordingly the
only one liable to occur in the
urine, which is cleared up by
the addition of both alkalies
and acids.

Deposits of the urates, when
first thrown down, are pulver-
ulent in form, presenting un-
der the microscope only the
appearance of a collection of
minute granules. After a day
or two they sometimes crystal-
lize in the form of bundles or
globular masses of radiating
needles, often with straight or
curved projections, extending
from the outer surface. If
a few drops of free acid be
added to this deposit while under the microscope, the crystalline masses
of sodium urate may be seen to grow transparent, and slowly dissolve

CRYSTALLINE MASSES OF SODITTM URATE,
from a urinary deposit.

392 THE URINE.

from without inward, while rhomboidal tabular crystals of uric acid
make their appearance in the adjacent fluid.

Crystals of uric acid sometimes appear spontaneously in a deposit
of the urates within a few hours after its formation, owing to the de-
velopment of a free acid in the urine ; and they are sometimes formed
within the urinary passages, so as to be present when the urine is first
passed. Owing to their density and angularity they are the cause of
much irritation to the mucous membrane of the bladder and urethra,
and are known as the "gravel" of the urine. In a mingled precipitate
of the urates and uric acid, the urates form an abundant light, pulver-
ulent, pinkish turbidity ; while the uric acid is a comparatively scanty,
dense, deeply colored, crystalline deposit, which sinks rapidly and accu-
mulates at the bottom of the vessel, the urates being more slowly depos-
ited above it.

Blood. — Urine containing blood is more or less tinged throughout its
mass with a dull reddish color which is easily distinguished from that
due to a concentration of the normal color of the urine itself. After
one or two hours of repose in a cylindrical glass vessel, the blood-
globules are slowly deposited ; and when, as frequently happens, they
are entangled in minute filamentous coagula, these form a strongl}-
colored red layer at the bottom of the vessel. The nature of the deposit
is recognized by two well-marked characters, namely : 1st. The blood-
globules are easily distinguished by microscopic examination, their
natural form not being entirely lost even after they have remained in
the urine for several hours ; and 2d. The supernatant fluid, when de-
canted from the deposit, is found to contain albumen.

Mucus. — The slight quantity of vesical mucus which is normally con-
tained in the urine is at first uniformly disseminated throughout its mass,
and even after being left in repose is insufficient to produce any well
marked or consistent deposit. The light cloudy opalescence, which it
forms at the bottom of the vessel, is visible only on close inspection, and
is readily disseminated again by the least agitation. But in cases of
inflammation of the urinary bladder, the mucus discharged is much
increased in quantity and altered in quality. It then appears as a con-
sistent mass, which does not mix uniformly with the rest of the urine,
but subsides to the bottom as a semifluid deposit. Mucus by itself
is transparent and colorless, but it frequently contains a certain
number of epithelium cells exfoliated from the inner surface of the
bladder; and when crystalline or pulverulent deposits begin to take
place in the urine, they occur first in contact with the mucus, so that
its surface is often sprinkled with a thin layer of the urates or phos-
phates, which give it a partly opaque appearance. It is distinguished
by its viscid and semifluid consistency. It is not affected by heat, but
is coagulated and shrivelled by the action of alcohol and of nitric or
acetic acid. Urine containing mucus is especially liable to rapid de-
composition, and often has, soon after being discharged, a peculiarly
offensive odor from this cause.

DECOMPOSITION OF THE URINE. 393

Pus. — When pus is contained in the urine it subsides on standing,
and forms at the bottom a dense, homogeneous-looking, creamy-white
layer. It is perfectly fluid in consistency and may be easily dissemi-
nated by agitation. Microscopic examination shows it to be composed
exclusively of colorless, granular, nucleated " pus-globules," identical
in appearance with the white globules of the blood, but distinguishable
from those belonging to a deposit of blood by their much greater
abundance and by the absence of red globules. If the supernatant fluid
be poured off, and a few drops of a solution of caustic alkali added to
the purulent deposit, it loses its white color and opacity, owing to the
solution of its granular cells, and swells up into a transparent, colorless
substance of gelatinous consistency, which can no longer be poured
out of the vessel in drops, but slides out in a single semi-solid mass.
This character alone will serve to distinguish a deposit of pus from
any other liable to occur in the urine. The supernatant fluid, when
carefully filtered, is found to contain a small quantity of albumen, the
interstitial fluid of pus being itself albuminous.

Decomposition of the Urine.

After its discharge from the body, the urine undergoes spontaneous
changes, by wrhich its ingredients are altered and finally disappear. This
process of spontaneous decomposition is closely dependent upon the
small quantity of mucus contained in the urine, since it is very much
retarded if the mucus be separated by immediate filtration, and is hast-
ened in a corresponding degree when the mucus is abnormally abundant.
It is characterized by two different stages, which are distinguished from
each other by the successive development of an acid and an alkaline
reaction. They are known accordingly as the acid and the alkaline
fermentations.

Acid Fermentation of the Urine. — This process, which is the first to
show itself in the urine, takes place for the most part within the first
twelve, twenty-four, or forty-eight hours after the discharge of the urine,
according to the elevation of the surrounding temperature. It consists
in the production of a free acid, usually lactic acid, from some of the
undetermined organic ingredients of the excretion. The urine when
fresh contains no free acid substance, its reaction to test-paper being
due to the presence of its sodium biphosphate. But lactic acid has,
notwithstanding, been so often found in nearly fresh urine as to be
sometimes regarded as one of its normal constituents. Observation has
shown, however, that urine, although entirely free from lactic acid when
first passed, may present distinct traces of this substance after some
hours of exposure to the air. Its production in this way, although not
constant, appears to be sufficiently frequent to be regarded as a normal
process.

During the period of the acid fermentation, there is reason to believe
that oxalic acid is also sometimes produced in a similar manner. It is
26

394

THE URINE.

Fig. 132.

certain that a deposit of lime oxalate is frequently present in perfectly
normal urine after a day or two of exposure to the atmosphere, and may
be observed, under these circumstances, without the existence of any
morbid symptom. Whenever oxalic acid is formed in the urine it must
unite with the lime in preference to any other of the bases present, and
is consequently deposited under the form of lime oxalate ; a salt which
is quite insoluble both in water and in the urine, even when heated to
the boiling point. In these cases, the lime oxalate crystals gradually
appear in the light cloud of mucus collected at the bottom of the vessel,

while the supernatant fluid re-
main s clear. They are of minute
size, for the most part just
visible to the naked eye, rather
scanty in amount, transparent,
and colorless. They have the
form of regular octohedra, or
double quadrangular pyramids,
united base to base. They make
their appearance usually about
the commencement of the sec-
ond day, the urine at the same
time continuing clear and re-
taining its acid reaction. They
frequently appear as a deposit
when no substance containing
oxalic acid or oxalates has been
taken with the food. The pre-
cise source from which the oxalic acid, under these circumstances, is
derived has not been fully determined, but it is most probably produced
from a metamorphosis of a small portion of the uric acid of the urine.
If uric acid be boiled in two parts of water with lead peroxide, it is de-
composed, with the production, among other substances, of urea and
oxalic acid ; and it is supposed that some similar change may take place
in the urine, causing the appearance of a minute quantity of oxalic acid,
which decomposes a portion of the lime salts and thus appears as a
crystalline deposit of lime oxalate.

Alkaline Fermentation of the Urine. — At the end of a few days the
changes above described come to an end, and are Succeeded by a different
process, which consists essentially in the decomposition of the urea of
the urine and its transformation into ammonium carbonate. This
change, which may be produced artificially in a watery solution of urea
by continued boiling, takes place in the urine slowly at low tempera-
tures, more rapidly during warm weather. The elements of two
molecules of water unite with those of the urea undergoing decomposi-
tion, to produce ammonium carbonate, as follows :

Urea. Ammonium carbonate.

CH4N20 + H40, = (NH4).C03.

CRYSTALS OF IJIME OXALATE, deposited
from healthy urine, during the acid fermentation.

DECOMPOSITION OF THE URINE. 395

The first portions of the ammoniacal salt thus produced neutralize a
corresponding quantity of the sodium biphosphate, so that the acid
reaction of the urine diminishes in intensity. This reaction gradually
becomes weaker, as the fermentation proceeds, until it at last disappears
altogether and the urine becomes neutral. The production of ammonium
carbonate still continuing, the reaction of the fluid then becomes alkaline,
and its alkalescence grows more pronounced with the constant accumu-
lation of the ammoniacal salt.

The time at which the alkaline reaction of the urine becomes estab-
lished varies with its original degree of acidity and with the rapidity of
its decomposition. Urine which is neutral when first passed, as often
happens with that discharged during the earlier part of the day, will of
course become alkaline more readily than that which has at , first a
strongly acid reaction. In the summer, urine will become alkaline, if
freely exposed, on the third, fourth, or fifth day ; while in the winter, a
specimen kept in a cool place may still be neutral at the end of fifteen
days. In cases of paralysis of the bladder accompanied with cystitis,
where the vesical mucus is increased in quantity and altered in quality,
and the urine is retained in the bladder for ten or twelve hours at the
temperature of the bod}r, it may change so rapidly as to be distinctly
alkaline and ammoniacal at the time of its discharge. In these cases it
is acid when first secreted by the kidneys, and becomes alkaline while
retained in the interior of the bladder.

The first effect of the alkaline condition of the urine, thus produced,
is the precipitation of the earthy phosphates. This precipitate slowly
settles upon the sides and bottom of the vessel, or is partly entangled
with certain animal matters which rise to the surface and form a thin,
opaline scum upon the urine. There are no crystals to be seen at this
time, but the deposit is entirely amorphous and granular.

The next change consists in the production of a new salt, the
ammonio-magnesian phosphate, by the combination of the ammonia
formed from the urea with the magnesium phosphate already present in
the urine. The change may be represented as follows :

Magnesium phosphate. Ammonia. Ammonio-magnesian phosphate.

MgHP04 + NH3 = MgNH4PO,

The crystals of this salt are very elegant and characteristic. They
show themselves throughout all parts of the mixture, growing gradually
in the mucus at the bottom, adhering to the sides of the glass, and
scattered abundantly over the film which collects upon the surface. By
their refractive power they give to this film a peculiar glistening and
iridescent appearance, which is nearly always visible at the end of six
or seven days. The crystals are perfectly colorless and transparent, and
have the form of triangular prisms, generally with bevelled extremities.
Their edges and angles are frequently replaced by secondary facets.
They are insoluble in alkalies, but are easily dissolved by acids, even
in very dilute form. At first they are of minute size, but gradually

396

THE URINE.

CRYSTALS OP AMMO>- IO-MAGNESIA w
PHOSPHATE, deposited from healthy uriue,
during the alkaline fermentation.

133- increase, so that after seven or

eight days they may become
visible to the naked eye.

As the decomposition of the
urine continues, the ammonium
carbonate which is produced,
after saturating all the other
ingredients with which it is ca-
pable of entering into combina-
tion, begins to be given off in a
free form. The urine then ac-
quires an ammoniacalodor; and
a piece of moistened test-paper,
held a little above the surface,
will have its color turned by
the alkaline gas escaping from
the fluid. This is the source
of the ammoniacal vapor given

off wherever urine is allowed to remain and decompose. It continues

until all the urea has been decomposed.

Renovation of the Body in the Nutritive Process.

As the materials of nutrition are constantly introduced with the food,
while, on the other hand, the products of excretion are removed from
the body and discharged externally by the breath, the perspiration, the
urine, and the feces, an incessant renewal takes place in the ingredients
of which the animal system is composed. During the early periods of
growth and development, the quantity of material introduced is greater
than that discharged, and the body consequently increases in weight
and size. In wasting diseases and in advanced age, the loss of sub-
stance by excretion exceeds the gain by nutrition, and the weight of
the body is therefore diminished. But during health, in adult life, the
two processes are equal; and, with certain temporary fluctuations
which counterbalance each other, the weight of the body remains the
same.

The total quantity of material, introduced and discharged within a
given time, forms, accordingly, a measure of the rapidity with which the
internal changes of nutrition and metamorphosis go on in the animal
system. It is not possible to indicate this quantity in either case with
absolute accuracy; but the observations which have been made in this
direction are sufficiently definite to show, in a general way, the average
results of the two corresponding actions of waste and supply. The
following table gives, approximately, the daily quantity of material
absorbed and discharged in a healthy adult, the weight of the body
remaining sensibly unaltered :

RENOVATION OF THE BODY. 397

Absorbed during 24 hours. Discharged during 24 hours.

Water . . . 2250 grammes. Carbonic acid . . 750 grammes.

Oxygen . . . 700 " Aqueous vapor . . 500 "

Albuminous matter . 130 " Perspiration . . 850 "

Starch and sugar . 300 " Water of the urine . 1200 "

Fat .... 100 " Urea and salts 70 "

Salts 20 Feces . . .130

3500 grammes. 3500 grammes.

Rather more than 5 per cent., therefore, of the entire bodily weight is
absorbed and discharged daily by the healthy adult human subject;
and, for a man having the average weight of 65 kilogrammes, a quantity
of material, equal to the weight of the whole body, thus passes through
the system in the course of twenty days.

SECTION II.
THE NERVOUS SYSTEM.

CHAPTER I.

GENERAL STRUCTURE AND FUNCTIONS OF THE
NERVOUS SYSTEM.

THE nervous system is an apparatus of intercommunicating fibres and
cells, disseminated throughout the body, and standing in anatomical
connection with the various organs of the animal system. It has pro-
perties which are different from those of the other organized tissues,
and the effect of its operation is to bring the active phenomena of vari-
ous parts of the body into a definite relation with each other, and with
those of the outside world. It is therefore a medium of communica-
tion, by which the different animal functions are associated together in
harmonious action, and are stimulated or modified according to the
demands of the system itself or the varying influence of external condi-
tions.

Each organ and tissue of the body possesses, independently of the
nervous system, certain characteristic properties or modes of activity,
which may be called into operation by any appropriate stimulus or
exciting cause. If the heart of a frog, after its removal from the body,
be touched with the point of a steel needle, it contracts and repeats
very nearly the movement of an ordinary pulsation. If the leg of the
same animal be separated from the thigh, the integument removed, and
the poles of a galvanic batter}^ applied to its exposed surface, a mus-
cular contraction takes place at the moment the electric circuit is com-
pleted. The application of heat, friction, or an irritating liquid to a
particular part of the integument brings on a local redness which again
subsides after the removal of the exciting cause ; and a solution of
belladonna dropped upon the cornea, when absorbed by the tissues and
brought in contact with the iris, produces a change in the condition of
its fibres and a dilatation of the pupil. In these instances, the organ
which performs the vital act is excited by the direct application of a
stimulus to its own tissues.

But this is not the mode in which the natural functions of the animal
system are excited during life. The physiological stimulus which calls

( 399 )

400 GENERAL STRUCTURE AND FUNCTIONS

into action the organs of the living body is not direct but indirect in its
operation. In the healthy and uninjured condition of the frame, the
muscles are never made to contract by an external stimulus applied
immediately to their own fibres, but by one which first operates upon
some other organ, adjacent or remote. The various secreting glands
have their functional activity increased or diminished by causes which
are directly applied not to themselves but to other parts of the body ;
as where a flow of saliva from the parotid is produced by food intro-
duced into the cavity of the mouth, or where the discharge of perspira-
tion by the skin is modified by the influence of mental conditions. As
a rule, therefore, in the natural state of the system, the various organs
situated in different parts of the body are connected with each other by
a mutual sympathy which regulates their physiological action. This
connection is established through the medium of the nervous system.

The function of the nervous system is therefore to associate the
different parts of the body in such a manner, that stimulus applied to
one organ may excite the activity of another.

The instances of this mode of action are as numerous as the different
vital phenomena. The stimulus of light falling upon the retina pro-
duces contraction of the pupil. The introduction of food into the
stomach causes the gall-bladder to empty itself into the duodenum.
The contact of alimentary substances with the mucous membrane of
the intestine, excites the peristaltic action of its muscular coat. The
presence of a growing foetus in the uterus is accompanied by an increased
growth of the mammary glands. Every organ is subservient, in the
manifestation of its functional activity, to influences from other parts, of
a structure different from its own.

General Structure of the Nervous System,

The nervous system consists of two kinds of nervous tissue, differing
from each other in appearance, structure, and physiological endowments.
One of these is the white substance, composed of nerve fibres alone ; the
other is the gray substance, which contains, in addition to the nerve
fibres, interstitial matter and nerve cells. The white substance is found
in the trunks and branches of the nerves, on the surface of the spinal
cord, and in the internal parts of the brain. The gray substance forms
the external layer or convolutions of the brain, as well as various de-
posits about its base and central parts, the central portion of the spinal
cord, and a large number of small detached masses in different parts of
the body. These two kinds of nervous tissue are so different in their
properties and function as to require for each a separate description.

Nerve Fibres.

The nerve fibres are cylindrical filaments, arranged in bundles or
tracts, in which they run, for the most part, in a direction parallel to
each other. Their diameter varies considerably, even in the same

OF THE NERVOUS SYSTEM.

401

Fig. 134.

locality ; some of the fibres in a single bundle being 10, 15 or 18 micro-
millimetres in diameter, while others are not more than 2.5 mmm. Their
average size also varies in different parts of the nervous system. The
larger fibres are found in the peripheral trunks and branches of the
nerves, where they have an average diameter of 12.5 mmm. ; in the
white substance of the brain and spinal cord their average diameter is
5 mmm., and in the gray substance it is reduced to 2 mmm. Two por-
tions of the nervous system, both of which contain nerve fibres, are
often distinguished from each other by the relative numbers of their
larger and smaller fibres. Thus in the cutaneous nerves of man, accord-
ing to Bidder, Yolkmann, and Kolliker, the larger and smaller fibres are
present in about equal quantity, while in the muscular nerves the larger
fibres are three times as abundant as the smaller. In the nerves of bony
tissue the proportion of small fibres is double that of the large ones,
and in the gray substance of the cerebral hemispheres there are none
larger than 6 or 7 mmm. in diameter. The nerve fibres belonging to the
same bundle or tract may even become increased or diminished in diameter
in different parts of their course ; as Kolliker has shown that the fibres
of the posterior roots of the spinal nerves, in passing through the cord
from the exterior to the gray
substance, are reduced in their
average diameter from 10 to 5
mmm. ; and those of the white
substance, of the cerebral hemi-
spheres, on entering the gray
matter of the convolutions, are
reduced from 5 mmm. to 2
mmm. in diameter.

The structure of the nerve-
fibre, in its most complete
form, presents three distinct
elements, namely : an external
tubular sheath, an intermediate
medullary layer, and a central
axis cylinder.

The Tubular Sheath The

exterior of the nerve fibre is
composed of a colorless, trans-
parent tubular membrane,
which closely invests the re-
maining portions and is seen
with some difficulty in the
natural condition of the fibre, owing to its extreme thinness and
delicacy. It may often, however, be distinguished at certain points
where the nervous fibre is accidentally compressed or indented, as at c,
Fig. 134; or it may be brought into view for considerable distances
according to the method of Kolliker, by treating the fibres with a cold

NBRVB FIBRES from the Sciatic Nerve.— At
a, the torn extremity of a nerve fibre with the axis
cylinder (b) protruding from it. At c, the medul-
lary layer is nearly separated by accidental com-
pression, but the axis cylinder passes across the
injured portion. The outline of the tubular mem-
brane is also seen at c on the outside of the remain-
ing portions of the fibre.

402

GENERAL STRUCTURE AND FUNCTIONS

solution of sodium hydrate, and afterward boiling them for an instant
in the same fluid. This extracts the greater part of their contents, and
leaves the tubular sheath in the form of an empty cylindrical canal. Jn
its general chemical relations, the tubular sheath is similar to the sar-
colemma of muscular fibre, its principal physical properties being its
cohesion and elasticity. Its physiological function is undoubtedly that
of a protecting envelope, by which the internal portions are maintained
in place and preserved from mechanical injury.

The Medullary Layer. — Immediately within the tubular sheath is a
layer of transparent, highly refractive, nearly fluid material, of oleagi-
nous consistency, termed the medullary layer, or medulla, which gives
to the nerve fibres, and the tracts composed of them, a white and
shining aspect. This substance is readily altered by a diminution of
temperature, or by the contact of unnatural fluids, even by exposure to
the air or the imbibition of water, or by the ordinary manipulations
required in preparing it for microscopic examination. Under these in-
fluences it undergoes a sort of coagulation, being increased in density
and in refractive power, so that both its external and internal limits are
indicated by a dark and strongly marked outline. This gives to the
nerve fibre the very characteristic appearance of a cylinder with a
double contour, presenting two distinct parallel outlines at each edge ;
an appearance by which it may be easily distinguished from any other
anatomical element. As the coagulation of the medullary layer goes
on, its outlines become more or less irregular, and after a certain time
it involves the whole of the fibre in a more or less confused mass of
irregularly refracting substance. The fibres containing a medullary
layer, and exhibiting the characteristic double contour due to its pre-
sence, are called " medullated nerve fibres."

In the smaller variety of nerve fibres from the substance of the brain

and spinal cord, the external
tubular sheath is wanting, or
at least cannot be demon-
strated ; and such fibres, owing
to their want of support and
their soft consistency, are read-
ily distorted by accidental pres-
sure, or by the contact of rea-
gents. They become swollen
or varicose at many points;
and the medullary substance
is forced out or exudes from
their torn extremities in irre-
gularly globular, fusiform, or
filamentous masses, which show
on their exterior the double

NERVE FIBRES, from the white substance of contour due to a Superficial
the brain.— a, a, a Portions of the myeline, pressed „„ , , ,

out, and floating in irregularly rounded drops. Coagulation. 1 hese detached

Fig. 135.

OF THE NERVOUS SYSTEM. 403

portions, which are everywhere visible in ordinary microscopic prepa-
rations of the brain substance, are termed " myeline drops," and owe
their peculiar appearance to the nature of the ingredients which form
the medullary layer of the nerve fibre. The medullary layer is com-
posed of a substance termed myeline, which is not, however, a distinct
proximate principle, but is itself a mixture of various different mate-
rials. It consists mainly of cerebrine, a nitrogenous matter found only
in the nervous centres, together with a large proportion of cholesterine
and fat. There is also a certain proportion of lecithine, a nitrogenous
and phosphorized matter, which is also found in the gray substance.
The mixture of these ingredients gives to the myeline its peculiar con-
sistency and reaction.

In regard to its physiological function, the medullary layer of the
nerve fibre is generally considered as an isolating substance, like the
gutta-percha envelope of a submarine telegraph wire, so arranged as to
confine the transmission of nerve force within proper limits, and prevent
its diffusion to neighboring parts. We have no absolute proof that
such is its true character, but there are some facts which lend a certain
probability to this view. The medullary layer exists throughout the
main portion of a large majority of the nerve fibres, where they trans-
port the nervous stimulus uninterruptedly from one point to another ;
but they are destitute of it both at their origins and terminations,
where they come in contact with the elements of the gray matter, or are
connected with the peripheral organs of sensation and motion. What-
ever may be its exact function, therefore, the medulla evidently plays a
secondary, and not a principal part, in the physiological action of the
nerve fibre.

The Axis Cylinder — The central part of the nerve fibre consists of a
pale, homogeneous, or finely granular cord, of a cylindrical or slightly
flattened form, occupying the position of the longitudinal axis of the
fibre. From these characters it has received the name of the " axis
cylinder." It differs from the medullary layer, by which it is enveloped,
in consistency ; for while the latter is nearly fluid in its natural condi-
tion, the axis cylinder is solid, and, though very delicate, possesses a
certain degree of elasticity. By some observers (Schultze, Gerlach) the
axis cylinder is regarded as composed of many excessively minute fibril-
Ise, united into a uniform bundle; by others of equal authority (K61-
liker) the indications of such a fibrillated constitution of this part of the
nerve fibre are considered as uncertain.

The axis cylinder is composed of an albuminous substance which is
insoluble in water, alcohol, and ether ; becomes pale and swollen by the
action of concentrated acetic acid ; and is readily dissolved by a boiling
solution of sodium hydrate. It is stained red by treatment with a solu-
tion of carmine, while the enveloping medullary layer remains un-
colored; and by this means a visible distinction may be made between
the two. The application of a solution of gold chloride, and subsequent
exposure to light, stains the axis cylinder of a dark purple, nearly

GENERAL STRUCTURE AND FUNCTIONS

black color; and by this mode of preparation nervous fibres of extreme
delicacy have been traced among surrounding tissues, where they would
otherwise escape observation.

In its physiological properties, the axis cylinder is undoubtedly the
most essential element of the nerve fibre, since it is the only one univer-
sally present, and always extending throughout the whole length of a
fibre from its origin to its termination. Its albuminous nature also
distinguishes it from other parts of the nerve fibre, and indicates the
relative importance of its function. It is probably through the axis
cylinder that the passage of the nerve current takes place, and in its
substance that the principal changes accompanying this action are
effected.

Non-Medullated Nerve Fibres. — Beside the nerve fibres constituted,
as above, by an axis cylinder, surrounded by a medullary layer, with or
without an external tubular membrane, there are others which consist
of the axis cylinder destitute of any medullary layer, and which conse-
quently do not exhibit the appearance of a double contour. These are
called " non-medullated nerve fibres." They are found, in man, only in
certain parts of the sympathetic nerves, in the terminal nervous expan-
sions of the muscles and organs of sense, and in the nervous centres in
the immediate vicinity of the cells of the gray substance. In the sym-
pathetic nerves, they are, for the most part, mingled with a considerable
proportion of inedullated fibres, though some of the sympathetic branches
distributed to the intestine and the spleen, according to Schultze, are
composed of non-medullated fibres exclusively. The branches of the
olfactory nerve, distributed to the nasal mucous membrane, also consist
altogether of fibres of this kind. Such nervous branches have not the
white, opaque aspect belonging to other nerves, but are grayish-looking
and semi-transparent in appearance ; a peculiarity which is evidently due
to the absence of the myeline or medullary layer.

The same nerve fibre may be inedullated for the greater part of its
course, and become destitute of medulla at its termination, as is the rule
with the cerebro-spinal nerves generally ; or fibres may originate in the
gray substance as non-medullated axis cylinders, and become invested,
after a short distance, with a distinct medullary layer. The non-medul-
lated nerve fibres are not, therefore, regarded as essentially different
from the others, but only as presenting a less complicated form of struc-
ture.

Course and Mutual Relation of the Nerve Fibres. — In the white sub-
stance of the brain and spinal cord, the nerve-fibres form continuous
tracts, of larger or smaller size, lying in contact with each other, and
not mingled with any considerable proportion of other tissue. But on
passing out of the bony cavities toward the exterior, they become col-
lected into small bundles, each of which is invested with a thin pro-
longation of connective tissue, derived from the dura mater and
periosteum ; these bundles are associated into larger ones which are
held together by a denser layer of the same connective tissue ; and

OF THE NERVOUS SYSTEM.

405

finally the whole are united into a single compound mass by its exterior
investment, which is known as the u neurilemma." Such a complete
bundle is called a nerve, and the nerve fibres of which it is composed
are usually all distributed, after a longer or shorter transit, to associated
organs, or to adjacent regions of the body.

The nerve fibres themselves are not known to divide, branch, or inoscu-
late with each other in any part of their course through the main trunks
and branches of the nerves. So far as observation goes, each nerve
fibre is continuous and independent, from its origin in the nervous
centres to within a microscopic distance of its peripheral termination.
When a nerve therefore divides during its course into several branches,
or when the branches of adjacent nerves inosculate with each other
to form a plexus, like the cervical, brachial, or lumbar plexuses, this is
only because certain ultimate nerve fibres, or bundles of fibres, leave
those with which they were previously associated, and pursue a different

Fig. 136.

Fig. 137.

DIVISION OF A NKRVOUS BRANCH
(a), into its ultimate fibres, 6, c, d, e.

Inosculation of NERVES.

direction. A nerve which originates, for example, from the spinal cord
and runs down the upper extremity, to be finally distributed to the in-
tegument and muscles of the hand, contains at its point of origin all the
filaments into which it is afterward divided, and which are merely sepa-
rated at successive points from the main bundle. Jn case of the inoscu-

406 GENERAL STRUCTURE AND FUNCTIONS

lation of two nerves, the communication between them is effected by
some of the fibres belonging to the first passing over from it to join the
second, while some of those belonging to the second may also cross and
join the first ; the individual fibres in each instance remaining distinct,
and retaining their identit}r throughout. In whatever way, therefore,
the nerve fibres are associated in the various trunks and branches of
the nerves, they may still act independently and preserve their specific
functions in every part of their course.

Peripheral Termination of the Nerve Fibres. — Near the termination
of the nerve fibres in the tissues to which they are distributed, they
present certain important modifications both in structure and arrange-
ment.

First, the smaller nervous branches, or bundles of nerve fibres, after
penetrating the substance of the tissues, suddenly divide and subdivide
with unusual rapidity ; and these subdivisions, uniting with each other
by inosculation, form abundant plexuses, from which are given off the
individual fibres supplying the anatomical elements of the tissues. In
the skin there are two such nervous plexuses, a deeper and a more
superficial, of which the latter is the more closely set and composed of
more slender bundles, containing only one or two fibres each. As a
general rule, also, in other tissues, the last or terminal plexus is the
finest, and incloses between its meshes the narrowest interspaces. The
nerve fibres, on reaching the situation of the terminal plexus, are also
considerably reduced in size, being diminished both in the skin and the
muscles from 10 or 15 mmm. to 4 or 5 mmm. in diameter. According
to Kolliker it is sometimes possible to observe this diminution in the
size of a single nerve fibre in different parts of its course through the
muscular tissue.

Secondly, both in the terminal plexus and the branches given off from
them, the nerve fibres themselves undergo division; so that a single
fibre in this situation may give rise to two or more branches, each branch
retaining all the original anatomical characters of a nerve fibre. There
is usually a marked constriction at the point where the nerve fibre
divides ; but this is followed by a corresponding enlargement, so that
the secondary fibres soon become nearly or quite equal in diameter to
that from which they were derived. A nerve fibre may accordingly pass
undivided, so far as we know, throughout its course in the roots, trunks,
and principal branches and ramifications of the nerve, and may then,
shortly before its termination, break up into a number of separate but
closely adjacent secondary fibres. It has been estimated by Reichert,
that, in the subcutaneous muscle of the frog, ten primitive nerve fibres
may give rise by their division, to about 300 terminal extremities.

Thirdly, the nerve fibre, when near its peripheral termination, be-
comes altered in structure. This alteration consists in a disappearance
of the medullary layer, by which the fibre loses its double contour; and
by a similar disappearance or a separation of the tubular sheath. The
nerve fibre, thus altered, is reduced, in its constituent parts, to the axis

OF THE NERVOUS SYSTEM. 407

cylinder alone; that is, all the secondary elements of its structure are
lost, and there remains only the essential conducting filament of the

Fig. 138.

DIVISION o* WERVE FIBRES, in a small branch from the subcutaneous muscle of a

frog. (Kolliker.)

axis cylinder. Lastly the nerve fibre, at the point of its final termina-
tion, is frequently brought into relation with cell-like bodies, which are
sometimes regarded as analogous in character to the nerve cells of the
gray substance in the nervous centres.

The ultimate termination of the nerve fibres in the skin has been most
distinctly seen in the so-called " Pacinian bodies" and the " tactile cor-
puscles." The Pacinian bodies are ovoid-shaped masses from 1 to 4.5
millimetres in length, found in the subcutaneous connective tissue of the
hands and feet, and various other parts of the body, consisting of a
series of concentric laminae of connective tissue, with a central cavity,
inclosing a transparent, colorless, fluid or semifluid material. A single
ultimate nerve fibre penetrates the Pacinian body at one extremity, and
passes into its central cavity. At the point of entrance, the external
tubular sheath leaves the nerve fibre and becomes continuous with the
connective tissue laminae of the Pacinian body. The medullary layer
also disappears, and the nerve fibre, thus reduced to its axis cylinder,
runs longitudinally through the greater part of the central cavity and
terminates, toward its farther end, in either one or several slightly
rounded extremities. The "tactile corpuscles," found in the sensitive
papillae of the skin of the hands and feet, are similar in form to the
Pacinian bodies, but of much smaller size ; having an average length,

408

GENERAL STRUCTURE AND FUNCTIONS

in man, of about 100 mmm. They consist each of a central, trans-
parent, gelatinous mass, surrounded by an envelope of connective
tissue, which is marked by many tranverse elongated nuclei. Each
corpuscle receives one or two nerve fibres which run upward, in either
a straight or spiral course, and, after losing their medullary layer, in
some instances reach the central gelatinous nucleus, though for the
most part their terminations are not distinctly visible.

The simplest form of tactile corpuscle is that known as the "terminal
bulbs" of the sensitive nerves, in the conjunctiva, the lips, the papillae
of the tongue, and the soft palate. They are round or elongated ovoid
bodies, consisting of a closed sac of connective tissue, sometimes marked
with transverse nuclei, and containing a homogeneous or finely granular
substance. Into this body is received the ultimate branch of a nerve

Fig. 139.

Fig. 140.

TERMINAL BULB of a sensi-
tive nerve; from the conjunctiva
of the calf. (Frey.)

TACTILE CORPUSCLES, from the edge of the
tongue of the sparrow.— 1, 2. 3. IWedullated nerve
fibres supplying four tactile corpuscles. One
fibre divides into two branches; and one of them
is traced to near the extremity of the correspond-
ing corpuscle, where it ends in a cell-like expan-
sion. (Ihlder.)

fibre, which is reduced to its axis cylinder and terminates in the inte-
rior by a free extremity. In some regions, as, for example, the lips in
the human subject, and the tongue in birds, are to be seen structures
which are intermediate in form between the terminal bulbs and the
tactile corpuscles.

In the muscles, as a rule, each muscular fibre has, connected with it,
at least one nerve fibre, and sometimes more than one. The ultimate

OF THE NERVOUS SYSTEM. 409

nerve fibre, given off as a branch from the terminal Fig. 141.

plexus, approaches the muscular fibre, usually at
a right angle, and penetrates its exterior; the
tubular sheath of the nerve fibre becoming con-
tinuous with the sarcolemma. At the same time
its medullary layer ceases abruptly, and the axis
cylinder spreads out into a thin oval expansion
of granular matter interspersed with nuclei, called
the " terminal plate," and lying in immediate con-
tact with the contractile substance of the muscular TERMINATION OF A

fibre. Some variations in the form and disposi- NERVE FIBRE in mus-
cular fibre, from the fowl,
tion of the axis cylinder in the terminal plate are (ROUget.)

to be seen in the muscles of amphibia ; but the

above represents its essential characters in the muscles of birds and

mammalians.

Physiological Properties of the Nerve Fibres. — The nerve fibres are
organs of communication. They serve as connecting filaments between
the nervous centres on the one hand and the peripheral organs of sensa-
tion and motion on the other. For this purpose they are endowed with
a power of irritability by which, when excited at one or the other
extremity, they transmit the nervous impulse throughout their entire
length, and produce a corresponding effect at their opposite termination.
Thus the nerve fibres distributed to the skin, when excited at their
peripheral extremities, produce in the brain a sensation corresponding
to the external impression. On the other hand, those which are distri-
buted to the muscles, when excited at their origin by the impulse of the
will, produce a contraction in the muscular fibres at their periphery.
This physiological action produces no visible change in the nerve fibre
itself. Its effects are manifest only at the extremities of the nerve, in
the organs where it terminates. Nevertheless, it is evident that the
nerve fibre serves to communicate in some way an action from one of
its extremities to the other ; since, if it be divided in any part of its
course, the communication at once ceases, and sensation can no longer
be perceived from impressions made upon the skin, nor voluntary con-
traction excited in the muscles.

Owing to the different effects thus produced, at their central and peri-
pheral extremities, the nerve fibres and the nerves composed of them
have been distinguished by different names. Those which transmit the
stimulus of sensation, from the periphery to the nervous centres, are
called sensitive nerves or nerve fibres ; those which transmit the stimulus
of motion, from the nervous centre outward to the muscles, are called
motor nerves or nerve fibres. As a general rule, both sensitive and
motor nerve fibres are associated together in the same nervous bundle,
and separate from each other only when near their final distribution in
the skin or mucous membranes on the one hand, and in the muscles on
the other. But in some situations, near the origin of the nerves as well
as near their termination, the sensitive and motor fibres run in distinct
27

410 GENERAL STRUCTURE AND FUNCTIONS

bundles ; as for example in the sensitive and motor roots of the fifth
pair of cranial nerves, and in the anterior and posterior roots of the
spinal nerves generally. The fibres belonging to the facial nerve are
all motor fibres, making this exclusively a motor nerve. The three
branches of the fifth pair, on the other hand, which are distributed to
the integument and mucous membranes of the face, are composed exclu-
sively of sensitive fibres ; while the branch of the same nerve distributed
to the muscles of mastication is made up principally or entirely of motor
fibres.

No essential distinction has been discovered in the anatomical char-
acters of sensitive and motor nerve fibres. In nerves and nervous
branches which perform a motor function, the nerve fibres, as a rule, are
of comparatively large size, averaging 15 mmm. in diameter ; while in
those performing a sensitive function they are smaller, averaging not
more than 10 mmm. in diameter, and many of them being considerably
less. But this difference is only one of proportion in numbers between
the larger and smaller fibres ; since both large and small fibres are found
in both motor and sensitive nerves. Even in the motor nerves, the
large fibres become reduced to the size of the smaller ones before their
termination in the muscular tissue; and the nerve fibres generally are
diminished or increased in diameter on passing into or out of the gray
substance of the nervous centres. No absolute distinction therefore can
be made between sensitive and motor nerve fibres as regards their size ;
and in regard to the essential details of their structure, namely, the
tubular sheath, the medullary layer, and the cylinder axis, they are to
all appearance completely identical.

Effect of Division upon the Nerve Fibres. — The immediate effect of
dividing or seriously injuring the nerve fibres is a suspension of their
physiological function. The physical communication being cut off be-
tween their extremities, the sensitive fibres can no longer transmit an
impression from the skin to the nervous centre, and the motor fibres
can no longer convey the stimulus of voluntary motion from the nervous
centre to the muscles. In addition to this result, when the divided
nerve fibre is permanently separated from its central connections, there
also follows a change in its texture, which is propagated mainly in
one direction, and which consists in an atrophy or degeneration of
the nervous substance. The most distinct effects of this degeneration
of a divided nerve fibre are to be seen in its medullary layer. According
to the observations of Yulpian and Philippeaux, the alteration in struc-
ture, which takes place from the point of division toward the periphery,
begins to be perceptible in mammalians, by microscopic examination, at
the end of five days. The transparency of the fibre is first diminished,
its contents having a more or less cloudy appearance. At the end of
eight or ten days, the double contour of the fibre has become irregular
and at various points partially or completely interrupted ; and the sub-
stance of the medullary layer is broken up into separate masses of
varying size, presenting the appearance of a coagulation and dislocation.

OF THE NERVOUS SYSTEM. 411

As the process goes on, the continuity of the medullary layer is entirely
destroyed, and this substance is reduced to the condition of isolated
oily-looking drops, scattered through the interior of the tubular sheath,
which become gradually transformed into a diffused mixture of minute
granules. Finally, the granules themselves disappear, and the tubular
sheath, partially emptied by the atrophy of the medullary layer, becomes
collapsed and wrinkled. The nerve which has suffered these changes
has lost its white glistening color, and has assumed a grayish hue. The
axis cylinder either does not participate in the above alterations, or its
changes are not so manifest to the eye ; since, according to some ob-
servers, it remains visible after the medullary layer has disappeared.

According to various observers (Waller, Krause, Yulpian), the de-
generation of divided nerve fibres, both in the sensitive and motor
nerves, may be propagated throughout their peripheral extremities,
extending even to the sensitive papillae of the tongue and the tactile
corpuscles of the skin. Yulpian1 has found that in dogs, six weeks
after the division of the sciatic nerve, no nerve fibres could be dis-
covered in the muscles of the foot which had not undergone the same
alteration.

The rapidity with which degeneration takes place in the fibres of a
divided nerve varies with the species and age of the animal to which it
belongs. The change is less rapid in the cold-blooded, more so in the
warm-blooded animals. In those of the same species, it goes on more
quickly in the young, more slowly in animals which are fully grown.
According to Yulpian, in young dogs, as a general rule, the disappear-
ance of the medullary layer is complete at the end of six weeks or two
months from the date of the injury.

The degeneration of the peripheral portions of divided nerves has
often been utilized in order to determine the source of particular bun-
dles of nerve fibres. If a nerve, for example, receives roots or commu-
nicating branches from two different sources, and afterward supplies
by its ramifications several organs, it may be ascertained whether the
fibres coming from one source are or are not distributed to a particular
organ. For this purpose the root or communicating branch in question
is divided ; and when the subsequent process of degeneration is com-
plete, the atrophied nerve fibres derived from this source may be fol-
lowed by microscopic examination throughout their course, and recog-
nized in the organ to which they are distributed.

Union and Regeneration of divided Nerves — The loss of function
in a divided nerve is not permanent ; but, if the neighboring parts be
healthy and no other injury have been inflicted, the nerve fibres may
reunite, and their power of communication be restored. When the
division has been a simple one, the two extremities of the divided nerve
remaining in contact or in close proximity with each other, their union
takes place with comparative readiness ; but even when a considerable

1 Leqons sur la Physiologie du Systdme Nerveux. Paris, 1866, p. 243.

412 GENERAL STRUCTURE AND FUNCTIONS

portion of the nerve has been cut out, there may be a reproduction of
the lost parts, and the nerve may finally regain its natural continuity.
The fibres of new formation, thus produced, are at first of small diameter
and of grayish aspect. They gradually increase in size, become pro-
vided with a medullary layer, and at last present all the anatomical
characters of the healthy nerve fibre. Schiff, Yulpian, and Philippeaux
have found that it is possible for the continuity of a nerve to be re-
established, after the excision of portions of its trunk equal to five or
even six centimetres in length. According to Yulpian, in very young
animals, a loss of nerve substance from one to two centimetres in length
may be restored at the end of six weeks ; and the same observer has
seen, in young rats, a portion of the sciatic nerve, six millimetres long,
reproduced in the course of seventeen days.

At the same time, the degenerated portion of the nerve, situated
beyond the point of its division, becomes restored. There is a reproduc-
tion of the medullary layer, which had become atrophied by the de-
generative process, and the entire nerve again exhibits its normal
anatomical character. The time required, for the complete regeneration
of the peripheral portion of a divided nerve, is in general from three to
twelve months, according to the age and species of the animal upon
which the experiment is performed.

The complete regeneration of a divided or exsected nerve is indicated
by the restoration of its normal function. If it be a sensitive nerve, the
power of sensation, which was at first lost, returns in that portion of
the integument to which its fibres are distributed ; if it be a motor
nerve, the power of voluntary motion is regained in the corresponding
muscles. The observations of Yulpian have shown that, after the ex-
cision of the central extremity of the hypoglossal nerve in dogs, its
peripheral portion may become capable of exciting contraction in the
muscles of the tongue at the end of four months j1 and according to
those of Schiff upon young dogs and cats, sensibility may reappear in
the tongue and lip in fourteen days after the excision of portions of the
lingual and infra-orbital nerves, from two to two and a half centimetres
in length.

In the human subject, at least in adult life, the restoration of divided
nerves is much less rapid ; and, according to L'Etievant2 and Weil-
Mitchell,3 often either does not take place at all, when the injured nerves
are of considerable size, or does so very imperfectly.

The smaller nervous branches supplying the skin are frequently
divided by accidental incisions, causing a local anaesthesia, or loss of
tactile sensibility in the immediate neighborhood. This anaesthesia
persists usually for weeks, or even months, after the healing of the
wound ; but it almost invariably disappears at last, and the skin re-

1 Le<jons sur la Physiologie du SystSme Nerveux. Paris, 1866, p. 272.

2 Trait6 des Sections Nerveuses. Paris, 1873.

3 Injuries of Nerves, and their Consequences. Philadelphia, 1874, p. 84.

OF THE NERVOUS SYSTEM.

413

covers its normal sensibility. Restoration may also undoubtedly take
place in nerves of larger size, as in the case reported by L'EtieVant,1
where the median nerve was divided in a man twenty-six years of age,
at the upper third of the arm. The power of motion and sensibility,
dependent on the fibres of this nerve, remained abolished for ten
months, but began to reappear in fourteen months, and were almost
completely restored at the end of a year and a half.

Nerve Cells,

The nerve cells, which form the characteristic anatomical element of
the gray substance, are rounded or irregularly shaped bodies, consisting
of a soft, semi-transparent, finely granular, albuminous matter, and con-
taining a rather large, distinctly marked nucleus and nucleolus. Some-
times they also contain a certain quantity of brown, yellowish, or
blackish pigment grains, which are especially abundant in the imme-
diate neighborhood of the nucleus. The nerve cells vary in size in dif-
ferent parts of the gray substance. The smaller ones, from 10 to 20
mmm. in diameter, are found in the ganglia of the sympathetic system,
the convolutions of the cerebral hemispheres, and in the posterior horns
of gray matter in the spinal cord. The larger, averaging from 40 to 60
mmm., are in the convolutions of the cerebellum, and in the medulla
oblongata ; the largest of all, as a general rule, being met with in the
anterior horns of gray mat-
ter of the spinal cord, where
they reach the diameter of
130 or 135 mmm., or seven-
teen times the size of the red
globules of the blood.

The most marked anato-
mical features of the nerve
cells are their prolonga-
tions. These are narrow
processes or extensions of
the cell substance, and con-
sisting apparently of the
same material. In the gan-
glia of the sympathetic sys-
tem, and in those situated
upon the roots of the spinal
and cranial nerves in man,
the nerve cells have for the
most part a rounded form,
and only one or two pro-
longations. Throughout the
gray substance of the braiu

Fig. 142.

**" ™

°' ""

Trait6 des Sections Nerveuses, p. 54.

414 GENERAL STRUCTURE AND FUNCTIONS

and spinal cord, on the contrary, they present three, four, five, or even
eight prolongations, running in different directions and giving to the
cell a peculiar radiated appearance. The prolongations after a certain
distance become branched, the branches thus formed again dividing
and subdividing, growing at the same time smaller in size, until they
terminate in a more or less abundant tuft or ramification of exceedingly
slender filaments. According to Gerlach, the terminal fibres of this
ramification constitute a plexus of fine nervous threads, penetrating
the interstitial substance of the gray matter. It is not, however, known
with certainty whether these fibres terminate by free extremities, or
whether they form a network of communication between different nerve
cells.

Connection between the Nerve Cells and Nerve Fibres. — In all cases
the nerve fibres are connected, at their central origin, with masses of
gray substance, into which they penetrate and in which they are inti-
mately mingled with the nerve cells. In some instances, a direct con-
tinuity can be seen between the nerve fibres and certain prolongations
of the nerve cells ; in others, such a direct anatomical connection is only
rendered more or less probable by the similarity in direction between
the nerve fibres and the processes of the nerve cells, and by their resem-
blance in physical constitution.

In the ganglia of the sympathetic system and in those of the roots of
the spinal and cranial nerves, the nerve cells of a rounded form give
off, as a rule, in man and the mammalians, only a single, pale, undivided
process, which at first presents the appearance of an axis cylinder of
small diameter, but which subsequently increases in size and becomes
provided with a medullary layer, assuming at the same time the distinct
double contour, characteristic of a fully formed nerve fibre. These cells,
sending out a single nerve process in one direction, are called " unipolar"
nerve cells. In the ganglia of the spinal nerve roots, and in the Gasse-
rian ganglion of fishes, nerve cells are found which send off two such
processes in opposite directions ; the medullary layer of the nerve fibre
ceasing on each side just before its union with the body of the cell.
Such cells, with two opposite nerve processes, are called "bipolar" nerve
cells. These connections have been recognized by all observers, and
there is no doubt as to their existence.

In the gray substance of the brain and spinal cord, the nerve cells, as
above described, are " multipolar," or send out a number of prolonga-
tions, in different directions, which divide and ramify without making
any certain anatomical connection with other parts. Beside these
branching prolongations, however, according to the observations of
Deiters, confirmed by Schultze, Gerlach, and Kolliker, the multipolar
nerve cell also sends out a single prolongation which is different from
the others, in that it does not branch but continues on its course for a
considerable distance, presenting the usual physical aspect of a naked
axis cylinder. This simple unbranched process is called the "axis
cylinder process," to distinguish it from the remaining ramified pro-

OF THE NERVOUS SYSTEM. 415

longations. Cells of this description, provided both with ramified pro-
longations and with a single unbranched axis cylinder process, are
found abundantly in the spinal cord, the medulla oblongata, the cerebel-
lum, the corpora striata, and the optic thalami. The axis cylinder pro-
cess, in the spinal cord, passes into the bundles of medullated nerve
fibres forming the roots of the nerves and the columns of the cord ; and
in the convolutions of the cerebellum and the cerebral ganglia, the nerve
fibres which penetrate the gray substance lose their medullary layer
and become reduced to the condition of a naked axis cylinder, similar in
appearance to the prolongations of the nerve cells. For these reasons
it is considered probable that the nerve fibres are connected by con-
tinuity of substance with the axis cylinder process of the nerve cells.
But, according to the most careful observers,1 this connection is more or
less hypothetical, and is not positively shown by direct observation. It
is evident that there is a physiological communication between the nerve
fibres and the nerve cells-; but it is possible that such a communication
may take place by other methods than an immediate continuity of their
substance.

Finally, it is certain that there are nerve cells in the gray matter
which are not directly connected with nerve fibres. According to the
observations of Gerlach, there is a tract throughout the dorsal portion
of the spinal cord, near the central part of its gray substance, where all
the nerve cells are provided with branching prolongations, but do not
possess any undivided process resembling a cylinder axis. It is not
known whether such cells exist also in other portions of the nervous
system.

Physiological Properties of the Nerve Cells. — The nerve cells, and
the gray substance of which they form a part, act as centres, in which
the nervous impressions are received through the sensitive nerve fibres
from the periphery, and from which a stimulus is sent out through the
motor fibres to the muscles. Every collection of gray substance is
therefore called a "nervous centre." While the nerve fibres accordingly
are organs of transmission onty, the gray substance and its nerve cells
constitute an apparatus in which the nervous influence is modified in
character, and changed from one form to another. Their function is
to receive impressions conveyed to them by the nerve fibres, and to
convert these impressions into impulses which are transmitted to dis-
tant organs. The nature of the process by which this change is effected,
and the action which goes on in the nerve cells during its accomplish-
ment, are entirely unknown to us ; but it is evidently essential to the
physiological operation of the nervous system, since neither sensation
nor movement is ever excited, in the natural condition, through the
nerve fibres, unless they are in communication with the gray substance
of a nervous centre.

1 Kolliker, Elements d'Histologie Humaine, 5me Edition. Paris, 1868, pp. 361,
363, 365, 399.

416 GENERAL STRUCTURE AND FUNCTIONS, ETC.

Reflex Action of the Nervous System. — The nervous system thus
stands as a medium of communication between different parts of the
living body, so that a stimulus applied to one organ may excite the
activity of another. This communication between adjacent or distant
parts is never direct, but always a circuitous one. It passes invariably
through an intermediate nervous centre, which receives the impression
conveyed to it by nerve fibres from one organ, and reacts by sending
out a stimulus which calls into activity the other. This is called
the "reflex action" of the nervous system, because the stimulus is first
sent inward to the nervous centre and then returned or reflected in the
opposite direction. In this process, the intermediate act between the
inward and outward passage of the nervous stimulus is accomplished in
the gray substance of the nervous centres.

CHAPTEE II.

NERVOUS IRRITABILITY AND ITS MODE OF
ACTION.

THE property possessed by nerves of being called into excitement by
an appropriate stimulus is termed their " irritability." This property
is not confined to the elements of the nervous system, but exists also in
other tissues and organs. Each organ or anatomical element, when
subjected to the application of a stimulus adapted to its physiological
character, reacts in a way peculiar to itself and produces a visible result
of a definite kind. Thus a glandular organ, when excited, exhibits the
phenomena of secretion ; a muscle or a muscular fibre, those of contrac-
tion. The visible result of glandular activity is the accumulation and
discharge of the secreted fluids, that of muscular contraction is a change
of form in the muscle, and a movement of the parts to which it is at-
tached. The irritability of a nerve or a nerve fibre, on the other hand, is
not manifested by any perceptible change in its own substance, but by
the phenomena of sensation or motion in the organs to which it is
distributed.

Irritability of Sensitive Fibres.

The irritability of the sensitive nerve fibres is most directly mani-
fested during life by the production of sensation. This sensation,
however, does not exist in the nerve itself, but in the nervous centre
where its fibres terminate. The proof of this is that if the communica-
tion between any part of a sensitive nerve and the brain be cut off by
division of the nerve fibres, no stimulus subsequently applied to the
separated trunk or branches of the nerve will produce any perceptible
sensation. If, however, the connection between the nerve and the
nervous centre be retained, while that with the external integument be
cut off, stimulants of various kinds applied to the nerve itself will pro-
duce a sensation which is more or less acute according to the stimulus
employed. Pinching or pricking the nerve, variations of temperature,
or the passage of an electric current, will all have the effect of bringing
into action the nervous irritability, and thus producing the effect of a
sensation.

In order to accomplish this result, however, two conditions are essen-
tial. First, the nerve must be, as above mentioned, in communication
with the nervous centre where the sensation is to be perceived ; and
secondly, the nerve fibres themselves must retain their power of
irritability. The irritability of a sensitive nerve may be so deadened

(417)

418 NERVOUS IRRITABILITY

by the compression of a bandage or the application of cold, that no
stimulus applied to the part will produced any perceptible effect. Ac-
cording to the observations of Weir Mitchell,1 the application of extreme
cold, in man, to the region of the ulnar nerve at the elbow produces,
when the chilling process has reached a certain stage, complete loss of
sensibility in the parts to which the nerve is distributed. The irrita-
bility of sensitive nerve fibres may also be temporarily suspended by
mechanical injuries in their immediate neighborhood, not involving the
fibres themselves. Thus a division of certain parts of the white sub-
stance in the brain or spinal cord, is known to produce a loss of sensi-
bility in particular regions of the body, which may disappear after a
short time, notwithstanding that the wounded fibres remain ununited ;2
and according to the observations of L'Etievant,3 section of one branch
of a sensitive nerve, beside the persistent anaesthesia of the divided
fibres, may also cause a temporary loss of sensibility in neighboring
fibres, derived by anastomosis from other branches.

The irritability of sensitive nerve fibres may also be abnormally
increased by vascular congestion, or local injuries. The application of
cold, or shutting off the supply of blood by the ligature of arteries,
may produce in the nerve, before it reaches the stage of insensibility, a
condition of unnatural excitement which is indicated by pain, in the
parts corresponding to its distribution.

During life the irritability of sensitive nerves is manifested by the
evidences of conscious sensation. After death, as in a decapitated
animal, it may also be shown to exist, for a certain time, by the reflex
actions taking place in the spinal cord or in other parts of the nervous
system.

Irritability of Motor Fibres.

The motor nerves are especially convenient for studying the action
of nervous irritability, because their excitement has for its result a
visible muscular contraction ; and this may take place, even when the
nerve and its muscle have been separated from the rest of the body.
To produce this result, however, as in the case of the sensitive nerves,
two conditions are requisite, namely; first, the nerve fibre must pre-
serve its normal irritability ; and secondly, the muscular tissue must
also be capable of responding to a stimulus by the contraction of its
fibres. The laws regulating these two sets of phenomena may therefore
be studied in connection with each other.

Mode of exhibiting Muscular Irritability. — This is best shown in the
cold-blooded animals, since in them it continues active for a longer time
than in the birds and mammalians. A frog's leg is separated from the
body of the animal, the skin removed, and the poles of a galvano-electric

1 Injuries of Nerves and their Consequences. Philadelphia, 1872, p. 59.

2 Veyssiere, Recherches sur PHemianaesthe'sie. Paris, 1874, p. 78.
8 Traite des Sections Nerveuses. Paris, 1873, pp. 171, 192.

AND ITS MODE OF ACTION.

419

apparatus (Fig. 143, a, 6) applied to the surface of Fig. 143.

the denuded muscles. A contraction takes place

each time the circuit is completed, when the elec-

tric discharge passes through the limb. In this case,

the stimulus is applied directly to the muscles, and

shows that their irritability, or power of contrac-

tion under the influence of an exciting cause, does

not depend upon their remaining in connection

with the nerves or nervous centres. A single mus-

cular fibre, in fact, separated from all neighboring

parts, may sometimes be seen to contract under the

microscope for a certain time after its removal from

the muscular tissue. The muscles will also respond

by contraction to various other kinds of mechanical

or chemical stimulus, such as pinching, pricking,

cauterizing, the contact of hot or cold bodies, or FROG'S LEG, with

the application of various acid, alkaline, or saline vanic battery applied

solutions. The most efficient and manageable stimu- to the muscles at

lus, however, is the electric discharge.

Mode of exhibiting Nervous Irritability. — In order to exhibit the
irritability of the motor nerve fibres, a frog's leg is prepared, as in the
preceding experiment, except that the sciatic nerve is cut off at its
point of emergence from the spinal canal, and dissected from the adja-
cent tissues, so that a considerable portion of it is left exposed, but
retaining its connection with the separated limb
(Fig. 144). If the two poles of a galvanic battery
be now placed in contact with different points (a, 6)
of the exposed nerve, and a current allowed to pass
between them, at the moment of its passage a con-
traction takes place in the muscles below. It will
be seen that this experiment is altogether different
from the one represented in Fig. 143. In that case
the electric discharge passes through the muscles
themselves, and acts upon them by direct stimulus.
Here the current passes only from a to b through
the tissues of the nerve, and acts directly upon the
nerve alone; while the nerve, acting upon the
muscles by its own special agency, causes in this
way a muscular contraction. So long, therefore,
as the muscles are in a healthy condition, their con-
traction, under the influence of a stimulus applied
to the nerve, demonstrates the irritability of the
latter, and may be used as a convenient measure of
its intensity.

The irritability of a motor nerve continues after
death. The knowledge of this fact follows from the "cittto
what has been said with regard to experimenting attached
upon the frog's leg, prepared as above. The irrita-

Fig. 144.

b, Poles

420 NERVOUS IRRITABILITY

bility of the nerve, like that of the muscles, depends directly upon its
anatomical structure and constitution; and so long as these remain
unimpaired, the nerve will retain its vital properties, though respira-
tion and circulation may have ceased. For the same reason, nervous
irritability lasts longer after death in the cold-blooded than in the
warm-blooded animals. Yarious artificial irritants may be employed
to call it into activity. Pinching or pricking the exposed nerve with
steel instruments, the application of caustic liquids, and the passage of
galvanic discharges, all have this effect. The galvanic current, how-
ever, is the best means to employ for this purpose, since it is more
delicate in its operation than the others, and will continue to succeed
for a longer time.

The nerve is so sensitive to the galvanic current that it will respond
to it when insensible to all other kinds of stimulus. A frog's leg
freshly prepared, as above, with the nerve attached, will react so readity
when a discharge is passed through the nerve, that it forms an ex-
tremely delicate instrument for detecting the presence of electric cur-
rents of low intensity, and has been sometimes used for this purpose
under the name of the " galvanoscopic frog." It is only necessary to
introduce the nerve as part of the electric circuit ; and if even a very
feeble current be present, it is at once betrayed by a muscular con-
traction.

Nervous irritability, like that of the muscles, is exhausted by repeated
excitement. If a frog's leg, prepared in the manner above described,
with the sciatic nerve attached, be allowed to remain at rest in a damp
and cool place, where its tissue will not become altered by desiccation,
the nerve will remain irritable for many hours ; but if it be excited,
soon after its separation from the body, by repeated shocks, it begins
to react with diminished energy, and becomes gradually less irritable,
until at last it ceases to exhibit any further excitability. If it be now
allowed to remain for a time at rest, its irritability will be partially
restored ; and muscular contraction will again ensue on the application
of a stimulus to the nerve. Exhausted a second time, and a second
time allowed to repose, it will again recover itself; and this may be
repeated several times in succession. At each repetition, however, the
recovery of nervous irritability is less complete, until it finally disap-
pears altogether, and can no longer be recalled. The irritability of the
muscles may be exhausted, in a similar way, by repeated excitement.

Yarious circumstances tend to diminish or suspend the irritabilit}^ of
the motor nerve fibres. As in the case of the sensitive fibres, compres-
sion, cold, or other similar agencies will depress the power of the
muscular nerves, so that they can no longer excite a contraction when
subjected to the galvanic current. Severe and sudden mechanical in-
juries often have the same effect ; as where general muscular relaxation,
or diminished power of voluntary motion, is produced by any extensive
contusion or laceration of one of the limbs. Such an injury produces a
general disturbance or shock^ which affects the entire nervous system,

AND ITS MODE OF ACTION. 421

and destroys or suspends its irritability. The effects of a nervous
shock of this kind may frequently be seen in man after railroad acci-
dents, where the patient, though extensively injured, may remain for
some hours in a state of unusual muscular debility, and at the same time
without the sensation of pain. It is only after reaction has taken place,
and nervous irritability has been restored by repose, that the powers of
sensation and voluntary motion are re-established.

It is often found, on preparing the frog's leg for experiment as above,
that immediately after the limb has been separated from the body and
the integument removed, the nerve is destitute of irritability. Its
vitality has been suspended by the violence inflicted in the preparatory
operation. In a few moments, if kept under favorable conditions, it
recovers from the shock, and regains its natural irritability.

Different Action of the Direct and Inverse Currents. — The action
of the galvanic current upon the nerves, as first shown by Matteucci, is
in many respects peculiar. If the current be made to traverse the nerve
in the natural direction of its fibres, namely, from its origin toward its
distribution, as from a to b (Fig. 144), it is called the direct current.
If it be made to pass in the contrary direction, as from b to a, it is called
the inverse current. When the nerve is fresh and exceedingly irritable,
or when the galvanic current is of sufficient intensity, a muscular con-
traction takes place at both the commencement and termination of the
current, whether it be direct or inverse. But when the activity of the
nerve has become somewhat diminished, or when the current emploj^ed
is of feeble intensity, contraction takes place only at the commencement
of the direct and at the termination of the inverse current. This may
readily be shown by preparing the two legs of the same frog in such a
manner that they remain connected with each other by the sciatic nerves

Pi?. 145.

and that portion of the spinal column from which these nerves take their
origin. The two legs, so prepared, are placed each in a vessel of water,
with the nervous connection hanging between. (Fig. 145.) If the posi-
tive pole, a, of the battery be now placed in the vessel which holds leg

422 NERVOUS IRRITABILITY

No. 1, and the negative pole, 6, in that containing log No. 2, it will be
seen that the galvanic current will traverse the two legs in opposite
directions. In No. 1, it will pass in a direction contrary to the course
of its nervous fibres, that is, it will be for this leg an inverse current ;
while in No. 2 it will pass in the same direction with that of the nervous
fibres, that is, it will be for this leg a direct current. It will now be
found that at the moment when the circuit is completed, a contraction
takes place in No. 2 by the direct current, while No. 1 remains at rest ;
but at the time the circuit is broken, a contraction is produced in No. 1
by the inverse current, while no movement takes place in No. 2. A suc-
cession of alternate contractions may thus be produced in the two legs
by repeatedly closing and opening the circuit. If the position of the
poles, a, 6, be reversed, the effects of the current will be changed in a
corresponding manner.

After a nerve has become exhausted by the direct current, it is still
sensitive to the inverse ; and after exhaustion by the inverse, it is still
sensitive to the direct. It was even found by Matteucci that after a
nerve has been exhausted for the time by the direct current, the return
of its irritability is hastened by the subsequent passage of the inverse
current ; so that it will become again sensitive to the direct current
sooner than if allowed to remain at rest. Nothing, accordingly, is so
exciting to a nerve as the passage of direct and inverse currents, alter-
nating with each other in rapid succession. Such a mode of applying
the electric stimulus is that afforded by the Faradic apparatus, in which
momentary currents of induced electricity are made to traverse the cir-
cuit in two opposite directions in rapid alternation.

The irritability of motor nerves is distinct from that of the muscles.
This is shown by the fact that the two properties may be destroyed
or suspended independently of each other. When the frog's leg has
been prepared and separated from the body, with the sciatic nerve at-
tached, the muscles contract, as shown above, whenever the nerve is
irritated. The irritability of the nerve, therefore, is manifested in this
instance only through that of the muscle, and that of the muscle is
called into action only through that of the nerve. But the action of
woorara has the power, as first pointed out by Bernard,1 of destroying
the irritability of the nerve without affecting that of the muscles. If a
frog be poisoned by this substance, and the leg prepared as above, the
poles of a galvanic battery applied to the nerve will produce no effect.
But if the galvanic discharge be passed directly through the muscles,
contraction takes place. The muscular irritability has survived that
of the nerves, and must therefore be regarded as essentially distinct
from it.

There are, therefore, two kinds of paralysis : first, a muscular par-
alysis, in which the muscular fibres themselves are directly affected ;

1 Le<jons sur la Physiologic du Systfeme nerveux. Paris, 1858, tome i. p. 199.

AND ITS MODE OF ACTION. 423

and secondly, a nervous paralysis, in which the affection is confined to
the nerve fibres, the muscles retaining their natural properties, and being
still capable of contraction under the influence of direct stimulus.

Identity of Action in the Sensitive and Motor Nerve Fibres.

The results which are produced by the physiological action of the
nerve fibres differ from each other in the two classes to which they
belong. The stimulation or excitement of the sensitive fibres produces
a sensation, or a sensitive impression in the nervous centre ; that of the
motor fibres causes contraction of the muscles to which they are distrib-
uted. Moreover, if a sensitive nerve or nerve fibre be divided, stimulus
applied to its central or attached extremity still excites a sensation,,
while the application of the same stimulus to its separated or peripheral
portion produces no apparent result. On the other hand, if a motor
nerve be divided, irritation of its attached extremity, which is still in
connection with the nervous centre, is without effect ; but irritation of
its peripheral portion causes a muscular contraction as before. In other
words, the nervous force, in a sensitive nerve, appears to move always
in a centripetal direction, that is from without inward ; in a motor nerve,
on the other hand, in a centrifugal direction, or from within outward.
In the natural condition of the parts, also, the excitement of a sensitive
nerve never produces directly any other effect than sensation ; that of a
motor nerve only gives rise to the phenomena of movement.

These facts easily suggest the idea that the two kinds of nerve fibres
may be distinct in their properties and modes of action ; that the sensi-
tive fibres may be capable of acting only in a centripetal direction and
of exciting the phenomena of sensibility ; and that the motor fibres
can only act from within outward and transmit a special kind of nerve
force, adapted to excite muscular contraction.

It is evident, however, that the reasons given above are not sufficient
to indicate a difference in the activity of the nerves themselves, but only
in the sensible results of its operation. In neither case is there any
perceptible effect produced in the nerve, but only in the organ with
which it is in connection. When a sensitive nerve is excited, the sensa-
tion is perceived in the nervous centre ; when a motor nerve is called
into activity, the contraction is performed by the muscular fibres at its
periphery. It is possible that the condition of the nerve fibres, when in
a state of excitement, may be the same in each instance, and that the dif-
ference in the effect produced may be due to the different physiological
properties of the organs in which they terminate ; just as the conducting
wire of a galvanic battery may be made to ring a bell or move an index,
according to the mechanism with which its poles are connected. There
are certain facts which can hardly bear any other interpretation than
this, and which lead to the conclusion that the physiological action in
the nerve fibres themselves is not essentially different in different kinds
of nerves.

42-i NERVOUS IRRITABILITY

1. The stimulus applied to a nerve, whether sensitive or motor, pro-
duces the same effect throughout its entire length.

In the natural condition of the parts, the impressions made upon the
external integument, when they give rise to sensation, are transmitted
by the sensitive nerve through its whole course to the nervous centre.
There it is perceived as a sensation; and the sensation thus produced is
referred by the individual, not to the brain or to any part of the nerve,
but to the integument where the nerve originated. If an irritation be
applied to the nerve in the middle of its course, the sensation is still
perceived as if it came from the same portion of the integument and had
travelled through the same distance as before. It is well known that
after amputation of a limb in the human subject, if the severed extremity
of one of the nerves happen to be compressed or otherwise irritated by
the tissues of the cicatrix, or if it be the seat of inflammatory action,
many different sensations of pain, movement, heat, or cold, are excited,
which are always referred by the individual to the amputated portion
of the limb ; and patients often assert that they can feel the separated
parts as distinctly as if they were still attached to the body. The im-
pression conveyed through the remaining portion of the nerve is the
same as if the whole of it were still in existence.

The action of the motor nerves is of a similar kind. A voluntary
stimulus, which originates in the brain, passes through the entire length
of a motor nerve to reach the muscles and excite their contraction.
But if the nerve be divided at any intermediate point, and a galvanic
stimulus applied to the peripheral portion, a contraction follows in the
same muscles as before. In each case, the physiological effect is pro-
duced at the extremity of the nerve fibres ; and it seems to make no
essential difference in its character from how great a distance it has
been transmitted.

So far as yet known, therefore, the nerve fibre, whether sensitive or
motor, when its irritability is excited, may be thrown at once into a
condition of activity throughout its entire length; the whole nerve
assuming a state of polarity, analogous to that of a magnetized bar, in
which the visible phenomena of attraction or repulsion are manifested
only at its extremities, although the whole substance of the bar partici-
pates in its magnetic molecular action. When the exciting stimulus, as
in the sensitive nerves, is naturally applied at the peripheral extremity,
it must necessarily be communicated from without inward ; and when
it commences at the inner extremity, as in a motor nerve, it must move
in a direction from within outward. But nothing thus far shows that
it may not be capable of moving in either of these two directions in the
same nervous fibre. The following experiments show that this is in
reality the case, so far as regards the sensitive nerves.

2. Sensitive impressions may pass, in the fibres of a sensitive nerve,
either from without inward or from within outward.

This of course never takes place in the natural condition of the parts ;
but its possibility has been demonstrated, in the experiments of Paul

AND ITS MODE OF ACTION. 425

Bert,1 by dividing a sensitive nerve and then reversing its position,
so that its peripheral extremity is brought into connection with the
nerve centres. The end of the tail, in a young rat, was deprived of its
integument for a length of five centimetres, and the denuded portion
inserted beneath the integument of the back of the same animal. At
the end of eight days, when the ingrafted portion had become adherent
to the subcutaneous tissues, and had contracted sufficient vascular con-
nection for its support, the tail was amputated at its base, and thence-
forward remained attached to the body of the animal only by what was
previously its peripheral extremity. In three months the signs of sensi-
bility again began to be manifested when the end of the tail, thus re-
versed, was subjected to compression ; and at the end of six months its
sensibility was re-established to an unmistakable degree. The nerves
of the tail, which before the operation transmitted sensitive impressions
from its point toward its base, afterward transmitted the same impres-
sions from its base toward its point.

There is no evidence, therefore, that nerve fibres are endowed with two
different modes of action, one for sensation, the other for motion. In
each case the condition of the nerve itself may be of the same nature.
But, being thrown into a state of excitement throughout its entire length,
it communicates a stimulus to the organ with which it is connected. If
this organ be a perceptive nervous centre, the effect produced is a sen-
sation ; if a muscle, it results in contraction and movement. These acts
cannot be interchanged with each other, because the muscle cannot feel
and the nervous centre is incapable of contraction ; but they are both
indirect effects of the nervous influence, and do not necessarily depend
upon any difference in its nature.

Rapidity of Transmission of the Nerve Force,

It is a matter of conscious experience that the operations of the nerv-
ous system require a certain time for their accomplishment. The action
both of the senses and of the will is exceedingly rapid, but still is not
absolutely instantaneous. Between the mental decision to perform a
voluntary movement and its actual execution, there is a short but real
interval of time, during which the nervous mechanism is called into
activity. A certain period also intervenes between the contact of a
foreign body with the skin, and our complete perception of its existence
and qualities. There is even more or less difference between individuals
in the length of time required for the performance of nervous action ;
the quickness of the senses and the promptitude of the will frequently
varying to a perceptible degree. In the case of a voluntary movement,
the period consumed in its entire accomplishment may be occupied
by three different processes, namety : 1. The act of volition, taking
place in the brain ; 2. The transmission of the motor impulse, through
the spinal cord and nerves, to their peripheral terminations ; and 3. The

1 La Vitalit6 propre des Tissues animaux. Paris, 1866, p. 12.

28

426 NERVOUS IRRITABILITY

excitement of the muscular fibres to a state of contraction. In the case
of a sensation, there are also three analogous successive acts, namely :
1. The reception of the impression by the sensitive membrane; 2. Trans-
mission of the stimulus through the nerve fibres inward; and 3. Its per-
ception in the brain as a conscious sensation. It is an important phy-
siological problem to determine the degree of rapidity with which the
transmission of stimulus takes place through the nerve fibres in either
direction ; and it has recently become a matter of practical interest in
relation to pathology.

Methods of determining the Rate of Transmission of the Nerve Force.
— The measurement of the rate of transmission of the nerve force was
first accomplished by Helmholtz,1 and has since been carried out by a
number of different observers with essentially similar results. The
principle adopted is in all cases the same. Muscular contraction is
excited by a stimulus which passes through two nerves of different
length, or through two different lengths of the same nerve ; the delay
in contraction, when the stimulus passes through the greater of these
two distances, gives the time required for its transmission by the inter-
vening nerve fibres.

These experiments were first performed upon nerves rnd muscles
freshly separated from the body in the cold-blooded animals. The gas-
trocneinius muscle of a frog is prepared, with a portion of the sciatic
nerve attached. A galvanic battery with an induction apparatus is also
provided, so that the closure of the circuit of the battery will produce
an instantaneous electric current in the induction coil. By this means
the stimulus of the induced current is first applied to the muscle itself,
and the time noted which intervenes between the closure of the circuit
and the muscular contraction. This represents the period required for
the excitement of the muscular fibres themselves, and was found in the
experiments of Helmholtz to be about T^ of a second. If the stimulus
be now applied to the nerve in immediate proximity to the muscle, the
above interval is not perceptibly altered. But if it be applied to the
nerve at a point one, two, or three centimetres distant, a decided retarda-
tion is manifested in the muscular contraction ; and this retardation
becomes greater as the length of the nerve, between the muscle and the
point of stimulation, is increased.

The intervals of time in these experiments have been measured by
various contrivances, the most successful of which depend upon the use
of an automatic registering apparatus, on the principle of that employed
by Marey.2 In this apparatus, a card, with its surface blackened by
smoke, moves by clockwork, with uniform velocity, in a horizontal
direction. Upon this card the extremity of a diapason or tuning fork,
vibrating 500 times per second, traces an undulating line (Fig. 146, a)
which records the time occupied by the card in moving from one point

1 Comptes Eendns de 1'Academie des Sciences. Paris, 1851. tome xxxiii. p. 262.

2 Du Mouvemcnt duns les Fonctioris de la Vie. Paris, 1868, p. 422.

AND ITS MODE OF ACTION. 427

to another. A straight horizontal line (b , is also traced upon the card
by the extremity of a slender steel lever, the other end of which forms
a part of the galvanic circuit. The closure of the circuit is accom-
plished by a movement which pushes aside this lever, and thus causes a

Fig. 146.

DIAGRAM OF THE REGISTERING APPARATUS, according to the plan of Marey.
a. Undulating line traced by the diapason, which marks the time consumed by the card in
moving from one point to another, b. Line traced by the first lever, forming part of the
galvanic circuit, c Line traced by the second lever, which is moved by the contraction of
the muscle, d. Deviation of the line 6, indicating the closure of the galvanic circuit and the
stimulation of the nerve, e. Deviation of the line c, indicating the muscular contraction.

deviation (d ) in the line traced by its extremity. This deviation registers
upon the card the instant of the closure of the circuit, and consequently
that of the stimulation of the nerve. The muscle used for experiment
is fixed in position, with its tendon attached to a second lever in such a
way that any muscular contraction will draw aside its free extremity.
This lever traces upon the card a second straight horizontal line (c)
parallel to the first ; and when the muscle contracts, the line is devi-
ated, as at (e), by the lateral movement of the lever.

Thus when the experiment has been performed, there are left upon the
surface of the card two deviations d and e, one of which represents the
stimulation of the nerve, the other the muscular contraction; and between
the two is included a certain interval. The number of undulations in
the diapason-trace (a), corresponding to this interval, gives the time
which has elapsed between the stimulation of the nerve and the contrac-
tion of the muscle. In the example shown in Fig. 146, as the interval
between the deviations includes 13 simple variations, of which 500
would represent one second, the time occupied is 0.026 of a second.
By this means, intervals of time of very short duration may be registered
and compared with accuracy.

Subsequently to the experiments upon separated nerves and muscles
in the lower animals, investigations of a similar kind were extended to
the human subject during life. In the experiments of Baxt,1 this was
done by applying the electrodes to the surface of the skin immediately
over the situation of the median nerve, and at varying distances from
the muscles to which its fibres are distributed. The nerve was thus

1 Monatsbericlit dor Eoniglichen Freussischen Akademie, April, 1867, and
March, 1870.

428 NERVOUS IRRITABILITY

stimulated at the wrist, at the elbow, and at the upper arm near the
lower extremities of the coraco-brachialis and deltoid muscles ; the effect
of the stimulation being marked by the swelling of the muscles at the
ball of the thumb. Here also it was found that the intervening time
between the application of the electrodes and the muscular contraction
was greater when the stimulus was applied to the nerve at the upper
arm, than when applied at the wrist ; this increased interval being evi-
dently the time required for the transmission of the nervous impulse
from one point to the other. The rate of transmission, as ascertained
by these experiments, was found to vary considerably according to the
different conditions of cold and warmth; the transmission in the me-
dian nerve, when subjected to cold, being sometimes less than one-half
as rapid as in the same nerve at a higher temperature.

Finally, in the experiments of Burckhardt,1 the rate of transmission of
the nerve force, for voluntary motion and the acts of conscious sensa-
tion in man, has been investigated at considerable length. In these
experiments, an automatic registering apparatus was employed, in which
the beginning and end of the nervous transmission were marked, as
above, by corresponding deviations of a traced line.

Hate of Transmission in the Motor Nerves. — The transmission of
the voluntary impulse was measured in Burckhardt's investigations as
follows : The galvanic battery and the registering apparatus being pro-
perly attached to the person serving for experiment, the signal for the
contraction of a particular muscle was given by the sound of a bell
connected with the battery. Thus the entire interval registered was
that between the sound of the bell and the muscular contraction. A
part of this time was consumed in the double act of hearing the sound
and producing the volitional impulse. A part was also taken up in the
local process of muscular contraction, and only the remainder was occu-
pied in that of nervous transmission. But it is evident that, if, in two
different observations, the same signal were used for the contraction of
two -muscles supplied by different lengths of nerve, the process taking
place in the brain and that taking place in the muscle would be alike
in both ; and any difference in the time observed must be due to the
different distances of nerve fibre traversed by the voluntary motor
impulse. The muscles employed for this purpose were, in the lower
limb, the extensor digitorum communis brevis, tibialis anticus, and
semimembranosus, supplied by branches of the sciatic nerve, and the
quadriceps extensor cruris, supplied by the anterior crural nerve; in
the upper limb, the interosseus externus primus, extensor digitorum
communis, flexor digitorum and deltoid, all supplied by branches of
the brachial plexus. The result of all the observations upon eight
different healthy persons was, that the mean velocity of transmission
for the voluntary impulse, in the peripheral nerves of the upper and

1 Die Physiologische Diagnostik der Nervenkrankheiten. Leipzig, 187o,
p. 32.

AND ITS MODE OF ACTION. 429

lower extremities, is a little over 2t metres per second. The minimum
velocity was 20 metres, and the maximum 36 metres ; but of all the
observations, which were thirty in number, twenty-three, or nearly four-
fifths, gave results between 26 and 28 metres.

In one instance the rate of movement in the same nerve, for the
voluntary impulse and for that excited by galvanism, was tested com-
paratively, and but little difference was found to exist in the two cases.

According to Burckhardt, also, the rate of transmission does not vary
essentially for weak or strong motor impulses; that for a muscular con-
traction of moderate force passing as rapidly through the nerve as that
for contractions of greater power.

Rale of Transmission in the Sensitive Nerves. — The rate of trans-
mission for impressions of conscious sensibility is determined by an
analogous method. An irritation or tactile impression is produced
upon the skin at varying distances from the nervous centres — as, for
instance, upon the foot, the thigh, and the loins ; and the instant at
which the sensation is perceived is indicated by a movement of the
finger. As the time required for the act of conscious perception in
the brain and for the voluntary movement of the finger is the same
in all cases, the difference between two successive observations is owing
to the different lengths of the nerves transmitting the stimulus.

In the investigations of Burckhardt, which were made upon thirteen
different individuals, the mean rate of transmission for sensitive impres-
sions through the peripheral nerves was found to be a little less than
47 metres per second; that is, more than one and a half times as rapid
as that for voluntary motion. The variations were from a minimum
of 20 to a maximum of 73 metres; but in nearly three-fourths of all the
observations, the results were confined within a variation of from 40 to
56 metres. The rapidity of transmission varied but little with the in-
creased or diminished intensity of the impression; the difference, on
the average, being but little over one per cent.

Eate of Transmission in the Spinal Cord. — The investigations of
Burckhardt first indicated a difference between the rate of transmission
in the spinal cord and that in the peripheral nerves. This rate was
determined for the spinal cord by comparing the time consumed in
the passage of a voluntary impulse to the extremities of two nerves,
like the sciatic and the ulnar, which emerge from the spinal cord at
different points. In this case the voluntary impulse, after leaving the
brain, will traverse different lengths of the spinal cord ; and as its rate
of movement in the peripheral nerves is known, the difference in the
time of its entire passage may be easily referred to its increased or
diminished rate of movement in the spinal cord. Thus a motor impulse,
which calls into action the interosseous muscles of the hand, passes
through the cervical portion of the spinal cord, and thence through the
lower cervical nerves, the brachial plexus^ and the whole length of the
ulnar nerve. An impulse which excites contraction in the quadriceps
extensor cruris passes through both the cervical and dorsal portions of

430 NERVOUS IRRITABILITY

the spinal cord, and thence through the lumbar plexus and the anterior
crural nerve to the thigh. Consequently its transit through the spinal
cord is about three times as long in the second instance as in the tirst ;
and its amount of retardation will indicate the rate of transmission in
the spinal cord as compared with that in the nerves.

By this means it was found that the transmission of voluntary motor
impulses in the spinal cord is considerably slower than in the nerves.
Its average rapidity was a little over 10 metres per second ; the mini-
mum being 8, the maximum 14 metres. Thus the difference in rapidity
of transmission through the nerves and the spinal cord becomes very
manifest.

TRANSMISSION OF VOLUNTARY MOTOR IMPULSES.
Through the spinal cord . . . .10 metres per second.
" " nerves . . . . 27 "

A comparison of observations on the two opposite sides of the body
gave a difference in the rate of transmission, for the right and left
lateral halves of the spinal cord, of from 1 to 3 metres per second,
always in favor of the left side.

The transmission of sensitive impressions through the spinal cord,
on the other hand, was found to be nearly as rapid as through the
nerves, the average rate being a little over 42 metres per second. A
remarkable difference, however, appeared in the transmission of simple
tactile impressions and of those which were painful in character. The
former are comparatively rapid, as above stated, while painful impres-
sions are communicated through the spinal cord at a much slower rate,
amounting on the average to not more than 13 metres per second.
Thus the transmission of motor impulses and of tactile and painful
impressions respectively, through the spinal cord, is as follows :

RATE OF TRANSMISSION THROUGH THE SPINAL CORD.
For tactile impressions . . . .42 metres per second.

" painful 13 "

" motor impulses ... . 10 "

According to these results the passage of a motor impulse, from the
brain to the muscles of the foot, would occupy 0.088 of a second ; of
which time about one-half would be required for transmission through
the spinal cord, and one-half for transmission through the fibres of the
sciatic nerve.

Rapidity of Nervous Action in the Brain. — In all the experiments
detailed above, an essential part of the nervous operation consists in
the hearing of the signal for a voluntary movement and in the act of
volition which sets in motion the voluntary impulse. This process,
which takes place in the brain, includes both the action of the gray
substance of the nervous centres and its transmission b}r the nerve
fibres of the white substance to the origin of the spinal cord. The time
thus consumed is ascertained by deducting, from the whole period
intervening between the signal given and the contraction of the muscle,

AND ITS MODE OF ACTION. 431

first, the time requisite for the mechanism of muscular contraction,
namely, 0.0 1", and, secondly, that occupied in the transmission of the
impulse through the spinal cord and nerves. Thus if the entire period
be 0.220", and the time required for transmission through the spinal
cord and nerves be 0.088", there remains 0.132", which is occupied in
muscular contraction and in the acts of sensation and volition. Burck-
hardt's experiments, like those of Ilelmholtz, fix the time required for
local stimulation of the muscle at 0.01" ; and he estimates that about
an equal interval is necessary for the mechanism of hearing in the
external, middle, and internal parts of the ear. The whole process,
therefore, of executing a voluntary movement in the foot, at the signal
given by a bell, would be divided in time as follows :

TIME OCCUPIED IN EXECUTING A VOLUNTARY MOVEMENT AT A GIVEN SIGNAL.

Mechanism of hearing 0.010"

Acts of perception and volition in the brain . . . 0.112"
Transmission through the spinal cord . . . . 0.044"

Transmission through the sciatic nerve .... 0.044"
Mechanism of muscular contraction ..... 0.010"

0.220"

It appears that the nervous action in the brain, which represents the
operation of the gray substance of the nervous centres, requires a con-
siderably longer time than the transmission of a nervous impulse through
the nerve fibres.

The physiological variation in rapidity of any or all the nervous
actions above enumerated, in different individuals, causes a difference
in the promptitude with which sensible phenomena are perceived and
recorded by different observers. This fact was first distinctly noticed
in astronomical observations, where it was found that the exact time
of the passage of a star across the thread of a transit instrument was
differently recorded by different observers ; this variation in some cases
amounting to as much as one second. Subsequent observations showed
that in no case was the time of the transit recorded with absolute
accuracy ; but that a certain delay always intervened, due to the time
necessarily occupied by the nervous mechanism of the observer. This
fact was established by imitating the transit of a star by means of a
single luminous point moving in a circle with uniform velocity before
the field of a telescope. By contrivances similar to those described
above, the real instant of the passage of this luminous point across the
thread of the telescope field was recorded upon a revolving cylinder,
and the observer also marked its passage by similar means. The
difference between the real and the observed time represented the
" personal error" of the observer. The amount of this error, however,
although it varies for different persons, is constant, or nearly so, for the
same individual ; and, when it has been once ascertained, the results of
observation may be so corrected as to r.pproach nearly to absolute
precision.

CHAPTEE III.

GENERAL ARRANGEMENT OF THE VARIOUS
PARTS OF THE NERVOUS SYSTEM.

IN man and the vertebrate animals the nervous system may be divided
into two secondary systems, or groups of nervous centres with their
commissural fibres and nerves. These are, first, the ganglionic or sym-
pathetic, and secondly, the cerebro-spinal system.

Ganglionic System. — The ganglionic or "sympathetic" system oc-
cupies mainly the great cavities of the body. It is connected by its
nervous branches and ramifications with the internal organs concerned
in the functions of nutrition, and more especially with the heart and
bloodvessels, which it follows throughout their peripheral distribution.
Its especial anatomical character consists in its being composed of numer-
ous separate masses or collections of gray matter, of small size and
rounded form, called "ganglia;" from which circumstance the whole
ganglionic system takes its name. These ganglia, connected with each
other by slender nervous filaments, form a double chain of distinct but
associated nervous centres, situated in front of the spinal column
throughout the neck and thorax ; while in the abdomen they are at
certain points fused together into larger and more irregularly shaped
masses upon the median line. There are also scattered ganglia about
the head, outside the cranial cavity ; and everywhere the ganglia or
their nerves receive some fibres of communication from the other divi-
sion of the nervous system. The scattered arrangement of the sym-
pathetic ganglia, and their deep situation among the thoracic and
abdominal organs, have hitherto prevented a complete investigation of
their functions ; and it is doubtful how far any one portion exercises a
central or controlling influence over the remainder.

Cerebro- Spinal System. — The cerebro-spinal system, as its name indi-
cates, is made up of the brain and spinal cord as the great nervous cen-
tres, with the nerves which originate from them and which are distributed
to the voluntary muscles and integument, the organs of special sense,
and the commencement and termination of the internal passages of
the body. It is especially distinguished by the fact that its deposits of
gray substance, instead of being distributed in separate nodules as in
the ganglionic system, are collected into two principal continuous masses,
the brain and the spinal cord, occupying the cranial and spinal cavities,
where they are enveloped and connected by tracts of white substance,
which often conceal in an external view the divisions between them.

The cerebro-spinal nervous system is also distinguished by a nearly
( 432 )

GENERAL ARRANGEMENT OF NERVOUS SYSTEM. 433

Fig. 147.

complete symmetry of arrangement. The internal abdominal organs
are in great measure unsymmetrical, and the corresponding nerves and
nervous centres of the ganglionic S3'stem present the same want of
regularity in their locality and distribution. But while the ganglionic
system presides over the internal organs and
functions of nutrition, the cerebro-spinal sys-
tem, on the other hand, is connected with the
apparatus of animal life, namely, the organs
of sensation and movement by which the
living body is brought into relation with the
exterior. As these organs, in man and the
vertebrate animals, are symmetrically ar-
ranged, tlie cerebro-spinal nervous system
presents the same character. Both the brain
and the spinal cord are composed of two,
right and left, lateral halves ; each one of
which furnishes the nerves of sensation and
motion to the corresponding sides of the
body.

Another striking peculiarity of this part
of the nervous system is the mutual decus-
sation of the nerve fibres belonging to its
two sides. Both the brain and spinal cord
have their right and left halves connected
by fibres which pass across the median line
from one to the other ; the different bundles
being often interwoven with eacli other, at
the point of transit, in a somewhat compli-
cated manner. This peculiarity extends to
the origins of the nerves, which decussate
with each other internally ; so that the nerve
fibres emerging from the right side of the
cerebro-spinal mass have their origin from
the gray substance of the left lateral half,
and those emerging from the left side origi-
nate from the gray substance of the right
lateral half. The only uncertainty in this
respect is whether the decussation be com-
plete or partial; that is, whether all the
fibres of a given nerve root be connected
with the opposite side of the central mass, or
whether a part of them originate from the
same and a part from the opposite side. The decussating fibres, in a
large number of instances, are anatomically demonstrated. In some
remaining exceptions their course is more or less a matter of doubt.

The Spinal Cord is a nearly cylindrical nervous mass, inclosed in the
cavity of the spinal canal, commencing by a slightly enlarged extremity

THE BRAIN AND SPINAL
CORD, in profile.

434 GENEKAL ARKANGEMENT OP

at the brain above, and terminating below in a conical point at the level
of the first lumbar vertebra. Its inner portions are occupied by gray
substance, which forms a continuous chain of ganglionic matter, run-
ning from one extremity of the cord to the other. Its outer portions
are composed of white substance, the fibres of which run mainly in a
longitudinal direction, connecting its different parts with each other,
and forming a communication between it and the brain.

The spinal nerves are given off from the cord at regular intervals
and in symmetrical pairs ; one pair for each successive portion of the
^ body, their branches being distributed to the integument and muscles
of the corresponding regions. In fish and serpents, where locomotion
is performed by means of simple, alternating, lateral movements of the
spinal column, the cord is nearly or quite uniform in size; or tapers
gradually from its anterior to its posterior extremity. But in the other
vertebrate classes, where the body is provided with special organs of
locomotion as fore and hind limbs, or wings and legs, the cord is in-
creased in size where the nerves of these organs are given off; and the
nerves supplying the limbs are larger than those which originate
from other parts of the cord. In man, the lower cervical nerves,
which form the brachial plexus and supply the arms, and the sacral
nerves forming the sacral plexus, which supplies the legs, are larger
than those given off in the upper cervical, dorsal, and lumbar regions.
The cord itself, furthermore, presents two marked enlargements cor-
responding with the points of origin of these nerves, namely, the cervical
enlargement, which is the source of the nerves for the upper extremity,
and the lumbar enlargement, which gives off the nerves destined for the
lower extremity.

A transverse section of the spinal cord shows that it is incompletely
divided into right and left lateral halves by an anterior and posterior

median fissure ; of which the

Fig. 148. anterior is the wider and pene-

trates for a comparatively short
distance, while the posterior is
narrower but extends inward
nearly or quite to the centre of
the cord. The gray substance
in the interior of the cord forms
a double crescentic-shaped mass,
writh the concavities of the
crescents turned outward. As
TRANSVERSE SECTION OP THE SPINAL these masses are found at all

CORD, showing its central mass of gray sub- tg of the CQrd they haye in

Btance, and the roots of the spinal nerves.— a, b.

Spinal nerves of right and left sides, d. Origin of reality the form of elongated
anterior root. e. Origin of posterior root. c. ribbons or bands of gray sub_
Ganglion of posterior root.

stance, one on each side, run-
ning continuously throughout the length of the cord. The two are
united with each other by a transverse band of gray substance, known

THE NEKVOUS SYSTEM. 435

as the "gray commissure," in the centre of which is a narrow longi-
tudinal canal, the " central canal," but little over 0.2 millimetre in di-
ameter, and lined internally with epithelium.

The anterior and posterior portions of gray substance, in each lateral
half of the cord, are called the anterior and posterior horns. Imme-
diately in front of the gray commissure is a transverse band of white
substance, the " white commissure" of the cord.

The spinal nerves originate from the cord on each side by two dis-
tinct sets of fibres, forming the anterior and posterior roots. The
anterior root (Fig. 148, d) passes out from the surface of the cord near
the extremity of the anterior horn of gray matter. The posterior root
(e) originates at a point corresponding with the posterior horn of gray
matter. Both roots are composed of a considerable number of fibres,
united with each other in parallel bundles. The posterior root is dis-
tinguished from the anterior by the presence of a small rounded mass
of gray matter, or ganglion, with which it is incorporated and through
which its fibres pass. The two roots unite with each other soon after
leaving the cavity of the spinal canal, and mingle their fibres in a common
trunk.

The white substance of each lateral half of the spinal cord is thus
divided into three portions or " columns ;" so called because the nerve
fibres composing them run, for the most part, parallel with each other,
in a longitudinal or vertical direction. The portion which is included
between the anterior median fissure and the origin of the anterior nerve
roots is the anterior column ; that between the anterior and posterior
nerve roots is the lateral column; while that between the posterior
nerve roots and the posterior median fissure is the posterior column.
As the posterior median fissure penetrates deeply into the substance of
the cord, quite down to the gray substance, the posterior columns ap-
pear entirely separated from each other in a transverse section ; but the
anterior median fissure is more shallow and stops short of the gray
matter, so that the anterior columns are connected with each other by
the white commissure above mentioned.

The brain, or "encephalon," is that portion of the cerebro-spinal
system contained in the cranial cavity. It forms a more or less
rounded mass of nervous matter, consisting, as in the spinal cord, of
right and left lateral halves which remain connected with each other by
their central parts. In man and the higher vertebrate animals, it pre-
sents, above and behind, two principal divisions, namely, the cerebrum
and cerebellum, which are composed externally of a convoluted layer of
gray substance, these two divisions together forming at least nineteen-
twentieths of the whole encephalon ; while beneath them is a smaller
portion composed externally of white substance, like the spinal cord, and
forming the communication between the cord below and the brain above.
This inferior portion is called the "isthmus," and comprehends the
medulla oblongata, the tuber annulare, and the peduncles of the cere-
brum. Beside, however, the portion visible externally, there are, in

436

GENERAL ARRANGEMENT OF

Fig. 149.

each of these divisions, various deep-seated deposits of gray substance,
which are concealed by the overlying parts.

The construction of the brain, as a whole, may therefore be represented
by considering it as a double series of nervous centres or deposits of
gray substance, of varying size and position, connected with each other
and with the spinal cord by transverse and longitudinal tracts of white
substance. The number and relative importance of these nervous
centres, in different kinds of animals, depend upon the perfection of the
bodily organization in general, and more especially upon the develop-
ment of the functions and capacities connected with particular parts of
the nervous system. In the inferior classes, as fish and reptiles, the
brain is more simple in its anatomical characters ; while it becomes suc-
cessively more complicated in birds, quadrupeds, and man.

In fish and reptiles the different nervous centres of the brain are so
distinctly separated, and of such moderate size, that they are frequently
designated as " ganglia." In the brain of the alligator (Fig. 149) there
are five pairs of these ganglia, arranged one behind the other in the
cavity of the cranium. The first of these are two rounded masses ( a ),

lying just above and behind the nasal cavi-
ties, which distribute their nerves upon the
olfactory membrane. These are the olfac-
tory ganglia. They are connected with the
rest of the brain by two long and slender
commissures, the " olfactory commissures."
The next pair(3) are somewhat larger and
of a triangular shape, when viewed from
above downward. They are termed the
u hemispherical ganglia," or the hemispheres,
and correspond to the " cerebrum" in the
higher classes. Immediately following them
are two quadrangular masses (3) which give
origin to the optic nerves, and are therefore
called the optic ganglia. They are termed
also the " optic tubercles ;" and in some of
the higher animals, where they present an
imperfect division into four nearly equal
parts, they are known as the "tubercula
quadrigemina." Behind them is a single tri-
angular collection of nervous matter (4), the
cerebellum. Finally, the upper portion of the cord, just behind and
beneath the cerebellum, is seen to be enlarged and spread out laterally,
so as to form a broad oblong mass(5), the medulla oblongata. It is
from this latter portion of the brain that the pneumogastric or respira-
tory nerves originate, and its ganglia are therefore sometimes termed
the " pneumogastric" or " respiratory" ganglia.

It will be seen that the posterior columns of the cord, as they diverge
laterally, to form the medulla oblongata, leave between them an open

BRAIN OF
1. Olfactory ganglia. 2. Hemi-
spheres. 3. Optic tubercles. 4.
Cerebellum. 5. Medulla oblon-
gata.

THE NERVOUS SYSTEM.

437

Fig. 150.

BUAIN OF PIGEON — Profile view.—
1. Cerebrum. 2. Optic tubercle. 3. Ce-
rebellum. 4. Optic nerve. 6. Medulla
oblongata.

space, which is continuous with the posterior median fissure of the
cord. This space is known as the " fourth ventricle." It is partially
covered in by the backward projection of the cerebellum, but in the
alligator is still somewhat open posteriorly, presenting a kind of chasm
or gap between the two lateral halves of the medulla oblongata.

The successive ganglia which compose the brain, being arranged in
pairs as above described, are separated from each other on the two
sides by a longitudinal median fissure, which is continuous with the
posterior median fissure of the spinal cord. In the brain of the alligator
this fissure appears to be interrupted at the cerebellum ; but this is due
to the incomplete development of the
lateral portions of this organ, as com-
pared with its middle. The same pe-
culiarity is to be seen in birds and in
most quadrupeds ; while in man the
lateral portions of the cerebellum are
so highly developed as to project, on
each side, above the level of its central
part, and the longitudinal median fis-
sure, accordingly, appears complete
throughout.

In birds the hemispheres, or cere-
brum, are of comparatively larger size, and partially or completely con-
ceal the optic tubercles in a view taken from above. The cerebellum is
well developed in this class, and presents on its surface a number of
transverse foldings or convolutions
by which its gray substance is con-
siderably increased in quantity. The
cerebellum extends so far backward as
to completely cover the medulla ob-
longata and the fourth ventricle.

In quadrupeds the cerebrum and
the cerebellum attain a still greater
size as compared with the remain-
ing parts of the brain. There are
also two other collections of gray
substance on each side, situated in the
inferior part of the hemispheres, ante-
riorly to the tubercula quadrigemina.
These are the "corpora striata" in
front, and the " optic thalami" behind.
These bodies are frequently designated
by the name of the " cerebral gan-
glia," Since they are collections of BRAIN OF RABBIT, viewed f.-om
,, ... above.— 1. Olfactory ganglia. 2. Hemi-

gray matter Which OCCUpy the lower spheres of the cerebrum, turned aside.

and central parts of the cerebrum, and 3 CorP°ra striata. 4 Optic thaiimi.

, 5. Tubercula quadrigemina. 6. Cerebei-

intervene between the tracts of white ium.

Fig. 151.

438 GENERAL ARRANGEMENT OF

substance, coming up from below, and those which continue upward to
the convolutions of the hemispheres. The cerebellum, in the quadru-
peds, is somewhat enlarged by the increased development of its lateral
portions, and shows an abundance of transverse convolutions. It con-
ceals from view the fourth ventricle and the greater part of the medulla
oblongata.

In the more highly developed quadrupeds, the cerebral hemispheres
increase in size so as to cover more or less completely the olfactory
ganglia in front and the cerebellum behind. Their surface also becomes
covered with numerous convolutions, which are mainly longitudinal or
curvilinear in direction, instead of being transverse as in the cere-
bellum.

In Man the development of the cerebral hemispheres reaches its
highest point, so that they preponderate completely over all the other
nervous centres in the cranial cavity. In the human brain, accord-
ingly, when viewed from above, there is nothing to be seen but the
convex convoluted surface of the hemispheres ; and even in a posterior
view they conceal everything but a portion of the cerebellum. The
remaining parts, which are concealed by the cerebrum and cerebellum,
participate, however, in the structure of the entire encephalon, and
form, as in the lower animals, a series of associated nervous centres and
connecting tracts of nerve fibres.

As the spinal cord passes upward into the cranial cavity, it enlarges,
by a kind of lateral expansion, to form the medulla oblongata. This
portion of the cerebro-spinal axis is distinguished from the cord below,
not only by its external form, but also by the somewhat different
arrangement of its gray and white substance. The gray substance,
which in the cord presents on each side, in front and rear, the pro-
jections of the anterior and posterior horns, recedes, in the medulla
oblongata, more and more in a backward direction, and becomes accu-
mulated in a nearly single mass at its posterior surface. At the same
time, the masses of white substance on each side of the posterior median
fissure, which in the cord are called the " posterior columns," diverge
from each other at an acute angle, leaving between them the space of
the fourth ventricle, and assume the name of the resitform bodies.
They become continuous with the inferior peduncles of the cerebellum,
and send some of their fibres, in a radiating direction, into the white
substance of the cerebellum, to terminate in the gray substance of its
convolutions. The floor of the fourth ventricle, thus exposed by the
divergence of the posterior columns, is formed by the graj7 substance
of the medulla oblongata, which is accordingly continuous with that of
the cord, although it has a different position and a different form.

Yiewed in front, the medulla oblongata presents two longitudinal
eminences of white substance, one on each side of the median line, the
anterior pyramids, which take the place of the anterior columns of the
cord. At their commencement below, the anterior pyramids are narrow,
but grow wider as they ascend. At their lower portion they exhibit a

THE NERVOUS SYSTEM.

439-

remarkable decuxsation, easily seen by gently separating the sides of
the anterior median fissure, formed by distinct bundles of white sub-
stance crossing the median line obliquely, from below upward and from
side to side. Thus the right anterior pyramid is formed of fibres which
come from the left side of the cord, and the left anterior pyramid of
those which come from the right side of the cord.

Fig. 152.

MEDULLA OBLONGATA AND BASE OF THB BRAIN IN MAN— Anterior view.—
1. Decussation of the optic nerves. 2,2. Middle lobes of the cerebrum. 3, 3. (Jrura cerebri.
4. Tuber annulare. 5,6. Lateral lobos of the cerebellum. 6. Anterior pyramid. 7. Olivary
body. 8. Eestiform body. (Hirschfeld.)

Immediate!}7' outside of the pyramids, in a lateral direction, are two
elongated oval masses, the olivary bodies, whicli consist externally of
white substance, but internally contain each a distinct thin convoluted
layer of gray substance, resembling in miniature the convolutions of the
cerebrum. The olivary bodies are, therefore, special deposits of gray
substance in the anterior portion of the medulla oblongata, superadded
to the rest and not continuous with that of the spinal cord.

At the upper limit of the medulla oblongata is the tuber annulare, so
called because it forms a ring-like protuberance at this part of the base
)f the brain. Superficially, when viewed in front, it consists of trans-
verse bundles of white substance, containing fibres passing over, in an
arched form, from one side of the cerebellum to the other, and decus-
sating with each other at the median line. Where they cross the tuber annu-
lare these fibres constitute the " pons Varolii ;" at the two sides, where
they pass backward to the cerebellum, they form the " middle peduncles
)f the cerebellum."

440

GENERAL ARRANGEMENT OF

Fig. 153.

In its deeper parts, the tuber annulare contains longitudinal tracts of
white substance, passing upward from the medulla oblongata toward
the cerebrum. The continuation of the anterior pyramids in front, and
the remainder of the longitudinal bundles of the medulla oblongata
behind, pass into and through the substance of the tuber annulare, where
they are mingled with an irregular diffused deposit of gray substance.

From the upper border of the tuber annu-
lare, the longitudinal tracts of white sub-
stance emerge in the form of two thick,
obliquely diverging, bundles of nerve fibres,
the crura cerebri, or peduncles of the brain.
They are joined posteriorly by other longi-
tudinal bundles coming from the cerebellum,
known as the "anterior peduncles of the
cerebellum*" which are the organs of com-
munication between the cerebellum and the
cerebrum. The fibres of the crura cerebri,
thus constituted, then plunge into the sub-
stance of the two collections of gray matter
known as the " cerebral ganglia," namely,
the corpora striata and optic thalami ; thus
making a connection between these ganglia
and the medulla oblongata and spinal cord
below.

Finally, from the outer and upper por-
tions of the cerebral ganglia, the nerve fibres
of the white substance radiate in all direc-
tions, following a more or less curvilinear
course from within outward, until they reach
the gray substance of the convolutions at
the surface of the hemispheres. The cere-
bral convolutions of the two sides are also
united by the transverse fibres of the cor-
pus callosum.

The entire brain may, therefore, be con-
sidered as a symmetrical series of nervous centres connected with each
other and with the spinal cord by longitudinal tracts of white substance.
They occur in the following order : 1. The olfactory lobes, of small size
and concealed beneath the anterior portion of the brain ; 2. The cerebral
hemispheres, surrounding and covering the remaining parts by their
lateral and posterior extension; 3. The corpora striata, 4. The optic
thalami, and 5. The tubercula quadrigemina, occupying the central por-
tion of the base of the cerebrum, and resting upon 6, the crura cerebri;
Y. The tuber annulare ; 8. The cerebellum, and 9. The medulla oblon-
gata. Of the collections of gray substance just enumerated, the cere-
brum and cerebellum only are convoluted externally, the others being

MEDTTLLA OBLONGATA,
TUBER ANNTJLAEK, AND
CRURA CEREBRI.— The super-
ficial and deep transverse fibres
of the tuber annulare have been
cut away, showing the continua-
tion of the longitudinal fibres in
its interior. 1. Decussation of the
optic nerves. 2. Crus cerebri. 3.
Lateral portion of the pons Va-
rolii. 4. Anterior pyramid. 5. Oli-
vary body. (Hirschfeld.)

either smooth and rounded or irregular in form.

THE NERVOUS SYSTEM. 441

It is not to be supposed that the nervous communications between
the successive deposits of gray matter are necessarily of so simple a
character as those represented in Fig. 154. This is only a diagram,
representing the general fact of the longitudinal connection existing

Fig. 154.

DIAGRAMATIC SECTION OP HUMAN BRA i N ; showing the situation of the nervous
centres and the longitudinal tracts of white substance.— 1, Olfactory lobe. 2, 2. Convolutions
of the cerebral hemispheres. 3. Corpus striatum. 4. Optic thalamus. 6. Tubercula quadri-
gemina. 6. Crura cerebri. 7. Tuber annulare. 8. Cerebellum. 9. Medulla oblongata.

between the spinal cord and the different parts of the encephalon. It
is by no means certain that all or any of the fibres of the cord run con-
tinuously through the medulla oblongata, the tuber annulare, and the
cerebral ganglia, to the gray matter of the convolutions. On the con-
trary, careful examination of successive microscopic sections by the best
observers have failed to show such a direct continuity. It appears more
probable that the fibres coming from the spinal cord terminate in the
medulla oblongata, and that other fibres originating from the gray matter
of the medulla pass upward, partly to the cerebellum and partly to the
corpora striata and optic thalami ; while other fibres still, originating
from these ganglia, diverge thence to form the connection between them
and the cerebral convolutions. According to this view, the longitudinal
tracts of white substance consist of nerve fibres which are interrupted
in their course by the nerve cells of different deposits of gray matter,
so that an impression or impulse conveyed from one to the other is not
the same throughout its course, but is modified by the action of the
nervous centres which successively receive and transmit it.

Each portion of the cerebro-spinal axis has its right and left halves
connected with each other by transverse commissures, and sends out
nerves, containing motor and sensitive fibres, to corresponding regions
of the body. The spinal cord supplies the integument and muscles of
the neck, trunk, and extremities. The medulla oblongata sends out
motor and sensitive nerves to the muscles of the head and face, and to
the skin and mucous membranes of the same region; while it also sup-
29

442 GENERAL ARRANGEMENT OF NERVOUS SYSTEM.

plies nerves of a special character to the mucous and muscular coats of
the pharynx, oesophagus, and stomach, and to those of the organs of
respiration in the neck and thorax. From the medulla oblongata and
the inferior or central parts of the brain, are also supplied the nerves
destined for the organs of special sense.

In every region of the cerebro-spinal system, the two functions of
sensibility and motion are associated with each other by means of the
gray substance of the nervous centres. In the spinal cord the gray
substance is continuous and of nearly the same configuration through-
out. In the different parts of the brain it presents itself under the form
of more or less distinct deposits, of varying form and size. In either
of these parts a reflex action may take place independently of those
beyond, and calling into operation the special functions of the nervous
centre involved. But a nervous action may also pass through the entire
series, by the longitudinal connections of the cord, medulla oblongata,
tuber annulare, and cerebral ganglia, and thence through the radiating
fibres of the white substance to the cortical layer of the cerebral convo-
lutions. This layer may be regarded as a sort of concave mirror, where
the impressions coming from without are finally received and reflected,
in the form of conscious sensation and intelligent voluntary acts ; the
whole nervous mechanism of the cerebro-spinal system being thus called
into operation at the same time.

CHAPTEE IV.

THE SPINAL COED.

THE spinal cord is that part of the cerebro- spinal system which is
contained within the spinal canal, and which sends its nerves to the
muscles and integument of the trunk and limbs. It consists externally
of white substance, forming longitudinal tracts of nerve fibres, the con-
tinuations of which make connection with those of the brain above ; and
internally of gray substance arranged in two symmetrical bands occupy-
ing the central portions of its right and left lateral halves. It is so
constituted, therefore, as to act in a double capacity: First, as an organ
of nervous communication between the brain and the external parts ;
and secondly, as an independent nervous centre, with endowments and
functions of its own.

Arrangement of Gray and White Substance in the Spinal Cord,

The mutual relations of the gray and white substance form the neces-
sary basis for a complete physiological anatomy of this part of the
nervous system. The connections of the nerve fibres with the cells of
the gray substance and with various parts of the longitudinal columns,
as well as those of the different nerve cells with each other, are the most
important for this purpose. It has not yet been possible to make out
these connections with certainty for all parts of the cord ; but much has
been accomplished in this respect by the examination of microscopic
sections made in various directions, after hardening the tissues of the
cord in alcohol or in weak solutions of chromic acid or potassium bichro-
mate, and by making the fibres and cells more distinct by means of
staining preparations. With regard to the relative proportions, in dif-
ferent parts of the cord, of its two constituent elements, it is evident,
as shown by Kolliker and Gerlach, that the gray substance is increased
in quantity at the situation of the cervical and lumbar enlargements,
and that the white substance, on the other hand, diminishes gradually,
from its upper to its lower extremity. This fact corresponds with the
known physiological relations of the cord ; namely, that by its gray sub-
stance it acts as a nervous centre for the corresponding regions of the
body ; and also that the fibres of its white substance form communica-
tions between the parts above and the spinal nerves which are given
off below.

The Or ay Substance. — The gray substance in the spinal cord, as
elsewhere, consists of a mixture of nerve cells and nerve fibres, of which
the nerve cells are the peculiar and distinctive element. They are all

(443)

444

THE SPINAL CORD.

" multipolar" cells ; that is, they send out several prolongations in vari-
ous directions, transverse, longitudinal and oblique, most of which are
abundantly subdivided and terminate in minute ramifications, while a
single one frequently continues its course for a long distance undivided,

Fig. 155.

TRANSVERSE SECTION OF THE SPINAL CORD; lower cervical region. — 1. Anterior
median fissure; immediately behind it are seen the decussating fibres of the white commis-
sure. 2. Central canal, situated in the middle of the gray commissure. 3. Posterior median
fissure. 4, 4. Anterior columns of white substance. 5, 5. Posterior columns. 6, 6. Lateral
columns. 7, 7. Anterior horns of gray substance. 8, 8. Posterior horns. 9, 9. Anterior
nerve roots. 10, 10. Posterior nerve roots.

and assumes the appearance of an axis cylinder. They vary in form
and size in different parts of the gray substance. The most remarkable
of these cells are situated in the anterior horns, where they are dis-
tinguished by their large size, being, according to the measurements of
Kolliker, from 67 to 135 mmm. in diameter, the largest known cells in
the nervous system. They are arranged in two or three more or less
distinct groups near the extremity and outer portion of the anterior
horns. Beside these there are found scattered everywhere in the gray
substance, but more abundantly in the posterior horns, nerve cells which
are much smaller in size than the preceding, but of similar form and
provided with similar branching prolongations. The anterior and pos-
terior horns are not therefore absolutely distinguished from each other
by the character of their nerve cells, but only by the relative proportions
of their size and numbers ; since a few cells of comparatively large size
are found in the posterior horns, and the smaller ones exist in both
situations.

GRAY AND WHITE SUBSTANCE. 445

The nerve fibres of the gray substance are, in general, of much
smaller diameter than those of the white substance, but otherwise pre-
sent the same anatomical characters. Most of them run in a horizontal
transverse, antero-posterior, or radiating direction. They consist, first,
of fibres which have penetrated into the gray substance from the ante-
rior and posterior roots of the spinal nerves; secondly, of fibres which
cross the median line in the gray commissure, from one side of the cord
to the other, thus forming a commissural connection between the two
lateral halves of the gray substance ; and, thirdly, of fibres which run
in a great variety of directions with regard to each other, and of which
the origin and terminations are unknown.

The White Substance. — The white substance of the spinal cord con-
sists of nerve fibres, the large majority of which run in a longitudinal
direction, forming tracts or "columns," designated, according to their
situation, by the names of the anterior, lateral, and posterior columns
of the cord. In transverse sections of the cord which have been prop-
erly hardened, the longitudinal fibres are readily distinguished by their
presenting the circular outline of a minute cylinder cut across ; while
those which are horizontal or oblique are seen in profile for a longer or
shorter distance in the preparation.

The anterior, lateral, and posterior columns consist almost exclu-
sively of longitudinal fibres. But at the bottom of the anterior median
fissure there is a band of white substance, the fibres of which run hori-
zontally across from the inner portions of each anterior column to the
opposite side of the cord. This is called the white commissure of the
cord; but the name is not entirely appropriate, since its fibres do not
form a connection between exactly corresponding parts on the right and
left sides. According to both Kolliker and Gerlach, the fibres which
pass across at the median line from the right anterior column spread
out in the gray substance of the left anterior horn ; and those coming
from the left anterior column spread out in the gray substance of the
right anterior horn. The transverse fibres, accordingly, of the white
commissure connect the right and left anterior columns respectively
with the gray substance of the opposite side of the cord.

Counting the transverse fibres, therefore, of both the gray and the
white commissures, it may be said that there is a direct bilateral con-
nection, by means of communicating nerve fibres, between the right
and left halves throughout the length of the cord ; but it is not possible
to determine, with precision, the exact origin or termination of the indi-
vidual fibres by which this connection is made.

Connection of the Spinal Nerve-roots with the Spinal Cord. — The
fibres of the anterior roots of the spinal nerves are distinguished from
those of the posterior by their relatively larger size ; but on penetrating
into the white substance of the cord, their diameter is diminished, and
they assume all the characters of the central nerve fibres. They then
pass inward, in a horizontal or oblique and backward direction, and
reach the gray substance of the anterior horn.

446 THE SPINAL CORD.

The exact termination of the nerve fibres in the gray substance of the
cord is a matter of much importance, but which is not yet fully eluci-
dated. The strong probability is 'that some of the fibres of the anterior
nerve roots are directly connected with radiating nerve cells in this
locality by means of the long axis-cylinder processes of these cells ; but
the most accomplished and careful microscopists have found it impos-
sible to actually see this connection. Its probability rests upon the
facts that, first, the long processes of the nerve cells in the anterior
horns closely resemble, as their name indicates, the axis-cylinder of the
nerve fibres ; and, secondly, these processes are often seen, in horizontal
or antero-posterior vertical sections, to pass forward toward the origin
of the anterior root fibres, and emerge, in company with them, from the
gray into the white substance of the cord.1 Beside these fibres, how-
ever, others, forming a part of the anterior nerve roots, pass distinctly,
according to Kolliker, from the gray substance of the anterior horn into
the white commissure, and thence, crossingt the median line, into the
anterior column of white substance on the opposite side ; while others,
radiating backward and outward, may be seen to emerge from the ex-
ternal border of the gray substance, and to join the longitudinal fibres
of the lateral column on the same side.

Thus it is certain that the immediate connection of all the fibres of
the anterior nerve roots is with the gray substance of the anterior
horn ; but some of them pass subsequently to the anterior column of
the opposite side of the cord, others to the lateral column of the same
side.

The posterior roots are distinguished from the anterior, first, by the
generally smaller size of their nerve fibres ; secondly, by the presence
of the ganglia, known as the " spinal ganglia," or the ganglia of the
spinal nerve roots, The gray substance of these ganglia contains nerve
cells which are distinguished from those of the spinal cord by not pos-
sessing ramified prolongations. They present, however, often one,
sometimes two or more, pale, unbranched axis-cylinder processes, which
subsequently become continuous with medullated nerve fibres, running
outward with the other nerve fibres toward the periphery. These ganglia
therefore give origin to additional nerve fibres, which afterward form
part of the trunk of the spinal nerve. The fibres of the posterior nerve
roots, on the contrary, coming from the spinal cord, according to Kolli-
ker, only traverse the gray matter of the ganglion, without making any
anatomical connection with its substance.

The fibres of the posterior roots, on entering the spinal cord, between
its posterior and lateral columns, pass into the posterior horns of gray
matter ; after which some of them change their direction and become
longitudinal, still remaining in the gray substance, others become trans-

1 Kolliker, Elements d'Histologrie Humaine. Paris, 1868, p. 343. Gerlach, in
Strieker's Manual of Histology, Buck's edition. New York, 1872, pp. 636, 637.

TRANSMISSION OF IMPULSES. 447

verse, passing into both the gray and white commissures, while others
lose themselves in the gray substance of the posterior and even of the
back part of the anterior horns.

The connection of the anterior and posterior root fibres of the spinal
nerves with the cord is therefore not exactly the same ; but they both,
so far as known, first reach the gray matter, where a portion of them
terminate, or at least escape further observation, while the rest partly
become longitudinal on the same side, and partly cross over to the
opposite side of the spinal cord.

Transmission of Motor and Sensitive Impulses in the Spinal Cord and

Nerves.

The experimental methods adopted for determining the functions of
different pnrts of the nervous system are twofold ; first, by applying an
artificial stimulus to the nerve or nervous tract, and observing the effect
which is produced ; secondly, by dividing or destroying it, and seeing
what nervous function is abolished in consequence of the operation. In
the peripheral parts of the nervous system, and in those generally which
serve as simple organs of transmission, both these methods yield defi-
nite and positive results. In the central parts, they are sometimes
complicated by the peculiar properties or the mutual reactions of the
gray and white substance.

Motor and Sensitive Transmission in the Spinal Nerves and Nerve
Hoots. — If the spinal canal of a living animal be opened, and a mechanical
or galvanic stimulus be applied to the anterior root alone of a spinal
nerve, the effect of this irritation is a convulsive movement of the part
to which the nerve is distributed. The muscular contraction is imme-
diate, involuntary, and instantaneous in duration ; and is repeated with
mechanical precision each time the stimulus is applied. It is usually
unaccompanied by any indication of sensibility, and is evidently a
direct result of the excitement of the nerve fibres of the anterior root.
This root is therefore said to be " excitable," because its irritation
excites a movement in the corresponding parts.

Furthermore, if the anterior root of a spinal nerve, under the same
circumstances, be cut across, the remaining nervous connections being
left untouched, the result is an immediate and total paralysis of volun-
tary movement in the muscles to which that nerve is distributed. At
the same time, the power of sensibility is undiminished, and the animal
is still capable of feeling the contact of foreign bodies, or a galvanic cur-
rent applied to the skin, as before. If the anterior roots of a series of
spinal nerves be thus divided, as, for example, those of all the lumbar
and sacral nerves on one side, the above effect will be produced for an
entire corresponding region of the body, and the whole posterior limb
on that side will lose the power of voluntary motion while retaining its
sensibility. This is not clue to any loss of the physiological properties
of either the nerve or the muscles, since irritation of the nerve or nerve
root, outside the point of section, still produces muscular contraction as

4-48 THE SPINAL CORD.

before. All these facts prove that the path by which impulses for vol-
untary motion pass, from the brain and spinal cord to the muscles, is
exclusively the anterior root of the spinal nerve.

On the other hand, if the posterior root be irritated, by pinching,
pricking, or galvanism, a sensation is produced, more or less acute ac-
cording to the amount and quality of the irritation applied. This sen-
sation, when of a certain intensity, is accompanied by movements. But
these movements are general and not necessarily confined to the part to
which the nerve is distributed; and if the corresponding anterior root
have been previously divided, this part will remain motionless, while
muscular contractions continue to be produced elsewhere. The move-
ments which follow irritation of the posterior root, accordingly, are
not produced directly by its influence, but are caused indirectly by
the reaction of the nervous centres. The only immediate result of irri-
tation of a posterior nerve root is a sensation, and this root is therefore
said to be " sensitive."

Furthermore, if the posterior root be divided, the consequence is a
loss of the power of sensation in the corresponding region of the body.
Here also the effect is simply to cut off the medium of communica-
tion between the integument and the nervous centres ; since irritation
of that part of the divided nerve which is still attached to the spinal
cord produces a sensation as before. Thus the channel of communica-
tion for sensitive impressions, in this part of the nervous system, is
exclusively the posterior root of the spinal nerve.

But just beyond the situation of the spinal ganglia, the two roots
unite to form the trunk of the spinal nerve. Here, the fibres of the
anterior and those of the posterior root become intimately mingled, and
inclosed within the neurilemma in such close juxtaposition that they
can no longer be separately irritated by artificial means. They pass,
still associated in this manner, into the branches and subdivisions of
the nerve ; and only finally separate from each other at its terminal
ramifications, where the sensitive fibres are distributed mainly to the
integument and the motor fibres to the muscles.

The trunk and branches of a spinal nerve, therefore, outside the
spinal canal, contain both sensitive and motor fibres, and it is conse-
quently said to be a " mixed" nerve. It is both excitable and sensitive,
since its artificial irritation causes at the same time sensation and con-
vulsive movement ; and if it be divided, this injury is followed by the
loss of both sensibility and voluntary motion in the corresponding
parts. It is also important to remember that, in all these instances of
section of the trunk, or branches, or anterior or posterior roots of a
spinal nerve, the consequent loss of sensibility or motion is permanent
while the injury lasts ; and the nervous functions are not restored until
the divided nerve fibres have reunited, and have again acquired their
natural continuity of texture. This shows that the suspension of func-
tional activity is directly due to the division of the nerve fibres, and is
not produced by the sympathetic action of other parts.

TRANSMISSION OF IMPULSES. 449

Motor and Sensitive Transmission in the Spinal Cord. — The simplest
fact determined, in this respect, both by experimental research and
pathological observation, is that the spinal cord is the exclusive organ
of communication between the brain, on the one hand, and the external
organs of sensation and motion, on the other; since if it be divided by
a transverse section, or compressed by fractured bone, or disorganized
by diseased action at any part of its length, the result is a complete
loss of voluntary motion and sensibility in the muscles and integument
below the point of injury. The general nervous function, performed by
the cord as a whole, is therefore easily and completely demonstrated,
and is not subject to any doubtful interpretation.

But the precise path which is followed by the motor and sensitive
impulses respectively in different parts of the spinal cord is much less
easy of determination than in the two sets of nerve roots. The fibres
of the nerve roots pass directly to the gray matter in the interior of the
cord ; and their subsequent course has not been completely followed by
microscopic examination. The white substance of the cord, at least in
the lateral columns, is partly formed of fibres which come from the
nerve-roots ; but the greater part of both anterior, lateral, and posterior
columns may consist of fibres which originate in the gray matter, and
thus form secondary tracts of communication between it and the brain.
The close juxtaposition and continuity of texture between the gray
substance and the various columns of white substance in the spinal
cord give it a more or less complicated structure ; and the investigation
of the functional endowments of its different parts has yielded results
which are less simple and uniform than in the case of the nerves and
the nerve roots. The methods and objects of the investigation, however,
are the same in both instances ; and are intended to ascertain the
following points, namely, first, what parts of the spinal cord are found
to be sensitive or excitable under the application of an artificial
stimulus? and secondly, what parts act as the natural channels of
transmission for the two functions of sensation and motion? The
latter of these questions is the more important in a purely physiological
point of view; but the former is also of consequence as a guide in
experimental research, and also for the explanation of many pathological
phenomena.

I. What parts of the Spinal Cord are sensitive or excitable under the
influence of artificial stimulus?

When the spinal canal is opened in the living animal, the first por-
tions of the cord which present themselves for examination are the
posterior columns. The irritation of these columns by artificial stimu-
lus, according to the united testimony of all observers, produces evident
signs of sensibility in the animal. It is also found by experimenters
generally that this sensibility is most marked in the immediate neigh-
borhood of the attachment of the posterior nerve roots, while at the
greatest distance from this point, namely, at the inner edge of the poste-
rior columns, on each side of the median line, their sensibility may be

450 THE SPINAL CORD.

nearly absent. It is evident that the sensibility of the posterior columns
is largely due to the presence of fibres of the posterior nerve roots,
which may be included in the irritation, and many of which traverse the
outer portion of the posterior columns horizontally in their passage
toward the gray matter. The only discrepancy on this subject is in
regard to the question whether the fibres of the nerve roots are the only
sources of sensibility for the posterior columns, or whether the longitu-
dinal fibres of the columns themselves are also sensitive. According to
some authors (Yan Deen, Brown-Sequard, Poincare'), the posterior
columns have no sensibility of their own, but only what is due to that
of the posterior nerve roots; since if these roots be torn out, irritation
of the posterior columns no longer produces any perceptible sensation.
In the experiments of Schiff and Vulpian, on the other hand, the poste-
rior columns, after being divided by a transverse section, and then
separated from the adjacent parts for a distance of several centimetres
in front of the point of section, still indicate the existence of sensi-
bility when subjected to irritation. Irritation of the posterior columns,
like that of sensitive tracts generally, produces also movements in va-
rious parts ; but these movements are reflex in character, and are simply
the signs of an irritation communicated to the nervous centres.

Sensibility also exists, according to Yulpian, in that portion of the
lateral columns which is contiguous to the outer edge of the posterior
columns, and to the line of attachment of the posterior nerve roots.
But as the irritation is applied to points farther forward, the signs of
sensibility in the lateral columns rapidly diminish, and soon disappear
altogether. In all these parts, of both posterior and lateral columns, the
sensibility, as found by all observers, is most marked, or even exclu-
sively situated, in their superficial portions; and experimenters are also
generally agreed that the gray substance of the cord, throughout, is
destitute of sensibility to the application of any ordinary artificial
stimulus.

Whatever minor points, therefore, may remain in doubt, the principal
fact is unquestioned, namely, that the posterior parts of the spinal cord,
consisting of the posterior columns and the adjacent parts of the lateral
columns, are sensitive to external irritation, especially at their surface;
and accordingly inflammation of the meninges, or other diseased action
in this locality, may be accompanied by painful irritation of the spinal
cord. The irritation thus produced is still more liable to cause pain, on
account of the attachment at the surface of the cord of the posterior
nerve roots, which are themselves acutely sensitive.

The properties shown by the anterior columns on the application of
artificial stimulus are, on the whole, quite different from those of the
posterior columns. There is some difference in the results obtained in
this respect by different experimenters. This difference mainly con-
sists in the fact that, according to the large majority (Magendie, Longet.
Bernard, Brown-Se'quard, Yulpian, Flint), irritation of the anterior
columns produces convulsive movement in the parts below ; while

TRANSMISSION OF IMPULSES. 451

others (Calmeil and Chauveau) have found these columns quite inexcita-
ble, and incapable of causing muscular contraction. But in such in-
stances experiments with a positive result are much more decisive than
those which are merely negative, since the natural excitability of the
anterior columns might be temporarily suspended by the operation of
opening the spinal canal, or other incidental conditions; but nothing
of this kind could confer upon them a property which they did not
naturally possess.

Vulpian has shown1 that, if in the living animal the spinal cord be
divided transversely, and both posterior and lateral columns, together
with the anterior and posterior nerve roots, separated from it for a
distance of four or five centimetres below the point of section, leaving
this portion of the cord to consist of the anterior columns and the
gray substance only, irritation of the anterior columns, thus isolated,
will still produce convulsive movement in the parts below.

There can be no doubt, accordingly, of the excitability of the anterior
columns. This excitability, which produces simple convulsive move-
ments in the parts below, is also in most instances unaccompanied by
pain or other evidences of sensibility. The absence of pain, in cases
where the convulsive action is well marked, has been especially noticed
by Flint,2 and is also mentioned by various other writers.

The sensibility of these parts which has sometimes been observed is
comparatively slight in degree, and is frequently altogether suspended
or abolished by the opening of the vertebral canal and the exposure of
the spinal cord.

The lateral columns are also excitable in their anterior portions, near
the attachment of the anterior nerve roots ; while as we approach their
posterior portions, this direct excitability, according to Vulpian, dimin-
ishes in degree, and gradually gives place to the phenomena of sensi-
bility characteristic of the posterior parts of the cord.

The anterior, lateral, and posterior columns of the cord are not there-
fore absolutely limited and distinguished from each other by their
physiological properties. The fibres of the anterior and posterior nerve
roots pass in horizontally between the longitudinal fibres of the adjacent
columns ; but both the anterior and lateral columns, on each side of the
anterior nerve roots, are excitable and produce movement on being irri-
tated, and both the posterior and lateral columns, near the entrance of
the posterior nerve roots, are endowed with sensibility. Inflamma-
tory or other irritation of the meninges, over any part of the anterior
aspect of the cord, may accordingly cause convulsive movements in the
regions situated below the diseased point ; and it is possible that either
pain alone or convulsions alone may be the symptoms of inflammatory
irritation of the posterior or anterior portions of the cord respectively.
But it is most frequently the case that the morbid action extends more

1 Systeme Nerveux. Paris, 1866, p. 360.

2 Physiology of Man ; Nervous System. New York, 1872, p. 276.

452 THE SPINAL COBD.

or less to both regions, and the disturbances of sensibility and motion
are both present at the same time, or at different periods in the progress
of the disease.

II. What parts of the Spinal Cord are the natural channels of trans-
mission for sensation and movement?

This question cannot be settled by the experiments which consist in
applying an artificial stimulus to the various parts of the cord. Such
experiments can only determine the sensibility or excitability of a
nervous tract, but not its function as a channel of transmission. A
part of the spinal cord might be sensitive to direct external irritation,
and yet the natural impulses of sensation, coming from the peripheral
nerves, might follow a different route. On the other hand, a part might
be perfectly capable of transmitting the nervous impulses of sensation or
of motion, received from the corresponding nerve fibres, and yet might
not itself be either excitable or sensitive. In the peripheral nerves and
the nerve roots, the two sets of properties coexist. The nerve fibres of
the posterior roots, which transmit sensation, are themselves sensitive ;
and those of the anterior nerve roots, which transmit the power of
motion, are also excitable. But although these properties are connected
in the nerves and nerve roots, they are not necessarily so in the nervous
centres ; and investigation shows that in the spinal cord they are often
independent of each other.

The only method of ascertaining what path is followed, in the spinal
cord, by the sensitive and motor impulses respectively, is to divide or
destroy, in successive experiments, different portions of the cord, and to
observe which of these injuries is accompanied by the loss or preserva-
tion of sensation or voluntary movement. Even these experiments are
not always as decisive in the spinal cord as in the nerves and nerve
roots ; for the reason that the different parts of the white and gray sub-
stance influence each other, and are sometimes affected by sympathetic
action. If the division of one of the columns of the spinal cord be fol-
lowed by a continuance of the power of sensation, we know that column
cannot be the natural channel for sensitive impressions. But if, on the
other hand, it be followed by immediate loss of sensibility, we cannot be
sure, in this case, that the column in question is really the organ of
transmission ; because the loss of sensibility may be temporary, and due
to the shock inflicted upon neighboring parts of the cord. Nothing is
more common, in experiments on the nervous system, than to see a par-
alysis of sensation or motion, more or less complete, follow directly
upon the injury of a particular part, and yet these symptoms disappear
within a few hours or days, although the injury to the nerve substance
may remain for a much longer period. The immediate effect, in these
cases is not due directly to the division of the injured nerve fibres, but
to their sympathetic reaction upon neighboring parts of the nervous
centre. The most decisive experiments, accordingly, upon the spinal
cord, for determining the channels of transmission for sensation and

TRANSMISSION OF IMPULSES. 453

motion, are those in which these functions have remained, notwith-
standing the section of certain parts of the cord.

By investigating in this way the nervous channels for sensation in
the spinal cord, the first fact which is demonstrated in such a manner as
to be generally accepted, is that after division of the posterior columns
of white substance the power of sensibility is undiminished, and the
animal continues to feel impressions made upon the integument of the
corresponding parts. This result, which was obtained by several of the
older experimenters, is fully confirmed by the observations of Brown-
Se'quard1 and Yulpian.2 The posterior columns therefore are not the
channels for ordinary sensitive impressions, notwithstanding they have
themselves a certain degree of sensibility. The converse of this experi-
ment, namely, transverse division of all parts of the spinal cord excepting
the posterior columns, as performed by the same observers, is followed
by complete loss of the power of sensation.

On the other hand, if both the anterior and lateral columns of white
substance be divided, leaving only the posterior columns and the gray
substance, sensibility is preserved ; and Brown-S^quard has varied the
mode of procedure by dividing both anterior, lateral, and posterior
columns in the same animal at different levels, one above the other,
so that the continuity of the cord as a whole is preserved, but all the
longitudinal tracts of white substance are divided, leaving only the gray
substance uninjured. In this case sensibility is preserved, although
diminished in intensity.

The transmission of sensitive impressions, therefore, takes place
through the gray matter. This substance, which is itself insensible to
direct irritation, forms the medium of communication between the
peripheral fibres of the sensitive nerves and the brain above. It is not
known whether this communication be made by nerve fibres running
continuously through the gray substance in a longitudinal direction, or
by successive connections of the nerve cells.

With regard to the channels for voluntary motion in the cord, the
posterior columns, it is certain, take no direct part in the transmission
of these impulses, since after their complete section the power of vol-
untary motion remains unimpaired ; and if all the remaining parts of
the cord be divided, according to the observations of Brown-Se'quard,
leaving the posterior columns untouched, voluntary motion is entirely
lost. Further experiments by the same author on the anterior and
lateral columns and the gray substance of the anterior horns lead to the
conclusion that, for the transmission of the voluntary impulses from
the brain to the muscles of the body and limbs, both the white and gray
substance of the anterior half of the cord must be in a state of integrity;
since section of either the white substance alone or of the gray sub-

1 Physiology and Pathology of the Central Nervous System. Philadelphia,
1860, p. 19.

2 Systeme Nerveux. Paris, 1866, p. 373.

454 THE SPINAL CORD.

stance alone is followed by almost complete paralysis of the parts below
the level of the injury. In the dorsal region, injury of the anterior
columns produces a greater amount of paralysis than that of the lateral
columns; in the cervical region, on the other hand, this relation is
reversed, the lateral columns taking a more important part in voluntary
transmission than the anterior.

It is evident, accordingly, that in the spinal cord the transmission of
sensitive and motor impulses does not take place with the same sim-
plicity as in the nerves and nerve-roots. The various nervous tracts,
as well as the white and the gray substance, are associated in such a
manner as to make of the cord a single organ, more or less complicated
in structure, which cannot be separated, so far as our present knowledge
extends, into completely independent parts.

Crossed Action of the Spinal Cord,

The spinal cord, as a medium of nervous communication between the
brain and the external parts, exerts a crossed action. That is, the
sensitive impressions received by the integument on one side of the
body are conducted through the cord to the opposite side of the brain ;
and the voluntary motor impulses which originate on one side of the
brain pass to the nerves and muscles on the opposite side of the body.
This is established both by experiments upon animals and by patholo-
gical observations in man ; since injury or disease situated upon the
right side of the brain is known to cause paralysis, both of sensation
and voluntary motion, on the left side of the body, and vice versa.
These two nervous functions may be paralyzed either together or
separately, according to the locality and extent of the injury to the
brain substance ; but when the paralysis is distinctly confined to one
side of the body, the alteration of nervous tissue upon which it depends
is found after death to be seated upon the opposite side of the brain.

The crossing or decussation of the motor and sensitive tracts, from
side to side, takes place in the following manner :

Decussation of the Motor Tracts. — It may be said, in general terms,
that the transmission of voluntary motor impulses, in the spinal cord
itself, takes place continuously upon the same side. That is, if a trans-
verse section of one lateral half of the cord be made at any point in the
lumbar, dorsal, or cervical region, a paralysis of voluntary motion is
produced upon the same side for all parts situated below the level of
the injury. This observation, which was first made by Galen, has been
confirmed by all subsequent experimenters. But in the cervical region,
the lateral columns gradually preponderate in importance, as the organs
of transmission for voluntary motion, over the anterior columns ; and
on approaching the level of the medulla oblongata, their fibres pass in «
direction forward and inward, until they reach the inner and anterior
part of the cord. At the medulla oblongata, these fibres cross the
median line, as distinct bundles of considerable size passing obliquely
upward, to form the anterior pyramids of the opposite side. This

CROSSED ACTION OF THE SPINAL CORD. 455

constitutes the so-called "decussation of the anterior pyramids;" and
beyond this point the longitudinal fibres of the medulla oblongata con-
tinue their course toward the peduncles of the brain and the cerebral
ganglia above. Thus the crossing of the tracts for voluntary motion is
completed in the lower half of the medulla oblongata. Injury of one
lateral half of the brain above this situation causes muscular paralysis
on the opposite side of the body ; injury of one lateral half of the spinal
cord below it causes paralysis on the same side of the body.

These are the general results obtained from both pathological observa-
tion and physiological experiment; and they evidently point to the
medulla oblongata as the principal or exclusive seat of the bilateral
decussation of the channels for voluntaiy motion. At the same time it
is shown, by mircroscopic examination, that this is not the only spot
where an anatomical intercharge of fibres takes place between the two
lateral halves of the spinal cord. On the contrary, a decussation of
fibres exists everywhere, throughout the length of the cord, from left to
right, and vice versa, at the situation of the " white commissure," at the
bottom of the anterior median fissure ; the right anterior column con-
stantly receiving fibres from the left side of the cord, and the left anterior
column from the right side of the cord. This continuous decussation is
concealed from view externally, and is only discoverable by means of
transverse microscopic sections ; while that at the level of the anterior
pyramids is easily visible, owing to the size of the decussating bundles
and their oblique direction.

The anatomical distinction between the two sets of decussating fibres
may answer to a corresponding difference in their physiological action ;
and the decussation at the white commissure may be connected with
the reflex action of the cord, or with the simultaneous action of its twro
opposite sides. It is certain that this commissure does not take part in
the transmission of voluntary impulses; since in the celebrated experi-
ment of Galen,1 "if the spinal cord be divided by a longitudinal section,
from above downward, in the median line," so as to separate its two
lateral halves from each other, this operation is not followed by loss
of motion either on one side or the other. This result has also been
obtained by Brown-Se'quard2 in the lumbar region, voluntary motion
being retained in both the posterior limbs. On the other hand, as
shown by the same observer, a longitudinal section of the medulla
oblongata alone in the median line, so as to divide the decussating fibres
of the anterior pyramids, produces complete loss of voluntary movement
in all the limbs at once.

Decussation of the Sensitive Tracts. — The sensitive impressions,
conveyed from the integument to the nervous centres, undergo, like the
motor impulses, a complete bilateral decussation by the time they arrive

1 De Administrationibus Anatomicis. Liber viii. cap. vi.

2 Physiology and Pathology of the Central Nervous System. Philadelphia,
1860, p. 33.

456 THE SPINAL CORD.

at the upper part of the medulla oblongata ; since lesions of the brain
above this point cause a diminution or loss of sensibility on the opposite
side of the body.

But while the tracts for voluntary motion have a continuous or uni-
lateral course in the spinal cord itself, and decussate only or principally
at the level of the anterior pyramids, those for sensation in great
measure cross from side to side at successive points throughout the
length of the spinal cord. This is shown by the fact that a transverse
section of one lateral half of the spinal cord, which paralyzes motion
on the same side with the injury, causes, on the contrary, a loss of sen-
sation on the opposite side ; while sensibility remains upon that side of
the body where the section of the cord has been made. Thus if the
lateral section of one-half the spinal cord be made at the lower end of
the dorsal region on the right side, the right hind leg is paralyzed of
motion but retains its sensibility ; the left hind leg, at the same time,
retains its power of motion but loses its sensibility. Furthermore, the
sensibility of the parts is not only retained on the side of the section,
but is even exaggerated in a very perceptible manner ; so that an im-
pression upon the skin is perceived on that side more acutely than before
the section.

These results, which were partially obtained by several of the older
experimenters, were first .distinctly brought out by Brown-Sequard.
According to his experiments, the phenomena are so complete as to imply
an entire crossing of the sensitive tracts in the spinal cord. Other
observers have found the appearances not so decisive ; Yulpian, among
others, maintaining that the loss of sensibility on the opposite side, after
section of a lateral half of the cord, is never complete but only partial,
and that the sensitive impressions conveyed through the gray matter
may even continue to pass, after one lateral half of the cord has been
divided in the dorsal, and the other in the cervical region, by two sec-
tions placed at a considerable distance from each other.

It is certain, however, that after section of one lateral half of the
cord the phenomena which indicate a crossing of the sensitive tracts are
distinctly marked. We have repeated this experiment, and have found
that after such a section, in the dog, in the dorso-lumbar region, the
difference in the effects produced upon sensation and motion on the two
sides is very striking. Sensibility is either lost or very much diminished
upon the opposite side, while upon the same side with the section, where
there is complete muscular paralysis, the sensibility remains and is in-
creased in intensity. On the opposite side, there is power of motion
with diminution or loss of sensibility ; on the same side, there is hyper-
sesthesia with loss of voluntary motion.

What is the cause of the local hyperaesthesia, after section of one
lateral half of the spinal cord? This is an instance of the indirect
influence exerted upon the nervous centres by injury of any part of
their substance. After transverse division of one-half of the cord, not
only are its motor and sensitive fibres cut off, causing paralysis of motion

CROSSED ACTION OF THE SPINAL CORD. 457

on the same side and paralysis of sensibility on the opposite side, but
the gray substance is irritated in the neighborhood of the section and
is thrown into a state of unusual activity. The sensitive fibres of the
posterior nerve roots on the same side pass into this gray substance
below the point of section, and thence make communication with the
opposite side of the spinal cord and the brain. The irritation of
the gray matter thus causes an increase in the intensity of the nervous
impressions coming from the side of the injury and an apparent hyper-
aesthesia of the integument on that side. For this purpose it is not
necessary to make a complete section of all the lateral parts of the cord ;
since Brown-Se'quard has found that division of the posterior columns
alone will cause hyperaesthesia, more or less pronounced ; and according
to Vulpian, the same effect may be produced by simply pricking with a
pointed instrument the posterior or lateral parts of the cord on one side.

Another experiment is much relied on by Brown-Sequard to demon-
strate the crossing of the sensitive tracts in the spinal cord. According
to him, if the spinal cord be divided, in the lumbar region, by a longi-
tudinal section in the median line, so as to separate its two lateral
halves from each other without further injury, the operation is followed
by complete loss of sensibility in both hind legs. This result by itself
would not be decisive, since such an operation might readily cause a
temporary suspension of sensibility, owing to the shock inflicted on the
spinal cord as a whole ; but it is of much value when taken in connec-
tion with the fact that after this operation, while sensibility is lost, the
power of voluntary movement, on the contrary, is retained in both the
posterior limbs.

Finally, instances in the human subject, where a lesion of one side
of the spinal cord is accompanied by loss of voluntary motion on the
same side and loss of sensibility on the opposite side, below the seat
of the disease, confirm the results derived from experiments on animals.
The decussation of both motor and sensitive tracts is completed at the
medulla oblongata ; but below this point the cord acts as a conductor
for motor impulses going to the muscles on the same side of the body, '
and for sensitive impressions coming from the integument of the oppo-
site side.

Various forms of Paralysis, from lesions of the Cerebro-spinal
Axis. — In consequence of disease or injury in di fie rent parts of the
cerebro-spinal axis, a variety of symptoms may be produced affecting
sensation and voluntary motion. The two most simple forms of paraly-
sis from this cause are, first, " paraplegia," or paralysis of the entire
lower portion of the body and inferior limbs ; and secondly, " hemiple-
gia," or paralysis of one lateral half of the body, and of one or both
limbs on the corresponding side.

I. In Paraplegia, the injury affects the whole substance of the spinal
cord at a particular level, and the result is loss of sensation and volun-
tary motion on both sides, for the whole of that part of the body
supplied with nerves which originate at or below the level of the injury.
30

458 THE SPINAL CORD.

The seat of the lesion in the spinal cord is determined by the line at
which paralysis of sensation and motion begins in the external parts.
If the lesion occupy the lumbar portion of the cord, the legs and the
pelvic regions are paralyzed and insensible, while the arms and remain-
ing parts of the trunk retain their feeling and power of motion. If it
be in the dorsal region, a corresponding part of the abdomen and thorax
is also deprived of sense and movement ; and if situated in the middle
cervical region, it produces at the same time paralysis and insensibility
of both upper and lower extremities, together with that of the chest and
intercostal muscles. A paralysis of this kind, affecting the arms and
intercostal muscles, is more dangerous than that of the legs alone ;
because a slight extension of the lesion above the middle cervical region
will paralyze the fibres of origin of the phrenic nerves, and produce
death by stoppage of respiration.

In complete paraplegia, sensation and motion are both abolished in
the affected parts ; because the injury or disease, when sufficient to
destroy one of these nervous functions, almost necessarily reaches those
portions of the cord which preside over the other. But in slight or
incomplete cases, either sensibility or movement may be more or less
affected, according as the lesion is more or less advanced in different
parts of the thickness of the cord.

II. In Hemiplegia of the simplest form, there is loss of sensation and
voluntary motion in the right or left arm and leg, the limbs on the
other side of the body remaining uninjured. Sensibility and the power
of movement are also lost in the integument and muscles of the chest
and abdomen on the corresponding side. It is, therefore, a complete
paralysis of one lateral half of the body ; the affection being usually
exactly limited by the median line, both in front and rear. In these
cases the paralysis is due to some lesion within the cavity of the cra-
nium, on the opposite side, and above the decussation of the anterior
pyramids ; namely, in the upper part of the medulla oblongata, the crura
cerebri, the cerebral ganglia, or the hemispheres. It appears to be most
frequently seated in the cerebral ganglia or the hemispheres.

In hemiplegia from this cause, the loss of sensibility and of the power
of motion, though occupying the same half of the body, are not necessa-
rily equal in degree. According to Hammond,1 when the cause of tin
difficulty is a cerebral hemorrhage, they are rarely present to the
extent. If the lesion be situated lower down, in the crus cerebri or th<
tuber annulare, they would be more likely to resemble each other in degi

When hemiplegia is due, 011 the other hand, to a lesion of the spinj
cord on one side, the paralysis of motion is on the same side of
body, and that of sensibility on the opposite side. A number of thei-
cases have been collected by Brown-Sequard, in most of which it
ascertained that the injury was seated in the lateral half of the cord
corresponding to the paralysis of motion.

1 Diseases of the Nervous System. New York, 1871, p. 77.

ACTION AS A NEEVOUS CENTRE. 459

Action of the Spinal Cord as a Nervous Centre.

So far as the spinal cord is concerned in the phenomena of sensation
and voluntary motion, it acts as a medium of communication between
the brain, where consciousness and volition reside, and the integument
and muscles of the external parts. Its complete division accordingly at
any point destroys this communication, and suspends the nervous func-
tions dependent upon it ; so that the commands of the will are no longer
transmitted to the muscles below, and the individual is incapable of
perceiving impressions made upon the integument of the paralyzed
parts. But after such an operation motion is not altogether abolished
in the body and limbs ; and impressions conveyed by the sensitive
nerve fibres, though no longer perceived by the individual, are still
capable of producing an effect, and of exciting a reaction in the organs
of movement. These phenomena, which take place without the inter-
vention of the brain, are produced by the action of the spinal cord as a
nervous centre, and are due to the independent properties of its gray
matter.

Eeflex Action of the Spinal Cord. — If a frog be decapitated, and
allowed to remain at rest for a few moments, until the depressing effects
of the shock upon the nervous system have passed off, movements can
readily be excited in either the anterior or posterior limbs. If the skin
of one of the feet be irritated by pinching with a pair of forceps, or by
immersing it in a weak acidulated solution, the leg is immediately
drawn upward toward the body, as if to escape the source of irritation.
If the stimulus applied be of slight intensity, the corresponding leg only
will move ; but if it be more severe in character, motion will often be
produced in the corresponding limb on the opposite side, or even in all
the extremities at once. These phenomena may be repeated a great
number of times, until the irritability of the nervous system has been
exhausted, or until some structural change has taken place in the
tissues.

Two important peculiarities are noticeable in the movements thus
produced after decapitation :

First, they are never spontaneous ; but are only excited by the appli-
cation of an external stimulus. The decapitated frog, if left to itself,
always remains perfectly motionless, in a nearly natural attitude, but
without any tendency to alter its position. Each application of a
stimulus causes a movement, after which the limbs again assume a con-
dition of quiescence until a repetition of the stimulus calls out a new
movement.

Secondly, the muscular action thus manifested is not produced by a
stimulus directly applied to the muscles themselves. The stimulus is
applied to the integument of the foot, and the muscles of the leg and
thigh are contracted in consequence. This shows that both sensitive
and motor nerve fibres take part in the action. The sensitive fibres
distributed to the integument first receive the impression and convey it

460 THE SPINAL CORD.

inward ; after which the motor fibres transmit an outward stimulus to
the muscles in a different part of the limb. Even the other limbs, as
already mentioned, may be set in motion by an irritation applied to
the integument of one.

Furthermore, the nervous action is not transmitted, in these cases,
directly from the integument to the muscles; it passes through the
spinal cord, which thus forms a necessary link in the chain of communi-
cation ; for if the posterior limb be left uninjured, while its connection
with the cord is severed by dividing the sciatic nerve in the cavity of
the abdomen, no further action can be excited, and the limb remains
motionless whatever irritation be applied to the integument.

Lastly, if the spinal cord itself be destroyed by the introduction of a
stilet into the spinal canal, this also puts an end to the phenomena, and
irritation of the integument will no longer produce a muscular reaction.
After that, the muscles can only be excited to contraction by a stimulus
applied directly to themselves, or to their motor nerves.

All these facts show that the phenomena in question are due to the
reflex action of a nervous centre, in which three different nervous ele-
ments take part ; namely, first, the sensitive nerve fibres, conveying an
impression inward from the integument ; secondly, motor nerve fibres,
transmitting a stimulus outward to the muscles ; and, thirdly, a nervous
centre which intervenes between the two, and in which the reflex action
is accomplished. The nervous centre, in this instance, is the gray sub-
stance of the spinal cord.

It is evident, accordingly, that consciousness is not a necessary ac-
companiment to the reception of sensitive impressions by a nervous
centre ; and that a motor impulse may also originate in a nervous centre
without the act of volition. The reflex action of the spinal cord takes
place without either consciousness or volition ; and yet it is completely
efficient, and produces muscular contraction at once on the application
of a stimulus to the skin.

Diminution or Increase of Beflex Action in the Cord. — The reflex
action of the spinal cord, like other forms of nervous activity, may suffer
a temporary depression, or even total suspension, by any shock or injury
to the system at large. The operation of separating the head from the
trunk in the frog will often be followed, for a few moments, by an
interval of complete nervous paralysis, in which no phenomena of reac-
tion can be obtained. Even injuries in which the nervous centres are
not directly interested, such as the opening of the abdomen and the
removal of the abdominal organs, may produce a similar temporary
effect. In some instances the duration of this period of depression is
very short, so as to be almost imperceptible ; in others it lasts for
several minutes. After it has passed off, the reflex irritability of the
cord returns to its natural condition, and, if the cord itself have been
wounded or divided, may even be perceptibly increased in intensity.

It is for this reason that the reflex action of the cord often seems to
be more vigorous and prompt in the frog after the removal of the head,

ACTION AS A NERVOUS CENTRE. 461

or the transverse division of the cord itself at its upper part. The
wound of the nervous substance induces an increased excitability of its
gray matter, in consequence of which sensitive impressions of a moderate
character produce a more energetic muscular reaction. This is shown
by the observations of Tiirck, Bernard, and Yulpian, in which, after a
section of one lateral half of the cord, the posterior leg on that side is
withdrawn more rapidly from an acidulated solution than the other ; and
in which the reflex action of the cord, in decapitated animals, becomes
more and more marked, for the posterior limbs, in consequence of suc-
cessive transverse sections made from before backward, in the cervical
and lumbar regions.

The reflex action of the cord may also be increased by poisonous
substances. Strychnine is the most efficient in this respect, and pro-
duces very rapidly an exalted condition of irritability in the spinal cord,
in consequence of which a slight irritation of the skin is followed by
excessive muscular reaction. If a frog be simply decapitated and left
in repose for a short time, the reflex action of the cord manifests itself,
as usual, in a distinct but moderate degree. Slight irritations have no
perceptible effect, and the pinching of the skin in one hind foot usually
causes retraction of that limb only. But if a solution of strychnine
be injected underneath the skin, at the end of ten or fifteen minutes,
when absorption has taken place, the reflex irritability of the cord is
found to be exaggerated in a very marked degree. The animal still
remains motionless if undisturbed ; but the slightest irritation applied
to the skin, the contact of a hair or feather, or the jar produced by
striking the table upon which it is placed, will often be sufficient to
throw it into violent convulsive action, in which all the limbs take part.
As these effects are produced in the decapitated animal, no influence can
be attributed to the action of the brain. Strychnine, accordingly, is a
poison which acts directly upon the spinal cord by increasing its excita-
bility, and by thus causing convulsive movements in consequence of
slight external irritation.

Similar results are known to follow from wounds or injuries either of
the cord itself or of peripheral parts of the nervous system. Brown-
S^quard has found1 that in Guinea-pigs a section of one lateral half of
the spinal cord sometimes produces, after a few weeks, such a condition
of the nervous centres that the animal becomes epileptic, and that epi-
leptiform convulsions of a very intense character may be excited by
pinching the skin of part of the face and neck, on the side corresponding
with the lateral section of the cord. The phenomena of tetanus in man,
following wounds of the peripheral nerves, are also of a reflex convulsive
character. The tetanic spasm is often, if not always, excited by an
external cause ; but this cause is so slight that in the healthy condition
it would have no perceptible effect. The accidental movement of the
bedclothes, the shutting of a door, the passing of a carriage in the

1 Researches on Epilepsy. Boston, 1857.

462 THE SPINAL COED.

street, or even a current of air upon the skin, may be sufficient to throw
the muscular system into severe spasmodic action. The reflex irrita-
bility of the spinal cord may, therefore, be increased or diminished by
various causes acting upon it from without.

Reflex Action of the Cord in Warm-blooded Animals and in Man. —
In the frog, as well as in other cold-blooded animals, the reflex action
of the spinal cord lasts for a comparatively long time after decapitation
or the stoppage of the circulation ; continuing sometimes, if the animal
be kept in repose and sufficiently cool and moist, for twenty-four hours
or even longer. In the warm-blooded animals, it disappears much more
rapidly ; and it must be sought for, if at all, within a very short time
after death, since a nearly constant supply of blood is essential in these
animals to a continuance of the physiological action in every part of the
nervous system. If artificial respiration be kept up, however, so as to
maintain the circulation, the reflex action of the cord will continue to
manifest itself, independently of the brain ; and the same thing may be
accomplished, by dividing the spinal cord in the lower cervical or upper
dorsal region below the origin of the phrenic nerve. The animal then
continues to breathe by means of the diaphragm ; and although deprived
of both sensibility and voluntary motion in the posterior limbs, move-
ments of the leg are produced by pinching the skin of the foot.

Robin has observed the phenomena of reflex action of the cord, after
decapitation, in man, in the case of an executed criminal whose body
was subjected to examination. The reflex muscular contractions were
produced about one hour after the execution.1 " While the right arm
was lying extended in an oblique position by the side of the trunk,
with the hand about 25 centimetres distant from the upper part of the
thigh, I scratched with the point of a scalpel the skin of the chest at
the areola of the nipple, for a space of 10 or 11 centimetres in extent,
without making any pressure upon the subjacent muscles. We im-
mediately saw a rapid and successive contraction of the great pectoral
muscle, the biceps, probably the brachialis anticus, and lastly the mus-
cles covering the internal condyle."

" The result was a movement by which the whole arm was made to
approach the trunk, with rotation of the arm inward and half-flexion of
the forearm upon the arm ; a true defensive movement, which brought
the hand toward the chest as far as the pit of the stomach. Neither
the thumb, which was half bent toward the palm of the hand, nor the
fingers, which were half bent over the thumb, presented any move-
ments."

" The arm being replaced in its former position, we saw it again exe-
cute a similar movement on scratching the skin, in the same manner as
before, a little below the clavicle. This experiment succeeded four
times, but each time the movement was less extensive than before ; and

1 Journal de 1'Anatomie et de la Physiologic. Paris, 1869, p. 90.

ACTION AS A NERVOUS CENTRE. 463

afterward the scratching of the skin over the chest produced only con-
tractions in the great pectoral muscle which hardly stirred the arm."

The neck had been severed, in the above case, at about the level of
the fourth cervical vertebra.

The reflex action may also be seen very distinctly in the human sub-
ject, in certain cases of disease of the spinal cord. If the upper portion
of the cord be disintegrated by inflammatory softening, so that its
middle and lower portions lose their natural connection with the brain,
paralysis of voluntary motion and loss of sensation ensue in all parts
of the body below the seat of the anatomical lesion. Under these con-
ditions, the patient is incapable of making any muscular exertion in the
paralyzed parts, and is unconscious of any injury done to the integu-
ment in the same region. But if the soles of the feet be gently irritated
with a feather or with the point of a needle, a convulsive twitching of
the toes will often take place, and even retractile movements of the leg
and thigh, altogether without the patient's knowledge. Such move-
ments may frequently be excited by simply allowing the cool air to
come suddenly in contact with the lower extremities. We have
repeatedly witnessed these phenomena, in a case of disease of the spinal
cord, where the paralysis and insensibility of the lower extremities
were complete. Many similar instances have been reported by various
authors.

Physiological Action of the Spinal Cord, as a Nervous Centre, during
health. — The physiological character of the reflex action of the spinal
cord, as it takes place in the healthy condition, is not easily brought
under observation. In animals, unless the head be removed or the
spinal cord separated from the brain, the reflex and voluntary move-
ments are liable to be confounded ; and in man during health the phe-
nomena of sensation and volition are so prominent, as to conceal or
obscure those which are performed independently of the consciousness
and the will. Nevertheless, the latter are exceedingly important, and
many of them in almost constant operation.

The general character of the reflex actions of the spinal cord is that
they tend unconsciously to the defence or preservation of the body.
This character is even seen in the simple experiments performed upon
the decapitated frog. If the frog in this condition be suspended in the
air by its anterior extremity, the posterior limbs hang downward in a
perfectly relaxed condition. On pinching the integument of a foot, or
immersing it in acidulated water, the limb is drawn upward by contrac-
tion of its flexor muscles, and the result of this movement is a with-
drawal of the foot from the source of irritation. When the muscles
relax, the limb lengthens until the foot again touches the irritating
liquid, when it is again drawn up ; and so on, until the irritability of
the cord is so far diminished, or accustomed to that particular stimulus,
that it no longer reacts. In this case, therefore, it is not all the mus-
cles of the leg and thigh which are thrown into activity by irritating
the skin, but only the flexors, which tend to withdraw the foot from the

464 THE SPINAL CORD.

irritation to which it is subjected. When an irritation is applied to the
skin on the side of the trunk, it is common to see a hind foot applied to
the irritated spot, as if to protect if from a repetition of the stimulus ;
and in some instances the adaptation of reflex movements to accom-
plish a definite result is very marked. This cannot be attributed to
any faculty of perception belonging to the spinal cord ; since we know,
from pathological cases in man, that when the cord is separated from
the brain by disease or injury, the parts below are left absolutely with-
out conscious sensibility or power of volition. The character of the
movement produced therefore depends directly upon the anatomical
structure of the limbs and the nervous mechanism of the spinal cord.
In the case of reflex action observed by Robin in a decapitated criminal,
the effect of gentle irritation of the skin over the front of the chest
was a simple movement of flexion and inward rotation of the arm and
forearm; and this necessarily brought the hand near the point irri-
tated. It is evident that the connection of the sensitive nerve fibres
with motor fibres, through the gray matter of the cord, may be such as
to call into action muscles which are adapted to accomplish a particular
movement, without the intervention of any perception or voluntary im-
pulse. This is the character of the reflex action of the spinal cord.

As a general rule, movements of flexion are adapted to protect the
part from external irritation or injury, and are excited by ordinary or
moderate causes ; those of extension are calculated to repel the foreign
substance or to escape from it by moving the whole body, and are only
called out by an unusual or excessive stimulus. The defensive or pro-
tective character of these movements is often to be seen, in a state of
health, when the brain takes no part in their production. If the surface
of the skin, for example, be unexpectedly brought in contact with a
heated body, the injured part is often withdrawn by a rapid and con-
vulsive movement, before we feel the pain, or even fairly understand the
cause of the involuntary act. When the body by any accident suddenly
loses its balance, the limbs are thrown into a flexed position, calculated
to protect the exposed parts and to break the fall, by a similar invol-
untary and instantaneous movement. Notwithstanding, therefore, the
evident utility of these actions, they have no intentional character, and
there is not even any distinct consciousness of their object.

The spinal cord has also an important action in regard to the attitude
and to locomotion. The preservation of the attitude alone requires the
harmonious action of many different muscles, all of which contribute
in various degrees to the position of the whole body. This is especially
the case in man, where, in the standing posture, the bod}*- is balanced
upon its narrow supports, in such a way as to preserve its equilibrium
without attention or fatigue. In the movements of locomotion also, the
different flexors and extensors of the anterior and posterior limbs are
associated in a manner peculiar to each species of animal ; and in man
the balancing of the body requires, in progression, a still more exten-
sive combination of muscular action than when at rest.

ACTION AS A NERVOUS CENTRE. 465

The spinal cord by itself is not sufficient to produce the muscular
actions required for standing and locomotion; since we know that any
sudden lesion which deeply injures the brain, or cuts off the medulla
oblongata, or divides the spinal cord above the cervical or lumbar enlarge-
ments, either in mammalia or in man, instantly destroys the power of
standing upright, or of making any effective movements of locomotion.
In the frog, an attitude very similar to the natural one is often preserved
after decapitation, since the body rests by most of its under surface
upon the ground ; and the contact of the integument, through the reflex
action of the spinal cord, brings the limbs underneath it in a flexed
position. If such a frog be held suspended in the air, the limbs hang
down in a relaxed condition, and again assume the natural attitude of
flexion, when replaced in contact with a hard surface ; and, according to
Poincare,1 it can sometimes be made to execute a series of leaps, each
concussion, as the body strikes the ground, giving a fresh stimulus for
another reflex movement of extension in the limbs. But in the case of
the frog and of the amphibious reptiles generally, the muscular actions
required, both for the attitude and for locomotion, are of the simplest
character. In the warm-blooded quadrupeds and in man, on the other
hand, the act of volition is essential for either standing or progression;
and both these powers are abolished by cutting off the communication
of the spinal cord with the brain.

But, although the voluntary impulse is necessary to produce the acts
of standing or walking, it does not seem to be concerned in the details
of their mechanism. Once excited, the nervous action by which walking
is accomplished may be kept up without any mental effort, the attention
being directed to something else. All we have to do is, to commence
the process by an act of volition, and the requisite nervous machinery
is at once set in motion. If we decide to turn a corner, all the muscular
combinations necessary for that purpose are effected without the imme-
diate intervention of the consciousness or the will. This secondary
action, by which the different motor impulses are combined in the limbs
and trunk, is undoubtedly dependent upon the integrity of the spinal
cord.

The precise mode in which this action is accomplished is not positively
ascertained. The most probable explanation at present known is that
it is due to a constant reflex activity of the cord, by which the muscles
in different parts of the body and limbs are kept in the proper degree
of tension or relaxation ; and that the different parts of the cord are
united with each other for this purpose by longitudinal commissural
fibres which enter and leave its gray substance at successive points.
Some authors (Todd, Vulpian, Poincare) adopt the opinion that the
posterior columns constitute such longitudinal commissures. The
reasons for this opinion are not fully satisfactory, since anatomical
investigation has thus far failed to show what is the actual origin and

1 Lecjous sur la Physiologic dn Systfeme Nervcux. Paris, 1873, p. 72.

466 THE SPINAL CORD.

termination of the longitudinal fibres of these columns ; but there are
several facts which give it a strong degree of probability. The three
principal reasons in support of this view are as follows :

I. The posterior columns, as fully shown by direct experiment, are
not the necessary organs of transmission for either sensation or volun-
tary motion ; and they are, nevertheless, composed of nerve fibres which
run in a longitudinal direction. In all the white columns of the cord,
in their deeper parts, where they lie in contact with the gray substance,
there are oblique or horizontal fibres, entering or emerging from the
gray substance, which may either belong to the anterior and posterior
nerve roots, or may be commissural fibres running lengthwise from one
part of the cord to the other.

II. According to Yulpian,1 if the posterior columns be divided by
several transverse sections, at intervals of two or three centimetres dis-
tance from each other, the effect of the operation is a singular disturb-
ance in the power of locomotion, like what would be produced by a loss
of harmony in muscular action.

III. The most important facts, however, bearing on this question, are
those connected with the disease in man, known as locomotor ataxia.
In this affection there is a remarkable difficulty in walking, of such a
character that the patient's natural gait is altered, and he is no longer
sure of his movements. He loses more or less the power of equilibrium,
and cannot guide his foot to a particular point without looking at it
and at the same time making a direct effort of the will. Consequently
locomotion, as it is usually performed, becomes impossible ; and yet the
patient has not lost the power of voluntary movement in any degree,
since he can often exert as much muscular force as ever in grasping an
object or in simply pushing or pulling with his legs or arms. But he
has lost the power of guiding his movements by an involuntary combi-
nation, so as to perform with ease the act of ordinary locomotion. It
is for this reason that the affection is called " ataxia," and not paralysis.

In this disease the only parts of the nervous system which are always
found to be affected are the posterior columns of the spinal cord. They
are the seat of a structural degeneration termed " sclerosis," in which
the elements of the connective tissue are increased in quantity and den-
sity, while the nerve fibres are altered and atrophied, or finally disappear
altogether. According to Brown -Sdquard, an alteration limited to a
small extent of the posterior columns does not usually affect the volun-
tary movements ; but if it extend for a few inches in length, in either
the cervical or the dorso-lumbar region, it always causes a disturbance
of these movements ; and when it occupies the whole length and thick-
ness of these columns, the patient can neither stand nor walk, although
while lying down and with the aid of vision he can move his limbs
freely in any direction.

1 Leqons sur la Physiologie du Systfeme Nerveux. Paris, 1866, p. 381.

ACTION AS A NERVOUS CENTRE. 467

Another important action of the spinal cord, as a nervous centre,
consists in its control over the sphincters and the organs of evacuation.

While the small intestine, the caecum, and the colon are supplied ex-
clusively with nerves from the abdominal plexuses of the sympathetic
system, the lower portion of the rectum receives branches from the
sacral plexus of spinal nerves, which are distributed both to its mucous
membrane and its muscular apparatus. The lower part of the large
intestine acts in great measure as a temporary reservoir, in which the
feces, brought down from above by peristaltic movement, accumulate
until the time arrives for their evacuation. The rectum, in man, is
usually empty, or nearly so, until shortly before evacuation ; and when
the feces begin to pass into it from above, it is still capable of retaining
them for a certain period. Their retention and discharge are provided
for, in this part of the alimentary canal, by two sets of muscular fibres ;
namely, first, the sphincter ani, which keeps the orifice of the anus
closed; and secondly, the levator ani and the circular fibres of the
rectum itself, which by their contraction open the anus and expel the
feces. Both these acts are regulated by the reflex influence of the
spinal cord.

In the natural condition, the sphincter ani is habitually in a state of
contraction, thus preventing the escape of the contents of the intestine.
Any external irritation, applied to the verge of the anus, causes increased
contraction of its fibres and a more complete occlusion of its orifice.
This habitual closure of the sphincter is an entirely involuntary act, as
efficient during profound sleep as in the waking condition, and depends
upon the reflex action of the spinal cord.

But when the rectum is distended to a certain point by feces passing
into it from above, the nervous action changes. The impression then
produced upon the mucous membrane of the rectum, conveyed inward
by its sensitive nerve fibres to the spinal cord, causes a relaxation of
the sphincter ani. At the same time the levator ani draws the borders
of the relaxed orifice upward and outward, and the feces are expelled by
the contraction of the muscular fibres of the rectum itself.

Both these actions are in some degree associated, in a state of health,
with sensation and volition. The distension of the rectum which pre-
cedes an evacuation is usually accompanied by a distinct sensation, and
the resistance of the sphincter may be intentionally prolonged for a cer-
tain period. But this voluntary power over the muscular contractions
is limited. After a time the involuntary impulse, growing more urgent
with the increased distension of the rectum, becomes irresistible ; and
the discharge finally takes place by simple reflex action of the spinal
cord.

If the irritability of the cord be exaggerated by disease, while its
connection with the brain remains entire, the distension of the rectum
is announced by the usual sensation ; but the reflex impulse to evacua-
tion is so urgent that it cannot be controlled by the will, and the patient

468 THE SPINAL CORD.

is compelled to allow it to take place at once. The discharges are then
said to be ''involuntary."

If the cord, on the other hand, be injured or divided in its middle or
upper portions, the sensibility and voluntary action of the sphincter are
lost, because its connection with the brain has been destroyed. The
evacuation then takes place at once, by the ordinary mechanism, as soon
as the rectum is filled, but without any knowledge on the part of the
patient. The discharges are then said to be " involuntary and uncon-
scious."

Finally, if the lower portion of the cord, in the living animal, be broken
up by means of an instrument introduced into the spinal canal, the tonic
contraction of the sphincter ani at once disappears. The same effect is
produced, in man, by disorganization of the lower part of the spinal
cord from injury or disease. The sphincter ani is then permanently
relaxed, and the feces are evacuated almost continuously, without the
knowledge or control of the patient, as fast as they descend into the
rectum from the upper portions of the intestinal canal.

The urinary bladder is also an organ both of reservoir and evacua-
tion, which is protected by the circular bundle of muscular fibres at the
commencement of the urethra, known as the " sphincter vesica?." While
the nerves distributed to the kidneys are derived exclusively from the
coeliac plexus of the sympathetic system, those of the bladder consist
partly of sympathetic filaments from the mesenteric ganglia, and partly
of cerebro-spinal filaments from the lumbar portion of the spinal cord,
both of these sets having united in the abdomen to form the hypogastric
plexus.

The tonic contraction of the vesical sphincter during health, by which
the urine is retained in the bladder, is a continuous, involuntary, and
unconscious act, like that of the sphincter ani. When the time comes
for evacuation, the sphincter is relaxed by a voluntary impulse, and the
muscular coat of the bladder contracts so as to expel its contents; but
although the commencement of this process is a voluntary one, the sub-
sequent contraction of the muscular walls of the bladder continues with-
out any effort of the will. According to the experiments of Giannuzzi1
on dogs, irritation of the lumbar portion of the spinal cord by pricking
with a steel needle, causes contraction of the urinary bladder ; and
these contractions are no longer produced after division of the roots of
the sacral nerves. Irritation of either the sympathetic or the spinal
nerve filaments going to the hypogastric plexus produced contraction
of the bladder, but these contractions were more energetic in the latter
case than in the former.

Diseases or injuries of the spinal cord which cause complete para*
plegia, also usually produce a paralysis of the bladder. So far as re-
gards contraction of the bladder itself, therefore, this act is under the
influence both of the sympathetic and cerebro-spinal systems ; but its

1 Journal dc la Physiologic. Paris, 1863, tome vi. p. 22.

ACTION" AS A NERVOUS CENTRE. 469

most energetic stimulus is derived from the spinal cord through the
sacral nerves.

The closure or relaxation of the sphincter vesicse, on the other hand,
is regulated by nervous influences coming from the cerebro-spinal sys-
tem alone. The contraction of the sphincter offers a resistance to the
escape of fluid from the bladder, which may be measured, and which
was found by Kupressow,1 in the rabbit, to be equal to the pressure of
a column of water more than 40 centimetres in height. That is, if in
the living animal one of the ureters were closed by a ligature, and an
upright tube fastened in the other, the bladder and the upright tube
might be filled with water to a height, on the average, of 44 centimetres
without any of it escaping by the urethra ; beyond that point the con-
tractile power of the sphincter was overcome, and the water was dis-
charged by the urethral orifice.

The experiments of Kupressow also show that the nervous centre
upon which the sphincter vesicae depends for its reflex stimulus is in
the lumbar portion of the spinal cord. For if the cord were divided at
the level of the first or second lumbar vertebrae, no difference was per-
ceptible in the amount of resistance to pressure offered by the sphincter ;
and sections at the levels of the third and fourth lumbar vertebrae made
a difference of only two centimetres. But if the section of the cord were
made at the fifth lumbar vertebra, the resistance of the sphincter was at
once reduced to 14 centimetres; and the same effect was produced by
section at the sixth and seventh vertebrae of the same region. The
tonic contraction, therefore, of the sphincter vesicae, although it may be
aided by an act of volition, is directly dependent upon a nervous centre
situated, in the rabbit, about the "middle of the lumbar portion of the
spinal cord ; since this contraction persists after the cord has been
separated from the brain by a section at or above the fourth lumbar
vertebra, while it disappears if the section be made at or below the fifth
lumbar vertebra, thus either destroying the nervous centre itself or
cutting off its communication with the bladder.

Both the retention of the urine in the bladder and its evacuation may
also be accomplished without the aid of any voluntary act. This is
shown by the experiments of Goltz,2 who found that after division of
the spinal cord, in dogs, between the dorsal and lumbar regions, the
animals, though deprived of sensibility and voluntary motion in the
posterior parts of the body, could often retain their urine for a con-
siderable time, and also evacuate it by a regular and forcible contrac-
tion of the bladder.

In man, when the sensibility of the mucous membrane of the bladder
or neighboring parts is increased by inflammation, the reflex impulse to
micturition is increased in intensity, producing an intolerance of urine.
Under these circumstances the urine is discharged by a reflex act as

1 Archiv fur die gesammte Physiologic. Bonn, 1872, Band v. p. 291.

2 Archiv fur die gesammte Physiologic. Bonn, 1874, Band viii. p. 474.

470 THE SPINAL CORD.

soon as a small quantity of it has accumulated in the bladder. The
impression which excites this discharge is accompanied by a conscious
sensation, but is too urgent to be resisted by the will.

On the other hand, injury or destruction of the spinal cord in the
dorsal region may cut off all sensibility and voluntary power over the
bladder, and yet the organ may be evacuated at regular intervals by
the reflex action of the lumbar portion of the cord. But in diseases or
injuries affecting extensively the lower portion of the cord, a complete
paralysis of the bladder is often produced. The patient is consequently
unable to discharge his urine in the ordinary way, and requires to be
relieved by the introduction of a catheter. If this be not done, the
urine accumulates in the bladder; being retained for a time by the
elastic tissues surrounding the neck of the bladder and the urethra.
But after the distension of its walls has reached a certain point, the
mechanical resistance of the bladder becomes too great to allow any
further accumulation; and the urine dribbles away from the urethra as
fast as it is excreted by the kidneys. Paralysis of the bladder, accord-
ingly, first causes a permanent distension of the organ, which is after-
ward followed by a continuous, passive and incomplete discharge of its
contents.

The spinal cord, therefore, in its character as a nervous centre, exerts
a general protective influence over the whole body. It presides over
the involuntary movements of the limbs and trunk; it supplies the
requisite nervous connection between different muscular actions for the
attitude and locomotion ; and by its control over the muscular appa-
ratus of the rectum and bladder, it regulates the accumulation and
discharge of the excrementitious products of the system.

CHAPTEE Y.

THE BRAIN.

THE brain, or encephalon, comprises all that portion of the cerebro-
spinal axis which is contained within the cavity of the cranium. It
consists of a variety of nervous centres, or collections of gray substance,
connected with each other and with that of the spinal cord by tracts of
longitudinal, transverse, oblique, and radiating nerve fibres. The results
of experimental investigation leave no doubt that each one of these
different nervous centres has a special function, more or less independent
of the others in its immediate action, though necessarily connected with
the rest in the production and external manifestation of the nervous
phenomena. They are situated upon both sides of the median line, and
are, for the most part, evidently arranged in symmetrical pairs, like the
hemispheres of the cerebrum, the cerebral ganglia, the olfactory lobes,
the tubercula quadrigemina, and the two halves of the cerebellum. The
largest of these nervous centres, forming in man nearly four-fifths of the
mass of the entire brain, are the two convoluted masses known as the
"hemispheres" of the cerebrum.

The Hemispheres.

The hemispheres form two ovoidal masses of nervous matter, flattened
against each other at the median line, where they are separated by the
great longitudinal fissure, corresponding to the posterior median fissure
of the spinal cord, and presenting on their lateral surfaces a general
rounded or hemispherical form, whence their name is derived. They
consist externally of a layer of gray nervous substance, and internally
of a mass of white substance, the fibres of which may be said in general
terms to radiate from the cerebral ganglia (corpora striata and optic
thalami) toward the cortical layer of the hemispheres. The external
layer of gray substance, and consequently the surface of the hemis-
pheres, is thrown into numerous folds or convolutions, which are sepa-
rated from each other by fissures, generally from 10 to 25 millimetres
deep. These fissures, like the great longitudinal fissure in the median
line, are simply spaces where the opposite surfaces of two adjacent con-
volutions lie in contact with each other ; and they indicate the points
at which the external layer of gray matter dips down toward the interior,
to return upon itself and form the next convolution. The larger quan-
tity of gray substance is, therefore, situated at the fissures rather than
at the projecting edges of the convolutions between them ; and the more

(471 )

472

THE BRAIN.

numerous and deeper the fissures upon the surface of a brain, the greater
is the amount of gray substance which it contains.

Although the cerebral fissures and convolutions are never all precisely
the same in any two brains, nor even exactly symmetrical in the two
hemispheres of a single brain, yet the principal ones are sufficiently
constant to be regarded as essential features of the organ ; and the
remainder, while varying within certain limits, exhibit a general arrange-
ment which is characteristic of the species of animal to which they belong.
In man they attain a very high degree of development ; and their nomen-
clature is important as enabling us to recognize different parts of the
cerebral surface.

PLAN OF THE FISSURES AND CONVOLUTIONS OP THE HUMAN BRAIN. — The
fissures are designated by letters, the convolutions by numbers. S. Fissure of Sylvius; a.
Anterior ascending branch; b. Posterior horizontal branch. E. Fissure of Rolando. P.
Parietal fissure. 1. First frontal convolution. 2. Second frontal convolution. 3. Third
frontal convolution. 4. Anterior central convolution. 5. Posterior central convolution.
6. Supra-Sylvian, or supra-marginal convolution. 7. Superior temporal convolution. 8.
Angular convolution. 9. Middle temporal convolution. 10. Inferior temporal convolution.
11. Upper parietal convolution. 12. Occipital convolutions.

Next in importance to the great longitudinal fissure, which separates
the two hemispheres upon the median line, is the Fissure of Sylvius (S).
This is a much deeper cleft than the others, and exists, according to
Prof. Wilder, in the brains of all animals where the cerebral surface is
fissured at all. In the human foetus it is the first to appear, being visi-
ble as early as the third month ; and in the adult it forms a basis for

THE HEMISPHERES. 473

the whole geographical division of the hemisheres. It commences as a
transverse indentation on the under surface of the brain, running thence
outward, backward, and upward, thus forming the anterior boundary
of the middle or temporal lobe. In the inferior animals, the whole
hemisphere is seen to be curved round this fissure, the convolutions
generally following its course and bending round its upper extremity in
an arched form ; and in the human brain this arrangement of the lateral
convolutions is also distinctly visible.

On the outer side of the cerebral hemisphere, where it emerges from
the base of the brain, the fissure of Sylvius presents, in man, two dis-
tinct branches, namely a shorter, anterior, ascending branch (a), and a
longer, posterior, more horizontal branch (6, 6, 6). At its middle and
anterior portions, this fissure is very deep, and conceals within its folds
a projecting group of short radiating convolutions, belonging to the
under surface of the brain, between the anterior and temporal lobes,
called the "Island of Reil."

The second fissure in importance, visible upon the convexity of the
hemisphere, is the Fissure of Rolando (II). This fissure runs from
near the median line transversely outward and somewhat obliquely for-
ward, reaching nearly to the middle of the fissure of Sylvius, and form-
ing the boundary line between the frontal and parietal portions of the
hemisphere. It is bordered b}^ two convolutions, one on each side,
running parallel wTith itself, namely, the anterior and posterior central
convolutions (4, 5).

The third principal fissure is the Parietal Fissure (P). It starts
from immediately behind the posterior central convolution, and runs
backward through the parietal portion of the hemisphere, curving some-
what downward upon itself toward its posterior extremity. Outside
and below it are the arched convolutions about the fissure of Sylvius;
inside and above it is a convolution running parallel with the great
longitudinal fissure.

Beside the three fissures just named there are five others, which, though
less deep and strongly marked, are constantly present and show a con-
siderable regularity in their position and arrangement. Three of them
are in the anterior or frontal lobe, in front of the fissure of Rolando.
The first runs parallel with the fissure of Rolando, and a little in
advance of it, toward the anterior extremity of the hemisphere. It is
called the "prsecentral fissure." The second runs through nearly the
whole length of the frontal lobe, in a general direction parallel with
that of the great longitudinal fissure. It divides the upper from the
middle portion of the frontal lobe, and is called the " superior frontal
fissure." The third is the "inferior frontal fissure," and surrounds the
upper end of the short ascending branch of the fissure of Sylvius. The
two remaining fissures of this grade, visible in a lateral view of the
brain, are situated in the temporal lobe, below and behind the fissure of
Sylvius, with which they run in a general parallel direction.

In addition to the fissures already described there are many others
31

474: THE BKAIN.

of secondary importance and more irregular in location, which increase
the convoluted aspect of the cerebral surface. Some of them run longi-
tudinally along the middle of a convolution, dividing it into two nar-
rower parallel folds ; and some of them pass transversely from one of
the main fissures to another, appearing to cut across the intervening
convolution. But in many instances, if the arachnoid and pia mater be
removed, it will be found that these secondary fissures are merely super-
ficial indentations on the surface, or furrows for the accommodation of
a vascular branch ; and that they do not, like the others, penetrate deeply
into the substance of the brain.

The principal convolutions to be distinguished on the convexities of
the hemispheres are as follows :

The First Frontal Convolution (1) runs from the upper end of the
anterior central convolution, just in front of the commencement of the
fissure of Rolando, forward along the edge of the great longitudinal
fissure to the anterior extremity of the frontal lobe, where it bends
downward and backward, terminating below in a straight convolution
next the median line, and resting upon the upper surface of the orbital
plate. This convolution is divided and folded in many ways by secon-
dary transverse, oblique, and longitudinal fissures, but its general direc-
tion is easily recognized. It is bounded externally by the superior
frontal fissure.

The Second Frontal Convolution (2) also takes its origin at the anterior
central convolution, from which it is more or less completely separated
by the praecentral fissure ; thence running downward and forward over
the anterior and lateral part of the frontal lobe. This is the widest of
the three frontal convolutions, and the most abundantly variegated by
secondary folds and fissures. It is separated from the first frontal con-
volution by the superior frontal fissure, and from the third by the inferior
frontal fissure.

The Third Frontal Convolution (3) is situated at the lower and outer
part of the frontal lobe, and curves round the anterior ascending branch
of the fissure of Sylvius. It communicates posteriorly with the lower
end of the anterior central convolution, and by this portion of its sub-
stance helps to cover in and conceal the island of Reil at the bottom of
the fissure of Sylvius.

The Anterior Central Convolution (4) runs transversely outward and
forward along the front edge of the fissure of Rolando. It is usually
a single convolution, but is more or less folded laterally by transverse
indentations. It communicates with the first frontal convolution above
and with the third frontal convolution below. It also curves round the
lower end of the fissure of Rolando, to unite with the following convo-
lution, which may be said to be a continuation of it.

The Posterior Central Convolution (5) also runs parallel with the fissure
of Rolando, but behind it. Above, it turns backward and is continuous
with the convolutions of the upper part of the parietal lobe.

THE HEMISPHERES. 475

The Supra-Sylman or Supra-marginal Convolution (6) starts from the
lower end of the posterior central convolution and thence arches round
the extremity of the fissure of Sylvius. It then continues its curvilinear
course, running downward and forward, parallel with the inferior margin
of the fissure of Sylvius, toward the anterior extremity of the temporal
lobe. In this situation it is known as the First Temporal Convolution (7).
Throughout its course, it is generally divided into two parallel convolu-
tions by a secondary fissure running along its axis, and both of these
secondary convolutions are more or less folded transversely.

The Angular Convolution (8) originates from the preceding and follows
the inferior edge of the parietal fissure backward to its posterior extremity,
where it makes a rather sharp turn downward and forward, whence its
name of the " angular convolution." It then becomes continuous with
the Second Temporal Convolution (9) running downward and forward to
the extremity of the temporal lobe. Below this portion, and running
parallel with it, is the Third Temporal Convolution (10) which forms the
inferior border of the temporal lobe.

The Upper Parietal Convolution (11) is situated above the parietal
fissure, between it and the posterior part of the great longitudinal
fissure. Like the corresponding frontal convolutions, it is much divided
by irregular secondary foldings, and is connected with other convolutions
which are concealed within the great longitudinal fissure. There are also
a number of Occipital Con volutions (12), both longitudinal and transverse,
but these are not conspicuous in a lateral view of the cerebral hemi-
spheres. They are more or less continuous with the upper parietal con-
volution above, and with the second and third temporal convolutions
below.

On a transverse horizontal section of the brain, the convolutions are
seen to penetrate into its substance for varying distances at different
regions. In the anterior and posterior parts the foldings are more
nearly regular in depth, and leave a comparatively thick layer of white
substance between the cerebral ganglia and the gray matter of the con-
volutions. But at the sides of the brain, at the situation of the fissures
of S}Tlvius, the convolutions reach to a much greater depth. The cere-
bral ganglia are placed on each side the median line, near the centre
of the brain; the corpora striata being separated from each other ante-
riorly by the septum lucidum and the cavity of the lateral ventricles,
and the two optic thalami being separated in a similar manner by the
cavity of the third ventricle, except where they are united by the- soft
commissure.

The optic thalami (Fig. 157, 9 ) are surrounded on their outer borders,
and separated from the corpora striata, by a band of white substance,
the internal capsule (10) consisting of fibres passing upward from the
crura cerebri. The corpora striata (*,8) form on each side, at their in-
ferior portions, a continuous mass of gray substance; but for the greater
part of their thickness they are divided into two parts by a tract of
white substance, continuous with the internal capsule, and, like it, con-

476 THE BKAIN.

sisting of bundles of ascending fibres derived from the crura cerebri.
The anterior and more internal of the two parts into which the corpus
striatum is thus divided is the caudate nucleus ( 7 ), so called because a
horizontal section through its uppermost portion exhibits a slender,

Fig. 157.

HORIZONTAL SECTION OF THE HUMAN BRAIN, at the level of the cerebral ganglia.
—1, 2. Anterior and posterior portions of the great longitudinal fissure. 3, 4. Anterior and
posterior parts of the corpus callosum. 5. Fissure of Sylvius. 6. Beginning of the convolu-
tions of the Island of Reil. 7, 8. Corpus Btriatum. 7. Caudate nucleus. 8. Lenticular
nucleus. 9. Optic thalamus. 10. Internal capsule. 11. External capsule. 12. Claustrum.

tail-like prolongation in a backward direction ; the posterior and more
lateral part is called the lenticular nucleus (s), from its having, in a
section at its mid-level, a tolerably regular lens-like figure. Both the
optic thalamus and the corpus striatum are traversed b.y slender bundles
of fibres, visible to the naked eye, and which have a generally radiating
direction upward and outward.

The outer surface of the lenticular nucleus is inclosed by a thin layer
of white substance, the external capsule (n), in which is also to be
seen a very narrow band of isolated gray substance, termed the " claus-
trum" (12). At this situation the layer of gray substance at the bottom
of the fissure of Sylvius is separated from the corpora striata by only a
very narrow interval ; and the fibres running outward and downward

THE HEMISPHERES. 477

from these bodies would reach almost immediately the convolutions of
the Island of Reil.

Intimate Structure of the Hemispheres.— As the longitudinal tracts
of white substance pass upward and forward from the medulla oblongata
and tuber annulare to the base of the hemispheres, they form the two
irregularly cylindrical masses known as the " crura cerebri." Their
fibres plunge, for the most part, directly into the substance of the cor-
pora striata in front, and of the optic thalami behind ; while from these
two pairs of ganglia other fibres emerge into the white substance of the
hemispheres. A portion of the fibres, however, coming from the crura
cerebri, pass, according to Vulpian, Henle, and Meynert, uninterruptedly
onward, in the internal capsule between the optic thalamus and corpus
striatum, and between the two nuclei of the corpus striatum; thus
reaching the white substance of the hemispheres without having tra-
versed the gray matter of the ganglia.

From this level, that is, above and outside of the cerebral ganglia, the
ascending divergent tracts of white substance form a spreading crown
of nerve fibres, which radiate in all directions to the layer of gray sub-
stance on the exterior. These fibres are of very small size, as compared
with those in the peripheral portion of the nervous system ; their aver-
age diameter, according to Kolliker, being 4.5, and none of them being
larger than 6.7 micro-millimetres in thickness.

The general direction of the radiating nerve fibres is easily seen, in
brains hardened in alcohol, to be that described above. At the same
time, microscopic examination shows that they are abundantly mingled
with other fibres which cross them at right angles, or nearly so, and
which are to be found more or less in every portion of the white sub-
stance of the hemispheres. These horizontal or curvilinear cross fibres
are derived in great measure from the lateral expansions of the corpus
callosum, the transverse fibres of which spread out in various direc-
tions, bending toward the convolutions of the upper, middle, and lower
part of the hemispheres. As these fibres come from the median line at
the level of the corpus callosum. they necessarily cross those which are
ascending from the cerebral ganglia below. The corpus callosum is
consequently a great transverse commissure, uniting the two hemi-
spheres of the cerebrum with each other. There are also fibres imme-
diately beneath the cortical layer of gray substance, following the curve
of the convolutions where they project inward into the white substance.
These are known as the " arciform fibres," and are regarded as connect-
ing filaments between the gray substance of adjacent convolutions.

The gray substance of the cerebral convolutions forms an external
layer, from two to three millimetres in thickness, into which the fibres
of the white substance penetrate from within in a perpendicular manner.
It consists of a uniform granular matrix, in which are imbedded the
nerve cells, and through which the fibres continue their course in va-
rious directions. The nerve cells are rounded or irregular in form, with
a varying number of simple or branched prolongations. In the middle

478

THE BRAIN.

VERTICAL SECTION OF ONE OP THE CE-
REBRAL CONVOLUTIONS ; showing pyramidal
cells, and bundles of fibres passing outward from
the white substance. Magnified 300 diameters.
(Henle.)

portion of the layer of gray
substance, the cells are distin-
guished by their pyramidal
form ; the pointed extremity of
the cell being, with few excep-
tions, directed toward the surface
of the brain, and the base toward
the white substance of the inte-
rior. According to Henle, they
have an average diameter of 15
mmm. Two, three, or sometimes
even four prolongations extend
from the angles at the base of
the cell, running inward toward
the white substance, and be-
coming more or less divided and
ramified ; while the pointed ex-
tremity, on the other hand, ex-
tends outward in a single pro-
longation toward the cerebral
surface.

The fibres, as they penetrate
from the white into the gray
substance, are arranged in bun-
dles, where they at first run in
a general direction parallel with
each other. But these bundles
rapidly diminish in size, as the
fibres diverge laterally to pursue
a more or less horizontal course ;
and in the external portions of
the gray substance there are
only isolated fibres running in
various directions. In the gray
substance, the nerve fibres be-
come reduced to their smallest
dimensions, measuring, accord-
ing to Kolliker, from about 1 to
2 mmm. in diameter. Some of
them spread out at various levels
in the cortical layer, while others
continue a vertical or oblique
course quite to the superficial
portions of the gray substance.

The immediate relation be-
tween the fibres and cells of the
gray substance of the hemi-
spheres has not been determined

THE HEMISPHERES. 479

with absolute certainty. Although a few isolated instances have been
reported in which a cell prolongation has been seen to become con-
tinuous with a medullated nerve fibre, it is usually impossible to
demonstrate this by direct observation, and some of the best micro-
scopists have been unable to see it in a single instance. The probability
that such a connection exists is assumed from the fact that many of the
nerve fibres in the gray substance become so slender and pale as to
resemble very closely the cell prolongations ; and, on the other hand,
the cell prolongations frequently run in the same direction with the
nerve fibres. According to Henle1 the prolongations, given off from
the bases of the pyramidal cells, are so often seen to lose themselves in
the bundles of nerve fibres coming from the white substance as to justify
the assumption that the fibres in these instances terminate in the cells.
The delicacy of texture of the gray substance and the distance through
which a cell prolongation runs before it attains the character of a nerve
fibre may be sufficient reason whjr the connection is not more frequently
seen in microscopic preparations.

Physiological Properties of the Hemispheres. — The importance of
the hemispheres, in connection with the higher manifestations of nervous
action, is sufficiently indicated by their excessive development in man,
as compared with the other portions of the encephalon. For while in
the lower mammalians they are of medium size, and often smooth or
sparingly convoluted upon their surface, and in reptiles and fish are
sometimes hardly larger than the other nervous centres of the brain, in
man they acquire such an extension as to cover and surround almost
completely every other part of the encephalic mass, their superficial
layer of gray substance being at the same time still further increased by
the multiplied convolutions of its surface.

Notwithstanding, however, the evident importance of the hemispheres
as special parts of the nervous system, the first fact certainly known in
regard to them is that they are not, even in man, directly essential to
life. That is to sa}r, they do not hold under their immediate control
any of the physiological acts, like those of respiration and circulation,
which are necessary to the continuance of vitality. They often influ-
ence these acts, in an indirect manner, by the sympathetic connections
of the nervous system; but life will continue for a certain period under
the influence of other nervous centres, without the aid of the cerebral
hemispheres.

This is readily demonstrated in some of the lower animals by the
entire removal of the hemispheres on both sides. In man, extensive
morbid changes may take place in these parts, or severe mechanical
injuries, accompanied by greater or less loss of substance, may be in-
flicted upon them without producing a fatal result. In a case reported
by Prof. Detmold,2 of abscess in the anterior lobe of the brain, a knife

1 Anatomie des Menschen. Braunschweig, 1871, Nervenlehre, p. 270.

2 American Journal of the Medical Sciences. Philadelphia, January, 1850.

480 THE BRAIN.

was passed into the cerebral substance, making a wound one inch in
length and half an inch in depth, when the abscess was reached and pus
discharged. The patient immediately aroused from his comatose con-
dition, and was able to speak; but the collection of pus afterward
returned, and the patient finally died at the end of seven weeks from
the time of opening the abscess.

In another case,1 a pointed iron bar, three feet and a half in length,
and one inch and a quarter in diameter, was driven through a man's
head by the premature blasting of a rock. The bar entered the left side
of the face, near the angle of the jaw, and passed obliquely upward,
inside the zygomatic arch and through the anterior part of the cranial
cavity, emerging from the frontal bone at the median line, just in front
of the point of union of the coronal and sagittal sutures. The patient
became delirious within two days after the accident, and subsequently
remained partly delirious and partly comatose for about three weeks.
He then began to improve, and at the end of rather more than two
months from the date of the injury was able to walk about. At the
end of sixteen months the wounds were healed, and the patient had
recovered his general health, though with loss of sight in the eye of the
injured side.

The patient survived for a little over twelve years, being able to do
the ordinary work of an ostler, coachman, and farm-laborer, in all of
which occupations he was employed at various intervals. He died in
1861, after a short illness accompanied by convulsions. The skull,
which was subsequently deposited in the Warren Anatomical Museum,2
shows the openings corresponding with the points of entrance and exit
of the iron bar.

The conclusions derived from comparative anatomy, from pathological
observations in man, and from experiments upon animals, all show that
the cerebral hemispheres are especially connected with the manifesta-
tions of conscious intelligence, as distinguished from involuntary reflex
actions, simple sensations, or instinctive movements.

I. So far as we can judge of the character and extent of these mani-
festations in the lower animals, they correspond directly with the develop-
ment of the hemispheres, rather than with that of any other portion of
the encephalon. In many of the lower animals, muscular power and
endurance, the activity of some of the special senses, and the promptitude
and certainty of the instincts, are much greater than in man ; while in
the human species, the intelligence is the only faculty which is invari-
ably superior to that of animals, and which always gives to man the
advantage over them. Even among animals, that which especially cha-
racterizes certain species, and which most nearly resembles that of man,
is a teachable intelligence ; that is, one which understands the meaning

1 American Journal of the Medical Sciences, Philadelphia, July, 1850.

2 J. B. S. Jackson, Descriptive Catalogue of the Warren Anatomical Museum.
Boston, 1870, p. 145.

THE HEMISPHERES. 481

of impressions or objects presented to it, and thus enables its possessor,
by comprehending and retaining new ideas, to profit by experience.

II. The general result of injury, disease, or disorganization of the
hemispheres in man, especially affecting the gray substance of the con-
volutions, is a disturbance, diminution, or suspension of the intellectual
faculties. In these cases, among the earliest and most constant of the
morbid phenomena is a loss or impairment of memory. The patient
forgets the names of particular objects or of particular persons ; or he
is unable to calculate numbers with his usual facility. His mental
derangement is often shown in the undue estimate which he forms of
passing events. He is no longer able to appreciate the relation between
different objects and phenomena. He will show an exaggerated degree of
solicitude about a trivial occurrence, and will pay no attention to matters
of real importance. As the difficulty increases, he becomes careless of
directions and advice, and must be managed like a child or an imbecile.
Finally, when the injury to the hemispheres is complete, the senses may
still remain active and impressible, while the patient is completely de-
prived of intelligence, memory, and judgment. The constancy of these
results when the lesion is situated in the hemispheres, and the fact that
they often occur without being accompanied by any loss of sensibility
or motion, show the close connection between the mental powers and
the nervous action of this portion of the brain.

The same connection is seen in the existence of congenital idiocy with
imperfect development of the brain. In many cases the immediate con-
dition upon which the idiocy depends is the small size of the brain as a
whole, particularly conspicuous in the cerebral hemispheres. The general
and special senses, and the activity of the nervous system at large, are
sometimes fully developed in these instances, while the intelligence
proper remains at so low a grade, that no improvement in the mental
operations is possible and teaching is almost without effect.

This was the case, in a marked degree, with a pair of dwarfed and
idiotic Central American children, who were exhibited at one time in
the United States, under the name of the " Aztecs." They were a boy
and a girl, aged respectively about seven and five years.

The antero-posterior diameter of the boy's head was only 4j inches,
the transverse diameter less than 4 inches. The antero-posterior diameter
of the girl's head was 4^ inches, the transverse diameter only 3| inches.
The habits of both, so far as regards feeding and taking care of them-
selves, were those of children two or three years of age. They were
incapable of learning to talk, and could only repeat a few isolated words.
Notwithstanding, however, their limited intelligence, they were remark-
ably vivacious and excitable. While awake they were in almost con-
stant motion, and any new object or toy presented to them immediately
awakened a lively curiosity. They understood readily the meaning of
those who addressed them, so far as it could be conveyed by gesticula-
tion and the tone of voice ; but they could not be made to comprehend

482 THE BRAIN.

Fig. 159.

THE "AZTEC" IDIOTIC CHILDREN. — Taken from life, at five and seven years of age.

articulate language, and, as in other idiots, mental instruction was with-
out result.

III. Experiments performed upon the lower animals, by removal of
the hemispheres, lead to a similar result. In large and full grown mam-
malians the injury is usually fatal, owing in* great measure to the.
attendant hemorrhage ; but it may be performed in fish, reptiles, birds,
and sometimes in young quadrupeds without producing death. Vulpian
has succeeded in maintaining life, after this operation, in the frog, the
turtle, the pigeon, the cock, the rabbit, and the rat. The result is that
these animals retain their sensibility and power of motion, and continue
to maintain the normal attitude and to perform many instinctive and
reflex movements ; but spontaneous action, and its conscious adaptation
to external conditions, is abolished with the removal of the cerebral
hemispheres.

The operation is very readily performed upon the pigeon, and its
effects in this animal are uniform and distinctly marked. After removal
of both hemispheres, the bird maintains without difficulty the standing
posture, and will even rest upon a perch with security if undisturbed ;
but he remains in a state of profound quietude, almost completely indif-
ferent to surrounding objects. He stands upon the ground or rests
upon his perch, with the eyes closed and the head sunk between the
shoulders. The plumage is smooth and glossy, but is uniformly ex-
panded, by erection of the feathers, so that the body appears puffed out
and larger than natural. Occasionally the bird opens his eyes, stretches
his neck, shakes his bill once or twice, or smooths down the feathers
upon his shoulders, and then relapses into his former apathetic condi-
tion. This characteristic state of immobility comes on immediately after
removal of the hemispheres.

It is not accompanied, however, by loss of either general or special
sensibility. If the foot of the bird be pinched with a pair of forceps, he
becomes partially roused and moves uneasily once or twice from side to
side, as if to escape the irritation. Yulpian has seen a pigeon within a

THE HEMISPHERES. 483

short time after the operation shake the head briskly in consequence of
a fly having alighted on the wound. Hearing and sight also remain.
The discharge of a pistol behind the back of the pigeon will often cause
him to open his eyes and turn his head partially round, giving evident
signs of having heard the report ; though he immediately becomes quiet
again and pays it no further attention. In a rat which had been sub-
jected to this operation by Yulpian, a sharp hissing sound made by the
lips produced a sudden start and movement of the whole body. The
same observer found that in a pigeon, after the animal had been roused

Fig. 160.

PIGEON, AFTER REMOVAL OF THE CEREBRAL HEMISPHERES.

by pinching the foot, the sudden approach of a hand toward the eye
caused a winking movement with partial turning of the head. Some-
times such a pigeon will fix his eye on a particular object, and watch it
for several seconds together. Longet found that by moving a lighted
candle before the animal's eyes in a dark place, the head of the bird would
often follow the movements of the candle, showing that the impression
of light was perceived.

The animal is still capable, therefore, after removal of the hemispheres,
of receiving sensations from external objects. But these sensations
make upon him no lasting impression. He is incapable of connecting
with his perceptions any distinct succession of ideas. If he hears the
report of a pistol, he is not alarmed by it ; for the sound, though dis-
tinctly enough perceived, does not suggest any idea of danger or injury.
There is accordingly no power of perceiving the relation between ex-
ternal objects. The memory, particularly, is destroyed, and the recol-
lection of sensations is not retained from one moment to another. The
muscles are still under the control of the will ; but the will itself is
inactive, because it lacks its usual stimulus and direction. The powers
which have been lost, therefore, are those of a mental character ; that is,
the power of comparing different sensations or ideas, of perceiving the

484 THE BRAIN.

proper relation between them, and of originating in consequence an in-
telligent volitional act.

The cerebral hemispheres as a whole are therefore evidently the
centres in which the nervous mechanism of mental action is accom-
plished. The mental endowments which are concerned in the manifesta-
tions of the intelligence are mainly the memory, the reason and the
judgment.

Memory is the simplest and most essential of these faculties for the
due performance of intelligent acts. The recollection of names, and of
the objects to which they belong, is indispensable even to the use of
articulate language ; and a deficiency of memory seems often to be the
immediate condition upon which the incapacity of idiotic children to
talk depends. It is also constantly essential in the ordinary occupations
of life, in enabling us to retain past impressions as a guide for imme-
diate or future acts.

The reason may be considered as the faculty by which we appreciate
the character of the nervous impressions received, and are enabled to
refer them to their external source. This is quite different from the
simple power of perception, which continues, as experiment has demon-
strated, after the removal of the cerebral hemispheres. The mental
action which is excited by an impression coming from without is one
which transfers the attention from the internal sensation to its external
source ; and when this action is prompt and effectual, we at once acquire
an idea of whence the impression originated and what is its significance.
The perfection of this quality consists in the certainty with which it
appreciates the relation between an effect and its cause, and the relative
importance of different phenomena. This capacity is deficient or absent
in idiots, and consequently they cannot avoid dangers or provide for
their necessities. For the same reason it is useless to punish an idiot,
because, although he may feel the pain inflicted, he does not refer it as
a consequence to any previous action of his own. A deficiency of the
same quality in the insane, or in those in whom it is naturally imper-
fect, produces a want of power to comprehend the importance and connec-
tion of different events. They are said to be " unreasonable," because
they expect results which are unlikely to follow from certain causes,
and because they assume the existence of causes which are not realty
indicated by the results.

The judgment is the faculty by which the appropriate means are
selected for the accomplishment of a particular end. Its exercise re-
quires the existence of reason and memory, which supply the necessary
conditions upon which it is based ; but its own action is one which
looks to the future rather than to the past. An individual in whom the
judgment is well developed employs, under the guidance of experience,
means which are well adapted to attain the end he has in view ; one
who is deficient in this respect resorts to means which are insufficient
or inappropriate, and is consequent!}' unsuccessful. Whether the act
performed in this manner be a simple mechanical operation, like that of

THE HEMISPHERES. 485

shutting a door to exclude the cold, or a complicated plan involving
many parts, the mental process is the same in kind, and differs only in
degree ; its essential character being that it is an intelligent act, based
upon an understanding of the previous conditions, and intended to
accomplish a definite result.

It is evident that all such manifestations of intelligence, taking place
through the cerebrum, are reflex actions. Their starting point is a sen-
sation coming from without, which gives rise in the mind to a succession
of internal operations, terminating in an intelligent volitional impulse.
This is reflected from within outward, and thus finally calls into action
the nerves of voluntary motion. There can be little doubt that the
intermediate process, between the sensation and the volitional impulse,
takes place in the gray substance of the cerebral convolutions.

Special Seat of the Facility of Articulate and Written Language. —
Most of the lower animals have the power of communicating with each
other by certain movements and vocal sounds in such a way as to
attract their attention, and enable them to act in concert. The lan-
guage thus employed is always a language of expression, and consists
in such modifications of the tone of voice or the position of the limbs as
indicate pleasure or dislike, excitement or alarm, or a friendly or hostile
disposition. In man the same methods are largely used to express
similar feelings, and to represent others, such as surprise, contempt,
amusement, or doubt, which do not seem to exist in animals to an ap-
preciable degree.

But man has also the faculty of conveying definite information by
means of articulate speech, in which arbitrary sounds are used to indi-
cate special objects, qualities, or acts, as well as all the relations which
may exist between them. The power of using articulate language, as a
vehicle for the expression of the thoughts, is generally in proportion to
the development of the intelligence as a whole. In order that it may
be exercised, two faculties must come into action; namely, first, the
memory, by which the particular words required are brought to the
mind ; and, secondly, the voluntary combination of motor impulses
necessary for their articulation. These acts are performed, in health,
with such rapidity that we are not conscious of them ; and the exercise
of speech seems to be a direct consequence of the ideas which are to be
expressed. But pathological cases show that either one or both of
these faculties may be absent, while the ideas and the desire to express
them are as distinct as ever.

The affection, in these cases of loss of the power of language, is termed
aphasia. It does not depend upon a want or confusion of ideas, be-
cause the patient is often perfectly clear as to what he wishes to say,
although he cannot say it. It i's not due to paralysis of the organs of
articulation, since the tongue, lips, and palate can be moved in every
direction with the usual facility. It is a deficiency or suspension of the
power, either to recall the word needed, or to set in motion the nervous
actions required to pronounce it. In the former instance it is called

486 THE BRAIN.

u amnesic aphasia." The patient cannot say what he wishes, because
he cannot recollect the word he wants. For the same reason he is also
incapable of writing it. But if the word which he requires be spoken
to him, he can repeat it immediately, though in a few seconds it has
again escaped him. This disease is an aggravated form of that condi-
tion to which many otherwise healthy persons are occasionally liable ;
namely, that of forgetting for a time a particular word at the moment
they wish to use it. In some cases of aphasia the loss of power is so
complete that the patient can utter only two or three words, which he
employs indiscriminately whenever he speaks at all.

In the second variety of the affection, the patient knows the word he
wants, but cannot succeed in articulating it. He can, therefore, express
himself by writing perfectly well, but cannot read aloud even what he
has written himself. This is called " ataxic aphasia," because it de-
pends not upon an imperfection of memory, but upon a want of power
to effect the necessary nervous combinations.

There is no question that the power of language resides somewhere
in the cerebral hemispheres, and many observations have tended to
locate it more especially in the convolutions surrounding the lower end
of the fissure of Sylvius, and in those of the Island of Eeil. Broca
fixes it more especially in the third frontal convolution, surrounding the
anterior, ascending branch of the fissure of Sylvius, while others have
referred it to the frontal lobe in general. The evidence for this locali-
zation of the faculty of language consists in the number of instances in
which aphasia more or less complete has been found, on post-mortem
examination, to be accompanied by lesions of the brain substance con-
fined to the points indicated. It is often accompanied by hemiplegia
of the opposite side of the body, but may sometimes exist independently
of any paralytic affection.

According to Broca, it is, as a rule, the third cerebral convolution of
the left hemisphere alone which is concerned as a nervous centre in the
production of articulate language. This conclusion is derived from the
fact, which is generally conceded by pathologists, that in the large
majority of cases in which aphasia is accompanied by hemiplegia, the
hemiplegia is on the right side of the body, the lesion accordingly occu-
pying the left side of the brain. But as aphasia is generally due to
occlusion of the middle cerebral artery by an embolism, and as embolism
is more likely to occur on the left side than on the right, owing to the
different angle at which the vascular branches are given off, this fact may
not indicate the exclusive, or even preponderating influence of the left
side of the brain in the function of articulate language. Notwithstand-
ing some remarkable cases which would tend to show a special location
of this function upon the left side, such as that of chronic left hemiplegia
without aphasia, followed in the same individual by a sudden attack of
right hemiplegia with aphasia,1 yet instances of an opposite kind are

Bateman on Aphasia. London, 1870, p. 152.

THE HEMISPHERES. 487

also so numerous that the physiological question cannot be regarded as
settled. We are only certain that aphasia is most frequently produced
by lesions occupying the left hemisphere, in the convolutions about
the bottom and edges of the fissure of Sylvius ; that is, in the parts
nourished by branches of the middle cerebral artery.

Special Centres of Motion in the Cerebral Hemispheres.— As a rule,
both the white and gray substance of the hemispheres are found to be
both insensible and inexcitable under the application of ordinary artifi-
cial stimulus ; neither sensation nor motion being produced in the living
animal by mechanical irritation or injury of these parts. In man, also,
it has been repeatedly observed that the substance of the brain, when
exposed by accident or disease, gives no indication of sensibility or of
motor endowments, if subjected to external irritation.

More careful and extended observations, however, upon the lower
animals, have shown that under the influence of galvanic stimulus of a
low degree of intensity certain points on the surface of the cerebral con-
volutions will give rise to definite movements in the muscles of the head,
body, and limbs. The fact was first discovered by Fritsch and Hitzig
in 1870,1 and has been subsequently fully confirmed by other observers.
The experiments were performed first and most frequently on dogs ;
afterward on cats, guinea pigs, rabbits, and monkeys ; the animals being
sometimes stupefied by ether, chloroform, or morphine, sometimes not
subjected to any anaesthetic influence.

The general results derived from these experiments, as given by
Hitzig, are as follows :

I. One portion of the convexity of the cerebrum, in the dog, is motor ;
another portion is not motor.

II. The motor portion lies, in general terms, more anteriorly; the
non-motor portion more posteriorly.

III. Electrical stimulation of the motor portion produces co-ordinated
muscular contraction on the opposite side of the body.

IY. With very weak electric currents, the contractions produced are
distinctly limited to particular groups of muscles; with stronger cur-
rents, the stimulus is communicated to other muscles of the same or
neighboring parts.

Y. The portions of the brain intervening between these motor centres
are inexcitable by similar means.

These conclusions have been verified by a variety of observations in
Germany, France, England, and the United States.'2 The experiments,
which are most readily performed on dogs, owing to the large size of
the cerebrum, and the comparatively little injury suffered from hemor-

1 Archiv fur Anatomie, Physiologic und Wissenschaftliche Medicin. Leipzig,
1870, p. 300. Hitzig, Untersuchungen liber das Gehirn. Berlin, 1874.

2 Report of a Committee of the New York Society of Neurology and Electro-
logy on the Existence and Localization of Motor Centres in the Cerebral Con-
volutions. New York Medical Journal, March, 1875, p. 225.

488 THE BRAIN.

rhage, yield results which are sufficiently uniform to show that they
depend upon important physiological conditions. In those performed
by the committee of the New York Society of Neurology and Electro-
logy, the animals were etherized and kept more or less completely under
the influence of the anaesthetic during the whole course of the experi-
ments. The stimulus employed was a galvanic current from a battery
of from 8 to 16 cells, of an intensity just sufficient to be distinctly per-
ceptible, but not painful, when applied to the surface of the tongue.
The electrodes were rounded platinum points, fixed at a distance of one
millimetre apart. They were applied to the surface of the cerebrum in
such a manner as not to wound but only to touch it, and were held in
contact with the brain for about one second only at each application.
The applications were repeated at short intervals at the same spot for
from ten to forty times in succession, in order to make sure that the
reactions obtained were not accidental. The results show plainly that
there are certain limited spots, on the surface of the cerebral convolu-
tions, at which the application of a faint galvanic current will cause dis-
tinct momentary contraction of separate muscles, or groups of muscles,
on the opposite side of the body. These spots correspond in all essential
particulars with those discovered by Hitzig, and are near!}', though not
quite, uniform in location on the two opposite sides, and in different
animals.

All the centres of motion for the anterior and posterior limbs are
situated, in the dog, in the convolution immediately surrounding the
frontal fissure (Figs. 161, 162, F), a nearly transverse furrow running
outward and forward from the median line, which may be considered
as corresponding to the fissure of Rolando in the human brain, but
placed farther forward in the dog, owing to the inferior development of
the frontal lobe. In a majority of cases, the motor centres for the
anterior limbs (3, 4) are situated more in front, near the outer extremity
of this fissure ; those for the posterior limbs (5, 6) farther backward and
inward. At certain points, movements of flexion are produced, at
others, movements of extension ; sometimes flexion of a single paw alone
takes place, sometimes flexion or extension, more or less complete, of a
whole limb ; and sometimes, at certain spots, there is flexion or extension
of the fore and hind limbs together, or partial flexion of one, accompanied
by extension of the other. But in the majority of cases, the movements
produced are isolated movements of flexion or extension of a single limb.

The centre for flexion of the head on the neck in the median line (1)
is in the lateral and anterior part of the convolution situated in advance
of the frontal fissure, where this convolution bends downward and out-
ward ; tha.t for flexion of the head on the neck, with rotation toward the
side of the stimulus, is in a part of the same convolution (2), situated
still farther forward and downward, so as to be invisible in a view of
the brain taken from above.

The centre of motion for the orbicularis oculi, and, according to
Hitzig, for the facial muscles generally, is in a region situated upon the

THE HEMISPHERES.

489

lateral part of the hemisphere (7, 8, 9), immediately about the supra-
Sylvian fissure.

The action of the cerebral convolutions in producing muscular con-
traction, when this contraction is definite and limited, is always a

Fig. 161.

Fig. 162.

BRAIN OF THE DOG.— Fig. 161, view from above; Fig. 162, profile view; showing the cen-
tres of motion in the cerebral convolutions. F. Frontal fissure. S. Fissure of Sylvius. The
unshaded part is that exposed by the opening in the skull, F. Frontal fissure. S. Fissure
of Sylvius. 1. Flexion of head on the neck, in the median line. 2. Flexion of head on the
neck, with rotation toward the side of the stimulus. 3,4. Flexion and extension of anterior
limb. 5, 6. Flexion and extension of posterior limb. 7, 8, 9. Contraction of orbiciilaiia oculi,
and the facial muscles in general.

crossed action ; galvanization of the convolutions, on either side of the
brain, exciting movement in the muscles, both of the limbs and face,,
on the opposite side of the body.. On the other hand,, galvanization of
32

490 THE BRAIN.

the dura mater or other sensitive parts, produces, by reflex action,
muscular twitching on the same side of the body.

The existence of these excitable points in the cerebral convolutions
does not show that they are nervous centres for the immediate pro-
duction of voluntary movement. On the contrary, we know that the
parts of the brain containing them, and, in some animals, even the whole
hemispheres, may be removed and yet the power of movement in the
limbs may be preserved. But they are evidently points from which an
influence may extend inward toward the central parts of the brain, excit-
ing there the immediate cause of motor action ; and this influence is
transmitted through the cerebral substance by definite paths, as much
so as that passing in the ramifications and fibres of the peripheral motor
nerves.

The only doubt which has been entertained in regard to the signifi-
cance of these experiments is that which attributes the muscular con-
traction, not to the galvanization of the convolutions themselves, but to
a diffusion of the electric current from without inward, and a consequent
extension of the galvanic stimulus to the deeper parts of the brain, espe-
cially the corpus striatum and ascending fibres of the crus cerebri. But
the conditions of the experiment show that this is not the case. When
the distance between the two electrodes, and consequently the length of
the current traversing the surface of a convolution, is only one milli-
metre, their application to a particular spot may produce, many times
in succession, a definite muscular contraction ; and yet their application
to other spots not more than five millimetres distant from the first, and
equally near the base of the brain, may be entirely without effect.

Furthermore, direct proof of the part taken by the convolutions in
the production of these phenomena is supplied by the experiments of
Braun1 and Putnam.2 In these experiments points were found upon
the cerebral convolutions which produced, under the application of elec-
tric stimulus, the usual definite muscular contractions. A horizontal
section was then made at a depth of one or two millimetres beneath the
surface, leaving the flap in place but cutting off the anatomical con-
tinuity of brain tissue. The irritation, being then reapplied to the
original spot, failed to excite any muscular contraction ; but if the flap
were turned up and the electrodes applied to the cut surface beneath,
a current of similar or slightly increased strength again produced the
same movements as before. Repeated trials of this kind, the flap being
alternately removed and readjusted, yielded the same results. It is
evident, therefore, that when the electrodes, applied to the surface of the
uninjured brain, cause movements on the opposite side of the body, this
effect is not due to a diffusion of the electric current itself toward the
base of the brain, but to a nervous stimulus originating in the convolu-
tions, and thence transmitted inward by the fibres of the white substance.

1 Centralblatt fur die Medicinischen Wissenschaften. Berlin, June 13, 1874,
p. 455.

2 Boston Medical and Surgical Journal, July 16, 1874.

THE CEREBRAL GANGLIA* 491

The Cerebral Ganglia.

The corpora striata and optic thalami, from the position which they
occupy at the central part and base of the cerebrum, in the course of
the ascending fibres of the crura cerebri, must be regarded as nervous
centres interposed between the medulla oblongata below and the hemi-
spheres above. According to Henle, the bundles of white substance
from the posterior portion of the cms cerebri, on passing into the optic
thalamus, spread out in pencil-like tufts of diverging fibres, which become
generally distributed throughout the gray substance of the ganglion,
and are even mingled in its interior with transverse or interlacing fila-
ments. It is conceded by both Kolliker and Henle that some, or even a
considerable proportion, of these fibres terminate in the gray substance ;
while a portion, or perhaps other fibres originating in the gray substance,
pass outward again, from the anterior and lateral parts of the thalamus,
to continue their course upward to the cerebral convolutions.

In the corpus striatum, the relation of the fibres to the gray substance
is, in general, the same as in the thalamus ; that is, they are derived
from the ascending bundles of the crus cerebri and terminate in the
gray substance of the ganglion. The difference between the two bodies
is that in the thalamus the mixture of the fibres with the gray substance
is more intimate and uniform throughout, while in the corpus striatum
the fibres are arranged in distinct bundles, readily visible to the naked
eye, which only disappear, by the dispersion and termination of their
filaments, at the distance of about one millimetre from its outer edge ;
so that the ganglion is bordered externally at this situation by a
thin layer of gray substance in which no white striations are to be
seen. In the corpus striatum, as in the optic thalamus, there are also
bundles of fibres, according to the observations of Kolliker, which at
certain levels pass from the gray matter of the ganglion into the white
substance of the hemispheres. Both the corpus striatum and optic
thalamus contain nerve cells with ramified prolongations, some of which
closely resemble the finest nerve fibres with which they are mingled,
and with which many anatomists believe them to be continuous.

The exact physiological function of the cerebral ganglia, as distin-
guished from the hemispheres proper, is not precisely determined. It
is plain that they exert some influence, of an intermediate character,
between the action of the cerebral hemispheres above and the direct
transmission of motor and sensitive stimulus to or from the parts
below. They have both been found to be, like the hemispheres, insen-
sible to ordinary mechanical irritation, unless this be applied so deeply
as to reach the fibrous bundles of the crura cerebri in their inner and
deeper parts. They cannot be extirpated or extensively injured with-
out at the same time cutting off more or less completely the connection
of the hemispheres with the peripheral nervous system ; but they may
be removed at the same time with the hemispheres, in some of the lower

492 THE BRAIN.

animals, and yet the power of motion and of sensibility may be retained
to a considerable extent.

It is certain, however, from the known facts of pathology, that their
influence is an important one, since, in man, lesions of these ganglia are
almost always followed by more or less complete hemiplegia on the
opposite side of the body. In general terms, the effect of cerebral
hemorrhage, whether from injury or disease, may be said to vary accord-
ing to its location; hemorrhage upon the surface of the hemispheres
producing coma, that in the cerebral ganglia causing hemiplegia. The
usual significance attached to the term " hemiplegia" is that of loss of
voluntary motion on one side, while a corresponding loss of sensibility
is designated as hemiansesfhesia. In cases of lesion of the cerebral
ganglia or adjacent parts, the loss of motion is usually the most promi-
nent symptom, hemiansesthesia being either entirely absent or disap-
pearing rapidly, while the motor paralysis lasts a longer time. On the
other hand, hemiansesthesia may continue after the power of motion is
recovered, and it may also be produced in animals by lesions of the
brain without being accompanied by any muscular paralysis.

Attempts have been repeatedly made by various authors to locate
more distinctly the physiological acts of sensation or motion in one or
the other of the cerebral ganglia separately ; but thus far these attempts
have not been so successful as to command general assent. The most
exact experiments in regard to sensibility are those of Yeyssiere,1 who
operated by introducing into the brain of the dog a slender trocar
armed with a spring, which could be expanded at the bottom of the
wound and thus produce, by rotation of the instrument, a lesion of
the deeper parts of the brain without serious injury of the more super-
ficial portions. After study of the symptoms caused by the operation,
the animal was killed, and the exact location of the injury ascertained.
The observer found by this means that hemiansesthesia, either alone or
accompanied by more or less paralysis of motion, was produced by
lesions of the cerebral ganglia and the white substance included be-
tween them ; but that it was the white substance of the internal capsule
which was most constantly affected in these cases. The gray substance
of the cerebral convolutions, as well as that of the cerebral ganglia,
might be extensively injured without causing loss of sensibility; but
this effect was produced in proportion to the extension of the injury
to the internal capsule and the commencement of the expansion of
radiating fibres derived from it.

The above experiments and observations do not show that the physio-
logical functions, either of sensibility or voluntary motion, are seated
in the cerebral ganglia or the internal capsule. The paralysis of motion
and sensation resulting from injury to these parts is due evidently, in
great measure, to the shock communicated, through descending fibres,
to other parts of the brain below ; since, as in several of Yeyssiere's

1 Recherches sur riTemiansesth^sie de cause c£r6brale. Paris, 1874.

THE CEREBELLUM.

493

experiments, a hemiplegia or hemianaesthesia, following laceration of
the brain substance, may disappear within a few days, or even in twenty-
four hours, though the mechanical injury be not yet repaired. While
therefore we cannot say that either of the cerebral ganglia are the phys-
iological organs of sensation or motion, yet their injury, both in animals
and in man, generally produces, as its immediate result, hemiplegia or
hemiansesthesia, either singly or combined, on the opposite side of the
body.

The Cerebellum.

The cerebellum, although in man and the quadrupeds much inferior in
size to the cerebrum, consists, like it, of a folded layer of gray matter
surrounding the mass of white substance which forms its internal por-
tion. The cortical layer of gray substance is only about one-half as
thick as that of the cerebral hemispheres; being nowhere over 1.5 milli-
metre in thickness. But the convolutions of the cerebellum are more
compactly arranged than those of the cerebrum, and penetrate into its
substance in the form of thin, closely adjacent laminae ; so that it con-
tains a comparatively large quantity of gray matter in proportion to its
mass. In the white substance of the cerebellum on each side, not far
from the median line, there is an isolated deposit of gray matter in the

i. 163.

VERTICAL TRANSVERSE SECTION OF THE HUMAN CEREBELLUM AND ME-
DULLA OBLONGATA, a little behind the pons Varolii; posterior portion.— 1. Medulla
oblongata, showing the nucleus of the olivary bodies. 2. Fourth ventricle. 3, 3. White
substance of the cerebellum. 4,4. Corpus dentatum of each side. (Henle.)

form of a thin lamina, folded in irregular, tooth-like convolutions,
whence its name of corpus dentatum. This lamina is everywhere closed
on its external lateral aspect, but presents an opening at one point
toward the median line. It seems to occupy, in the cerebellum, a place
analogous to that of the cerebral ganglia above, and to that of the
olivary nuclei in the medulla oblongata.

The gray matter of the cerebellar convolutions is penetrated by fibres

494 THE BRAIN.

coming from the interior white substance, and contains nerve cells of
various form and size. The most characteristic are flask-shaped cells,
arranged in a single or rarely in a double row ; the rounded extremity
of each cell being directed inward, the pointed extremity outward.
According to Kb'liiker and Henle, the cells usually give off prolonga-
tions in two opposite directions ; that which passes inward toward the
white substance being unbranched and resembling the axis-cylinder of
a nerve fibre, while that which passes outward toward the surface of
the convolution divides into numerous fine ramifications.

The cerebellum is connected with the rest of the cerebro-spinal axis
by, 1st, the fibres of the posterior peduncles, or restiform bodies, which
come from the posterior and lateral parts of the medulla oblongata, to
radiate in the white substance of the cerebellum ; and 2d, by those of
the anterior peduncles, orprocessus e cerebello ad corpora quadrigemina,
which originate from the cerebellum nearer the median line than the
termination of the restiform bodies, and thence pass upward and forward,
joining the longitudinal tracts of the posterior part of the tuber annulare
and crura cerebri. The two lateral halves of the cerebellum are further-
more connected with each other by, 3d, the fibres of the middle peduncles,
which originate from the white substance on each side, then pass forward
and downward to meet in front upon the under surface of the tuber
annulare, forming the arched commissure of the pons Varolii.

Physiological Properties of the Cerebellum. — The general result of
experimental operations upon the cerebellum shows that the surface of
this organ is inexcitable by ordinary means, and that its mechanical
irritation gives no evidence of sensibility. Flourens, Longet, Yulpian,
and experimenters in general, have recognized the fact that neither
sensation nor muscular contractions are produced by touching or
wounding the external gray substance of the cerebellum ; while in its
deeper portions both excitability and sensibility become manifest, in
proportion as the irritation is applied nearer the medulla oblongata and
the commencement of the cerebellar peduncles. Furthermore, its re-
moval, either in part or in whole, does not destroy nor essentially
diminish either the power of sensation or that of movement. The
senses remain active, and the mental faculties are still unchanged, pro-
vided the cerebral hemispheres have not been injured. Operations
upon this part of the brain are more difficult to perform than those
upon the cerebrum, and are much more liable to produce a fatal result.
This, however, does not seem to depend upon any direct influence of
the cerebellum upon the more vital functions, but is due to its deeper
position, the difficulty of exposing it without causing too much hemor-
rhage, and especially its proximity to the medulla oblongata. If injury
from these causes be avoided, the organ may be extensively wounded
or even totally removed without causing death. One-half or two-thirds
of it have often been taken away without causing death ; and in one of
the experiments of Flourens, a fowl lived for more than four months
after its complete extirpation.

THE CEREBELLUM. 495

Aside from the particulars above mentioned, experiments which con-
sist in mutilation or removal of the cerebellum have yielded very uni-
form results of a striking character, and not similar to those caused by
injury to other parts of the brain. These effects were first described by
Flourens in 1842;1 and notwithstanding the great activity of research
upon the nervous system since that time, the results obtained by him
have been uniformly corroborated in all essential particulars by subse-
quent observers. The phenomena, which are of a similar nature in
different species of animals, have been seen, by Flourens or others, in
the pigeon, fowl, duck, turkey, and other birds ; and, among quadrupeds,
in the dog, the cat, the mole, the rat, and the guinea pig.

The effect produced by destruction or removal of the substance of the
cerebellum consists in a peculiar disorder of the movements of the body
and limbs, from want of harmony in their muscular action. The power
of associating the contractions of different muscles, in such a way as to
produce co-ordinated movements, is lost or impaired in proportion to
the injury inflicted upon the nervous centre. If in a living pigeon the
cerebellum be exposed, and a portion of its substance removed, the
animal exhibits at once a characteristic uncertainty in the gait, and in
the movement of the wings. If the injury be more extensive, the bird
loses altogether the power of flight, and can walk, or even stand, only
with difficulty. This is not owing to any actual paralysis, for the
movements of the limbs are often quite rapid and energetic ; but is due
to a deficient control over the muscular contractions, similar to that
seen in a man in a state of intoxication. The movements of the legs
and wings, though forcible, are confused and blundering ; so that the
animal cannot direct his steps to any particular spot, nor support him-
self in the air by flight. He reels and tumbles, but can neither walk
nor fly.

The senses and the intelligence are at the same time unimpaired, and
this circumstance causes a striking difference between the phenomena
produced by removal of the cerebrum, and those following removal of
the cerebellum. If these two operations be done upon different pigeons,
and the two animals placed side by side, the first pigeon, from which
the cerebrum only has been removed, remains standing firmly upon his
feet, in a condition of complete repose; and when compelled to stir,
he moves sluggishly and unwillingly, but otherwise acts in a perfectly
natural manner. The second pigeon, on the other hand, from which
the cerebellum only has been taken away, is in a constant state of
agitation. He is easily excited, and frequently endeavors, with violent
struggles, to escape from one place to another ; but his movements are
sprawling and unnatural, and no longer under the effectual control of
the will. If the entire cerebellum be destroj'ed, the animal is incapable
of assuming or retaining any natural posture. His legs and wings are

1 Recherches Exp6rimentales sur les Propri6t6s et les Fonctions du Systfeme
Nerveux. Paris, 1842, pp. 37, 53, 102, 133.

496 THE BKAIN.

agitated with ineffectual movements, which are evidently voluntary in
character, but are at the same time irregular and confused.

The direct inference which may be derived from these phenomena is
that the power of co-ordination or association of voluntary movements
of the body and limbs resides in the cerebellum as a nervous centre, and
that this power is accordingly lost or impaired by injury of its sub-
stance. It is evident that such a power really exists under some form
in the nervous system. No natural co-ordinated movements are effected
by the independent contraction of separate muscles, but always by a
number of muscles, or groups of muscles, acting in harmony with each
other. The extent and variety of this muscular association vary in
different classes of animals. They are very considerable in birds and
quadrupeds as compared with fish and reptiles, and reach in man their
highest grade of development. Even in maintaining the ordinary pos-
tures of standing or sitting, many different muscles are brought into
action together, in each of which the degree of contraction must be
accurately proportioned to that of the others. In the motions of walk-
ing and running, or in the still more delicate movements of the hands
and fingers, this harmony of action is indispensable to the efficiency of
the muscular apparatus.

Notwithstanding the fact that this power of co-ordination is invariably
disturbed by injuries of the cerebellum, it is doubted by some writers
whether it can be strictly attributed, as a physiological function, to this
particular part of the nervous system. The grounds upon which this
doubt is based are twofold ; first the subsequent recovery of the power
of co-ordination by animals after injury or partial removal of the cere-
bellum, and secondly, the results of certain pathological observations
in the human subject.

I. Eestoration of the Co-ordinating Power in Operated Animals. —
It is certain that animals may be affected, after partial extirpation of
the cerebellum, with well marked loss of co-ordinating power, and that
they may, in some instances, subsequently recover this power without
regeneration of the lost nervous substance. This recovery was observed
by Flourens in the fowl and in the pigeon, and has been seen by Flint1
in the pigeon after removal of about two-thirds of the whole mass of the
cerebellum. We have also met with four instances of the same kind.
In the first, about two-thirds of the cerebellum was taken away by an
opening in the posterior part of the cranium. Immediately afterward,
the pigeon showed all the usual effects of the operation, being incapable
. of flying, walking, or even of standing still, but only reeled and sprawled
in a perfectly helpless manner. In five or six days from that time, he
had regained a very considerable control over the voluntary movements,
and at the end of sixteen days his power of muscular co-ordination was
so nearly perfect, that its deficiency, if any existed, was imperceptible.
He was then killed ; and on examination, it was found that his cerebel-

1 The Physiology of Man ; Nervous System. New York, 1872, p. 367.

THE CEREBELLUM. 497

lum remained in nearly the same condition as immediately after the
operation; about two-thirds of its substance being deficient, with no
regeneration of the lost parts. The accompanying figures show the
appearances in this brain as compared with that of a healthy pigeon.

Fig. 164. Fig. 165.

BRAIN OP HEALTHY PIGEON— Pro- BRAIN OP OPERATED PIGEON —

file view.— 1. Cerebral hemisphere. 2. Optic Profile view— showing the mutilation of

tubercle. 3. Cerebellum. 4. Optic nerve. the cerebellum.
5. Medulla oblongata.

Fig. 166. Fig. 167.

BRAIN OP HEALTHY PIGEON— Pos- BRAIN OP OPERATED PIGEON —

terior view. Posterior view— showing the mutilation

of the cerebellum.

In the three remaining cases the quantity of nervous substance
removed amounted to about one-half the mass of the cerebellum. The
loss of co-ordinating power, immediately after the operation, though
less complete than in the preceding instance, was perfectly well marked ;
and in little more than a fortnight the animals had nearly or quite
recovered the natural control of their motions, so far as could be seen
while they were kept under observation.

It is evident that in these cases, if the cerebellum be really the seat
of a physiological co-ordinating power, there are two effects produced
by the operation, which should be carefully distinguished from each
other. The first of these effects is the shock due to the sudden injury
of the cerebellum as a whole. This effect is temporary, and may be
recovered from in time, provided the animal be sufficiently strong to
survive the immediate mechanical lesion. The remaining effect is that
due to the loss of nervous substance ; and this effect must of course be
permanent, unless the nervous matter be regenerated. In the cases
detailed above, the greatest amount of disturbance seems to have
depended upon the sudden injury to the nervous centre as a whole ; and
the animals recovered, to a great extent, their power of co-ordination,
notwithstanding that from one-half to two-thirds of the substance of
the cerebellum was permanently lost.

498 THE BKAIN.

The recovery of a nervous function, after permanent loss of nervous
substance, is not peculiar to the cerebellum. Flourens has observed
the same thing in regard to the cerebral hemispheres in the pigeon;
the intellectual and perceptive faculties being totally suspended im-
mediately after partial removal of the hemispheres, but again restored
after the lapse of several days. But this restoration only takes place
where the removal of the nervous centre is partial ; and in the cerebel-
lum, as well as in the cerebrum, after complete extirpation, the loss of
function is a permanent one. In the experiment of Flourens, where a
fowl lived for four months after entire removal of the cerebellum, there
was no recovery of co-ordinating power.

It is to be remembered that birds and other animals, when confined to
the limited space of a laboratory, have no opportunity of exercising the
more complicated and active movements natural to them in a condition
of freedom ; and accordingly, they might not show any great deficiency
of muscular co-ordination while in confinement, though they might still
be incapable of executing all the movements of natural flight. The
simpler motions may continue to be performed with only a part of the
cerebellum remaining ; but we are not sure that, even in these cases, a
portion of the co-ordinating power, corresponding with the destruction
of nervous substance, has not been permanently lost.

II. Pathological Observations in the Human Subject. — The same re-
mark will apply to the pathological observations in man which have been
sometimes considered as neutralizing the result of experiments. These
are mainly cases in which lesions of the cerebellum, more or less ex-
tensive, have existed without recorded disturbances of co-ordination
similar to that produced in animals by mechanical injury of the part.
In a large majority of these instances the patients were confined to a
sick-room, and in many of them to the bed ; consequently there could
be no opportunity of observing a want of natural co-ordination in the
more complicated movements, if any such existed. A patient, also, in
whom the loss or diminution of a motor nervous function comes on
gradually, accommodates himself to it by abstaining from the attempt
to perform movements of which he is incapable, and confines himself to
those which he is still able to perform. Furthermore, in many cases of
disease of the cerebellum, symptoms of want of co-ordinating power
have been distinctly noticed and recorded.

The data derived from comparative anatomy show a general corre-
spondence in the development of the cerebellum and the variety and
complication of muscular action. In fish, as a rule, it is of good size
compared with other parts of the brain; and although direct progression
in this class is accomplished by a comparatively simple mechanism,
namely, the lateral flexion and extension of the spinal column with its
expanded fins and tail, yet their movements through the water or in
leaping out of it, while pursuing and taking their prey, are remarkably
rapid and vigorous, and are promptly varied in any direction. In the
frog, on the other hand, the movements of progression consist of little

THE TUBER AISTNULARE. 499

else than straightforward flexion and extension of the posterior limbs ;
and the cerebellum is exceedingly small, much inferior in size to that
of fishes, and forms only a thin narrow ribbon of nervous matter
stretched across the upper part of the fourth ventricle. In the che-
lonia, or turtles, the movements of the body are accomplished by the
consentaneous action of the anterior and posterior limbs, and those of
the head and neck are also much more varied than in the frog, while the
cerebellum exhibits a corresponding increase of development. In the
alligator and allied species, whose motions approximate more closely to
those of the quadrupeds than is the case with other reptiles, the cere-
bellum is also larger in proportion to the remaining parts of the brain.
In birds, in quadrupeds, and in man there is a very evident increase in
the size and convolutions of the cerebellum, corresponding with the
greater variety and delicacy of movements which they are capable of
performing. These facts are not decisive in determining the physio-
logical function of this portion of the brain, since other nervous endow-
ments also vary in their degree of development in different animals and
in man ; but they show that the assumption of a co-ordinating power in
the cerebellum is not at variance with the comparative anatomy of the
nervous system.

Everything which we know with certainty, therefore, in regard to the
cerebellum, indicates its close connection with the power of co-ordination
for the movements of the body and limbs. It cannot be regarded as
exclusively presiding over this function ; since there is strong evidence
that the posterior columns of the spinal cord are in great measure
devoted to the same purpose, and their morbid alteration necessarily
induces, in man, the disease known as locomotor ataxia. But the pos-
terior columns of the cord form by their divergence, at the level of the
fourth ventricle, the inferior peduncles of the cerebellum. The cerebel-
lum accordingly is a highly developed and convoluted nervous centre,
placed at the upper extremity of the cord, and communicating, by tracts
of white substance, with its posterior columns. The spinal cord itself
is, of course, essential to the co-ordinated motions of the body, arms,
and legs, since its posterior columns are for them the direct agents of
control and communication ; but the cerebellum may also be regarded
as a focus or nervous centre of reflex action for all the more vigorous
and complicated movements of the trunk and limbs.

The Tuber Annulate.

The tuber annulare is an isthmus, which makes connection between
the remaining parts of the encephalon above, and, through the medulla
oblongata, with the spinal cord below. It may be described in general
terms as constituted, 1st, by longitudinal tracts of white substance,
the prolongation of the anterior pyramids of the medulla oblongata,
which pass through it in a nearly straight course, becoming continuous
above with the crura cerebri ; 2d, by transverse bundles of white sub-
stance coming from the two sides, and encircling it with the superficial

500 THE BRAIN.

band of arched fibres, known as the pons Yarolii, or great commissure of
the cerebellum ; and 3d, by a deposit of gray substance contained in its
anterior, and more or less mingled with its other portions. The tuber
annulare is, therefore, like the other central masses of the encephalon,
at the same time a channel of communication between the interior and
the exterior, and a nervous centre with special endowments of its own.

In the most superlicial portions of the pons Yarolii, the transverse
bundles of nerve fibres are closely packed together, without any percep-
tible admixture of nerve cells. The deposit of gray substance commences,
however, according to Henle* at a short distance below the surface, occu-
pying minute spaces between the transverse bundles, and containing
stellate nerve cells. Beneath the superficial transverse bundles of the
pons come the longitudinal tracts of pyramidal nerve fibres, and be-
neath these again a deeper layer of transverse commissural fibres. The
deposit of gray matter in the pons is still more abundant in its deep
than in its superficial layer ; often alternating, according to Henle,
with the transverse bundles, in interspaces of J millimetre in thickness.
It also fills a space about 2 millimetres wide, on each side the median
line, between the two pyramidal tracts of white substance.

Physiological Properties of the Tuber Annulare. — In the tuber
annulare the phenomena both of excitability and sensibility, under
artificial irritation, become much more marked than in the great centres
of the cerebrum and cerebellum. According to Longet, a galvanic
stimulus, when the electrodes are passed into the substance of this
organ, produces distinct convulsive movements even in recently killed
animals, although its external surface does not appear to be excitable by
similar means either in front or behind. Yery slight irritation of its
posterior surface has been found, by both Longet and Yulpian, to give
rise in the living animal to indications of pain ; but this effect may be
partly due to the contiguity of the sensitive nerve-roots which traverse
the nervous substance in this situation. Excitability and sensibility
are also manifested on irritating the crura cerebri, between the tuber
annulare and the cerebral ganglia.

The nature of the physiological actions taking place in the tuber
annulare, as a nervous centre, can only be studied by observing the
effects produced by its injury or removal, in comparison with other
parts of the encephalic mass. It is seen that the cerebrum and cere-
bellum may be taken away, either together or separately, without de-
stroying the evidences of sensibility or the power of motion. According
to the experiments of both Longet and Yulpian, the cerebral hemi-
spheres, the cerebellum, the corpora striata, the optic thalami, and the
tubercula quadrigemina may all be removed, in dogs and rabbits, and
yet the signs of sensibility and the power of motion in the limbs con-
tinue to exist ; and, if the cerebellum remain, the normal attitude of
the body and limbs, and even the power of progression, may still be
maintained.

The manifestations of these nervous functions, however, are so much

THE TUBER ANNULAKE. 501

diminished after extirpation of the cerebral hemispheres, that some
writers have suspected that they might belong to the category of un-
conscious and involuntary reflex actions. Longet and Vulpian, on
the other hand, insist upon the fact, observed by both, that after
removal of the whole brain, with the exception of the tuber annulare
and medulla oblongata, irritation of the external parts or of a sensitive
nerve will produce, in dogs and rabbits, cries which are evidently the
expression of a conscious sensation. This alone shows that the animals
after such a mutilation may be still capable of feeling pain ; and,
according to Vulpian,1 after extirpation of the hemispheres and the
cerebral ganglia in the rat, movements of the head and limbs were not
only produced by pinching the integument, but blowing suddenly upon
one of the ears caused shaking of the head, accompanied by winking of
the eyes ; showing that the animal was still sensitive to ordinary tactile
impressions, as well as to those of a painful character. The same
experimenter has found that in a rat, after the above operation, a
hissing sound made by the lips excited repeatedly distinct signs of
agitation. From these facts it can hardly be doubted that sensations
are actually perceived by the animal so long as the tuber annulare
remains uninjured.

There is no evidence, however, that in these cases there is anything
more than the simple sensation, without conscious recognition of its
origin or significance. So far as we can judge, the animal under these
circumstances may be capable of feeling pain, but not of understanding
the cause by which it was produced. He may be conscious of the
sensations of light or of sound, as existing in himself, without refer-
ring them to any external source. This is the full extent of sensibility,
as it can be supposed to exist in the tuber annulare.

A similar limitation must be placed on the action of the voluntary
muscles so far as it is excited by the tuber annulare. These motions
have the appearance of volition, so far as they consist in attempts to
maintain or recover the natural attitude, or in those of progression; but
it is not a volition which has any intelligent understanding of its pur-
pose. It follows immediately upon the receipt of the sensation which
excites it, and is therefore a reflex action; but it differs from the reflex
action of the spinal cord mainly in the fact, that it is accompanied or
preceded by a conscious sensation.

The evidence thus far in our possession goes to show that the tuber
annulare is especially connected with reflex actions of an emotional and
instinctive character. These actions differ from those connected with
the mental faculties in being comparatively little under the control of
the judgment or the will, and in being directed by an unreasoning im-
pulse, where the act follows immediately upon the receipt of the sensa-
tion. To this class belong the purely instinctive acts performed by
animals or man, in which there is no direct recognition of their nlti-

1 LeQons sur la Physiologie du Systfeme Nerveux. Paris, 1866, p. 543.

502 THE BRAIN.

mate object, but only of the immediate stimulus upon which they depend.
All the emotions, and the expressions to which they give rise, are ner-
vous phenomena of this kind. The feelings of cheerfulness or depres-
sion, satisfaction, hilarity, or displeasure, are expressed, whenever they
reach a certain degree of intensity, by tears or laughter, by inarticulate
sounds, attitudes or movements of the body, which, though not inten-
tionally calculated to produce that effect, are at once understood by all
who see or hear them. Jn man, certain diseases of the brain induce a
condition in which the emotional phenomena are much more easily
excited than in health, either from an undue activity of the nervous
centre in which they are located, or from the .diminished influence
exerted over them by the cerebral hemispheres. In these instances,
the individual is moved to anger, laughter, or tears on the most trivial
occasions, and from causes which would not produce such an effect in a
condition of health ; the feelings thus expressed being quite uncontrol-
lable for the time, although the patient may be conscious that they have
no reasonable motive.

The action of the tuber annulare, as the centre of the emotional im-
pulses, is no doubt closely connected with its influence over the attitude
and locomotion. The manner in which these two functions are performed,
even in man, takes a great share in the manifestation of the emotions, and
in many of the lower animals forms the principal means by which they
are expressed. The normal postures of the body and limbs and the
movements of progression, although they are still possible after de-
struction of the cerebral hemispheres and ganglia, are at once abolished,
according to Vulpian, if the tuber annulare be removed or extensively
injured.

There is no doubt, also, that the other nervous faculties which have
been enumerated as connected with the tuber annulare come to an end
as soon as this organ is subjected to mutilation. With the destruction
of the tuber annulare, according to the general testimony of experi-
menters, all indications of sensibility and volition disappear, and the
animal body is reduced to the condition of a helpless and unconscious
machine, in which the functions of respiration and circulation, with cer-
tain other involuntary reflex phenomena, are the only remaining mani-
festations of nervous action.

The Medulla Oblongata.

The medulla oblongata is distinguished from the spinal cord, of which
it is a continuation, not only by its external form, but also by the dif-
ferent arrangement both of the bundles of nerve fibres and of the gray
substance in its interior.

In the spinal cord, the anterior, middle, and posterior columns of
white substance all consist mainly of parallel fibres running in a longi-
tudinal direction ; while there is a narrow band of transverse fibres, the
white commissure, at the bottom of the anterior median fissure. In the
medulla oblongata, a much larger number of horizontal and oblique

THE MEDULLA OBLONGATA. 503

fibres make their appearance, passing from one side to the other. The
greater part of these fibres come from the continuations of the lateral
and posterior columns, and from the posterior horns of gray matter,
whence they pass forward and inward, and cross each other on the
median line at the place previously occupied by the white commissure.
The increasing number of these interchanging fibres, and the fact that
they cross the median line in bundles of considerable size, and in an ob-
lique direction from below upward, produce the conformation visible at
the anterior surface of the medulla oblongata, and known as the decus-
xation of the pyramids. After crossing from one side to the other, the
fibres again gradually take a longitudinal direction, and it is on this
account that the pyramids increase in size from below upward. The
pyramids accordingly consist of fibres which are derived from the lateral
and posterior columns of the opposite side of the cord. They are not
the continuation of the longitudinal tracts which form the anterior
columns below j these columns, on the contrary, diminishing rapidly in
size from within outward, until they disappear almost completely above
the level of the decussation of the pyramids. Thus the decussation of
the pyramids represents that of all the remaining longitudinal fibres of
the spinal cord, so far as it takes place in the medulla oblongata.

The longitudinal fibres of the posterior columns also diminish con-
siderably in number in the medulla oblongata, as shown by Henle,
owing to their taking a horizontal direction, forward and inward, to
reach the decussation of the anterior pyramids ; while the remaining
longitudinal fibres of these columns pass into and through the restiform
bodies to the white substance of the cerebellum.

The arrangement of the gray substance in the medulla oblongata is
also different from that presented in the spinal cord. In the first place,
according to the observations of Kolliker, it increases in quantity from
below upward. Secondly, the central mass of gray substance, which in
the cord surrounds the central canal, and sends out on each side the
anterior and posterior horns, recedes in the medulla oblongata farther
and farther backward ; the posterior horns spreading out laterally, and
the remainder occupying the space between them. The posterior
median fissure also becomes gradually shallower and wider by the
divergence of the posterior columns ; and the central canal approxi-
mates the posterior wall of the medulla, finally opening upon its surface
at the lower part of the fourth ventricle. The gray substance of the
medulla oblongata is thus uncovered posteriorly, and forms a layer
spread out laterally, on each side of the median line, immediately be-
neath the floor of the fourth ventricle. It extends forward, without any
complete interruption, beneath the whole length of the fourth ventricle
and the aqueduct of Sylvius ; and it is this layer of gray substance
which gives origin, at various points, to the fibres of all the cranial
nerves, excepting the olfactory and the optic.

Thirdly, the medulla oblongata is distinguished by the appearance,
in its interior, of other deposits, or nuclei, of gray substance, detached

504

THE BRAIN.

from those belonging to the spinal cord. The most marked of these is
the olivary nucleus ; a convoluted lamina about one-third of a milli-
metre in thickness, occupying the interior of the olivary body on each
side, just below the inferior border of the pons Yarolii.

No

TRANSVERSE SECTION OF HUMAN MEDULLA OBLONGATA, at the lower part
of the fourth ventricle.— No, Olivary nucleus. E, Raphe, at the median line. Ngl, Nucleus
of the glosso-pharyngeal nerve. Nv, Nucleus of the pneumogastric nerve. Nh, Nucleus
of the hypoglossal nerve. IX, Roots of the glosso-pharyngeal nerve (9th pair) at their point
of emergence from the medulla. XII, Roots of the hypoglossal nerve (12th pair) at their
point of emergence from the medulla. Magnified 8 diameters. (Henle.)

In transverse sections, near its upper or lower extremity, the olivary
nucleus appears completely closed, but a section through its middle
shows a gap toward the median line. It forms, therefore, an ovoid
sac, with its long diameter parallel to the axis of the medulla, and an
opening at its middle directed inward. Through this opening bundles
of nerve fibres penetrate from the white substance of the medulla, and,

THE MEDULLA OBLONGATA. 505

after filling the space inclosed by its convoluted wall, pass through it,
and spread out laterally in a divergent direction.

Physiological Properties of the Medulla Oblongata. — The simplest
examination of the medulla oblongata shows that its physiological pro-
perties are more distinctly marked than those of any other part of the
encephalic mass. It is both sensitive and excitable to a high degree,
especially in its posterior portions. Artifical irritation, by mechanical
or galvanic stimulus, causes at once a painful sensation, provided the
rest of the brain be uninjured, and in the recently killed animal produces
general convulsive movements of considerable intensity. These effects
are due to the irritability of the longitudinal fibres connecting the me-
dulla with the spinal cord, and to the roots of the sensitive and motor
cranial nerves which take their origin from this part of the encephalic
mass. Since the medulla is the only bond of nervous communication
between the brain and the spinal cord, its section at any point also
destroys voluntary motion and sensibility throughout the body and
limbs-

Action of the Medulla as a Nervous Centre. — The various deposits
of gray substance in the interior of the medulla, and their connection
with nerves of widely different distribution and functions, are the pecu-
liar features of its anatomical structure. The results of experiment
show that the reflex actions taking place in this part of the nervous
system are also of a special and distinctive character.

The most important of these actions is connected with respiration.
So long as the medulla oblongata is left uninjured, although the cranium
be emptied of all the other nervous centres, the movements of respira-
tion and circulation go on without essential modification. But if the
medulla be destroyed, respiration ceases instantaneously. This effect may
be produced, without injuring other parts of the brain, in dogs or other
warm-blooded animals, by introducing a steel instrument from behind,
between the edges of the occipital foramen and the first cervical verte-
bra, carrying it forward in the median line until its point rests upon
the basilar process of the occipital bone. It is then moved from side to
side in such a way as to break up the substance of the medulla oblon-
gata, when all the movements of respiration are at once arrested. The
circulation continues, and the pulsations of the heart are even increased
for a time in force and frequency ; but as the deficiency of aeration in
the blood becomes more marked, the circulation is gradually retarded
and after several minutes comes to an end. The effect of this operation
upon the two functions of circulation and respiration is very different.
The circulation is interfered with and finally suspended in a secondary
manner, and only because the blood is no longer arterialized ; respira-
tion is abolished instantaneously, as the immediate result of the destruc-
tion of the medulla oblongata.

The medulla is, therefore, the most important nervous centre in the
brain for the immediate preservation of the vital functions, and the
only one whose injury or removal produces at once a fatal result.
33

506 THE BRAIN.

In man, quadrupeds, and birds, it is a vital point; since in them the
function of respiration, over which it presides, is necessary for the con-
tinuance of life from one moment to another.

The fact that sudden death may be produced by injury of the cerebro-
spinal axis in this region was known to Galen, who described the method
of killing an animal by section of the spinal cord " at the upper cervical
vertebrae." The respiratory movements of the chest and abdomen are
however necessarily arrested by section of the cord anywhere above
the third cervical vertebra, since this paralyzes at once both the dia-
phragm and the intercostal muscles. But movements of inspiration,
simultaneous with those of the chest and abdomen, are also performed
by the glottis ; and in most of the quadrupeds there is at the same time
an expansion of the nostrils, all associated with each other in the act
of respiration. If the spinal cord be divided at the third cervical verte-
bra the movements of the chest and abdomen cease, but those of the
glottis and the nostrils continue, since the nerves supplying these parts
are still in communication with the medulla oblongata. Destruction
of the medulla itself, on the other hand, arrests at the same instant all
movements of respiration, both in the trunk, the glottis, and the face.
It is, therefore, a centre from which the respiratory apparatus in general
derives its stimulus.

The more exact location of this centre was investigated by Flourens1
by making transverse sections of the medulla at different parts of its
length, and observing the effect produced upon respiration. The result
showed that injuries of this kind, inflicted just behind the point of
emergence of the pneumogastric nerves, destroyed at once all the move-
ments of respiration together. Below this point the movements of the
chest and abdomen were stopped, but those of the nostrils and glottis
continued ; above it the movements of the nostrils were arrested, while
those of the chest and abdomen went on.

Similar experiments performed by Longet show that the respiratory
centre does not extend through the entire thickness of the medulla;
since either the anterior pyramids in front or the restiform bodies
behind may be destroyed without putting a stop to respiration ; while a
lesion passing through the intermediate layer at once causes its sus-
pension. Flourens subsequently2 limited the position of this centre
still more closely, and found that in rabbits it occupies a space of about
2.5 millimetres on each side the median line, situated at the lower end
of the fourth ventricle, a little in advance of the divergence of the
posterior pyramids, and just at the point of gray substance formed by
the ala cinerea. A section of the medulla at this spot, with a double-
edged knife only 5 millimetres wide, or its perforation at the same
point with a sharp-edged canula not more than 3 millimetres in

1 Kecherches Experimentales sur les Proprietes et les Fonctions du Systeme
Nerveux. Paris, 1842, pp. 196-204.

2 Comptes Kendu de 1' Academic des Sciences. Paris, 1858, tome xlvii. p. 803.

THE MEDULLA OBLONGATA. 507

diameter, caused immediate stoppage of the respiration; while this
effect was not produced by similar injuries inflicted either above or
below. This spot, which contains the nervous centre of the movements
of respiration, corresponds in level, in front of the medulla oblongata,
with the upper end of the decussation of the anterior pyramids, or the
lower extremity of the olivary bodies, and is somewhat below the
apparent origin of the pnenmogastric nerves.

Respiration accordingly is an act consisting of various associated
movements, which have their nervous centre in the medulla oblongata.
The respiratory movements themselves are completel3r involuntary in
character ; for although those of the chest and abdomen may be for a
short time increased in frequency, the surplus movements thus per-
formed are not necessary to respiration, and soon produce a fatigue which
prevents their continuance. Respiration goes on with its natural rhythm,
and entirely unaccompanied by fatigue, under the influence of the me-
dulla, from the first moment of birth and without any necessary con-
sciousness of its existence. If arrested by a voluntary effort, the
internal stimulus which prompts the movement grows gradually
stronger, until the will is no longer capable of resisting its demands.
As soon as the voluntary resistance is overcome or discontinued, the
respiratory movements recommence by the independent action of the
medulla oblongata.

The action of the medulla in respiration is one of a reflex nature.
The impression by which it is called out has its origin in the partial
want of arterialization of the blood, and especially in the commencing
accumulation of carbonic acid in the lungs and in the tissues. In
normal respiration, this impression is sufficient to excite the reflex
action of the medulla without producing a conscious sensation ; and on
the renewal of the air in the lungs by inspiration, the impulse is satisfied,
the muscles relax, and expiration is accomplished by the passive col-
lapse of the lungs and thorax. In a few seconds the previous condition
recurs and the actions are repeated as before, causing in this way the
regularly alternating movements of inspiration and expiration.

Since the acts of inspiration are performed partly by the diaphragm
and partly by the intercostal muscles, they will be differently modified
by injuries or lesions of the nervous system, according to the spot at
which they are situated. If the spinal cord be divided or compressed
in the lower cervical region, all the intercostal muscles are necessarily
paralyzed, and respiration is then performed only by the diaphragm.
If the phrenic nerve, on the other hand, be divided, the diaphragm alone
is paralyzed, and respiration is performed altogether by the rising and
falling of the ribs. If the injury inflicted upon the spinal cord be above
the origin of the third cervical nerve, both the phrenic and intercostal
nerves are paralyzed, and death takes place from suffocation. The at-
tempt at respiration, however, still continues in these cases, showing
itself by ineffectual inspiratory movements of the mouth and nostrils.
Finally, if the medulla itself be broken up at the situation of the

508 THE BRAIN.

respiratory centre, both the power and the stimulus to breathe are at
once taken away. No attempt is made at inspiration and there is no
appearance of suffering. The animal dies by want of aeration of the
blood, which leads after some moments to arrest of the circulation.

An irregularity in the movements of respiration is accordingly one
of the most threatening symptoms in affections of the brain. A sus-
pension of the intellectual powers does not necessarily indicate imme-
diate danger to life. Even sensation and volition may be impaired
without direct injury to the organic functions. Cerebral apoplexy at
the surface of the hemispheres, in the lateral ventricles, or in the cerebral
ganglia, is seldom immediately fatal, however extensive may be the in-
jury of the parts. But when occurring in the substance of the medulla
oblongata or its immediate neighborhood, it produces death instan-
taneously by the same mechanism as where this part is intentionally
destroyed by experiment in the lower animals. When the medulla is
beginning to be implicated, in man, by a progressive disease or by
gradual failure of the nervous functions, the respiratory movements
first affected are those of the nostrils and lips, while those of the chest
and abdomen go on for a time as usual. The cheeks are drawn in with
every inspiration and puffed out with every expiration, the nostrils
sometimes participating in these abnormal movements. A still more
threatening symptom, and one which frequently precedes death, is an
irregular and hesitating respiration, sometimes noticeable even before
the remaining cerebral functions are seriously impaired. These phe-
nomena depend on the connection between respiration and the reflex
action of the medulla oblongata.

The process of deglutition is also accomplished under the control of
the medulla. Mastication of the food by the movements of the jaws,
and its transfer by the tongue to the entrance of the fauces, are volun-
tary actions which may be continued or arrested at will. But when the
food has passed from the mouth into the pharynx, the act of deglutition,
by which it is carried down into the stomach, is reflex and involuntary
in character. Once commenced, it cannot be arrested by the influence
of the will, as it consists of a series of muscular contractions following
each other in regular and undeviating succession. These contractions
receive their impulse from the medulla oblongata. In the experiments
of Flourens and Longet, fowls and pigeons, after removal of the cerebral
hemispheres, never picked up their food spontaneously, nor ever swal-
lowed it when placed in the mouth at the end of the beak; but if carried
backward and placed in the commencement of the pharynx, it was at
once embraced by the muscular walls of this organ, and carried into
the stomach by a continuous movement of deglutition. This includes,
not only the associated contraction of the walls of the pharynx and
oesophagus, but also the stoppage of respiration and the closure of the
glottis, by which the food is prevented from passing into the larynx.
According to Yulpian, after all parts of the brain have been removed,
in cats or guinea pigs, excepting the medulla, swallowing may still be

THE MEDULLA OBLONGATA. 509

accomplished by reflex action ; but it becomes impossible as soon as
this part is removed or seriously injured. The muscular combinations
necessary to deglutition cannot take place, except under the influence
of the medulla as a nervous centre.

This action may consequently be performed, in man, after all sensi-
bility and voluntary power have disappeared. In cases of compression
of the brain from injury or disease, when the individual is in a state of
complete unconsciousness, and even when the respiration is diminished
in frequency, solid or liquid food, if carried into the upper part of the
pharynx, may be successfully swallowed by the ordinary movements of
deglutition. When this process is no longer possible, or is accompanied
by choking or regurgitation, it indicates that the medulla has become
seriously affected, and that death is probably near at hand.

The medulla is furthermore connected with the act of phonation. The
production of a vocal sound is usually the result of a voluntary impulse
derived from the operation of the cerebral hemispheres. It is sometimes
also a purely emotional act, originating in the excitement of the tuber
annulare, and without any reasonable or intelligent motive. But in
these cases its production is a secondary result, requiring the co-opera-
tion of other nervous elements, and its immediate centre is located in
the medulla. This is shown by the fact that a cry may still be produced
when the upper parts of the encephalon have been destroyed or removed,
and when an irritation is applied to the medulla alone. If a stilet be
introduced into the cranium of a frog, the cerebral hemispheres may
be broken up without producing any excitement of the vocal organs ;
but when the instrument touches the medulla, its contact is often fol-
lowed by a distinct and spasmodic cry. Yulpian has shown that a similar
effect may be produced in mammalians, after removal of the whole
encephalon excepting the medulla, by a reflex action. A cry is pro-
duced each time the integument of the foot is pinched by the blades of
a forceps. This sound, however, gives no indication of consciousness
or sensibility on the part of the animal. It is short, abrupt, and momen-
tary in duration, and is repeated only when the irritation is again applied
to the external parts. It is a purely mechanical effect of the tension of
the vocal cords and the sudden expulsion of air through the rima glot.
tidis. After the destruction of the medulla, on the other hand, no vocal
sound can be produced, and the same irritation of the integument is.
then followed only by the ordinary spasmodic movement of the limbs,
dependent on the reflex action of the spinal cord.

In the exercise of the voice, therefore, the preliminary actions of in-
telligence, volition, or emotional excitement require the co-operation of
the cerebrum and the tuber annulare ; but the immediate mechanism by
which a vocal sound is produced in the larynx has its nervous centre in
the medulla oblongata.

This part of the brain, with the adjoining part of the tuber annulare,
is also the direct source of the movements of articulation. It is the
gray substance of this region that gives origin to the hypoglossal and

510 THE BRAIN.

facial nerves which animate the muscles of the tongue and lips, as well
as the motor fibres which regulate the condition of the rima glottidis.
Disease or injury in this situation, sufficient to impair the action of these
nerves, consequently makes articulation difficult or impossible, by para-
lyzing the muscles upon which it is dependent. This affection is quite
distinct from " aphasia," which is of cerebral origin and consists in a
loss or deterioration of mental faculties alone, the external mechanism
of speech being unaffected and the muscles of the tongue and lips re-
taining their power of movement in any direction. When the difficulty
is seated in the medulla, on the other hand, the muscular paralysis is
very evident, and is distinguished by being more or less confined to
those groups of muscles which are concerned in articulation and phona-
tion.

Such an affection is that first described by Duchenne and now gene-
rally recognized under the name of glosso-labio-laryngeal paralysis.1 It
is a paralysis due to chronic degeneration of gray nervous tissue in the
medulla oblongata, which affects the motor nerves of the tongue, the
face, the hanging palate, and the larynx. The first difficulty is generally
noticeable in the movements of the tongue, which cannot be applied
accurately to the upper teeth or to the roof of the mouth ; and the
lingual and dental consonants are therefore pronounced imperfectly or
not at all. The lips are next affected, so that they cannot be brought
in contact with each other, and B and P are pronounced like Y or F.
As the debility of the orbicularis oris increases, the lips cannot even be
partially approximated and the vowels 0 and U are no longer sounded ;
and by the continued exaggeration of these difficulties the patient's
speech becomes at last unintelligible. Deglutition is also affected, and
attempts at swallowing are liable to cause choking, from the imperfect
protection of the rima glottidis. Phonation becomes impaired from
debility of the laryngeal muscles, and in advanced cases no vocal sound
can be produced. The disease is uniformly progressive, and terminates
life usually by affecting the movements of respiration.

The medulla oblongata is accordingly the seat of reflex actions which
are directly or indirectly connected with the immediate preservation of
life, since it maintains the movements by which air and food are intro-
duced into the interior of the body. It also presides over the immediate
muscular combinations concerned in the production of the voice and
articulation, and by this means establishes an intelligible communica-
tion with the external world.

1 Hammond, Diseases of the Nervous System. New York, 1871, p. 676.

CHAPTEE YI.

THE CRANIAL NERYES.

OP the twelve pairs of nerves which take their origin from the brain,
the greater number present distinct analogies, both anatomical and
physiological, with the spinal nerves. All those which are distributed
to the integument and mucous membranes, or to the superficial and deep
muscles of the head and face, correspond in all important characters
with the sensitive and motor nerves formed from the anterior and pos-
terior spinal nerve roots. Three of them, however, show no resem-
blance, either in their anatomical distribution or their physiological
properties, with the rest. They are the so-called olfactory, optic, and
auditory nerves. After leaving their points of origin in the brain, they
are distributed neither to muscles nor to the integument or mucous
membranes ; but terminate in nervous expansions of special form and
structure, in which the gray substance or collections of nerve cells
reappear as prominent elements of the tissue. During their passage
through the cavity of the cranium, these nerves are neither sensitive
nor excitable in the ordinary sense of the word. Their irritation causes
no tactile or painful sensation, nor any direct muscular contraction ;
and their section produces no paralysis of the voluntary muscles, nor
any loss of general sensibility in the neighboring parts. They are to
be considered rather in the light of tracts or commissures than of ordi-
nary nerves, and their physiological properties are those connected with
the operation of the special senses alone.

The remaining cranial nerves, on the other hand, are similar, both
in structure, arrangement and function, to those in other parts of the
cerebro-spinal system. Some of them, like the oculo-motorius, the
patheticus, and the facial, are plainly motor in character, are distributed
to muscles, produce convulsive motion on being irritated, and, when
injured or divided, leave the corresponding parts in a state of paralysis.
Others, such as the trigeminus, the glosso-pharyngeal, and the pneumo-
gastric, are sensitive nerves, possessing either an acute tactile sensibility,
like the trigeminus, or one of a more obscure and special nature adapted
for the production of involuntary reflex actions, like the glosso-pharyn-
geal and pneumogastric. Like the posterior roots of the spinal nerves,
these are also provided with a ganglion situated at a short distance
from their points of emergence at the base of the brain ; and they are
distributed either to the integument or mucous membranes or to both.

The analogy in anatomical arrangement between the spinal and cranial

(511)

512 THE CRANIAL NERVES.

nerves is in some instances very marked. The fifth pair or trigeminus
emerges from the tuber annulare in two distinct bundles or roots, of
which one is sensitive, the other motor ; the sensitive root presenting
soon afterward a well developed ganglion, with which the fibres of the
motor root do not mingle. This nerve beyond the ganglion, therefore,
contains both motor and sensitive fibres, and is distributed both to
muscles and to the integument. In a similar manner the glosso-pha-
ryngeal nerve is joined, beyond its ganglion, by motor fibres from the
facial; and the pneumogastric receives abundant communications from
the spinal accessory and other motor nerves. Both the sensibility and
motion therefore of the parts to which they are distributed are provided
for, in a manner not essentially different, by both the cranial and spinal
nerves.

The other points, both of difference and analogy, in the cranial nerves,
relate to their origin and distribution. Their apparent origin, that is,
the point at which they become detached from the surface of the brain,
is not their real origin ; but in every case their fibres can be traced from
this point inward, between other longitudinal or transverse tracts of
white substance, until they reach a mass of gray matter, often placed at
a considerable distance and in quite a different locality from their
apparen origin. All the cranial nerves, excepting the olfactory and
the optic, are thus found to originate from a mass of gray substance
upon and beneath the floor of the fourth ventricle, and extending forward
to surround the aqueduct of Sylvius. This layer of gray substance is a
continuation of that in the spinal cord ; but while in the cord it has the
form of a central mass with lateral anterior and posterior horns, in the
medulla oblongata it takes the shape of a lamina occupying only the
posterior part of the cerebro-spinal axis. In its various divisions and
expansions, which are rarely, if ever, completely discontinuous from
each other, it forms the so-called " nuclei" of the cranial nerves.

In their distribution, these nerves present also certain anatomical
features which are more apparent than real in their importance. The
oculomotorius, patheticus, and abducens emerge from the substance of
the brain at very different points, and, running forward through the
cranial cavity in the form of separate cords, are enumerated as three
distinct nerves. But they all originate from the layer of gray substance
already mentioned, two of them, the oculomotorius and the patheticus,
in close proximity to each other ; they all pass out of the cranium, into
the orbital cavity, by the sphenoidal fissure ; and they are all distributed
to the group of muscles moving the eyeball. In a physiological point
of view, therefore, they are branches of a single nerve, rather than three
separate trunks. Even when two or more nerves emerge from the
cranium by different foramina, like the three divisions of the trigeminus,
they are nevertheless, properly speaking, parts of the same nerve, if they
have similar physiological properties and are distributed to the muscles
or integument of the same regions. It is the ultimate distribution of a
nerve, and not its course through the bones of the skull, that determines

THE OLFACTORY NERVES.

513

its physiological character and position. The details of branching and
division of the cranial nerves vary in different species of animals, or
even to some extent in the same individual on the two opposite sides
of the body, but their physiological characters remain the same. Thus
in the bull-frog, as shown by Wyman,1 both the facial nerve and the
abducens, instead of existing as distinct trunks, are given off as branches
from the fifth pair ; and in most of the quadrupeds, the terminal frontal
branches of the ophthalmic division of the fcrigeminus are wanting, or
reduced to trifling dimensions, in accordance with the absence of sensi-
bility in the skin of the forehead and vertex.

The cranial nerves may, therefore, be conveniently arranged in pairs
according to their distribution and functions, rather than the incidental
peculiarities of their course or subdivision. The olfactory, optic, and
auditory nerves thus form a group by themselves of a specific character ;
while the remainder consist of the motor and sensitive nerves, supply-
ing the muscular apparatus and the integument or mucous membrane
of different regions.

CRANIAL NERVES.
Nerves of Special Sense.

Distributed to the

Upper, middle, and
lower facial regions.

Tongue and pharynx.
Passages of respira-
tion and deglutition.

This division of the nerves, though based on their physiological
characters and distribution, is not absolutely perfect in all particulars.
For while the hypoglossal nerve supplies the muscles of the tongue
alone, its associate, the gloss-pharyngeal, sends a part of its sensitive
fibres to the tongue and a part to the pharynx ; and while the trigeminal
nerve is mainly distributed to the external parts of the face, one of its
deeper branches, the lingual, is distributed to the tongue. Notwith-
standing, however, these irregularities, such an arrangement of the
cranial nerves is substantially correct, and may serve as a useful guide
in the study of their functions.

First Pair. The Olfactory Nerves.

What is called in man the " olfactory nerve," is a three-cornered pris-
matic tract, composed of both gray and white substance, running forward
in a longitudinal groove upon the inferior surface of the anterior cerebral

1. Olfactory.

2. Optic. 3. Audil

Motor nerves.

Sensitive nerves.

f Oculomotorius

Patheticus

1st PAIR. -

| Abducens
Facial

Trigeminus.

2d PAIR.
3d PAIR.

[ Small root of 5th pair
Hypoglossal
Spinal accessory

Glosso-pharyngeal.
Pneumogastric.

1 Nervous System of Rana pipiens ; published by the Smithsonian Institution.
Washington, 1853.

514

THE CRANIAL NERVES.

lobe, near the median line, and terminating anteriorly in a flattened
ovoid mass of gray substance, the "olfactory bulb." The olfactory
bulb rests upon the cribriform plate of the ethmoid bone, and gives off,
through the perforations in this bone, the true nervous filaments sup-
plying the olfactory membrane in the nasal passages. The prismatic
tract which connects the olfactory bulb with the rest of the brain is in
reality, according to both Henle and Meynert, a prolongation of one of
the cerebral convolutions. It originates in a rounded eminence called
the " olfactory tubercle," situated at the back part and under surface
of the anterior cerebral lobe, just inside the island of Reil, with which it
is connected. It consists, like the other cerebral convolutions, of gray
substance containing pyramidal cells. Its peculiarity, as shown by
Henle, consists in the fact that bundles of nerve fibres from the interior

Fig. 169.

Cba

LiOXGITTTDINAL SECTION OF THE CEREBRAL HEMISPHERE, through the Situa-
tion of the olfactory tubercle and part of the olfactory nerve.— 1. Olfactory nerve. 2. Olfac-
tory tubercle. Cs. Corpus striatum. Coa. Anterior cerebral com'missure. Cba. Anterior
commissure of the base of the brain. Magnified once and one half. (Henle.)

pass through its cortical layer of gray matter, and appear upon its
surface as more or less distinct striations of white substance. It is
these white striations which have been designated as the olfactory
"roots," and which give to the tract terminating in the bulb the external
appearance of a nerve. They are derived from the white substance of
the cerebral hemispheres, and continue forward to the gray matter of
the olfactory bulb. A communication is established between the olfac-
tory nerves of the two opposite sides through the internal white sub-
stance of the olfactory tubercles. According to Yulpian, there is also
a more direct communication, visible in the dog, the sheep, and the

THE OLFACTORY NERVES. 515

rabbit, formed by one of the so-called olfactory nerve roots, which turns
inward and crosses the median line, in company with the fibres of the
anterior cerebral commissure.

Physiological Properties of the Olfactory Nerve. — The olfactory
nerve thus formed is a tract of communication between the central
parts of the brain and the olfactory bulb. Its physiological connection
with the sense of smell is indicated by, 1st, its anatomical relations ;
2d, its comparative development in different species of animals ; and 3d,
the results of its injury or disease.

I. The only anatomical connection of the olfactory nerve, at its
anterior extremity, is with the olfactory bulb; and the nerve fibres
given off from this part are distributed only to the olfactory region of
the nasal passages. In this region ordinary sensibility is but slightly
developed, while the parts are highly endowed with the sense of smell.

II. In such of the lower animals as possess a more acute sense of
smell than man, like the dog, the cat, the sheep, and other quadrupeds,
the olfactory bulbs are increased in proportion, forming prominent
masses at the anterior extremity of the hemispheres ; while the parts
representing the olfactory nerves are of so large a size that they are
generally designated by the name of the u olfactory lobes." They also
contain a central tubular cavity, which is a prolongation from that of
the lateral ventricles. There is accordingly a direct correspondence
between their development and that of the special sense with which
they are connected.

III. A considerable number of cases are quoted by Longet in which
congenital absence of the olfactory nerves, in man, was accompanied by
congenital incapacity to distinguish odors ; and others in which a loss
of the sense of smell was also observed after morbid affections causing
compression or destruction of these nerves.

According to the experiments of Magendie upon dogs,1 the olfactory
nerves are not sensitive to mechanical irritation, since their compres-
sion, puncture, or laceration in various directions, in the living animal,
causes no perceptible indications of sensibility.

Finally, experimental division or destruction of these nerves in dogs
abolishes, so far as observation can show, the power of discriminating
odors ; although it leaves the nasal mucous membrane sensitive to the
irritation of pungent or caustic vapors. In the experiments of Magendie,
a dog, after destruction of both olfactory nerves, would disentangle a
package containing meat when openly presented to him; but he did
not find it, when placed near by without his knowledge. The same
result was obtained by Vulpian'2 in operating upon hunting dogs.
These animals, after recovering from the immediate effects of the
operation, were kept fasting from 36 to 48 hours, and then introduced

Journal de Physiologic Experimental^ et Pathologique. Paris, 1825, tome
iv. p. 170.

2 Legons sur la Physiologic du Systeme Nerveux. Paris, 1866, p. 882.

516 THE CRANIAL NERVES.

into an apartment where a piece of cooked meat was concealed ; but
they were never able to discover it by its odor, when the division of
the nerves had been complete. Notwithstanding, therefore, the com-
parative difficulty of experimenting upon so obscure a function as that
of smell, there is no doubt that the olfactory nerves and bulbs are really,
the internal organs of the olfactory sense, and that they are disconnectedS
both with ordinary sensibility and the power of motion.

Second Pair. The Optic Nerves.

The optic nerves take their first origin from the anterior pair of the
tubercula quadrigemina, two small rounded prominences, on each side
of the median line, situated just behind the posterior extremity of the
optic thalami. They consist essentially of swellings of the gray sub-
stance which surrounds at this situation the aqueduct of Sylvius, and
which is consequently continuous with that extending forward from the
floor of the fourth ventricle. Their surface is covered by a layer of
white substance from 1.5 to 4 millimetres in thickness, consisting of
nerve fibres which have mainly a transverse direction. Their gray sub-
stance contains nerve cells, some of which are small and rounded, while
others, especially in the anterior pair, are of larger size and provided
with branched prolongations. According to Henle, the fibres of origin
of the optic nerve pass from these bodies outward and downward to the
corpus geniculatum internum, an ovoidal prominence of gray matter
attached to the posterior border of the optic thalamus. They cover the
surface of this body in a thin superficial layer, and continue their course,
winding round the lateral surface of the crus cerebri ; where they are
joined at an acute angle by a second bundle of fibres, coming from the
corpus geniculatum externum, a gray eminence similar to the last,
lying in contact with the under part of the optic thalamus, but isolated
from its gray matter by a thin investing layer of white substance.
These two bundles of fibres, coming, one from the anterior tubercula
quadrigemina and the corpus geniculatum internum, the other from the
corpus geniculatum externum, form in man the two roots of the optic
nerve ; and the collections of gray matter contained in these bodies are
regarded as its " nuclei," or the nervous centres with which it is in
anatomical communication. It also receives some fibres from the sub-
stance of the optic thalamus itself.

The fibres derived from these sources form a flattened band which
continues its course in a spiral direction, winding round the crus cerebri
to the base of the brain ; it thence runs forward and inward until the
two, from the right and left sides, meet upon the median line in the
so-called "chiasma," or decussation. From this they again diverge out-
ward and forward, leave the cavity of the cranium by the optic fora-
mina, and, joining the eyeballs, terminate in the nervous expansion of
the retina. That portion of the optic nerves situated behind the decus-
sation is sometimes designated by the special name of the "optic
tract."

THE OPTIC NERVES. 517

Real Origin of the Optic Nerves. — The fibres of the optic nerves, in
man, as shown by the above description, cannot all be distinctly traced
in a direct manner to the tubercula quadrigemina ; but those of one
root are evidently connected with the corpus geniculatum externum,
while those of the other pass to the corpus geniculatum internum, and
through the intervention of that body alone reach the anterior quadri-
geminal tubercule. And yet the data derived from comparative anatomy,
as well as the results of experiments upon the tubercula quadrigemma,
show that in the lower animals these bodies are the real sources of the
optic nerves. In all the mammalian quadrupeds the optic nerves are
readily seen to have their direct origin in the tubercula quadrigemina.
In the birds, reptiles, and fish these bodies are divided only into two
symmetrical prominences by a shallow, longitudinal, median furrow ;
and in these classes, accordingly, they are called the " tubercula bigem-
ina." But they are of comparatively larger size than in the mammalians,
and give origin still more distinctly to the optic nerves. Furthermore,
their destruction, as shown by the united testimony of all observers,
produces at once a loss of sight, although the remaining parts of the
brain be left uninjured; while it is certain, on the other hand, that
both the hemispheres and the optic thalami may be removed without
destroying sensibility to light. Even in man, according to the obser-
vations of Yulpian, the optic thalami may be the seat of extensive
lesions, from hemorrhage or softening, without any sensible disturb-
ance of the power of vision.

The apparent variation in man from the general type, in respect to
the origin of the optic nerves, is most readily explained by the variation
in the comparative size of the tubercula quadrigemina and the optic
thalami. In the inferior vertebrate animals, namely, fish and reptiles,
the tubercula quadrigemina or their representatives are very large, and
the optic thalami are either wanting or so slightly developed as to make
their significance uncertain. In birds the optic thalami are present, but
are still inferior in size to the tubercula bigemina. In mammalians
they increase in size in the ascending series, but the tubercula quadri-
gemina are still, in such animals as the dog and cat, comparatively con-
spicuous, and, throughout this class, consist of four tubercles instead
of two. In man the optic thalami are very much larger than the tuber-
cula quadrigemina, which are reduced altogether to a secondary grade.
The corpora geniculata probably represent in man portions of gray
substance included, in the lower animals, in the tubercula quadrigemina
or bigemina ; but which in the human brain are crowded outward and
backward by the increased development of the optic thalami, and there-
fore appear as appendages of these bodies.

Physiological Properties of the Optic Nerves. — The optic nerves,
like the olfactory, are nerves of special sense, and may be regarded as
tracts of fibres connecting the gray matter of the cerebrum with the
retinal expansion of the globe of the eye. They are destitute of sensi-
bility to tactile or painful impressions, and convey from without inward

518 THE CRANIAL NERVES.

only the impression produced upon the retina by luminous rays. In
the central parts of the brain with which they are connected, this im-
pression becomes the sensation of light ; and the optic nerves are there-
fore the channels for the sense of vision. Magendie found that in
quadrupeds both the retina and the optic nerves throughout their
length were insensible to mechanical irritation; and, in man, that touch-
ing the retina with the point of a cataract needle excited no perceptible
sensation. It has also been remarked, in cases of extirpation of the
eyeball, that the section of the optic nerve is not a painful part of the
operation; and, according to the observations of Longet upon animals,
these nerves may be pinched, pricked, cauterized, divided, or injured in
various ways without producing any signs of pain.

On the other hand, division of these nerves at once produces a state
of blindness. The impressions received by the retina are no longer
transmitted to the central organ, and the animal becomes insensible to
light, without losing any of his ordinary tactile sensibility or power of
voluntary motion.

Beside their immediate function in the perception of light, the optic
nerves are also channels for a special reflex action, connected with the
mechanism of vision ; namely, that of the contractile movements of the
iris. By these movements the orifice of the pupil enlarges or diminishes
according to the intensity of the light to which the eye is exposed. On
first entering a dark room everything is nearly invisible; but gradually,
as the pupil dilates and as more light is admitted, objects show them-
selves with greater distinctness, and at last we can see tolerably well
where it was at first almost impossible to perceive a single object. On
the other hand, when the eye is exposed to a brilliant light, the pupil
contracts and shuts out so much of it as would be injurious to the retina.

These movements, by which the quantity of light admitted to the eye
is regulated to suit the sensibility of the retina, are involuntary in cha-
racter, but are due to impressions conveyed inward by the optic nerve.
On the division of these nerves, or the destruction of the tubercula
quadrigemina, not only is the perception of light abolished, but the pupil
remains immovable, whatever may be the intensity of the light to which
it is exposed. In the production of this reflex act, the impression, which
is first received upon the retina, passes inward through the fibres of the
optic nerve to the tubercula quadrigemina. Its transformation into a
motor impulse is either accomplished in these bodies, or is commenced
in them and completed by transmission to the gray matter at the origin
of the oculomotorius nerves. Thus both the optic nerves and the tuber-
cula quadrigemina are essential to the movements of the pupil under the
influence of light. The proof that this action is of a reflex nature is
afforded by the results of dividing and irritating the optic nerves. After
section of the nerve, according to the experiments of Herbert Mayo and
Longet, upon pigeons, dogs, and rabbits, irritation of its peripheral end,
that is, the portion still connected with the eyeball, produces no effect
upon the pupil ; but irritation of its central portion, which is connected

THE OPTIC NERVES.

519

only with the brain, readily causes a movement of contraction. On the
other hand, division of the oculomotorius nerve, which paralyzes the
iris, puts an end to the movements of the pupil, although the eye may be
otherwise uninjured and the perception of light unimpaired.

Decussation of the Optic Nerves. — The decussation of these nerves
forms one of their most prominent anatomical features, being in all cases
readily visible on superficial examination, while in many classes of the
lower animals and in man it presents, on closer inspection, certain marked
varieties of detail. In fish, as a general rule (Fig. 1TO), the two optic
nerves cross each other's path from side to side at different levels, with-
out any admixture or even contact of their fibres ; that from the right side
of the brain passing independently to the left eye, and that from the left
side of the brain to the right eye. In the herring, according to Wagner,
the optic nerve of the right eye perforates that of the left, passing bodily
through it by a distinct slit, without forming a chiasma. In the sharks
and rays, which have a higher general grade of organization than other
fish, the fibres of the two nerves cross each other in separate fasciculi.

Fig. 170.

Fig. 171.

INFERIOR SURFACE OF THE BRAIN
OF THE COB.— 1. Optic nerve of right eye.
2. Optic nerve of left eye. 3. Right optic
tubercle. 4. Left optic tubercle. 5, 6. Cere-
bral hemispheres. 7. Medulla oblongata.

INFERIOR SURFACE OF THE BRAIN
OF FOWL. — 1. Optic nerve of right eye. 2.
Optic nerve of left eye. 3. Right optic
tubercle. 4. Left optic tubercle. 5, 6. Cere-
bral hemispheres. 7. Medulla oblongata.

In birds the two optic nerves appear externally to be united at their
point of crossing (Fig. 171), but dissection shows that the decussation
of their fibres is complete. Those coming from the left side pass, in
the form of slender bundles, altogether over to the right, and those
from the right side pass in the same manner over to the left ; so that in
this class each optic tubercle is connected exclusively with the eye of
the opposite side.

In man the decussation is more complicated, and is arranged in such

520

THE CRANIAL NERVES.

a manner as to form a connection at the same time between the two
opposite sides, and between the eye and the quadrigeminal tubercle on
the same side. Here also the apparent majority of the fibres cross each
other completely from side to side, though intermingled at the chiasma
in such slender bundles that they are distinguishable only by microscopic
examination. But at each side of the chiasma there is also a layer of
fibres, which, according to Henle, hardly exceeds one-twentieth of a

Fig. 172.

COURSE OF THE OPTIC NERVES IN MAN.— 1,2. Right and left eyeballs. 3. Decussation
of the optic nerves. 4,4. Tubercula quadrigemina.

millimetre in thickness, passing continuously along its outer border and
thence running forward with the optic nerve to the eye of the same side.
These fibres, like those of the white substance in general, do not keep the
same horizontal level, but follow a more or less spiral course, winding suc-
cessively outward, downward, and inward, from the upper surface of the
chiasma to reach the under surface of the optic nerve in front- It is
not known in what special parts of the retina the two sets of fibres on
each side, namely, the decussating and the direct, find their termination.
At the anterior angle of the chiasma there are also fibres which pass
from side to side in a curved direction, running symmetrically across
from one optic nerve to the other, and forming a transverse commissural
baud between the retinae of the two eyes ; and finally at the posterior
angle of the chiasma there are similar transverse commissural fibres,
which pass forward on each side with the corresponding optic tract,
cross the median line at the chiasma, and return backward with the optic
tract of the opposite side. Thus there is effected a fourfold connection

THE OPTIC NERVES. 521

between the two eyes and their nervous centres, namely, 1st, that be-
tween each nervous centre and the opposite eye ; 2d, that between each
nervous centre and the corresponding eye; 3d, that between the two
eyes by the anterior transverse commissure; and 4th, that between the
two nervous centres by the posterior transverse commissure.

The physiological significance of this compound decussation is not
clearly understood. When compared as it presents itself in different
classes of animals, it appears to be connected with the decree of diver-
gence or parallelism between the visual axes of the two eyes. Thus in
fish, where the e3^es are so placed on opposite sides of the head that
their axes cannot be brought into parallelism with each otherT the optic
nerves cross from side to side as distinct cords going to the opposite
eyes. In birds, where the eyes have nearly the same relative position as
in fish, the decussation is also complete, though less evident externally.
In quadrupeds as a class, the eyes are set more obliquely forward, while
in man they are situated completely at the front, so that their visual
axes are both directed forward, and parallel with each other, or may
even converge, and the two eyes can thus be brought to bear at the same
time upon near objects. The quadruple communication which exists in
man is, therefore, usually regarded as connected in some way with the
capacity for distinct and single vision with the simultaneous use of
both eyes. Cases, however, like that related by Yesalius,1 in which the
decussation was wanting, each optic nerve going independently to the
eye of its own side, without any noticeable defect of vision, show that
such a communication is not directly or absolutely necessary, even in
man, to distinct vision of single objects. It more probably serves in an
indirect manner, by reflex action, to facilitate the harmonious muscular
control of the two eyeballs, by which the corresponding parts of the
retina on the two sides receive the visual rays coming from a single
object.

Crossed Action of the Optic Nerves. — The results of observation
show that the action of the optic nerves, as channels for the sense of
sight, is mainly a crossed action. The experiments of Flourens, Longet,
and Vulpian coincide in this respect ; and in regard to birds the fact is
easily established. If in the pigeon, as we have frequently observed,
the right optic tubercle alone be removed, when the bird has recovered
from the immediate effects of the wound, the sight is to all appearance
completely lost in the eye of the opposite side, but remains unimpaired
in the eye of the same side. After such an operation an instrument
may be carefully brought in close proximity to the left eye, without
producing any sign of its perception ; but the instant it is moved a little
in front, so as to come within the range of the right eye, the animal
starts backward to avoid it. Flourens obtained similar results in the
dog and rat, leading to the conclusion, which agrees with that of Longet,
that in quadrupeds also visual impressions are transmitted by the optic

1 De Humani Corporis Fabrica. Liber iv. cap. iv.
34

522 THE CRANIAL NERVES.

nerves entirely in a crossed direction. There is no question that these
animals after destruction of the tubercula quadrigemina on one side are
mainly blinded in the opposite eye, since they use exclusively the eye
of the wounded side to guide them in their motions.

In man, the partial blindness of both eyes, sometimes observed in
cases of hemiplegia, makes it probable that the transmission of sight
takes place by both the crossed and direct fibres of the optic tracts.

The reflex influence which causes contraction of the pupil is also
transmitted, in the lower animals, in a crossed direction ; that is, the
stimulus of light falling upon the retina of one eye passes to the optic
tubercle of the opposite side. But here, owing to the transverse con-
nections between the central parts of the brain, the stimulus becomes
duplicated, and contractions are produced in the pupils of both eyes
simultaneously. This is because, although the sensitive impression is
conveyed inward to the nervous centres by one optic nerve only, when
transformed into a motor impulse it may be sent outward by both
oeulomotorrus nerves at the same time. Consequently if, in a pigeon,
one eye be blinded by removal of the opposite optic tubercle, both pupils
will still contract under the stimulus of light applied to the sound eye.
In examining one eye, therefore, either in animals or in man, to ascer-
tain whether or not its retina be sensitive to light, the opposite eye
should always be covered, in order to prevent its exciting a movement
by reflex action.

Third Pair. The Oculomotorius.

The oculomotorius nerve, so called because it supplies four out of six
of the muscles moving the eyeball, originates from a collection of gray
substance situated next the median line, beneath the tubercula quadri-
gemina and the aqueduct of Sylvius. As this group of nerve cells is
continuous with that which gives origin to the fourth nerve or pathe-
ticus, it is sometimes designated as the common nucleus of the oculo-
motorius and patheticus nerves. From this nucleus the fibres of the
oculomotorius nerve pass downward and forward, through the substance
of the crus cerebri, until they emerge, in the form of several flattened
bundles, from its inner border, a little in front of the anterior edge of
the pons Yarolii. From this point, the apparent origin of the nerve,
its fibres unite into a rounded cord, which runs forward and outward,
to penetrate the cavity of the orbit by the sphenoidal fissure. During
its transit along the walls of the cavernous sinus, it receives one or two
fine twigs of sensitive fibres from the trigeminus nerve. In entering
the orbit, it divides into several branches, and supplies, the superior,
inferior, and internal straight muscles of the eyeball, the inferior oblique,
and the levator palpebroe superioris. The oculomotorius is accordingly
concerned both in the vertical and lateral movements of the eyeball, and
in those of rotation; while of the two other muscular nerves of this
organ, the abducens and patheticus, one is connected only with the
movement of lateral abduction, the other only with that of rotation.

THE OCULOMOTORIUS. 523

Decussation of the Oculomotor ius Nerve. — According to the observa-
tions of Meynert, a decussation takes place between the oculomotorius
nucleus and the opposite side of the brain, by means of fibres emerging
from the raphe upon the median line, near which the nucleus is situated.
These fibres come originally from the corpus striatuin, thence running
backward along the inner border of the crura cerebri, into the longitu^
clinal lamina forming the raphe between them. Underneath the aque^
duct of Sylvius they decussate with each other at acute angles, those
from the right corpus striatnm passing to the nucleus of the left side,
and vice versa. Each oculomotorius nerve is therefore in connection
with the opposite side of the brain, not by means of its own fibres, but
through the intervention of its nucleus and the fibres which pass thence,
through the raphe, toward the opposite corpus striatum.

Physiological Properties of the Oculomotorius Nerve. — The oculomo-
torius is in itself an exclusively motor nerve, and has been found by
Longet, when examined in the living animal, near its point of emergence
from the crus cerebri, to be insensible to mechanical irritation ; but at
some distance farther forward, after receiving its branches of commu-
nication from the fifth pair, it exhibits a certain degree of sensibility.
Its excitability, on the contrary, is very manifest ; and its irritation
within the cranial cavity, even after it has been separated from its con-
nection with the brain, causes convulsive action in the muscles of the
eyeball.

The physiological function of this nerve is distinctly shown by the
nature of the paralysis following its section either before or after its
entrance into the orbit. These results are for the most part very sim-
ple and well marked, and are established by the uniform testimony of
various observers. They consist of the paralysis of the five muscles to
which the nerve is distributed, and induce, consequently —

1. External strabismus, from continued action of the external straight
muscle of the eyeball, which is no longer controlled by that of the
internal.

2. General immobility of the eyeball, owing to the abolition of its
natural upward, downward, lateral, and rotatory movements. For
although two of the muscles of the eyeball, namely, the external rectus
and the superior oblique, remain unparalyzed ; yet, as they are no
longer antagonized by the remainder, they can only produce a perma-
nent deviation of the eyeball, but no alternate movement in opposite
directions. In most of the lower animals there is also an unusual
prominence of the eyeball, owing to the relaxed condition of the muscles
which serve for retraction.

3. Drooping of the upper eyelid. In the ordinary action of opening
the eye, it is the upper eyelid alone which moves, being raised so as to
uncover the cornea and pupil, by the contraction of the levator palpebrse
superioris. As this muscle is animated by a nervous branch coming
from the oculomotorius, it is paralyzed by section of this nerve at the
same time with the muscles moving the eyeball. The consequence is

524 THE CRANIAL NERVES.

that the eye can no longer be opened to its full extent ; although it can
still be closed as usual by the action of the orbicularis oculi, which
does not depend upon the oculomotorius, but is animated by branches
derived from the seventh pair, or facial nerve. The superior eyelid
therefore droops, resting by. its own weight in such a position as to
cover the upper portion of the cornea, and the greater part or even the
whole of the pupil. In man this condition of the eyelid is known as
ptosis, and is one of the consequences following paralysis of the oculo-
motorius nerve.

The influence of the oculomotorius upon the contractile movements of
the iris is important, though less distinct and uniform in its action, as
shown by experiment, than that exerted upon movements of the eyeball
itself. The connection of the oculomotorius with the muscular appa-
ratus of the iris is not a direct one, but takes place through the inter-
vention of the ophthalmic ganglion, to which this nerve sends a commu-
nicating motor branch, and which in turn gives off the ciliary nerves
destined for the iris. Some observers (Herbert Mayo, Longet) have
found well-marked paralysis of the iris following division of the oculomo-
torius nerve, and enumerate, as consequences of this injury, a permanent
dilatation and immobility of the pupil. In the experiments of Longet,
which were performed on dogs, rabbits, and pigeons, irritation of the
cephalic extremity of the optic nerve caused contraction of the pupil in
both eyes ; but after division of the oculomotorius nerve the effect was
no longer produced upon the operated side. Bernard has also found
that division of the oculomotorius is followed, in the rabbit, by dilata-
tion of the pupil, and that in the operated e}^e the iris contracts only
very slowly and imperfectly under the influence of light. It is not,
however, completely paralyzed, since it may still move with considera-
ble promptitude under the influence of painful impressions conveyed by
the fifth pair. The action of the oculomotorius upon the pupil, there-
fore, is energetic and constant in the ordinary reflex movement of con-
traction under the stimulus of light ; but it takes place through the
ophthalmic ganglion, to which it communicates, in a certain degree, its
motive power.

Fourth Pair. The Patheticus.

This nerve presents a variety of peculiarities, which have always,
notwithstanding its minute size, attracted to it more or less special
attention. It is distributed exclusively to the superior oblique muscle
of the eyeball ; its name having been derived from the mistaken idea
that this muscle turned the e}re upward and inward. The two oblique
muscles, however, have been fully shown to cause in the eyeball a nearly
simple movement of rotation about its longitudinal axis. They are
antagonistic to each other; and by their contraction and relaxation,
during movements of inclination of the head from side to side, they
maintain the horizontal planes of the two eyeballs in the same position.
If this parallelism were not preserved, objects would appear to stand in

THE PATHETICUS. 525

different degrees of obliquity to the two eyes, producing uncertainty
and double vision.

The apparent origin of the patheticus nerve is directly behind the
tubercula quadrigemina, on the upper surface of the valve of Vieussens,
a thin lamina of white substance, extending from this situation back-
ward to the cerebellum, and thus covering in the anterior part of the
fourth ventricle. The fibres of the nerve, however, can be traced from
without inward in a transverse direction through the substance of the
valve. According to Henle and Meynert, a great part of these fibres
cross the median line, decussating with those coming in the opposite
direction from the corresponding nerve on the other side; then, turning
downward and forward, they reach a collection of gray matter seated
just behind the nucleus of the oculomotorius nerve, and continuous
with it anteriorly. According to Henle, a portion of the fibres also
remain upon the same side of the median line, and terminate, without
crossing, in this and another nucleus not far distant. The collection
of gray matter just described is, however, regarded as the main nucleus
or point of origin for the fibres of the patheticus nerve. This nucleus
is situated beneath the aqueduct of Sylvius, near the median line, and
at a situation corresponding with the anterior tubercula quadrigemina ;
while the point of exit of the nerve is above the aqueduct of Sylvius
and behind the posterior tubercula quadrigemina. Its fibres, accord-
ingly, after leaving the gray matter in which they originate, encircle
the lateral walls of the aqueduct, running obliquely upward and back-
ward, and then, curving inward, cross the median line to their point of
emergence on the opposite side.

From this point the nerve passes forward, as a slender, rounded fila-
ment, not more than one millimetre in diameter, but containing, accord-
ing to the estimate of Rosenthal, about 1100 ultimate nerve fibres. It
passes along the upper wall of the cavernous sinus, where it lies in
immediate proximity to the oculomotorius; and thence, entering the
cavity of the orbit by the sphenoidal fissure, terminates in the sub-
stance of the superior oblique muscle of the eyeball.

The course of the fibres of the oculomotorius and patheticus, when
compared with each other, shows a remarkable relation between two
nerves which are apparently distinct. The fibres of both originate from
adjacent portions of the same nucleus, situated in the thickness of the
crus cerebri. Those of the oculomotorius pass downward and forward,
to emerge from the inner free border of the crus, at the base of the
brain ; while those of the patheticus pass upward and backward, to
emerge from the upper and posterior part of the cerebro-spinal axis,
between the cerebrum and cerebellum. But the two nerves afterward
pass side by side, in their passage toward the orbit, and are finally dis-
tributed to muscles which are associated in the accomplishment of the
same movements.

Physiological Properties of the Patheticus Nerve. — The anatomical
distribution of this nerve to a muscle which receives filaments from no

526 THE CRANIAL NERVES.

other source indicate in great measure its motor character, which is
furthermore fully established by the results of observation. Both the
experiments of Chauveau on the horse and rabbit, and those of Longet
on the horse, ox, and dog, show that galvanization of this nerve in
the interior of the cranium produces always contraction of the supe-
rior oblique muscle of the eyeball, with rotation of the eyeball on its
longitudinal axis from without inward ; and in those of Longet there
was also a perceptible deviation of the pupil outward. In cases quoted
by Longet, in the human subject, attributed to paralysis of this nerve,
there was incapacity of rotation of the eyeball on the affected side, and
consequently double vision, the image perceived by the affected eye being
oblique and inferior in regard to the other ; but these disturbances of
vision disappeared when the head was inclined toward the opposite
side.

The patheticus is, accordingly, the motor nerve of the superior ob-
lique muscle, and acts in harmony with the oculomotorius to preserve
the horizontal plane of the eyeball.

Fifth Pair. The Trigeminus.

The fifth pair occupies, in every respect, a prominent place among
the cranial nerves. It is the great sensitive nerve of the face, being
the only source of general sensibility for the integument and mucous
membranes of this region ; and, by communicating branches sent to
the corresponding motor nerves, it also provides for the imperfect
degree of sensibility belonging to the facial muscles. While in its main
portion, however, it is thus pre-eminently a sensitive nerve, it also pos-
sesses motor fibres, derived from a distinct root, and distributed to
muscles of a distinct group. Before emerging from the cranial cavity
it separates into three main divisions, destined for the corresponding
regions of the face ; and its name, trigeminus, is derived from the fact
that these three primary divisions of the nerve are nearly alike in size
and importance.

The apparent origin of the fifth nerve is from the lateral portion of
the pons Yarolii, where its two roots emerge in close approximation
to each other, but usually separated by a narrow band of the trans-
verse fibres of the pons. The anterior or motor root is the smaller,
being about two millimetres in diameter; the posterior or sensitive root
is the larger, and having a diameter of about five millimetres. Both
these roots may be traced, through the fibrous bundles of the pons
Varolii, backward, upward, and inward toward the gray substance be-
neath the floor of the anterior part of the fourth ventricle. The two
roots, which remain distinctty separated throughout most of their pas-
sage through the pons, join each other above and become closely entan-
gled by the interweaving of their bundles ; though their fibres may still
be distinguished, on microscopic examination, by the generally larger
size of those belonging to the motor root. They finally reach a collec-
tion of gray matter, the u nucleus of the fifth nerve," which is situated

THE TRIG-EMINUS.

527

next behind that of the oculomotorius and patheticus, but farther out-
ward from the median line, occupying the extreme lateral part of the
fourth ventricle, where its floor forms an angle with the roof. The
fibres of the nerve terminate partly in or among the large, stellate, and
dark-colored cells of the nucleus. According to Henle, a portion of
them also pass through the nucleus, nearly to the surface of the floor
of the ventricle, and thence inward to the raphe at the median line,
where they cross to the opposite side ; while another portion still, re-
maining upon the same side, pass upward with the superior peduncles
of the cerebellum, and lose themselves in the substance of the tubercula
quadrigemina. The fibres of the fifth nerve, accordingly, which termi-
nate in the nucleus proper, form partly a direct, and partly a crossed
connection between the external organs and the nervous centres.

Fig. 173.

VNt

TRANSVERSE SECTION OP THE FLOOR OF THE FOURTH VENTRICLE, at -the
situation of the nucleus of the Trigeminua Nerve; Human brain.— Nt, Nt', median and
lateral portions of the nucleus. V. Fibres of the nerve root. Magnified 8 diameters
(Henle.)

After emerging from the pons Yarolii, the two roots of the fifth nerve
pass outward and forward in company with each other, the larger, pos-
terior, or sensitive root being placed above, the smaller, anterior, or
motor root underneath. On reaching the apex of the petrous portion
of the temporal bone, a little outside and behind the posterior clinoid

528

THE CRANIAL NERVES,

processes of the sella turcica, the fibres of the sensitive root spread out
into a comparatively loose network of inosculating bundles, and pass
into and through the substance of the Gaxserian .ganglion. This gan-
glion forms a flattened, crescentic mass of gray matter, mingled with

Fig. 174.

DIAGRAM OF THE FIFTH NERVE AND ITS DISTRIBUTION — 1. Sensitive root.
2. Motor root. 3. Gasserian ganglion. I. Ophthalmic division. II. Superior maxillary
division. III. Inferior maxillary division 4 Supra-orbital nerve, distributed to the skin
of the forehead, inner angle of the eye, and root of the nose. 5. Infra-orbital nerve; to the
skin of the lower eyelid, side of the nose, and skin and mucous membrane of the upper lip.
6. Mental nerve; to the integument of the chin and edge of the lower jaw, and skin and
mucous membrane of the lower lip. n, n. External terminations of the nasal branch of the
ophthalmic division , to the mucous membrane of the inner part of the eye and the nasal
passages, and to the base, tip, and wing of the nose. /. Temporal branch of the superior
maxillary division ; to the skin of the temporal region, m. Malar branch of the superior
maxillary division; to the skin of the cheek and neighboring parts, b. Buccinator branch
of the inferior maxillary division ; passing along the surface of the buccinator muscle, and
distributed to the mucous membrane of the cheek, and to the mucous membrane and skin
of the lips. I. Lingual nerve; To the mucous membrane of the anterior two-thirds of the
tongue, at. Auriculo-temporal branch of the inferior maxillary division; to the skin of the
anterior part of the external ear and adjacent temporal region, a?, #, x. Muscular branches}
to the temporal, masseter, and internal and external pterygoid muscles, y. Muscular branch ;
to the mylo-hyoid and anterior belly of the digastric muscles. /. Sensitive branch of com-
munication to the facial nerve.

the fibres derived from the sensitive root. According to the observa-
tions of Kb'lliker, the fibres of the sensitive root simply pass through
the gra3T matter of the ganglion, making no anatomical connection with
its nerve cells ; while the ganglion cells, which are mostly unipolar in

THE TRIGEMINUS. 529

form, give off additional fibres in a peripheral direction. Thus the
branches of the fifth nerve beyond the ganglion contain, beside the fibres
derived from its sensitive root, others which have originated from the
ganglion itself. The motor root passes underneath the ganglion as a
distinct bundle, and neither gives to nor receives from it any nerve
fibres. At the anterior or convex border of the Gasserian ganglion, the
nerve separates into three nearly equal cylindrical bundles, namely, the
first, or ophthalmic; the second, or superior maxillary; and the third,
or inferior maxillary divisions of the fifth nerve.

The ophthalmic division passes forward through the sphenoidal fis-
sure into the orbit of the eye, where it gives filaments to the ophthalmic
ganglion and to the ej^eball ; a nasal branch which supplies the integu-
ment and mucous membrane of the inner part of the eye, the mucous
membrane of the middle and inferior nasal passages, and the integument
of the root, wing, and tip of the nose; and a branch to the lachrymal
gland and the integument of the upper eyelid and adjacent region. It
then emerges from the cavity of the orbit by the supra-orbital notch,
and is distributed to the skin of the forehead and side of the head, as
far back as the vertex.

The superior maxillary division passes out of the cranial cavity, by
the foramen rotundum, at the base of the skull, into the spheno-maxil-
lary fossa, where it gives a sensitive branch to the spheno-palatine gan-
glion of the sympathetic, thence into and through the longitudinal
canal in the floor of the orbit, giving off a branch which runs upward
and outward to terminate in the skin of the malar and temporal regions,
and numerous descending branches, which supply the teeth, gums, and
adjacent mucous membrane of the upper jaw, and, by a nasal filament,
the mucous membrane of the bottom of the nasal passages. The nerve
then emerges upon the face by the infra-orbital foramen, and is distri-
buted in abundant diverging branches to the integument of the lower
eyelid and the side of the nose, and to the skin and mucous membrane
of the upper lip.

The inferior maxillary division leaves the anterior border of the
Gasserian ganglion at a different angle from the two others, passing
almost vertically downward through the foramen ovale. This division
receives all the fibres of the motor nerve root, which become more
or less intimately united to it during and after its passage through the
base of the skull. While the two other divisions of the fifth nerve are
therefore exclusively sensitive, the inferior maxillary division is a mixed
nerve, containing both motor and sensitive fibres. Its sensitive portion,
however, is still the most abundant, and all its motor branches are given
off a short distance below its point of exit from the skull.

After emerging from the foramen ovale, this division of the fifth pair
supplies one or two filaments to the otic ganglion of the sympathetic,
which is situated near its inner surface, and passes downward toward
the inferior dental canal ; sending off, in the mean time, two sensitive
branches, namely, 1st, the buccinator branch (6), destined for the mucous

530 THE CRANIAL NERVES.

membrane of the cheek, and the skin and mucous membrane of the lips ;
and 2d, the auricula-temporal branch (at), which turns backward and
upward behind the neck of the inferior maxilla, to be distributed to
the integument of the anterior wall of the external auditory meatus,
the anterior part of the external ear, and the adjacent temporal region.
From this branch a twig of considerable size is given off (/"), which
turns forward to join the facial nerve, and communicates to its branches
in front of this point a perceptible degree of sensibility.

Continuing its course, the nerve enters the dental canal of the inferior
maxilla, through which it runs from behind forward, giving off filaments
to the teeth and gums of the lower jaw. It then emerges at the mental
foramen, and radiates, like the corresponding portion of the superior
maxillary division, in diverging branches and ramifications, which ter-
minate in the integument of the chin and edge of the under jaw, and in
the skin and mucous membrane of the lower lip.

The remaining sensitive branch of this portion of the fifth is the
lingual nerve (/), which separates from it before its entrance into the
dental canal, sends filaments to the submaxillary gland, the sympathetic
submaxillary ganglion, and the adjacent mucous membrane of the
mouth, and is finally distributed to the mucous membrane and papillae
of the tip, edges, and surface of the anterior two-thirds of the tongue.
Finally, the motor branches are those (#, x, x} going to the temporal,
masseter, and two pterygoid muscles, and that which is distributed (y)
to the mylohyoid muscle and the anterior belly of the digastric.

Physiological Properties of the Fifth Pair. — The most prominent
and important character belonging to this nerve is that of its general
sen'sibility. The regions of the face to which it is distributed, namely,
the skin of the cheeks, the eyelids, the tip of the nose, the lips, mucous
surfaces of the anterior nares, and especially the tip of the tongue, possess
a tactile sensibility of much higher grade than most other regions of the
body. The nerve itself, with all its principal branches, is also acutely
sensitive to mechanical irritation, and will give rise to indications of
sensibility on being wounded or galvanized, under conditions when the
spinal nerves generally are nearly or quite inactive.

But the most direct and conclusive experiment bearing on the physio-
logical functions of this nerve and its branches is that of dividing them,
either separately or together, by a transverse section. Either the infra-
orbital or mental nerve maybe divided, in the quadrupeds, at the points
where they emerge from the corresponding foramina in the maxillary
bones. A more decisive method is that of dividing the fifth nerve in the
interior of the cranium by a section passing through its trunk at the
situation of the Gasserian ganglion. This operation was first performed
by Magendie, and has since been frequently repeated by various ex-
perimenters. It may be done, upon the cat or the rabbit, by means of
a steel instrument with a slender shank and a narrow cutting blade
projecting at nearly a right angle from its extremity. The instrument
is introduced in a horizontal direction through the squamous portion

THE TRIGEMINUS. 531

of the temporal bone, and pushed inward and a little forward, with its
cutting blade laid flatwise upon the surface of the petrous portion, until
it strikes the posterior clinoid process. It is then withdrawn slightly,
its cutting edge turned downward, and the fifth nerve divided where it
crosses the apex of the pyramid formed by the petrous portion of the
temporal bone. The instrument is again turned with its cutting blade
flatwise, and withdrawn from the skull in this position. When this
manoeuvre is successfully carried out, all the fibres of the fifth nerve are
divided at a single stroke, and the only part of the brain necessarily
wounded is the inferior portion of the temporal lobe. The hemorrhage
is small in amount, producing only a slight degree of cerebral compres-
sion, from which the animal soon recovers.

The immediate effect of this operation is a complete loss of sensibility,
upon the operated side, in the integument and mucous membranes about
the face. The cornea or conjunctiva can be touched or pricked without
exciting an}*- movement of the eyelids ; while upon the opposite side
these parts retain their natural acuteness of sensibility. A probe may
be deeply introduced into the nasal passages, or the upper or lower lip
may be pierced throughout its substance with a steel needle, without
producing any indication of pain, or eliciting any sign of sensation on
the part of the animal. At the same time the power of motion in these
parts is unaffected. The eyelids may be opened or closed under the
influence of visual impressions, and the movements of the lips and other
parts continue to be performed in a nearly natural manner. In the cat,
the loss of sensibility and the persistence of the power of motion is
readily seen by irritating at different points the integument of the ex-
ternal ear, which in this animal has naturally an acute tactile sensibility.
If the point of a steel instrument be brought in contact, upon the
operated side, with the anterior part of the ear, which is supplied by
fibres from the third division of the fifth nerve, no effect is produced.
But if the same irritation be applied to the back part of the ear, which
is supplied by the great auricular nerve from the cervical plexus, a
vigorous twitching movement is at once excited. According to Longet,
the most violent injuries, such as exsection of the eyeball, evulsion of
the hairs about the lips, extraction of the teeth, or destruction of the
integument by the acutual cautery, may be performed after complete
division of the fifth nerve without causing any painful sensation. There
is entire anaesthesia of all the parts supplied by filaments of this nerve.

The fifth pair is accordingly the exclusive source of sensibility in the
superficial regions of the face, and all parts of the nasal and buccal
cavities to which it is distributed.

Painful Affections of the Fifth Pair. — This nerve is also the seat of
all the neuralgic painful affections about the head and face. The most
common of these is headache ; which may be general, extending over
both sides of the forehead and vertex, or confined strictly to one side.
It often seems to be located in the nerves supplying the periosteum,

532 THE CRANIAL NERVES.

especially that lining the orbit of the eye, or the frontal sinuses. Where
the pain is deep seated, its location may even be in the dura mater or the
bones of the skull ; since each division of the fifth pair, either before or
immediately after leaving the cavity of the cranium, sends backward a
slender recurrent branch, destined for the dura mater and the cranial
bones. That from the ophthalmic division is traced backward into the
tentorium, in the substance of which it ramifies as far as the sinuses
bordering its attached edge.

In cases of toothache, which depends upon irritation of the dental
filaments of the fifth pair, the cause of the neuralgia is usually the
decay of the bony substance of the tooth, and consequent exposure of
the tooth pulp to external injury or inflammation. It is usually con-
fined to the single tooth affected by decay ; but in severe cases the pain
may radiate to other teeth in the immediate neighborhood, or may even
spread over the entire corresponding side of the maxilla. Neuralgia of
the teeth may also be wholly sympathetic in its origin, as where it is
caused, like headache, by indigestion, exposure, or fatigue; the pain
existing simultaneously in several teeth, without any morbid alteration
of their structure.

The most severe and persistent form of neuralgia in this nerve is that
known as tic douloureux ; in which the pain is habitually located in one
of its three principal divisions as they emerge upon the face. Here
also the pain is not constant, but intermittent, recurring in great
severity at longer or shorter intervals, and usually lasting but a few
minutes at a time. It is more frequently seated in the upper or middle
region of the face, corresponding with the distribution of the supra or
infra-orbital nerves.

Lingual Branch of the Fifth Pair. — This branch, which is designated
by the special name of the " lingual nerve," possesses an especial interest
because it communicates to the mucous membrane of the tongue both
the property of tactile sensibility and the special sense of taste. The
general sensibility of the tongue is highly developed over the whole
of its anterior two-thirds, where it is supplied by the lingual nerve ; and
at its tip is more acute than in any other region of the body. This
sensibility disappears completely on the operated side, together with
that of the external portions of the face, when the fifth nerve has been
divided in animals in the interior of the cranium ; and Longet has found
that after section of both lingual nerves, the surface of the anterior two-
thirds of the tongue may be cauterized with potassium hydrate or the
red-hot iron, without producing any indication of pain. The tactile
sensibility of the tongue is of great importance in man, and also in
some of the lower animals, as an aid in the process of mastication, by
enabling this organ to appreciate the simple physical qualities of the
food introduced into the mouth, to perceive when it is uniformly re-
duced to the proper consistency for swallowing, and to detect any
remnants left among folds or crevices of the mucous membrane. These

THE TRIGEMINUS. 533

functions are therefore seriously interfered with by injury or destruc-
tion of the sensitive filaments supplying the tongue.

The lingual nerve is also endowed with the special sensibility of
taste. This function is a difficult one to investigate upon the lower
animals, owing to the uncertainty of its external indications and the
difficulty of isolating, for the purposes of observation, separate re-
gions of the cavity of the mouth. Experiments upon man, however,
which are made with comparative facility, have been performed by
Guyot, Verniere, Duges, and Longet in such a manner as to leave no
doubt that the sense of taste is highly developed in those portions of
the tongue which are supplied exclusively by the lingual nerve. These
experiments consist mainly in applying to different parts of the mucous
membrane, in the cavity of the mouth, a small globule of lint, moistened
with a solution of some substance, like quinine or colocynth, possessing
a distinct taste without irritating qualities. In this way it is ascertained
that the point, edges, and superior surface of the tongue, throughout
its anterior two-thirds, is capable of perceiving the sensations of taste,
without aid from other parts of the buccal mucous membrane. Accord-
ing to the experiments of Bernard and Longet on animals, division of
the lingual nerve destroys the faculty of taste as well as that of general
sensibility in the corresponding parts of the tongue; and similar obser-
vations are quoted by Henle, after section of this nerve in the human
subject.

Muscular Branches of the Fifth Pair. — These branches, as enume-
rated above, are given off from the inferior maxillary division, for the
most part a short distance below its exit from the skull, and are dis-
tributed to the temporal, the masseter, and the external and internal
pterygoid muscles ; while the mylohyoid branch, which separates from
the trunk somewhat farther down, supplies the muscle of the same
name as well as the anterior belly of the digastric. All these nerves
are, therefore, concerned in the movements of mastication. The most
powerful of the muscles to which they are distributed, namely, the
temporal and the masseter, act by bringing the teeth of the lower jaw
forcibly in contact with those of the upper. The contraction of the two
pterygoid muscles produces a lateral grinding movement, by which the
trituration of the food is accomplished ; and finally those supplied by
the mylohyoid branch facilitate the partial separation of the jaws, to
allow a repetition of the former motions. In different species of
animals these movements vary in their relative importance. In the
carnivora, it is the closure of the jaws which preponderates over the
rest, enabling the animal to seize and tear his prey, by means of the
pointed canine and sharped-edged molar teeth. In the herbivora, on
the other hand, the lateral grinding movements are more important for
the complete comminution of the seeds, grains, or other hard vegetable
tissues upon which they feed. In man, both movements coexist in a
nearly equal degree.

The movements of mastication are accordingly paralyzed by section

5,'U TIIK (MiANIAI, NKKVES.

of the fifth pair, and :uv tin- only muscular functions directly interfered
with liy this operation. There is a diHerenec, ho\\ ever, in Mir ultimate
consequences uhich follow |>:i ralysis of mast icat ion, according to the
species of animal alfcctcd. If the fifth pair, or its inferior maxillary
division, \\civ destroyed on both sides in either u carnivorous or
herbivorous animal, death would follow from inanition, owing to the
impossibility of preparing the food for deglutition. If the injury were
inllictcd upon one side only, it, would be equally fatal in the hcrbivora,
by preventing the alternate lateral movements of the jaw; while in a
carnivorous animal the vertical movements, which are more import-nut,
would be less seriously alleetcd, since they might still be performed,
though imperfectly, by the muscles of the opposite side.

I'.iit the most peculiar secondary result, of paralysis of the muscles of
mastication on one side is seen in the rodcntia. In these animals the
most important teeth are the four incisors, two in the upper and two in
Mir lower jaw, which are used for gnawing through hard substances, and
which grow continuously from the tooth pulp below, thus supplying the
waste caused by wearing away their edges. The tooth move against
each other in an exact vertical plane, the upper and lower incisors on
each side meeting e:ich other, and thus by mutual attrition keeping their
chisel like edges at a con espoiiding level. If the fifth nerve be divided
in I hese animals, the lower jaw becomes deviated toward the operated
side in consequence of the paralysis of the corresponding petrygoid
muscles. The edges of the four incisor teeth then no longer correspond
with each other, but are so shifted that one of those in the upper and
one in the lower jaw do not meet \\ith any opposing edge, and are con-
sequently no longer worn away. According to the experiments of Ber-
nard on rabbits, (he line of junction between the edges of t he teeth,
instead of being hori/.ontal, then becomes oblique, being directed from
abo\e downward, from the operated toward the sound side, and the
same fact has been observed by Hint.1 If the animal survive for a
considerable time, tin- teeth which are no longer worn away, as they
continue to grow from the tooth-pulp below, may become excessively
elongated. \\'e have seen an instance in the woodchuck ( A ret omys
monax) of lateral deviation of the teeth from a reunited fracture of the
lower jaw, in which the upper incisor on one side and the lower on the
other had increased to live or six times their natural length, and had
probably caused the death of the animal by penetrating the soft pails
about, the head and interfering with the movement of the jaws.

Antixtainoh'c lirtuicln-K <>/' fhc /•'//'//» /'rt/>. — Although the separate
regions of the face are supplied in a general way by the three great
divisions of this nerve, there is yet more or less communicat ion between
them by intermingled filaments from (litl'erent sources, and the separate
branches of each division communicate with considerable frequency.
Thus the infra-orbital nerve, which sends filaments to the lower eyelid,

1 Physiology of Man ; Nervous Svstem. Now York. 1872, p. 198.

THE TRIGEMINUS. f>;>f>

inosculates by a distinct twig with one of the nasal branches of the oph-
thalmic division. The integument of tlio 11OSO is supplied by the nasal
branches of tin' ophthalmic division, and also by tllOSC coming from the
infraorbital nerve. The upper :md lower lips arc supplied both from
tlu- infraorhital Mild mental nerves on t ho outside, and from the terminal
filaments of (he buccinator nerve on the inside; ;ind the temporal region
receives branches both from the superior and inferior maxillary divisions.
A most important, Miiastomotic branch of the fifth pair is that which its
inferior maxillary division sends to the facial nerve (Fig. It4,y), and
by means of \\hich it .supplies sensitive filaments to the great motor
ncrvo of the face. As a general rule, nerves which are distributed
exclusively to muscles receive at some part, of their origin or course
sensitive filaments which accompany them to their destination. The
muscular tissue consequently has a certain degree of sensibility ; and it,
is this sensibility, sometimes called the u muscular sense," \\ Inch enables
us to appreciate the existence and degree of contraction in any particular
muscle or group of muscles. Many of the sensitive filaments supplied
to the facial nerve by tlu4 communicating branch of the fifth are un-
doubtedly destined to reach the muscles of the face \\ilh the terminal
branches of this nerve; but there are also abundant anastomoses be-
tween the facial nerve and the fifth near the final distributions of the
latter nerve. These anastomoses are quite numerous, between the
branches of the infraorbital and mental nerves and those of the facial;
and certain regions of the integument may, therefore, be supplied with
sensibility by filaments from both these sources- The observations of
1/Mtievant1 have shown that ii is impossible to abolish the sensibility
of any extended region of the face by section of either division of tin'
fifth pair alone. A complete anaesthesia can only be produced by divi-
sion of the whole nerve within the cranial cavity. This destroys at
once not, only the sensibility supplied directly by the fifth pair, but also
that communicated to the facial by its anastomotic branch.

According to llenle, there is still a portion of the side of the face
which may derive a certain degree of sensibility, apart from that due to
the fifth pair, from the great auricular nerve of the cervical plexus ; since
the anterior branch of this nerve, after supplying the under part of the
lobe of the ear, sends some slender filaments anteriorly to the integu-
ment, of the cheeks, running in some instances as far forward as the
neighborhood of the malar bone.

In lli« -nee of the Fifth Pair on the Special Senses The results of

experiment show that this nerve has an important influence upon the
special senses, since they are always more or less interfered with, and in
some instances practically destroyed, by its division or injury. This
influence, however, is mainly not a direct but an indirect one; and shows
itself by a disturbance of nutrition in the tissues of the organ. For the
perfect action of any of the special senses, two different conditions are

1 Trait6 des Sections Nervcuscs. Paris, 1873, p. 179.

636 THE CRANIAL NERVES.

requisite : first the peculiar sensibility of its own special nerveT and
secondly the integrity of the component parts of the organ itself. As
the nutrition of the organ is affected by injury or disease of the fifth
pair, this necessarily causes a derangement in its physiological action
and thus interferes with the exercise of the special sense belonging to it.
These effects seem to depend, not so much upon the division of the ordi-
nary sensitive fibres of the fifth nerve, as of those which are derived
from the nerve cells of the Gasserian ganglion, or which are supplied
by the fifth pair to the special sympathetic ganglia connected with the
organs of sense.

Influence on the Sense of Smell. — The nasal passages are supplied
by two different nerves derived from the cerebro-spinal S3rstem, namely,
the olfactory nerve distributed to their upper portions, and endowed
with its own special sensibility; and the nasal branches of the fifth pair,
distributed in the lower portions, to which they communicate the gene-
ral sensibility of the mucous membrane. The mucous membrane also
contains filaments from the spheno-palatine ganglion of the sympathetic ;
and this ganglion receives its sensitive root -from the superior maxillary
division of the fifth pair.

The general sensibility of the nasal passages may accordingly remain
after the special sense of smell has been destroyed. If the fifth pair,
however, be divided, not only is general sensibility destroyed in the
Schneiclerian membrane, but a disturbance also takes place in its nutri-
tion, by which the power of smell is also lost* The mucous membrane
becomes swollen, and the nasal passage is obstructed by an accumula-
tion of mucus. According to Longet, the membrane also assumes a
fungous consistency, and is liable to bleed at the slightest touch. The
effect of this alteration is to blunt or destroy the sense of smell. It is
owing to a similar condition of the mucous membrane that the power
of smell is impaired in cases of influenza. The olfactory nerves become
inactive in consequence of the alteration in their mucous membrane and
its secretions.

Influence on the Sense of Sight. — The anterior parts of the eyeball
are also supplied with nerves of ordinary sensibility from the fifth pair,
while the special impressions of light are transmitted exclusively by the
optic nerve. In addition, the iris and cornea are supplied by filaments
coming from the ophthalmic ganglion of the sympathetic, which re-
ceives its sensitive root from the fifth pair. If this nerve be divided
within the cranium, by a section passing in front of or through the Gas-
serian ganglion, a change of nutrition often follows in the cornea, by
which its tissue becomes the seat of vascular congestion and ulceration,
and which frequently goes on to complete and permanent destruction
of the eye. These changes may be observed in the cat, after intra-
cranial section of the fifth nerve by the usual method. Immediately
after the operation the pupil is contracted and the conjunctiva loses its
sensibility. At the end of twent}r-four hours the cornea begins to be-
come opaline, and by the second day the conjunctiva is visibly congested,

THE TRIGEMINUS. 537

and discharges a purulent secretion. This process, after commencing
in the cornea, increases in intensity and spreads to the iris, which be-
comes covered with an inflammatory exudation. The cornea grows
more opaque, until it is at last altogether impermeable to light, and
vision is consequently suspended. Sometimes the diseased action goes
on until it results in sloughing and perforation of the cornea and dis-
charge of the humors of the eye; sometimes, after a few days, the
inflammatory appearances subside, and the eye is finally restored to its
natural condition.

According to the observations of Bernard, although these, conse-
quences usuall3r follow division of the fifth nerve when performed at the
situation of the Gasserian ganglion, or between it and the eyeball, they
are either retarded in their appearance or altogether wanting when the
section is made posteriorly to the ganglion, between it and the base of
the brain. Thjs indicates that the influence exerted by this nerve upon
the nutrition of the eyeball does not reside in its own proper fibres, but
in additional filaments derived from the Gasserian ganglion.

Influence on the Sense of Taste. — The lingual branch of the fifth
pair communicates to the anterior portion of the tongue at the same
time its acute general sensibility and its sensibility of taste ; both of
which are, of course, abolished by its division. Whether both kinds of
sensibility reside in the same or in different fibres cannot yet be deter-
mined ; but cases which have been observed in man, of impairment of
the sense of taste, while tactile sensibility remains entire, make it pos-
sible that there may be two distinct sets of fibres in the lingual nerve,
one devoted to general sensibility, the other to that of taste. How-
ever that may be, it is evident that the exercise of the sense of taste is
facilitated by the presence of general sensibility in the mucous mem-
brane of the tongue, and is influenced by the state of the local circula-
tion and the buccal secretions. In a tongue which is dry or coated, as
in the febrile condition, taste is practically abolished ; as much so as
the sense of sight from opacity of the cornea. The sense of taste,
accordingly, depends for its exercise, not only upon the special sensi-
bility of the lingual nerve, but also upon all the physiological conditions
requisite for the integrity of the mucous membrane.

Influence upon the Sense of Hearing. — The influence of the fifth pair
upon the sense of hearing is less certainty known than that exerted
upon the other special senses, and is only to be surmised from the simi-
larity of its anatomical relations. This nerve provides for the general
sensibility of the external ear by twigs from its auriculo-temporal branch,
which supply the skin of the anterior border of the concha and that of
the anterior wall of the external auditory meatus. Its relation with the
deeper parts of the organ is established by means of the otic ganglion
of the sympathetic, which receives a few short fibres from the inferior
maxillary division of the fifth pair, and which sends a filament back-
ward to join the tj'mpanic plexus on the inner surface of the membrane
of 'the tympanum. This plexus is also supplied with filaments from
35

538

THE CRANIAL NERVES.

the ganglion situated upon the trunk of the glosso-pharyngeal nerve;
and is consequently made up of interlacing fibres derived from both
these sources. Its peripheral sensitive fibres terminate in the mucous
membrane lining the cavity of the middle ear. The secretions, both of
this cavity and of the external auditory meatus, are important for the
preservation of the integrity of the parts and for the mechanism of
audition ; and they are undoubtedly in great measure under the control
of the nervous supply, of which a considerable portion is derived from
the fifth pair.

Sixth Pair. The Abducens.

The abducens nerve, so called because it is distributed only to the
single muscle which causes the movement of abduction of the eyeball,
originates mainly from a collection of gray matter on the floor of the
fourth ventricle, near its widest part and at a point corresponding with
the posterior section of the pons Varolii. It is situated next the median

TRANSVERSE SECTION OF THE FLOOR OF THE FOURTH VENTRICLE of the
Human Brain, showing the nucleus and roots of the abducens and facial nerves.— Nf, Nu-
cleus of gray matter. VI', Fibres of the abducens nerve (6th pair). VII', Fibres of the facial
nerve (7th pair). VII", Bundle of longitudinal fibres, connected with the root of the facial
nerve. R, Raphe, at the median line, showing transverse or decussating fibres from the
facial nerve roots. Magnified 35 diameters. (Henle.)

line, and is indicated on each side by a longitudinal prominence, known
as the " fasciculus teres." This collection of gray matter is the common
nucleus of the abducens and facial nerves ; since the fibres of both these
nerves are traced to a connection with it, although running in some-
what different directions. The fibres of the abducens, as shown by Dean,
Meynert, and Henle, originate from the inner border of the nucleus
without showing any apparent decussation with those of the opposite
side. They then pass almost directly downward and forward, in a verti-
cal longitudinal plane, through the substance of the tuber annulare, to
their point of emergence at the base of the brain, at the posterior edge

THE FACIAL. 539

of the pons Yarolii. From this point, the nerve, which is about two mil-
limetres in thickness, runs nearly straight forward, beneath the under
surface of the pons, passes, in company with the oculomotorius and
patheticus, along the wall of the cavernous sinus and through the
sphenoidal fissure, into the cavity of the orbit, where it terminates in
the external straight muscle of the eyeball.

Physiological Properties of the Abducens. — The physiological pro-
perties of this nerve have been examined, in the experiments of Longet
on rabbits, and in those of Chauveau on rabbits and horses, by irritating
its trunk within the cranium and at its point of emergence from the
pons Yarolii. The abducens is thus shown to be, at its origin and for
some distance beyond, exclusively a motor nerve ; since its galvanization
produces at once continued contraction in the external straight muscle
of the eyeball, and mechanical or other irritation applied to its fibres
causes no indication of suffering. In the experiments of Longet, which
were performed upon the living animal, the difference in this respect
between the abducens nerve and the trigeminus was very marked ; irrita-
tion of the trigeminus always giving rise to signs of acute sensibility,
while that of the abducens had no other effect than local muscular con-
traction.

Division of this nerve causes internal strabismus from paralysis of
the external straight muscle, and loss of the lateral motion of the eye-
ball in a horizontal plane ; although its vertical movements are still
preserved, owing to the continued activity of the oculomotorius nerve.
Cases of internal strabismus, in man, are recorded, with the accompa-
nying symptoms mentioned above, which were apparently due to com-
pression of the abducens nerve by morbid growths within the cranial
cavity.

Seventh Pair. The Facial.

With regard to the innervation of the external parts of the face, this
nerve holds an equal rank with the fifth pair, and may be regarded as
complementary to it in physiological endowments. As the fifth pair is
the nerve of sensation for the integument of this region, the facial is the
motor nerve for its superficial muscles. It is the nerve of facial expres-
sion, by which the features are animated in their varying movements,
corresponding with the different phases of mental or emotional activity.
Although at its origin an exclusively motor nerve, it receives, soon after
its emergence from the cranium, a communicating branch from the fifth
pair, which gives to it, and to the muscles in which it terminates, a cer-
tain share of sensibility.

The facial nerve has its principal source in a collection of gray matter,
which has already been described as also giving origin to the fibres of
the abducens (Fig. 175). This nucleus extends for a short distance
longitudinally along the floor of the fourth ventricle near the median line,
as a layer about 1.5 millimetre in thickness, and containing, according

540 THE CRANIAL NERVES.

to Dean,1 stellate, oval, or fusiform nerve cells, among which the nerve
fibres penetrate. The nucleus constitutes, at this situation, the gray
matter of the " fasciculus teres." The fibres of the abducens and facial
nerves are given off from its internal and external borders respectively ;
those of the abducens passing directly downward through the tuber
annulare, near the median plane, those of the facial first passing out-
ward and then bending downward, to reach their point of emergence at
the posterior edge of the lateral portion of the pons Varolii.

According to Dean, Meynert, and Henle, a considerable portion of the
root fibres of the facial nerve communicate, either directly or through
the nucleus, across the median line, with the opposite side of the brain.

After emerging from the posterior edge of the pons Varolii, the facial
nerve, in company with the auditory, passes into and through the in-
ternal auditory meatus. It then enters, by itself, the aqueduct of Fal-
lopius, and, following the course of this canal through the petrous
portion of the temporal bone, comes out at the stylomastoid foramen
and turns forward upon the side of the face. It spreads out between
the lobules of the parotid gland into a number of branches, which by
their mutual interlacement form the well-known " parotid plexus," or
" pes anserinus," of this nerve. Its branches then diverge upward, for-
ward, and downward, to be distributed to the superficial muscles of the
facial region. It also supplies, by branches given off immediately after
its emergence from the stylomastoid foramen, the muscles of the exter-
nal ear, as well as the stylohyoid and the posterior belly of the digastric ;
and by a twig which descends below the jaw to the submaxillary region,
it supplies filaments to the upper part of the platysma myoides muscle,
and communicates with an ascending branch of the superficial cervical
nerve from the cervical plexus.

Physiological Properties of the Facial Nerve. — The facial is shown,
by the result of abundant corresponding investigations, to be, at its
origin and in its main physiological characters, an exclusively motor
nerve. Not only is the tactile sensibility of the facial region imme-
diate^ destroyed by the section of the fifth pair within the skull,
though the facial itself remain uninjured, but, according to the ex-
periments of Magendie and Bernard, the trunk of this nerve, when irri-
tated at its source in the living animal, after opening the cranial cavity,
shows no sign of sensibility, although that of the sensitive cranial
nerves is at the same time perfectly manifest. On the other hand,
Chaveau has found that in the recently killed animal, galvanization of
the intracranial portion of the facial nerve causes at once contraction
of the muscles of the face and of the external ear. This nerve is accord-
ingly, at its source, insensible and excitable.

Furthermore, the most decisive results are obtained from division of
the facial nerve at various parts of its course. This may be done, in

1 Gray Substance of the Medulla Oblongata and Trapezium. Washington,
1864, pp. 58, 61.

THE FACIAL. 541

most quadrupeds, at the point of exit of the nerve from the stylomas-
toid foramen, or, as practised by Bernard, during its passage through
the aqueduct of Fallopius, by means of a cutting instrument intro-
duced into the cavity of the tympanum, thus reaching the nerve through

Fig. 176.

DIAGRAM OP THE FACIAL NERVB AND ITS DISTRIBUTION. — 1. Facial nerve at
its entrance into the internal auditory meatus. 2. Its exit, at the stylomastoid foramen.
3, 4. Temporal and posterior auricular branches, distributed to the muscles of the external
ear and to the occipitalis. 5. Branches to the frontalis muscle. 6. Branches to the stylohyoid
and digastric muscles. 7. Branches to the upper part of the platysma myoides. 8. Branch
of communication with the superficial cervical nerve of the cervical plexus.

its upper wall. The effect of this section is to paralyze at once all the
superficial muscles of the face on the corresponding side. The visible
effects vary in the different facial regions, according to the function of
the muscles which have lost their power of motion,

Effect upon the Eye. — The orbicularis* oculi being paralyzed, the eye
upon the affected side cannot be closed, but remains permanently open ;
even, according to the observation of Bernard, while the animal is
asleep. This depends upon the fact that the two muscles serving to
open and close the eyelids are animated by two different nerves ; the
levator palpebrae superioris, which lifts the upper eyelid, being supplied
by the ocnlomotorius, while the orbicularis oculi receives its nervous

542 THE CRANIAL NERVES.

filaments from the facial. After paralysis of this nerve, therefore,
complete closure of the lids becomes impossible, although the move-
ments of the eyeball are unaffected, and the pupil is capable of dilata-
tion and contraction as before.

At the same time the motion of winking is suspended upon the
affected side. This movement is an involuntary reflex action, excited
by the contact of air with the surface of the cornea, and the accumula-
tion of the tears along the edge of the lower eyelid. At short intervals
this produces an instantaneous contraction of the orbicularis, by which
the edges of the eyelids are brought together, and again immediately
separated ; thus spreading the moisture of the lachrymal secretion uni-
formly over the cornea and protecting its surface from dryness or irri-
tation. After section of the facial nerve, this movement ceases, and
on thrusting a solid body suddenly toward the face of the animal it can
be seen that the eye on the sound side instinctively closes, while the
other remains open. Even touching the conjunctiva or the cornea on
the operated side fails to cause contraction of the eyelids, although the
animal shrinks and the eyeball turns in the orbit; showing that the
motor power of the orbicularis alone has been affected while sensibility
remains.

Two precisely opposite effects, accordingly, are produced upon the
movements of the eye, by section of the fifth nerve, or its ophthalmic
branch, and by that of the facial. After division of the fifth nerve,
touching the cornea fails to produce closure of the eyelids because the
sensibility of its surface has been destroyed, though the power of motion
remains. When the facial has been divided, it is the muscular action
which is paralyzed, the sensibility of the parts remaining entire.

Effect on the Nostrils. — In some animals, as in man, the nostrils are
more or less rigid and nearly inactive in the ordinary condition. They
expand, however, with considerable vigor when the movements of
respiration are increased in frequency, or when the air is forcibly in-
spired to assist in the sense of smell. In many species, furthermore,
as in most graminivorous quadrupeds, and especially in the horse, they
alternately expand and collapse in a regular and uniform manner, with
each inspiration and expiration ; executing in this way a series of
respiratory movements synchronous with those of the chest and abdo-
men. Even in man the expansion of the nostrils, at the time of in-
spiration, becomes very marked whenever the breathing is hurried or
laborious, owing to increased muscular exertion or to any accidental
obstruction of the air-passages.

All these movements are suspended by section of the facial nerve.
The muscles by which they are performed being paralyzed, the nostril
on the affected side becomes flaccid, and, instead of opening for the
admission of air into the nares, it collapses and forms more or less of
an obstruction to its entrance. As the partial dyspnoea thus induced
tends to accelerate the breathing, the paralyzed nostril is still further
compressed by the air in the movement of inspiration; while at the

THE FACIAL. 643

time of expiration, on the other hand, it is forced outward by the exit
of the air. The natural movements of the nostril in respiration, are
therefore reversed by paralysis of the facial nerve. In the normal con-
dition they exhibit an active expansion in inspiration, and a partial
collapse in expiration. After section of the nerve the nostril collapses
in inspiration, and partially opens in expiration ; moving passively
inward and outward, like an inert valve, with the changing direction of
the current of the air.

Effect on the Lips. — In the lower animals generally, but especially
in the herbivora, the movements of the lips are mainly serviceable in
the prehension of the food ; and if these movements be paralyzed on
the two sides at once, by section of both the facial nerves, the conse-
quent incapacity to introduce food into the mouth may be sufficiently
serious to cause death by inanition. In the carnivora the motions of
retraction and elevation of the lips, by which the canine teeth are un-
covered, have also a marked effect on the expression of the face. In
most of these animals, after division of the facial nerve, the change in
the appearance of the corresponding side, even in the quiescent condi-
tion, is distinctly perceptible. The lips are flaccid and motionless, and
the corner of the mouth hangs down and cannot be completely closed,
owing to the paralysis of the orbicularis oris muscle.

Effect on the Ears. — In most of the quadrupeds the action of the
external ears is much more important than in man, owing to their
superior mobility and the greater development of the corresponding
muscles. In all, the varying position of these organs is of great influ-
ence in modifying the expression ; and their rapid and extensive move-
ments are also serviceable as an essential aid to the sense of hearing.
When the facial nerve has been divided, the ear on the corresponding
side becomes flaccid and motionless ; and in species where the organ is
long and narrow, as in the hare and rabbit, it can no longer be main-
tained in the erect position.

All the superficial muscles accordingly of the head and face, which
are supplied by filaments from this nerve, are paralyzed by its section ;
while the sensibility of the skin, in the corresponding parts, is pre-
served entire.

Facial Paralysis in Man. — Facial paralj'sis, from disease involving
the nerve itself, its sources of origin in the brain, or the walls of its bony
canal in the cranium, is not an uncommon affection in the human sub-
ject. It is usually confined to one side, being limited by the median
line, and produces accordingly a marked difference in the appearance
of the two sides of the face. In particular cases, where the cause of
the difficulty is located in the branches of the nerve, certain portions
of the muscular apparatus may be affected to the exclusion of others ;
and the muscles about the lips may be paralyzed without any percepti-
ble loss of motion in the parts above. Or the affection may be fully
developed in one region of the face, and only partial in the remainder.
But when the disease is seated upon the trunk of the nerve within the

544

THE CRANIAL NERVES.

aqueduct of Fallopius, or involves the whole of its central origin, its
consequences extend uniformly over one side of the face, forming a com-
plete unilateral facial paralysis.

The external signs of paralysis of the facial nerve from disease in
man are, in general, the same with those which follow experimental
division of this nerve in animals. The main peculiarity depends upon
the greater development of the facial muscles in man as the organs of
expression. The most marked effect, therefore, of this disease in the
human subject, is a loss of expression on the paralyzed side of the face.

Fig. 177.

FACIAL PARALYSIS of the right side.

All the features have a collapsed and flaccid appearance. The eyelids
remain motionless, and the eye is constantly open, not only on account
of the impossibility of bringing down the upper e^yelid, but also because
the lower lid sinks down more or less below the level of the cornea ;
thus giving to the eye a staring, vacant appearance. The act of winking
is no longer performed upon the affected side. Owing to the paralyzed
condition of the frontalis and superciliary muscles, all the characteristic
lines and wrinkles on this side disappear, and the forehead and eyebrow
become smooth and expressionless. The same thing is true of the

THE FACIAL. 545

cheek, which, as well as the nostril, is flattened and collapsed. The
corner of the mouth hangs downward, and the lips cannot be kept in
contact with each other at this point, sometimes allowing the saliva to
escape by drops from the cavity of the mouth.

Beside these symptoms there is also, in man, a deviation of the mouth
towards the sound side, owing to the facial muscles on that side being
no longer antagonized by those opposite. In many instances this de-
viation is not observable during a state of quiescence, since both sets
of muscles are then equally relaxed ; and it becomes evident only when
the patient begins to move the muscles of the sound side, as in speaking
or laughing, or when the emotions are excited. But in some cases, where
the face has naturally an abundance of expression, the distortion of the
features, and the consequent difference between the two sides of the
face, are distinctly shown even in the quiescent condition, and become
still more marked when the patient is excited or engages in conversa-
tion.

Another secondary effect of facial paralysis in man is difficulty in
drinking and in mastication. The first is due to the impossibility of
contracting the orbicularis oris on the affected side ; so that the lips at
this corner of the mouth cannot be kept firmly in contact with the sides
of the goblet. The consequence is that a portion of the fluid escapes
and runs over the lower part of the face, unless the patient take the
precaution to aid the paralyzed part by pressure with his fingers. The
difficulty in mastication is not owing to any paralysis of the muscles
moving the lower jaw. These muscles are animated by the inferior
maxillary division of the fifth pair, and are unaffected in disease of the
facial nerve. It results from the paratysis of the buccinator muscle,
and the relaxed condition of the side of the cheek. In consequence of
this, the food in mastication lodges partially in the space between the
outside of the gum and the inside of the cheek; and the patient is often
obliged to remove it by mechanical means in order to complete its
mastication.

The loss of power in the orbicularis oris also produces an imperfect
articulation. The lips cannot be brought together with sufficient pre-
cision, and consequently the labials, such as B and P, are imperfectly
pronounced. If the paralysis be bilateral, existing on both sides of the
face at a time, cases of which have been sometimes observed, the features
are no longer deviated from their symmetrical position, but the diffi-
culty of articulation becomes much increased, extending not only to
the labials proper, but also to such of the vowels, as 0 and U, which
require a certain contraction of the orbicularis oris. This affection is
distinguished from that known as " glosso-labio-laryngeal paralysis." in
which articulation is also impaired. In the latter disease, which is of
central origin, the paralysis affects the muscles of the tongue and larynx
as well as those of the lips ; in facial paralysis it is confined to those
which receive their filaments from the facial nerve. Facial paralysis
ma}T therefore exist without danger to life.

546 THE CRANIAL NERVES.

Crossed Action of the Facial Nerve. — The results of minute examina-
tion of the mode of origin of this nerve give indications of a transverse
communication by decussating nerve fibres, between its nucleus at the
floor of the fourth ventricle and the opposite side of the tuber annulare.
It has not yet been possible, however, to follow with certainty the indi-
vidual fibres to their termination, or to decide whether the decussating
fibres are part of the original root fibres which have simply passed
through the nucleus, or whether they originate anew from the nerve
cells of the nucleus and thence pass to the opposite side. The opinion
usually adopted by anatomists from the examination of microscopic sec-
tions is that a part of the fibres of each cranial nerve root terminate in
the nucleus of the same side, and a part cross over, as decussating fibres,
to the opposite side. This is plainly shown in the case of the patheticus,
which is the only one of the cranial nerves, beside the optic, exhibiting
a distinct decussation of its root fibres outside their connection with
the nucleus.

That the action of the facial nerve is in great part a crossed action is
evident from the results of pathological observation. Facial paralysis
is a frequent accompaniment of hemiplegia; and in the great majority
of instances, that is, when the cerebral lesion is situated above the tuber
annulare, the hemiplegia of the body and limbs and the paralysis of
the face are upon the same side with each other. The injury to the
brain, therefore, in these cases, produces both hemiplegia and facial
paralysis on the opposite side. When the injury is seated lower down,
on the contrary, in the substance of the tuber annulare, it may affect at
the same time the roots of the facial nerve outside its nucleus, and the
longitudinal tracts of the anterior pyramids above their decussation ;
and may cause in this way a facial paralysis on the same side and
hemiplegia on the opposite side. It thus appears that the facial par-
alysis is on the same side with the injury when this is seated externally
to the nucleus, and on the opposite side when it is seated above the
nucleus and near the central parts of the brain. This shows that for
a large part of its functions, the action of the facial nerve. is entirely a
crossed action.

The communication, however, between the nucleus and the opposite
side of the brain, upon which this crossed action depends, does not affect
all the fibres of the nerve, nor the whole of the physiological functions
which are under its control. The only decussation of the nerve fibres
connected with the facial known to exist, is that which takes place at
the raphe on the floor of the fourth ventricle. If all the fibres of the
nerve root or their continuations crossed at this point, from right to
left and from left to right, then a longitudinal section at the raphe,
following the median line between the two nuclei, would completely
paralyze both sides of the face at the same time. But this effect is not
produced ; since, in the experiments of Yulpian,1 who has performed this

1 Lemons sur la Physiologic du Systeme Nerveux. Paris, 1866, p. 480.

THE FACIAL. 547

operation on dogs and rabbits, the animals were still capable of wink-
ing with both eyes ; only the action of the two nerves was no longer
simultaneous, and the closure of each eye was performed at irregular
intervals independently of the other.

It is evident, therefore, that the reflex act of winking takes place for
each eye upon the same side, undoubtedly in the gray matter of the
facial nucleus ; and the two nuclei habitually act in harmony with each
other by means of the commissural fibres passing between them. But
the mental and emotional influences, which cause the movement of the
features in expression or in voluntary acts, are transmitted by decus-
sating fibres from the opposite side of the brain.

This is still further indicated by the different effects caused by peri-
pheral and central lesions of the facial nerve. In man, as in animals, if
this nerve be divided or destroyed during or after its passage through
the aqueduct of Fallopius, all the movements of the facial muscles are
paralyzed together. But in cases of facial paralysis depending upon a
lesion in the cerebrum itself, that is, above the situation of the nucleus,
it is generally observed, according to Yulpian and Hammond,1 that the
loss of movement is not complete; but that, while all the other parts of
the face are paralyzed, the patient retains the power of winking on the
affected side. This peculiarity is even given as a means of diagnosis
between facial paralysis dependent upon injury of the nerve itself and
that caused by a lesion in the brain.

Sensibility of the Facial Nerve. — Although this nerve is exclusively
motor at its origin, it receives filaments of communication from the fifth
pair, which give it a certain degree of sensibility. The most important
of these branches, given off from the inferior maxillary division of the
fifth nerve, joins the facial soon after its emergence from the stylo-
mastoid foramen, and runs forward with its principal branches and rami-
fications. The facial nerve, therefore, according to the united testimony
of all modern experimenters, if examined upon the side of the face, is
found to be sensitive to mechanical irritations, although the degree of
its sensibilty is much less than that of the fifth pair. Owing to this
communication, the pain, in cases of tic douloureux, sometimes follows
the course of the horizontal branches of the facial nerve. The proof,
however, that the sensitive fibres of this nerve are derived from its
anastomoses and do not orginally form a part of its trunk, is that the
sensibility of the facial regions to which it is distributed disappears
completely after division of the fifth pair, notwithstanding that the facial
nerve itself remains entire.

Beside the principal communication above mentioned, this nerve con-
tracts abundant anastomoses, at the anterior part of the face, with the
radiating filaments of the supraorbital, infraorbital, and mental branches
of the fifth pair.

1 Diseases of the Nervous System. New York, 1871, p. 78.

548 THE CRANIAL NERVES.

Twigs and Communications of the Facial Nerve in the Aqueduct of
Fallopius. — While passing through its canal in the petrous portion of
the temporal bone, the facial nerve gives off a number of slender fila-
ments by which it communicates with other nerves or with ganglia
belonging to the sympathetic system. The physiological character of
most of these filaments is imperfectly understood ; but certain facts have
been established in regard to them, and they are of interest because
they are usually involved in injury or disease of the nerve within its
bony canal, and thus other secondary symptoms are produced in addi-
tion to those of external facial paralysis.

Fig. 178.

THE FACIAL NERVE AND ITS CONNECTIONS, within the aqueduct of Fallopius.—
1. Fifth nerve, with the Gasserian ganglion. 2. Ophthalmic division of the fifth nerve. 3.
Superior maxillary division of the fifth nerve. 4. Lingual nerve. 5. Sphenopalatine gan-
glion. 6. Otic ganglion. 7. Submaxillary ganglion. 8. Facial nerve in the aqueduct of Fal-
lopius. 9. Great superficial petrosal nerve. 10. Small superficial petrosal nerve. 11 Stapedius
branch of facial nerve 12. Branch of communication with pneumogastric nerve. 13. Branch
of communication with glossopharyngeal nerve. 14. Chorda tympani.

At the elbow formed ~by the anterior bend of the facial nerve, soon
after its entrance into the aqueduct of Fallopius, there is a minute col-
lection of gray matter, known as the u ganglion geniculatum." From
this point a slender filament, the great superficial petrosal nerve (Fig.
178, 9), runs forward, passing obliquely through the base of the skull,
and terminates in the sphenopalatine ganglion. This ganglion, which is
also in connection, by another root, with the Superior maxillary division
of the fifth nerve, lends filaments to the mucous membrane of the pos-
terior part of the nasal passages and that of the hard and soft palate
and to the levator palati and uvular muscles ; that is, to the dilators of
the isthmus of the fauces.

This nerve, which forms communication between the facial and the
sphenopalatine ganglion, is without doubt the motor root of the gan-
glion, supplying motive force from the facial to the muscular branches
given off from it beyond. This conclusion is derived from the phe-
nomena of paralysis of the palatal muscles accompanying certain cases

THE FACIAL. 549

of facial paralysis, where the lesion is deep seated. The paralysis is
recognized by an incapacity to lift the soft palate, which hangs down in
a passive manner, and by the deviation of the uvula, which, according to
the observations recorded by Longet, is always toward the sound side.
The levator palati, and especially the uvular muscle, being paralyzed, its
fellow in contracting draws the uvula into an oblique position, with its
point directed toward the non-paralyzed side. As there is no other
communication between the facial nerve and the palatal muscles, than
that through the sphenopalatine ganglion by the great superficial petro-
sal nerve, this nerve must be regarded as containing motor fibres running
from the facial to the ganglion.

A little below the origin of the last-mentioned filament, the facial nerve
gives off a second, the small superficial petrosal nerve do ), which com-
municates both with the otic ganglion and with the plexus of nerve
filaments on the inner wall of the tympanum, known as the " tympanic
plexus," which supplies nerve fibres to the lining membrane of the
tympanic cavity, while the otic ganglion sends a motor filament to the
tensor tympani muscle.

From the concave border of the facial nerve, as it bends downward, a
fine motor filament, the stapedius branch (n), passes forward to supply
the stapedius muscle. The facial nerve, therefore, in this part of its
course, has an influence on the mechanism of hearing, through the
muscles which regulate the position of the bones of the middle ear, and
consequently the tension of the membrana tympani. This influence is
exerted directly by its stapedius branch, and indirectly, through the otic
ganglion, by the filament supplied to the tensor tympani. Cases of
facial paralysis have been known to be accompanied, sometimes by par-
tial deafness, and sometimes by abnormal sensibility to sonorous im-
pressions ; but it has not been determined how far these symptoms were
due to the implication of other parts, or how far to paralysis of the
muscles of the middle ear from disease of the facial.

From its descending portion, the facial nerve gives off two small
branches of communication ( 12, 13 ), one to the pneumogastric and one
to the glossopharyngeal nerve. They are usually regarded as motor
filaments, which transmit to these two nerves the power of causing mus-
cular contraction. This seems nearly certain in regard to the branch
communicating with the glossopharyngeal nerve ; since Cruveilhier de-
scribes a separate filament of the facial passing to the styloglossus and
palato-glossus muscles, and Longet cites an instance in which a branch
of the facial, on one side, without making any connection with the glosso-
pharyngeal nerve, was distributed directly to the palato-glossal and
glossopharyngeal muscles ; that is, to the constrictors of the isthmus
of the fauces.

, Finally the facial nerve, shortly before its exit from the stylomastoid
foramen, gives off from its concave border another slender branch of
considerable interest, the chorda tympani (u). It first passes upward
and forward, in a recurrent direction, traverses the cavity of the tym-

550 THE CRANIAL NERVES.

panum near the inner surface of the membrana tympani, curves down-
ward and forward, and joins the descending portion of the lingual nerve.
It is certain that some of its fibres again leave the lingual nerve at the
situation of the subm axillary ganglion, to reach this ganglion and the
tissue of the submaxillary gland ; and it is also certain that some of
them continue onward with the lingual nerve, and accompany it to its
distribution in the tongue.

The most positive knowledge in our possession with regard to the
physiological character of the chorda tympani is that it is distinctly a
motor nerve, influencing the acts of circulation and secretion. This
results from the numerous experiments of Bernard1 on the dog and cat,
which show that, in these animals, galvanization of the chorda tympani
increases at the same time the activity of the circulation and the secre-
tion of saliva in the submaxillary gland. The gland, with its excretory
duct and nervous connections, is exposed in the living animal. It is then
seen that the introduction of vinegar into the fauces causes, by reflex
action, an increased current of blood through the vessels of the gland,
and excites an abundant flow of submaxillary saliva. But if the chorda
tympani be tied or cut across, the action above described no longer takes
place, and the gland remains inexcitable under the influence of a sapid
substance introduced into the fauces. On the other hand, if the peri-
pheral extremity of the nerve be galvanized, this stimulus excites the
circulation and secretion as before ; and the same effect is produced by
stimulating, either the lingual nerve itself, or the filament which it sends
to the submaxillary gland. Finally, while section of the chorda tym-
pani in the cavity of the tympanum, or evulsion of the facial nerve from
the aqueduct of Fallopius, will arrest the secretive activity of the sub-
maxillary gland, section of the facial at the stylomastoid foramen does
not have this effect, but only paralyzes the muscles of the face. A dif-
ference accordingly exists, in the effects produced by injury of the facial
nerve, according to its location, within the aqueduct of Fallopius or out-
side of this canal. If the lesion be external, there is simple paralysis of
the facial muscles. If it be internal, there is also a diminished activity
of circulation and secretion in the submaxillary gland.

Another symptom sometimes observed in deep-seated lesions of the
facial nerve, which is also dependent on injury of the chorda tympani,
is a diminution or disturbance of the sense of taste in the tip and sur-
face of the tongue. In this affection, the taste is not absolutely abol-
ished, but is diminished in acuteness, and especially in promptitude.
In a person presenting this difficulty, or in an animal after division of
the chorda tympani, if a bitter substance be placed alternately upon
the two sides of the tongue, it is perceived almost immediately upon
the sound side, but only after a considerable interval on the side of the

1 Systeme Nerveux. Paris, 1858, tome ii. pp. 150-157. Liquides de TOrganisme
Paris, 1859, tome i. pp. 310-315.

THE AUDITORY. 551

paralysis. Various explanations are given to account for these phe-
nomena. By some writers they are referred exclusively to the motor
properties of the chorda tympani. If the fibres of this nerve which
accompany the branches of the lingual in their peripheral distribution
have an influence upon the circulation and secretion in the tongue
similar to that which they exert in the submaxillary gland, it is plain
that when these actions are depressed by section of the chorda tym-
pani, the sense of taste may be diminished in the corresponding parts
as an indirect result of its paralysis. Others, on the contrary, attri-
bute this effect to sensitive fibres in the chorda tympani, which convey
the impressions of sapid substances directly from without inward, and
which, of course, cease their action when the nerve is divided. The
indications obtained by experiment on this point are as yet too obscure
to allow of a decisive opinion. The precise manner in which the chorda
tympani takes a share in the exercise of the sense of taste is more or
less a matter of uncertainty. But there is no question that its paralysis
interferes, to an appreciable degree, with this sense; and an alteration
of the taste, accompanying facial paralysis upon the same side, is a
symptom which fixes the location of the nervous lesion at some point
inside the stylomastoid foramen.

Eighth Pair, The Auditory.

On the posterior surface of the medulla oblongata, a little behind the
widest part of the fourth ventricle, a number of white striations run
from the neighborhood of the median line, transversely outward, toward
the posterior edge of the peduncles of the cerebellum. These striations,
which are sometimes exceedingly distinct, represent the commencement
of the roots of the auditory nerve. The nucleus from which they
originate is a mass of gray substance situated directly beneath them,
containing nerve cells of various form and size, some of which belong
to the smaller variety, while some of them, according to Dean, are
among the largest of those met with in the nervous system. The gray
matter of the nucleus, at its lateral portion, extends outward and upward
toward the white substance of the cerebellum, with which it is connected
by numerous bundles of radiating fibres.

The fibres originating from this ganglion partly run directly outward
in a superficial course, forming the white striations visible at this point,
and, uniting with each other, curve round the posterior border of the
peduncles of the cerebellum to reach the lateral surface of the medulla
at the lower edge of the pons Varolii. Some of them follow a deeper
course, passing obliquely through the substance of the medulla outward
and downward to the same point. These fibres, united with each other,
form the posterior root of the auditory nerve.

The anterior root consists of fibres which are traced backward from
their point of emergence, partly to the floor of the fourth ventricle, but
also in. great measure, according to Clarke, Dean, and Henle, into the
white substance of the cerebellum, where they mingle with fibres coming

552 THE CRANIAL NERVES.

from the interior of this organ. The main anatomical peculiarity,
therefore, which distinguishes the central origin of the auditory from
that of the other cranial nerves, is its abundant and direct connection
with the substance of the cerebellum

The auditory nerve, formed by the union of these two bundles of root
fibres, emerges from the lateral surface of the medulla oblongata, at the
inferior edge of the pons Yarolii, and immediately outside the facial
nerve. In company with the facial it then passes forward and outward,
enters the internal auditory meatus, penetrates through the perforations
at the bottom of this canal, and terminates in the nervous expansions
of the internal ear.

Physiological Properties of the Auditory Nerve. — The auditory
nerve is evidently a nerve of special sense, and serves to communicate
to the brain the impression of sonorous vibrations. In the experiments
of Magendie upon dogs and rabbits, the auditory nerve, when exposed
in the cranial cavity, was found to be insensible to the severest me-
chanical irritation, although the roots of the fifth pair exhibited at the
same time an acute sensibility. Its exclusive distribution to the inter-
nal ear, for which it forms the only nervous connection with the bitf in,
leaves no doubt that its function is that of transmitting to the central
organ the nervous influences which produce the sensation of sound.

Behind the situation of the auditory there commences a special divi-
sion of the cranial nerves, which differ in great measure from the pre-
ceding. All the foregoing nerves, excepting those of special sense, are
either distinctly motor or have a highly developed general sensibility ;
they are distributed to the integument and to muscles which are con-
cerned in the execution of voluntary movements ; and they are all asso-
ciated in the production of nervous action in the various regions of the
face.

The second division of the cranial nerves, on the other hand, com-
prising the glossopharyngeal, the pneumogastric, and the spinal acces-
sory, are distributed to the deeper parts about the commencement of
the digestive and respiratory passages, where the general sensibility is
comparatively deficient, and the movements are, for the most part,
involuntary ; and they exhibit phenomena which have more especially
the character of reflex actions. Externally, they show a marked simi-
larity of anatomical arrangement, originating one behind the other, in
a continuous line, along the lateral furrow of the medulla oblongata
and the side of the spinal cord, each by a series of separate filaments ;
and in such juxtaposition that it is in some instances difficult to say,
from external inspection, where the root fibres of one terminate, and
those of the other begin. The two sensitive nerves belonging to this
group, namely, the glossopharyngeal and the pneumogastric, have their
source in two nuclei which are continuous with each other at the pos-
terior surface of the medulla oblongata ; and, according to the observa-

THE GLOSSOPHARYNGEAL. 553

tions of Dean, in the medulla of the sheep, the transition between the
pneumogastric and glossopharyngeal roots or nuclei is so gradual that
it is impossible to point out any exact line of demarcation. Each of
these nerves has upon its trunk a distinct ganglion, situated within its
point of emergence from the cranium. The motor portion of the group,
or the spinal accessory, originates from a special nucleus of its own,
and sends branches of communication to both the other nerves. While
the three nerves of this group, therefore, can hardly be regarded as a
single pair, they have nevertheless a close mutual relation both in ana-
tomical arrangement and in their physiological properties.

Ninth Pair. The Glossopharyngeal,

The fibres of the glossopharyngeal nerve originate from a nucleus
situated a little behind and below that of the auditory, and near the
outer border of the fasciculus teres, by which it is separated from the
median line. This nucleus is continuous posteriorly with that of the
pneumogastric nerve, which projects above it on the floor of the fourth
ventricle (Fig. 168, Ngl, Nv). The nerve fibres, after leaving the nu-
cleus, pass downward and outward through the substance of the medulla,
and emerge from its lateral surface, next behind the auditory nerve, in
a series of five or six filaments which soon afterward unite into a single
cord. The nerve then passes into and through the jugular foramen, in
company with its associated nerves, the pneumogastric and spinal
accessor}*. While passing through this opening in the skull, it presents
a ganglionic enlargement, similar to those of the posterior spinal nerve
roots, and known as the petrosal ganglion, from its occupying a shallow
depression in the petrous portion of the temporal bone. At the situa-
tion of the petrosal ganglion it gives off a small branch, the " nerve of
Jacobson," which is distributed to the mucous membrane of the tym-
panum and Eustachian tube, and sends a filament of communication to
the otic ganglion of the sympathetic system. The trunk of the glosso-
pharyngeal nerve then passes downward and forward, receiving branches
of communication from both the facial and the pneumogastric nerves,
after which it separates into two main divisions, one of which is des-
tined for the tongue, the other for the pharynx; a double distribution,
to which the nerve owes its name. The portion passing to the tongue
is distributed to the mucous membrane of the posterior third of this
organ, namely, to that portion situated behind the V-shaped row of cir-
cumvallate papillae, and to these papillae ; it also supplies filaments to
the tonsils and to the mucous membrane of the pillars of the fauces and
of the soft palate. The remaining portion of the nerve is distributed
to the mucous. membrane of the pharynx and certain of the adjacent
muscles, namely, the digastric and stylopharyngeal muscles, by union
with a branch of the facial to the styloglossal muscle, and by union

1 Gray Substance of the Medulla Oblongata and Trapezium. Washington.
1864, p. 30.
36

554 THE CRANIAL NERVES.

with branches of the pneumogastric to the mucous membrane and the
superior and middle constrictors of the pharynx. The muscles, accord-
ingly, to which this nerve is directly or indirectly distributed are those
by which the tongue is drawn backward (styloglossal), the larynx and
pharynx elevated (digastric and stylopharyngeal), and the upper part
of the pharynx contracted (superior and middle constrictors) ; that is,
those concerned in the act of deglutition.

Physiological Properties of the Glossopharyngeal. — The glossopha-
ryngeal nerve is evidently for the most part a nerve of sensibility. Its
origin from the tract of gray matter in the medulla oblongata correspond-
ing to the posterior horns of gray matter in the spinal cord, the distinct
ganglion located upon its trunk in the jugular foramen, and the fact that
it is mainly distributed to the mucous membranes of the tongue and
pharynx, all indicate its resemblance in anatomical arrangement to other
well known sensitive nerves or nerve roots. The result of direct experi-
ment corroborates this view. Longet, in irritating the glossopharyngeal
nerve within the cranium, was never able to produce muscular contrac-
tion ; and although Chauveau, in experimenting upon this nerve in the
same situation in recently killed animals, saw its galvanization followed
by contraction of the upper part of the pharynx, the effect may have
been due to reflex action, since the nerve w~as still in connection with
the medulla oblongata. This conclusion is rendered certain by the in-
vestigations of Reid,1 who found that irritation of the glossopharyngeal
nerve produced movements of the throat and lower part of the face ;
but that these movements were, in a great measure, reflex and not
direct, since they were also produced after the nerve had been divided,
by applying the irritation to its cranial extremity. Its sensibility to
mechanical or galvanic irritation, however, appears to be of a low grade,
as compared with that of the trigeminal nerve. While some observers
(Reid) found its irritation in the living animal, outside the jugular fora-
men, give rise to evident signs of pain, others (Panizza) have failed to
see any indications of suffering from this cause ; and others still (Longet)
speak of the signs of pain, thus produced, in a more or less uncertain
manner. This variation in the observed results is sufficient to show the
inferior capacity of the glossopharyngeal nerve for the receipt of painful
impressions; since no experimenter has ever doubted the acute sensibility
of the fifth pair.

But notwithstanding the comparative deficiency of the nerve itself,
and the parts to which it is distributed, in ordinary sensibility, it serves
to transmit sensitive impressions of a special character, which are con-
nected with two different but associated functions, namely : 1. The sense
of taste, and, 2. The reflex act of deglutition.

Connection with the Sense of Taste. — The power of perceiving sensa-
tions of taste exists not only in the anterior portion of the tongue which

1 Todd's Cyclopaedia of Anatomy and Physiology. Article, Glossopharyngeal
Nerve.

THE GLOSSOPHARYNGEAL. 555

contains filaments derived from the lingual branch of the fifth pair, but
also at the base of the organ, throughout its posterior third, and in the
mucous membrane of the arches of the palate, which are supplied only
by the fibres of the glossopharyngeal. The difference between these two
regions is that while that supplied by the fifth pair possesses tactile
sensibility of a high grade in addition to that of taste, in the posterior
region the general sensibility is less acute than the special sensibility to
impressions of taste. The appreciation of savors is provided for by
both the lingual and glossopharyngeal nerves, each in its separate de-
partment of the oral cavity. The sense of taste accordingly, in the
experiments of Reid, was never completely abolished by division of
either one of these nerves. For its complete suspension, both of them
must be destroyed on both sides. The method adopted by Longet for
examining the condition of the taste in dogs, before and after division
of the glossopharyngeal nerves, was to place upon the base of the tongue
a few drops of a concentrated solution of colocynth. Although this
always produced in the animals, while in their natural condition, mani-
fest signs of disgust, it had no such effect, as a general rule, after sec-
tion of the glossopharyngeal nerves on both sides, provided the solution
were applied only to the posterior part of the tongue and the pharynx ;
while if even a minute quantity came in contact with the tip or edges
of the tongue it caused brisk movements of the jaws with all the in-
dications of a sense of repugnance. While in the anterior and more
movable parts of the tongue, accordingly, the sensations of taste are
appreciated, during the process of mastication, by the filaments of the
lingual nerve which are distributed there, the glossopharyngeal is the
nerve of taste for the posterior part of the organ. It is called into ac-
tivity after mastication is accomplished and at the moment when the
food is carried backward and compressed by the base of the tongue, the
pillars of the fauces^ and the walls of the pharynx.

Connection with the Reflex Act of Deglutition. — In the fauces and
pharynx, the glossopharyngeal nerve also possesses a peculiar sensibility
to certain impressions, which excite at once the muscles of the neigh-
boring parts and bring into play the complicated mechanism of degluti-
tion. This consists in drawing backward and upward the base of the '
tongue, thus bringing the masticated food into and through the isthmus
of the fauces. The muscles of the pillars of the fauces (palato-glossal
and palato-pharj'iigeal) afterward contract and close the opening of the
isthmus, while the soft palate is drawn backward and extended across
the upper end of the pharynx, thus shutting off its communication with
the posterior nares ; and the contraction of the constrictor muscles of
the pharynx then forces its contents downward into the beginning of the
oesophagus. This process is an involuntary one. Both the contraction
of the special muscles, and their regular co-ordination in the necessary
series of successive movements, are actions which do not depend on the
exercise of the will, but which take place even in a state of unconscious-
ness under the stimulus supplied by contact of food or liquids with the

556 THE CKANIAL NERVES.

inner surface of the fauces and pharynx. This contact produces an im-
pression which is conveyed by the glossopharyngeal nerve inward to the
medulla oblongata, whence it is reflected outward in the form of a motor
impulse. The sensibility which, by the contact of masticated food or
nutritious liquids, thus produces the movements of swallowing, if sub-
jected to the influence of nauseous or irritating substances, will cause an
inverted muscular reaction, equally involuntary in character.

Natural stimulants, therefore, applied to the mucous membrane of the
pharynx, excite deglutition; unnatural stimulants excite vomiting. If
the linger be introduced into the fauces and pharynx, or if the mucous
membrane of these parts be irritated by tickling with the end of a
feather, the sensation of nausea, conveyed through the glossopharyngeal
nerve, is sometimes so great as to produce immediate vomiting. This
method may be employed in cases of poisoning, when it is desirable to
excite vomiting rapidly, and when emetic medicines are not at hand.

Motor Properties of the Glossopharyngeal. — Although this nerve is
shown, by the result of observation, to be exclusively sensitive at its
origin, it is found, if examined outside the cavity of the cranium, to
possess motor properties. In the experiments of Herbert Mayo upon
the ass, confirmed by those of Longet on the horse and the dog, irritation
of this nerve in the neck produced contraction in the stylopharyngeal
muscles and in the upper part of the pharynx. These movements were
not the result of reflex action, but were excited through the nerve from
within outward; since, in the experiments of Longet, they were called
out after the nerve had been divided, by applying the irritation to its
peripheral extremity.

The glossophaiyngeal, therefore, after its exit from the jugular fora-
men, is a mixed nerve. In addition to its own original sensitive fila-
ments, it has received a branch of communication from the facial which
is undoubtedly of a motor character, and also a branch from the pneu-
mogastric. The pneumogastric branch is also regarded, on anatomical
grounds, as really made up, wholly or in part, of motor fibres derived
from the spinal accessory, through its anastomosis with the pneumogas-
tric. According to Cruveilhier. it sometimes comes directly and exclu-
sively from the anastomotic branch of the spinal accessory; sometimes
partly from this and partly from the pneumogastric itself. The results
obtained by experiment also indicate a double source for the motor
fibres which join the glossopharyngeal before its exit from the skull.
If these fibres were derived exclusively from the facial or exclusively
from the spinal accessory, the division or destruction of one or the
other of these nerves above its communicating branch would abolish
entirely the motor power of the glossopharyngeal. But the experiments
of Bernard upon rabbits, in which the facial nerve was divided in the
aqueduct of Fallopius, and those of Bernard and Longet on cats and
rabbits, in which the spinal accessory was destroyed on both sides,
show that the process of deglutition, though more or less retarded, is
not abolished by either of these ope rations.

THE PNEUMOGASTRIC. 557

Beside the anastomotie branches received by the glossopharyngeal,
near its origin, from the facial and the spinal accessory, it also has com-
munication with both these nerves near its peripheral distribution. It
is joined by a branch of the facial, which accompanies it to the stylo-
glossal muscle, and perhaps also to the pillars of the fauces ; and, accord-
ing to Cruveilhier, a branch derived from the spinal accessoiy takes
part in the formation of the pharyngeal plexus which supplies the upper
constrictor muscles of the pharynx. The process of deglutition, there-
fore, is excited at its commencement by sensitive impressions conveyed
through the glossopharyngeal nerve ; but its movements are executed
by a reflex impulse transmitted through the motor fibres of several
distinct branches of communication.

Tenth Pair. The Pneumogastric.

The pneumogastric nerve, remarkable for its varied and extensive
course and the distribution of its fibres to a number of different locali-
ties, has received its name from the two most important organs in which
it terminates, the lungs and stomach. It arises from the side of the
medulla oblongata by a series of from ten to fifteen separate filaments,
arranged in a linear series, continuously with those of the glossopha-
ryngeal. The nucleus from which these fibres take their origin is an
extended tract of gray matter running in a longitudinal direction
along the posterior surface of the medulla oblongata, just outside the
lower extremity of the fasciculus teres. This collection of gray matter
(Fig. 168, Nu) which is uncovered by the divergence of the posterior
columns of the cord, and is thus exposed to view on the floor of the
fourth ventricle, is known as the ala cinerea. At its anterior ex-
tremity it covers, and is continuous with, the nucleus of the preceding
nerve, the glossopharyngeal ; and at its posterior extremity it joins
that of the following nerve, the spinal accessory. From its deep sur-
face it gives out the fibres of origin of the pneumogastric nerve, which
run downward and outward through the substance of the medulla, and
emerge, as above mentioned, in a series of filaments from its lateral
surface.

The filaments of the pneumogastric, after leaving the side of the
medulla oblongata, unite into a single trunk which passes out of the
cranium, in company with the glossopharyngeal and the spinal accessory,
by the jugular foramen (Fig. 179). Here it presents upon its trunk a gan-
glionic swelling, known as the "jugular ganglion." At or immediately
beyond the situation of the ganglion, the nerve is joined by an important
motor branch of communication from the spinal accessory ; and it after-
ward receives filaments from four other sources; namely, the facial, the
hypoglossal, and the anterior branches of the first and second cervical
nerves.

While passing down the neck the pneumogastric nerve takes part, by
an anastomotic branch, in the formation of the pharyngeal plexus. Its
first important branch of distribution is the superior larynyeal nerve.

,"58

THE CRANIAL NERVES.

Fig. 179.

which runs downward and forward, penetrates the larynx by an open-
ing in the side of the thyro-hyoid membrane, and is distributed to the
mucous membrane covering the epiglottis and lining the interior of the
laryngeal cavity. This is the main portion of the nerve, and it is sensi-
tive in character; providing for the peculiar sensibility of the glottis and'
epiglottis and for that of the inner surface of the larynx in general.
The nerve gives off, however, a small muscular branch which terminates
in the inferior constrictor of the pharynx and in the crico-thyroid mus-
cle of the larynx. It also supplies several filaments, which 'unite with
others coming from the great sympathetic, to form the laryngeal plexus ;
and by this plexus the superior laryngeal branch of the pneumogastric
furnishes filaments to the upper cardiac nerves of the cervical portion

of the sympathetic. Other filaments
pass off from the trunk of the pneumo-
gastric while passing down the neck,
which also join the cardiac branches
of the sympathetic, and which in some
instances, according to Cru veilhier, pass
directly downward, to unite with the
cardiac plexus beneath the concavity
of the arch of the aorta.

The next branch is the inferior
laryngeal nerve, which separates from
the trunk of the pneumogastric after
entering the cavity of the chest, curves
round the subclavian artery on the
right side and the arch of the aorta on
the left, and ascends, in the groove
between the trachea and oesophagus,
to the larynx, giving off branches to
the oesophagus and the inferior con-
strictor muscle of the pharynx. In
the larynx it is distributed to all the
muscles of this organ, excepting the
crico-thyroid, which is supplied by the
superior laryngeal. The larynx is
therefore supplied by two different
branches of the pneumogastric nerve,
which are mainly distinct from each
other in their properties and functions.
The superior laryngeal branch is for
the most part a sensitive nerve, sup-

ORIGIN AND COURSE OF THE G-LOSSOPHARYNGE A L, PNETTMOGASTRIC, AND
SPINAL ACCESSORY NERVES.— 1. Facial nerve. 2. Glossopharyngeal. 3. Pneumogastric.
4. Spinal accessory. 5. Hypoglossal. 6. External (muscular) branch of the spinal accessory.
7. Superior laryngeal branch of the pneumot-astric. 8. Pharyngeal plexus. 9. Laryngeal
plexus and uppercardiac branches of the pneumogastric. 10. Tympanic plexus, from a branch
of the glossopharyngeal. (Hirschfeld.)

THE PNEUMOGASTRIC. 559

plying the mucous membrane of the larynx; the inferior laryngeal
branch is a motor nerve, and is essential to the activity of nearly all
the muscles of the organ.

After entering the cavity of the chest, the most important dependency
of the pneumogastric nerve is the pulmonary plexus, formed by the
separation of the nerve into a considerable number of inosculating
branches which send their terminal filaments along the course of the
bronchi and their subdivisions, to the ultimate bronchi and lobules of
the lungs. In the inferior portion of the chest, the inosculating fila-
ments on both sides surround the oesophagus with the cesophageal
plexus, from which fibres are supplied to the mucous membrane and
muscular coat of this organ.

The two pneumogastric nerves, after being reconstructed by the union
of their branches below the pulmonary plexus, penetrate the cavity of
the abdomen and spread out in two sets of gastric branches, which
supply the mucous membrane and muscular coat of the stomach. Those
belonging to the left pneumogastric nerve supply the anterior wall of the
organ, and, extending toward the right as far as the pylorus, send a con-
tinuation of nervous filaments to the transverse fissure of the liver, into
which they penetrate, together with those of the hepatic plexus of the
sympathetic ; those belonging to the right pneumogastric send filaments
to the posterior wall of the stomach, and finally communicate with the
solar plexus of the sympathetic.

The pneumogastric nerve, therefore, is distributed, by its various
branches, to the mucous membranes and muscular apparatus of the pas-
sages by which air and food are introduced into the interior of the body.
It also forms connection at several points with branches of the great
sympathetic, and, through it, sends fibres to the central organ of the cir-
culation, and to the radiating sympathetic plexuses of the abdominal
organs.

Physiological Properties of the Pneumogastric. — According to the
results obtained by Longet, the pneumogastric is, at its origin, exclu-
sively a sensitive nerve. Galvanic irritation applied to the nerve roots,
carefully separated from the medulla and from adjacent filaments, was
not found to produce any muscular contractions ; but when applied to
the trunk of the nerve at a lower level, muscular contractions were
readily excited. At this situation the nerve already contains motor
fibres derived from inosculation with the spinal accessory, the facial and
the hypoglossal, and from the loop of communication between the two
upper cervical nerves. In its trunk, accordingly, it has the characters
of a mixed nerve, and is capable of providing both for movement and
sensibility in the organs to which it is distributed.

The sensibility of the pneumogastric nerve, however, to mechanical
irritation and to painful impressions, is but slightly marked, as shown
by the experience of all observers. It may frequently be divided in
the middle of the neck in the living, unetherized animal, without any
sign of pain being manifested ; and this want of reaction is at times so

560 THE CRANIAL NERVES.

complete as to indicate an entire absence of ordinary sensibility. This
does not seem to be invariably the case ; but although Bernard has
found in some instances a well-marked sensibility in this nerve, and in
others only a very indistinct one, it is not possible to say with certainty
upon what special conditions the difference depends. As a general
rule, the pneumogastric nen'e is decidedly deficient in that kind of sen-
sibility which produces pain ; and we know that the organs to which it
is distributed have but little appreciation of tactile impressions. Never-
theless, there is abundant evidence that this nerve is endowed, in its
various divisions, with sensibility of a peculiar kind, and one which is of
the highest importance for the due performance of the vital functions.

Connection with the movements of Respiration. — The most important
endowment of the pneumogastric nerve is undoubtedly that by which it
is connected with the reflex movements of expansion and collapse of
the chest in respiration. Its influence in this respect is at once made
evident by the results which follow the division of both nerves in their
course through the neck. This may be readily done in adult dogs by
etherizing the animal and exposing the nerves in the middle of the neck
during the continuance of insensibility. After the etherization has
passed off, and the circulation and respiration are restored to a quies-
cent condition, both nerves may be simultaneously divided, and the
effects of the operation observed.

After the nerves have been divided, and the slight disturbance which
immediately follows their section has subsided, the most striking change
produced in the condition of the animal is a diminished frequency in
the movements of respiration. The respirations sometimes fall at once
to ten or fifteen per minute, becoming, in an hour or two, still further
reduced. Respiration is performed easily and quietly ; and the animal,
if undisturbed, remains usually crouched in a corner, without any spe-
cial sign of discomfort. If he be aroused and compelled to move, the
frequency of respiration is temporarily augmented ; but as soon as he
is again quiet, it returns to its former standard. By the second or
third day the respirations are often reduced to five, four, or even three
per minute ; when the animal usually appears very sluggish, and is
roused with difficulty from his inactive condition. Respiration is also
performed in a peculiar manner. The movement of inspiration is slow,
easy, and silent, occupying several seconds in its accomplishment;
while that of expiration is sudden and audible, and is accompanied by
a well marked effort, which has, to some extent, a convulsive character.
The intercostal spaces sink inward during the lifting of the ribs ; and
the whole movement of respiration has an appearance of insufficiency,
as if the lungs were not thoroughly filled with air. This is undoubtedly
owing to a peculiar alteration in the pulmonary texture, which has by
this time already commenced.

Death takes place from one to six days after the operation, according
to the age and strength of the animal. The only marked symptoms
which accompany :* are a steady failure of the respiration, with increas-

THE PNEUMOGASTRICc 561

ing sluggishness. There are no convulsions, nor any evidences of pain.
After death the lungs are found in a peculiar state of solidification.
They are not swollen, but rather appear smaller than natural. They
are of a dark purple color, leathery, and resisting to the touch, destitute
of crepitation, and infiltrated with blood. Pieces of the lung cut out
sink in water. The pleural surfaces, at the same time, are bright and
polished, and their cavity contains no effusion or exudation. The lungs
are simply engorged with blood, and, to a greater or less extent, empty
of air; their tissue having undergone no other alteration.

These phenomena point to the pneumogastric nerves as the main
channels through which the stimulus which excites the movements of
respiration is conveyed inward to the medulla oblongata. Respiration
is a reflex act, consisting, like other nervous manifestations of a similar
character, of two different elements; namely, first, an impression con-
veyed from without inward by a sensitive nerve to the appropriate
nervous centre; and, secondly, of a motor impulse transmitted thence
through motor nerves to the muscular apparatus. But by dividing the
pneumogastric nerves in the neck, neither the intercostal muscles nor
the diaphragm are paralyzed. The muscular apparatus which effects
the expansion of the lungs remains untouched, and yet the movements
of respiration become gradually slower until they cease altogether. At
the same time the disturbance of respiration, under these circumstances,
although sufficient to produce death after a short interval, is not accom-
panied by any apparent sense of suffocation. The retarded breathing,
and the consequent imperfect aeration of the blood, are not felt by the
animal, and he accordingly makes no attempt to compensate for them
by voluntary effort.

In dividing the pneumogastric nerves, therefore, it is not the motor,
but the sensitive element in the reflex act of respiration which is inter-
fered with. The experiments of Waller and Prevost1 show conclusively
that this is the part performed by the nerves in question. In these
experiments the pneumogastric nerve was exposed in the living dog,
and divided in its course down the neck; after which, galvanization of
its central extremity produced a succession of forcible inspirations and
expirations, expelling the air through the trachea with an audible sound.
The respiratory impulse, therefore, is propagated through the pneu-
mogastric nerve in a centripetal, not in a centrifugal direction. The
impression which normally originates in the lungs, and is thence con-
veyed through these nerves to the medulla oblongata, produces in the
nervous centre, though unperceived as a conscious sensation, the stimu-
lus which calls into activity the muscles of respiration. If this impres-
sion be not at once satisfied by filling the lungs with air, it increases in
intensity ; and if the breath be voluntarily suspended or forcibly ob-
structed, the impression soon becomes perceptible as a sensation of
distress, or " demand for breath," which reacts upon the entire system.

1 Archives de Physiologic normale et pathologique. Paris, 1870, p. 190.

562 THE CRANIAL NERVES.

On the other hand, if the pneumogastric nerves be cut off, the customary
impression is no longer conveyed from the lungs to the medulla, and
the movements of respiration are consequently retarded. The imperfect
aeration of the blood thus induced reacts in turn upon the medulla, as
well as upon the other nervous centres, diminishing its sensibility, and
rendering it less able to respond to impressions of any kind. Thus the
difficulty, which consists in a want of the nervous reaction necessary
for respiration, increases from hour to hour, the breathing becomes con-
stantly more imperfect and sluggish, and at last ceases altogether. The
alteration in the tissue of the lungs, their engorgement and solidifica-
tion, add to the difficulty in aeration of the blood, and probably have,
at last, a considerable share in producing the fatal result.

It is evident, however, that the pneumogastric nerves, although the
principal means for conveying to the medulla the stimulus for respira-
tion, are not the only ones. If they were so, respiration would stop
instantly after section of these nerves, as it does after destruction of the
medulla itself. The lungs are, no doubt, especially sensitive to the want
of oxygen and accumulation of carbonic acid in the blood ; and the
nervous impression thus produced is accordingly first felt in them.
There is reason to believe that all the vascular organs are more or less
capable of originating this impression, and that all the sensitive nerves
are capable, to some extent, of transmitting it. Although the first dis-
agreeable sensation, on holding the breath, makes itself felt in the
lungs, yet if we persist in suspending respiration, the feeling of dis-
comfort soon spreads to other parts ; and at last, when the accumula-
tion of carbonic acid has become excessive, all parts of the body are
pervaded by a general feeling of distress. It is easy, therefore, to under-
stand why respiration should be retarded, after section of the pneumo-
gastrics, since the chief source of the stimulus to respiration is cut off;
but the movements still go on, though more slowty than before, because
the other sensitive nerves, which continue to act, are in some measure
capable of conveying a similar impression.

In order that the movements of respiration should go on with the
requisite frequency to maintain the aeration of the blood, it is necessary
that the pnenmogastric nerves, which are especially endowed with this
kind of sensibility, retain their integrity as nervous conductors between
the lungs and the medulla oblongata. In this function, they act alto-
gether as sensitive nerves; while the muscles of respiration receive
their reflex motor stimulus by way of the spinal nerves.

Connection with the Respiratory Movements of the Glottis. — The
respiratory movements of the glottis, already described in a former
chapter (p. 277) are essential parts of the mechanism of respiration.
They consist in the active opening of the glottis in inspiration, followed
by its partial collapse at the time of expiration. The opening of the
glottis, which is requisite for the free admission of air into the trachea,
is effected by the action of the posterior crico-arytenoid muscles. These
muscles, in contracting, rotate the arytenoid cartilages outward, and

THE PNEUMOGASTRIC. 563

thus separate the vocal chords from each other and largely increase the
transverse diameter of the orifice of the glottis. When they relax at
the time of expiration, the arytenoid cartilages return to their former
position, and the opening of the glottis is again narrowed by the passive
approximation of the vocal chords. As the movements of expansion
are accomplished by the action of the laryngeal muscles, they depend
upon the influence of the pneumogastric nerve and its inferior laryngeal
branch.

Both the movements of the glottis in respiration and their dependence
upon nervous influence may be seen in the dog by means of an operation
which consists in making a dissection along the side of the neck, in
such a way as to expose the pharynx and a considerable portion of the
oesophagus. The superior laryngeal nerve on that side is necessarily
cut across, but the inferior laryngeal, as well as the trunk of the pneu-
mogastric, are left uninjured. By a longitudinal incision through the
pharynx and oesophagus, the upper and posterior surfaces of the larynx
are then exposed, and, notwithstanding the previous division of the
superior laryngeal nerve, the alternate movements of expansion and
collapse of the glottis are seen going on in their natural order, and
keeping pace with the corresponding respiratory movements of the
chest. If now the inferior laryngeal nerve be divided upon either the
right or the left side, the vocal chord of that side becomes motionless,
while that of the opposite side continues to move as before. If the re-
maining laryngeal nerve be divided, all movements of expansion in the
vocal chords instantly cease ; and the same effect is produced by section
of both pneumogastric nerves in the middle of the neck, since the in-
ferior laryngeals are given off as branches below that point.

If the section of both pneumogastric nerves, or of their inferior laryn-
geal branches, be made simultaneously under these circumstances while
the breathing is tolerably rapid, the injurious effect of laryngeal paralysis
upon respiration at once becomes manifest. Both vocal chords being
then deprived of the active control of their muscles, the borders of the
rima glottidis are left in a condition of passive flexibility. They have
not only lost the power of separating from each other and thus opening
the glottis at the time of inspiration, but they are also drawn downward
and inward by the current of air passing into the trachea, and thus, like
a double membranous valve, they occlude more or less completely the
orifice of the glottis, and offer a physical obstacle to the free entrance
of the air. In very young animals, where there is but little rigidity of
the laryngeal cartilages, the occlusion of the glottis thus produced after
section of the inferior laryngeal nerves, may be so complete as to produce
immediate death by suffocation ; in adult animals the occlusion is only
partial, but is still sufficient to diminish perceptibly the capacity of res-
piration.

The natural movements of the glottis in breathing are therefore
reversed after section of the inferior laryngeal nerves. Before this
operation, in the normal condition, the glottis is opened at inspiration

564: THE CRANIAL NERVES.

and collapses in expiration ; after the section of the nerves, it is nar-
rowed in inspiration and passively opened in expiration by the forcible
expulsion of the air. The effects thus produced on the glottis, by division
of the inferior laryngeal nerves, are the same with those which take place
in the nostrils after division of the facial nerves. Both these sets of
movements are connected with the mechanism of respiration, and both
are influenced in a similar manner by division of their motor nerves.

As the laryngeal muscles are necessarily paralyzed by division of the
pneumogastric nerves in the middle of the neck, the effects of this mus-
cular paralysis are necessarily added to those which result from in-
terruption of the sensitive function of the pneumogastric branches in
the lungs. In very young animals, as mentioned above, the effects due
simply to laryngeal paralysis are more marked than m adults ; and in
order to determine the extent of its influence upon the lungs we have
performed a comparative experiment, in the following manner. Two
pups were taken belonging to the same litter, and of the same size and
vigor, about two weeks old. In one of them (No. 1) a section was made
of both pneumogastric nerves in the middle of the neck ; in the other
(No. 2), the inferior laryngeal nerves only were divided, the pneumogas-
trics being left untouched. In No. 1, therefore, the natural stimulus to
respiration was diminished at the same time that the muscles of the
larynx were paralyzed ; in No. 2, there was laryngeal paralysis alone,
the sensibility to the demand for respiration remaining the same. For
the first few seconds after the operation there was but little difference in
the condition of the two animals, the laryngeal symptoms being most
prominent in both. There was the same obstruction at the glottis owing
to paralysis of the lar}rngeal muscles, the same difficulty of inspiration,
and the same frothing at the mouth. Very soon, however, in No. 1, the
respiratory movements became quiescent, and at the same time much
reduced in frequency, falling to ten, eight, and five respirations per
minute, as usual after section of the pneumogastrics ; while in No. 2
the respiration continued frequent as well as laborious, and the general
signs of agitation and discomfort were kept up for one or two hours, after
which there followed diminished excitability of the nervous centres, and
the animal became exhausted, cool, and partially insensible, like the
other. They both died between thirt}7 and forty hours after the opera-
tion. On post-mortem inspection it was found that congestion and
solidification of the lungs existed to a similar extent in each instance;
and the only appreciable difference between the two bodies was that in
No. 1 the blood was coagulated, and the abdominal organs natural, while
in No. 2 the blood was fluid and the abdominal organs congested. The
alteration in the tissue of the lungs, therefore, after the pneumogastric
nerves have been divided, is not a direct effect, produced by cutting off
the influence of these nerves upon the pulmonary tissue, but results
indirectly from the diminished activity of respiration and imperfect
aeration of the blood.

THE PNEUMOGASTRIC. 565

Protection of the Glottis from the Intrusion of Foreign Substances. —
The influence of the pneumogastric nerve in the larynx is not confined
to its motor action upon the muscles ; it also supplies, by its superior
laryngeal branch, a peculiar sensibility to the mucous membrane of these
parts, which is essential for the protection of the respiratory passages.
In the first place, it stands as a sort of guard, or sentinel, at the entrance
of the larynx, to prevent the intrusion of foreign substances. If a crumb
of bread fall within the aryteno-epiglottidean folds, or on the edges of
the vocal chords, or upon the posterior surface of the epiglottis, the
sensibility of the parts excites an expulsive cough, by which the foreign
body is dislodged. The impression received and conveyed inward by
the sensitive fibres of the superior laryngeal nerve, is reflected upon the
expiratory muscles of the chest and abdomen, by which the movements
of coughing are accomplished. Touching the above parts with the point
of a needle, or pinching them with the blades of a forceps, will produce
the same effect. This reaction is dependent on the sensibility of the
laryngeal mucous membrane ; and it can no longer be produced after
section of the superior laryngeal branch of the pneumogastric nerve.

Connection with the Formation of the Voice. — In addition to its func-
tion in the mechanism of respiration, the larynx is also an organ for
the production of vocal sounds. The formation of the voice can be
studied in the lower animals by exposing the larynx and glottis. in the
manner described above, and in man by the use of the laryngoscope ;
that is, a small mirror held at a suitable angle at the back of the pharynx
in such a way as to reflect a more or less complete view of the laryngeal
orifice. The first important fact to be observed in this respect is that
the voice is formed always in expiration, never in inspiration. It is
the column of outgoing air which is set in vibration to produce a vocal
sound, and which continues and modifies its resonance while passing
through the pharynx, mouth, and nasal passages. Secondly, it requires
an active tension and close approximation of the vocal chords, so that
the orifice of the glottis is narrowed to a comparatively minute crevice.
So long as the vocal chords preserve their relaxed condition during
expiration, nothing is heard except the faint whisper of the air passing
through the cavity of the larynx. When a vocal sound, however, is to
be produced, the chords are suddenly made tense and applied closely to
each other, thus diminishing considerably the diameter of the orifice :
and the air, driven by forcible expiration through the glottis, in passing
between the vibrating vocal chords, is itself thrown into vibrations which
produce the sound required. The tone, pitch, and intensity of this sound
vary with the conformation of the larynx, the degree of tension and
approximation of the vocal chords, and the force of expiration. The
narrower the opening of the glottis, and the greater the tension of the
chords, the more acute the sound ; while a wider opening and a less
degree of tension produce a graver note. The quality of the sound is
also modified by the length of the column of air included between the
glottis and the mouth, the tense or relaxed condition of the walls of the

566 THE CRANIAL NERVES.

pharynx and fauces, and the state of dryness or moisture of the mucous
membrane lining the passages.

The actual formation of the voice, or the production of sonorous
vibrations, takes place, therefore, exclusively in the larynx; while
articulation, or the division of the vocal sound into words and phrases
by vowels and consonants, is accomplished by the aid of the lips,
tongue, teeth, and palate. Consequently, division of the pneumogas-
tric nerve or of its inferior laryngeal branch on both sides, by para-
lyzing the muscles of the larynx which serve to approximate and extend
the vocal chords, produces among its other effects a loss of voice. Fur-
thermore, as the two functions of vocalization and articulation are
accomplished by distinct nervous and muscular actions, they may be
deranged independently of each other, by injury or disease of different
parts of the nervous system. That of articulation is regulated by the
action of the facial and hypoglossal nerves ; while vocalization is under
the control of the pneumogastric.

Connection with Deglutition. — The reflex act of deglutition, which
commences in the fauces and pharynx under the control of the glosso-
pharyngeal nerve, is continued and completed by the lower portion of
the pharynx and the tube of the oesophagus. These parts receive both
their sensitive and motor filaments exclusively from the pneumogastric
nerve, and it is under its influence that the food, once started upon its
downward passage, is conducted by the peristaltic action of the oesoph-
agus into the stomach.

The inferior constrictor muscle of the pharynx and the cervical por-
tion of the oesophagus both receive filaments from the inferior laryngeal
nerve ; while the thoracic portion of the oesophagus is supplied entirely
from the trunk of the pneumogastric. Some fibres are also sent to the
inferior constrictor of the pharynx by the superior laryngeal nerve.
Deglutition, therefore, becomes incomplete, as shown by the experiments
of Bernard upon dogs, horses, and rabbits, by division of the pneumo-
gastric nerves in the middle of the neck. The masticated food is still
conveyed, by the action of the pharynx, from the fauces into the
oesophagus ; but here it accumulates, distending the inert walls of the
paralyzed canal, and finding its way into the stomach only in small
quantities and by the imperfect effect of compression from above. In
the natural condition, the process of swallowing is a connected series
of rapidly succeeding contractions, beginning at the fauces and ending
at the cardiac orifice of the stomach. Each portion of the mucous
membrane receives in turn a stimulus from the contact of the food,
which is followed by excitement of the corresponding muscles ; so that
the alimentary mass is carried rapidly from above downward by an
action which is reflex in character and independent of voluntary control.
Section of the pneumogastric nerves destroys at once sensibility and
motive power in the whole of the oesophagus, and thus interferes with
complete deglutition.

There is no doubt that the sensitive nerves of the cesophageal mucous

THE PNKUMOGASTRIO. 567

membrane take their shun' in exciting tlui action of its muscular coat.
The general sensibility of this canal, however, is very slight, as coin-
pared with the parts above, and is not usually sntlicient to cause a
perceptible impression from the food in the a.ct of swallowing. Its
muscular contraction takes place, as a general rule, without any ell'ect
on the consciousness; and it is only when the food is very cold or very
hot, or when it contains pungent or irritating ingredients, that it8
passage through the (esophagus produces a distinct sensation.

Jt appears that the filaments of the superior laryngeal nerve, dis-
tributed about the anterior surface of the epiglottis and borders of the
larynx, take an active part in exciting the movements of deglutition.
In the experiments of Waller and I'revost on dogs and cats, galvaniza-
tion of the superior laryngeal nerve produced, in many repeated trials,
rhythmical movements of deglutition, consisting of contraction of the
pharynx and elevation of the larynx, followed by peristalt ic motion of
the whole length of the oesophagus. All the sensitive fibres of the
pneumogMsl.ric, therefore, distributed to the parts concerned in the net
of swallowing, undoubtedly assist in exciting the necessary muscular
contractions,

1'ntlccfion of Ike Glottis in the act of Deglutition. — As the larynx
communicates, by its superior orifice, directly with the cavity of the pha-
rynx, and as all solids and liquids, in the act of swallowing, necessarily
pass over its surface, portions of the food would be constantly liable to
find their way through the rima glottidis into the respiratory passages,
unless then' were some provision against it. The epiglottis, which
stands in front of the glottis ill a nearly upright position, and which
shuts down over its orifice like a cover when the base of the tongue is
drawn back at the time of deglutition, might seem to be adapted to
secure protection in this respect

Kxperienee shows, however, that the epiglottis is not essential for
the safety of the glottis in deglutition. The entire organ may be cut
off in dogs, as we have verified by repeated experiments, without any dif-
ficulty being afterward exhibited by the animal in swallowing either
liquid or solid food. The epiglottis, furthermore, is an organ which
exists only in mammalians, being absent, in all the remaining classes of
vertebrate animals. In birds especially, the orifice of the glottis can IK;
readily seen on opening the beak, unprotected by anything similar to
an epiglottis, and performing the alternate movements of expansion
and collapse connected with respiration. Finally, the existence of the
epiglottis in man does not prevent foreign substances from passing into
the glottis whenever the other conditions of normal deglutition are sus-
pended or dist urbed. The protection of the glottis against the entrance
of solid or liquid food does not depend upon a mechanical obstacle, but
upon a definite association of nervous acts.

The first requisite for the act, of swallowing is the sunjHtnuion of respi-
ration. This takes place, at the beginning of deglutition, by a nervous
influence which it is difficult to describe, but which may be designated

568 THE CRANIAL NERVES.

as an "action of arrest." The same nervous impression which excites
by reflex action the constrictors of the pharynx, suspends for a time
the movements of inspiration. This effect is very perceptible in the
ordinary act of swallowing, and was witnessed by Waller and Prevost in
many of their experiments on this subject ; galvanization of the central
extremity of the superior laryngeal nerve causing immediate relaxation
of the diaphragm, with stoppage of its movements.

The effect of the arrest of breathing upon the glottis is to prevent the
customary opening of its orifice at the time of inspiration. As the res-
piratory movements of the glottis are coincident with those of the chest,
and are excited and maintained by the same nervous influence, the
impression which puts a stop to one suspends the other also. The glot-
tis consequently, not being opened at the time the food enters the
pharynx, its liability to admit any portion of the alimentary mass is
much diminished by the mere fact of its passive condition. But this
condition furthermore allows the rima glottidis to be completely closed
by the contraction of the inferior constrictor of the pharynx, the most
active muscle in the apparatus of deglutition ; since the fibres of this
muscle are attached laterally to the external surface and free borders
of the thyroid cartilage, and thus compress the larynx on both sides at
the moment the food is carried downward by their contraction. It is
by this means alone that the glottis is protected in birds and in other
animals where the epiglottis is wanting, and it is also the essential part
of the same process in man and in mammalians.

The accident in which food or foreign substances sometimes gain
access to the larynx is always produced by a sudden attempt at in-
spiration. This, which cannot take place during deglutition in the
ordinary condition of the nervous system, may nevertheless be produced
in many instances by an unexpected shock or excitement, which disturbs
momentarily the harmonious -co-ordination of the reflex actions. Any
sudden impression produces in general, as its first effect, a spasmodic
movement of inspiration ; and if this take place while food is contained
in the pharynx, a portion of it almost necessarily passes in, together
with the current of air, through the widely open orifice of the glottis.

Connection with the Stomach and Stomach Digestion. — The effect
produced upon the stomach and digestion by division of the pneumo-
gastric nerve shows that its influence upon this organ is in the main
similar to that which it exerts on the oesophagus ; that is, it confers on
its mucous membrane a certain sensibility to the presence of food, and
provides for the peristaltic action of its muscular coat. After experi-
mental section of both pneumogastric nerves in the region of the neck,
the sensations of hunger and thirst remain ; the animals often exhibiting
a desire for food and drink, and sometimes taking it in considerable
quantity, although little, if any, reaches the stomach, owing to the
paralysis of the muscular walls of the oesophagus. In the experiments
of Bernard on dogs, the secretion of gastric juice was suspended after
this operation, and food introduced into the stomach through a gastric

THE PNEUMOGASTRIC. 569

fistula remained undigested. But Longet has found that if food be
introduced under these circumstances in small quantity, it may cause
the secretion of gastric juice, and may be finally digested and absorbed*
These results indicate that the functions of secretion and digestion in
the stomach are not immediately under the control of the pneumogastric
nerve, but that they become deranged after its section and practically
suspended, owing to the indirect influence of other causes.

On the other hand, the muscular contractions of the organ and the
sensibility of its mucous membrane are both directly abolished by
division of the pneumogastrics. According to the observations of
Bernard, the finger, introduced into the cavity of the stomach through
a gastric fistula in the dog, is compressed with considerable force by
the walls of the organ ; but this pressure disappears completely if the
pneumogastric nerves be divided. The absence of muscular power in
the paralyzed stomach is of itself sufficient to account for the failure
of digestion when the influence of these nerves has been cut off. The
peristaltic action of the organ is essential to the digestive process, in
order to bring successive portions of the food in contact with its mu-
cous membrane1, and to cause the intimate admixture of the gastric
juice with all parts of the alimentary mass. The natural movement
and agitation of the food, by the action of the muscular coat, is no
doubt, also, an important stimulus to the continued secretion of the
gastric juice ; and when it no longer takes place, the digestive fluid will
necessarily be supplied in smaller quantity. It is evident, therefore,
that the pneumogastric nerves supply to the walls of the stomach a
certain amount of sensibility and a motor power, which are practically
essential to the process of digestion.

Influence on the Action of the Heart. — The pneumogastric nerve, as
already shown, gives off a number of filaments which are destined for
the cardiac plexus, and ultimately for distribution in the substance of
the heart. One or two of these filaments come from the superior
laryngeal branch of the pneumogastric, and immediately join the upper
cardiac nerve derived from the superior cervical ganglion of the sympa-
thetic. Several others are furnished by the main trunk of the pneumo-
gastric in the neck, which inosculate with each other and with the con-
tinuation of the upper cardiac nerve. The inferior laryngeal branch, in
its reascending course through the lower part of the neck, supplies so
many inosculating filaments to the same plexus of cardiac nerves that,
according to Cruveilhier, it appears in some instances to be distributed
in almost equal proportions to the larynx and to the keart. Finally
other small branches are supplied by the pneumogastric in the cavity
of the chest, which lose themselves at once in the cardiac plexus proper,
beneath the arch of the aorta. All the filaments, accordingly, which
are finally distributed to the heart through the cardiac plexus, originate
from the sympathetic and the pneumogastric nerves; and the entire
group is characterized by the frequent and intimate admixture of the
fibres derived from these two sources. A considerable proportion of
37-

570 THE CRANIAL NERVES.

the cardiac filaments are, therefore, made up of fibres originally belong-
ing to the pneumogastric nerve.

The effect produced upon the heart's action by irritating the pneumo-
gastric in the region of the neck is precisely the opposite to that usually
caused by irritating the nerves going to a muscular organ. This effect
may be seen by opening the chest, and exposing the heart to view, at the
same time that the pneumogastric nerves are separated from their con-
nections in the neck for a sufficient distance to apply to them the poles
of a galvano-electric apparatus. In the cold-blooded animals, as the
frog or the turtle, no other precaution is required; in the dog and
other warm-blooded species, artificial respiration must be maintained
by the nozzle of a bellows inserted in the trachea.

When a galvano-electric current of moderate strength is applied to
the pneumogastric nerves prepared in this way, the cardiac pulsations
are reduced in frequency ; and if the current be increased in strength,
the heart's action stops altogether, and remains suspended so long as
the stimulus continues to be applied to the nerve. When the galvani-
zation ceases, the cardiac pulsations recommence ; and the same thing
may be repeated for an indefinite number of successive trials.

There are two important facts to be noted in regard to these effects
of irritating the pneumogastric :

1. When the heart ceases its movements under the galvanization of
the nerves, its walls are not in a contracted condition, but in a state of
relaxation. Neither are its cavities distended with blood ; but the organ
simply remains quiescent, lying at rest without any indication of mus-
cular activity.

2. If the pneumogastric nerves be divided at their point of exposure
in the middle of the neck, and if the central extremities be galvanized,
no effect is produced upon the heart. But if the stimulus be applied to
their peripheral extremities, the above phenomena are reproduced, the
heart remaining flaccid so long as the galvanization is continued. The
effect in question, therefore, is not due to reflex action, but to a direct
influence convej^ed through the pneumogastric filaments to the muscu-
lar substance of the heart. This conclusion is fully confirmed by the
fact that a similar retardation or stoppage of the cardiac pulsations is
caused in frogs and turtles by galvanization of the medulla oblongata
itself, the pneumogastric nerves remaining entire ; but if the nerves be
previously divided, no such effect is produced. On the other hand,
division of the pneumogastric nerves, or sudden destruction of the
medulla oblongata, causes increased rapidity of the cardiac pulsations.
Section of these nerves, accordingly, in the warm-blooded animals, pro-
duces opposite effects upon the respiration and the pulse, one being
accelerated and the other retarded. According to Bernard, these
effects, though opposite in direction, are produced in similar propor-
tions ; so that, if the respirations are diminished one-half, the cardiac
pulsations are increased to double their former frequency. Thus when
the influence of the pneumogastric nerve is cut off, the motions of the

THE SPINAL ACCESSORY. 571

heart increase in rapidity, when it is stimulated, they experience a
retardation.

This influence, exerted upon the heart by the pneumogastric nerve, is
of the peculiar kind known as the "action of arrest." Such a power
certainly exists in the nervous system, though its nature is not easy
of explanation. An instance of it has already been given in the fact,
observed b}" Waller and Prevost, of suspension of the movements of
the diaphragm by galvanizing the trunk of the superior laryngeal nerve.
The natural stoppage of respiration in the act of swallowing, and the
relaxation of the sphincters preliminary to the evacuation of the rectum
and the bladder, are effected by nervous influences of a similar kind.
There are evidently nervous fibres which transmit their stimulus di-
rectly to the muscles, and which, in this respect, belong to the category
of motor nerves ; but which, when called into activity, instead of ex-
citing muscular contraction, serve to moderate or even suspend it. The
most palpable instance of this mode of action is that of the pneumogas-
tric nerves in their relation with the heart ; but there is evidence that
it occurs, in a more obscure manner, in various other parts of the
nervous system.

Eleventh Pair. The Spinal Accessory.

This nerve, which has received its name from the singularity of its
origin and subsequent course, consists of filaments which emerge from
the side of the cervical portion of the spinal cord, from the level of the
fourth or fifth cervical nerve upward (Fig. 179,4). These filaments
unite into a slender, rounded cord, which ascends in a vertical direction
between the anterior and posterior roots of the cervical spinal nerves,
gradually increasing in size from the addition of new root fibres from
the spinal cord, to the level of the foramen magnum, where it enters the
cranial cavity. Here it receives a new supply of accessory root fibres
from the side of the medulla oblongata, which emerge in a continuous
line with those of the pneumogastric nerve. The nerve trunk, thus con-
stituted by the union of its spinal and its medullary roots, joins the
pneumogastric and glossopharyngeal nerves in their passage through
the jugular foramen.

The central origin of the root fibres of this nerve is a collection of
nerve cells situated in the upper portion of the spinal cord and the com-
mencement of the medulla oblongata, on the outer and posterior aspect of
the anterior horn of gray matter. In the remainder of the medulla, this
nucleus is situated farther backward, receding from front to rear with
the rest of the gray matter in this part of the nervous centres. At its
anterior extremity, it becomes continuous with the nucleus of the pneu-
mogastric. From the gray matter of its nucleus, the fibres of the spinal
accessory nerve curve downward and outward until they emerge, as
above mentioned, in a series of bundles, from the lateral surface of the
medulla.

While passing through the foramen lacerum, the spinal accessory

572 THE CRANIAL NERVES.

becomes adherent externally to the jugular ganglion of the pneumogas-
tric, but without taking any part in its formation, except by furnishing
one or two small filaments of communication. Immediately upon its
exit from the foramen it divides into two main branches; namely, 1st,
the internal, or anastomotic branch, which joins the trunk of the pneu-
mogastric and becomes more or less intimately blended with it, and
2dly, the external, or muscular branch, which passes downward and
outward and is distributed to the sterno-mastoid and trapezius muscles.
According to many different observers (Bernard, Cruveilhier, Henle,
Longet) the internal or anastomotic branch is made up of nerve fibres
coming from the medulla oblongata ; the external or muscular branch
consists of those originating from the spinal cord.

The spinal accessory is without question a motor nerve. According
to the experiments of Longet on dogs, its mechanical irritation in the
cranial cavity does not give rise to signs of pain, and although Bernard
found evidences of sensibility on galvanizing the uninjured nerve in
the same situation, if it were divided and the irritation applied to its
central extremity no indications of sensibility were manifest. On the
other hand its fibres may be traced in great part directly to their termi-
nation in muscular tissues, and its division or evulsion induces effects
which consist exclusively in loss of motive power.

The most complete method of experimenting upon the effects pro-
duced by destruction of this nerve is that first adopted by Bernard,
namely, its evulsion, For this purpose, the muscular branch of the
nerve is followed by dissection from without to its point of emergence
from the jugular canal, where it separates from the anastomotic branch.
The combined trunk is then seized between the blades of a forceps, and
by a steady and continuous traction the whole of the nerve, witli both
its medullary and spinal roots, may be separated from their central
attachments and extracted entire. By appropriate variations of the pro-
cedure, either the medullary portion with the anastomatic branch, or the
cervical portion with the external branch, may be taken away separately,
and the comparative effects of the two operations observed. But when
the entire trunk is extracted as above, the source of the fibres destined
both for anastomosis with the pneumogastric, and for the muscular
branch of the nerve, is destroyed at the same time.

The most striking effects of this operation are due to paralysis of the
internal or anastomotic branch. It is this branch which supplies to the
pneumogastric nerve a large share of its motor fibres ; and those espe-
cially which form the pharyngeal branch of the pneumogastric nerve, are
shown by dissection to be derived from the anastomotic branch of the
spinal accessory. According to Cruveilhier, the pharyngeal filament is
sometimes given off exclusively from the anastomotic branch of the
spinal accessory, sometimes partly from this branch and partly from the
pneumogastric itself. Beyond the pharyngeal branch, the fibres of the
pneumogastric nerve derived from the spinal accessory can no longer
be followed with certainty by means of dissection ; but the results of

THE SPINAL ACCESSORY. 573

experiment show that they are finally distributed, through the inferior
laryngeal branch, to the muscles of the larynx, where they preside over
its actions as a vocal organ.

After the spinal accessory nerve has been torn away on both sides in
the manner above described, the most noticeable result is a loss of
power to produce vocal sounds. The other movements of the larynx
are not interfered with. Especially those of respiration go on in a natu-
ral manner. But the voice is completely lost, as much so as if the infe-
rior laryngeal nerves, or the pneumogastric trunks themselves, had been
divided. The difference between the two cases, however, is very impor-
tant. Section of the pneumogastrics, or of their inferior laryngeal
branches, paralyzes at once all the movements of the glottis, those of
respiration as well as those of phonation ; since these nerves contain all
the motor fibres distributed to the larynx, except those of the crico-thy-
roid muscles. On the other hand, section or evulsion of the spinal
accessory nerves paralyzes the movements of phonation alone, namely,
those in which the vocal chords are approximated and the rima glottidis
narrowed, while it leaves untouched the movements of respiration, in
which the vocal chords are separated and the rima glottidis opened.

Thus the muscular apparatus of the lar}7nx, which is destined to per-
form separately two distinct functions, is supplied with motor nerves
from two different sources. Those which preside over the production
of vocal sounds originate exclusively from the spinal accessory ; those
which excite the movements of respiration are derived from the other
motor nerves (facial, hypoglossal, cervical) which also inosculate with
the pneumogastrics.

The special function of the external or muscular branch of the spinal
accessory nerve is not so fully understood. The stern o-mastoid and
trapezius muscles, to which its fibres are distributed, also receive fila-
ments from the cervical spinal nerves ; and they still retain the power
of motion after division or evulsion of the spinal accessory on both
sides. The sterno-mastoid and trapezius muscles have no such peculiar
and easily recognizable mode of action as that of the larynx in the for-
mation of the voice ; and consequently it has not been easy to distin-
guish with certainty what special movement of these muscles is para-
lyzed by division of the spinal accessory, and what remains unaffected.
The most plausible conclusions are those derived by Bernard from
continued observation of animals preserved for some time after the
division of these nerves.

According to this explanation, the fibres of the external branch of
the spinal accessory, like th6se of the internal branch, perform a func-
tion which is antagonistic to the movements of respiration. Respira-
tion is naturally suspended in all steady and prolonged muscular efforts.
In the acts of straining, lifting, pushing, and the like, respiration ceases,
the spinal column is made rigid, and the head and neck are placed in a
fixed position largely by the aid of the sterno-mastoid and trapezius

574: THE CRANIAL NERVES.

muscles. Such efforts cannot be made with success if the muscles in
question are paralyzed. In the lower animals, according to the obser-
vations of Bernard, they also take part in the production of a cry, or
prolonged vocal sound. If the entire spinal accessory be destroyed, as
already shown, the voice is completely abolished by loss of power in
the laryngeal muscles. If the external branch alone be divided, the
animal can still produce a sound in the larynx ; but this sound cannot
be prolonged into a cry, and the voice is confined in duration to the
ordinary length of an expiratory movement. Although the animals,
furthermore, are not apparently inconvenienced by this operation so
long as they remain quiet, any increased exertion, as in running or
leaping, causes a want of harmony between the movements of respira-
tion and those of the limbs, which results in unusual shortness of
breath.

The sterno-mastoid and trapezius muscles, like those of the larynx,
are therefore animated by two sets of motor nerve fibres. One set,
coming from the cervical spinal nerves, provides for all the movements
connected with ordinary changes of attitude and locomotion ; the
others, derived from the spinal accessory, supply the requisite stimulus
for continuous muscular exertion, or for a prolonged vocal sound.

Twelfth Pair. The Hypoglossal.

The hypoglossal nerve, the motor nerve of the tongue, emerges from
the anterior part of the medulla oblongata by a linear series of ten or
twelve slender filaments in the furrow between the outer edge of the
anterior pyramids and the rounded 'projection of the olivary bodies
(Fig. 179,5). The vertical line along which these filaments make their
appearance corresponds exactly with the line of origin of the anterior
roots of the cervical spinal nerves below ; and the whole external aspect
of their anatomical relations resembles that of a motor nerve root.

The central origin of the hypoglossal root fibres, according to
Clarke, Dean, Kolliker, Henle, and Meynert, is a nucleus of gray matter
situated at the posterior part of the medulla oblongata next the median
line, at the inferior extremity of the fourth ventricle. This collection of
gray matter has an elongated, irregularly cylindrical form, extending
longitudinally from about the level of the divergence of the posterior
columns upward and forward to that of the auditory nucleus. It is,
therefore, parallel in its position with the spinal accessory and pneumo-
gastric nuclei, but situated between them and the median line. In
transverse sections of the medulla, made successively from below up-
ward, this nucleus is first seen (Fig. 180) to be placed immediately
about the central canal, which is already approaching the posterior sur-
face of the medulla ; and the roots of the nerve run in a curvilinear
course downward and outward to their point of emergence.

Above this point, after the central canal has opened into the cavity
of the fourth ventricle (Fig. 181), the hypologlossal nucleus has itself
receded quite to the posterior surface of the medulla, where it occupies

THE HYPOGLOSSAL.

575

upon the floor of the fourth ventricle, on each side of the median line,
the longitudinal eminence known as the " fasciculus teres." Its root
fibres thence run downward through the whole thickness of the medulla

180.

***

Xli

TRANSVERSE SECTION OP THE HUMAN MEDULLA OBLONG ATA, just belowthe
divergence of the posterior columns, and through the inferior extremity of the olivary
nucleus.— Cc. Central canal. R. Raphe. No. Olivary nucleus. Nh. Nucleus of the hypo-
glossal nerve. XII'. Hypoglossal nerve roots. Magnified 8 diameters. (Henle.)

at this part, passing for some distance in a nearly vertical plane, and
then curving outward, to reach the furrow between the olivary bodies
and the anterior pyramids, where they emerge.

During the passage of the hypoglossal nerve roots through the medulla
oblongata, they pass along the surface of the olivary nucleus, between it
and the anterior pyramid, and in great measure between the folds or
even through the substance of its convoluted wall. It is shown by
Dean1 that although a direct continuity cannot be made out between
the root fibres of the nerve and the stellate cells of the olivary nucleus,
yet prolongations of the cells can sometimes be traced for a consider-

1 Gray Substance of the Medulla Oblonsrata and Trapezium. Washing-ton,
1864, p. 36.

576

THE CRANIAL NERVES.

able distance upward and inward, in company with the nerve roots, to-
ward the hypoglossal nucleus ; and in the sheep, the tracts of fibres con-
necting the two nuclei are very evident. According to Henle, in some

No

xn

TRANSVERSE SECTION OF THE HUMAN MEDULLA OBLONGATA, through the
middle of the hypoglossal nucleus and the olivary body. — No. Olivary nucleus. R. Raphe
Ngl. Nucleus of the glossopharyngeal nerve. Nv. Nucleus of the pneumogastric nerve.
Nh. Nucleus of the hypoglossal nerve. IX. Glossopharnygeal nerve roots. XII. Hypoglossal
nerve roots. Magnified 8 diameters. (Henle.)

transverse sections through the hilum, or opening of the olivary body
(Fig. 182), fibres from the hypoglossal nerve roots may be seen bending
round the inner border of the nucleus into its interior ; while other fibres
emerge in a corresponding manner from the opposite edge of the hilum
and continue onward, with the main root-bundles, to the hypoglossal
nucleus. Although the details of minute anatomical structure in these
parts have not been fully made out, it is evident that a close relation of
some kind exists between the gray matter of the olivary bodies and the
liypoglossal nucleus and roots.

THE HYPOGLOSSAL.

577

Fig. 182.

Kolliker regards the roots of the hypoglossal nerves as decussating
completely with each other through the raphe, at the level of the nuclei.
According to both Clarke and
Dean, on the other hand, a
portion of the fibres of each
root terminate in the corre-
sponding nucleus, while an-
other portion bend inward
and cross the raphe at the
median line, decussating with
those of the opposite side,
Henle describes a few thin
bundles of fibres which con-
nect the roots of the nerve on
each side, at their point of
emergence, with the raphe in
front of the medulla. It is

certain that the hypoglossal,
like the other cranial nerves,

xn

TRANSVERSE SECTION ov THE HTTMA.N
MEDULLA OBLONGATA, through the olivary
nucleus and root of the hypoglossal nerve.— A p.
Anterior pyramid. XII. Hypoglossal nerve roor.
Magnified 8 diameters. (Henle.)

has, in some way, a connec-
tion with the opposite side of
the brain ; since cases of facial
paralysis from cerebral hemor-
rhage are often accompanied by paralysis of the tongue on the same
side with that of the face, and on the opposite side to that of the lesion.
One of the genio-hyo-glossal muscles having lost its power, while the
other remains active, if the patient attempts to protrude the tongue in
such cases, its point is deviated toward the paralyzed side.

After leaving the anterior surface of the medulla oblorigata the fibres
of the hypoglossal nerve become parallel with each other, and, passing
through the anterior condyloid foramen of the occipital bone, emerge
from the skull in the form of a cylindrical cord. Immediately after
escaping from the condyloid foramen it presents one or two branches
of inosculation with the pneumogastric, at the point where it crosses the
track of this nerve. According to Cruveilhier, the dissection of the parts,
after maceration in dilute nitric acid, shows distinctly that this inoscula-
tion consists of fibres which leave the hypoglossal nerve and join those
of the pneumogastric, running with them in a peripheral direction. The
hypoglossal nerve then passes downward, nearly to the level of the hyoid
bone, where it curves forward, giving filaments to the styloglossal and
hyoglossal muscles, and to those immediately beneath the hyoid bone;
after which it turns upward, penetrates the tongue from below, inoscu-
lates by two or three filaments with the lingual branch of the fifth pair,
and is finally distributed to all the muscles of the substance of the
tongue. It, therefore, animates not only the lingual muscles proper,
but also those which draw the tongue backward and upward (stylo-
glossal), and backward and downward (hyoglossal and infra-hyoid mus-

578 THE CRANIAL NERVES.

cles). The trunk of the nerve also receives communicating filaments
from the first and second cervical spinal nerves, which, according to
Cruveilhier, are filaments of reenforcement, accompanying the hypo-
glossal nerve toward its peripheral termination.

Physiological properties of the Hypoglossal Nerve. — The motor char-
acter of the hypoglossal nerve is easily established by the results which
follow its irritation and division. If the nerve be exposed in the living
or recently killed animal at the top of the neck, where it runs parallel
to and a little above the hyoid bone, pinching or wounding its fibres, or
the application of the galvanic stimulus, produces immediately convul-
sive action of the muscles of the tongue. The same effect follows if the
trunk of the nerve be divided at this point, and the irritation applied to
its peripheral extremity ; showing that the contractions thus produced
are not due to reflex action, but to a direct stimulus conveyed through
the hypoglossal nerve to the muscular fibres. The excitability of the
nerve is consequently beyond question. Whether it possess also any
sensitive fibres of its own is not so certain. Longet obtained in this
respect only negative results ; the division of the filaments of origin of
the nerve, in his experiments on dogs, through the space between the
occiput and the atlas, not producing perceptible signs of pain. The
trunk of the hypoglossal nerve outside the cranial cavity, certainly pos-
sesses some degree of sensibility, according to the testimony of nearly all
experimenters ; but this is regarded as derived, like that of other motor
nerves, from inosculations beyond its point of origin, especially from
those of the first and second cervical spinal nerves near the base of
the skull, and from branches of the fifth pair near its terminal distri-
bution. Whatever sensibility it may possess is destined only for the
muscular substance of the tongue, and not for its mucous membrane;
since, in the first place, division of the lingual branch of the fifth pair
and of the glossopharyngeal nerve destroys both tactile and gustatory
sensibility over the whole surface of the tongue, though the hypoglossal
be left untouched ; and secondly, according to the experiments of Lon-
get, after division of both hypoglossal nerves in the dog the surface of
the tongue, when touched with the point of a needle, evinces its ordinary
tactile sensibility, the application of bitter solutions causes signs of dis-
gust, and the contact of foreign bodies at the base of the organ excites
the action of vomiting.

The distinct and uniform result of section of both hypoglossal nerves
is a loss of muscular power in the whole substance of the tongue, while
its tactile and gustatory sensibilities are preserved. In the experiments
of Panizza, confirmed by those of Longet, the animals upon which this
operation had been performed were unable to move the tongue in any
direction, or even to restore it to its natural position when it was turned
back, except by hanging the head downward and shaking it, thus allow-
ing the organ to fall forward by its own weight, as a helpless mass. In
the movements of the jaws, which were not interfered with, the tongue

THE HYPOGLOSSAL. 579

was liable to be caught between the teeth and wounded ; an accident
which evidently caused suffering to the animal, thus showing the con-
tinued sensibility of the paralyzed organ.

Connection of the Hypoglossal Nerve with Mastication and Degluti-
tion.— Although the movements of the tongue do not take a direct part
in mastication, they are yet of essential importance to its accomplish-
ment, by bringing successive portions of the food between the teeth and
removing those which have already undergone tritu ration. In species
where liquids are introduced into the mouth by the act of lapping, this
movement becomes also impossible after section of the hypoglossal
nerves ; and both liquid and solid food, the latter already reduced to a
pulp, must be introduced far backward into the fauces in order to allow
of their deglutition. The natural action of the lingual muscles is prac-
tically of so much importance that, according to Longet, it requires a
great expenditure of time and patience, in animals with paralysis of the
tongue from division of the hypoglossal nerves, to supply them with
sufficient nourishment for the support of life.

Connection of the Hypoglossal Nerve with Articulation. — In man,
another important function is performed by the tongue as a muscular
organ, namely, that of articulation. As the lingual muscles take an
important part in the pronunciation of all the consonants except the
labials (6, ?n, p} and the labio-dentals (/, v), as well as in that of the
vowels a, e, t, and y, their paralysis will necessarily produce a nearly
complete incapacity of articulation. In man, disease or injury of the
hypoglossal nerve alone is a rare occurrence, and is almost invariably
confined to one side. In the glosso-labio-laryngeal paralysis, described
in connection with the functions of the medulla oblongata (p. 510), the
disease is of central origin, and affects, in various proportions, other
muscles as well as those of the tongue. Here, however, according to
Hammond, the earliest signs of imperfect action show themselves in the
lingual muscles, and when the disease is fully developed the tongue
becomes completely paralyzed, and all power of articulation is lost.

The hypoglossal nerve, accordingly, though one of the simplest of
the cranial nerves in the nature of its physiological endowments, is
essential for the expression of ideas by articulate language, and is also
important as an aid in the mastication and deglutition of the food.

General Arrangement and Mode of Origin of the Cranial Nerves

Notwithstanding the apparent irregularity in source and distribution
of the cranial nerves, as compared with the spinal, an examination of
their internal origin shows that they are arranged on a definite plan,
not essentially dissimilar to that of the spinal nerves. The difference
between them depends only upon the changed position of the gray
substance in the medulla oblongata as compared with that in the spinal
cord. When the central canal of the cord opens into the cavity of the
fourth ventricle, just above the point of divergence of the posterior
columns, the gray matter surrounding it becomes posterior instead of

580

THE CRANIAL NERVES.

Fig. 183.

central in its position; what corre-
sponds to the posterior horns of
gray matter in the cord spreading
out lateral!}', and what corresponds
to the anterior horns following the
central canal as it recedes, and at
last occupying the middle of the
floor of the fourth ventricle, next the
median line. All the sensitive and
motor cranial nerves take their origin
from this layer of gray matter, or its
continuation, from the commence-
ment of the fourth ventricle to the
aqueduct of Sylvius beneath the tu-
bercula quadrigemina. The relations
of origin between the motor and sen-
sitive nerve roots are still preserved.
In the spinal cord, the motor roots
originate from the anterior horns of
gray matter, the sensitive roots from
the posterior horns. In the medulla
oblongata and tuber annulare, the
nuclei of the motor cranial nerves
form a series near the median line;
those of the sensitive nerves are
placed farther outward. A series of
sections of the spinal cord, medulla
oblongata, and tuber annulare, made
in succession from below upward,
show that the collections of gray
matter, or nuclei, in the medulla
oblongata and tuber anuulare, from
which the different motor or sensitive
nerves take their origin, are not com-
pletely disconnected from each other
any more than the successive portions
of gray matter in the spinal cord;

I. Transverse Section of the Tuber Annulare, through the lower border of the pons Varolii.
1. Nucleus of the facial and abducens nerves. 2. Nucleus of the auditory nerve. F. Facial
nerve. Ab. Abducens nerve.

II. Transverse section of the medulla oblonjata, through the middle of the olivary bodies,
and just above the opening of the central canal. 1. Hypoglossal nucleus. 2 Pneumogastric
nucleus. H. Hypoglossal nerve. Pn. Pneumogastric nerve.

III. Transverse section of the medulla, through the lower end of the olivary bodies, and
just below the opening of the central canal. 1. Hypocrlossal nucleus. 2. Pneumogastiic
nucleus. H. Hypoglossal nerve. Pn. Pneumogastric nerve.

IV. Transverse section of the medulla, through the decussation of the anterior pyramids.
Sp. Spinal accessory nerve.

V. Transverse section of the spinal cord in the dorsal region, a, a. Anterior nerve roots.
p, p. Posterior nerve roots.

THE CKANIAL NERVES 581

but at certain points, the gray substance takes on a special degree of
development, and presents an abundant collection of nerve cells. These
collections are called the "nuclei" of the nerves, on account of their
evident importance as points of origin from which the nerve roots can
be traced to their points of emergence at the base of the brain. The
foregoing diagram shows the changes in external form of the cerebro-
spinal axis, and in the position of its gray matter, as examined at differ-
ent levels in the cranium and spinal canal.

CHAPTEE VII.

THE SYMPATHETIC SYSTEM.

THE sympathetic system of nerves, when compared with the cerebro-
spinal system, presents anatomical peculiarities of arrangement and
distribution so distinct and noticeable, that it is naturally regarded as
occupying a place by itself. The slender double cord of its main trunk
extending throughout the great cavities of the body, the number and
scattered position of its ganglia, which are united with each other only
by filaments of small size, the frequent and plexiform arrangement of
its branches, and the distribution of its terminal fibres to the organs
of circulation and nutrition, all form a well marked group of features
by which it is easily recognized. But notwithstanding the general im-
portance of these characters, the sympathetic nerves and ganglia do not
constitute a separate and independent nervous system. Neither the
minute structure of their anatomical elements, nor their external con-
nections, are essentially different from those of the cerebro-spinal nerves
and nervous centres. The sympathetic trunks and branches contain
medullated nerve fibres of the same anatomical character as those of
the spinal cord and its nerves ; and its ganglia are provided with nerve
cells which send off one or more prolongations in the form of nerve
fibres. The main peculiarity of intimate structure in the sympathetic
nerve fibres is that they are, as a rule, of small diameter, though not
smaller than the average of those in the cerebro-spinal nerves. The
cells of the sympathetic are also generally of comparatively small size,
never, according to Kb'lliker, equalling the largest of those in the gray
substance of the spinal cord or the brain ; and they are also charac-
terized by the frequency with which they send out only a single pro-
longation, thus apparently becoming a source of new fibres.

But, on the other hand, the cerebro-spinal system contains both
fibres and nerve cells of small as well as large size. The posterior roots
of all the spinal nerves have connected with them ganglia which are
similar in structure to those of the sympathetic system; the fibres
which come from the spinal cord simply passing through them, as
shown by the observations of Kolliker, and being joined by other fibres
originating from the gray matter of the ganglion itself. The same
arrangement exists in the ganglia of the cranial nerves, as, for instance,
in the Gasserian ganglion of the fifth pair. Thus all the sensitive and
mixed cerebro-spinal nerves contain some fibres of ganglionic origin, in
addition to those derived directly from the brain or spinal cord.
Furthermore, all the sympathetic ganglia receive filaments of communi-
(582)

THE SYMPATHETIC SYSTEM. 583

cation from the cerebro-spinal nerves, which, there is every reason to
believe, consist of fibres coming from the brain or spinal cord, and pass-
ing through the ganglion to form part of the peripheral branches of the
sympathetic system. This conclusion is drawn not only from the fact
that many of these fibres cannot be shown by microscopic examination
either to originate or terminate in the substance of the ganglion, but
also from the paralyzing effect produced upon muscular organs supplied
with sympathetic fibres, by division of the cerebro-spinal nerve which
communicates with its ganglion. This is more particularly shown by
the paralysis of the iris following division of the oculomotorius nerve,
which gives a motor branch to the ophthalmic ganglion. The numerous
branches of communication supplied by the pneumogastric nerve to the
cardiac branches of the sympathetic, and to the cardiac plexus itself,
afford an equally striking instance of the same kind.

The ganglia seated upon the spinal and cranial nerve roots are there-
fore undoubtedly analogous, in their anatomical relations, with the
detached ganglia of the sympathetic system proper ; and the whole of
this system may be considered as made up of a set of nervous centres
disseminated throughout the great cavities of the body, and of nervous
filaments which both receive fibres from the cerebro-spinal centres, and
communicate by some of their own with the cerebro-spinal nerves. All
the organs in the body, accordingly, are supplied with fibres from both
sources ; the difference consisting in the proportions in which one kind
or the other are present in particular parts. The cerebro-spinal nerves
are supplied in the greatest abundance, and manifest their most striking
properties, in the organs and functions of animal life ; those of the sym-
pathetic system preponderate in the organs of vegetative life, and in
their influence upon the functions of nutrition, secretion, and growth.

Anatomical Arrangement of the Sympathetic System. — The sympa-
thetic system consists of a double chain of nervous ganglia, running
from above downward along the front and sides of the spinal column,
and connected with each other by longitudinal filaments. Each gan-
glion is reenforced by motor and sensitive fibres from the cerebro-spinal
system, and thus the organs under its influence are brought indirectly
into communication with external objects and phenomena. Its nerves
are distributed to glands and mucous membranes, many of which are
destitute of general sensibility, and to muscular parts which are re-
moved from the control of the will. The sympathetic ganglia are
situated successively in the head, neck, chest, and abdomen; and in
each of these regions are connected with special organs by their fibres
of distribution.

The first sympathetic ganglion in the head is the ophthalmic gan-
glion, situated within the orbit of the eye, on the outer aspect of the
optic nerve. It communicates by slender filaments with the carotid
plexus, and receives a motor root from the oculomotorius nerve, and a
sensitive root from the ophthalmic branch of the fifth pair. Its fila-
ments of distribution, known as the " ciliary nerves," pass forward upon

584

THE SYMPATHETIC SYSTEM.

Fig. 184.

the eyeball, pierce the scelerotic, and terminate in the muscular tissue
of the iris.

The next is the xpheno-palatine ganglion, situated in the spheno-

maxillary fossa. It commu-
nicates, like the preceding,
with the carotid plexus, and
receives a motor root from
the facial nerve, and a sensi-
tive root from the superior
maxillary branch of the fifth
pair. Its filaments are dis-
tributed to the levator palati
and uvular muscles, to the
mucous membrane of the pos-
terior part of the nasal pas-
sages, and to that of the hard
and soft palate.

The third sympathetic gan-
glion is the submaxillary )
situated upon the submaxil-
lary gland. It communicates
with the superior cervical gan-
glion of the sympathetic by
filaments which accompany
the facial and external carotid
arteries. It derives its sensi-
tive filaments from the lingual
branch of the fifth pair, and
its motor filaments from the
facial nerve, by means of the
chorda tympani. Its branches
of distribution pass mainly to
the subm axillary gland and
Wharton's duct.

The last sympathetic gan-
glion in the head is the otic
ganglion. It is situated be-
neath the base of the skull,
on the inner side of the third
division of the fifth pair. It
receives filaments of communication from the carotid plexus ; a motor
root from the facial by means of the small superficial petrosal nerve,
as well as one or two short fibres from the inferior maxillary division
of the fifth pair ; and a sensitive root from the glossopharyngeal by
the nerve of Jacobson. Its branches are sent to the internal muscle of
the malleus in the middle ear (tensor tympani), to the circurnflexus palati,
and to the mucous membrane of the tympanum and Eustachian tube.

GANGLIA AND NERVES OP THE SYMPA-
THETIC SYSTEM.

THE SYMPATHETIC SYSTEM. 585

The continuation of the sympathetic nerve in the neck consists of
two and sometimes three ganglia, the superior, middle, and inferior.
These ganglia communicate with each other, and also with the anterior
branches of the cervical spinal nerves. Their filaments follow the
course of the carotid artery and its branches, and are distributed to the
substance of the thyroid gland, and to the walls of the larynx, trachea,
pharynx, and oesophagus. By the superior, middle, and inferior cardiac
nerves they also supply sympathetic fibres to the cardiac plexus, and,
through it, to the substance of the heart.

In the chest, the sympathetic ganglia are situated on each side the
spinal column, just over the heads of the ribs. Their communications
with the spinal nerves in this region are double ; each ganglion receiving
two filaments from the intercostal nerve next above it. The filaments
originating from the ganglia are distributed upon the thoracic aorta,
and to the lungs and oesophagus.

In the abdomen, the continuation of the sympathetic S37stem consists
mainly of the aggregation of ganglionic enlargements situated upon the
coeliac artery, known as the semilunar or cceliac ganglion. From this
ganglion a multitude of radiating and inosculating branches are sent out,
which, from their common origin and their diverging Bourse, are termed
the " solar plexus." From this, other plexuses originate, which accom-
pany the abdominal aorta and its branches, and are distributed to the
stomach, small and large intestine, spleen, pancreas, liver, kidneys,
supra-renal capsules, and internal organs of generation.

Beside the above ganglia there are in the abdomen four other pairs,
situated in front of the lumbar vertebrae. Their filaments join the
plexuses radiating from the semilunar ganglion.

In the pelvis, the sympathetic system is continued by four or five pairs
of ganglia, situated on the anterior aspect of the sacrum, and terminat-
ing, at the lower extremity of the spinal column, in the u ganglion impar,"
which is probably to be regarded as a fusion of two separate ganglia.

The entire sympathetic series is thus composed of numerous small
ganglia connected throughout, first with each other; secondly, with the
cerebro-spinal system ; and thirdly, with the viscera.

Physiological Properties of the Sympathetic Ganglia and Nerves. —
The properties and functions of the sympathetic nerves have been less
successfully studied than those of the cerebro-spinal system, owing,
perhaps, to the anatomical difficulties in the way of reaching and ope-
rating upon them for purposes of experiment The principal part of
the sympathetic S3^stem is situated in the interior of the chest and abdo-
men ; and the mere opening of these cavities, to reach the ganglionic
centres, causes such a disturbance in the functions of vital organs, and
such a shock to the system fit large, that the results of these experiments
are liable to be more or less unsatisfactory, The connections of the sym-
pathetic ganglia with each other and with the cerebro-spinal axis are so
numerous and scattered, that these ganglia cannot be completely isolated
without resorting to a still more extensive operation. And finally, the
38

586 THE SYMPATHETIC SYSTEM.

sensible phenomena obtained by experimenting on the sympathetic
nerves are, in many cases, slow in making their appearance, and not
particularly striking or characteristic in their nature.

Notwithstanding these difficulties, however, some facts have been
ascertained with regard to this part of the nervous system, which give
a certain degree of insight into its character and functions.

Influence on Movement and Sensibility. — The sympathetic system is
endowed both with sensibility and the power of exciting motion ; but
these properties are less active than in the cerebro-spinal system, and
are exercised in a different manner. If we irritate a sensitive spinal
nerve in one of the limbs, or apply the galvanic current to its posterior
root, the evidences of pain or of reflex action are decisive and instanta-
neous. There is no appreciable interval between the application of the
stimulus and the sensation which results from it. On the other hand,
in experiments upon the sympathetic ganglia and nerves, evidences of
sensibility are also manifested, but much less acutely, and only after
somewhat prolonged application of the irritating cause. These results
correspond with what we know of the physiological properties of the
organs supplied by the sympathetic system. These organs are insen.
sible, or nearly so, to ordinary impressions. We are not conscious of
the changes going on in them, so long as the}7 retain a normal character.
But they are still capable of perceiving unusual or excessive irritations,
and may even give rise to acute pain when in a state of inflammatory
alteration.

There is the same peculiar character in the action of the motor nerves
belonging to the sympathetic system. If the facial or hypoglossal, or
the anterior root of a spinal nerve, be irritated, the convulsive movement
which follows is instantaneous, spasmodic, and momentary in duration.
But if the semilunar ganglion or its nerves be subjected to a similar
experiment, no immediate effect is produced. It is only after a few
seconds that a slow, vermicular, progressive contraction takes place in
the corresponding part of the intestine, which continues for some time
after the exciting cause has been removed.

Morbid changes taking place in organs supplied by the sympathetic
present a similar peculiarity in their production. If the body be exposed
to cold and dampness, congestion of the kidneys shows itself perhaps on
the following day. Inflammation of any internal organ is rarely estab-
lished within twelve or twenty-four hours after the application of the
exciting cause. The internal processes of nutrition, together with their
derangements, which are more especially under the control of the sym-
pathetic, require a longer time to be influenced by incidental causes,
than those which are regulated by the cerebro-spinal system.

Connection with the Special Senses. — In the head, the sympathetic
has an important connection with the special senses. This is noticeable
more particularly in the case of the eye, in the influences regulating the
expansion and contraction of the pupil. The ophthalmic ganglion sends
off a number of ciliary nerves, distributed to the iris, and receives a

THE SYMPATHETIC SYSTEM. 587

motor root from the oculomotorius. The reflex action, by which the
pupil contracts under the influence of light and expands under its
diminution, takes place, accordingly, through this ganglion. The impres-
sion conveyed by the optic nerve to the tubercula quadrigemina, and •
reflected outward by the fibres of the oculomotorius, is not transmitted
directly by the last named nerve to the iris ; but passes first to the
ophthalmic ganglion, and is thence conveyed to its destination by the
ciliary nerves.

The reflex movements of the iris exhibit consequently a somewhat
sluggish character, which indicates the intervention of the sympathetic
system. The changes in the size of the pupil do not take place instan-
taneously with the variation in the amount of light, but require an
appreciable interval of time. If we suddenly pass from a light into a
dark room, we are unable to distinguish surrounding objects until a
certain time has elapsed, and the expansion of the pupil has taken
place ; and vision even continues to grow more distinct for a consider-
able period afterward, as the expansion of the pupil becomes more com-
plete. If we cover the eyes of another person with the hand or a folded
oloth, and then suddenly expose them to the light, we can see that the
pupil, which is at first dilated, contracts somewhat rapidly to a certain
extent, and afterward continues to diminish in size for several seconds,
until its equilibrium is fairly established. Furthermore, if we pass sud-
denly from a dark room into bright sunshine, we are immediately con-
scious of a painful impression in the eye, which results from the inability
of the pupil to contract with sufficient rapidity. All such exposures
should therefore be made gradually, in order that the movements of the
iris may keep pace with the varying quantity of stimulus, and thus
protect the eye from injurious impressions.

The reflex movements of the iris, though accomplished through the
medium of the ophthalmic ganglion, derive their original stimulus,
through the motor root of this ganglion, from the oculomotorius nerve.
For if the oculomotorius nerve be divided between the brain and the
eyeball, the pupil becomes sensibly dilated, and loses in great measure
its power of contracting under the influence of light. The motive power,
originally derived from the brain, is, therefore, modified by passing
through the ophthalmic ganglion before reaching its destination in the
iris.

Three organs of special sense, the eye, the nose, and the ear, are
each provided with two sets of muscles, superficial and deep, which
regulate the quantity of stimulus admitted to the organ and the mode
in which it is received. The superficial set is animated by branches of
the facial nerve ; the deep-seated or internal set, by filaments from a
sympathetic ganglion.

Thus, the front of the eyeball is protected by the orbicularis and
levator palpebrse superioris muscles, which open or close the eyelids at
will, and allow a larger or smaller quantity of light to reach the cornea.
These muscles are supplied by the oculomotorius and facial nerves, arid

588 THE SYMPATHETIC SYSTEM.

are mainly voluntary in their action. The iris, on the other hand, is a
deep-seated muscular curtain, which regulates the quantity of light
admitted through the pupil. It is supplied by filaments from the oph-
thalmic ganglion, and its movements are involuntary.

Division of the sympathetic nerve in the middle of the neck has a
marked effect on the muscular apparatus of the eye. Within a few
seconds after this operation has been performed upon the cat, the pupil
of the corresponding eye becomes contracted, and remains in that con-
dition. At the same time the third
Fig. 185. .. . t.t .

eyelid, or " nictitating membrane,"

with which these animals are pro-
vided, is drawn partially over the
cornea, and the upper and lower
eyelids also approximate to each
other; so that all the apertures
guarding the eyeball are percep-
tibly narrowed, and the expression
of the face on that side is altered
in a corresponding degree. This
effect has been explained by sup-
posing the circular fibres of the

OAT, after section of the right sympathetic. . . , . , •,

iris, or the constrictors, to be ani-
mated by filaments derived from the oculomotorius, and the radiating
fibres, or the dilators, to be supplied by the sympathetic; so that, while
division of the oculomotorius would produce dilatation of the pupil by
paralysis of the circular fibres only, division of the sympathetic would
be followed by exclusive paralysis of the dilators, and consequently by
contraction of the pupil. This explanation, however, is not entirely
satisfactory ; since, after division of the sympathetic nerve in the cat,
not only is the pupil contracted, but both the upper and lower eyelids
and the nictitating membrane are also drawn partially over the cornea,
and assist in excluding the light. The last-named effect cannot be
owing to direct paralysis, from division of the fibres of the sjonpathetic.
It is more probable that the section of this nerve operates by exaggerat-
ing for a time the sensibility of the retina, owing to vascular congestion;
and that the partial closure of the eyelids and pupil is a consequence
of that condition.

In the olfactory apparatus, the superficial set of muscles are the com-
pressors and elevators of the alee nasi, which are animated by filaments
of the facial nerve. By their action, odoriferous vapors are snuffed up
and directed into the upper part of the nasal passages, where they come
in contact with the sensitive portions of the olfactory membrane ; or,
if too pungent or disagreeable in flavor, are excluded from entrance.
These muscles are not very important in the human species ; but in
many of the lower animals, as in the carnivora, they play a very im-
portant part in the mechanism of olfaction. Furthermore, the levators
and depressors of the velum palati, which are deep-seated, serve to open

THE SYMPATHETIC SYSTEM. 589

or close the posterior nares, and accomplish a similar office with the
muscles already named in front. The levator palati and uvular muscles
are supplied by filaments from the spheno-palatine ganglion, and are
involuntary in character.

The ear has two sets of muscles, similarly supplied. The superficial
set are those attached to the external ear. They are comparatively
inactive in man, but in many of the lower animals are well developed
and important. In the horse, the deer, the sheep, and various other
species, they turn the ear in different directions to catch more distinctly
feeble sounds, or to exclude those which are disagreeable. These mus-
cles are supplied by filaments of the facial nerve, and are voluntary in
their action.

The deep-seated set are the muscles of the middle ear. Sounds are
transmitted to the middle ear through the membrane of the tympanum,
which may be made more or less sensitive to sonorous impressions by
varying its condition of tension or relaxation. This condition is regu-
lated by the two muscles of the middle ear, namely, the tensor tympani
and the stapedius. The first named muscle is supplied with nervous
filaments from the otic ganglion of the sympathetic. By its contraction,
the handle of the malleus is drawn inward, bringing the membrana tym-
pani with it, and thus increasing its tension. On the relaxation of the
muscle, the chain of bones returns to its ordinary position, and the pre-
vious condition of the tympanic membrane is restored. This action, so
far as we can judge, is purely involuntary. The stapedius muscle, on
the other hand, is supplied by a branch of the facial nerve (p. 549). It
is probable that its contraction serves to relax the membrana tympani,
and enables us to make a certain degree of voluntary exertion in listen-
ing for faint or distant sounds.

Connection with the Circulation. — Perhaps the most important fact
concerning the sympathetic S3rstem is that of its influence over the
vascularity of the parts supplied by it. In the first place, division of
the sympathetic trunk produces a vascular congestion in the corre-
sponding parts. If this nerve be divided, in any of the warm-blooded
quadrupeds, in the middle of the neck, a vascular congestion of all parts
of the head, on the corresponding side, immediately follows. This con-
gestion-is most distinctly evident in the rabbit, in the thin and trans-
parent ears; and within a few minutes after the operation, the difference
in their appearance on the two sides is strongly pronounced. All the
vessels of the ear on the affected side become turgid with blood ; and
many which were before imperceptible, are distinctly apparent. This
effect, which was first pointed out by Bernard, and has been observed by
many other experimenters, we have often verified. It lasts for a con-
siderable time, and may even be very distinct at the end of three weeks.
It remains longer when a portion of the nerve has been cut out, or the
cervical ganglion extirpated, than when its filaments have been simply
divided by a transverse section. It finally disappears when the separated
filaments have reunited and regained their functional activity.

590 THE SYMPATHETIC SYSTEM.

The vascular congestion thus produced by division of the sympathetic
nerve is accompanied by three important phenomena, all intimately con-
nected with each other.

First, the quantity of blood circulating in the part is increased, and
its movement accelerated. It is not a state of passive congestion ; but
all the vessels are simultaneously dilated, a larger quantity of blood
passes through the capillaries in a given time, and returns by the veins
in greater abundance than before.

Secondly, there is a remarkable elevation of temperature in the affect-
ed part. This elevation of temperature is very perceptible to the touch,
both in the ear and in the integument of the corresponding side of the
head. Measured by the thermometer, it has been found by Bernard to
reach, in some cases, 4.5 or 5 degrees (8° or 9° F.). It results from
the increased quantity of blood circulating in the vessels ; since the
blood coming from the interior and warmer parts of the body supplies
more heat, in proportion to the abundance and rapidity with which it
traverses the vascular tissues.

Thirdly, the color of the venous blood becomes brighter. This effect
is also due to increased rapidity of the circulation. The blood is de-
prived of its oxygen and darkened in color by the changes of nutrition
which take place in the tissues. But if the rapidity of the circulation
be suddenly increased, a certain proportion of the blood escapes deoxi-
dation, and its change in color, from arterial to venous, is incomplete.
The blood accordingly returns by the veins of the affected part in greater
abundance, of a higher temperature, and of a more ruddy color, than in
the corresponding parts on the opposite side.

When a local vascular congestion has thus been produced by divi-
sion of the sympathetic nerve, if that portion of the divided nerve
which remains in connection with the tissues be galvanized, all the above
effects rapidly disappear ; the bloodvessels of the ear and corresponding
side of the head contract to their previous dimensions, the quantity of
blood circulating through the tissues is diminished, the temperature is
reduced in a corresponding degree, and the blood in the veins returns
to its ordinary dark color. The variations in the rapidity of the circu-
lation, dependent on the condition of the sympathetic nerve, have been
shown by Bernard' in the following manner. In a living rabbit the upper
part of one ear is cut off with a pair of very sharp scissors, so that the blood
may escape in jets from the divided ends of the small arteries. The
force and height of the arterial jets having been observed, the sym-
pathetic nerve is then divided in the middle of the neck on the corre-
sponding side Immediately the blood escapes from the wounded ear in
greater abundance, and the arterial jets rise to double or even triple
their former height. The galvanic current is then applied to the di-
vided extremity of the sympathetic, above the point of section, when the
streams of blood escaping from the wound diminish or disappear ; but

1 Journal de la Physiologie de 1'Uomme et des Animaux. Paris, 1862, p. 397.

THE SYMPATHETIC SYSTEM. 591

they recommence and again increase in intensity so soon as the gal-
vanization of the nerve is suspended.

The same author has shown that a similar influence is exerted by the
sympathetic nerve upon the circulation in the limbs.1 If the lumbar
nerves of one side be divided, in the dog, within the cavity of the spinal
canal, paralysis of motion and sensibility is produced in the correspond-
ing limb, but there is no change in its vascularity or temperature ; while
if the lumbar portion of the sympathetic be divided or excised, without
disturbing the spinal nerves, all the signs of increased temperature and
activity of the circulation are manifested in the limb below, without loss
of motion or sensibility. Exsection of the first thoracic ganglion of the
sympathetic produces similar effects in the anterior extremity ; and
these effects are diminished or suspended by electric irritation of the
divided nerve.

Division of the sympathetic nerve, accordingly, produces dilatation
of the bloodvessels and consequent increased rapidity of the circula-
tion, and causes the blood to retain its red color in the veins ; while gal-
vanization of the same nerve produces contraction of the vessels, dimin-
ishes the quantity of the circulating fluid, and causes the change in
color of the blood, from arterial to venous.

The same thing takes place in the glandular organs. If the submax-
illary or parotid gland be exposed in the living animal,2 so long as the
gland is in its ordinary condition the blood passing through it is seen
to undergo the usual changes, and returns dark colored by the veins.
But if the sympathetic filament which accompanies the external carotid
artery be divided, the quantity of blood flowing through the gland is at
once increased, and appears of a red color in the veins. The same
changes occur when the gland is excited to secretion by stimulating
the organs of taste.

An apparent antagonism exists, in regard to the circulation, between
the sympathetic nerve and those derived from the cerebro-spinal
system. If the chorda tympani, which sends filaments to the submax-
illary ganglion, be galvanized, it causes an excitement of the secretion3
in the submaxillary gland, increased activity of the circulation, and a
red color of the blood in the veins. The division of this nerve is followed
by a contrary result. The effects produced, therefore, by galvanization
of the chorda tympani are those produced by division of the sympa-
thetic ; and the effects produced by galvanizing the sympathetic are
those which follow division of the chorda tympani.

The vascularity of the parts, accordingly, as well as the glandular
activity of vascular organs, are under the control of the nervous system.
The filaments of the sympathetic nerve accompany everywhere the blood-
vessels, enveloping the arterial branches with an abundant plexus, and

1 Journal de la Physiologic de PHomme et des Animaux. Paris, 1862, p. 397.

2 Bernard, Legons sur les Liquides de I'Organisme. Paris, 1859, tome i. p. 230.
9 LeQons sur les Liquides de 1'Organisme. Paris, 1859, tome i. p. 312.

592 THE SYMPATHETIC SYSTEM.

following them to their minutest ramifications. They appear to act by
causing a contraction in the organic muscular fibres of the small arteries,
thus regulating the resistance of the vessels, and the' passage of the
blood through them. When the sympathetic nerve is excited, the vessels
contract, the blood passes through them slowly, and is fully converted,
during its passage, into venous blood. When the influence of this nerve
is diminished or suspended, the vessels dilate, and the blood, passing
through them with greater rapidity, is not completely changed from the
arterial to- the venous condition.

Connection with Reflex Actions. — The influence of the sympathetic
nerve upon the thoracic and abdominal viscera has been only imperfectly
investigated. It undoubtedly serves as a medium of reflex action between
the sensitive and motor portions of the digestive, excretory, and gene-
rative apparatus ; and it is certain that it takes part in reflex actions
in which the cerebro-spinal system is also interested. There are accord-
ingly three different kinds of reflex action, taking place wholly or par-
tially through the sympathetic system, which may occur in the living
body.

1. Reflex actions taking place from the internal organs, through the
sympathetic and cerebro-spinal systems, to the voluntaiy muscles and
sensitive surfaces. — The convulsions of children are often due to the
irritation of undigested food in the intestinal canal. Attacks of indi-
gestion may also produce temporary amaurosis, double vision, stra-
bismus, and even hemiplegia. Nausea, and a diminished or capricious
appetite, are prominent symptoms of early pregnancy, induced by the
condition of the uterine mucous membrane.

2. Reflex actions taking place from the sensitive surfaces, through
the cerebro-spinal and sympathetic systems, to the involuntary muscles
and secreting organs. — Exposure of the integument to cold and wet is
often a determining cause of diarrhoea. Mental and moral impressions,
excited through the special senses, will affect the motions of the heart,
and disturb the acts of digestion and secretion. Terror, or an absorb-
ing interest of any kind, will produce dilatation of the pupil, and com-
municate in this way an unusual expression to the eye. Disagreeable
sights or odors, or even unpleasant occurrences, are capable of hastening
or arresting the menstrual discharge, or of inducing premature delivery.

3. Reflex actions taking place, through the sympathetic system, from
one part of the internal organs to another. — The contact of food with
the mucous membrane of the intestine excites a peristaltic movement in
its muscular coat. The mutual influence of the digestive, urinarj', and
internal generative organs upon each other is exerted through the
medium of the sympathetic ganglia and nerves. The variations of the
capillary circulation in different abdominal viscera, corresponding with
the activity or repose of their associated organs, are due to a similar
nervous influence. These phenomena are not accompanied by conscious
sensation, nor by any apparent intervention of the cerebro-spinal system.

CHAPTEE VIII.

THE SENSES.

THE senses are the endowments by which we perceive the physical
properties of external objects and the phenomena produced by their
various reactions, such as solidity, pressure, smoothness or inequality of
surface, temperature, light, sound, and sapid and odoriferous qualities.
All our information with regard to the objects of nature is obtained
through these channels, which are consequently the primitive source
of all conscious relation with the external world. Sensation alone in-
dicates merely the perception of some impression derived from without,
whatever may be its nature. The senses, on the other hand, form so
many subdivisions of the main function, each of which is devoted to
the perception of a particular class of physical properties or reactions.
They are divided into five different groups, namely : 1. General sensi-
bility. 2. The sense of taste. 3. The sense of smell. 4. The sense of
sight. 5. The sense of hearing.

General Sensibility.

General sensibility is that by which we appreciate the simpler physi-
cal properties of external objects, such as their consistency, roughness
or smoothness of surface, temperature, and mass. It is so called be-
cause it is generally diffused over the external integument, beside being
present in most of the mucous membranes near the surface. Notwith-
standing that this endowment includes the power of perceiving several
different kinds of impression, they are all, so far as we know, communi-
cated to the perceptive centres by the same nerves ; and the grade of
sensibility for all varies, as a general rule, in the same direction and to
the same degree in different parts of the body. The sensations thus
produced, though presenting some peculiarities by which they may be
distinguished from each other, are therefore naturally comprised under
the single head of general sensibility.

Sensations of Touch. — This is, perhaps, the least complicated form
of sensory impression, and is known as "tactile sensibility." It is
produced by the simple contact of a foreign body with the sensitive
surface, and gives information as to its solidity, its external configura-
tion, and its indifferent or irritating qualities. Although there is a
certain variety in these impressions, yet they evidently belong to the
same group, and there is no essential difference in the effect produced
by the contact of sharp-pointed instruments, and that caused by irri-
tating substances, like mustard, applied to the skin, the continuous or

(593)

594 THE SENSES.

interrupted galvanic current, pungent liquids placed upon the tongue,
or pungent vapors in the nasal passages. These are all impressions of
tactile sensibility, and depend upon a similar irritation- of the peripheral
nervous extremities.

The structures especially devoted to the exercise of tactile sensibility
are minute bulbous organs developed upon the terminal extremities of
the nerve fibres in the papillae of the skin and adjacent mucous mem-
branes, in each of which two situations they present certain distinguish-
ing features, though their essential character is the same in both. In
the skin, these organs are known as the tactile corpuscles. They are
elongated oval bodies, measuring, according to Kolliker, about -^ of a
millimetre in length by ^0 of a millimetre in thickness. They are
situated in the substance of certain of the papillae, with their long axes
placed longitudinally, and extending nearly to the free extremity of the
organ. They are not to be found in all of the papillae, since even at the
end of the index finger, where they are most abundant, according to
the observations of Meissner, not more than one papilla in four is pro-
vided with a tactile corpuscle. The papillae containing the corpuscles
are not supplied with bloodvessels ; while the remainder, constituting
the large majority, contain capillary blood-
vessels, but no tactile corpuscles. The tactile
corpuscle itself consists, 1st, of a sheath, ex-
hibiting a number of transverse nuclei, and
considered as representing a form of connec-
tive tissue; 2d, of an inclosed mass of trans-
parent, homogeneous material ; and, 3d, of
one or two medullated nerve fibres, which pass
upward from the superficial plexus of the skin
through the substance of the papilla, reach the
tactile corpuscle, wind round it in a spiral
direction toward its apex, and finally, losing
their medullary layer, terminate in some man-
™r »<* 7* disti"'«y ascertained. Tactile
puscie and nerve fibres. (Koi- corpuscles have been found, in man, upon the
dorsal and palmar surfaces of the hand and

foot, upon the nipple, and upon the anterior part of the forearm. As
their abundance in these different regions corresponds with the local
acuteness of sensibity, they are undoubtedly to be regarded as the special
organs of touch, though not perhaps the only form of nerve structure
capable of exercising this function.

In the conjunctiva, the red portion of the lips, the tongue, the sub-
lingual mucous membrane, and the glans penis, the organs of touch are
constituted by the terminal bulbs of the nerve fibres in these regions.
These organs differ from the tactile corpuscles mainly in their smaller
size and the greater simplicity of their structure. In man, according to
Kolliker, they are for the most part nearly spherical in form, though
in the inferior animals they are often elongated and club-shaped. They

GENERAL SENSIBILITY. 595

consist of a very thin, external envelope of connective tissue, inclosing,
as in the tactile corpuscle, a mass of homogeneous or finely granular
substance. The medullated nerve fibre which penetrates the bulb, loses
its medullary layer at its entrance, and runs through the central homo-
geneous substance, to terminate by a free extremity near its apex.
Both the tactile corpuscles and the terminal bulbs are therefore anatomi-
cal forms, in which the axis cylinder of the sensitive nerve fibre termi-
nates, after divesting itself of its medullary layer.

The tactile sensibility varies considerably in different regions of the
integument. The best method of appreciating this variation is that
adopted by Weber and Valentin. It consists in applying to different
parts the points of a pair of compasses, tipped with suitable pieces of
cork. If these points be applied to the skin when fixed at very short
distances apart, the two sensations cannot be accurately distinguished
from each other but are blended into one ; and the impression thus pro-
duced is that of a single contact. The minimum distance at which the
two points can be distinguished by the integument thus becomes a
measure of its sensibility at that spot. The observations of Valentin,1
which are the most varied and complete in this respect, give the follow-
ing as the limits of distinct perception in different regions :

DISTANCE AT WHICH TWO POINTS MAY BE SEPARATELY DISTINGUISHED.

At the tip of tongue 1.00 millimetre.

" palmar surface of tips of fingers . . 1.50

" " " of second phalanges . 3.24 "

of first phalanges . . 3.44

" dorsum of tongue 5.22 "

" dorsal surface of fingers ... 8.12 "

cheek 9.46

back of hand 14.50

skin of throat 17.27

dorsum of foot 26.10

" front of sternum 33.07 "

middle of back 50.43

This method does not necessarily give an absolute measure of tho
aculeness of sensibility in the different regions, since the two points
might be less easily distinguished from each other in any one region,
and yet the absolute amount of sensation produced might be as great
as in the surrounding parts; but it undoubtedly affords an accurate
estimate of the delicacy of tactile sensation, by which we distinguish
slight inequalities in the surface of solid bodies. There is every reason
to believe that the two qualities of delicacy and acuteness of local sensi-
bility correspond with each other in their degree of development in
various localities; since the regions where tactile sensibility is most
delicate are frequently found to be also those where the amount of
sensation is the greatest. A feeble galvanic current msy be perceived

1 In Todd's Cyclopaedia of Anatomy and Physiology, vol. iv., article on Touch.

596 THE SENSES.

when applied to the tips of the fingers, though it will produce no impres-
sion on the rest of the limbs or trunk ; and one which is too faint to be
distinguished by the fingers may be perceptible at the tip of the tongue.

Certain parts of the body, furthermore, are especially well adapted
for use as organs of touch, not only on account of their acute sensibility,
but also owing to their conformation and mobility. In man, the hands
are the most favorably constructed for this purpose, by the numerous
articulations and varied power of movement of the fingers, b}r wMch
they may be applied to solid surfaces of any form, and brought succes-
siveljT in contact with all their irregularities and depressions. We are
thus enabled to obtain the most precise information as to the texture,
consistency, and configuration of foreign bodies.

But the hands are not the exclusive organs of touch, even in man,
and in the lower animals the function is mainly performed by other parts.
In the cat and in the seal, the long bristles seated upon the lips are used
for this purpose, each bristle being connected at its base with a nervous
papilla ; and in the elephant the end of the nose, which is developed
into a flexible and sensitive proboscis, is employed as the principal organ
of touch. This function, therefore, may be performed by one part of
the body or another, provided the accessory organs be developed in a
favorable manner.

About the head and face, the sensibility of the skin is principally de-
pendent upon branches of the fifth pair. In the neck, trunk, and extre-
mities it is due to the sensitive fibres of the cervical, dorsal, and lumbar
spinal nerves. It exists, to a considerable extent, in the mucous mem-
branes of the mouth and nose, and of other passages leading to the in-
terior. The sensibility of the mucous membranes is most acute in parts
supplied by branches of the fifth pair, namely, the conjunctiva, anterior
part of the nares, inside of the lips and cheeks, and the anterior two-
thirds of the tongue. The tactile sensibility, which is resident in the
skin and in a certain portion of the mucous membranes, diminishes in
degree from without inward, and disappears altogether in the internal
organs which are not abundantly supplied with nerves from the cerebro-
spinal sj'stem.

While the general sensibility of the skin, and of the mucous mem-
branes, varies in acuteness in different parts of the bod3r, it is every-
where the same in kind. The tactile sensations produced by the con-
tact of a foreign body are of the same nature, whether they be felt by
the tips of the fingers, the dorsal or palmar surfaces of the hands, the
lips, cheeks, or any other part of the integument. Their only difference
is in the intensity and distinctness of the impressions produced.

The appreciation of the weight or mass of a foreign body is obtained
from the degree of pressure which it causes upon the integument, when
supported by the hand or other part of the body. It does not appear
that any other kind of sensation is necessary for this purpose, although
we generally also employ, in estimating a weight, the degree of muscular
effort required to sustain it. If the hand, however, be rested upon some

GENEKAL SENSIBILITY. 597

solid support, and the foreign body placed upon it, its weight is then
appreciated solely by the amount of pressure which it causes. The
sensation of muscular contraction is itself a result, so far as we can
judge, of the physical impression produced upon the sensitive nerve
fibres in the muscular tissue ; and there is nothing to indicate that it
differs essentially from that caused by pressure upon the nerves of the
integument.

Sensations of Temperature. — The appreciation of temperature is also
most highly developed, as a general rule, in those parts which have the
greatest share of tactile sensibility. The difference in this respect be-
tween the integument of the face and that of the scalp is very marked ;
since hot applications may be readily borne upon the scalp, which would
be nearly or quite intolerable upon the face. The extent of surface ex-
posed to a given temperature has also an influence upon the effect pro-
duced, and a moderate degree of either warmth or cold applied over a
considerable portion of the skin is much more readily perceived than
if confined to a limited region. There is evidence that the impres-
sions of temperature and those of touch, if transmitted by the same
fibres, depend upon two different forms of nervous excitation, or are
received by different peripheral nervous structures ; since abundant
instances have been observed in which one of these two kinds of sensi-
bility was impaired independently of the other. In various forms of
paralysis, tactile sensibility may be lost while that of temperature re-
mains ; or, on the other hand, the power of appreciating temperatures
may disappear while impressions of contact continue to be perceived.1

Sensations of Pain. — The sense of pain is different in character from
that caused by tactile impressions or by variations in temperature. It
is caused by any exaggerated mechanical irritation or by the application
of excessive heat or cold ; but in all these instances, when the intensity
of the impression rises above a certain point, the ordinary perceptions
produced by it disappear, and that of pain takes their place. Thus if
the blade of a knife or the point of a needle be placed gently in contact
with the skin, we perceive, by means of tactile sensibility, the character
and form of its surface. But if the pressure be increased beyond a cer-
tain degree, or if the integument be actually wounded, we obtain no pre-
cise information of the physical qualities of the foreign body, and are
only conscious of the pain which results. The appreciation of cold or
warmth, in like manner, is only possible within moderate limits ; and
when the variations are so excessive as to produce pain, all accurate
perception of the degree of temperature is lost. The contact of a red-
hot iron and that of one much below the freezing point of water produce
sensations which are not essentially different from each other, and which
are marked only by their painful character.

It is not known whether the sensation of pain be confined to nerve

1 Brown-Sequard, Physiology and Pathology of the Central Nervous System.
Philadelphia, 1860, pp. 84, 98, 125.

598 THE SENSES.

fibres which are distinct from those endowed with other forms of general
sensibility, but it is certain that it may be preserved or lost independently
of the other varieties. The anaesthesia which is produced by the inha-
lation of ether or chloroform may be carried to such a point that the
capacity for feeling pain is abolished, while tactile sensibility remains ;
so that the wounds caused by puncturing or cutting instruments may
be felt, though unaccompanied by any sense of suffering. Similar ob-
servations have been made in cases of paralysis where, it is well known,
the patient may perceive the contact of foreign bodies or the prick of
a pin, but at the same time may not experience from them any painful
sensation ; or, on the other hand, the sense of pain may persist in the
affected parts, while that of touch is diminished or lost.1 Notwith-
standing this apparent independence of the immediate conditions neces-
sary for the sensation of pain, it is transmitted by fibres of the same
nerves, belonging to the cerebro-spinal system, which convey ordinary
impressions ; and nerves which are endowed with the most acute tactile
sensibility, like the branches of the fifth pair, are also capable, when
irritated by injury or disease, of giving rise to the severest painful im-
pressions.

Mode of Action of the Senses in general. — There are certain facts
connected with the exercise of general sensibility which are also com-
mon to the operation of all the senses, and which are of sufficient im-
portance to be considered by themselves.

In the first place, an impression of any kind, made upon a sensitive
organ, remains for a short time after the removal of its immediate
cause. The state of excitement produced in the nervous expansions
and fibres has a certain degree of persistence, which is longer in duration
for some organs than for others, but which exists in some degree for
all. The sense of simple contact or pressure of a foreign body upon
the skin, especially if it be somewhat forcible and continued, remains
for a perceptible interval after the foreign body is removed. The feel-
ing of cold or warmth, from the application of ice or heated liquids,
lasts more or less after the application is discontinued. Even in the
case of sight and hearing it is easy to verify the same fact ; and the
duration of continuance of the nervous impression, though very short,
has been found in many instances susceptible of measurement.

Secondly, the organs of sense after a time become accustomed to a con-
tinued impression, so that the}7 no longer perceive its existence. If a
uniform pressure be exerted upon any part of the body, the compressing
substance at last fails to excite sensation, and we remain unconscious of
its existence. In order to attract our notice, it is necessary to increase
or diminish the pressure or to change its locality or direction.

The olfactory apparatus also becomes habituated to odors, whether
agreeable or disagreeable in their nature, in the confined air of a close

1 Brown-Sequard, Physiology and Pathology of the Central Nervous System.
Philadelphia, 1860, pp. 97, 126. Hammond, Diseases of the Nervous System.
New York, 1871, p. 82.

GENERAL SENSIBILITY. 599

apartment ; although, on first entering from without, the attention may
have been attracted by them in a decided manner. A continuous and
uniform sound, like the steady rumbling of carriages, or the monotonous
hissing of boiling water, becomes after a time inaudible ; but as soon as
the sound ceases, we notice the alteration, and our attention is at once
excited. The senses, accordingly, receive their stimulus more from the
variation and contrast of external impressions, than from these impres-
sions themselves.

Another important particular, in regard to the senses, is their capacity
for education. The touch can be so trained that the blind may read
words and sentences by its aid, in raised letters, where an ordinary
observer would hardly detect more than a slight inequality of surface.
The educated eye of the artist or the naturalist will distinguish varia-
tions of color, size, and outline, quite inappreciable to ordinary vision ;
and the senses of taste and smell, in those who are in the habit of
examining wines and perfumes, acquire a similar superiority of discrimi-
nating power.

In these instances, it is not the organ of sense itself which becomes
more perfect in organization, or more susceptible to sensitive impres-
sions. The functional power, developed by cultivation, depends upon
the increased delicacy of the perceptive and discriminating faculties.
It is a mental and not a physical superiority which gives the painter or
the naturalist a greater facility for distinguishing colors and outlines,
and which enables the medical observer to detect nice variations in the
sounds of the heart or the respiratory murmur of the lungs. The
impressions of external objects, to produce their complete effect, must
first be received by a sensitive apparatus, which is perfect in organiza-
tion and functional activity ; and, secondly, they must be subjected to
the action of an intelligent perception, by which their nature, source,
and relations are fully appreciated.

Beside the endowment of general sensibility distributed over the
integument, there are other faculties by which we appreciate particular
physical qualities or phenomena, namely, those of taste, odor, light, and
sound, the exercise of which is confined to special organs, having a struc-
ture adapted to that purpose alone. These are called the special senses.
Their organs differ from the general integument in their more compli-
cated structure and in the delicate and varied character of the functions
which they perform. They are incapable of feeling pain, similar to that
perceived by the nerves of general sensibilit}', though they may com-
municate disagreeable as well as pleasing impressions. The light, how-
ever intense, has no perceptible effect when allowed to fall upon the
skin, and causes a sensation only when admitted to the eye. The impres-
sion of sound is appreciated only by the ear, and that of odors only by
the olfactory membrane. These different sensations, therefore, are not
merely exaggerations of ordinary sensibility, but are peculiar in their
nature, and are in relation with distinct properties of external objects.

600 THE SENSES.

Each organ of special sense consists — First, of a nerve, endowed with
the special sensibilitj' required for its peculiar function ; and, Secondly,
of certain accessory parts, forming an apparatus adapted to aid in the
performance of this function, and render it more delicate and complete.

Sense of Taste.

The sense of taste is, in some measure, intermediate in character
between the functions of general and special sensibility. First, the
organ by which it is exercised forms a part of the mucous membrane
lining the commencement of the alimentary canal, furnished with vas-
cular and nervous papillae analogous in structure to those of the general
integument. Secondly, this mucous membrane is also endowed with
general sensibility. Although it is highly probable that certain minute
formations in its epithelial layer, known as " taste buds," may be espe-
cially connected with the perception of savors, there is thus far no cer-
tainty in this respect ; and in any case the tactile and gustatory sensi-
bilities are closely intermingled in the substance of the mucous mem-
brane. Thirdly, the sensibility of taste is not confined to the fibres of
one special and distinct nerve, but resides in portions of two, namely,
the lingual branch of the fifth pair and the glossopharyngeal nerve,
which also supply general sensibility to the corresponding parts.
Fourthly, this sense gives rise to impressions only from the actual con-
tact of sapid substances with the mucous membrane, and can establish
no communication with objects at a distance ; and Fifthly, though some
of the impressions derived from this source are of a distinct and special
character, others, like the taste of oily or mucilaginous substances, differ
but little in kind from those of tactile sensibility.

The sense of taste is localized in the mucous membrane of the tongue,
the soft palate, and the pillars of the fauces. The tongue, which is more
particularly the seat of this sense, is a flattened, leaf-like muscular organ,
attached to the inner surface of the symphysis of the lower jaw in front,
and to the os hyoides behind. It has a vertical sheet or lamina of fibrous
tissue in the median line which serves as its framework, and is provided
with longitudinal, transverse, and radiating muscular fibres, by which it
can be elongated, retracted, and moved in every direction.

The mucous membrane of the fauces and posterior third of the tongue,
like that lining the cavity of the mouth, is covered with vascular papillae,
analogous in structure to those of the skin, but imbedded and concealed
in the smooth layer of epithelium forming the surface of the organ.
Upon the dorsum of the tongue, about the junction of its posterior and
middle thirds, there is a double row of rounded eminences, arranged in
a V-shaped figure, running forward and outward, on each side, from the
situation of the foramen caecum ; and from this point forward, the
mucous membrane is covered with thickly-set papillae, containing nerves
and bloodvessels, and giving a soft velvety texture to the surface of the
organ.

The lingual papillae are of three different kinds. First i\\Q filiform

SENSE OF TASTE. 601

papillae, which are the most numerous, and which cover most uniformly
the upper surface of the tongue. They are long and slender, and are
covered with horny epithelium, usually prolonged into filamentous tufts.
At the edges of the tongue they are often united into parallel ranges
or ridges of the mucous membrane. Secondly, the fungiform papillae.
These are thicker and larger than the foregoing, of a club-shaped
figure, and covered with soft epithelium. They are most abundant
at the tip of the tongue, but may be seen elsewhere on the surface of
the organ, scattered among the filiform papillae. Thirdly, the circum-
vallate papillae. These are the rounded eminences, eight or ten in
number, which form the V-shaped figure near the situation of the fora-
men caecum. Each consists of a central eminence, surrounded by a wall
or circumvallation, from which they derive their name. The circum.
vallation, as well as the central eminence, has a structure similar to that
of the fungiform papillae.

The sensitive nerves of the tongue, as above mentioned, are two in
number, namely, the lingual branch of the fifth pair, and the lingual
portion of the glossopharyngeal. The lingual branch of the fifth pair
enters the tongue at the anterior border of the hyoglossal muscle. Its
branches pass from below upward and from behind forward, between the

Fig. 187.

DIAGRAM OP THE TONGUE, with its sensitive nerves and papillae. — 1. Lingual branch
of the fifth pair. 2. Glossopharyngeal nerve.

muscular bundles of the organ, until they reach its mucous membrane.
The nerve fibres then penetrate the lingual papillae, where they termi-
nate, partly in the " terminal bulbs" already described (p. 594), and
partly in a manner not yet distinctly ascertained.

The lingual portion of the glossopharyngeal nerve passes into the
tongue below the posterior border of the hyoglossus muscle. It then
divides into various branches, which pass through the muscular tissue,
and are distributed to the mucous membrane of the base and sides of
the organ.

The mucous membrane of the base of the tongue, of its edges, and
of its under surface near the tip, as well as that of the mouth and fauces
generally, is also supplied with mucous follicles furnishing a viscid
39

602 THE SENSES.

secretion by which its free surface is lubricated. The muscles of the
tongue are animated exclusive^ by filaments of the hypoglossal nerve.

The exact seat of the sense of taste has been determined by placing in
contact with different parts of the mucous membrane a small sponge,
moistened with a solution of some sweet or bitter substance. The ex-
periments of Duges, Verniere, and Longet, have shown that taste resides
in the whole superior surface, the point and edges of the tongue, the soft
palate, fauces, and part of the pharynx. The base, tip, and edges of
the tongue possess the greatest amount of sensibility to savors, the
middle portion of its dorsum less, and its inferior surface little or none.
As the whole anterior part of the organ is supplied by the lingual branch
of the fifth pair alone, and the whole of its posterior portion by the
glossopharyngeal, it follows that the sense of taste is derived from both
these nerves.

Furthermore, the tongue is supplied, at the same time and by the same
nerves, with general sensibility and with the special sensibility of taste.
The general sensibility of the anterior portion of the tongue, and that
of the branch of the fifth pair with which it is supplied, are sufficiently
well known. Section of the fifth pair destroys the sensibility of this
part of the tongue as well as that of the rest of the face. Longet found
that after division of the lingual branch of this nerve, the mucous mem-
brane of the anterior two-thirds of the tongue might be cauterized with
a hot iron or with potassium hydrate in the living animal, without pro-
ducing any sign of pain. Reid, on the other hand, determined that
ordinary sensibility exists in a marked degree in the glossopharyngeal
nerve, and is supplied by it to the parts in which its branches are dis-
tributed.

A distinction is to be made, in the action of foreign substances taken
into the mouth, between the special impressions derived from their sapid
qualities, and the general sensations produced by their ordinary physical
properties. As the same substance is often capable of exciting both
tactile and gustatory impressions, the two are sometimes liable to be
confounded with each other The truly sapid qualities, which we per-
ceive by the special sense of taste, are savors, designated by the terms
sweet, bitter, salt, sour, alkaline, and the like. Beside these, however,
there are other characters, belonging to various articles of food, which
partake largely of the nature of ordinary physical properties, appreci-
able by means of general sensibility. A starchy, oily, or mucilaginous
taste, when uncomplicated with additional savors, is but little different
in kind from the tactile impressions produced by the same substances.
The quality of pungency, communicated to the food by the use of con-
diments, as pepper or mustard, is one which is appreciated altogether
by the general sensibility. The styptic taste seems to be a combination
of an ordinary astringent effect with a peculiar excitement of the gus-
tatory nerves, analogous to that caused by the galvanic stimulus.

Furthermore, the taste or savor of a substance is to be distinguished
from its odoriferous properties or flavor. In most aromatic articles of

SENSE OF TASTE. 603

food, such as tea and coffee, and the various kinds of wine, a great part
of the effect produced is due to the aroma or smell which reaches the
nares during the act of swallowing. Even in many kinds of solid food,
such as freshly cooked meats, their odor takes a very important share in
producing the impression on the senses. If, during the deglutition of
such substances, the nares be compressed so as to suspend in great
measure the sense of smell, their ordinary flavor becomes nearly imper-
ceptible ; and a similar effect is produced by catarrhal inflammation of
the nasal passages, which suspends more or less completely the sensi-
bility of the olfactory membrane.

Necessary Conditions of the Sense of Taste. — There are certain con-
ditions requisite for the production of gustatory impressions, beside the
integrity of the organ by which they are received.

In the first place, the sapid substance, in order that its taste may be
perceived, must be brought in contact with the mucous membrane in a
state of solution. So long as it remains solid, however marked a savor
it may possess, it gives no other impression than that of a foreign body
in contact with the tongue. But if applied in a liquid form, it spreads
over the surface of the mucous membrane, and its taste is perceived.
Thus it is only the liquid and soluble portions of the food which are
tasted, such as the animal and vegetable juices and the soluble salts.
Saline substances which are insoluble, such as calomel or lead carbonate,
when applied to the tongue, produce no gustatory sensation.

The mechanism of the sense of taste is, in all probability, a direct
and simple one. The sapid substances in solution penetrate the lingual
papillae by endosmosis, and, coming in contact with the terminal nervous
filaments, excite their sensibility by uniting with the substance of which
they are composed. The rapidity with which endosmosis will take
place under certain conditions is sufficient to account for the instanta-
neous perception of sapid substances when introduced into the cavity
of the mouth.

It is on this account that a free secretion of the salivary fluids is
essential to the full performance of the gustatory function. If the
mouth be dry and parched, the food seems to have but little taste.
When the saliva, on the other hand, is freely secreted, it mixes readily
with the food in mastication, and assists the solution of its sapid ingre-
dients; and the fluids of the mouth, impregnated with the savory sub-
stances, are absorbed by the mucous membrane, and excite the gusta-
tory nerves.

An important part is also taken in this process by the movements of
the tongue. By these movements the food is carried from one part of
the mouth to another, pressed against the hard palate, the gums, and
the cheeks, its solution assisted, and the penetration of fluids into the
papillae more rapidly accomplished. If powdered sugar, or a bitter
extract, be simply placed upon the dorsum of the tongue, little or no
effect is produced ; but when pressed by the tongue against the roof of
the moutli, as in eating or drinking, its taste is immediately perceived.

604: THE SENSES.

This effect is easily explained ; since it is well known bow readily move-
ment over a free surface, combined with slight friction, will facilitate
the solution and imbibition of solid substances. The nervous papillae
of the tongue may therefore be regarded as the essential organs of taste,
and the lingual muscles as its accessory organs.

Impressions of taste made upon the tongue remain for a certain time
afterward. When a very sweet or a very bitter substance is taken into
the mouth, its taste is retained for several seconds after it has been
ejected or swallowed. Consequently, if several different savors be pre-
sented to the tongue in rapid succession, we become unable to distinguish
them, and they produce only a confused impression, made up of the
union of various different sensations. The taste of the first, remaining
in the mouth, is mingled with that of the second, the taste of both with
that of the third, and so on, until neither one can be distinguished. It
is notoriously impossible to recognize several different kinds of wine
with the eyes closed, if they be repeatedly tasted in quick succession.

If the substance first tasted have a particularly marked savor, its
impression will preponderate over that of the others. This effect is
especially produced by substances which excite the general sensibility
of the tongue, such as acrid or stimulating powders; and it belongs,
in the greatest degree, to substances which are at the same time sapid,
pungent, and aromatic, like sweetmeats flavored with the volatile oils.
Advantage is sometimes taken of this in the administration of disagree-
able medicines. By first taking into the mouth some highly flavored
and pungent substance, nauseous drugs may be swallowed immediately
afterward with but little perception of their disagreeable qualities.

Sense of Smell.

The distinguishing character of the sense of smell is that it gives us
intelligence of the physical quality of bodies in a gaseous or vaporous
condition. Thus by its aid it is possible to detect the existence of an
odoriferous substance at a distance, and although it may be concealed
from sight. The minute quantity of volatile material emanating from
it, and pervading the atmosphere, produces, by contact with the olfactory
membrane, the special sensation of smell. The sense of smell differs,
furthermore, from that of taste in being more distinctly localized. While
the gustatory sensibility is distributed over the whole mucous mem-
brane covering the dorsum and base of the tongue, and is supplied to
its various parts by two different sensitive nerves, that of smell is con-
fined to the upper portion of the nasal passages and is dependent on
the filaments of a single special nerve.

The mucous membrane covering the superior and middle turbinated
bones and the upper part of the septum nasi, which is alone capable of
receiving odorous impressions, and is limited by a tolerably well-defined
outline, is known as the olfactory membrane. It is easily distinguish-
able from that of the rest of the nasal passages: 1st, by its color, which
in man, the sheep, and the calf is yellow, but in most of the other mam-

SENSE OF SMELL.

605

Fig. 188.

malia has a brownish tinge; 2dly, in its softer and more succulent
consistenc}7^ ; and 3dly, in the greater thickness, not only of the whole
membrane but also of its epithelial layer. According to Kolliker, the
epithelium of the olfactory membrane, in the sheep and the rabbit, is
from 60 to 66 per cent, thicker than that of the remaining nasal mucous
membrane. It also differs, according to the same observer, in the
character of its surface. In most of the quadrupeds the epithelium of
the Schneiderian mucous membrane generally is covered with vibrating
cilia, which are absent in the olfactory portion ; though in man the vibrat-
ing cilia may also be found in the epithelium of the olfactory portion
itself. This difference of structure is probably connected with the
inferior acuteness of the sense of smell in man, as compared with many
of the lower animals.

The nasal passages are provided with nerves • from three different
sources.

I. The first and most important of these are the filaments of the
olfactory nerve (Fig. 188, i). They are derived immediately from the
olfactory bulb, which rests upon the cribriform plate of the ethmoid
bone, and from which they penetrate the nasal passages through the
perforations in this bony
lamina. An important pecu-
liarity, however, shows itself
in the nerve fibres of this
region. While the substance
of the so-called olfactory
nerves within the cranial
cavity, as well as that of the
olfactory bulb, contains dark
bordered medullated nerve
fibres, like those in other
parts of the white substance
of the brain, the filaments
which are given off from the
under side of the olfactory
bulb, and are distributed to
the Olfactory membrane, Con- DISTRIBUTION OF NEBVES i* THE NASAL
tain Only pale, flattened, PASSAGES.— 1. Olfactory bulb, with its nerves. 2.

nucleated nerve-fibres with- ™™ ^JiT™11 °f the fifth pair< 3< sPhen°-Palatine
out a medullary layer. The

main question of interest in regard to them is that of their final mode
of termination; but this, as in so many other similar cases, has thus far
escaped absolute demonstration. The branches of the olfactory nerves
frequently divide and subdivide, forming microscopic plexuses in the
substance of the olfactory membrane ; and the finest nervous ramifica-
tions are to be followed without doubt nearly to the epithelial surface
f the membrane itself. According to the researches of Schultze, con-
firmed by these of Kolliker and Babuchin, the epitheMum of this part

THE SENSES.

consists of two different kinds of elongated cells, both standing verti-
cally upon the mucous membrane, and closely adherent to each other by
their lateral surfaces. One portion are analogous in form to ordinary
nucleated columnar epithelium cells ; the remainder are very slender and
filamentous, except in their middle portion, at the situation of their oval
nucleus. The deeper portion of these cells, which is also more slender
than the rest, has been found to resemble the material of the nerve fibres
in its reaction with solutions of gold chloride ; but a direct continuity
of substance between the fibres and the cells has not been shown in an
unequivocal manner.

There is no doubt that the nerve filaments given off from the olfac-
tory bulb are the special agents for communicating impressions of smell,
and that they are the only ones endowed with olfactory sensibility.
This follows from their exclusive and abundant distribution to the olfac-
tory portion of the nasal membrane, from their comparatively large
development in animals of acute smell, from the absence of this sense
in cases of congenital absence of the olfactory bulbs, and from its loss
in animals after their destruction (p. 515). So far as we can judge
from the results of experiment, they are not capable of receiving or
transmitting any other kind of sensibility than that excited by odor-
iferous substances.

II. The second set of nerves distributed to the nasal passages con-
sists of the nasal branch of the fifth pair, and its ramifications (Fig.
188, 2). This nerve, after entering the cavity of the nose just in advance
of the cribriform plate of the ethmoid bone, sends its filaments mainly
to the mucous membrane covering the inferior turbinated bone and the
walls of the inferior meatus, which are thus supplied with general sen-
sibility, though they are destitute of the power of smell. JSome filaments
from this nerve, however, are also continued into the mucous membrane
of the olfactory region, where they run in proximity to those of the
olfactory nerves; and this region, according to the observations of
Babuchin,1 possesses consequently a certain amount of general sensi-
bility, though much less than the remainder of the nasal passages.

III. The third set are those derived from the spheno-palat ine gan-
glion of the sympathetic (Fig. 188, 3) which supply the mucous mem-
brane of the posterior part of the nasal passages and the muscles aiding
in the closure of the posterior nares. Finally, the muscles which regu-
late the expansion of the anterior nares are supplied by filaments of the
facial nerve.

Necessary Conditions of the Sense of Smell In order to produce

an olfactory impression, the emanations of the odoriferous body must
be drawn freely through the nasal passages. As the sense of smell is
situated only in the upper part of these passages, whenever an unusu-
ally faint or delicate odor is to be perceived, the air is forcibly directed
toward the superior turbinated bones, by a peculiar inspiratory move-
In Strieker's Manual of Histology, Buck's Edition. New York, 1872, p. 799.

SENSE OF SIGHT. 607

ment of the nostrils, a movement which is very marked in many of the
lower animals. As the odoriferous vapors arrive in the upper part of
the nasal passages, they are probably dissolved in the secretions of the
olfactory membrane, and thus brought into relation with its nerves.
Inflammatory disorders consequently interfere with the sense of smell,
both by altering the secretions of the part, and by producing a tume-
faction of the mucous membrane, which prevents the free passage of
air through the nasal fossae.

A distinction is also to be made between the perception of true odors.
and the excitement of the general sensibility of the Schneiderian mu-
cous membrane by irritating substances. Some of the true odors are
similar in their nature to impressions perceived by the sense of taste.
Thus we have sweet and sour smells, though none corresponding to the
alkaline or the bitter tastes. Most of the odors, however, are of a pe-
culiar nature and are difficult to describe ; but they are always distinct
from the simply irritating properties which may belong to vapors as
well as to liquids. Thus, pure alcohol has little or no odor, and is only
stimulating to the mucous membrane ; while the odor of wines, cordials,
and perfumes, is communicated to them by other ingredients of a vege-
table origin. The vapor of pure acetic acid is simply irritating ; while
vinegar has also a peculiar odor, derived from its vegetable constituents.
Ammonia is an irritating gas, but contains no proper odoriferous prin-
ciple.

The sensations of smell, like those of taste, remain for a certain time
after they have been produced, and modify in this way other less strongly
marked odors presented afterward. Asa general rule, the longer the
olfactory membrane is exposed to a particular odor, the longer its
effect continues ; and in some cases it may be perceived for many hours
after the odoriferous substance has been removed. Odors, however, are
particularly apt to remain after the removal or destruction of the source
from which they were derived, owing to the facility with which the}' are
entangled by porous substances, such as plastered walls, carpets, hang-
ings, and woollen clothes.

The sense of smell, which is only moderately developed in the human
species, is excessively acute in some of the lower animals. Thus, the
clog will not only discover game and follow it by the scent, but will dis-
tinguish particular individuals by their odor, or recognize articles of
dress belonging to them by the minute quantity of odoriferous vapor
adhering to their substance.

Sense of Sight.

This is the most remarkable of all the senses, both for the special
nature of the impressions which it receives, the complicated structure
of its apparatus, and the variety and value of the information which it
affords with regard to external objects. It is by this sense that we
receive the impressions of light and color, with all their modifications
of intensity and combination, and acquire our principal ideas of form,

608

THE SENSES.

space, and movement. The organs of touch, taste, and smell, in order
to perform their functions, must be placed in actual contact with the
foreign substances which excite their activity ; and even that of hearing
is affected only by the sonorous vibrations of the atmosphere, or of some
other solid or fluid medium. But the eye is equally sensitive to the
impressions of light, whether it come from near or remote objects, or
even from the immeasurable distances of the fixed stars. It is also
superior to the other organs of special sense in the rapidity of its action,
and in the delicacy of the distinctions which it is capable of making
in the physical qualities of external objects ; and it affords the most
continuous and indispensable aid for all the ordinary occupations of
life.

Organ of Vision. — The eyeball consists of a spheroidal fibrous sac,
the sclerotic coat (Fig. 189, 2), filled with fluid and gelatinous material,

Fig. 189.

HORIZONTAL SECTION OF THE RIGHT EYEBALL.—!. Optic nerve. 2. Sclerotic
coat. 3. Cornea. 4. Canal of Schlemm. 5. Choroid coat. 6. Ciliary muscle. 7. Iris. 8.
Crystalline lens. 9. Retina. 10. Hyaloid membrane. 11. Canal of Petit. 12. Vitreous
body.

provided anteriorly with a transparent portion, the cornea (s), and
lined at its posterior part with a nervous expansion, the retina (s),
which is sensitive to light, and which receives the luminous rays admit-
ted through the cornea. The cavity of the eyeball is therefore like that
of a room with but one window, where all the light which enters from the
front necessarily strikes the back wall of the apartment. There are, in
addition to the above-mentioned parts, a transparent refracting body
with convex surfaces, the crystalline lens (s), by which the light is

SENSE OF SIGHT. 609

concentrated at the level of the retina ; a perforated muscular curtain
or diaphragm, the iris (7), placed in front of the lens,' which regulates
the quantity of light admitted through its central orifice, the pupil ; and
finally a vascular membrane with an opaque layer of blackish-brown
pigment, the choroid (s), which lines the whole inner surface of the
sclerotic and the posterior surface of the iris, thus preventing reflec-
tions within the eye, and absorbing all the light which has once passed
through the substance of the retina. The construction of the eyeball,
in its general arrangement as an organ of vision, is not unlike that of
a photographic camera; where the sensitized plate at the back part
represents the retina, the blackened inner surface of the box the choroid,
wrhile the lenses of the tube in front perform the office of the crystalline
lens and cornea of the eyeball.

Sclerotic Coat. — The sclerotic, so named from its toughness and re-
sistance, is the external coat and protective membrane of the eyeball. It
is composed of condensed layers of connective tissue, similar to those
of the fasciae and membranous tendons in general ; and toward its an-
terior third it receives the tendons of the external muscles of the eyeball,
which become fused with its substance. Posteriorly it is continuous
with the neurilemma of the optic nerve (Fig, 189, i), which penetrates it
from behind at its point of entrance into the eyeball. A portion of the
sclerotic is visible anteriorly through the conjunctiva, forming the so-
called "white" of the eye.

Cornea. — The cornea, which derivesMts name from its firm consistencjr
and homogeneous appearance, resembling that of horn, forms the anterior
part of the wall of the eyeball. It is inserted into the nearly circular
space left at this situation by the deficiency of the sclerotic, with the
texture of which it is continuous at its edges ; the difference in the phy-
sical appearance of the two being that the sclerotic is white and opaque,
while the cornea is colorless and transparent, so that the colored iris
and dark pupil are visible through its substance. The surface of the
cornea has a sharper curvature than that of the sclerotic, so that it pro-
jects from the front of the eyeball, like a smaller dome set upon a larger
one. Its outline, where it joins the edge of the sclerotic, is a little oval
in form, the transverse diameter of the cornea, in man, being slightly
longer than the vertical. At its centre, it is about 0.8 millimetre in
thickness, becoming a little thicker at its edges. Its anterior surface is
kept polished and brilliant by the watery secretion of the lachrymal
glands, distributed over it by the frequent movements of the eyeball
and the lids.

At the outer border of the cornea, where it joins the sclerotic, and
where the tissues of the two membranes pass into each other, there is a
small cavit}', running, in the form of a circular canal, the canal of
Schlemm (Fig. 189, 4), through the thickness of this part of the wall
of the eyeball. The inner wall of the canal of Schlemm is composed of
elastic and tendinous tissue, and gives attachment to the fibres of the
ciliary muscle on the one hand, and on the other to the outer border of

610 THE SENSES.

the iris. The canal itself is regarded by most anatomists as occupied
by a venous plexus, which receives veins from the ciliary muscle and
from the anterior part of the sclerotic.

Choroid. The choroid coat is a vascular and pigmentary membrane,

lining the inner surface of the sclerotic, and presenting anteriorly a thick-
ened portion, the " ciliary body." The inner part of the ciliary body
is thrown into a series of radiating folds, the " ciliary processes," which
surround the borders of the crystalline lens. The internal surface of the
choroid is occupied by a layer of hexagonal nucleated cells, closely packed
side by side, and filled with granules of blackish-brown pigment. Similar
pigment is also deposited, though less abundantly, in the substance and
near the external surface of the choroid. At its anterior part, the cho-
roid is separated from the internal surface of the sclerotic by the ciliary
muscle (Fig. 189, e). This muscle is composed of unstriped fibres, which
arise from the inner wall of the canal of Schlemm, at the junction of
the sclerotic and cornea, and thence diverge in a radiating direction,
outward and backward, to be inserted into the external surface of the
choroid, at the point where it begins to pass into the folds of the ciliary
processes. At the anterior and inner part of the muscle there are also
bundles of circular fibres, running parallel with the margin of the cornea.
The whole muscle is thus composed of two parts ; namely, an internal
circular, and an external radiating portion, the fibres of which are more or
less interwoven with each other at the inner edge of the muscular layer.

Iris. — The iris is a variously colored membrane, extending across
the antero-posterior axis of the eyeball, attached by its external border
to the inner wall of the canal of Schlemm, and presenting at its centre
the nearly circular orifice of the pupil. It consists of connective and
muscular tissue, with an abundant supply of bloodvessels, and is covered
on its posterior surface by a layer of blackish-brown pigment cells, con-
tinuous with that of the choroid. The color of the iris, which appears,
in different individuals, blue, gray, brown, or black, depends upon the
abundance and disposition of its pigmentary elements. In gray and blue
eyes, the visible hue of the iris depends upon the diffused light of its
semi-transparent tissues, seen against the dark back-ground of the pig-
ment layer upon its posterior surface. In brown and black eyes, the
pigment is more abundant, and is deposited, according to Kolliker and
Cruveilhier, not only upon the posterior aspect of the iris, but also in
its stroma, between its fibres, and to some extent even upon its anterior
surface. It thus predominates, and extinguishes more or less com-
pletely the reflected and diffused light of the remaining elements of the
tissue.

The position of the iris is such that while its outer border is attached
to the junction of the cornea and sclerotic, its central portion lies in
contact with the anterior surface of the crystalline lens. According to
the observations of Helmholtz,1 the iris in myopic eyes is sometimes so

1 Optique Physiologique, traduit par Javal et Klein. Paris, 1867, p. 20.

SENSE OF SIGHT. 611

nearly flat that it throws no perceptible shadow under an extreme late-
ral illumination ; but in normal eyes, as a rule, the portion immediately
surrounding the pupil is sufficiently prominent to throw a distinct
shadow ; and if the source of illumination be not more than one milli-
metre in advance of the edge of the cornea, this shadow may extend
even to the opposite border of the iris.

When the pupil dilates, the central prominence of the iris of course
diminishes, or even disappears altogether; but, according to Helmholtz,
the pupillary border of the iris hardly separates from the anterior face
of the lens, even in the most complete dilatation obtainable by bella-
donna.

An important portion of the structure of the iris is formed by its
muscular fibres. These are arranged in two sets, both of which consist
of unstriped fibres, namely, the sphincter and the dilator muscles of the
pupil.

The sphincter pupillse is composed of bundles of muscular fibres,
situated at the pupillary margin of the iris, and circularly disposed, in
such a manner that their contraction has the effect of diminishing the
orifice of the pupil, while their relaxation allows of its enlargement.
When the sphincter is in a state of moderate contraction, the remaining
non-contractile portions of the iris are thrown into radiating folds,
which can be readily seen, under the influence of ordinary daylight,
extending from the pupillary margin for one-third or one-half the dis-
tance toward its outer border.

The dilator pitpillde, which consists of radiating muscular fibres, is
much more difficult of demonstration, and its existence in man con-
tinued to be a matter of uncertainty, even after it was known to be
present in the lower animals. It has, however, been described by so
many independent observers, that there can be no doubt of its forming
a normal part of the muscular apparatus of the iris. Its fibres are
interwoven with those of the sphincter at the pupillary margin, and
extend thence in a diverging direction toward the attached border ;
either as isolated bundles running between the bloodvessels (Briicke,
Kolliker), or as a very thin, continuous sheet of fibres, covering the
whole posterior surface of the iris, immediately underneath its pig-
mentary layer (Henle, Iwanoff). According to Kolliker, the iris also
contains elements analogous to the fibres of elastic tissue, which may
thus assist the action of the dilator.

Notwithstanding the acknowledged existence of both these muscles,
and their evident physiological association with each other, the action
of the sphincter is much the most prominent and the most clearly
understood. It is this muscle which contracts under the influence of
light falling upon the retina, causing contraction of the pupil, and which
relaxes when the stimulus is withdrawn, causing dilatation. The con-
traction of the pupil is therefore, for the most part, an active movement;
its dilatation a passive one. Division of the oculomotorius nerve, loss
of sensibility in the retina, opacity of the crystalline lens, or insensi-

612 THE SENSES.

bility from cerebral compression, are all followed by dilatation of the
pupil ; and the same thing takes place immediately after death. In the
normal reflex actions of expansion and contraction of the pupil, under
the varying intensity of illumination, the fibres of the sphincter are
those which alternately contract and relax in a manner analogous to
that of the voluntary muscles ; while those of the dilator are more con-
tinuous in their operation, and are under the control of different nervous
influences.

The pigmentary layer which is continued uninterruptedly, except at
the entrance of the optic nerve, over the internal surface of the choroid,
the ciliary processes, and the posterior surface of the iris, is called the
system of the uvea, from its resemblance to the skin of a purple grape
separated from its stem ; the opening of the membranous sac at the
point of detachment representing the orifice of the pupil. Owing to the
existence of this continuous pigmentary layer, no light can penetrate
the eyeball excepting that which enters through the pupil; and the
rays, furthermore, which reach the retina at any point are arrested
there, and prevented from being dispersed by reflection over other parts
of the membrane.

Aqueous Humor and Vitreous Body. — By the transverse partition of
the iris, the cavity of the eyeball is divided into two portions, an anterior
and posterior. The portion situated in front of the iris, called the "an-
terior chamber," is filled with a colorless, transparent fluid, of watery
consistency, the aqueous humor. This fluid is to be regarded as an
extremely dilute exudation from the bloodvessels of the surrounding
parts, especially from those of the iris ; since it consists mainly of water,
holding in solution less than two per cent, of solid ingredients, namely,
sodium chloride and other inorganic salts derived from the blood, with
a trace of albuminous matter. It is faintly alkaline in reaction, and
has a refractive power but slightly different from that of water. It
is rapidly reproduced after evacuation by puncture of the cornea. It
serves to maintain the internal tension of the anterior parts of the eye-
ball, and to allow of the changes of figure of the iris and crystalline
lens, without affecting the external configuration of the cornea. The
posterior and larger portion of the cavity of the eyeball is filled mainly
by a semifluid substance, the vitreous body, so called from its trans-
parent and glassy appearance. Its composition is similar to that of the
aqueous humor, excepting for the larger proportion of albuminous
matter, which gives it more or less of a gelatinous consistency. Its
refractive power, according to Helmholtz, though slightly greater than
that of the aqueous humor, does not differ much from that of water.
It distends the principal part of the cavity of the sclerotic, supports the
retina which is extended over its surface, and preserves the general
spheroidal form of the eyeball.

The vitreous bocty is enveloped by an exceedingly thin, colorless
membrane, for the most part without definite structure, and measuring,
according to Kolliker, not more than 4 mmni. in thickness. This is the

SENSE OF SIGHT. 613

" hyaloid membrane" (Fig. 189, 10). Its inner surface is in contact with
the vitreous body, its outer surface with the retina. It extends unin-
terruptedly over the posterior and middle portions of the vitreous body
until it reaches a point anteriorly corresponding with the ciliary body
of the choroid. Here it becomes thicker and divides into two layers.
The anterior layer, which is the stronger of the two, the zone of Zinn,
extends forward and inward, remaining adherent to the folds of the
ciliary body, and terminates in the capsule of the crystalline lens, just
in front of its lateral border. The posterior layer of the hyaloid mem-
brane, after separating from the anterior, passes inward and a little
backward, and terminates also in the capsule of the lens, but a little
behind its lateral border. The triangular canal left between the two
separated layers of the hyaloid membrane and the lateral border of the
lens is the canal of Petit (Fig. 189, n), and is filled with a little trans-
parent serosity. The lens is thus suspended on all sides by a double
layer derived from the hyaloid membrane. The anterior portion of
this double layer, or the zone of Zinn, being the stronger of the two,
and presenting a distinctly fibrillated texture, is regarded as more
especially fulfilling the part of a suspensory ligament of the crystalline
lens.

Crystalline Lens — The lens is a transparent, refractive body, of cir-
cular form, with convex anterior and posterior surfaces, placed directly
behind the pupil, and retained in its position by the counterbalancing
pressure of the aqueous humor and the vitreous body, and by the two
layers of the hyaloid membrane attached to its capsule round its circular
border. It is composed of flattened fibres, adherent to each other by
their adjacent surfaces and edges, and so arranged as to pass in a
curvilinear direction, parallel to the surface of the lens, from one of its
two opposite poles to the other. Notwithstanding the fibrous structure
of the lens, the ribbon-shaped elements of which it is composed being
united by simple juxtaposition, without the intervention of any different
material, the entire body is transparent, and allows the passage of the
light without perceptible absorption or irregular dispersion.

As the refractive power of the substance of the crystalline is greater
than that of the cornea or the aqueous humor, it acts, by virtue of its
double-convex form, as a converging lens, to change the direction of
the luminous rays passing through it, and bring them to a focus at
some point situated behind its posterior surface. The amount of con-
vergence thus effected by a refractive lens depends both upon the index
of refraction of the substance of which it is composed and the greater
or less curvature of its surfaces. The stronger the curvatures, for
lenses composed of the same material, the greater the amount of con-
vergence impressed upon luminous rays passing through them. In the
case of the crystalline lens of the human eye, the two surfaces are dif-
ferent in curvature ; the anterior surface being comparatively flat, the
posterior much more convex. According to the estimates of Listing,
based upon a variety of measurements, and adopted by Helmholtz, the

614 THE SENSES.

radius of curvature for the anterior surface is, on the average, 10 milli-
metres, that for the posterior surface 6 millimetres.

This makes the crystalline lens the most powerfully refracting body in
the eyeball, and by it said parallel or diverging luminous rays, after pass-
ing through the pupil, are brought to a focus at the situation of the
retina. This effect is not due entirely to the lens, since the convex form
of the cornea and the more or less spheroidal figure of the whole eye-
ball necessarily have in some degree a similar action upon rays enter-
ing from the front. According to Helmholtz, parallel rays would be
brought to a focus "by the cornea alone, if they were sufficiently pro-
longed, at a point situated 10 millimetres behind the retina. But on
passing through the lens, their convergence is increased to such a degree
that they are concentrated at the situation of the retina itself.

The function of the crystalline lens is to produce distinct perception
of form and outline. If the eye consisted merely of a sensitive retina,
covered with transparent integument, although the impressions of light
would be received by such a retina, they could give no idea of the form
of particular objects, but would only produce the sensation of a confused
luminosity. This condition is illustrated in Fig. 190, where the arrow,
a, 6, represents the luminous object, and the vertical dotted line, at the
right of the diagram, represents the retina. The rays, diverging from
every point of the object in every direction, will thus reach every part
of the retina. The different parts of the retina, consequently, 1, 2, 3, 4,
will each receive rays coming both from the point of the arrow, a, and
from its butt, b. There will, therefore, be no distinction, upon the retina,
between the different parts of the object, and no definite perception of
its figure. But if, between the object and the retina, there be inserted a
double convex refracting lens, with the proper curvatures and density,
as in Fig. 191, the effect will be different. All the rays emanating from

Fig. 190. Fig. 191.

VISION WITHOUT A LENS. VISION WITH A LENS.

a will then be concentrated at a?, and all those emanating from ~b will be
concentrated at y. Thus the retina will receive the impression of the
point of the arrow separate from that of its butt ; and all parts of the
object, in like manner, will be distinctly and accurately perceived.

The action of a refractive body with convex surfaces, in thus focussing
luminous rays at a particular point, may be readily illustrated in the
following manner. If a sheet of white paper be held at a short distance
from a candle flame, in a room where there is no other source of light,

SENSE OF SIGHT. 615

the whole of the paper will be moderately and uniformly illuminated by
the diverging rays. But if a double convex glass lens, with suitable
curvatures, be interposed between the paper and the light, the outer
portions of the paper will become darker and its central portion brighter,
because a portion of the rays are diverted from their original course and
bent inward toward each other. By varying the position of the lens
and its distance from the paper, a point will at last be found, where
none of the light reaches the external parts of the sheet, but all of it is
concentrated upon a single spot ; and at this spot will be seen a distinct
inverted image of the end of the candle and its flame.

Distinct perception of the figure of external objects thus depends
upon the action of the crystalline lens in converging all the rays of
light, emanating from a given point, to an accurate focus at the retina.
For this purpose, the density of the lens, the curvature of its surfaces,
and its distance from the retina, must all be properly adapted to each
other. If the lens were too convex, and its refractive power excessive,
or if its distance from the retina were too great, the rays would con-
verge to a focus too soon, and would not reach the retina until after
they had crossed each other and become partially dispersed, as in Fig.
192. The visual impression, therefore, coming from any particular point
in the object, would not be concentrated and distinct, but diffused and
dim, from being dispersed more or less over the retina, and interfering
with the impressions from other parts. On the other hand, if the lens
were too flat, as in Fig. 193, or placed too near the retina, the rays

Fig. 192. Fig. 193.

INDISTINCT IMAGE from excessive INDISTINCT IMAGE from deficient

refraction. refraction.

would fail to come together at all, and would strike the retina sepa-
rately, producing a confused image, as before. In both these cases, the
immediate cause of the confusion of sight is the same, namely, that
rays coming from the same point of the object strike different points of
the retina ; but in the first instance, this is because the rays have actually
converged and crossed each other ; in the second, it is because they have
only approximated, but have never converged to a focus.

The proof that the rays emanating from luminous objects are ac-
tually thus concentrated, in the interior of the living eye, upon the
retina, is furnished by the use of the ophthalmoscope. This instrument
consists essentially of a mirror, so placed as to illuminate by reflected
light, through the pupil, the bottom of the eye which is under observa-

616 THE SENSES.

tion, and perforated at its centre by a small opening through which the
observer looks. By this means the retina and its vessels, as well as
the images delineated upon it, may be distinctly seen. According to
the observations of Helmholtz, objects at a certain distance, which are
perceived with distinctness, present to the eye of the observer, if suffi-
ciently illuminated, perfectly well-defined inverted images upon the ret-
ina, like those which would be thrown upon a screen by a system of glass
lenses properly arranged. If the eyeball furthermore be taken out from
a recently killed animal, and a circular portion of the sclerotic and ch.oroid
removed from its posterior part, similar inverted images of illuminated
objects in front of the cornea may be seen by transparency upon the
exposed portion of the retina.

It is accordingly certain that luminous rays in passing through the
eyeball are brought to a focus at the retina, principally by means of the
crystalline lens. The formation of a visible image at this- spot does
not by itself explain all the phenomena of vision, since these images
are not seen by the individual, and we should not even know of their
existence except for the results of physiological experiment and obser-
vation. But the formation of such an image shows that all the light
coming from each different part of the object is made to fall upon a
separate and distinct point of the retina ; and it thus becomes possible
to perceive the figure and extension of an object, as well as its luminosity.

Retina. — The retina is the most essential part of the organ of vision,
since it is the only one of its tissues directly sensitive to light. It
forms a delicate, colorless, nearly transparent membrane, composed
of nervous elements, situated between the inner surface of the choroid
and the outer surface of the hyaloid membrane, and extending from the
entrance of the optic nerve outward and forward to the commencement
of the ciliary body. Here it terminates by an indented border, termed
the or a serrata, which is situated nearly at the plane of the posterior
surface of the crystalline lens. In front of this region it is replaced by
an attenuated layer, which remains in contact with the surface of the
ciliary body, but which contains no nervous elements. The retina
proper has, accordingly, the form of a thin membrane moulded upon a
nearly hemispherical surface, the concavity of which is directed for-
ward, and which receives the luminous rays admitted through the pupil,
and traversing the transparent and refracting media of the ej^eball. Its
greatest thickness is in the immediate vicinity of the entrance of the
optic nerve, where it measures, according to Kolliker, 0.40 millimetre.
At a short distance from this point it is reduced to 0.20, and thence
becomes gradually thinner in its middle and anterior portions. At its
terminal border, at the ora serrata, it is only 0.09 millimetre in thickness.

The retina consists of a variety of superimposed Ia3'ers, in which
many different microscopic elements alternate with each other. In re-
gard to its physiological properties, so far as these have been deter-
mined with a sufficient degree of certainty, four of these layers may be
distinguished as representing the essential constituent parts of the

SENSE OF SIGHT. 617

membrane. These layers, counting from the internal to the external
surface of the retina, are as follows: 1. The layer of nerve fibres, de-
rived from the expansion of the optic nerve; 2. The ganglionic layer
of nerve cells; 3. The layer of nuclei; 4. The layer of rods and
cones.

1. Layer of Nerve Fibres. — The optic nerve joins the posterior part
of the eyeball at a point about 2 millimetres inside its longitudinal axis,
and slightly below the horizontal plane of this axis. The neurilemma
of the nerve at once becomes continuous with the sclerotic coat of the
e}*eball, while the nerve fibres alone penetrate into its cavity. Up to
this point the fibres of the optic nerve present the usual dark-bordered
appearance of medullated nervfc fibres, and have, according to Kolliker,
a diameter of from 1 to 4.5 mmm. But at their entrance into the cavity
of the eyeball the nerve fibres not only lose the prolongations of con-
nective tissue which previously surrounded their different bundles, but
also become much smaller in size, being reduced, on the average, to
less than 2 mmm., and many of them to less than 1 mmm. in diameter.
Owing to these changes, the nerve appears suddenly diminished in size
at its passage through the sclerotic and choroid membranes. Internally
it forms a slight prominence on the inner surface of the wall of the eye-
ball, the so-called papilla ; and from a depression at its middle part, the
central artery and vein of the retina send out their branches to supply the
retinal capillary plexus. From the papilla as a centre the optic nerve
fibres, which have thus reached the inner surface of the retina, diverge
in every direction under the form of a closely set layer. This layer
diminishes gradually in thickness from within outward, and from behind
forward, owing to the fact that the nerve fibres of which it is composed
terminate successively in the deeper parts of the membrane, thus estab-
lishing a connection between every point of the retina and the nervous
centres in the brain. The longest fibres continue their course until they
reach the ora serrata at the anterior limit of the retina, beyond which
none are visible.

2. Ganglionic Layer of Nerve Cells. — This layer is situated imme-
diately outside the former, and contains, as its special distinguishing
element, multipolar nerve cells, similar to those of the gray matter of
the brain. According to Kolliker, they vary in size from 9 to 36 mmm.
in diameter, and are provided with a number of pale, ramified prolonga-
tions. Some of these prolongations are directed outward, penetrating
into the more external portions of the retina; others pass in a horizon-
tal direction, and, according to some observers (Kolliker, Miiller, Corti),
become connected with optic nerve fibres. For the most part, however,
it is only the identity in appearance between some of the prolongations
of these nerve cells and the more slender optic nerve fibres, which leads
to the presumption of their direct terminal continuity. It is, in any
case, possible that some of the fibres of expansion of the optic nerve
are connected with prolongations of the nerve cells, while others con-
tinue their course to the deeper layers of the retinal tissue.

40

618

THE SENSES.

Fig. 194.

3. Layer of Nuclei. — The layer of nuclei is so called because its most
characteristic elements have, in the main, the aspect of nuclei ; although
by some observers (Kolliker, Schultze), they are regarded as having
rather the signification of nucleated cells, in which the enveloping cell-
substance is in small quantity as compared with the size of the nucleus.
The nuclei themselves, sometimes called "grains" or "granules," are
oval bodies, placed with their long axes perpendicular to the surface
of the retina. There are two varieties of them mingled together, which
differ mainly in size ; the larger being from 9 to 13 mmm. in length, the
smaller one-half or two-thirds as long. They are all contained in the
interior of varicose enlargements of slender fibres, which are also di-
rected perpendicularly to the surface of Jthe retina, and extend uninter-
ruptedly through the whole thickness of the layer. These fibres are
presumed to be of the nature of modified nerve fibres, and to represent,
either directly or indirectly, the continuations of those derived from
the expansion of the optic nerve. At their outer extremities they are
immediately continuous with the elements of the following layer.

4. Layer of Rod* and Cones — This is undoubtedly the most remark-
able of the retinal layers, since it consists of elements which are more
peculiarly constituted than those found elsewhere, and which are most

immediately connected with the physiology
of luminous impressions. As the name
indicates, these elements are of two kinds;
distinguished, according to their shape, by
the name of "rods" and "cones." There
is reason to believe that their offices are
essentially similar, and that they are to be
regarded as modifications of each other.

The rods (Fig. 194) are straight, elon-
gated, cylindrical bodies, composed of a
transparent, homogeneous substance, re-'
markable for its highly refractive power.
They are about 50 mmm. in length by a lit-
tle less than 2 mmm. in diameter. They are-
all placed parallel with each other, closely
packed side by side, standing perpendicu-
larly to the surface of the retina, and ex-
tending through the whole thickness of
the layer. At its outer extremity each
rod terminates by a plane perpendicular
to its axis ; at its inner extremity it tapers
/ ^A A I \ h ' ) suddenly to a point and is continuous

wifch a fibre of the Preceding Kver, and
thus with one of its nucleated enlarge-
ments or grains. According to Schultze,
the internal half of each rod is slightly
thicker, and exhibits rather less refractive
power than its external half.

DIAGRAMMATIC SECTION,
from the posterior portion of the
human retina. — 1. Layer of rods
and cones. 2. Layer of nuclei.
(Schultze.}

SENSE OF SIGHT, 619

• The con es differ from the rods mainly in their tapering form and the
greater diameter of their internal portion, which, as a general rule, is
from two to three times as thick as that of the rods. They have the
same transparent, highly refractive appearance, and are intercalated
among the rods in the same position, that is, perpendicularly to the
surface of the retina. Their outer extremities, in some regions, stop
short of the external surface of the retina, while in others, particularly
in that of most perfect vision, they reach the same level with the ends
of the rods. Each cone is connected at its inner extremity with a nu-
cleated fibre belonging to the preceding layer, the only difference in this
respect being that both the fibres and the nuclei connected with the
cones are larger than those connected with the rods.

Over the greater part of the retina the rods are more abundant than
the cones. When viewed from the external surface (Fig. 195, J), their
closely packed extremities present the appearance of a fine mosaic pat-
tern, while the cones are interspersed among them in smaller numbers.
At the borders of the macula lutea (p. 623), on the other hand, the
cones are more abundant, being only separated from each other by single
ranges of rods (-S); and at its central portion (G) there are only cones,
the rods being entirely absent. The cones at this point are also longer
and more slender than elsewhere. The following figure indicates the
appearance of the rods and cones, as shown in an external view of
different parts of the retina. The smaller circles represent the rods,
the larger circles the cones. In the interior of each cone is seen the
section of its conical extremity.

OUTER SURFACE OF THE RETINA, showing the ends of the rods and cones. — A. From
the lateral portion of the eyeball. B. From the posterior portion, at the edge of the macula
lutea. C. From the macula lutea. (Helmholtz.)

Beside the distinctly marked layers above described, there are vari-
ous others of less certain signification and less uniformity of extent,
which are found in different parts of the retina. Throughout the mem-
brane there also exists a certain proportion of delicate connective tissue,
which serves for the support and attachment of its remaining anatomi-
cal elements.

Perception of Luminous Impressions by the Retina. — It appears,
from the description given above, that the retina is not simply an ex-
pansion of the fibres of the optic nerve. It is a membrane of special
structure, connected with the extremities of the optic nerve fibres, but
containing also many additional anatomical elements. It is accordingly
a peculiar nervous apparatus, adapted to receive the impression of lumi-
nous rays, and connected, by means of the optic nerve, witli the central

620 THE SENSES.

gray matter of the brain. An examination of the manner in which the
impressions of light are perceived brings into view the following facts.

The optic nerve and its fibres are insensible to light. Notwith-
standing that this nerve is capable of transmitting luminous impressions
from the retina to the brain, yet in order to do this, it must first receive
its own stimulus from the retina. The optic nerve fibres themselves,
though sensitive to mechanical or galvanic irritation, cannot be called
into activity by the direct influence of luminous rays. This is shown
by the experiment of Bonders, in which, by aid of the ophthalmoscope,
a light of a certain degree of intensity is concentrated upon the optic
nerve, without being allowed to reach the tissue of the retina. When
the bottom of the eye is illuminated by the ophthalmoscope, the ob-
server sees the general surface of the retina of a red or brownish color,
while the papilla, which corresponds to the entrance of the optic nerve,
presents itself as a white circular spot. This spot is occupied entirely
by optic nerve fibres, while the elements of the retina commence only
beyond its borders. If the minute image of a candle flame at some dis-
tance be thrown by reflection upon the retina, its light is perceived by
the person under observation, as well as its image by the observer. If
the eye however be turned in such a direction as to bring the image of
the flame upon the white circle of the optic nerve, this circle, and the
nerve fibres of which it is composed, are visibly illuminated to a certain
depth, owing to the translucency of their substance ; but the light of
the candle flame is no longer perceived by the person under examina-
tion. The moment, on the other hand, the image of the flame is allowed
to pass beyond the limits of the white spot, and to touch the retina, its
light becomes perceptible.

The Blind Spot. — The region, accordingly, occupied by the entrance of
the optic nerve, and in which the elements of the retina proper are ab-
sent, is a blind spot, where luminous rays make no perceptible impres-
sion. The real diameter of this spot, according to the average measure-
ments obtained by Listing, Hannover, and Helmholtz,is 1.G5 millimetre,
and it covers in the field of vision a space equivalent to about 6 degrees.
Notwithstanding the existence of this insensible part at the bottom
of the eye, no dark point is usually observed in the field of vision, for
the following reasons. The blind spot is not situated in the visual axis
of the eye, but is placed, corresponding with the entrance of the optic
nerve, nearer the median line (Fig. 189). Consequently the image of
an object which is directly examined in the normal line of vision can-
not fall upon this spot, but is always outside of it, at the end of the
visual axis. Even an object which is perceived in the field of vision out-
side the direct line of sight, can never reach the blind spot of both eyes
at the same time. If it happen to be so placed that its image falls upon
the blind spot of one eye, it will necessarily reach the retina of the other
eye at a different point, and is accordingly perceived. If, on the other
hand, one eye alone be employed, there is always a small portion of the
field of vision which is imperceptible. This deficiency is not generally

SENSE OF SIGHT. 621

noticeable, because it is located in a part of the field to which our at-
tention is not directed, and where the distinction of various objects,
under moderate illumination, is so imperfect, that the momentary ab-
sence of one of them is not regarded. It may, however, be readily made
apparent by using for the test a single strongly defined object, like a
white spot on a black ground, the presence or absence of which may be
noticed without difficulty, even in indirect vision.

If the left eye be covered and the right eye directed steadily at the
white cross in figure 196, the circular spot will also be visible, though

Fi>. 196.

DIAGRAM, for observing the situation of the blind spot. (Helmholtz.)

less distinctly, since it will be out of the direct line of sight. Let the
page be held vertically at the height of the eyes, and at a convenient
distance for seeing both objects in the above manner. If it be now
moved slowly backward and forward, a point will be found where the
circular spot disappears from sight, because its image has fallen upon
the blind spot ; while both within and beyond this distance it again be-
comes visible. It may also be made to reappear, even at the same dis-
tance, by inclining the page laterally to the right or left ; since this
brings the white circle either above or below the level of the blind spot.

The experiment may be varied by fixing two cards, at the height of
the eyes, upon a dark wall, two feet apart from each other. If the left
eye be covered, and the right eye fixed upon the left-hand card, the
other one will disappear from view at a distance of about eight feet
from the wall.

It is evident, furthermore, that the optic nerve fibres are not directly
sensitive to light, even outside the blind spot, and where they form
part of the retina. These fibres radiate from the point of entrance of
the optic nerve, forming a continuous sheet on the inner surface of the
retina ; some of them terminating at successive points in the retinal
membrane, others extending to its extreme border at the ora serrata.
A luminous ray striking the retina near the fundus of the eye must,
therefore, traverse a considerable number of nerve fibres, which are con-
nected at their peripheral extremities with different parts of the retina ;
and such a ray, coming from a single point, would necessarily cause the
sensation of multiplied luminous points or even of a more or less con-

622 THE SENSES.

tinuous bright line. As distinct points are actually perceived as such
by the retina, although the luminous ray emanating from each one has
passed through the whole layer of nerve fibres on its internal surface, it
follows that the sensibility of these fibres is not affected by the direct
action of light.

The sensitive elements of the retina are in its posterior or external
layers. This fact is deduced partly from the phenomena manifested
when the retinal bloodvessels are made visible in the interior of the eye.
These bloodvessels and their branches radiate from the central trunk
which enters with the optic nerve. Their ramifications, down to a cer-
tain size, are all situated in the nerve fibre layer of the retina, and it is
only the finest subdivisions which pass into the next layer of ganglionic
nerve cells. The two outer layers, namely, the layer of nuclei, and that
of the rods and cones, are completely destitute of bloodvessels. Owing
to this anatomical arrangement, the posterior or external layers of the
retina, situated behind the main branches of the retinal bloodvessels,
must lie m the shadow of these branches, the light coming directly from
the front through the pupil. The shadows thus thrown are not habitu-
ally perceived by any diminution of the light, because the portions of
the retina covered by them are always in shadow at the same points,
and its sensibility to light is greater, in proportion as the quantity of
light reaching it is less. But the shadows may be rendered perceptible
by a lateral or oblique illumination, thus causing them to be thrown
upon points of the retina unaccustomed to their presence.

Let a lighted candle be held, in a dark room, about three inches
distant from the external angle of either eye, and about 45 degrees in
advance of the plane of the iris. On moving the candle alternately
upward and downward, the field of vision becomes filled with an abun-
dant and elegant tracery of aborescent bloodvessels, the exact counter-
part of those of the retina. The form of the vessels is distinctly marked
in purpl.e-black, upon a finely granular grayish-red ground. The point
of entrance of the vascular trunks may even be seen, witli their division
into two principal branches passing respectively upward and downward,
and then breaking up into ramifications of various curvilinear form. Jf
the candle be held immovable, the appearances rapidly fade, since the
shadows in reality are quite faint, and are only made visible from the
sudden contrast produced by throwing them successively upon different
parts of the retina.

As the bloodvessels which throw these shadows are at or near the
anterior surface of the retina, the extent of their apparent movement
on varying the position of the light, gives a means of ascertaining how
far behind the anterior surface of the retina its sensitive elements arc
situated. According to the measurements of Miiller,1 this distance must
be, in various cases, from 0.17 to 0.36 millimetre; and the same ob-
server finds the posterior layers of the retina to be separated from its

1 Cited in Helmholtz, Optique Physiologique. Paris, 1867, p. 289.

SENSE OF SIGHT. 623

anterior surface by from 0.20 to 0.30 millimetre's distance. It is, there-
fore, one or both of the posterior layers, namely, that of the rods and
cones, and that of the nuclei immediately within it, which contain the
sensitive elements of the retina, and in which the luminous rays produce
their effect. This conclusion is rendered still more certain by the fact
that in the fovea central is, the point of most distinct vision, hereafter
to be described, the two external layers of the retina are the only ones
present.

Macula Lutea and Point of Distinct Vision. — The macula lutea, or
yellow spot of the retina, is an oval spot, measuring about 2 millimetres
in its horizontal diameter, situated between 2 and 2.5 millimetres out-
side the entrance of the optic nerve. According to Helmholtz, it is
placed a very little beyond the middle of the fundus of the eyeball,
toward the temporal side. It is distinguished from the remainder of
the retina by its yellow tinge, which depends upon the presence of a
peculiar organic pigment. This pigment is not deposited in grains, but
is completely hyaline, and imbibes the whole tissue of the retina at this
spot, with the exception, according to Schultze, of the two external
layers, which remain colorless.

At its centre is a minute depression, the fovea centralis, where,
owing to its steeply sloping sides, the retina is reduced, at the bottom
of the fovea, to less than one-half its usual thickness. The macula
lutea becomes perceptible, in ophthalmoscopic examination of the eye
with a moderate illumination, as a yellowish spot, less brilliant than the
rest, in wThich the position of the fovea centralis is marked by a peculiar
colorless reflection. The macula lutea, and especially the fovea cen-
tralis, is the point of most distinct vision, where the image of an object,
fixed by the eye in the direct line of sight, falls upon the retina. It is
well known that external objects are seen with perfect distinctness only
when their images fall in the immediate neighborhood of the optical
axis at the fundus of the eyeball. Outside this region, the perception
of their figure is more or less imperfect. According to the observations
of Donders, confirmed by Helmholtz, if, while the retina is illuminated
by the ophthalmoscope, the person under observation fixes the eye in
succession upon several different objects, or upon different points of the
same object, the minute reflection which marks the fovea centralis
always places itself upon the part of the optical image fixed by the eye ;
and this appearance is so constant that the observer can tell with cer-
tainty, from the place occupied by the reflection, what point of the
object has been fixed in the direct line of sight.

The evident importance of the macula lutea and the fovea centralis,
in the exercise of vision, gives a special interest to the anatomical
structure of this part of the retina ; and the researches of microscopic
anatomists have shown that its structure presents peculiarities fully
corresponding with its physiological endowments.

The macula lutea is distinguished, in the first place, by the fact that
the superficial layer of optic nerve fibres is absent. Those fibres, ac-

624

THE SENSES.

cording to Kolliker, which, in radiating from the entrance of the optic
nerve, pass directly to the edges of the macula, lose themselves among
the nerve cells of its ganglionic layer. The others curve round the
borders of the macula on each side, to resume their peripheral direction
beyond its limit ; so that the yellow spot itself is not covered, like the
rest of the retina, by a continuous superficial layer of nerve fibres.

Secondly, the nerve cells of the ganglionic layer are more abundant
in the macula lutea than elsewhere. Over the greater portion of the
retina, according to Schultze, these cells exist, in the ganglionic layer,
only in a single plane ; that is, they are arranged side by side, and
neither above nor below each other. But in the yellow spot they form
several ranges of superimposed cells. On the other hand, toward the
centre of the yellow spot the cells diminish in number, and are entirely
absent at the fovea centralis. Various other layers, which exist more
or less distinctly in surrounding regions of the retina, also diminish in
thickness, and disappear toward the centre of the macula lutea.

Fig. 197.

DIAGRAMMATIC SECTION OF HITMAN RKTIWA, through the macula lutea and foveu
centralis. — 1. Internal surface of the retina, in contact with the vitreous body. 2. Gan-
glionic layer of nerve cells. 3. Intermediate layers of the retina, disappearing at the centre
of the macula lutea. 4. Layer of nuclei, showing the oblique course of the fibres in this
region. 5. Layer of rods and cones ; consisting at its central portion exclusively of attenu-
ated and elongated cones. C. External surface of the retina, in contact with the choroid.
In the middle of the diagram is the depression of the fovea centralis. (Schultze.)

Thirdly, owing to the modifications described above, the retina, at
the situation of the fovea centralis, consists only of its two external
layers, namely the layer of nuclei and the layer of rods* and cones.
Even these two layers exhibit, at this point, certain important peculiari-
ties in the form and arrangement of their elements.

In the layer of nuclei, the nuclei themselves are present in nearly
their usual numbers and position ; but the fibres with which they are
connected, instead of passing through the layer in a direction perpen-
dicular to the surface of the retina, bend obliquely outward, to reach
the more superficial layers of the retina in the external portions, or
even beyond the borders, of the yellow spot. Thus this layer is very
much diminished in thickness, although it still contains its cell nuclei,

SENSE OF SIGHT. 625

and although these are still connected, by their fibrous extensions, with
the other parts of the retinal tissue.

Finally the layer of rods and cones, at the situation of the macula lutea
and fovea, though preserving its general character, shows special features
by which it is readily distinguished from the corresponding parts else-
where. In this la^'er, over the greater portion of the retina, the rods
are the most abundant element, the cones being distributed among them
in smaller numbers. In the borders of the macula lutea (Fig. 195, B),
the cones become more numerous in proportion to the rods, and in the
fovea centralis (Fig. 195, (7) the layer is composed exclusively of cones.
At this part, the cones are longer than elsewhere, and more slender, so
that a larger number are comprised within an equal space ; and the
layer itself, consisting of elongated cones standing perpendicularly, is
increased in thickness, in proportion to the greater length of its con-
stituent elements. The thickness of the cones at their base, over the
retina generally, according to the measurements of Schultze, is a little
over 6 mmm., and their length less than 50 mmm. ; but at the fovea cen-
tralis their thickness is reduced to 3 or 3.5 mmm., while their length,
in the same situation, may reach 100 mmm. Each cone is connected,
here as elsewhere, through the nucleus and nucleus fibre of the pre-
ceding layer, with the other portions of the retina, and beyond doubt,
in some direct or indirect way, with the optic nerve fibres of its internal
layer.

Thus the perception of light, in the act of vision, is a process con-
sisting of several successive acts. The luminous ray passes through
the transparent internal or superficial layers of the retina, until it
reaches the situation of the two outer layers. Here it produces a
change in the condition of the nervous elements, of whose nature we
are entirely ignorant. It might be compared with that which is caused
by the same agent in the sensitive film of a photographic camera ; but
this comparison would be only one of analogy, and would not imply
any identity of the ph3rsical or chemical change produced in the two
cases. It would simply express the fact, which is undoubtedly estab-
lished, that the luminous ray, after traversing all the other transparent
and refracting media of the eye without leaving any trace of its passage,
on arriving at the two outer layers of the retina, excites in one or both
of them a kind of action which is the first step in the visual process.
This condition of the retinal elements then calls into activity the fibres
of the optic nerve, which in turn transmit the stimulus to their point of
origin in the brain. Thus far, there is no conscious perception, nor
even any nervous effect resembling in itself our idea of lurninositj^.
The retina itself is distinguished from other nervous tissues by being
sensitive to light ; that is, it may be thrown into a state of activity
under the influence of a luminous ray. But it has no other perception
of light than this, any more than the silvered film of a photographic
plate ; and, if the optic nerve be severed, blindness results, however per-
fect may be the condition of the retina.

626 THE SENSES.

On the other hand, the optic nerve fibres, which are insensible to light
itself, are thrown into excitement by the changed condition of the retinal
tissue. There is no reason for believing that the action of the fibres
of the optic nerve is different in kind from that of other sensitive nerve
fibres. Their office is simply that of receiving and communicating a
stimulus from and to certain special structures containing nerve cells.
In the case of the optic nerve, the stimulus is received from the retina
and communicated to the nervous centres of the brain. These nervous
centres, when excited by the stimulus thus received, first produce the
phenomenon of the perception of light. The preceding nervous actions,
in the retina and optic nerve, though necessary to the final result, have
no direct connection with consciousness. The conscious perception of
light and of luminous objects is the last step in the process of vision,
and is effected by a special act of the gray matter of the brain.

Acuteness of Vision in the Retina. — The acuteness of vision, so far
as it is connected with the sensibility of the retina, depends upon the
minimum distance from each other of two visual rays, at which they
can still be perceived as distinct points. If the luminous rays, coming
respectively from the top and bottom of an object, are so closely ap-
proximated, where they strike the retina, that the two impressions are
confounded, there can be no distinct perception of its figure or dimen-
sions. On the other hand, if the sensibility of the retina be such that
the two impressions are still perceived as separate from each other, the
form of the object will be recognized as well as its luminosity, notwith-
standing the small size of its retinal image. The figure of a man, six
feet high, seen at the distance of ten yards, makes at the cornea a visual
angle of 11° 30', and forms upon the retina an image which is less than
half a millimetre (^ of an inch) in length ; and yet an abundance of
details are distinctly perceptible within this space. The extreme limit
of approximation at which two points may be distinguished from each
other has been examined by the observation of fixed stars, and by that
of parallel threads of the spider's web, or of fine metallic wires, placed
at known distances from each other.1 The general result of these
examinations has shown that, for the average of well-formed eyes, the
smallest visual angle, at which two adjacent points or lines can be dis-
tinguished, is from 60 to 13 seconds ; corresponding to a distance upon
the retina of from 4 to 5 rnmm. According to the measurements of
Schultze, the diameter of the retinal cones, at the fovea centralis, is
from 3 to 3.5 mmm. ; and if two points of light were separated at the
retina by a less distance than this, they would often fall upon the same
cone, and consequently excite the same nucleus and fibre in the adjacent
layer. If the diameter of the cones be the element which determines
the limit of acuteness of vision, two luminous points, to be distinctly
perceptible, must be separated upon the retina by a distance of at least
3 mmm., and must have a visual angle with each other of at least 42

1 Helmholtz, Optique Physiologique. Paris, 1867, p. 292.

SENSE OF SIGHT. 627

seconds. In the observations made upon fixed stars, it is found that
two stars can never be separately distinguished by the eye unless their
angular distance from each other is equal to 30 seconds ; and very
seldom, unless it be as great as 60 seconds. These measurements
correspond with each other only in an approximative manner ; perhaps
because there has never been an opportunity of examining the retinal
elements in an eye, of which the acuteness of vision has been tested
beforehand. But they are sufficient to indicate a probable connection
between the minute structure of the retina and the possible limit of its
sensibility to separate impressions.

Physiological Conditions of the Sense of Sight. — The apparatus of
vision, as above described, consists of various parts, each of which has
its appropriate share in producing the final result of visual perceptions.
The eye, so far as regards its physical structure, is an optical instrument,
composed of transparent and refracting media, a perforated diaphragm,
and a dark chamber lined with a blackened membrane, all of which act
upon the luminous rays according to the same laws as the corresponding
parts in a telescope or a camera ; and the accuracy of their adjustment
is one of the first requisites for the exercise of sight. The organ,
furthermore, is movable as a whole; and certain of its internal parts
are also under the control of muscular tissues, whose alternate con-
traction and dilatation contribute to determine its mode of action. It
is, in addition, a double organ ; and impressions may be derived from
the simultaneous employment of both eyes, which cannot be acquired
by the use of one alone. Finally, the special sensibility of its nervous
elements is liable to modifications of various kinds, which have an in-
fluence upon the nature and intensity of the sensations produced. The
principal conditions regulating the physiological exercise of the sense
of sight are the following :

Field of Vision. — As the eyeball is placed in the orbit with the
cornea and the pupil directed forward, there is, in front of each eye, a
circular space within which luminous objects are perceptible ; while
beyond its borders, laterally and posteriori}^, nothing can be seen.
This space is the "field of vision." Its extreme limit, in man, reaches
nearly to 180 degrees of angular distance ; that is to say, with the eye
directed straight forward, the light from a brilliant object may be per-
ceived, when the object itself is placed laterally almost as far back as
the plane of the iris. The possibilit}r, for light which has come from
this direction, of penetrating the pupil and finally reaching a sensitive
part of the retina, depends upon the refractive power of the cornea
and the curvature of its anterior surface, by which the luminous ray
is bent inward and thus enabled to enter obliquely the orifice of the
pupil. In many of the lower animals, where the eyes are more promi-
nent than in man, and the curvatures of the cornea and crystalline lens
more pronounced, the field of vision is enlarged in a corresponding
degree. In birds and fishes, it is still further modified by the lateral

628 THE SENSES.

position of the two eyes. The ostrich, with the head directed forward,
can easily see objects placed a few yards behind its back ; and in many
fish, when examined from different points in an aquarium, it is impossi-
ble for the observer to place himself in any position, above, behind, or
on either side, where he cannot see one or both of the pupils of the
animal. The field of vision consequently, for the animal, is a complete
sphere ; the light being perceptible from every point of the surrounding
space. In man, the external borders of the field of vision are very ill
defined ; and objects placed at a lateral distance of 90 degrees must be
very brilliant to attract attention. For practical purposes, the space
within which objects are perceptible is one of not more than 75 degrees
on each side, or 150 degrees for the entire field of vision.

Line of Direct Vision. — Within the field of vision, however, there is
onlyjone point, at its centre, where the form of objects can be perceived
with distinctness ; and the prolongation of this point, in the visual axis
of the eye, from the pupil forward, is called the "line of direct vision."
Objects met with upon this line can be distinctly seen ; all others, situ-
ated upon either side, above or below it, are perceived only in an imper-
fect manner. If the observer place himself in front of a row of vertical
stakes or palisades, he can see those placed directly in front of the e3'e
with perfect distinctness ; but those on each side appear as uncertain
and confused images. On looking at the middle of a printed page, in
the line of direct vision, we see the distinct outlines of the letters;
while at successive distances from this point, the eye remaining fixed,
we distinguish first only the separate letters with confused outlines,
then only the words, and lastly only the lines and spaces.

This limitation of serviceable sight to the line of direct vision is
practically compensated by the great mobility of the eyeball, which
turns successively in different directions ; thus shifting the field of vision
and examining in turn every part of the space attainable by the eye.
In reading a printed page, the eye follows the lines from left to right,
seeing each letter and word distinctly in succession. At the end of
each line, it returns suddenly to the commencement of the next, repeat-
ing the same movement from the top to the bottom of the page.

The deficiency of distinctness outside the line of direct vision depends
upon two causes, which are both present, although either separately
would tend to produce a similar result ; namely, 1st, inaccurate focus-
ing of the luminous rays ; and 2d, diminished acuteness of the retinal
sensibility.

Rays of light entering the eye from the front, in the line of direct
vision, may be brought to an accurate focus at the situation of the
retina. But those which enter at a certain degree of obliquity, whether
from above, from below, or from one side, suffer a more rapid conver-
gence and are accordingly brought to a focus and again dispersed, before
reaching the retina. Thus rays diverging from the point a (Fig. 198),
in the line of direct vision, are again concentrated at x, and form a dis-
tinct image upon the retina at that point. But those coming from 6,

SENSE OF SIGHT. 629

situated considerably on one side, under a similar degree of divergence,
fall upon the cornea and the crystalline lens in such a way that there is
more difference in their angles of incidence, and consequently more dif-
ference in the amount of their refraction. They are therefore brought
together too rapidly, and are dispersed upon the retina over the space
?/, z, forming an imperfect image. Ophthalmoscopic examination of the
retina shows that, in point of fact, the images formed at the fundus of

Fig. 198.

DIAGRAMMATIC SECTION OF THE EYEBALL, showing difference of refraction for
direct and indirect vision.— a, x. Rays from a point in the line of direct vision, focussed at
the retina. 6, y, z. Rays from a point outside the line of direct vision, brought to a focus
and dispersed before reaching the retina.

the eye, from luminous objects in the line of direct vision, present per-
fectly distinct outlines ; while those at a certain distance from this point,
toward the lateral parts of the retina, are comparatively ill-defined.

Secondly, there is reason to believe that the sensibility of the retina
is also less acute in its lateral regions than at the fundus, and particu-
larly at the macula lutea and fovea centralis; since, according to Helm-
holtz, the sharpness of sight for objects at a little distance from the
line of direct vision diminishes in greater proportion than the dis-
tinctness of their images formed upon the retina. The fovea centralis,
according^, is the spot where the retina possesses the most acute sensi-
bility, and it is also situated at the extremity of the visual axis, where
the refraction and covergence of the luminous rays are effected with the
greatest accuracy. Objects situated upon the line of this axis are seen
by direct vision, and are distinctly perceived; those situated in the
field of view, outside this line, are seen by indirect vision, and their
outlines appear more or less confused and uncertain.

Point of distinct vision, and Accommodation of the eye for different
distances. • An optical instrument, composed of refracting lenses, can-
not be made to serve at the same time for near and remote objects. In
a refracting telescope or spy-glass, if the instrument be directed toward

630 THE SENSES.

any part of the landscape, objects at a certain distance only are dis-
tinctly seen ; all others, situated within or beyond this distance, are
obscure or imperceptible. This is necessarily the case, since a lens or
system of lenses can bring to a focus at one spot only those rays which
strike its anterior surface within a certain degree of divergence. The
formation of a visible image at the desired spot depends entirely upon
the refracting power of the lenses being such, that all the rays diverg-
ing from a particular point of the object shall be again brought to an
exact focus at the plane where the image is to be perceived. If the object
be placed at an indefinite distance near the horizon, or if it be one of
the heavenly bodies, the rays emanating from any one point of such an
object reach the telescope under so slight a degree of divergence that
they are nearly parallel; and, on suffering refraction, they will be
brought to a focus at a short distance behind the lens. But if the
object be less remote, the rays emanating from it strike the lens under
a higher degree of divergence. The same amount of refractive power,
therefore, produces a less rapid convergence than in the former case,
the rays are consequently brought to a focus only at a greater distance
behind the lens. To provide for this difficulty, the spy-glass is pro-
vided with a sliding tube, by which the distance of the eye-piece from
the object-glass may be shifted at will. For the examination of remote
objects, the eye-piece is pushed forward, so as to bring into view the
image formed at a short distance behind the lens ; for the examination
of near objects it is drawn backward, to receive the image placed
farther to the rear. This is the accommodation of the spy-glass for
yision at different distances.

A similar necessity exists in the optical apparatus of the eye. If
one eye be covered, and two long needles placed vertically in front of
the other, in nearly the same linear range, but at different distances-
one, for example, at eight, and the other at twenty inches from the
eye — it will be found that they cannot both be seen distinctly at the
same time. When we look at the one nearer the eye, so as to perceive
its form distinctly, the image of the more remote one becomes con-
fused; and when we see the more distant object in perfection, that
which is nearer loses its sharpness of outline.

The same thing may be made evident by stretching in front of the
eye, at the distance of seven or eight inches, a plain gauze veil, or other
woven fabric formed of fine threads, with tolerably open meshes, so
that objects beyond may be readily visible through its tissue. The ob-
server, in using a single eye, may fix at will either the threads of the
veil, or the more distant objects placed beyond it ; but they alternate
with each other in distinctness, like the two needles in the experiment
described above. At the time when the threads are sharply defined,
other objects are indistinct ; and when the eye is fixed upon the more
distant objects, so that they are perfectly delineated in the field of
vision, the threads of the veil become almost imperceptible, and hardly
interfere by their presence with the images seen beyond.

SENSE OF SIGHT. 631

; It is evident, therefore, that the eye cannot perceive distinctly, at the
same time, objects which are placed at different distances, but it must
fix alternately the nearer and the more remote, and examine each in
turn. It is also evident that, in thus bringing alternately the one or
the other into distinct view, there is a change of some kind in the con-
dition of the eye, by which it adapts itself to the distance or nearness
of the object under examination. The observer himself, at the moment
of transferring the sight from one object to another, is conscious of a
certain effort, by means of which the eye assumes its new condition ;
and the alteration thus produced is not quite instantaneous, but re-
quires a certain interval for its completion. The process which takes
place at this time is the accommodation of the eye for vision at different
distances.

The method by which the accommodation of the eye is effected forms
one of the most important parts of the physiology of sight. The facts
which have been established by observation in regard to it are as
follows :

I. The change in ocular accommodation for different distances is
accompanied by an alteration in distinctness of the images formed upon
the retina.

This is demonstrated by the observations of Helrnholtz with the aid
Of the ophthalmoscope. When the retina is brought into view by this
instrument, if the person under examination fix his attention upon a
distant object, its image is shown upon the retina with distinct outlines;
but on changing the point of vision for a near object, the image of the
latter becomes distinct, while that of the former loses its sharpness.
This indicates that the result in question is not produced simply by the
mental effort of the individual, but depends upon a physical change in
the refractive condition of the eye.

II. Accommodation for distant objects is a passive condition of the
eye; that for near objects is the result of muscular activity.

This fact is in some degree made apparent by the nature of the sen-
sations accompanying the change. The eye rests without fatigue for
an indefinite time upon remote objects; but for the examination of
those in close proximity, especially if it be prolonged, a certain effort is
necessary, which, after a time, amounts to the sense of fatigue. It is
also remarked that solutions of atropine, which, when applied to the
eye, cause temporary paralysis of the sphincter muscle of the iris and
consequent dilatation of the pupil, suspend, more or less completely,
the power of accommodation for near objects, while that for remote
objects remains perfect. If both these changes were due to muscular
action, it would be necessary to assume that the same substance could
paralyze one of the internal muscles of the eyeball, and at the same
time leave the other intact, or throw it into a state of permanent rigid-
ity; and there is nothing known which would justify such an assump-
tion. Furthermore, there are certain cases of paralysis -of the oculo-
motorius nerve, where not only the corresponding external muscles of

632 THE SENSES.

the eyeball and the sphincter pupillae are relaxed, but the changes of
accommodation are also interfered with ; and in these instances, accord-
ing to Helinholtz, the eye invariably remains adapted for long distances,
and cannot be brought to a state of distinct vision for near objects.
The evidence in this direction is completed by the well-known facts
which accompany the usual diminution or loss of accommodative power
with advancing years. In old persons, where this change has taken
place, it is the accommodation for near objects which is deficient, while
that for distant objects remains perfect.

III. In accommodation for near cbjects, the crystalline lens becomes
more convex, thus increasing its refractive power. This is the essential
change upon which all the results of accommodation are directly de-
pendent. Its existence was demonstrated by Cramer and Donders,1 by
the aid of what are called the "catoptric
images," or images of reflection in the eye.
If a brilliant candle flame be so disposed, in a
room with dark walls, that its rays fall some-
what obliquely upon the cornea of the eye
tinder observation, and at an angle of about
30 degrees with its line of sight, and if the
observer place himself on the opposite side, at
an equal angle with the line of sight, three
^fleeted images of the flame will become visi-
of reflection, from the surface ble, as in the accompanying figure.

The first left-hand image (Fig. 199, a)
face of the lens. c. inverted which is brightest of all, and upright, is that
ie'n.?08 !ri°r 8Ur" reflected from the surface of the cornea. The

second, 6, which is also upright, but much
fainter, is the reflection from the convex anterior surface of the lens;
and the third, c, which is tolerably distinct, but inverted, is thrown
back from the posterior surface of the lens, acting as a concave mirror.
If the person under observation now changes his point of sight, from a
distant to a near object, the position of the eyeball remaining fixed, the
second image, 6, becomes smaller, and places itself nearer the first.
This indicates that the anterior surface of the lens, from which this
image is reflected, becomes more bulging, and approaches the cornea:
at the same time no change is observable in the other two images,
showing that the curvatures, both of the cornea and of the posterior
surface of the lens, remain unaltered.

Helmholtz has made the phenomenon above described much more
apparent by employing, instead of a single light, two similar sources of
illumination placed in the same vertical line. There are thus produced
two catoptric images, one above the other, from each surface of reflec-
tion ; and an increase or diminution in convexity of either of these sur-

1 DONDERS, Accommodation and Kefraction of the Eye, Sydenham edition.
London, 1864, p. 10.

SENSE OF SIGHT.

633

faces would be readily manifested by an approach or recession of the
two images belonging to it. In accommodation for remote objects (Fig.
200, A), the two images from the anterior surface of the lens are of
considerable size and somewhat widely separated ; in accommodation
for near objects (#), they diminish in size and approach each other.
The double reflections from the cornea and the posterior surface of the
lens, remain at sensibly the same

distance from each other in both Fig. 200.

states of accommodation.

The advance of the iris and pu-
pil, in consequence of the protru-
sion of the anterior face of the lens,
as remarked by Helmholtz,can also
be observed directly, by looking
into the eye from the side. If the
observer look from this direction
so as to obtain a profile view of the
cornea and part of the sclerotic be-
tween the opening of the e3^elids, he
will see the dark pupil in perspec-
tive under the form of an upright
elongated oval, a little in front of

the edge of the sclerotic. The person under observation fixes his sight
upon a distant object, and the observer places himself steadily in such
a position that the hither edge of the iris is just concealed by the ante-
rior border of the sclerotic. If the sight be now shifted from the dis-
tant to a near object, in the same linear range, the pupil visibly ad-
vances toward the cornea, and the edge of the iris shows itself a little
from behind the edge of the sclerotic. If the sight be again directed to
the distant object, the pupil recedes and the edge of the iris, disappears,
as before, behind the sclerotic.

The accommodation of the eye for near objects is therefore produced
by an increased refractive power of the lens, from the greater bulging

CHANGE OF POSITION IN DOUBLE
CATOPTRIC IMAGES during accommoda-
tion.— A. Position of the images in accom-
modation for distant objects. B. Position
of the images in accommodation for near ob-
jects, a. Corneal image, b. Image from an-
terior surface of lens. c. Image from poste-
rior surface of lens.

Fig. 201.

Fig. 202.

VISION FOR DISTANT OBJECTS.

VISION FOR NEAR OBJECTS.

of its anterior face. This has the effect of increasing the rapidity of
convergence of rays passing through it, and consequently compensates
for their greater divergence before entering its substance. In the ordi-
nary condition of ocular repose, when the eye is directed to distant ob-
41

634 THE SENSES.

jects, the rays coming from any point of such an object arrive at the
cornea in a nearly parallel position, and are then refracted to such a de-
gree that they meet in a focus at the retina (Fig. 201). When the eye
is directed to a nearer point (Fig. 202), the lens increases its anterior
convexity ; and the divergent rays, being more strongly refracted, are
still brought to a focus at the retina, as before. It thus becomes possi-
ble to fix alternately, in distinct vision, objects at various distances in
front of the eye.

Mechanism of the Change in Figure of the Lens in Accommodation. —
The mechanism by which the lens is rendered more convex, in vision
for near objects, is far from being completely demonstrated. The rea-
sons have already been given which lead to the conclusion that it is
accomplished, in some way, by muscular action ; and the two muscles
which, separately or together, undoubtedly produce this change, are the
iris and the ciliary muscle.

The iris certainly contracts in accommodation for near objects. This
is easily observed on examining by daylight the pupil of an eye which
is alternately directed to near and remote objects. The pupil visibly
diminishes in size when the eye is fixed upon a point near by, and again
enlarges when the sight is accommodated for the distance. The move-
ments of the ciliary muscle, on the other hand, are not subject to ob-
servation ; but the attachments and position of this muscle have led
many writers to attribute to it an important, if not the principal, part
in causing a change of form in the crystalline lens.

So far as we are at present able to form a judgment on this question,
it may be said that the diminution in size of the pupil is not by itself
an efficient cause of accommodation ; since, according to Helmholtz, if
the observer look through a perforated card, the orifice of which is
smaller than the pupil, near objects still appear indistinct when the
sight is directed to the distance, and vice versa, notwithstanding the
invariable dimensions of the artificial pupil thus employed. The con-
traction of the circular fibres of the sphincter papillae must, therefore,
have for its probable object to fix the inner border of the iris, thus
affording an internal point of attachment for the radiating fibres of the
same muscle. These fibres have for their external attachment the
elastic tissue at the inner wall of the canal of Schlemm (Fig. 189); and
from this circle also arise the fibres of the ciliary muscle, which radiate
outward and backward to their final attachment at the surface of the
choroid membrane. If the circular and radiating fibres of both these
muscles contract together, they will form a connected system, which
may exert a pressure upon the borders of the lens, sufficient to cause
the protrusion of its anterior face at the pupil, where alone its advance
is not resisted. The aqueous humor, displaced by the protrusion of the
lens, may find room in the external parts of the anterior chamber, where
the outer border of the iris recedes, under the traction of the ciliary
muscle. These are the general features of the mechanical action in
accommodation, as it is generally supposed to take place. At the same

SENSE OF SIGHT. 635

time, its details are by no means clearly understood ; and explanations,
varying more or less from that given above, have been proposed by
observers of very high authority. The direction and degree in which
pressure would be exerted, by muscular fibres attached like those in the
interior of the eye, are too imperfectly known to warrant a positive
statement in this respect.

Limits of Accommodation for the Normal Eye. — The normal eye is
so constructed that rays emanating from a single point, though coming
from an indefinite distance, and therefore sensibly parallel to each other,
are brought to a focus at the retina (Fig. 203). Vision is accordingly
distinct, even for the heavenly bodies, provided their light be neither too
dim nor too excessive in brillianc3T. For bodies situated nearer to the
eye, the convexity of the lens increases with the diminution of the dis-
tance, and vision still remains perfect. But there is a limit to the change
of shape which the lens is capable of assuming ; and when this limit is
reached, a closer approximation of the object necessarily destroys the
accuracy of its image. For ordinary normal eyes, in the early or middle
periods of life, accommodation fails and vision becomes indistinct, when
the object is placed at less than 15 centimetres (6 inches) from the eye-
Between these two limits, of 15 centimetres and infinity, the amount
of accommodation required is by no means in simple proportion to the
variation of the distance. The change of accommodation necessary for
objects situated respectively at 15 and 30 centimetres from the eye (6
inches and 12 inches), is much greater than that corresponding to the
distances of one yard and two yards. The farther the object recedes
from the eye, the less diiference is produced, in the sensible divergence
of the rays, by any additional increase of distance ; and consequently
less variation is required in the refractive condition of the eye to pre-
serve the accuracy of its image. It is generally found that no sensible
effort of accommodation is required for objects situated at any distance
beyond fifty feet from the observer ; while within this limit the amount
of accommodation necessary for distinct vision increases rapidly with
the diminution of the distance.

An eye which is capable of accommodating for distinct vision, through-
out the whole range included between 15 centimetres and an indefinite
distance, is, in this respect, a normal eye, and is said to be emmetropic ;
that is, its powers of accommodation are placed within the natural limits
or measurements of this function.

Presbyopia Eye. — The power of accommodation diminishes naturally
with the advance of age ; and observation shows that this diminution
dates from the earliest period of life. Infants often examine minute ob-
jects at very short distances, in a manner which would be quite imprac-
ticable for the healthy adult eye ; and the minimum distance of distinct
vision at twenty years of age is placed by some writers at ten centi-
metres instead of fifteen. The power of increasing the convex^ of the
lens to this extent is soon lost ; and, as it continues to diminish, a time
arrives, usually between the ages of 40 and 50 years, when the incapacity

636

THE SENSES.

of accommodation for near objects begins to interfere with the ordinary
occupations of life. When this condition is established the eye is said
to be presbyopia. Its vision is still perfect for distant objects, but it
can no longer adapt itself for the examination of those in close prox-
imity to the eye. To remedy this 'defect the patient employs a convex
eye-glass, which replaces for him the increased convexity of the crys-
talline lens, in accommodation for near objects ; and by the aid of such
a glass he is able to read or write at ordinary distances and in characters
of the ordinary size.

The use of a convex eye-glass does not restore the perfection of sight
as it existed beforehand. In the normal eye, the degree of accommoda-
tion varies for every change of distance within fifty feet ; and the organ
is thus adjusted, by an instantaneous and unconscious movement, for
the most delicate variations of refractive power. But an eye-glass, the
curvatures of which are invariable, can give perfect correction only for
a single distance. A glass is, therefore, usually selected of such a
strength as to serve for the most convenient distance in the ordinary
manipulation of near objects.

Fig. 203.

EMMETEOPIC EYE, iii vision at long distances. (Wundt.)
Fig. 204.

MYOPIC EYE, in vision at long distances. (Wundt.)

Myopic Eye. — In many instances, where the eye is otherwise of nor-
mal configuration, its antero-posterior diameter is longer than usual,
thus placing the retina at a greater distance behind the lens. The con-
sequence of this peculiarity is that while the luminous ra}^s are brought
to a focus at the usual distance from their point of entrance into the eye,
this focus is situated within the vitreous body; and the rays reach the
retina only after they have crossed and suffered a partial dispersion.

SENSE OF SIGHT. 637

(Fig. 204.) This produces an indistinct image for all remote objects.
Within, however, a certain distance from the eye, the rays enter the
pupil under such a degree of divergence, that their focus behind the lens
falls at the situation of the retina, and the object is distinctly seen.
Such an eye is said to be myopic, or, in ordinary language, "near
sighted," because its range of distinct vision is confined to objects
situated comparatively near the eye. The flexibility of the lens, and its
capacity for increasing its convexity, may be, in the myopic eye, fully up
to the normal standard, and consequently its power of accommodation
may be as great in reality, though not in distance, as that of the normal
eye. In the ernmetropic. condition, a certain degree of variation in the
curvature of the lens produces the necessary change of accommodation
for any distance between 15 centimetres and infintty. In the myopic
eye the same amount of accommodating power may be present, though
perfectly distinct vision be confined between the distances of 8 and 20
centimetres. The myopic eye consequently has distinct vision at shorter
distances than a natural one, but gives an imperfect image for remote
objects.

The remedy adopted for the myopic eye is to employ a concave eye-
glass, which increases the divergence of the incident rays. This enables
the eye to bring parallel or nearly parallel rays to a focus situated
farther back than it would otherwise fall, and at the actual position of
the retina ; thus giving distinct vision for remote objects. As the
accommodative power is normal in amount, this contrivance restores
completely the perfection of sight, in a myopic eye which is otherwise
well-formed ; and the patient can then accommodate accurately for all
distances within the natural limits of distinct vision.

Apparent Position of Objects, and Binocular Vision. — The apparent
position of an object is determined by the direction in which the lumi-
nous rays pass from it to the interior of the eye. The perception of
the light itself necessarily marks the direction from which it has arrived,
and therefore the apparent position of its source. It is difficult to under-
stand fully the precise physiological conditions which cause this appreci-
ation of the path followed by a luminous beam ; although there seems
reason for the belief that it is in some way connected with the posi-
tion of the rods and cones which stand perpendicularly to the curved
surface of the retina, and thus receive the impression of a ray, if at all,
in the direction of their longitudinal axes. But whatever may be the
optical or physiological mechanism of the process, its plain result is that
a ray coming from below attracts attention to the inferior part of the
field of vision ; and one coining from above is referred to its point of
origin in the upper part of the same field. Thus if two luminous points
appear simultaneously in the field of vision, they present themselves in a
certain position with regard to each other, above or below, to the right
or the left, according to the direction in which their light has reached
the eye.

638 THE SENSES.

This fact is fully demonstrated by the phenomena of angular reflec-
tion and refraction. If a candle be held behind the back, in such a posi-
tion as to be reflected in a mirror placed at the front, the light presents
itself to the eye as if it were really in front, because it is from this
direction that the luminous rays finally come. If we observe the reflec-
tion of objects in a mirror held horizontally, or in a smooth sheet of
water, the objects seem to be placed below the reflecting surface, although
they are really above it ; since the rays which make their impression
upon the eye actually come from below. A stick or pebble, seen ob-
liquely at the bottom of a transparent pool, appears nearer the surface
than it really? is, because the rays which reach the visual organ have
been bent from their course, in passing from the water into the atmos-
phere, and have consequently assumed a more oblique direction.

Erect Vision, with Inverted Retinal Image. — Since it is the direction
of the visual rays, rather than the point of their impact upon the retina,
which determines the apparent relative position of luminous objects,
such objects appear erect although their images upon the retina are
inverted. The retinal image is not the form which is seen by the eye
itself, but is only a phenomenon visible to the inspection of another
eye. It is an appearance which is incidental to the mode of refraction
of the visual rays ; and its position is quite a distinct matter from that
of the luminous impressions perceived by the retina. Its relation to
the picture really presented to the sensitive membrane, is like that of
the reversed engraving upon a wood-cut to the printed impression of
the same design ; or like that of the elevations and depressions of a
mould to the depressions and elevations of the cast taken from it. In
the field of sight, therefore, for each eye, every object appears above or
below, to the right or left, according to the position which it really
occupies in regard to the centre of the field and the line of direct vision.

Point of Fixation, in Vision with Two Eyes. — For each eye, distinct
perception is possible, as shown above (p. 628), only for objects situated
in a single range, which is known as the " line of direct vision." Since
the eyes are placed in their orbits at a lateral distance from each other
of about six centimetres, when they are both directed at the same object,
within a moderate distance, their lines of direct vision have a sensible
convergence, and, of course, cross each other only at a single point.
At this point of intersection of the two lines of direct vision, an object
may be seen distinctly by both eyes at the same time. But at every
other point, it must appear indistinct to one of them ; because if it be
in the line of direct vision for the right eye it will be out of that line
for the left, and vice versa. There is, accordingly, only a certain dis-
tance, directly in front, at which an object can be distinctly seen sim-
ultaneously by both eyes ; namely, that at which the two lines of direct
vision cross each other. This point is called the point of fixation, for
the two eyes. In fixing any object, for binocular vision, the accommo-
dation in each eye is at the same time adjusted for the required distance ;

SENSE OF SIGHT.

639

Fig. 205.

and thus the entire accuracy of both organs is concentrated upon a single
point.

Since it is the position of the two eyes in their respective orbits which
determines the point of fixation, the observer can form a tolerably accu-
rate judgment, as to whether another person within a moderate distance
be looking at him, or at some other object farther removed in the same
direction. For more considerable distances the estimate fails, because
the obliquity of the two eyes, which varies perceptibly within moderate
distances, diminishes so much in looking afc remote objects, that the
slight differences which exist are no longer appreciable by the observer.

Single and Distinct Vision with both Eyes. — From the preceding
facts it is evident that only one point can be found in the line of direct
vision, for both eyes at the same time.
When an object occupies this situation,
namely, the point of fixation, it is distinctly
perceived by both eyes in the centre of the
field of vision ; thus its two visual images
exactly cover each other in their apparent
position and so form but one. Consequently,
the object appears single, though seen simul-
taneously by both eyes (Fig. 205). But if
placed either within or bej'ond the point of
fixation, an object appears indistinct and at
the same time double. If the observer hold
a slender rod in the vertical position at a
distance of one or two feet before the face,
and in the same range with any small object,
such as a door-knob, on the opposite side of
the room, it will be found that when both
eyes are directed at the rod, it is seen single
and distinctly, but the door-knob appears
double one of its images falling upon each
side. If the eyes be now directed at the door-
knob, that in turn becomes distinct and single,
•while the rod appears double, one indistinct
image being placed on each side, as before.

These phenomena depend upon the different directions of the two
lines of direct vision. When the eyes are so directed that the nearer
object (Fig. 205, i) occupies the point of fixation, the farther object (a)
will also be seen, because it is still included in the visual field ; although
it will be seen indistinctly, because the accommodation of the eye is no
longer adjusted to its distance, and because it is not in the line of direct
vision. But for the right eye (a) it will be placed to the right of this
line, and for the left eye (b) to the left of it. Its two images do not cor-
respond with each other in situation, and the object accordingly appears
double.

If the eyes, on the other hand, be directed at the more distant object,

b

SlTTGLE ATTD DOTTBLE Vl-

SION, at different distances.— a.
Right eye. b. Left eye. 1. Ob-
ject at the point of fixation, seen
single. 2. Object beyond the
point of fixation, seen double.

64:0 THE SENSES.

the nearer one is no longer in the point of fixation. For the right eye,
its image will appear to the left of the line of direct vision, and for the
left eye to the right of this line. It therefore appears double and in-
distinct.

Thus, in the ordinary use of binocular vision every object but one
appears double and at the same time imperfectly delineated. This cir-
cumstance is so little noticed that it is never a source of confusion for
the sight, and even requires a special experiment to demonstrate its
existence. The reason for its passing, as a general rule, unobserved is
twofold. First, the attention is naturally concentrated upon the object
which is placed, for the moment, at the point of fixation. When this
point is shifted, the new object upon which it falls also appears single ;
and thus the idea of a double image, even if indistinctly suggested at
any time, is at once dispelled by the movement of the eyes in that
direction. Secondly, an object which is really placed in any degree
toward the right hand or the left will form an indistinct double image,
since it occupies a different apparent position for the two eyes. But
the obliquity of its rays, and consequently the indistinctness of its
image, will be greater for the right eye than for the left, or vice versa;
and the notice of the observer, if drawn to it at all, is occupied with
the more distinct of the two images, to the exclusion of the other.
The fact becomes palpable only in such an experiment as that detailed
above ; where two bodies are examined in the same linear range, so that
the double images produced are equal in intensity, and sufficiently de-
tached by contrast from surrounding objects to force themselves upon
the attention.

Double vision may also be produced at any time by pressure with
the finger at the external angle of one of the eyes, so as to alter its posi-
tion in the orbit, the other eye remaining untouched. But in this case
it is the whole field of vision which is displaced, and all objects are
doubled indiscriminately ; their images being separated to the same
degree and in the same direction, whatever may be their distance from
the eye. It is this form of double vision which is produced, in vertigo
or intoxication, by irregular action of the muscles of the eyeball.

Appreciation of Solidity and Projection. — When both eyes are direct-
ed simultaneously at a single point, the distance of the object may be
estimated with considerable accuracy by the degree of convergence of
the visual axes required for its fixation. Since this convergence is
in proportion to the proximity to the observer of the point of fixation,
another impression, of different kind but of equal importance, is also
produced by binocular vision, when the object has an appreciable volume
and thickness, and when it is placed within a moderate distance. Owing
to the lateral separation of the two eyes, and the convergent direction
of their visual axes, they do not both receive from such an object pre-
cisely the same image. Both e}res will see the front of the object in
nearly the same manner ; but in addition the right eye will see a little
of its right side, and the left eye will see a little of its left side. This

SENSE OF SIGHT.

is illustrated in Figs. 206 and 20T, which represent a skull as seen by
the two eyes, when placed exactly in front of the observer at a distance
of eighteen inches or two feet ; rather more of the details on one side
being visible to the left eye, and rather more of those on the other

Fig. 206. Fig. 207.

AS SEEN BY THE LEFT EYE. AS SEEN BY THE RIGHT EYE.

being visible to the right eye. As the central part of the mass is in the
point of fixation, at the junction of the two visual axes, the object
appears single. But the images which it presents to the two eyes are
not precisely identical in form ; and it is the combination of these dif-
ferent images into one which gives rise to the impression of solidity or
projection.

But this effect is complete only when the object is situated within a
moderately short distance. For those which are comparatively remote,
the convergence of the visual axes, and consequently the difference in
the apparent configuration of the two images, become inappreciable,
and the optical impression of solidity disappears. At a distance of
some miles even a large object, like a mountain, loses its projection,
and presents the form of a flattened mass against the horizon. It is on
this account that pictorial representations of distant views are often
extremely effective ; the idea of successive remoteness in different parts
of the landscape being conveyed by appropriate intersection of the out-
lines and by variations in tone, color, and distinctness, like those due
to the interposition of the atmosphere. On the other hand, a picture
of near objects, which aims to represent their solidity, can never de-
ceive us in this respect, however elaborate may be the details of surface,
shadow, and color ; since the flat surface of the picture presents the
same image to both eyes, and it is consequently evident that the ob-
jects delineated have no real projection. But if two pictures of the
same object, taken in two different positions, be presented in such a
way that only one of them is seen by the right eye, and only the other
by the left, the same optical effect may be produced as by the object
itself, and the appearance of solidity and projection may be perfectly

642 THE SENSES.

imitated. Such is the. principle of the instrument known as the stereo-
scope. This is simply a box or framework, holding two photographic
pictures of the same object, which have been taken from two different
points of view, corresponding to the different positions of the two eyes.
Thus one of the pictures represents the object as it would in reality be
seen by the right eye, and the other represents it as it would be seen
by the left. When these pictures are so placed in the stereoscope that
each eye has presented to it the appropriate view, the two images, occu-
pying the point of fixation, are fused upon the retina, and produce an
extremely deceptive resemblance to the projection and stolidity of the
real object.

The acuteness of perception, by which the eyes appreciate a slight
difference in the two retinal images, is the measure of what may be
called their stereoscopic sensibility. It has been observed that two
coins, composed of different metals, but struck from the same die, are
slightly different in volume, owing to the unequal dilatation of the
metals after receiving the impression of the die. This difference may be
quite inappreciable to the eye in ordinary examination, even when the
coins are placed in contact with each other ; but if they be made to take
the place of the two pictures in a stereoscope box and viewed together,
the resulting image, instead of presenting a plane surface, appears ob-
lique and convex.

The degree of stereoscopic sensibility was tested by Helmholtz in the
following manner: Three metallic pins were fixed upright in small
movable blocks of wood, placed side by side, so that the pins sh6uld be
about 12 millimetres distant from each other, and nearly in the same
vertical plane. The observer then, using both eyes simultaneously,
examined the appearance of the objects from a distance of 340 milli-
metres, the pins being arranged at right angles across the line of view.
The immediate object of the examination was to determine, from the
stereoscopic effect, whether the three pins were placed exactly in the
same plane, or whether either of them were in advance of or behind the
others. It was found possible to detect in this way a deviation in posi-
tion of one of the pins equal to one-half its own thickness, that is,
0.25 mm. ; and the deviation was recognized with absolute certainty
when it amounted to the entire thickness of the pin, that is, 0.50 milli-
metre.

General Laws of Visual Perception. — Beside the laws regulating the
formation and combination of optical images, there are certain pheno-
mena connected with visual perceptions in general, which are of con-
siderable importance in the physiology of sight. Some of these phe-
nomena require for their study special modes of investigation, while
others are made evident by comparatively simple means, and are often
of consequence in their hygienic relations.

Luminous impressions upon the eye remain for a certain time
after the cessation of the light. The persistence of luminous impres-
sions thus left upon the eye is very short, and is not usually noticeable,

SENSE OF SIGHT. 643

because these impressions are, under all ordinary conditions, immediately
followed by others upon the same part of the retina, and the new
sensation practically obliterates the old one. But, if the instantaneous
impression be not followed by a different one, or if it be sufficiently
vivid to be perceived, notwithstanding the presence of others, its con-
tinuance may be made evident to observation. Thus, in a dark room,
if a bright point, like the heated end of a wire, be carried round in a
circle with moderate rapidity, the eye follows its movement, as it presents
itself successively in different parts of the circle ; the light always ap-
pearing at one point only, the rest of the space remaining dark. But
if the rapidity of the circular movement be greatly increased, the bright
point seems to be drawn out more or less into a curved line; and, when
the rate of revolution has attained a very high degree of velocity, it
becomes transformed into a continuous circle of light, since the
impression made upon the retina, when the end of the wire is at one
part of the circle, lasts until it has completed a revolution and again re-
turned to the same point. The succession of sparks thrown off rapidly
from a knife-grinder's wheel often produce the effect, even by daylight,
of an unbroken stream of fire. A circular saw with large teeth, driven
by machinery under a high rate of speed, presents apparently a perfectly
smooth edge, the outline of which is formed by the moving points of the
teeth ; and the revolving spokes of a carriage wheel, in rapid motion,
become confused upon the retina with each other and with the interven-
ing spaces, and assume the appearance of a uniform glimmering disk.

The absolute duration of visual impressions upon the retina has been
the subject of various researches, but it is found that its length cannot
be expressed by any single number which would be correct for all cases.
A brilliant light leaves, on the whole, an impression which lasts longer
than that from a feeble one ; but, on the other hand, its relative intensity
to the light of surrounding objects diminishes more rapidly, and con-
sequently, when it is in motion, a higher degree of velocity is required
to produce the appearance of a uniformly bright line. The experiments
employed to determine the length of time, during which a luminous
impression remains upon the eye without appreciable diminution of
its intensity, have been usually those with revolving disks, the surface
of which is variegated in sectors of black and white. The rate of revo-
lution of the disk being known, as well as the width of the different sec-
tors, when the revolving surface presents to the eye the appearance of
an absolutely uniform gray tint, the time during which the black or white
impressions remain undiininished in strength is readily ascertained. The
result obtained, from experiments conducted in this manner, under
moderate illumination, gives the duration of perfect visual impressions as
one twenty-fourth of a second, and, for the oscillation of a very luminous
point following the vibrations of a tuning fork, one-thirtieth of a second.

The persistence and apparent continuity of successive visual images,
appearing at the same spot, is illustrated in the optical contrivance
known as the Thaumatrope, or magic wheel. It consists of an opaque

644: THE SENSES.

disk, with a perforation at one spot near its edge, through which another
disk is visible, placed immediately behind the first, and capable of re-
volving rapidly while the first remains stationary. Upon the second disk
is a circle of pictures representing the same figure in different positions ;
and when, by its revolution, these pictures are made to pass in quick
succession across the opening of the disk in front, they present the ar>
pearance of a single figure in rapid motion. The interval between the
perception by the eye of successive pictures is too short to be observed,
and the same object appears to take successively the different positions
in which it is represented.

Duration of a Luminous Impulse required for the Perception of
Visual Impressions. — This point has been investigated by Rood1 by
means of the light of an electric spark obtained from an induction coil
connected by its terminal wires with the inner and outer surfaces of a
Leyden jar. On breaking the primary current a discharge takes place
between the electrodes, which is of exceedingly short duration. This
duration was measured by Prof. Rood with the aid of a mirror revolv-
ing upon its transverse axis, by which the light of the electric spark
was thrown upon a plate of glass, where it could be examined by the
naked eye, or with a magnifying eye-piece, as in Fig. 208.

The light emanating from the spark S, was received by an achromatic
lens L, of nine inches focal length. It then fell upon a plane mirror
revolving with a uniform velocity of 340 times per second, and, after
reflection by the mirror, was brought to a focus upon a glass plate G,
where it could be examined by the telescope eye-piece E, magnifying

ten diameters. From the known
rate of revolution of the mirror, and
its distance from the glass plate G,
the necessary rate of movement of a
reflected beam upon the plate was
determined. If the spark, used in
these experiments, lasted long
enough for its reflected image to
move over an appreciable distance,
this image would appear to the eye
to be drawn out in the direction of
the movement, owing to the persist-
ence of its visual impression as de-
Apr AR A TUB for measuring the dura- scribed above. But with the mirror

tion of an electric spark -S Position of revolving at this Speed no SUCh de-
the spark. L. Achromatic lens. M. Re-
volving mirror. G. Glass plate for receiv- formation was perceptible, the spark
ing the image of the spark. E. Telescope image appearing of precisely the

same form as if the mirror were

stationary; showing that the duration of the light could not be greater
than .000002 (500'ooo) of a second.

1 The American Journal of Science and Arts. New Haven, September, 1871.

SENSE OF' SIGHT. 645

In a continuation of the experiments, there was interposed between
the spark and the mirror a blackened glass plate, ruled with parallel
transparent lines j% of a millimetre in width, and separated from each
other by the same distance. The image of this plate, when illuminated
by the spark, would appear upon the glass G, so long as the mirror
were stationary, as a series of equal alternating black and white lines.
With the mirror in motion, if the illumination lasted long enough for
the image to be shifted a distance equal to the combined width of a
black and white line, these lines would become undistinguishable from
each other, as in the case of the revolving disk with black and white
sectors. Thus the continuance of the visible lines, under a given rate
of motion, proved that the duration of the electric spark was less than
a certain calculable period. Their disappearance as distinct objects
indicated that the limits of this duration had been reached ; and that
it was long enough to allow of the shifting of two adjacent lines. The
result showed that the duration of the shortest measurable spark was
but little over .00000004 (^ooWo) of a second.

With a spark of this duration, distinct vision of motionless objects
was perfectly possible. The letters on a printed page were plainly to be
seen, and even the phenomena of polarization of light distinctly observ-
able. It is accordingly sufficient to produce a complete retinal impres-
sion.

These experiments do not indicate the time required for the necessary
nervous action in the perception of light. They only show that a lumi-
nous impulse having the above duration is sufficient to cause a distinct
sensation. But the time which is requisite for the sensation to be per-
ceived is very much longer. From the results given in a preceding
chapter (p. 431) it appears that the transmission of a luminous impres-
sion through the optic nerve, would undoubtedly require at least j^^
of a second, and its perception in the brain considerably more. It fol-
lows from this that, at the instant when the image of the electric spark
is seen, in the experiment of Prof. Rood, it has, in fact, already disap-
peared ; the interval which elapses between its actual occurrence and its
perception by the observer being very much greater than the duration
of the spark itself.

The facts detailed above explain the cause of a peculiar optical effect,
which has often been observed under the use of the electric spark ;
namely, that bodies in rapid motion, if illuminated by an instantaneous
discharge, appear to the observer as if at rest. A disk, painted with
black and white sectors, if set in revolution under continuous light,
appears of a uniform gray; or, if the sectors be painted of the rainbow
colors, their tints are mingled and the disk appears white. But if such
a disk, revolving in a dark room, be illuminated by the electric spark,
it becomes visible for an instant, with its different sectors as distinct
from each other as if they were at rest. A jet of water discharged from
an orifice at the bottom of a vessel, though transparent in the imme-
diate neighborhood of the orifice, is turbid lower down; and by instan-

646 THE -SENSES.

taneous illumination the turbid portion is seen to be composed of
separate drops, which appear to be motionless. A flash of lightning has
a similar effect in exhibiting objects which are in motion as if they were
quiescent. The passage of a cannon ball or a rifle bullet by daylight
is imperceptible ; because, as an opaque object, it does not remain long
enough at any one point to efface the persistent impression of the objects
visible behind it, and the sight of these objects accordingly does not
appear to have suffered any interruption. But if such a missile should
happen to be passing in front of the observer in the night time during
a thunder storm, at the moment of a flash, it would be visible equally
with the other parts of the landscape, and would appear as a motionless
object suspended in the air.

The momentary closure of the eyes in winking, for the same reason,
does not cause any noticeable interference with sight, and is not even
observed by the individual ; since the visual impression of external
objects appears to be continuous during the short interval occupied by
the movement of the lids.

The local sensibility of the retina is diminished by continued visual
impressions. This diminution of the retinal sensibility appears to be
continuous from the very commencement of a visual impression, so that
it may be made perceptible within a few seconds. In the experiment of
exhibiting the image of the retinal bloodvessels by changing the posi-
tion of their shadows (page 622) these shadows are visible for an instant
with extreme sharpness. But they begin to fade almost at once and
after a short interval become imperceptible. They can only be seen for
a considerable time, by keeping the light in motion, so that the shadows
fall alternately upon different parts of the retina. The portions of the
retina which are in full illumination have their sensibility so rapidly
diminished, that the shadow, if motionless, is no longer visible by con-
trast. Those which are in shadow, on the other hand, become compara-
tively more sensitive by repose ; and when the shifting of the light
brings them again into illumination, they not only receive more stimulus
than the adjacent parts, but are also more impressible to its influence.

If one eye be covered by a dark glass, and the other be used ex-
clusively, for an hour or two, in reading or writing, at the end of that
time the difference in retinal sensibility of the two eyes will be very
apparent. A single faintly luminous object in a dark room may then
be almost imperceptible to the eye which has been in use, while it will
appear to the other quite brilliant. If the application of the eye have
not been carried beyond the bounds of moderation, this difference is
transitory ; and by reversing the conditions, that is, covering the eye
previously in use, and reading or writing by aid of the other, that which
was before the most sensitive to light becomes less so, and that which
was previously fatigued recovers its sensibility.

The alternate diminution and recovery of the retinal sensibility, by
excitement and repose, is directly connected with the phenomena of
negative images. If the eye be steadily fixed for a short time upon a

SENSE OF SIGHT. 647

white spot in the middle of a black ground, and then suddenly directed
toward a blank wall of a uniform white or light gray color, a dark spot
will appear at its centre, of the same apparent size and figure with the
white one previously observed. This is the " negative image" of the
retinal impression. That part of the retina which was first impressed
by the rays from the white spot becomes less sensitive to light ; and
another white surface, looked at immediately afterward, appears darker
than usual. On the other hand, those parts which were exposed only
to the dark ground, that is, to the comparative absence of light, are
more sensitive than before ; and the surface of the white wall, outside
the central spot, appears brighter than usual. It is not necessary that
the contrast in hue between the different parts of a retinal image should
be as strong as that of black and white, in order to produce this effect.
Any decided difference in illumination will be sufficient. It is not even
essential to look at a different background, to observe the appearance
in question. If a piece of furniture of dark wood be placed against a
blank wall of white or gray surface, and looked at steadily for a short
time, on shifting the eyes to a different part of the same wall, the figure
of the chair or table will appear, with all its details of outline, expressed
in a lighter tint than that of the surrounding parts.

The above effect may be also produced in a still more simple man-
ner. Let a black ruler, about one inch wide, be laid upon a sheet of
white paper, and looked at steadily for thirty or forty seconds. If the
ruler be now removed by a sudden motion, the eye remaining fixed, its
image will appear as a bright band upon the paper, fading gradually as
the sensibilitjr of the retina becomes equalized in its different parts.

If the figure which is thus examined be a colored one, its negative
image, subsequently produced, will present a complementary hue to that
of the original object. A strip of red paper placed upon the white
sheet, and then suddenly removed, leaves a negative image which is
bluish-green ; and a green one leaves an image which has a decided
tinge of red. This shows that the sensibility of the retina may be in-
creased or diminished separately for the different colored rays of the
luminous beam. While looking at a red object, the retina becomes less
sensitive to the red rays, but more so for those at the opposite end of
the spectrum, and vice versa ; so that, on looking subsequently at a
white object, the negative image exhibits a tint corresponding to the
rays for which the retina has remained most sensitive. That this is the
mechanism of the production of complementary colors in negative
images becomes evident on simplifying the experiment. If the black
ruler be laid upon a book bound in blue cloth, on taking it away the
band which remains in its place is of a more intense blue than the rest.
If a red book be used for the same purpose, the negative image of the
ruler presents a remarkably pure red color, while the remainder of the
surface appears of a dull brown.

The variable sensibility of the retina, according to its exposure,
affords an explanation of the well-known fact, that under some condi-

648 THE SENSES.

tions an object may be most easily perceived by indirect vision. It
often happens that in searching for a star of very small magnitude and
feeble light, it may be momentarily perceived by looking not directly
at it, but at a point in its immediate neighborhood, at a small angular
distance from its real position. The star is not seen distinctly under
these circumstances, because it is out of the line of direct vision. But
its light falls upon a part of the retina near the fovea centralis, the sen-
sibility of which is more acute than usual, owing to its continued
exposure only to the dark sky ; while the fovea itself, which has been
receiving in succession the images of particular stars, is comparatively
deficient in impressibility to light. When the visual axis is turned
directly upon the fainter star, for the purpose of getting a distinct
image, its light disappears ; and thus it can only be seen as an evanes-
cent object by indirect vision.

If the eye be fixed immovably for too long a time upon the same
luminous object, the local diminution of retinal sensibility may amount
to fatigue ; and a persistence in its continuous application may produce
permanent injury of the visual organ. After steadily examining a
single object for even a short time, it becomes difficult to resist the
tendency to turn the sight in another direction by the automatic move-
ment of the muscles of the eyeball. Naturally, the eye never rests for
more than a few seconds upon an}r one point in the field of view ; but
is directed in succession at different objects, fixing each one in turn at
the point of distinct vision, and immediately passing to another more
or less remote. Thus the fatigue of the retina is avoided, since those
parts which at one instant have a stronger illumination, at the next
receive the impression of a shadow ; and no portion of the membrane
is .exposed sufficiently long to any single object to become insensible to
its grade of light or color.

There is also reason to believe that the eye requires, for its safety,
the periodical suspension of all visual impressions which is obtainable
in sleep. It is not essentially different in this respect from other parts
of the nervous apparatus of animal life ; but the delicacy of its sensi-
bility, which is requisite for the due performance of its function, and the
complication of its structure, which includes so many parts adjusted to
each other with mathematical accuracy, indicate that it is one of the
organs most liable to derangement if deprived of its natural interval
of restoration and repose.

Sense of Hearing.

By the sense of hearing we receive the impressions of sound, and
appreciate their intensity, their tone or pitch, with all the variations
of higher or lower notes, as well as their quality, that is, the different
character of sounds of the same tone and intensity, but produced by
different methods, as by reeds, strings, or wind instruments, or by the
concussion of solid bodies. Our idea of time, or the succession of
events, seems also to be connected more especially with auditory sensa-

SENSE OF HEARING. 649

tions. The impressions received in this way depend upon the vibrations
excited in the atmosphere by sonorous bodies, which are themselves
thrown into vibration by various causes, and which then communi-
cate similar undulations to the surrounding air. These undulations
are of such a kind that they cannot be directly appreciated by the
organs of general sensibility ; but when communicated to the auditory
apparatus they produce, through it, the sensation of sound.

Organ of Hearing. — The organ of hearing consist of, first, the ex-
ternal ear, a conch or trumpet-shaped expansion, destined to collect the
sonorous impulses coming from various quarters, and to conduct them
into its tubular continuation, the external auditory meatus ; secondly,
a membranous sheet or drum-head, the membrana tympani, stretched
across the bottom of the external auditory meatus, by which the sono-
rous vibrations are received and transmitted, through the chain of bones
or auditory ossicles, across the cavity of the tympanum or middle ear,
to the third portion of the auditory apparatus, namely, the labyrinth,
or internal ear ; a cavity excavated in the petrous portion of the tem-
poral bone, filled with fluid, and containing various membranous sacs
and canals, upon which are distributed the filaments of the auditory
nerve.

Thus the delicate terminal expansions of the auditory nerve, deeply
concealed in their bony cavities, and sustained by the surrounding fluid,
are protected from all other mechanical impressions, but are so placed
as to receive the impulse of sonorous vibrations.

External Ear. — The external ear consists of a cartilaginous frame-
work, covered with integument, loosely attached to the bones of the
head, and more or less movable by means of various muscles, which,
by their contractions, tend to turn its concavity in various directions.
In man, notwithstanding the existence of these muscles, their functional
activity is nearly imperceptible ; and it is only in exceptional cases that
thej7 are capable of producing a partial sliding or rotatory movement of
the external ear. In most of the quadrupeds, on the other hand, these
movements are vigorous and extensive, and play an important part, not
only in the changes of expression by varying the attitude of the ex-
ternal ear, but also in aid of the sense of hearing, by enabling the
animal to catch distinctly the sonorous vibrations, from whatever quarter
they may come. By their assistance the direction of a sound is also
appreciated, since the animal ascertains, in placing the ear in different
positions, the region from which it is received with the greatest distinct-
ness.

Membrana Tympani and the Chain of Bones — The membrana tym-
pani is a fibrous sheet of circular form, composed of a principal la}^er
not more than 0.05 millimetre in thickness, but quite strong, and con-
sisting of circular and radiating tendinous fibres with a trace of inter-
mingled elastic fibres. Its external and internal surfaces respectively
are covered by thin continuations of the integument of the external
auditory meatus on the one hand, and of the mucous membrane of the
42

650 THE SENSES.

tj'mpanic cavity on the other ; and all three layers together form a mem-
brane which is about 0.10 millimetre thick.

In its natural condition the membrane is drawn inward, by its attach-
ment to the handle of the malleus, in such a way that its external sur-
face • exhibits a funnel-shaped depression, the deepest point or bottom
of which corresponds to the situation of the end of the handle of the
malleus. According to the observations of Helmholtz,1 the sides of this
funnel-shaped depression are not plane but convex, somewhat like the
inner surface of the blossom of a morning-glory. It is only along a
single line, corresponding to the attachment of the handle of the malleus,
that the meridian of the funnel would be a nearly straight line ; else-
where the radial fibres of the membrana tympani are curved, with their
convexities looking toward the external auditory meatus.

As the only attachment of the membrana tympani, except at its cir-
cular border where it adheres to the bony walls of the meatus, is to
the movable handle of the malleus, any movement of the handle of the
malleus inward will draw the membrana tympani in the same direction,
deepen the funnel-shaped depression at its centre, and put its fibres
more upon the stretch. On the other hand, a movement of the mem-
brana tympani outward will draw the handle of the malleus outward ;
and, finally, if the malleus be held in a position of equilibrium, by its
elastic and muscular attachments internally to the membrana tympani,
any movement of this membrane, either outward or inward, will be
followed \)y a corresponding change of position in the malleus itself.

This is the physiological action of the membrana tympani. From its
thinness and tension and from its position at the bottom of the external
auditory meatus, it enters into vibration, under the impulse of sound
coming from the exterior, and communicates similar movements to the
handle of the malleus attached to its internal surface.

The chain of bones consists of three ossicles, articulated with each
other by their corresponding extremities, and forming a zigzag line
of jointed levers, extending from without in-
_*g' 209> ward, across the cavity of the tympanum.

They are known respectively, from the resem-
blances of their configuration, as the " malleus,"
"incus," and "stapes," or the hammer, the
anvil, and the stirrup. The malleus is about
OSSICLES of the human nine millimetres in length, of which a little

stags' M(Rfldin er I™"*' 3' more tna" one-third is occupied by the rounded
head and the neck, and a little less than two-
thirds by the comparatively straight and tapering handle. The very
slender long process projects laterally in a nearly horizontal direction
from behind forward in the natural position of the bone. The handle
is the only part of the malleus which is adherent to the membrana

1 Mechanism of the Ossicles of the Ear. Translated by Albert H. Buck, M.D.,
and Normand Smith, M.D. New York, 1873, p. 20.

SENSE OF HEARING. 651

tympani, the neck corresponding to the upper border of this membrane,
while the head projects above it, lying comparatively free in the cavity
of the tympanum. It is, however, maintained more or less closely in
its position by thin ligamentous bands arising from the bony wall of the
tympanic cavity and inserted into its head and neck, and by the tendon
of the internal muscle of the malleus or " tensor tympani," which, com-
ing from a direction anterior and internal to the bone, is inserted into
the upper extremity of its handle. The action of this muscle is to
draw the handle of the malleus inward, tightening the membrana tym-
pani, and rotating the head of the malleus slightly outward. The prin-
cipal movement of the malleus is therefore a rocking, to and fro move-
ment, about a nearly horizontal axis situated at the junction of the
handle and the neck.

The head of the malleus is articulated with the body of the incus by
acapsular joint with double-inclined surfaces. As Helmholtz has shown,
the surfaces are so different in their inclination, one being very steep,
the other but slightly oblique, that when the handle of the malleus is
drawn inward, the two articular surfaces lock together, and the incus
follows the movement of the malleus ; but when the latter bone is
drawn outward, the surfaces may glide upon each other, without the
incus necessarily moving at the same time.

The third bone of the middle ear, the stapes, has in its form the most
exact resemblance to its namesake, an ordinary metallic stirrup. It is
articulated by its angular extremity to the lower end of the long arm
of the incus in such a manner as to be nearly horizontal in position, its

Fig. 210.

RIGHT TEMPORAL BONE of the new-born infant, seen from its inner side; showing
the internal surface of the membrana tympani and the chain of bones in their natural posi-
tion. (Riidinger.)

two arms being placed, one anteriorly the other posteriorly. Its oval
base corresponds in form, and nearly in size, with the fenestra ovalis
of the bony labyrinth, in which it is inserted; being adherent by its
surface and its edges to the internal periosteum of the labyrinth.

652 THE SENSES.

The stapes accordingly forms a kind of movable lid or piston-head
occupying the orifice of the fenestra ovalis, and capable of transmitting
directly to the fluid of the labyrinth the impulses received from the
membrana tympani. The extent of inward and outward movement of
the base or footpiece of the stapes has been determined by Helmholtz
in the following manner. The cavity of the tympanum and that of the
vestibule having both been opened from above, the point of a line sewing
needle was inserted into the fibrous covering of the base of the stapes
from the side of the vestibule, and the needle allowed to rest, near the
point of its'insertion, upon an adjacent edge of bone. It thus formed a
kind of index-lever, which would indicate by the displacements of its
long arm, very slight movements of the stapes. The stapes was then
pressed inward and outward, as freely as its attachments would allow,
either by means of a needle applied to the bone itself, or by alternately
condensing and rarefying the air in the external auditory meatus ; the
force, in the latter case, being transmitted through the membrana t3'm-
pani and chain of bones. The same observer estimated these movements
according to another plan, by opening the superior semicircular canal
of the labyrinth, and inserting into it a slender glass tube of known
calibre, a portion of which, as well as the cavity of the vestibule, was
filled with water. Any inward pressure upon the stapes would accord-
ingly be indicated by a corresponding rise of the level of water in the
tube. The movement of the stapes, in these experiments, varied, accord-
ing to circumstances, from .025 to .072 millimetre.

The change of position of the stapes in the fenestra ovalis, due to the
impulses received through the chain of bones, is not a simple sliding
movement of advance and recession, but a rocking motion, in which its
upper border is tilted over toward the cavity of the vestibule and back
again, and its anterior end moves more freely than its posterior. This
feature of the action of the stapes, which has been described by several
observers, is shown by Helmholtz to depend upon the varying compact-
ness of its fibrous attachments ; these attachments being closer along
its inferior border and at its posterior end, thus allowing more freedom
of movement above and in front than below and behind.

The position of the stapes is also regulated by the action of the
stapedius muscle. This muscle, the smallest in the body, arises from a
bony canal behind the cavity of the tympanum ; and its slender tendon,
after entering this cavity, passes almost directly forward and is inserted
into the posterior side of the neck of the stapes, near its articulation
with the incus. Its contraction will, therefore, draw the angle of the
stapes backward and its anterior extremity outward from the fenestra
ovalis.

Physiological Action of the Chain of Bones and the Muscles of the
Middle Ear. — The cavity of the tympanum is an irregularly shaped
space, inside the membrana tympani, filled with air, across which the
vibrations received by the membrane from without are transmitted by
the chain of bones. In their natural position and with their natural

SENSE OF HEARING. 653

tendinous connections undisturbed, these bones are held in such close
connection with each other that they vibrate as a single solid body.

The vibratory movement of the ossicles of the ear has no immediate
dependence upon the action of the muscles attached to them, but results
from the shocks received by the tympanic membrane. The influence of
the muscles is to increase or diminish the tension of this membrane,
and thus to influence the mode of transmission of the sound.

The action of the internal muscle of the malleus, or tensor tympani,
is beyond doubt, as its name indicates, to increase the tension of the
membrana tympani. It has long been known that, on opening the canal
in which this muscle is lodged, as well as the cavity of the tympanum, by
drawing upon its tendon within the canal, the membrana tympani may
be manifestly rendered more tense ; and according to Helmholtz, all the
ligaments holding the ossicles in place are at the same time put upon
the stretch.

The effect produced upon the act of hearing by increased tension of the
membrana tympani has been interpreted in a different sense by different
observers. Savart,1 who first studied systematically the vibrations
induced in stretched membranes by the proximity of sounding bodies,
estimated the extent of these vibrations by the agitation of particles of
fine sand spinkled on the surface of the membranes ; and he found the
vibrations more difficult of production, other things being equal, when
the tension of the membrane was increased. He applied the same mode
of experimentation to the membrani tympani in the ear of man and
animals, and found not only that sand, sprinkled on its surface, would
be thrown into agitation by holding near it a sounding body, but that
also, as in the former case, these appearances were less easy of produc-
tion when the membrane was rendered more tense by traction upon the
tensor tympani muscle. He concluded from that, that during life the
ear is more susceptible to sounds of a given intensity when the mem-
brana tympani is relaxed, and less so when it is put upon the stretch ;
the tensor tympani, accordingly, exerting a protective action by lessen-
ing the apparent intensity of very loud sounds.

This view has been adopted by many eminent authors, owing in great
measure to the valuable experiments of Savart. But this observer was
not aware of an important fact which has been established by subse-
quent investigations, namely, that stretched membranes, like cords, can-
not respond indiscriminately to sounds of every grade of tone, but only
to a certain number of these tones, which are separated from each other
by definite intervals ;* and they will respond to a different set of tones
only after their tension has been increased or diminished. In order,
therefore, that a membrane may be easily thrown into induced vibra-
tion, its tension must correspond in a certain ratio with the tone of the
sound produced.

1 Journal de Physiologic. Paris, 1825, tome iv. p. 2^5.

2 Daguiu, Traite elementaire de Physique. Paris, 1867, tome i. p. 596.

654: THE SENSES.

These considerations have induced a different view of the action of
the tensor tympani in modifying the sensations of sound. With the
membrane in a state of moderate tension, a certain proportion of tones
only are distinctly appreciated, while the remainder are either inaudible
or imperfectly transmitted to the internal ear. This is the state in
which sounds generally are received by the organ of hearing, without
exact appreciation of their relative pitch. But when the ear follows
distinctly successive tones of varying pitch, or when it listens intently
for a particular note, the tension of the membrana tympani is increased
or diminished to such a degree as will enable the vibration to be trans-
mitted with the most complete distinctness by the chain of bones to the
fluid of the labyrinth. With regard to the modifications induced in the
apparent intensity of sound, it is probable that Savart's explanation
holds good ; and that a diminished tension of the membrane enables
the ear to catch more readily sounds which are faint or distant. This
partial relaxation is accomplished by the action of the stapedius muscle,
which is animated directly by a filament of the facial nerve ; while the
tensor tympani is supplied only from the otic ganglion of the sympa-
thetic.

The cavity of the tympanum is not hermetically closed, but commu-
nicates with the pharynx by means of the Eustachian tube. The exist-
ence of this opening secures the equality of atmospheric pressure within
and without the membrana tympani, a condition which is essential to its
proper vibration under the influence of sonorous impulses. The ex-
ternal barometric pressure varies from day to day, and even for dif-
ferent periods of the same day ; and if the middle ear were a closed
cavity, this variation would of itself change the tension of the mem-
brana tympani, independently of the action of the muscles. Although
the mucous surfaces of the Eustachian tube are habitually in contact
with each other, the}^ readily yield to a preponderance of atmospheric
pressure in either direction, and thus the equilibrium is maintained
between the air inside and outside the cavity of the tympanum.

Labyrinth. — The internal ear, or labyrinth, so called from the compli-
cated extension and windings of its various cavities and passages, is
situated in the petrous portion of the temporal bone. Its external wall
consists of a thin lamina of compact osseous tissue, which is readily
isolated in the foetus and in newly born infants, owing to its being im-
mediately surrounded by spongy tissue; while in the adult it is more or
less completely consolidated with the adjacent bony parts. It may be
divided physiologically into: 1. The vestibule and semicircular canals,
which constitute its most essential parts and are present in all verte-
brate animals ; and 2. The cochlea, which, in man and the mammalia, is
a more highly developed portion, of complicated structure, but which
is absent in the fishes and naked reptiles, and only partially developed
in the scaly reptiles and in birds.

The vestibule (Fig. 211,i) is so called because its cavity is that into
which the fenestra ovalis immediately opens, and from which those of

SENSE OF HEARING. 655

the semicircular canals and cochlea Fig. 211.

diverge in various directions. It is
of a more or less ovoid form, and
presents, toward the cavity of the
tympanum, two openings, namely :
1. The fenestra ovalis (5), corre-
sponding in form to the base of the
stapes, which nearly fills it, and
which is • adherent to the internal
periosteum of the labyrinth stretch-
ed across the opening ; and 2. The
fenestra rotunda (e) of smaller size BoNY LABYKINTH OF THE HUMAN

EAR, twice the natural size.— 1. Vestibule.

and Closed Only by a fibrOUfl mem- 2 Superior vertical semicircular canal. 3.
brane. The posterior portion of the Inferior vertical semicircular canal. 4.
.. . . Horizontal semicircular canal. 5. Fenestra

Vestibule gives origin to the three Ovalis. 6. Fenestra rotunda. 7. Cochlea.

semicircular canals, which commu-
nicate with its cavity at each extremity, namely: 1. The superior ver-
tical canal ( 2 ) the plane "of which is directed across the longitudinal
axis of the petrous bone. 2. The inferior vertical canal ( 3 ) the plane
of which is parallel with the internal surface of the petrous bone ; and
3. The horizontal canal (4) which is directed across the axis of the
petrous bone, but lies, as its name indicates, in a horizontal plane. Each
semicircular canal opens into the vestibule by two orifices, one at each
end ; except that the two vertical canals unite at one of their extremi-
ties into a branch and orifice common to both. Thus there are five
orifices leading from the vestibule into the three semicircular canals ;
and each canal has free communication at each end, directly or indi-
rectly with the interior of the vestibule. Each canal is enlarged at one
of its extremities where it joins the vestibule, into a slightly rounded
dilatation.

The common cavity of this part of the bony labyrinth contains a
limpid, colorless fluid, the perilymph, and, in addition, a closed mem-
branous sac, also filled with fluid, which, by its various prolongations,
presents a repetition of the form of the vestibule and semicircular canals.
This, together with its extension in the cochlea hereafter to be described,
constitutes the membranous labyrinth. It forms the most important
part of the internal ear, since in its walls the filaments of the auditory
nerve have their terminal distribution.

The cavity of the vestibule contains two membranous sacs, lying in
contact with each other, but separated by a transverse partition. One
of these, the smaller of the two, is the sacculus, a spherical vesicle, a
little over 1.5 millimetre in diameter, occupying the anterior and inferior
portion of the vestibule, and communicating by a narrow canal with the
ductus cochlearis of the cochlea. The other, or larger sac, is the utricle,
of ellipsoid form, measuring 3.5 millimetres in its long diameter. The
utricle nnd the three membranous semicircular canals communicate with
each other in the same way as the corresponding bony cavities in which

656 THE SENSES.

they are lodged. Each membranous semicircular canal presents at one
of its extremities, at the expanded part of its bony canal, a similar
rounded dilatation, known as the " ampulla."

The membranous sacs and semicircular canals are considerably
smaller than the osseous cavities which contain them, and occupy
nearly everywhere an eccentric position ; being, at certain points, in
contact with and adherent to the internal periosteum, while at others
they are surrounded by the perilymph. The sacculus and utricle
together occupy about two-thirds of the cavity of the vestibule; and,
according to Riidinger, are so placed that neither of them touches the
base of the stapes at the fenestra ovalis, but are separated from it by
an appreciable layer of fluid. Thus the sonorous impulses which reach
the membranous labyrinth come to it, not directly from the stapes, but
through the intermediate vibration of the perilymph.

The sacculus and the utricle are adherent to the internal periosteum
of the vestibule at the points of entrance of their corresponding branches
of the auditory nerve. The ampullae of the semicircular canals fill
almost completely the bony cavities in which they rest, their outer
surface lying for the most part in contact with the periosteum. On
the other hand, the membranous semicircular canals are very much
smaller in calibre than the osseous excavations which contain them,
and lie in contact with the periosteum only along the inner or smaller
curvature of the bony canals ; so that they are surrounded externally
by a comparatively large quantity of perilymph. They are, however,
attached and held in place, as shown by Riidinger, by slender, scattered,
fibrous bands and partitions, which traverse at various points the peri-
lymphic space.

The main point of interest in regard to the membranous labyrinth
relates to the mode of distribution and termination of the auditory
nerve.

The auditory nerve sends to the vestibule two branches; one of
which is distributed to the sacculus, the other to the utricle and
ampulla?. The mode of termination of the nerve fibres in both these
divisions is essentially the same. They are not distributed generally
over the membrane, but terminate only in particular well-defined spots,
characterized by a thickening or prominence of the membranous wall,
and by the presence of a peculiar form of epithelium provided with stiff,
pointed cilia, the so-called auditory hairs.

In the sacculus and in the utricle, the terminal nerve spot, or " macula
auditiva," is in the form of an oval plate, or lamina, 3 millimetres by
1.5 in the sacculus, and 3 millimetres by 2 in the utricle. In the am-
pullae, it forms a transverse ridge or fold of the membranous wall, pro-
jecting inward after the manner of the valvnlae conniventes of the small
intestine, but occupying only about one-third of the circumference of
the ampulla. Elsewhere, the membranous sacs of the labyrinth are
lined, according to Kolliker, by a single layer of pavement epithelium
cells. But at the spots in question the epithelium is twice or three

SENSE OF HEARING. 657

times as thick as in the remaining portions, and consists of elongated
cells of two different forms, namely, cylindrical and fusiform. It also
presents, standing upright upon its free surface, the pointed cilia above
mentioned, or auditory hairs, which in man are about 25 mmm. in
length. The terminal nerve fibres of the auditory nerve, which pass
up toward these thickened spots of epithelium, may be traced, accord-
ing to the testimony of all recent observers, into the epithelial layer
itself; and certain appearances give rise to the supposition that the
ultimate axis-cylinder of each nerve fibre is prolonged through the sub-
stance of a fusiform epithelium cell, and finally becomes the cilium or
auditory hair projecting from its free extremity. These appearances
are, 1st, the similarity in size and aspect between the axis-cylinder of
the nerve fibres and the slender downward prolongations of the fusiform
cells; and, 2d, the fact that both these structures become stained more
or less deeply of a blackish or brown color by the action of osmic acid
(Riidinger). Whatever the precise relations of the terminal nerve
fibres to the other elements of the epithelial layer may be, there is no
doubt that the projecting cilia act either mechanically, or by virtue of
a real nervous sensibility belonging to them, and are the immediate
recipients of the sonorous vibrations communicated by the surrounding
fluid.

A remarkable secondary feature connected with the auditory spots of
the sacculus and utricle is the existence, at each, of a deposit of minute
solid calcareous grains, the so-called otoconia, or ear sand. These grains
are embedded in a homogenous gelatinous material, and form a white
chalky-looking \ayer immediately over the auditory spot, by which the
situation of this spot is easily recognized. The grains are composed
almost exclusively of lime carbonate. They are rounded, elongated,
or distinctly prismatic and crystalline in form ; the largest measuring,
according to Kolliker, about 10 mmm. in length. The exact office per-
formed by these calcareous deposits is unknown, but it is evident from
their constant existence in the same situation in different animals, that
they have some important relation to the sense of hearing. In mam-
malians and birds they are pulverulent, as in man. In reptiles and fish
they assume the form, sometimes, of friable chalk}7 concretions, some-
times of rounded masses of considerable size, hard and dense as por-
celain. According to Wagner, they are completely absent only in the
cyclostomi, or lowest order of true fishes, including the lamprey and
the hag.

Physiological Action of the Membranous Labyrinth. — The sacculus
and utricle, contained in the cavity of the vestibule, are membranous
formations, to which the fibres of the auditory nerve are distributed, and
in which they terminate. These membranous expansions are supported
by the contact of fluid on each side, and are held in place by the partial
fibrous attachments which connect them with the wall of the vestibule.
They are the structures upon which the impressions of sound are finally
received, and correspond, in this respect, to the retina in the organ of

658 THE SENSES.

vision. The sonorous impulses, first communicated by the atmosphere
to the membrana tympaui, are thence transmitted through the bony
tissue of the malleus, incus, and stapes. From the base of the stapes
they pass to the perilymph of the vestibular cavity ; from that, through
the floating wall of the membranous sac, to the endolymph or the fluid
contained in its interior ; and it is the vibration of this internal fluid
which finally acts upon the sensitive nervous terminations in the audi-
tory spot. It is thus through a series of intermediate vibrations, that
sounds coming from the exterior produce their impression upon the
internal ear.

Office of the Semicircular Canals. — These singular appendages of
the bony and membranous labyrinth have attracted attention, especially
on account of the constancy of their occurrence and the peculiarity of
their position. The principal features of their anatomical history are
the following :

1. They are universally present, as portions of the internal ear, in
mammalians, birds, and reptiles, and nearly always in fish ; being entirely
absent only in amphioxus, where there is no organ of hearing whatever.

2. They are always three in number. The only exception to this rule
is found among fishes, in the lamprey and the hag ; where the entire struc-
tural development, especially in the organs of sense, is very incomplete.1
In the lamprey there are two, and in the hag one only, the cavity of
which is confounded with that of the utricle ; the whole forming a mem-
branous canal bent upon itself like a ring.

3. The three canals stand in three different planes, which are all per-
pendicular to each other. Thus one is vertical and longitudinal, in
respect to the axis of the petrous bone ; another vertical and transverse;
and the third transverse and horizontal. They represent accordingly,
by their position, the three dimensions of space ; and from this circum-
stance the idea was earty suggested that they might serve in some way
to indicate the direction in which sounds arrive from the exterior.
But subsequent researches have yielded nothing to corroborate this
assumption ; and it is evident, furthermore, that, from whatever quarter
sonorous impulses originally come, they must traverse the membrana
tympani and chain of bones, and finally reach the internal ear by the
same course. This view of the office of the semicircular canals is
therefore no longer entertained.

Lastly, an essential point in their anatomical structure is that they
are destitute of nerve fibres, and consequently are wranting in sensi-
bility. The only nervous distribution connected with them is that to
the ampullae situated at one of their extremities, but no nerve fibres
extend to the semicircular canals themselves. The function which they
perform must therefore in all probability be one of a mechanical or
physical kind.

1 Owen, Anatomy of the Vertebrates. London, 1868, vol. iii. p. 222. Wagrner,
Comparative Anatomy of the Vertebrate Animals, Tulk's translation. New York,
1845, p. 227.

SENSE OF HEARING. 659

In experimenting upon the internal ear in the lower animals, it has
been remarked that division or injury of the semicircular canals is fol-
lowed by a singular alteration in the position and movements of the
animal, indicating a disturbance of equilibrium. These phenomena were
first made known by Flourens in 1825,1 and have been corroborated by
many subsequent observations, the most recent being those of Cyon,
Curschman, Boettcher, and Berthold, in 18t4. The results met with are
not explained in the same way by all experimenters, but there is little
discrepancy in regard to the phenomena actually presented. The opera-
tion of exposing the semicircular canals during life is impracticable, as
a general rule, in the mammalia, owing to the density of the petrous
bone in which they are imbedded ; but it can be done without much
difficulty in birds, where they are surrounded only by a loose and
spongy osseous tissue. The pigeon is the species which has been most
frequently used for this purpose.

The most striking and constant effect produced by injury of the semi-
circular canals consists of abnormal oscillatory movements of the head,
together with an imperfect balancing of the whole body These phe-
nomena vary according to the particular canal which has been divided.
If a vertical canal be the one injured, the oscillation of the head is up-
ward and downward; if it be a horizontal canal, the oscillations are
lateral, from left to right, and vice versa. If the two corresponding
canals on both sides be divided, the abnormal movements are much
more rapid and continuous than if the injury be inflicted on one alone.
The animal is still capable of preserving the equilibrium of the body, so
long as he remains at rest ; but any attempt at movement brings on a
disorder of muscular action which makes walking, running, or flying-
difficult or impossible. The most simple interpretation of these results
is that the animal can no longer appreciate the direction or extent of
the changes in position of the head, and that the sense of equilibrium
is consequently impaired for movements of the body and limbs.

The manner in which the semicircular canals, in their natural condi-
tion, may be regarded as contributing to the sense of equilibrium, is as
follows : If a glass goblet, filled with water, be turned round its vertical
axis, it will be seen that the water does not readily turn with it; and
any small objects suspended in it, or floating upon its surface, will
remain in nearly the same position, while the goblet revolves through
an entire circle. The adhesion of the fluid to the sides of the glass
vessel is not sufficient to communicate to it at once the circular motion
of the parts with which it is in contact. Consequently the water lags
behind the glass; and if any flat object were cemented perpendicularly
to the inside of the goblet, so as to turn with it, it would be subjected
to a backward pressure from the water, whenever the goblet were put
in rotation.

1 Recherches Exp6rimentales sur les Propri£t6s et les Fonctions du Systfeme
Nerveux, 2me Edition. Paris, 1842, pp. 452, 454.

660 THE SENSES.

Somewhat similar conditions are present in the semicircular canals.
Whenever the head is rotated from side to side in a horizontal plane, a
momentary increase of pressure must take place in the fluid of the
horizontal semicircular canal (Fig. 211, *), either toward or from the
ampulla at one end; and this increase or diminution of pressure may be
preceptible by the nervous expansions which are situated there. If the
head be moved upward or downward, a similar variation of pressure
will take place in the inferior vertical canal (Fig. 211, a) ; and if it be
inclined laterally, toward the right or left shoulder, the superior vertical
canal (Fig. 211, 2), will experience a variation of the same kind. Thus,
although the membranous semicircular canals be not themselves sensi-
tive to pressure, they may serve as channels for conducting an impulse
to the sensitive organs in their ampullae. Even the peculiar configura-
tion of the nervous expansions in the ampullae seems especially adapted
for this purpose; since they are arranged in the form of transverse
crescentic folds, while in the sacculus and utricle they are simply flat-
tened prominences on the inner surface of these cavities.

If the question be asked, why an apparatus for appreciating changes
of equilibrium should be especially associated with the organ of hearing,
it may be remarked that in the auditory labyrinth alone there is to be
found a terminal distribution of sensitive nerve fibres in an epithelium
provided with hair cells, and surrounded by a fluid of watery consis-
tency ; all of which conditions are suitable for the perception both of
sonorous vibrations and of the variation in pressure due to changes of
position.

Cochlea. — The cochlea, named from its external resemblance to a
snail-shell, is a bony canal rolled spirally about a central axis, and

Fig. 212.

BONY COCHLEA OF THB HUMAN EAR, right side ; opened from its anterior face.

(Cruveilhier.)

making between two and three turns upon itself. Owing to the gradual
rise of the turns, it has a slightly conoidal form, the extremity of which,
or cupola, is directed forward, downward, and outward. The canal of

SENSE OF HEARING. 66i

the cochlea is divided longitudinally into two parts by a thin, bony par-
tition, the spiral lamina, which winds round its bony axis, following
its spiral turns, but limited externally by a free border.

From the free border of the bony spiral lamina a fibrous membrane,
the membrana basilaris, extends outwardly quite to the external wall
of the cavity, to which it is attached. The common canal of the cochlea
is thus divided into two parallel passages or stairways, one above the
other. The superior of these passages communicates freely at its base
with the cavity of the vestibule, and is the scala vestibuli. The inferior
reaches to the fenestra rotunda, and is terminated by the membrane
stretched across this opening, which alone divides its cavity from that
of the tympanum ; it is accordingly known as the scala tympani. Both
these canals extend, in their spiral course, to the summit or cupola of
the cochlea. At this point a minute orifice of communication between
the two has been described by some writers, and doubted by others.
According to the observations of Buck,1 it is probable that no such
opening exists in the natural condition of the parts, unless it be micro-
scopic in size. But whether the two canals communicate or not, at the
summit of the cochlea, the partition between them, throughout their
parallel course, is partly membranous ; and by this means an increase
or diminution of pressure upon the fluid of the vestibule at the fenestra
ovalis will be at once transmitted, through that of the scala vestibuli
and the scala tympani, to the membrane of the fenestra rotunda. Not-
withstanding, therefore, the incompressible character of the fluid of the
labyrinth, provision is made, to a certain extent, for the movement of
the stapes, according to the contraction or relaxation of the muscles of
the middle ear.

But the septum above described, formed by the spiral lamina and the
membrana basilaris, is not the only longitudinal partition in the cavity
of the cochlea. The scala vestibuli is also divided into two parallel
canals, an internal and an external, by a thin membranous sheet which
starts from the upper surface of the spiral lamina near its outer border,
and extends upward and outward to reach the external wall of the coch-
lear cavity. As this membrane leaves the plane of the spiral lamina
and membrana basilaris at an angle of about 45 or 50 degrees, it shuts
off from the scala vestibuli a separate canal of prismatic form, having
for its floor the membrana basilaris, for its outer wall the wall of the
cochlea, and for its upper boundary the oblique membranous partition
between it and the scala vestibuli. This canal contains the auditory
epithelium cells and the termination of the fibres of the auditory nerve.
It is therefore the essential part of the cochlea, and is termed accord-
ingly the ductus cochlearis,

The ductus cochlearis terminates at the summit of the cochlea by a

1 On the Mechanism of Hearing, Prize Essay of the Alumni Association of the
College of Physicians and Surgeons, New York. Published in the New York
Medical Journal, March, 1874.

662 THE SENSES.

blind extremity ; but at its base it communicates, by a narrow channel,
with the cavity of tlie sacculus. It is consequently an extension of the
sacculus, and a part of the membranous labyrinth ; while the scala ves-
tibuli is only an extension of the general cavity of the vestibule. The
ductus cochlearis may be considered as a tubular prolongation of the
sacculus, rolled upon itself in a spiral form, and maintained in position
by the bony and membranous partitions of the cochlea by which it is
enveloped. Like the rest of the membranous labyrinth, it is filled with
a watery fluid, and is bathed externally on both sides by the perilymph,
except where it is adherent to the wails of its bony cavity.

Organ of Corti. — The inner surface of the ductus cochlearis is lined
for the most part with a thin layer of pavement epithelium, except along
a longitudinal line situated at about the middle of the membrana basi-
laris. Here there is a continuous elevated ridge, four or five times
thicker than the epithelium elsewhere, following a spiral course, like
the rest of the cochlear structures, and consisting of enlarged and modi-
fied epithelium cells, with the terminal fibres of the auditory nerve.
This body is termed the organ of Corti, from the name of the observer
who first described it in 185 1.1 It is justly considered as the most
remarkable and complicated structure in the internal ear, although in
its essential features it is analogous to the auditory spots in the sac-
culus and utricle.

Fig. 213.

DIAGRAMMATIC SECTION OP THE ORGAN OF CORTI, in profile; from the descrip-
tions of various authorities. — 1. Membrana basilaris. 2,3. Internal and external fibres of the
arch. 4. Epithelium cells r.ear its inner and outer borders. 6, 5, 5, 5 Hair cells lying in con-
tact with the arch. Magnified 500 diameters.

The organ of Corti rests upon the upper surface of the membrana
basilaris. Its framework consists of a series of elongated, rafter-like
bodies, arranged in two rows, internal and external. These bodies,
the internal and external "fibres of Corti," are separated from each other
at their base, where they rest upon the membrana basilaris, by a consid-
erable interval ; but they lean toward each other and lie in contact by
their upper extremities or heads, thus forming a roof-like or arched con-
nection, the " arch of Corti." Near the situation of the arch of Corti, the
epithelium cells lining the ductus cochlearis become modified in form,
gradually increasing in size and length. At the inner border of the
arch there is a single row of epithelium cells which are nearly as long

Zeitschrift fur Wissenschaftliche Zoologie. Leipzig, 1851, Band III. p. 109.

SENSE OF HEARING. 663

as the internal fibres of Corti, and which lie immediately next to them
in a similar leaning position. The upper extremity of each of these
cells bears a tuft of rigid hairs or cilia, which are analogous to those of
the hair cells of the sacculus and utricle. On the outside of the arch
there are three such rows of hair cells, and in every instance the tufts of
cilia project through openings in a sort of fenestrated cuticle which lies
above the cells, and extends over them, inward and outward, from the
heads of the two bodies forming the arch of Corti.

The terminal fibres of the cochlear branch of the auditory nerve are
distributed to the organ of Corti. The bundles of nerve fibres forming
this branch penetrate the cochlea at the base of its central axis, and
pass from below upward through its interior, diverging successively
from writhin outward, to continue their course in a horizontal direction
between the two layers of the spiral lamina. At the level of the at-
tached border of the spiral lamina there is situated, within the cavity
of the osseous canal, a linear collection of bipolar nerve cells, in and
among which the nerve-fibres pass, and with many, if not all, of which
the nerve fibres are directly connected. This forms the "spiral gan-
glion'- of the cochlear nerve. After the bundles of nerve fibres have
passed through the ganglion, and while they are contained in the thick-
ness of the spiral lamina, they form, by repeated subdivision and re-
union, a complicated plexus, the filaments of which continue however
to follow a general diverging course toward the outer border of the spi-
ral lamina and the attached edge of the membrana basilaris. Arrived
at this point, the nerve fibres diminish in diameter and lose their me-
dullary layer ; and, in this form, penetrate into the ductus cochlearis,
where they continue to radiate toward the organ of Corti. It is at this
situation that the final termination of the slender and pale nerve fibres
in the substance of the epithelial hair cells has been most positively de-
scribed and figured by Waldeyer.1 There can be no doubt that this
structure represents, in the ductus cochlearis, the especial organ of au-
ditory sensibility.

Physiological Action of the Cochlea. — The cochlea is undoubtedly that
part of the internal ear, which, as compared with the remainder, serves
for the more precise discrimination of minute variations in sound. Its
elongated and spiral form, the two membranes of uniform tension which
inclose the ductus cochlearis above and below, and the remarkable com-
plication of structure, with the multiple rows of hair cells belonging to
the organ of Corti, all indicate that it is adapted for the distinct percep-
tion of particular sonorous impulses. The analogy of its construction
in some respects with the mechanism of a musical stringed instrument,
the fibres of the membrana basilaris representing its vibrating strings,
has induced the belief, in the minds of many eminent physiologists, that
it is the organ by which we appreciate the difference in tone or pitch
between different sounds. According to this view, the radiating fibres

1 In Strieker's Manual of Histology, Buck's edition. New York, 1872, p. 1040.

664 THE SENSES.

in successive portions of the membrana basilaris are attuned, by their
length or tension, to vibrate in response to different notes of the musical
scale ; and the vibration of each set, when excited, is communicated
to the corresponding hair cells of the organ of Corti, and thus reaches
the auditory nerve fibres terminating in their substance. Thus for every
note sounded in the atmosphere which gains admission to the internal
ear, only certain fibres and hair cells of the ductus cochlearis will be
thrown into vibration, and only certain terminal fibres of the codilear
nerve will receive a sonorous impression. Some writers have even found
in certain parts of the organ of Corti, an apparatus for damping the
vibration of the fibres after the cessation of the sound, and thus prevent-
ing the confused intermingling of separate impressions. There is cer-
tainly a suggestive appearance of similarity between the long row of
fibrous and cellular elements m the organ of Corti, with their various
appendages, and the ranges of strings, capable of vibrating to different
notes, in a harp or piano forte ; and the similarity is sufficient to suggest
a certain correspondence of mechanical and physiological action between
the two.

But the main difficult}^ in attributing to the cochlea, as its function,
the discrimination of musical notes, lies in the fact that its development
in different animals does not correspond with their capacity for the pro-
duction and perception of musical sounds. The cochlea, under the form
which it presents in man, is confined to the mammalia. In birds this
part of the auditory apparatus has not the form of a coiled spiral, but
is an obtusely conical eminence,1 containing two small cartilaginous
cylinders united by a membrane which represents the membrana basi-
laris ; and the part corresponding to the organ of Corti contains only
nerve terminations and hair cells somewhat resembling those of the
inner row in mammalia ; the arch of Corti, and the three outer rows of
hair cells, with their cuticular covering, being absent. In serpents and
lizards, the cochlea is similar to that of birds ; while in the naked rep-
tiles and in fishes it is completely undeveloped.

Thus, in all the mammalia, the cochlea is an important part of the
internal ear, apparently but little, if at all, inferior to the same organ in
man. But in the singing birds it is comparatively a rudimentary struc-
ture. Some of these birds may be taught artificially to repeat par-
ticular melodies, showing conclusively that their capacity of percep-
tion for musical notes is equal to their power of producing them by the
vocal organs. And yet that part of the auditory apparatus which
should be most highly developed in these animals, according to the view
in question, is in reality the least so. If we compare, for example, a
horse or a pig with a thrush or a mocking-bird, it is evident that the
grade of musical sensibility in these animals is in no relation with the

s Owen, Anatomy of the Vertebrates. London, 1866, vol. ii. p. 134. Wagner,
Comparative Anatomy of the Vertebrate Animals, Tulk's Translation. New
York, 1845, p. 95. Waldeyer, in Strieker's Manual of Histology, Buck's Edition.
New York, 1872, p. 1046.

SENSE OP HEARING. 665

development of the cochlea. In fact, the cochlea of a singing bird
resembles that of a crocodile or a serpent more closely than that of a
quadruped or a man. At the same time, the other parts of the internal
and middle ear in birds, the double sac of the vestibular cavity, the
membranous semicircular canals and ampullae, the fenestra ovalis and
rotunda, the chain of bones and the ineinbrana tympani, are all highly
developed ; some of them nearly or quite as much so as in the mamma-
lian class. These facts throw a certain degree of doubt upon the special
office of the cochlea in the perception of auditory sensations.

Persistence of Auditory Impressions and the Production of Musical
Notes. — The sensation excited by a sonorous vibration continues for a
short time after the cessation of its cause. Usually the interval be-
tween successive impulses is more than sufficient to allow the continued
impression to disappear, and the ear distinguishes without difficulty the
succession of sounds. But if the impulses follow each other at equal
intervals, and with a certain degree of rapidity, they produce upon the
ear the impression of a continuous sound, and this sound has a higher
or lower pitch according to the rapidity with which the vibrations are
repeated. The numerical relation of different musical notes thus pro-
duced has been studied by means of various instruments. One of these
is the siren of Savart, in which successive puffs of air are emitted from
the body of the machine through small openings, with a degree of
rapidity which can be varied at will and registered by an index attached
to the moving parts. Another method is that in which the shocks are
given by the points of a toothed wheel turning with known velocity,
and striking, in their passage, against the projecting edge of a card.
In another modification of the same plan, the revolving wheel carries
one or more projecting rods, which pass, in succession, through a cor-
responding slit in a stiff board ; making at each transit an atmospheric
concussion, owing to the instantaneous displacement and rebound of
the air at the opening. Finally, the number of vibrations correspond-
ing to a particular note may be registered by attaching to the extremity
of a diapason, or tuning-fork, a light stilet which traces upon the
blackened surface of a cylinder, revolving at a known rate, an undu-
lating line (Fig. 146, a) ; the number of undulations within a given
space indicating the frequency of the vibrations of the tuning-fork. A
simple vibration represents the single oscillation of a solid body, or the
particles of a fluid, in one direction ; a double vibration is the complete
to-and-fro movement of a particle, which brings it back to its original
position.

By this means it is found that sonorous impulses, which follow each
other with a rapidity of less than sixteen times per second, are readily
distinguishable as separate shocks ; but above that degree of frequency
they become merged into each other, and produce the sensation of a
continuous sound. In case the repetition of the shocks takes place
at irregular or unequal intervals, the only characters perceptible in
the sound are its intensity and the peculiarities due to the special
43

THE SENSES.

mechanism of its production. But if the shocks succeed each other at
regular intervals, the sound has then a definite position in the musical
scale, and is appreciated by the ear as a high or low note. The more
frequent the repetitions in a given time, the higher is the note produced,
until a limit is reached at which the ear fails to perceive a sound at all.
The physical reason why excessively high notes become inaudible is
probably this: In the special arrangement. of the auditory apparatus, a
vibration, in order to be perceptible, must have a certain degree of
extent or amplitude; that is, the particles of the vibrating body must
move to and fro, at each impulse, for a certain distance in space. The
intensity of a sonorous impression, accordingly, depends upon the am-
plitude of the vibrations, while its pitch or tone depends upon their
frequency. But the more frequently a body vibrates in a single second,
the less extensive must be its movements, if their velocity remain the
same. Consequently, when these vibrations arrive at a certain high
degree of frequency, unless the velocity of movement can be increased
in proportion, their amplitude becomes so small that they can make no
impression upon the ear, and the sound becomes inaudible.

It is evident, however, that such a sound would be perceptible if the
sensibility of the auditory apparatus were increased to the requisite
degree; and it has been suspected by some naturalists that certain
insects may be capable of perceiving sounds of so high a pitch as to be
inaudible for the human ear ; while, on the other hand, for them, a very
low note would appear as a succession of distinct impulses.

The limits of frequency, within which sonorous vibrations are percep-
tible to man as continuous musical sounds, are 16 double vibrations
per second for the lowest notes, and 38,000 for the highest. But,
according to Wundt, the exact discrimination of the pitch of musical
sounds is confined within much narrower limits, especially for the higher
notes.

Duration of a Sound required for the perception of Sonorous Impres-
sions.— This point has been investigated by Savart1 in the following
manner. He ascertained, by experiment, that the ear could appreciate
the pitch of a sound made by a toothed wheel revolving at such a rate
as to cause 10,000 shocks per second. By removing successively the
teeth from larger portions of the circumference, he diminished in a
corresponding degree the time during which the shocks were produced ;
and he found that such a wheel would give a sound of definite pitch
with only two adjacent teeth remaining. The double shocks thus pro-
duced would occupy only -g-^y of a second ; and this duration of the
impulses was sufficient to make upon the ear a distinct musical impres-
sion.

1 Daguin, TraitS ElSmentaire de Physique. Paris, 1869, tome i. p. 517.

SECTION III.
REPRODUCTION.

CHAPTEE I.

THE NATURE OF REPRODUCTION, AND THE
ORIGIN OF PLANTS AND ANIMALS.

REPRODUCTION is the process by which the different kinds of organized
bodies are perpetuated in continuous series, notwithstanding the limited
term of existence allotted to each individual. It includes the phe-
nomena of the production, growth, and development of new germs, as
well as the whole history of the successive changes in the organs and
functions, and the consequent modifications of external bodily form pre-
sented at different periods of life.

All organized bodies pass through certain successive stages of de-
velopment, in which their structure and functions undergo corresponding
alterations. The living animal or plant is mainly distinguished from
inanimate substances by the continuous changes of nutrition and growth
which take place in its tissues. These nutritive changes correspond in
activity with the other vital phenomena ; since the production of these
phenomena depends upon the regular and normal continuance of the
nutritive process. Thus the organs and tissues, which are the seat of
a double change of renovation and decay, retain nevertheless their
original constitution, and continue capable of exhibiting the vital phe-
nomena.

These changes, however, are not the only ones which take place.
Although the structure of the body appears to be maintained in an
unaltered condition by the nutritive process from one moment to an-
other, or from day to day, yet a comparative examination at greater
intervals of time will show that this is not precisely the case; but that
the changes of nutrition are, in point of fact, progressive as well as mo-
mentary. The composition and properties of the skeleton are not the
same at the age of twenty-five years that they were at fifteen. At the
later period the bones contain more calcareous and less organic matter
than before ; and their solidity is increased, while their elasticity is di-
minished. Even the anatomy of the bones alters in an equally gradual
manner; the medullary cavities enlarging with the progress of growth,

( 667 )

NATURE OF REPRODUCTION.

and the cancellated tissue becoming more open in texture. There is a
notable difference in the quantities of oxygen and carbonic acid inspired
and exhaled at different ages. The muscles, also, if examined after the
lapse of some years, are found to be less irritable than formerly, owing
to a slow, but steady and permanent deviation in their intimate con-
stitution.

The vital properties of the organs, therefore, change with their vary-
ing structure ; and a time comes at last when they are perceptibly less
capable of performing their original functions than before. The very
exercise of the vital powers is inseparably connected with the subse-
quent alteration of the organs employed in them ; and the functions of
life, instead of remaining indefinitely the same, pass through a series
of successive changes, which finally terminate in their complete cessa-
tion.

The history of a living animal or plant is, therefore, a history of suc-
cessive epochs or phases of existence, in each of which the structure
and functions of the body differ more or less from those in every other.
The organized being has a definite term of life, through which it passes
by the operation of an invariable law, and which, at some regularly
appointed time, comes to an end. The plant germinates, grows, blos-
soms, bears fruit, withers, and decays. The animal is born, nourished,
and brought to maturity, after which he retrogrades and dies. The
very commencement of existence, by leading through its successive
intermediate stages, conducts at last necessarily to its own termination.

But while individual organisms are constantly perishing and disap-
pearing from the stage, the particular kind, or species, remains in exist-
ence, without any important change in the appearance of the organized
forms belonging to it. The horse and the ox, the oak and the pine, the
different kinds of wild and domesticated animals, even the different
races of man himself, have remained without any essential alteration
since the earliest historical epochs. Yet during this period innumer-
able individuals, belonging to each species or race, have lived through
their natural term and successively passed out of existence. A species
may therefore be regarded as a type or class of organized beings, in
which the particular forms composing it die off and disappear, but which
nevertheless repeats itself from year to year, and maintains its ranks
constantly full by the regular accession of new individuals. This pro-
cess, by which new organisms make their appearance, to take the place
of those which are destroyed, is known as the process of reproduction.
The first important topic, in the study of reproduction, is that of the
conditions necessary for its accomplishment.

Reproduction by Generation. — It is well known that, as a rule, in
the reproduction of any particular kind of living organism, the young
animals or plants are produced, directly or indirectly, from the bodies
of the elder. The relation between the two is that of parents and
progeny. The progeny, accordingly, owes its existence to an act of
generation; and the new organisms, thus generated, become in turn the

NATURE OF REPRODUCTION. 669

parents of others which succeed them. For this reason, wherever such
plants or animals exist, they indicate the preceding existence of others
belonging to the same species ; and if by any accident the whole species
should be destroyed in any particular locality, no new individuals could
be produced there, unless by the previous importation of others of the
same kind.

The most prominent feature of generation, as a natural phenomenon,
is that the young animals or plants thus formed are of the same kind
with their parents. They reproduce all the essential specific characters
by which their predecessors were distinguished ; and this takes place
by a law so universal that it seems almost a truism to state it. But
this is only because it has been so constantly a matter of observation,
that in popular experience it appears as a natural necessity. In reality
it is one of the most remarkable phenomena connected with the genera-
tive process ; and it indicates an unbroken connection of physiological
acts, extending through the entire lives of many different individuals.
Thus we know that the progeny of a fox will always be foxes ; and that
if we sow oats, it will be a crop of oats tiiat is produced in consequence.
Generation, accordingly, not only gives rise to new animals and plants,
or increases their number, but it also serves to continue indefinitely the
existence of the particular species, with all its characteristic marks and
qualities.

Our idea, therefore, of a species, whether animal or vegetable, includes
two different elements, one of which is anatomical, the other physiologi-
cal. The anatomical character of a species consicts in the similarity of
form, size, and structure existing between all the individuals belonging
to it, and which we recognize at a glance j its physiological character
depends upon the fact, which has been learned by experience, that it
will reproduce itself, and that the different species in existence at any
one time remain distinct through an indefinite series of successive gene-
rations.

It is not possible to say that the anatomical characters of species
have remained absolutely the same throughout all previous time, or
that they will continue to do so without limit in the future. The
existence of many fossil remains of animals and plants, different from
those which are known at the present day, shows that species are not
invariable and persistent through very long periods of time ; and that
they may either very gradually become so modified as to present a
different appearance, or else that they may entirely come to an end,
like the extinct mastodons and fossil horses of the United States, and
be replaced by others from a different localit}'. But in whatever way
the succession of species in different geological epochs be explained, it
is certain that at any one period their essential physiological characters
are those above described ; and that each species, by the process of
generative reproduction, remains distinct from the others which are
contemporary with it.

But the production of young animals, similar in every respect to their

670 NATURE OF REPRODUCTION.

parents, although in all cases the final result of the generative process,
is never immediate. The young progeny when first produced is different
from its parents, and only reaches a condition of resemblance to them
through a series of changes, often of a very extraordinary kind. In
the vertebrate animals generally, the embryo, though quite incomplete
in structure, yet presents a certain analogy of form with the adult con-
dition. But in many of the invertebrate animals the young, even after
hatching, and when capable of active locomotion, are so different in
appearance from their parents that they would never be supposed to
belong to the same species, unless their identity were demonstrated by
their subsequent development. Thus the young mosquito is a wingless
creature living beneath the surface of the water in stagnant pools j and
the eggs of the butterfly, when hatched, give birth not to butterflies but
to caterpillars. These caterpillars, however, are not creatures of a
different species, but only young butterflies ; and they become fully
developed and similar to their parents after certain changes, which take
place at definite periods of their development.

The reproduction or repetition, therefore, of the form which distin-
guishes a particular species is accomplished by a series of changes which
follow each other in regular order; and this series, taken together, may
be represented by a circuit, which starts from the egg, is continued
through the different phases of growth, transformation and maturity of
the animal, and terminates again with the production of an egg. As
this egg is similar to the first, the changes repeat themselves in their
previous order, and the indefinite continuance of the species is thus
established.

Spontaneous Generation The commonest observation shows that

the facts detailed above hold good in regard to all animals and plants
with whose history we are familiarly acquainted. An opinion, however,
has sometimes been entertained that there may be exceptions to this
rule; and that living beings can, under certain circumstances, be pro-
duced from inanimate materials ; presenting, accordingly, the singular
phenomenon of a progeny without parents. Such a production of
organized bodies is known by the name of spontaneous generation Its
existence is doubted by most physiologists at the present time, and has
never been positively established for any particular organized species;
but it has been at various periods the subject of active discussion,
forming a somewhat remarkable chapter in the history of general
physiology.

It may be remarked in general terms that the organisms, in regard
to which the idea of the possibility of spontaneous generation has been
entertained, have been always those whose natural history was imper-
fect or obscure, owing either to their minute size or to certain of their
physiological peculiarities. Wherever animals or plants appeared in
considerable abundance without exhibiting any evidence of the source
from which they came, it was formerly conjectured, from that fact alone,
that their production was a spontaneous one. The ancient naturalists

NATURE OF REPRODUCTION. 671

supposed that all species of animals, excepting those which visibly either
laid eggs or produced living young, were formed spontaneously from
the combination of their organic ingredients. Maggots, shell fish, grubs,
worms, and even some fishes were thought to be produced in this way,
simply because they had no apparent specific origin.

But continued observation in natural history showed that in these
cases the animals were really produced by generation from parents ;
their secret methods of propagation being discovered, and their specific
identity being established by successive changes in development of the
young. The difficulty of doing this in any particular case is often in-
creased by the interval which elapses between the deposit of eggs by
the parents and the subsequent hatching of the young ; the new genera-
tion not showing itself until after the former has disappeared. A similar
instance is that of the American seventeen-year locust ( Cicada xepten-
decim), where a period of seventeen years intervenes between the hatch-
ing of the larva and the appearance of the perfect insect ; the larva all
this time remaining buried in the ground, while the life of the perfect
insect does not last over six weeks. But notwithstanding this difficulty,
all such doubtful cases were gradually traced to the usual method of
generation from parents.

Another source of error was the great dissimilarity in the figure some-
times existing between the parents and their young, especially as this is
accompanied by an equal dissimilarity in their habits of life. Until
about the middle of the seventeenth century there was supposed to be
no more undoubted instance of spontaneous generation than the appear-
ance of maggots in putrefying meat. These creatures always show
themselves in meat at a certain stage of its decomposition ; they never
appear elsewhere ; and they do not themselves manifest the power of
producing young: and for these reasons they were believed to originate
from the dead flesh and to die themselves without leaving a progeny.
But the simple experiments of Francisco Redi in 1668, demonstrated
the source of fallacy in this opinion and the true origin of the maggots.
He took, in the month of July, eight wide-mouthed glass bottles and
placed in them various pieces of dead flesh. Four of these bottles were
left open to the atmosphere, while the remaining four* were closed by
pieces of paper carefully adjusted over the mouth of each and fastened
by a cord round its neck. A short time afterward the flesh in the un-
covered bottles was filled with maggots, a peculiar kind of fly meanwhile
passing in and out by the open mouth ; but in the closed bottles not a
single maggot was visible, even after the lapse of several months.

Thus it was evident that the maggots were not formed from the dead
flesh, but that their germs came in some way from without ; and con-
tinued observation showed that they were hatched from eggs deposited
by the flies, and that after a time they became developed into perfect
insects similar to their parents. An extension of these observations to
other species of invertebrate animals made known a great variety of
instances in which the connection of parents and progeny might be traced

672 NATURE OF REPRODUCTION.

through several intermediate conditions ; so that the apparent difference
between them in configuration and structure no longer offered a serious
difficulty to the investigator. As a general rule, since that time, when-
ever a rare or comparatively unknown animal or plant has been suspected
to originate by spontaneous generation, it has only been necessary to
examine thoroughly its habits and functions, to discover its real methods
of propagation, and to show that they correspond, in all essential par-
ticulars, with the ordinary laws of reproduction. The limits within
which it is possible for the doctrine of spontaneous generation to be
applied have been successively narrowed, in the same degree that the
study of natural history has advanced ; the presumption of its existence
always hanging upon the outskirts of definite knowledge, and being
connected only with those animal or vegetable organisms which are for
the time imperfectly understood. The two groups from which it has
been most recently excluded by the progress of discovery are, 1. The
Entozoa, or internal parasites ; and 2. The Infusoria.

I. Entozoa. — These are organisms which live within the bodies of
other living animals, from whose organic juices they derive their nourish-
ment.

There are many different kinds of entozoa, all of which are confined,
more or less strictly, to certain parts of the body which they inhabit.
Some of them are found in the intestines, others in the liver, the kidneys,
the lungs, or the heart and bloodvessels ; others on the surface of the
brain ; others even in the muscles or in the interior of the eyeball.
Each particular kind of parasite, as a rule, is peculiar to the species of
animal which it inhabits, and even to a particular part of the body, often
to a particular part of one organ. Thus, Ascaris lumbricoides is found
in the small intestine, Oxyuris vermicularis in the rectum, Trichoce-
phalus dispar in the cteciun. One kind of Distoma has its place in
the lungs of the green frog, another in those of the brown frog. Cysti-
cercus cellulosae is found in the connective tissue ; Trichina spiralis in
the substance of the muscles.

With regard to many of these parasites the only difficulty in account-
ing for their existence, except on the presumption of their spontaneous
generation, lay in their being confined to such narrow limits and their
never being met with elsewhere. It seemed probable that some local
combination of conditions was necessary to the production of a para-
site, which was never to be found except in the biliary passages, the
kidneys, or the lungs of a living animal. A little consideration, how-
ever, makes it evident that these conditions are in reality neither neces-
sary nor sufficient for the production, but only for the development of
the parasites in question. Most of the internal parasites evidently
reproduce their species by generation. They have male and female
organs, and produce fertile eggs, often in great abundance. The eggs
contained in a single female Ascaris are to be counted by thousands ;
and in a tapeworm even by millions. These eggs, in order that they
may be hatched, and produce new individuals, require certain special

NATURE OF REPRODUCTION. 673

conditions which are favorable for their development ; in the same man-
ner as the seeds of plants require, for their germination and growth, a
certain kind of soil and a certain supply of warmth and moisture. It is
accordingly no more remarkable that Oxyuris vermicularis should in-
habit the rectum, and Ascaris lumbricoides the ileum, than that Lobelia
inflata should grow only in dry pastures, and Lobelia cardinally by the
side of running brooks. The lichens flourish on the exposed surfaces
of rocks and stone walls ; while the fungi vegetate in darkness and
moisture, on the decaying trunks of dead trees. Yet both these classes
of vegetables are well known to be reproduced by generation, from
germs which require special conditions for their growth and develop-
ment. If the germ of any species, whether animal or vegetable, be de-
posited in a locality where these requisite conditions are present, it is
developed and comes to maturity ; otherwise not. This accounts fully
for the fact that internal parasites, like other living organisms, are con-
fined to certain situations by the requirements of their nourishment and
growth.

But in regard to a few of the internal parasites a further difficulty
existed, owing to the presence of two peculiaries : first, these particular
kinds do not inhabit the open passages or canals of the body, but lie
encysted, in the solid substance of the tissues, where there are no visible
means of access from without ; and secondly, they are sexless, perform-
ing no generative function, and having no progeny of their own ; so that
it does not readily appear how they can themselves have been derived
from parents. The two kinds of entozoa which have presented this
difficulty in the most marked manner, and in which it has been most
fully explained by the results of observation and experiment, are those
known as Cysticercus cellulose and Trichina spiralis.

1. Cysticercus celluloses. — This is a bladder-shaped parasite of some-
what flattened form, about 10 millimetres in diameter, found in the sub-
cutaneous and intermuscular connective

tissue of the pig, where it appears under Fig- 214.

the form of whitish specks, giving to
the flesh the appearance known as that
of "measly pork." Each parasite is
enveloped in a perfectly closed c}Tst, but
the bladder-like body, when extracted,
exhibits at one spot a minute depression

Or involution of its wall. From this CYSTICBRCTTS CELLULOSE, from

point a slender neck, ending in a ^yS^.iSJ^SSSS

rounded head, may be extruded by and neck extruded. 2, a. The same,
pressure ; after which the animal is seen
to consist of a head and neck, termi-
nated posteriorly by a dilated, sac-like tail, whence its generic name of
cysticercus. Its specific name was derived from its inhabiting the con-
nective tissue, formerly known as the " cellular tissue." The head of
the parasite, when magnified, shows upon its surface four sucking disks,

674

NATURE OF REPRODUCTION.

. 215.

and near its extremity a double crown of curved calcareous processes or
hooks, implanted in its substance. There are no distinguishable internal
organs, and the caudal vesicle is filled simply with an albuminous
watery fluid. Thus there is no apparent source from which these or-
ganisms can have come, other than the tissues which they inhabit, nor
any visible mode of continuing the species by generation.

But it has been shown by the investigations of Van Beneden, Leuck-
art, Haubner, and Kiichenmeister,1 that Cysticercus celluloste is only
the embryonic progeny of Tsenia soliuin, or the solitary tapeworm, found
in the small intestine of the human subject. The specific identity of
the two was first suspected from the exact simi-
larity in the form and structure of the head and
narrow neck, which presents the same sucking
disks and double crown of hooks in Tsenia as in
Cysticercus. But in Taenia this neck, instead of
terminating in a vesicular appendage, is elongated
and transversely . wrinkled. The wrinkles, after a
certain distance, become deepened into superficial
furrows, marking off the body of the animal into
oblong divisions or articulations, each articulation
showing a double system of communicating vascu-
lar canals, and also distinctly marked generative
organs of both sexes. As they recede, by succes-
sive growth, farther and farther from the head, the
generative organs contained in the articulations
become more completely formed, and are at last
filled with mature fecundated eggs, in which the
embryos have begun to be developed. The entire
tapeworm then forms a continuous chain or colony
of articulations, sometimes from six to eight metres
in length, and attached to the mucous membrane of
the intestine only by the minute head at its ante-
rior extremity.

By the experiments above mentioned it was
found, 1st. That mature articulations from the
tsenia solium of the human subject, if administered
to young pigs with their food, produce an abundance
of Cysticercus cellulosse in the flesh of these ani-
mals ; and, 2d. That cysticercus cellulosse from
measly pork, if swallowed by man, becomes developed in the intestine
within a few days, into ribbon-like worms, distinctly recognizable as
young specimens of tsenia solium.

The manner in which the pig becomes infested with cysticercus is as
follows : In the fully-formed tapeworm, in the human intestine, the last

1 Kiichenmeister, Animal and Vegetable Parasites. Sydenham edition, Lon-
don, 1857, pp. 115, 120.

NATURE OF REPRODUCTION. 675

and most mature articulations separate spontaneously from the rest of
the colony, and either find their way out by the anus singly, or are dis-
charged with the evacuations. They have, while still living, a con-
siderable degree of contractility and power of locomotion ; and thus
become accidentally transferred to the surface of neighboring vegetable
matters, and are devoured by the pig with his food. In the stomach
and intestine, the substance of the articulation is digested and dissolved ;
but the embryos, which are 33 mmm. in diameter, and armed with three
pairs of calcareous spines, make their way through the intestinal walls,
and thence are dispersed, either by a continuance of the same movement
or by the bloodvessels, throughout the connective tissue, where they
are afterward found. Here they become encysted, and go through with
a partial development, remaining in the condition of C}Tsticer«us in the
flesh of the pig until this flesh is used for food, when they finally be-
come converted into tsenia solium. Thus the entire round of generation
and development is completed, and the original form of the parasite
reproduced. A similar relation has been shown by Kiichenmeister
and Siebold1 to exist between certain other species of taenia and cysti-
cercus.

2. Trichina spiralis — This is a sexless, encysted, worm-like para-
site, found in the muscular tissue of the pig, and sometimes in that of
the rat, the cat, and the human species. Each worm lies closely coiled,
in a spiral form, in the interior of its

enveloping cyst. It is about 0.75 Fig. 216.

millimetre in length, of a tapering
form, with a slender anterior and
rounded posterior extremity. It pre-
sents a nearly straight intestine ex-
tending through its whole length,
and rudimentary sexual organs which
are entirely inactive. The worm has TRICHINA SPIRALIS, encysted,

from muscular tissue of a trichinous cat.
been known Since 1835, as Occasion- Magnified 76 diameters.

ally found in the human muscular

tissue in the encysted form; but it is only since 1860, principally from
the investigations of Leuckart,2 that the different stages of its growth
and development have been made known. If muscular flesh containing
encysted trichinae be administered with the food to a rabbit, cat, rat,
mouse, or pig, the cysts become digested and the worms liberated in
the small intestine. Here they rapidly increase in size and develop-
ment, the females becoming impregnated and filled with living young,
and attaining, at the end of a fortnight, three or four times their pre-
vious size. The young emb^os are now discharged from the body of
the parent, make their way through the walls of the intestine, and are

1 Yon Siebold, On Tape and Cystic Worms. Sydenham edition. London,
1857, p. 57.

2 Untersuclmngen liber Trichina spiralis. Leipzig und Heidelberg, 1860.

676

NATURE OF REPRODUCTION.

dispersed throughout the body. They thus reach the muscular tissue,
where they become encysted, and remain quiescent until again intro-
duced into the intestine of another animal or of man. In this way the
existence of sexless and encysted parasites is seen to be entirely analo-
gous to that of the caterpillar or the maggot. They are sexless,
because they are still in the embryonic or incomplete stage of develop-
ment. But they have been produced by the regular mode of generation
from parents ; and they will, at a subsequent period, themselves produce
young by the same process.

II. Infusoria. — These are microscopic organisms, first discovered by
Leeuwenhoek, in 1675, in rain-water which had been kept in standing
vases. On account of their active movement and minute size he called
them ''animalcules ;" but as they were soon afterward discovered to

Fig. 217.

INFUSORIA, of various kinds.— 1. Urostyla grandis, from decaying sedge-grass 2.
Paramecium aurelia, from vegetable infusions. 3. Chlamydodon mnemosyne, Baltic Sea
water. 4. Kerona polyporum, on the fresh-water polype. 6. Oxytricha caudata, open
stagnant waters. 6. Ervilia fluviatilis, clear brook water. 7. Heteromita ovata, on aquatic
river-plants. Magnified 325 diameters. (Ehrenberg and Stein.)

make their appearance in great numbers and with remarkable rapidity
in watery infusions of organic matter exposed to the air, they received
the general name of "infusoria." They present themselves in great
variety, and under rapidly changing forms; so much so that Ehrenberg

NATURE OF REPRODUCTION. 677

in 18381 described more than 700 different kinds. They are generally
provided with cilia attached to the exterior of their bodies, and are, for
the most part, in constant and rapid motion in the fluid which they
inhabit.

In consequence of the numerous different forms of the infusoria, their
frequent changeability of figure, and their want of resemblance to any
previously known class of animal organisms, they were thought, by
some of the earlier observers, to have no regular mode of generation,
but to arise indiscriminately from the organic materials of the infusion ;
the particular form which they might assume being determined by the
special conditions of each case. Their inevitable appearance in organic
infusions, at all ordinary temperatures and exposures, contributed to
sustain this belief. The substance of the infusion might be previously
baked or boiled ; the water in which it was infused might be distilled, and
thus freed from all organic contamination ; and yet the infusoria would
make their appearance at the usual time and in the usual abundance,
provided only that the infusion were exposed to moderate warmth and
to the access of atmospheric air. But these conditions are essential to
maintaining the life of all organized creatures, from whatever source
they may come, and are not, therefore, more necessary to the infusoria
than to others.

Therefore the infusoria must either have been spontaneously gene-
rated from the materials of the infusion, or else they must have been
produced from germs introduced from the atmosphere. In the latter
case these germs must be wafted about, in a comparatively dry state
and in an inactive condition, by the atmospheric currents, to resume
their activity and development when brought in contact with sufficient
moisture and with the organic material requisite for their nutrition.

The researches relating to this question continued with the most extra-
ordinary persistence, and with various interruptions and revivals, from
1775, when they were carried on by Needham and Spallanzani, through-
out the greater part of the present century, in the hands of Cuvier,
Schultze, Helmholtz, Milne-Edwards, Longet, Pouchet, Pasteur, Wy-
man, and Bastian. The main object of investigation was to discover
whether, if all previous living germs were destroyed by heat, and the
access of others prevented by hermetically sealing the vessels, or
thoroughly purifying the air which was introduced, infusorial life
would, under such circumstances, be developed.

The general result of these experiments was that such precautions
diminished and often entirely prevented the production of infusoria.
Spallanzani2 had already shown in 1776 that organic infusions in her-
metically sealed glass flasks, if boiled for two minutes, failed to produce
any of the larger and more highly organized animalcules; and that
boiling for three-quarters of an hour prevented the appearance of the
more minute and simpler kinds.

1 Die Inftisionsthierchen als vollkommene Organismen. Leipzig, 1838.

2 Opuscoli de Fisica animale e vegetabile. Modena. 1776, vol. i. p. 10.

673 NATURE OF REPRODUCTION.

Schultze1 performed similar experiments, with the additional advan-
tage of admitting to the organic infusion fresh air purified from germs.
He placed his infusion in a glass flask, the stopper of which was pro-
vided with two narrow tubes, bent at right angles. When the infusion
had been thoroughly boiled, and all the air contained in the flask ex-
pelled, he fastened to each of the projecting tubes a series of bulbs
containing on the one side sulphuric acid, and on the other a solution
of potassium hydrate ; so that the air which re-entered the flask while
it was cooling must pass through these fluids, and thus be cleansed of
all living organic matter. The apparatus was then kept in a warm
place for two months, the air being renewed daily by suction through
the tubes, without any infusoria being detected in its contents. But
they showed themselves in great abundance after it had been taken
apart, and the infusion exposed for a few days directly to the atmo-
sphere.

Pasteur'2 found that if a flask containing an organic liquid were boiled
upon a high mountain, where the air is of unusual purity, allowed to
fill itself with this air while cooling, and then hermetically sealed, it
would often remain free from infusorial growth. He kept several such
flasks, boiled and filled with air upon the Montanvert in Switzerland,
for four years, without the liquids which they contained undergoing any
perceptible change. But on making, at the end of that time, a minute
opening in the neck of one of these flasks, it exhibited after three days
a perceptible growth of cryptogamic vegetation.

These results did not absolutely exclude the possibility of spontane-
ous generation, which was still maintained by Pouchet and a number
of other observers ; but they indicated in a very decisive manner that
the atmosphere might contain the inactive germs of infusoria, which
were capable of being developed on meeting with a suitable organic
infusion.

But in the mean time the study of the infusoria themselves had been
going on independently of the question of spontaneous generation, and
this alone has been sufficient to demonstrate that they are reproduced
in the usual way, like other animal species, by means of fertilized eggs
and embryonic development.

The apparent confusion and variability in form of the infusoria, at
the time of their first discovery, depended only upon their great num-
bers and upon the want of sufficient knowledge in regard to them. Sub-
sequent observation has shown that their organization is as definite as
that of other classes of the animal kingdom ; and they have now been
arranged, by the labors of Claparede and Lachmann,3 Stein,4 and Bal-
biani,5 into orders, families, genera, and species, which may be recog-

Poggendorf s Annalen, 1836. Band xxxix. p. 487.

Comptes Rendus de I'Academie des Sciences. Paris, Fevrier 20, 1865.

Etudes sur les Infusoires et les Rhizopodes. Geneve, 1856-1861.

Organismus der Infusionsthiere. Leipzig, 1859.

Journal de la Physiologic de PHomme et des Animaux. Paris, 1861.

NATURE OF REPRODUCTION.

679

nized with certainty by their distinctive marks. They are not confined
to infusions of decaying material artificially or accidentally prepared ;
but many of them have their natural habitation in the clearest waters
of lakes, pools, marshes, running brooks, or the open sea. Certain forms,
originally included in this class, such as Rotifer, Stephanoceros, and
Floscularia, have been found to possess a more complicated structure
than the rest, and to belong properly to the class of worms; while their
mode of reproduction is sufficiently manifest from the fact that living
embryos, in process of development, are often to be seen in their interior.

Fig. 218.

RTYLONTCHIA MYTILITS; a fresh-water infusorium.— 1. Unimpregnated. 2. Impreg-
nated, and containing mature eggs and two embryos. 3. Showing the form of the embryo.
Magnified 375 diameters. (Stein.)

Finally, the ciliated infusoria themselves have been shown to repro-
duce their species by means of eggs, formed in special generative organs
and fecundated by union of the sexes (Fig. 218). This fact, first demon
strated by Balbiani, has been since confirmed, in many instances, by
Stein, Engelmann,1 and Cohn ;2 Balbiani and Stein together having

Zeitsehrift fur Wissenschaftliche Zoologie.
Ditto. Band xii. p. 197.

Leipzig, 1862, Band xi. p. 347.

680

NATURE OF REPRODUCTION.

Fig. 219.

observed the occurrence of sexual generation in 47 different genera
and 66 different species.

Thus the infusoria proper are in their turn excluded from the field
of spontaneous generation. But, on the other hand, a considerable
group of organisms, formerly referred to the class of infusoria, are now
known to be of a different character. These are the forms included
under the general term of Bacteria, and comprising the special varieties
of bacterium, vibrio, spirillum, and micrococcus. They are demon-
strated to be of a vegetable nature, notwithstanding their frequent
exhibition of rapid and continuous movement; and they consist of cells,
which multiply, often in great abundance, by a process of repeated sub-
division. Whether they are also reproduced by means of spores or
germs, has not been determined ; but their minute size and their imper-
fect classification have thus far proved ^obstacles to the complete study
of their physiological characters.

The representative of this group may be considered to be the species
known as Bacterium termo, already described (page 83), in connection

with the phenomena of pu-
trefaction. It consists of
elongated or rod-like cells,
averaging 3 mmm. in length
by 0.6 mmm. in thickness,
sometimes single, often
double, two of them being
attached, more or less firmly,
end to end. The latter ap-
pearance is due to the pro-
gressive multiplication of
the cells, which takes place
by a transverse division at
the middle of their length.
The two new cells thus pro-
duced remain for a time in
connection with each other,
and afterward separate, to
repeat the process indepen-
dently of each other. The final separation of two cells may often be
seen to occur under the microscope. The bacterium cells, during a
considerable part of their existence, are in rapid vibratory and progres-
sive movement. The vibrations take place in a circular manner, about
some point situated either at or near one of the extremities ; so that the
rest of the cell performs a conical movement around this point, present-
ing, on superficial examination, the appearance of a lateral oscillation.
The mechanism by which this vibration is accomplished is unknown;
but it is no doubt analogous to the slower spiral undulations of the
Oscillatorise, among fresh-water algae ; and its effect is to propel the

Cells of BACTERIUM TERMO; from a putrefying
infusion.

NATURE OF REPRODUCTION. 681

bacterium cells, often with extreme velocity, through the fluid in which
they are immersed.

Of later years, the investigations in regard to spontaneous generation
have been almost exclusively confined to the bacteria and their allies,
since they now form the only group of organisms in which reproduction
by generation has not been fully established. Even for them, the rapid
multiplication by cell division, which takes place under favorable con-
ditions, indicates the usual mode of their increase in numbers; but in
order to establish an entire similarity between them and other living
organisms, they must also be shown to reproduce themselves by spores
or germs, which has not thus far been done. The experiments with
boiled infusions in sealed flasks have led to results which are not inter-
preted in the same manner by all writers ; but it is evident that for
bacteria, as well as for other organic forms, the application of heat
exerts in various degrees a preventive action on their subsequent appear
ance.

Among the most careful and satisfactory experiments on this part of
the subject are those of Prof. Wyman,1 who operated with infusions of
both animal and vegetable matters. The infusions, placed in sealed
flasks, with abundance of atmospheric air, were submerged in boiling
water for periods varying from thirty minutes to five hours, and after-
ward kept under observation at the ordinary temperatures requisite for
the development of bacteria. The result showed that the appearance
of these organisms was always delayed by the previous application of
heat, and that this dela}^ in different series of observations, was often in
direct proportion to the length of time during which the boiling had
been continued. Furthermore, in certain cases the bacteria failed to be
produced at all, and tlu; chances of their production decreased in pro-
portion to the length of time during which the liquid had been boiled.
Thus, of four series of flasks, each containing the same infusion, and
boiled respectively during one, two, three, and four hours, all of the first
and second series afterward produced bacteria, only one of the third,
and none of the fourth. Finally, in no instance, among numerous trials,
did they appear in any infusion which had been boiled for a period ex-
ceeding five hours. Thus a limit was reached to the production of bac-
teria, in fluids previously subjected to the action of heat.

There can be no doubt as to the scientific bearing of these and similar
experiments. Spontaneous generation is inadmissible at the present
day for everything except bacteria ; and with regard to them there is
no sufficient proof that they are ever generated without the concurrence
of previously existing germs.

1 American Journal of Science and Arts. New Haven, vol. xliv., September,
1867.

44

CHAPTEE II.

Fig. 220.

SEXUAL GENERATION, AND THE MODE OF ITS
ACCOMPLISHMENT:

SEXUAL generation is performed by two sets of organs, each of which
gives origin to a peculiar product, capable of uniting with the other,
to produce a new individual. These organs, belonging to the two dif-
ferent sexes, are called the male and
female organs of generation. The female
organs produce a globular body called
the egg or germ, which is capable of be-
ing developed into the body of the young
animal or plant ; the male organs produce
a substance which is necessary to fecun-
date the germ, and enable it to go througli
with the process of growth and develop-
ment.

Such are the essential and universal
characters of the organs of generation.
These organs, however, while exhibiting
everywhere the same principal features,
present certain modifications of structure
and arrangement in different classes of
organized beings.

In the flowering plants, the blossom,
which is the generative apparatus (Fig.
220), consists first of a female organ con-
taining the germ (a), situated usually
upon the highest part of the leaf-bearing
stalk. This is surmounted by a nearly
straight column, termed the pistil (6), dilated at its summit into a
globular expansion, and occupying the centre of the flower. Around it
are arranged several slender filaments, or stamens, bearing upon their
extremities the male organs, or anthers (c, c). The whole is surrounded
by a circle or crown of delicate colored leaves, termed the corolla (d),
which is frequently provided with a smaller sheath of green leaves out-
side, called the calyx (e). The anthers, when arrived at maturity, dis-
charge a fine organic dust, called the pollen, the grains of which are
caught upon the extremity of the pistil. Each pollen-grain then absorbs
the nutritious juices with which it is in contact, and develops from its
substance a tubular prolongation, the pollen-tube, which, by its con-
( 682 )

BLOSSOM OP IPOM<EA PUK-
PTJREA. (Morning-glory.) — a. Germ.
6. Pistil, c. c. Stamens, with anthers.
d. Corolla, e. Calyx.

SEXUAL GENERATION.

683

Fig. 221.

tinued growth, penetrates downward through the tissues of the pistil
until it comes in contact with the germ below. The germ thus fecun-
dated, the process of generation is accomplished. The pistil, anthers,
and corolla wither and fall off, while the germ increases in size, and
changes in form and texture, until it ripens into the mature fruit or
seed. It is then ready to be separated from the parent stem ; and, if
placed in the proper soil, will germinate and produce a new plant similar
to the old.

In many species of plants, the male and female organs, as above
described, are both situated upon the same flower ; as in the lily, the
violet, the convolvulus. In other instances, there are separate male
and female flowers upon the same plant, of which the male flowers pro-
duce only the pollen, the female,
the germ and fruit. In others still,
the male and female flowers are
situated upon different plants,
which otherwise resemble each
other, as in the willow, the poplar,
the sassafras.

In animals, the female organs
of generation are called ovaries,
since it is in them that the egg, or
" ovum," is produced. The male
organs are the testicles, which
give origin to the fecundating pro-
duct, the "sperm" or "seminal
fluid," by which the egg is fer-
tilized. In the taenia or tapeworm,
already described (page 674), each
articulation contains both ovary
•and testicle. The ovary (Fig. 221,
G, a, a) is a series of branching
tubes ending in rounded follicles,
and communicating with a central
canal. The testicle (6) is a narrower convoluted tube, closely folded
upon itself, and opening by an external orifice (c) upon the lateral
border of the articulation. The seminal fluid produced in the testicle
is introduced into the female generative passage, which opens at the
same spot, and, penetrating into the interior, comes in contact with the
eggs, which are thereby fecundated. Each egg then produces a young
embryo, which is capable of being afterward developed into a full-grown
tsenia.

In various other families of invertebrate animals, as the snail, the
slug, the leech and the earth worm, an ovary and a testicle are both
present in the body of the same individual. But in these instances
impregnation is effected only by the concurrent action of two different
organisms ; and when sexual union takes place, the eggs produced by

SINGLE ARTICULATION OF T.ENIA
CRASSICOLLIS, from the cat. — a, a, a.
Ovary filled with eggs, 6. Testicle, c. Genital
orifice.

684 SEXUAL GENERATION.

one animal are fecundated by the seminal fluid of another, and vice
versa.

In all the vertebrate animals, on the other hand, the two sets of
generative organs are located in separate individuals ; and the species
is divided into two sexes, male and female. Beside this, there are, in
most instances, certain secondary or accessory organs of generation,
which assist in the accomplishment of the process, and which occasion
a corresponding difference in the anatomy of the two sexes. In some
cases this difference is so great that the male and female would never
be recognized as belonging to the same species, unless they were seen
in company with each other, and were known to reproduce the species
by sexual congress. Not to mention some extreme instances of this
among insects and other invertebrate animals, it is sufficient to refer to
the well-known examples of the cock and the hen, the lion and lioness,
the buck and the doe. In the human species, the distinction between
the sexes shows itself in the mental constitution, the disposition, habits,
and pursuits, as well as in the general conformation of the body, and
the external appearance.

The special details of the generative process depend upon the struc-
ture of the male and female organs, the manner in which their products
are formed and discharged, the union of the two in the act of fecunda-
tion, and the changes which take place in the development of the
embryo.

CHAPTER III.

THE EGG, AND THE FEMALE ORGANS OF
GENERATION.

THE egg, in man and in all species of mammalians, presents an essen-
tial similarity of form, size, and structure. It is a globular body, about
0.25 millimetre in diameter, and consists of two parts, namely, first,
an external closed sac, the vitelline membrane ; and, secondly, a sphe-
rical mass contained in its interior, the vitellus. Of these two, the
vitellus is the essential constituent part of the egg, since it is from its
substance that the rudiments of the embryo are formed. The vitelline
membrane is a protective envelope, destined
to maintain the form and integrity of the
vitellus.

Vitelline Membrane. — The vitelline mem-
brane is a smooth, transparent, colorless
layer, about .01 millimetre in thickness.
When viewed with magnifying powers suffi-
ciently moderate to include the view of the
whole egg, the membrane presents a perfectly
homogeneous aspect; although with higher
powers, according to Klein, it exhibits an HUMAN OVUM, magnified 75

diameters.— a, Vitelline mem-

appearance of vertical striations. Notwith- brane. &. Vitellus. c. Germi-
standing its delicacy and transparency, it is ™ £jve vesicle- *. Germinative
very elastic, and has a considerable degree

of retistance. If the egg of the human species, or of any of the mam-
malians, be placed under the microscope, surrounded by fluid and
covered with a thin slip of glass, it may be perceptibly flattened out
by pressing upon the cover-glass with the point of a steel needle ; and
when the pressure is removed it readily resumes its globular form.
When the egg is partially flattened in this way, by the pressure of a
needle or by the weight of the cover-glass, the apparent thickness of the
vitelline membrane is increased, giving it the appearance of a rather
wide, pellucid border or zone, surrounding the granular and compara-
tively opaque vitellus. From this circumstance it has sometimes re-
ceived the name of the " zona pellucida."

In the vitelline membrane of many invertebrates, and also in that of
fishes, a minute opening has been discovered, termed the " micropyle,"
leading into the interior of the vitelline cavity ; and it is through this
opening that the filaments of the male seminal fluid penetrate, to reach
the vitellus. It is very possible that such an opening may also exist

( 685)

686 EGG AND FEMALE ORGANS OF GENERATION.

in the vitelline membrane of man and the other vertebrate animals ; but
the globular form of the egg, the transparent and homogeneous texture
of the vitelline membrane, and the absence of any other material, of dif-
ferent refractive power, in the canal or orifice of the micropyle itself,
prevent its being detected in microscopic examination.

Vitellus. — The vitellus is a globular mass, of semifluid, tenacious con-
sistency, composed of a transparent and colorless albuminous material,
with oleaginous looking granules thickly disseminated throughout its
substance. Owing to the physical admixture of these two constituents,
it has a distinctly granular aspect, and a considerable degree of opacity.
Imbedded in the vitellus, at a point near its surface, and consequently
almost immediately beneath the vitelline membrane, is a clear, colorless,
transparent vesicle, of a rounded form, the germinative vesicle. In the
mammalian egg, this vesicle measures about .04 millimetre in diameter.
It presents upon its surface a nucleus-like spot, known by the name of
the germinative spot. Both the germinative vesicle and germinate spot
are partially concealed, in the uninjured condition of the egg, by the
granules of the surrounding vitellus.

If the egg, while under the microscope, be ruptured by continued
pressure upon the covering glass, the semifluid vitellus is gradually

expelled by the elasticity of the vitelline mem-
Fig-. 223. brane. It retains the granules imbedded in
its substance, but often allows the germina-
tive vesicle to become detached, and therefore
more distinctly visible.

In man and the mammalians, the simple
form of egg above described, consisting mainly
of a vitellus of minute size, is sufficient for the
production of the embryo, since it is retained,
HUMAN OVUM, ruptured after fecundation, in the interior of the gene-
by pressure, showing the vi- rative passages, and absorbs the nutritious

tellus partially expelled, the . t &.^ '

germinative vesicle, with its materials for its subsequent growth from the

t.ata and the tissues of the female parent. In the naked

smooth fracture of the vitel-
line membrane. reptiles and in most fish, where the eggs are

deposited and hatched in the water, the vitel-
lus is also of small size ; since the hatching takes place at a compara-
tively early period of development, and the requisite additional fluid
is supplied from the surrounding medium. But in birds, and in most
of the scaly reptiles, as serpents, turtles, and lizards, the eggs are de-
posited in a nest or in the ground, and there is consequently no external
source of nutrition for the support and growth of the embryo during
its development. In these instances the vitellus, or " yolk," is of large
size ; and the bulk of the egg is still further increased by the addition,
within the female generative passages, of layers of albumen and various
external fibrous and calcareous envelopes. The essential constituents
of the egg, nevertheless, still remain the same in character, and the
process of embryonic development follows its usual course.

EGG AND FEMALE ORGANS OF GENERATION. 687

Ovaries and Oviducts. — The eggs are produced in the interior of
certain organs, situated in the abdominal cavity, called the ovaries.
These organs consist of a mass of vascular connective tissue, inclosing
a number of globular sacs or follicles, the " Graafian follicles ;" so
called from the name of the anatomist who first fully described them1
as constituent parts of the ovary. Each Graafian follicle contains an
egg, which varies more or less in size and appearance in different classes
of animals, but which has always the same essential characters, and
is produced in the same way.

The egg thus grows in the interior of the ovarian sac, like a tooth in
its follicle ; and forms, accordingly, a constituent part of the body of
the female. It is destined to be subsequently separated from its at-
tachments, and thrown off ; but until that time, it is one of the elements
of the tissue of the ovary, and is nourished like any other portion of the
female organism.

Since the ovaries are the. organs directly concerned in the production
of the egg, they form the most essential part of the female generative
apparatus. Beside them, there are usually present certain other organs,
which play a secondary part in the process of generation. The most
important of these accessory organs are two symmetrical tubes, or
oviducts, destined to receive the eggs at their inner extremity and con-
vey them to the external generative orifice. The mucous membrane
lining the oviducts is also adapted by its structure to supply certain
secretions during the passage of the egg,
which are requisite, either to complete it§
formation, or to provide for the nutrition
of the embryo.

In the frog, the oviduct commences at
the upper part of the abdomen, by a rather
wide orifice, communicating directly with
the peritoneal cavity. It soon afterward
contracts to a narrow tube, and pursues a
zigzag course down the side of the abdo-
men (Fig. 224), folded upon itself in nume-
rous convolutions, until it opens, near its
fellow of the opposite side, into the " clo-
aca" or lower part of the intestinal canal.
The oviducts present the general charac-
ters described above in nearly all species
of reptiles and birds.

The ovaries, as well as the eggs which

they contain, undergo at particular sea-

FEMALE GENERATIVE OR-

sons a periodical development or increase GANS OF FRoo.-a, a Ovaries.
in growth. In the female fros, during the 6» b Oviducts, c, c. Their internal

orifices, d. Cloaca, showing inle-

latter part of summer or the fall, the ova- ri0r orifices of oviducts.

Fig. 224.

Regner de Graaf, Opera Omnia. Arastelaedami, 1705, p. 228.

688 EGG AND FEMALE ORGANS OF GENERATION.

ries appear like small clusters of minute and nearly colorless eggs, the
smaller of which are perfectly transparent and less than 0.18 millimetre
in diameter. But in the early spring, when the season of reproduction
approaches, the ovaries increase to four or five times their former size,
forming large lobulated masses, crowded with dark-colored opaque
eggs, each 2 millimetres in diameter. At the generative season, in all
the lower animals, a certain number of eggs, which were previously in
an imperfect condition, increase in size and become altered in structure.
The vitellus especially, which was before colorless and transparent, be-
comes granular and increased in volume ; and it assumes at the same
time a black, brown, yellow, or orange color. In the mammalian egg
the change consists only in an increase of size arid granulation, without
any remarkable alteration of color.

The eggs, as they ripen in this way, gradually distend the Graafian
follicles and project from the surface of the ovary. When fully ripe,
they are discharged by a rupture of the follicles, and, passing into the
oviducts, are conveyed to the external generative orifice, and there ex-
pelled. In successive seasons, successive crops of eggs enlarge, ripen,
leave the ovaries, and are discharged. Those which are to be expelled
at the next generative epoch may be recognized by their greater degree
of development ; and in this way, in many animals, the eggs of no less
than three different crops may be distinguished in the ovary at once,
namely, 1st, those which are perfectly mature and ready to be dis-
charged ; 2d, those which are to ripen in the following season ; and 3d,
those which are as yet inactive and undeveloped. In most fish and
reptiles, as well as in birds, this regular process of the ripening and
discharge of eggs takes place but once a year. In different species of
quadrupeds it may occur annually, semi-annually, bi-monthly, or even
monthly ; but in every instance it returns at regular intervals, and
exhibits, therefore, a well-marked periodical character.

Action of the Oviducts and Female -Generative Passages. — In the
frog, after the ripening of the eggs and their discharge from the ovarian
follicles, they receive an additional investment while passing through
the oviducts. At the time of leaving the ovary, the eggs consist simply

of the dark-colored and granular vitellus,
225< inclosed in the vitelline membrane. They

are received by the inner extremity of
the oviducts, and carried downward by
the peristaltic movement of these canals,
aided by the contraction of the abdominal
muscles. During their passage, the mu-
cous membrane of the oviduct secretes

MATUKE FKOGS' EGGS.- a. an albuminous substance, which is de-
While still in the ovary, b. After .

passing through the oviduct. posited m successive layers, forming

round each egg a thick coating or en-
velope (Fig. 225). When the eggs are discharged, this envelope
absorbs moisture from the water in which the spawn is deposited, and

EGG AND FEMALE ORGANS OF GENERATION. 689

swells into a transparent gelatinous mass, in which the eggs are sepa-
rately imbedded. Jt supplies, by its subsequent liquefaction and ab-
sorption, a certain amount of nutritious material, for the development
and growth of the embryo.

In the scaly reptiles and in birds, the oviducts perform a more im-
portant function. In the common fowl, the ovary consists, as in the
frog, of follicles, loosely united by connective tissue, and containing eggs
in different stages of development (Fig. 226, «). As the egg which is
approaching maturity enlarges, it distends the cavity of its follicle, and
projects farther from the general surface of the ovary ; so that it hangs
at last into the peritoneal cavity, retained only by the attenuated waM
of the follicle, and a slender pedicle through which run the bloodvessels
by which its circulation is supplied. A rupture of the follicle then
occurs at its most prominent part, and the egg is discharged from the
lacerated opening.

At the time of leaving the ovary, the egg of the fowl consists of a
large, globular, orange-colored vitellus, or " yolk," inclosed in a thin
and transparent vitelline membrane. Immediately underneath the
vitelline membrane, at one point upon the surface of the vitellus, is a
round white spot, consisting of a la}'er of minute granules, termed the
" cicatricula," in which the germinative vesicle is imbedded at an early
stage of the development of the egg. At the time of its discharge from
the ovary, the germinative vesicle has usually disappeared; but the
cicatricula is still an important part of the vitellus, and it is from this
spot that the body of the chick begins afterward to be developed.

As the egg protrudes from the surface of the ovary, it projects into
the inner orifice of the oviduct ; so that, when discharged from its
follicle, it is embraced by the upper expanded extremity of this tube,
and commences its passage downward. In the fowl, the muscular coat
of the oviduct is highly developed, and its peristaltic contractions urge
the egg from above downward, somewhat in the same manner as the
oesophagus or the intestines transport the food in a similar direction.
While passing through the first five or six centimetres of the oviduct
(c, d), where the mucous membrane is smooth and transparent, the
yolk absorbs a certain quantity of fluid, becoming consequently rather
more flexible and yielding in consistency. It then passes into a second
division of the generative canal, in which the mucous membrane is
thicker and more glandular, and is thrown into longitudinal folds.
This portion of the oviduct (d, e) extends over about 22 centimetres,
or more than one-half its entire length. In its upper part, the mucous
membrane secretes a viscid material, by which the yolk is incased,
and which soon consolidates into a gelatinous deposit, thus forming a
second envelope, outside the vitelline meihbrane.

The peristaltic movements of this part of the oviduct are such as to
give a rotary, as well as a progressive motion to the egg ; and by this
means the two extremities of the gelatinous envelope become twisted
in opposite directions; forming two whitish looking cords, attached

690

EGG AND FEMALE ORGANS OF GENERATION.

Fig. 226.

to the opposite poles of the egg. These cords are termed the " chalazse,"
and the membrane with which they are connected, the " chalaziferous
membrane."

Throughout the remainder of the second division of the oviduct, the
mucous membrane exudes an albuminous substance, which is deposited
in successive layers round the yolk, inclosing the chalaziferous mem-
brane and the chalazae. This substance,
the so-called albumen, or "white of egg,"
is gelatinous in consistency, nearly trans-
parent, and of a faint amber color. It is
deposited in greater abundance in front
of the advancing egg than behind it, and
thus forms a conical projection anteriorly,
while behind, its outline is parallel with
the spherical surface of the yolk. In this
way, the egg acquires, when covered with
its albumen, an ovoid form, of which
one end is round, the other pointed ; the
pointed extremity being directed down-
ward, as the egg descends along the
oviduct.

In the third division of the oviduct
(f)i which is about nine centimetres in
length, the mucous membrane is arranged
in longitudinal folds, which are narrower
arid more closely packed than in the
preceding portion. The material secreted
in this part condenses into a firm fibrous
covering, composed of three different
layers which closely embrace the surface
of the albuminous mass, forming a tough,
flexible, semi-opaque envelope for the
whole. These layers are known as the
external, middle, and internal fibrous
membranes of the egg.

Finally the egg passes into the fourth
division of the oviduct (gr), which is wider
than the rest of the canal, but only a
little over five centimetres in length.
Here the mucous membrane, which is
arranged in abundant projecting, leaf-
like villosities, exudes a fluid rich in

FEMALE GENERATIVE ORGANS OF THE FOWL. — a. Ovary, b. Graafian follicle,
from which the egg has just been discharged, c. Yolk, entering upper extremity of oviduct.
d, e. Second division of oviduct, in which the chalaziferous membrane, chalazse, and albumen
are formed. /. Third portion, in which the fibrous shell membranes are produced, g. Fourth
portion laid open, showing the egg completely formed, with its calcareous shell, h. Narrow
canal through which the egg is discharged.

EGG AND FEMALE ORGANS OF GENERATION. 691

calcareous salts. The most external of the three membranes above
described is permeated by this secretion ; and soon afterward, owing to
the reabsorption of its fluid parts, the calcareous matter begins to crys-
tallize in the fibrous network of the membrane. This deposit of calcare-
ous matter goes on, growing thicker and more condensed, until the
external envelope is converted into a white, opaque, brittle, calcareous
shell, which incloses the remaining portions and protects them from
injury. The egg is then forced through a narrow portion of the oviduct
(/?,), and, gradually dilating the passages by its conical extremity, is
finally discharged from the external orifice.

The egg of the fowl, after its expulsion, consists, accordingly, of vari-
ous parts ; some of which, as the yolk and the vitelline membrane,
entered into its original formation,' while the remainder have been
deposited round it during its passage through the oviduct.

After the discharge of the egg there is a partial evaporation of its
watery ingredients, which are replaced by air penetrating through the
pores of the shell at its rounded extremity. The air thus introduced
accumulates between the middle and internal fibrous membranes, form-
ing a cavity or air-chamber (</), at the rounded end of the egg. Very

Fig. 227.

Diagram of FOWL' 8 EGO.— a. Yolk. b. Vitelline membrane, c. Chalaziferous
membrane, d. Albumen. e,f. Middle and internal shell membranes, g. Air-chamber.
h. Calcareous shell.

soon, the external layers of the albumen liquefy ; and the vitellus, being
specifically lighter than the albumen, rises toward the surface of the
egg, with the cicatricula uppermost. This part presents itself almost
immediately on breaking open the egg at any point corresponding to
the equator of the yolk, and is placed in the most favorable position
for the action of warmth and atmospheric air in the development of the
chick.

The vitellus, therefore, is still the essential constituent part, even in
the large and highly complicated fowl's egg ; while the remainder con-

692

EGG AND FEMALE ORGANS OF GENERATION.

sists of nutritious material, provided for the support of the embryo,
and of protective envelopes, like the shell and fibrous membranes.

In the quadrupeds, another important modification of the oviducts
takes place. In these animals, the egg, which is originally of minute
size, is retained within the generative passages of the female during the
development of the embryo. While the upper part of the ovi(Juct,
accordingly, is quite narrow, and serves merely to transmit the egg
from the ovary, and to supply it with a little albuminous secretion, the
lower portions are much increased in size, and are lined with a mucous
membrane which is adapted to provide for the protection and nourish-
ment of the embryo during gestation. The upper and narrower por-
tions of the oviduct are known as the "Fallopian tubes," from Fallopius1
who first described them in the 'human female ; while the lower and

UTERUS AND OVARIES OP THE Sow.— a, a. Ovaries. 6, b. Fallopian tubes.
c, c. Horns of the uterus, d. Body of the uterus, e. Vagina.

more highly developed portions constitute the uterus. The two halves
of the uterus unite with each other upon the median line near their
inferior termination, to form a central organ, termed its "body;" while
the ununited parts are known as its "cornua" or "horns."

In the human species, the ovaries consist of Graafian follicles, imbed-
ded in a somewhat dense connective tissue, supplied witli an abundance
of bloodvessels, and covered with an opaque, yellowish- white layer of
fibrous tissue, called the " albugineous tunic." Over the whole is a layer
of peritoneum, which is reflected upon the bloodvessels supplying the
ovary, and is continuous with the broad ligaments of the uterus ; but
which elsewhere is closely consolidated with the albugineous tunic.

The oviducts commence by a wide expansion, provided with fringed
edges, called the " fimbriated extremity of the Fallopian tube." The
Fallopian tubes themselves are narrow and convoluted, terminating, on
each side, in the upper part of the body of the uterus. The body of the
uterus, in the human species, is so much developed at the expense of the
cornua, that the latter hardly appear to have an existence, and no trace
of them is visible externally. But on opening the uterus, its cavity is

1 Opera Omnia. Francofurti, 1600. Observations Anatomicae, p. 421.

EGG AND FEMALE ORGANS OF GENERATION.

693

seen to be somewhat triangular in shape, its two superior angles running
out to join the lower extremities of the Fallopian tubes. This portion
evidently consists of the cornua, which have been consolidated with the
body of the uterus, and enveloped in its thickened layer of muscular
fibres.

Fig. 229.

GENERATIVE OROAKS OF THE HUMAN FEMALE.— a, a. Ovaries, ft, 6. Fallopian
tubes, c. Body of the uterus, d. Cervix, e. Vagina.

The cavity of the body of the uterus terminates below by a con-
stricted portion, termed the os internum, by which it is separated from
the cervix. These two cavities are not only different from each other
in shape, but also in the structure of their mucous membrane and in the
functions which they perform.

The mucous membrane of the body of the uterus in its usual condi-
tion is smooth and rosy in color, and closely adherent to the subjacent
muscular tissue. It consists of tubular follicles, ranged side by side,
and opening by distinct orifices upon its free surface. The secretion of
these follicles is destined for the nutrition of the embryo during the
earlier periods of its formation.

The internal surface of the cervix, on the other hand, is raised in
prominent ridges, arranged usually in two lateral sets, diverging from a
central longitudinal ridge ; presenting the appearance known as the
"arbor vitae uterina." The follicles of this part of the uterine mucous
membrane are of a globular or sac-like form, and secrete a tenacious
mucus, which serves, during gestation, to block up the cavity of the
cervix, and thus to prevent the escape or injury of the egg.

The cavity of the cervix uteri is terminated inferiorly by a second
constriction, the " os externum ;" and below this comes the vagina,
which constitutes the last division of the female generative passages.

The accessory female organs of generation consist, therefore, of ducts
or tubes, by means of which the egg is conveyed from within outward.
These ducts vary in the degree and complication of their development,

694: EGG AND FEMALE ORGANS OF GENERATION.

in different kinds of animals, according to the importance of the func-
tion which they perform. In the lower orders, they serve mainly to
convey the egg to the exterior, and to supply it more or less abundantly
with an albuminous secretion ; while in the mammalia and in man, they
are adapted to the more important office of retaining the egg during the
period of gestation, and of providing during the same time for the nour-
ishment of the embryo.

CHAPTER IV.

THE SEMINAL FLUID, AND THE MALE ORGANS OF

GENERATION.

THE mature egg is not by itself capable of being developed into the
embryo. If simply discharged from the ovary and carried through the
oviducts to the exterior, it soon dies and is decomposed, like any other
portion of the body separated from its connections. It is only when
fecundated by the seminal fluid of the male, that it is stimulated to con-
tinued development, and becomes capable of more complete organiza-
tion.

The product of the male generative organs is a colorless, somewhat
viscid, albuminous fluid, containing minute filamentous bodies, the sper-
matozoa. This name has been given to the bodies in question on ac-
count of their exhibiting, when recently discharged, a very active and
continuous movement suggesting the idea of an independent animal
organization.

Anatomical Characters of the Spermatozoa. — The spermatozoa of man
(Fig. 230, a) are about .045 millimetre in length, according to the mea-
surements of Kolliker. Their anterior extremity presents a somewhat
flattened triangular-shaped enlargement, termed the "head," which con-
stitutes about one-tenth part the entire length of the spermatozoon.
The remaining portion is a slender filamentous prolongation, called the
"tail," which tapers gradually backward, becoming so exceedingly deli-
cate toward its extremity, that it is difficult to be seen except when in
motion. There is no further organization visible in any part of the
spermatozoon ; and the whole appears to consist, so far as can be seen
by the microscope, of a homogeneous substance. The terms head and
tail, as remarked by Bergmann and Leuckart,1 are not used, when de-
scribing the different parts of the spermatozoon, in the same sense as
that in which they would be applied to the corresponding parts of an
animal ; but simply for the sake of convenience, as one might speak of
the head of an arrow or the tail of a comet.

In the lower vertebrate animals, the spermatozoa have the same gen-
eral form as in man ; that is, they are filamentous bodies, with the ante-
rior extremity more or less enlarged. In the rabbit, the head is roundish
and flattened in shape, somewhat resembling a blood globule. In the
rat (Fig. 230, 6) they are much larger than in man, measuring nearly
0.20 millimetre in length. The head is of a conical form, about one-

1 Vergleichende Physiologie. Stuggart, 1852.

(695)

696

MALE ORGANS OF GENERATION.

Fig. 230. twentieth the whole length of

the filament, and often slightly
curved at its anterior extremity.
In the frog and in reptiles gen-
erally, the spermatozoa are lon-
ger than in quadrupeds. In
Menobranchus, the great Amer-
ican water-lizard, they are of
very unusual size (Fig. 230, c),
measuring not less than 0.57
millimetre in length, about one-
third of which is occupied by
the head, or enlarged portion
of the filament.

The most remarkable peculi-
arity of the spermatozoa, as seen
under the microscope, is their
rapid and energetic movement.
In a drop of fresh seminal fluid,
if kept sufficiently moistened
and at its normal temperature,
the numberless filaments with
which it is crowded are seen to
be in a state of incessant mo-
tion. In many species of ani-
mals, the movement of the sper-
matozoa strongly resembles that of a tadpole ; particularly when, as in
the mammalia, they consist of a short, well-defined head, followed by
a long and slender tail. The tail-like filament keeps up a constant lat-
eral vibratory movement, by which the spermatozoon is driven from
place to place in the seminal fluid, as a fish or a tadpole is propelled
through the water. In other instances, as in the Triton, or water lizard,
the spermatozoa have a continuous wrrithing or spiral-like movement ;
presenting a peculiarly elegant appearance when large numbers are
viewed together.

It is this movement which gave origin to the name of spermatozoa,
to designate the filaments of the spermatic fluid. But, notwithstanding
its active character, and its resemblance in mechanism to the locomo-
tion of certain animals, it has no analogy with a voluntary act.

The spermatozoa are organic forms, produced in the. testicles, and
constituting a part of their tissue; just as the eggs, which are pro-
duced in the ovaries, naturally form a part of the texture of these or-
gans. Like the egg, the spermatozoon is destined to be discharged
from the organ where it grew, and to retain, for a certain time after-
ward, its vital properties. One of these properties is its power of move-
ment ; but this does not indicate the possession of independent vitality,
and is not even necessarily a proof of its animal origin. The move-

SPERM ATOZO A.— a. Human, b. Of the rat.
c. Of Menobranchus. Magnified 480 times.

MALE ORGANS OF GENERATION. 697

ment of a spermatozoon is not more active than that of a bacterium
cell, or that of the ciliated zoospores of certain fresh-water algae. It
is more strictly analogous to the motion of a ciliated epithelium cell
when detached from its mucous membrane, which will sometimes con-
tinue for many hours, if kept under favorable conditions of temperature
and moisture. The power of movement manifested by the spermatozoa
also continues for a time after their separation from the rest of the body ;
but it is limited in duration, and after a certain interval comes to an
end.

In order to preserve their vitality, the spermatozoa must be kept at
or near the normal temperature of the body, and preserved from the
contact of air or other unnatural fluids. If the seminal fluid be allowed
to dry, or if it be diluted by water, in the case of birds and quadrupeds,
or if it be subjected to extremes of heat or cold, the motion ceases, and
the spermatozoa soon begin to disintegrate.

Formation of the Spermatozoa. — The spermatozoa are produced in the
interior of certain glandular-looking organs, the testicles, which are
characteristic of the male, as the ovaries are characteristic of the female.
In man and mammalia, the testicles are solid, ovoid-shaped bodies, com-
posed of long, narrow, convoluted tubes, the " seminiferous tubes," some-
what similar to the tubuli uriniferi of the kidneys. They lie for the
most part closely in contact with each other, nothing intervening between
them except capillary bloodvessels and a little connective tissue. They
commence, by rounded extremities, near the external surface of the
testicle and pursue an intricately convoluted course toward its central
and posterior part. They are not strongly adherent to each other, but
may be readily unravelled by manipulation.

According to the investigations of Kolliker, the formation of the
spermatozoa takes place within peculiar cells occupying the cavity of
the seminiferous tubes. As the age of puberty approaches, beside the
ordinary pavement epithelium lining the tubes, other cells or vesicles
of larger size make their appearance, each containing from one to fifteen
or twenty nuclei, with nucleoli. In the interior of these vesicles sper-
matozoa are formed; their number corresponding usually with that of
the nuclei. They are developed in bundles of from ten to twenty, held
together by the membranous substance surrounding them, but are after-
ward set free by the liquefaction of the vesicle, and then nearly fill the
cavity of the seminiferous ducts, being mingled only with a minute
quantity of transparent fluid.

While in the seminiferous tubes, the spermatozoa are always inclosed
in their parent vesicles ; they are liberated, and mingled together, only
after entering the rete testis and the head of the epididymis.

Accessory Male Organs of Generation. — Beside the testicles, which
are the essential parts of the male generative apparatus, there are certain
accessory organs, by which the seminal fluid is conveyed to the exterior,
and mingled with various secretions which assist in the accomplishment
of its function.
45

MALE ORGANS OF GENERATION.

As the sperm leaves the testicle, it consists almost entirely of sperma-
tozoa, crowded together in an opaque, white, semi-fluid mass, which fills
the vasa efFerentia, and distends their cavities. It then enters the single
duct which forms the body and lower extremity of the epididymis, fol-
lowing the long and tortuous course of this tube, until it reaches the vas
deferens ; through which it is conveyed onward to the vesiculae seminalis.
Throughout this course, it is mingled with a scanty mucus-like fluid,
secreted by the walls of the epididymis and vas deferens. The vesiculse
seminales contain also a glairy fluid, produced by secretion from their
walls, which serves some secondary purpose in completing the formation
of the sperm. One of its functions is no doubt to dilute the mass of
spermatozoa, as they arrive from the testicles, and thus allow them
liberty of motion; as well as to increase the volume of the seminal fluid
and enable it to be expelled by the muscular contraction of the parts
about the urethra. Kolliker has found that the spermatozoa in the vas
deferens and epididymis are generally motionless ; and that they exhibit
their characteristic movements only in the vesiculse seminales and in the
ejaculated sperm.

At the moment of the final evacuation of the sperm, it first passes
from the vesiculae seminales into the prostatic portion of the urethra,
where it meets with the secretion of the prostate gland, which is then
poured out in unusual abundance ; and farther on, there are added the
secretions of Cowper's glands and of the remaining mucous follicles of
the urethra. All these fluids increase the quantity of the sperm, and
serve as vehicles for the transport of the spermatozoa.

Necessary Conditions of Fecundation by the Seminal Fluid. — There
are several conditions which are essential to the successful accomplish-
ment of the act of fecundation.

First, the spermatozoa must be present and in a state of active
vitality. Of all the organic ingredients, derived from different sources,
which go to make up the mixed seminal fluid, as discharged from the
urethra, it is the spermatozoa which constitute its essential part. They
are the true fecundating element of the sperm, while the others are of
secondary importance, and perform only accessory functions.

Spallanzani1 found that if frog's sperm be passed through a succes-
sion of filters, so as to separate the solid from the liquid portions, the
filtered fluid is destitute of fecundating properties ; while the sperma-
tozoa entangled in the filter, if mixed with a sufficient quantity of fluid
of the requisite density for dilution, may still be successfully used for
the artificial impregnation of eggs. It is well known that animals or
men, after removal of both testicles, are incapable of impregnating the
female, notwithstanding that all the other generative organs may remain
uninjured. The seminal fluid, furthermore, must be in a fresh condition,
so that the spermatozoa retain their anatomical characters and their
active movement. The experiments of Spallanzani have shown that,

1 Experiences pour servir a FHistoire de la Generation. Gen&ve, 1786.

MALE ORGANS OF GENERATION 699

if the above conditions be preserved, the seminal fluid, removed from
the spermatic ducts of the male, is capable of fecundating the eggs of
the female. But if allowed to remain exposed to the atmosphere, or to
an unnatural temperature, it becomes inert. So long as the spermatozoa
continue in active motion, they are usually found to retain their physio-
logical properties ; the cessation of this movement, on the other hand,
being a sign that their vitality is exhausted, and that they are no longer
capable of impregnating the egg.

Secondly, both eggs and spermatozoa must have arrived at a certain
degree of development before fecundation can take place. Previous to
this time the immature eggs are incapable of being impregnated, and the
imperfectly developed spermatozoa have not yet acquired their fecun-
dating power. The necessary process of growth takes place within the
generative organs ; and when it is complete, both the spermatozoa of
the male and the eggs of the female are ready to be discharged, and are
in condition to exert upon each other the necessary influence.

The fecundating power of the spermatozoa, when fully developed, is
exceedingly active. Spallanzani found that one-fifth of a gramme of
the seminal fluid of the frog, diffused in water, was sufficient for the
impregnation of several thousand eggs. The process seems to be ac-
complished almost instantaneously, " since eggs which were allowed to
remain in the fecundating mixture for only one second proved to be
impregnated, and were afterward hatched at the usual period."

Thirdly, the spermatozoa must come into direct contact with the egg
or its immediate envelopes. Spallanzani first demonstrated this by
attaching mature eggs to the concave surface of a watch-glass, which
he placed, in an inverted position, over a second watch-glass containing
fresh seminal fluid. The eggs, allowed to remain in this way for several
hours, exposed to the vapor of the fluid but without touching its surface,
were afterward found to have failed of impregnation ; while others, which
were actually moistened with the same seminal fluid, became developed
into living tadpoles.

Finally, the physiological act of fecundation is accomplished by the
entrance of the spermatozoa into the interior of the egg, through the
vitelline membrane, and their union with the substance of the vitellus.
This fact was first observed by Martin Barry1 in the fecundated egg
from the Fallopian tube of the rabbit. It has subsequently been seen
by Newport2 in the frog, by Bischoff, by Coste, by Robin3 in a species of
leech, by Flint4 in the pond snail, and by Weil,5 in repeated instances, in
the rabbit. According to some of these observations, the mechanism of
penetration is by means of a natural orifice or " micropyle" existing in

1 Philosophical Transactions. London, 1840, p. 533, and 1843, p. 33.

2 Philosophical Transactions, 1853, p. 271.

3 Journal de la Physiologic de 1'Homme et des Animaux. Paris, 1862, tome
v. p. 80.

4 Physiology of Man. New York, 1874, vol. v. p. 352.

6 Strieker's Medizinischer Jahrbucher. Wien, 1873, p. 18.

700 MALE ORGANS OF GENERATION.

the vitelline membrane, as first indicated by Barry. In others no such
orifice has been visible; the spermatozoa appearing to perforate the sub-
stance of the vitelline membrane by the impulsive movement of their
filamentous extremity (Newport). Such a mode of penetration is not
inadmissible, since the much larger embryos of the tsenia and trichina
(page 675) make their way without difficulty through the substance of
the intestinal mucous membrane.

After their arrival in the interior of the vitelline cavity, the sperma-
tozoa disappear as distinct organic elements. Their substance unites
with that of the vitellus ; and thenceforward the fecundated egg con-
sists of materials derived from both the male and female organisms.
The greater portion of this material is that produced by the female ;
but that which is supplied from the seminal filaments of the male is
equally essential for the production of an embryo. The offspring,
accordingly, may exhibit resemblances to either or both of the indi-
vidual parents, since it originates from a union of both the generative
products.

Union of the Sexes. — In most of the lower animals there is a peri-
odical development of the testicles in the male, corresponding in time
with that of the ovaries in the female. As the ovaries enlarge and the
eggs ripen in the one sex, so in the other the testicles increase in size, as
the season of reproduction approaches, and become turgid with sper-
matozoa. The accessory organs of generation at the same time share
the unusual activity of the testicles, and become increased in vascularity
and ready to perform their part in the reproductive function.

In fishes, as a general rule, where the testicles occupy, in the abdomen
of the male, the same relative position as the ovaries in the female, these
organs enlarge, become distended with their contents, and project into
the peritoneal cavity. Each of the two sexes is then at the same time
under the influence of a corresponding excitement. The unusual de-
velopment of the reproductive organs reacts upon the general system,
and produces a state of peculiar excitability, known as the condition of
"erethism." The female, distended with eggs, feels the stimulus which
leads to their expulsion ; while the male, bearing the weight of the
enlarged testicles and the accumulation of newly-developed spermatozoa,
is impelled by a similar sensation to the discharge of the seminal fluid.
The two sexes are led by instinct at this season to frequent the same
situations. The female deposits her eggs in some spot favorable to the
protection and development of the young ; after which the male, appa-
rently attracted and stimulated by the sight of the new-laid eggs, dis-
charges upon them the seminal fluid, and their impregnation is accom-
plished. It is in this way that fecundation takes place in nearly all the
osseous fishes, as the trout, the salmon, and the stickleback.

In instances like the above, where the male and female generative
products are discharged separately, the subsequent contact of the semi-
nal fluid with the eggs would seem to be dependent on the occurrence
of fortuitous circumstances, and their impregnation, therefore, liable to

MALE ORGANS. OF GENERATION. 701

fail. But, in point of fact, the simultaneous functional excitement of
the two sexes, and the operation of corresponding instincts, leading
them to ascend the same rivers and to frequent the same spots, provide
with sufficient certainty for the impregnation of the eggs. The number
of eggs produced by the female is also very large, the ovaries being
often so distended as nearly to fill the abdominal cavity; so that,
although many of the eggs may be accidentally lost, a sufficient number
will still be impregnated to provide for the continuation of the species.

In many of the cartilaginous fishes, on the other hand, as in sharks,
rays, and skates, an actual contact takes place between the two sexes at
the time of reproduction, and the seminal fluid of the male is introduced
into the generative passages of the female. Thus the eggs are fecunda-
ted while still in the body of the female, and in many species go through
with a nearly complete development in this situation and are born alive.

In the frog, the male fastens himself upon the back of the female by
means of the anterior limbs, which retain their hold by a kind of spas-
modic contraction. This continues for one or more days, during which
time the mature eggs, which have been discharged from the ovary, are
passing downward through the oviducts. As they are expelled from the
anus, the seminal fluid of the male is discharged upon them, and impreg-
nation takes place.

In serpents, lizards, and turtles, the sperm is introduced into the female
generative passage at the time of copulation, by means of a single or
double erectile male organ. Of these animals, some species lay their
eggs immediately after fecundation, others retain them until the embryo
is partly or fully developed.

In birds, the spermatozoa are introduced into the sexual orifice of
the female, and make their way into the upper portion of the oviduct,
where they may be found in active motion, mingled with the fluids of
this canal.1 The vitellus is thus fecundated immediately upon its- dis-
charge from the ovary, and before it has become surrounded with the
albuminous and membranous envelopes supplied by the middle and
lower portions of the oviduct.

Lastly, in the human species and in mammalians, where the impreg-
nated egg is to be retained in the body of the female parent during the
whole period of its development, the seminal fluid is introduced into the
vagina and uterus by sexual congress, and meets the egg at or soon
after its discharge from the ovary. A close correspondence between the
periods of sexual excitement, in the male and the female, is visible in
many of these animals, as well as in fish, birds, and reptiles. This is
the case in most species which produce young but once a year, as the
deer, the wolf, and the fox. In others, such as the dog, the rabbit, and
the guinea pig, where several broods of young are produced during the
year, or where, as in man, the generative epochs of the female recur at
short intervals, the time of impregnation is comparatively indefinite,

1 Foster and Balfour, Elements of Embryology. London, 1874, p. 21.

702 MALE ORGANS OF GENERATION.

and the generative apparatus of the male is almost constantly in a state
of full development. It is excited to action at particular periods, ap-
parently by some influence derived from the condition of the female.

In quadrupeds and in the human species, the contact of the sperm
with the egg, and the fecundation of the latter, take place in the gene-
rative passages of the female ; either in the uterus, the Fallopian tubes,
or upon the surface of the ovary; in each of which situations the sper-
matozoa have been found, after the accomplishment of sexual inter-
course.

CHAPTEE Y.

PERIODICAL OYULATION, AND THE FUNCTION
OF MENSTRUATION.

I. Periodical Ovulation.

THE periodical ripening of the eggs and their discharge from the
generative organs constitute the process, known by the name of "ovula-
tion," which may be considered as the primary act of reproduction.
The characteristic phenomena which distinguish the performance of this
function depend upon the following general laws, which apply with but
little variation to all classes of animals.

1st. Eggs exist originally in the ovaries, as part of their natural
structure. In fish, reptiles, and birds, the ovary is of comparatively
simple texture, consisting only of a number of Graafian follicles, united
by an intervening stroma of loose connective tissue, and thus aggre-
gated into the form of a rounded, elongated, or lobulated organ. In the
mammalians and in man, its essential constitution is the same; but its
connective tissue is denser and more abundant, and the figure of the
organ is more compact. But in all classes the interior of each Graafian
follicle is occupied by an egg, from which the embryo is afterward pro-
duced.

The process of reproduction was formerly regarded as essentially
different in the oviparous and the viviparous animals. In oviparous
animals, such as most fishes and reptiles and all birds, the young
animal was well known to be formed from an egg produced by the
female ; while in the viviparous species, or those which bring forth their
young alive, as certain fishes and reptiles and all the mammalians,
the embryo was supposed to originate in the body of the female in
consequence of sexual intercourse. But by the aid of the microscope,
as employed in the examination of the different organs and tissues, it
was subsequently found that, in mammalians also, the ovaries contain
eggs. The mammalian eggs had previously escaped observation owing
to their comparatively simple structure and minute size; but they were
nevertheless found to possess all the essential characters belonging to
the larger eggs of the oviparous animals.

The true difference in the process of reproduction, between the two
classes, is therefore merely an apparent, not a fundamental one. In the
oviparous fish, reptiles, and birds, the egg is discharged by the female
before or immediately after impregnation, and the embryo is subse-
quently developed and hatched externally. In quadrupeds and in the
human species, on the other hand, the egg is retained within the body

( 703 )

704 OVULATION AND MENSTRUATION.

of the female until the embryo is developed ; and the membranes are
ruptured and the young expelled at the same time. In all classes,
viviparous as well as oviparous, the young is produced from an egg ;
and in all classes the egg, sometimes larger and sometimes smaller, but
always consisting essentially of a vitellus and a vitelline membrane, is
contained originally in the interior of an ovarian follicle.

The egg is accordingly an integral part of the ovarian tissue. It
exists there long before the generative function is established, iind dur-
ing the earliest periods of life. It may be found without difficulty in
the newly born female infant, and may even be detected in the foetus
before birth. Its growth and nutrition are provided for in the same
manner with that of other portions of the bodily structure.

2d. The ovarian eggs become more fully developed at a certain age
when the generative function is about to be established. During the
early periods of life, the ovaries and their contents, like many other
organs, are imperfectly developed. They exist, but they are as yet
inactive and incapable of performing their special function. In the
young chick, for example, the ovary is of small size; and the eggs,
instead of presenting the voluminous, yellow, opaque vitellus which they
afterward exhibit, are minute, transparent, and colorless. In young
quadrupeds, and in the human female during infancy and childhood, the
ovaries are equally inactive. They are small, friable, and of a nearly
homogeneous appearance to the naked eye ; presenting none of the
enlarged follicles, filled with transparent fluid, which afterward become
a characteristic feature of the organ. At this time, accordingly, the
female is incapable of bearing young, because the ovaries are inactive,
and the eggs which they contain immature.

But at a certain period, which varies in the time of its occurrence for
different species of animals, the sexual apparatus begins to enter upon a
state of activity. The ovaries increase in size, and their circulation
becomes more active. The eggs, which have previously remained qui-
escent, take on a rapid growth, and the structure of the vitellus is
completed by a deposit of semi-opaque granular matter in its interior.
Arrived at this state, the eggs are ready for impregnation, and the
female becomes capable of bearing young. She is then said to have
arrived at the state of "puberty," or that condition in which the gene-
rative organs are fully developed. This change is accompanied by a
visible alteration in the S3rstem at large, which indicates the complete
development of the entire organism. In man}7- birds, the plumage as-
sumes at this period more varied and brilliant colors ; and in the com-
mon fowl, the comb, or "crest," enlarges and becomes red and vascular.
In the American deer (Cervus virginanus), the coat, which during the
first year is mottled with white, becomes in the second year of a uniform
tawny or reddish tinge. In nearly all species, the limbs become more
compact and the body more rounded ; and the whole external appear-
ance is so altered, as to indicate that the animal has arrived at the
period of puberty, and is capable of reproduction.

PERIODICAL OVULATION. 705

3d. Successive crops of eggs, in the adult female, ripen and are dis-
charged independently of sexual intercourse. The original formation
of the germ, in the bodies of viviparous animals, was formerly sup-
posed to be a consequence of sexual intercourse. Even after it became
known that the ovaries of these animals contain eggs before impregna-
tion, the discharge of the egg from its follicle was thought to occur only
under the influence of fecundation ; and the rupture of a follicle was
consequently regarded as an indication that sexual intercourse had taken
place.

But subsequent observation showed that not only the existence, but
also the ripening and discharge of the egg, are phenomena dependent
on the structure and functional activity of the female organism. In
many fish and reptiles, the mature eggs leave the ovary, pass through
the oviducts, and are discharged externally before coming in contact
with the seminal fluid of the male. In the domestic fowl it is a matter
of common observation that the hen, if well supplied with nourishment,
will continue to lay fully formed eggs without the presence of the cock ;
only these eggs, not having been fecundated, are incapable of producing
chicks. In oviparous animals, therefore, the discharge of the egg, as
well as its formation, may take place independently of sexual inter-
course.

This is also the case in the viviparous quadrupeds. The observa-
tions of Bischoff, Pouchet, and Coste, on the sheep, the pig, the bitch,
and the rabbit, have demonstated that if the female be carefully kept
from the male until after the period of puberty is established, and then
killed, examination of the ovaries will sometimes show that Graafian
follicles have matured, ruptured, and discharged their eggs, though no
sexual intercourse has taken place. Sometimes the follicles are found
distended and prominent upon the surface of the ovary ; sometimes re-
cently ruptured and collapsed ; and sometimes in various stages of cica-
trization and atrophy. Bischoff,1 in several instances of this kind, found
the unimpregnated eggs in the oviduct, on their way to the cavity of
the uterus. In species of animals where the ripening of the eggs takes
place at short intervals, as in the sheep, the pig, or the cow, it is very
rare to examine the ovaries where traces of a more or less recent rup-
ture of the Graafian follicles are not distinctly visible.

One of the most important facts, derived from these observations, is
that the ovarian eggs become developed and are discharged in succes-
sive crops, which follow each other at periodical intervals. In the ovary
of the fowl (Fig. 226), it may be seen at a glance that the eggs grow
and ripen, one after the other, like fruit upon a vine. In -this instance,
the process of evolution is rapid ; and it is easy to distinguish, at the
same time, eggs which are almost microscopic in size, colorless, and
transparent ; those which are larger, somewhat opaline, and yellowish

1 M6moire sur la chQte p£riodique de 1'oeuf, Annales des Sciences Naturelles,
Paris, Aotit — Septembre, 1844.

706 OVULATION AND MENSTRUATION.

in hue ; and finally those which are fully developed, opaque, of a deep
orange color, and nearly ready to leave the ovary.

Here, the difference between the undeveloped and the mature eggs
consists mainly in the size of the vitellus, which is very much larger
than in the quadrupeds. The ovarian follicle is distended .ind ruptured,
and the egg finally discharged, owing to the pressure exerted by the
increased1 size of the vitellus.

In man and mammalians, on the other hand, the microscopic egg
never becomes large enough to distend the Graafian follicle by its own
size. The rupture of the follicle and the liberation of the egg are accord-
ingly provided for, in these instances, by a different mechanism.

In the earlier periods of life, in man and the mammalians, the egg is
contained in a Graafian follicle which closely embraces its exterior, and
is consequently hardly larger than the egg itself. As puberty ap-
proaches, the follicles situated near the free surface of the ovary become
enlarged by the accumulation of serous fluid in their cavity. At that
time, the ovary, if cut open, shows a considerable number of globular,
transparent vesicles, the smaller of which are deep seated, but which
increase in size as they approach the free surface of the organ. These
are the Graafian follicles, which, in consequence of the advancing matu-
rity of their eggs, gradually enlarge at the arrival of the period of
generation.

The Graafian follicle then consists of a closed globular sac, the exter-
nal wall of which, though quite translucent, has a fibrous texture, and is
well supplied with bloodvessels. This fibrous and vascular wall is dis-
tinguished by the name of the " vesicular membrane." It is not very
firm in texture, and if roughty handled is easily ruptured.

The vesicular membrane is lined throughout by a layer of minute
granular cells, which form for it a kind of epithelium. This layer is
termed the membrana granulosa. It adheres but slightly to the vesicu-
lar membrane, and may easily be detached by careless manipulation
before the follicle is opened, being then mingled, in the form of light
flakes and shreds, with the serous fluid contained in its interior.

At the most superficial part of the Graafian follicle the membrana
granulosa is thicker than elsewhere. Its cells are here accumulated, in
a kind of mound or "heap," which has received the name of the cumu-
lus proligerus. It is also called the discus proligerus, because the
thickened mass, when viewed from above, has a nearly circular or disk-
like form. In the centre of this thickened portion of the membrana
granulosa the egg is imbedded. It is accordingly always situated at
the most superficial portion of the follicle, and advances in this way
toward the surface of the ovary.

As the period approaches at which the egg is to be discharged, the
Graafian follicle becomes more vascular, and enlarges by an increased
exudation into its cavity. It then begins to project from the surface
of the ovary, still covered by the albugineous tunic and its peritoneal

PERIODICAL OVULATION.

707

investment. (Fig. 231.) The constant accumulation of fluid in the fol-
licle exerts such a pressure from within outward, that the albugineous

Fig. 231.

GRAAFIAN FOLLICLE, nearthe period of rupture.- a. Vesicular membrane. 6. Membrana
granulosa. c. Cavity of follicle, d. Egg. e. Peritoneal surface. /. Tunica albuginea. g, g.
Tissue of the ovary.

Fig. 232.

tunic and the peritoneum gradually yield before it ; until the Graafian
follicle protrudes from the ovary as a tense, rounded, translucent vesicle,
in which fluctuation can be readily
perceived on applying the fingers
to its surface. Finally, the pro-
cess of effusion and distension still
going on, the wall of the vesicle
yields at its most prominent por-
tion, the contained fluid is driven
out with a gush, by the elastic re-
action of the ovarian tissue, carry-
ing with it the egg, still entangled
in the cells of the membrana
granulosa.

The rupture of the Graafian
follicle is accompanied, in some
instances, by hemorrhage from its
internal surface, by which its cavity

is filled with blood. This occurs in the human species, also in the pig,
and to some extent in several other of the lower animals. Sometimes,
as in the cow, where no immediate hemorrhage takes place, the Graafian
follicle, when ruptured, simply collapses ; after which a slight exudation,
more or less tinged with blood, is poured out during the course of a
few hours.

This process occurs in one or more Graafian follicles at a time, according
to the number of young produced at a birth. In the bitch and the sow,
where each litter consists of from six to twenty young ones, a similar
number of eggs ripen and are discharged at each period. In the mare,
in the cow, and in the human female, where there is usually but one

OVART WITH GRAAFIAN FOLLICLE
RUPTURED: at a, the egg, just discharged,
with a portion of the membrana granulosa.

708 OVULATION AND MENSTRUATION.

foetus at a birth, the eggs are matured singly, and the Graafian follicles
ruptured, one after the other, at successive periods of ovulation.

4th. The ripening and discharge of the egg are accompanied by a pe-
culiar condition of the general system, known as the " rutting" condition,
or " oestruation." The congestion and functional activity manifested by
the ovaries at each period of ovulation, act by sympathy upon the other
generative organs and produce in them a greater or less degree of ex-
citement, according to the particular species of animal. Usually there
is a certain amount of congestion of the entire generative apparatus.
The secretions of the vagina and neighboring parts are more particularly
affected, being increased in quantity and altered in quality. In the bitch,
the vaginal mucous membrane becomes red and tumefied, and pours out
a secretion which is more or less tinged with blood. The vaginal secre-
tions acquire at this time a peculiar odor, which appears to attract the
male, and to excite in him the sexual impulse. An unusual tumefaction
and redness of the vagina and vulva are also perceptible in the rabbit ;
and in some species of apes there is not only a bloody discharge from
the vulva, but also an engorgement and infiltration of the neighboring
parts, extending to the skin of the buttocks, the thighs, and the under
part of the tail.1

The system at large is also visibly affected by the process going on
in the organs of generation. In the cow, the approach of an cestrual
period is marked by unusual restlessness. The animal partially loses
her appetite. She frequently stops browsing, looks about uneasily, runs
from one side of the field to the other, and then recommences feeding, to
be disturbed again in a similar manner after a short interval. The
motions are rapid and nervous, and the hide often rough and disordered;
and the whole aspect of the animal indicates the presence of some special
excitement. After oestruation is fully established, the vaginal secretions
show themselves in unusual abundance, and so continue for one or two
days ; after which the symptoms subside, and the animal returns to her
usual condition.

It is a noticeable fact, in this connection, that the female of these
animals will allow the approach of the male only during and immedi-
ately after the oestrual period ; that is, when the egg is recently dis-
charged, and ready for impregnation. At other times, when sexual
intercourse would be necessarily fruitless, the instinct of the animal
leads her to avoid it ; and the concourse of the sexes is accordingly
made to correspond in time with the maturity of the egg and its apti-
tude for fecundation.

II. Menstruation.

In the human female, the return of the period of ovulation is marked
by a group of phenomena which are known as menstruation, and which
are of sufficient importance to be described lay themselves.

1 Pouchet, ThSorie positive de 1'ovulation. Paris, 1847, p. 230.

MENSTRUATION. 709

During infancy and childhood the sexual system is inactive. No dis-
charge of eggs takes place from the ovaries, and no external phenomena
show themselves, connected with the reproductive function.

But at the age of fourteen or fifteen years, a change begins to mani-
fest itself. The limbs become rounder, the breasts increase in size, and
the entire aspect undergoes a peculiar alteration, which indicates ap-
proaching maturity. At the same time a discharge of blood takes place
from the generative passages, accompanied by some disturbance of the
general system, and the female is then known to have arrived at the
period of puberty.

Afterward, the bloody discharge returns at regular intervals of four
weeks ; and, on account of this recurrence, corresponding with succes-
sive lunar months, its phenomena are designated by the name of the
" menses" or the " menstrual periods." The menses return with regu-
larity, from the time of their first appearance, until the age of about
forty-five years. During this period, the female is capable of bearing
children, and sexual intercourse is liable to be followed by pregnanc}'.
After the forty-fifth year, the periods first become irregular, and then
cease altogether ; and their final disappearance is an indication that
pregnancy cannot again take place.

During the period above referred to, from the age of fifteen to forty-
five years, the regularity and completeness of the menstrual periods
indicate to a great extent the aptitude of individual females for im-
pregnation. All causes of ill health which derange menstruation are
apt at the same time to interfere with pregnancy ; so that women whose
menses are regular and natural are more likely to become pregnant,
after sexual intercourse, than those in whom the periods are absent or
irregular.

Jf pregnancy happen to take place, however, at any time within the
normal period, the menses are suspended during its continuance. They
usually remain absent, after delivery, until the end of lactation, when
the}' recommence, and continue to recur at their regular periods, as
before.

The menstrual discharge consists of mucus mingled with blood.
When the period is about to come on, the female is affected with a
certain degree of discomfort and lassitude, a sense of weight in the
pelvis, and more or less disinclination to society. These symptoms
are in some instances slightly pronounced, in others more troublesome.
An unusual discharge of vaginal mucus then begins to take place, soon
becoming yellowish or rusty brown in color, from the admixture of a
certain proportion of blood ; and by the second or third day the dis-
charge has the appearance of nearly pure blood. The unpleasant sen-
sations, at first manifest, then usually subside ; and the discharge, after
continuing for two or three days longer, grows more scanty. Its color
changes from red to a brownish or rusty tinge, until it finally disap-
pears altogether, and the period comes to an end.

The menstrual epochs of the human female correspond with the

710 OVULATION AND MENSTRUATION.

periods of osstruation in the lower animals. Their general resemblance
to these periods is very evident. Like them, they are absent in the
immature female, and begin to take place only at the period of puberty,
when the aptitude for impregnation commences. Like them, they recur
during the child-bearing period at regular intervals, and are liable to
the same interruption by pregnancy. Finally, their disappearance
corresponds with the cessation of fertility.

The periods of oestruation, in many of the lower animals, are accom-
panied with an unusual discharge from the generative passages, fre-
quently more or less tinged with blood. In the human female the
bloody discharge, though more abundant than in other instances, differs
only in degree from that in many species of animals.

But the most complete evidence that the period of menstruation is in
reality that of ovulation, is derived from the results of direct observa-
tion. A sufficient number of instances have been observed to show that
at the menstrual epoch a Graafian follicle becomes enlarged, ruptures,
and discharges its egg. Cruikshank1 noticed such a case so long ago
as 1797. Ne'grier2 relates two instances in which, after sudden death
during menstruation, a bloody and ruptured Graafian follicle was found
in the ovary. BischofT3 speaks of four similar cases, in three of which
the follicle was just ruptured, and in the fourth distended, prominent,
and ready to burst. Coste4 met with several of the same kind. Michel5
found a follicle ruptured and filled with blood in a woman who was
executed for murder while the menses were present. Two instances
are reported by Letheby,6 in women who died while under observation
in the London hospitals, in one of which he succeeded in finding the
ovum, which had been expelled from the ovary, in the contents of the
corresponding Fallopian tube. We have also seen a Graafian follicle
recently ruptured and filled with blood, in a woman who died on the
second day of menstruation.

Ovulation. accordingly, in the human female, accompanies and forms
a part of menstruation. As the menstrual period comes on, a conges-
tion takes place in nearly the whole of the generative apparatus ; in the
Fallopian tubes and the uterus, as well as in the ovaries and their
contents. One of the Graafian follicles is especially the seat of vascular
excitement It becomes distended by the fluid accumulated in its cavity,
projects from the surface of the ovary, and is finally ruptured ; the
process taking place essentially in the same manner as in the mammalian
animals.

It is not certain at what particular period of the menstrual flow the
rupture of the follicle and discharge of the egg take place. According

1 Philosophical Transactions. London, 1^97, p. 135.

2 Recherches sur les Ovaires. Paris, 1840, p. 78.

3 Annales des Sciences Natnrelles. Paris, Aout, 1844.

4 Histoire du DSveloppement des Corps Organises. Paris, 1847, tome i. p. 221.
6 American Journal of the Medical Sciences. Philadelphia, July, 1848.

6 Philosophical Transactions. London, 1852, p. 57.

MENSTRUATION. 711

to the observations of Bischoff, Pouchet, and Raciborski, the regular
time for this rupture and discharge is not at the commencement, but
toward the termination of the period. According to those of Coste,1
the follicle ruptures sometimes in the early part of the menstrual epoch,
sometimes later. So far as we can learn, therefore, the precise period
is not invariable. Like the menses themselves, it may take place a
little earlier, or a little later, according to circumstances ; but it always
occurs in connection with the menstrual flow, and constitutes the essen-
tial part of the catamenial process.

The egg, when discharged from the ovary, enters the fimbriated
extremity of the Fallopian tube, and commences its passage toward
the uterus. The mechanism by which it finds its way into and through
the Fallopian tube is different, in quadrupeds and the human species,
and in birds and reptiles. In the latter, the bulk of the egg or eggs is
so great as to fill or even to distend the cavity of the oviduct ; and the
mass is accordingly embraced by the muscular wall of the canal and
carried downward by its peristaltic action. In the mammalians, on the
other hand, the egg is microscopic in size. The wide extremity of the
Fallopian tube, directed toward the ovary, is lined with ciliated epithe-
lium; and the movement of the cilia, which is from the ovary toward
the uterus, produces a kind of vortex, by which the egg is drawn toward
the narrow portion of the tube, and thence conducted to the cavity of
the uterus.

Accidental causes may sometimes disturb the regular course of
passage of the egg. It may be arrested at the surface of the ovary,
and thus fail to enter the tube at all. If it be fecundated and go on to
partial development in this situation, it will give rise to " ovarian
pregnancy." The egg may escape from the fimbriated extremity of the
Fallopian tube into the peritoneal cavity, and form attachments to a
neighboring organ, causing " abdominal pregnancy ;" or finally, it may
stop in some part of the Fallopian tube, and so give origin to u tubal
pregnancy."

The egg, immediately upon its discharge from the ovary, is ready for
impregnation. If sexual intercourse take place about that time, the
egg and the spermatozoa meet in some part of the female generative
passages, and fecundation is accomplished. It appears from the obser-
vations of Bischoff, Coste, and Martin Barry2 upon rabbits, that the
contact between the egg and the spermatozoa may take place either in
the uterus or any part of the Fallopian tubes, or even upon the surface
of the ovary. If, on the other hand, sexual coitus do not take place,
the egg passes down to the uterus unimpregnated, loses its vitality after
a short time, and is carried away with the uterine secretions.

It is easily understood, therefore, why sexual intercourse should be
more liable to be followed by pregnancy when occurring about the

1 Histoire du DSveloppement des Corps Organises. Paris, 1847, tome i. p. 221.
8 Philosophical Transactions. London, 1839, p. 315.

712 OVULATION AND MENSTRUATION.

menstrual epoch than at other times. This fact, established as a matter
of observation by practical obstetricians, depends upon the coincidence
in time between the occurrence of menstruation and the discharge of the
egg. Before its discharge, the egg is immature, and unfit for impregna-
tion ; and after the menstrual period has passed, it loses its freshness
and vitality. The exajct length of time, preceding and following the
menses, during which impregnation is possible, has not been ascer-
tained. The spermatozoa, on the one hand, retain their vitality for an
unknown period after coition, and the egg for an unknown period after
its discharge. Both these occurrences may either precede or follow
each other within certain limits, and impregnation may still take place;
but the precise extent of these limits is uncertain, and is probably more
or less variable in different individuals.

The above facts indicate the true explanation of certain exceptional
cases, in which fertility exists without menstruation. Various authors
(Churchill, Reid, Yelpeau) have related instances of fruitful women in
whom the menses were scanty and irregular, or even entirely absent.
The menstrual flow is only the external accompaniment of a more
important process tnking place within. It is habitually scanty in some
individuals, and abundant in others. Such variations depend upon the
condition of vascular activity of the system at large, or of the uterine
organs in particular ; and though the bloody discharge is usually an
index of the general aptitude of these organs for impregnation, it is
not an absolute or indispensable requisite. Provided a mature egg be
discharged from the ovary at the appointed period, menstruation properly
speaking exists, and pregnancy is possible.

The blood which escapes during the menstrual flow is supplied by the
uterine mucous membrane. If the cavity of the uterus be examined
after death during menstruation, its internal surface is found smeared
with a sanguineous fluid, which may be traced through the uterine
cervix into the vagina. The Fallopian tubes are sometimes congested,
and filled with a similar bloody discharge. The menstrual blood has
also been seen to exude from the uterine orifice in cases of procidentia
uteri, as well as in the natural condition by examination with the
vaginal speculum. It is discharged by a kind of capillary hemorrhage,
and, as a general rule, does not form a visible coagulum, owing to its
being gradually exuded from many minute points, and mingled with a
large quantity of mucus. When poured out more rapidly or in larger
quantity than usual, as in menorrhagia, the menstrual blood coagulates
in the same manner as that derived from other sources. Its discharge
takes place from the whole extent of the mucous membrane of the body
of the uterus, and is, at the same time, the consequence and the natural
termination of the periodical congestion of the parts.

CHAPTEE VI.

THE CORPUS LUTBUM, AND ITS CONNECTION
WITH MENSTRUATION AND PREGNANCY.

AFTER the rupture of the Graafian follicle at the menstrual period, a
bloody cavity is left in the ovary, which is subsequently obliterated by
a kind of granulating process, somewhat similar to the healing of an
abscess. The office of the Graafian follicle is to provide for the forma-
tion and growth of the egg within the ovary. After the ripening and
discharge of the egg, the Graafian follicle has no longer any function to
perform. It then only remains for it to pass through a process of
obliteration, as an organ- which has become obsolete. While undergoing
this process, the Graafian follicle is at one time converted into a pecu-
liar, solid, spheroidal body, called the corpus luteum; a name derived
from the yellow color which it acquires at a certain period of its forma-
tion.

In different species of mammalians, the corpus luteum is characterized
by certain peculiarities of size, color, rapidity of growth, and disappear-
ance, which are distinctive for each particular kind of animal ; although
. the general process of its formation and atrophy is the same in all. In
the human female it is marked by a moderately large size, a brilliant
yellow hue at a certain period of its development, and the presence of
blood in its central cavity, distinguishable by its color for two or three
weeks after the rupture of the follicle. The details of its growth and
retrocession, which follow a certain regular course during the normal
recurrence of the menstrual periods, are modified to an appreciable
degree by the occurrence of pregnancy. In the first instance, it is
known as the corpus luteum of menstruation; in the second as the
corpus luteum of pregnancy.

I. Corpus Luteum of Menstruation.

At each menstrual epoch, in the human female, a Graafian follicle
swells, protrudes from the surface of the ovary, ruptures, and discharges
its mature egg. At the moment of rupture, or immediately afterward,
a somewhat abundant hemorrhage takes place from the follicle, and
its cavity is filled with blood. This blood coagulates soon after its
exudation, as it would if extravasated elsewhere, and the coagulum
is retained in the interior of the Graafian follicle. The opening by which
the egg makes its escape is usually a minute rounded perforation, often
not more than one millimetre in diameter. A small probe, introduced

714

CORPUS LUTEUM.

233.

GRAAFIAN FOLLICLE
of the human ovary; re-
cently ruptured during
mestruation, and filled with
coagulated blood ; longitu-
dinal section. — a. Tissue of
the ovary, containing un-
ruptured Graaflan follicles.
b. Vesicular membrane of
the ruptured follicle, c.
Point of rupture.

through this opening, passes directly into the cavity of the Graafian
follicle. If the follicle be opened at this time by a longitudinal incision
through the substance of the ovary (Fig. 233),
it will be seen to form a globular cavity, between
one and two centimetres in diameter, containing
a soft, recent, dark-colored coagulum. The co-
agulum has no organic connection with the walls
of the follicle, but lies loose in its cavity, and
may be easily turned .out with the handle of a
knife. There is sometimes a slight mechanical
adhesion of the clot to the edges of the lacerated
opening ; but there is no continuity of substance
between them, and the clot may be separated by
careful manipulation. The membrane of the
vesicle presents at this time a smooth, trans-
parent, and vascular internal surface.

An important change soon afterward begins
to take place, both in the central coagulum and
in the vesicular membrane.

The clot, which is at first large, soft, and
gelatinous, begins to contract; and the serum
separates from the coagulum proper. The serum,
as it separates, is absorbed by the neighboring
parts; and the clot, accordingly, grows smaller and denser than before.
At the same time the coloring matter of the blood undergoes the usual
changes which occur in it after extravasation, and is partially reab-
sorbed together with the serum. This second change is somewhat less
rapid than the former, but a diminution of color is very perceptible in
the clot, at the expiration of two weeks from the rupture of the follicle.
The vesicular membrane during this time is beginning to undergo a
process of development, by which it becomes thickened and convoluted,
and tends partially to fill the cavity of the follicle. The hypertrophy
and convolution of the vesicular membrane commences first and pro-
ceeds most rapidly at the deeper part of the follicle, opposite the situa-
tion of the rupture. From this point, the membrane becomes thinner
and less convoluted as it approaches the surface of the ovary and the
edges of the ruptured orifice.

At the end of three weeks, the hypertrophy of the vesicular mem-
brane has reached its maximum. The ruptured Graafian follicle has
now become so completely solidified by the growth above described,
and by the condensation of its clot, that it presents the appearance of
a new bod}r imbedded in the ovarian tissue, and receives the name of
corpus luteum, although its yellow color is not yet distinctly developed.
It forms a perceptible prominence on the surface of the ovary, and may
be felt as a well-defined rounded tumor, nearly always somewhat flat-
tened from side to side. It measures about 19 millimetres in length

CORPUS LUTEUM OF MENSTRUATION.

715

Fig. 234.

HUMAN OVARY cut open, show-
ing a corpus luteum, divided longi-
tudinally ; three weeks after men-
struation. From a girl, twenty years
of age, dead of haemoptysis.

and about 12 millimetres in depth. On its surface may be seen a
minute cicatrix, occupying the spot of the original rupture.

On cutting it open at this time (Fig. 234), the corpus luteum is seen
to consist, as above described, of a central coagulum and a convoluted
wall. The coagulum is semi-transparent,
of a gray or light greenish color, more or
less mottled with red. The convoluted
wall is about 3 millimetres thick at its
deepest part, and of an indefinite yellow-
ish or rosy hue, not very different in
tinge from the rest of the ovarian tissue.
The convoluted wall and the contained
clot lie simply in contact with each other,
as at first, without any intervening or-
ganic connection ; and they may still be
readily separated from each other by the
handle of a knife or the flattened end of
a probe. The whole corpus luteum may
also be stripped out, or enucleated from
the ovarian tissue, just as might have
been done with the Graafian follicle pre-
viously to its rupture. When separated
in this way from the neighboring parts, it presents itself under the
form of a solid globular or flattened mass, with a convoluted external
surface covered with the remains of the connective tissue by which it;
was previously united with the substance of the ovary.

We have had an opportunity of examining a corpus luteum of this
period, in an ovary immediately after its removal from the body of the
living woman. It was on the occasion of the extirpation by Prof. T, T.
Sabine, in 1874, of the left ovary for obstinate ovarian neuralgia, from
an unmarried woman, otherwise healthy, 25 years of age.1 The last
menstrual period had terminated exactly three weeks before the date
of the operation, and a new one commenced twenty-four hours after-
ward. The extirpated ovary presented a perfectly normal appearance,
and contained a corpus luteum similar in all respects to that represented
in Figure 234. Its convoluted wall was fully formed, without any dis-
tinctly marked yellow tinge, and the central coagulum was partly, but
not entirely, decolorized. The patient recovered without difficulty.

After the third week from the close of menstruation, the corpus
luteum passes into a retrograde condition. It diminishes perceptibly
in size, and the central coagulum continues to be absorbed and loses
still farther its coloring matter. The whole body undergoes a process
of partial atrophy ; and at the end of the fourth week it is less than 10
millimetres in its longest diameter (Fig. 235). The external cicatrix
may still usually be seen, as well as the point where the central coagu-

1 New York Medical Journal, January, 1875, p. 37.

716

CORPUS LUTEUM.

Fig. 235.

HUMAN OVARY, show-
ing a corpus luteum, four
weeks after menstruation;
from a woman dead of apo-
plexy.

lum comes in contact with the peritoneal surface. There is still no
organic connection between the central coagulum and the convoluted
wall ; but the partial condensation of the clot
and the continued folding of the wall prevent
the separation of the two being so easily accom-
plished as before. The entire corpus luteum
may still be extracted from its bed in the ova-
rian tissue.

The color of the convoluted wall, during this
stage, instead of fading, like that of the fibrinous
coagulum, becomes more strongly marked. From
having a dull yellowish or rosy hue, as at first,
it gradually assumes a more decided yellow.
This change of color is produced simultane-
ously with a kind of fatty degeneration which
takes place in its texture ; a large quantity of
oil-globules being deposited in it at this time,
which are recognizable under the microscope.
At the end of the fourth week, the alteration in
hue is complete ; and the outer wall of the cor-
pus luteum is then of a clear chrome yellow color, by which it is readily
distinguished from the neighboring tissues.

After this period, the process of degeneration goes on rapidly. The
clot becomes more dense and shrivelled, and is converted into a minute,

stellate, white, or reddish-white cicatrix. The
yellow wall becomes softer and more friable,
and shows less distinctly the marking of its
convolutions. At the same time its surface
becomes confounded with the central coagu-
lum on the one hand, and with the neighbor-
ing parts on the other, so that it is no longer
possible to separate them fairly from each
other. At the end of eight or nine weeks
(Fig. 236) the whole mass is reduced to the
condition of an insignificant, yellowish, cica-
trix-like spot, measuring about 6 millimetres
in its longest diameter, in which the original
texture of the corpus luteum can be recog-
nized only by the peculiar folding and color-
ing of its constituent parts. Subsequently
its atrophy goes on less rapidly, and a period of seven or eight months
sometimes elapses before its complete disappearance.

The corpus luteum, accordingly, is a formation which results from
the obliteration of a ruptured Graafian follicle. Under ordinary con-
ditions, a corpus luteum is produced at every menstrual period ; and
notwithstanding the rapidity of its retrogression and atrophy, a new
one is always formed before its predecessor has entirely disappeared.

Fig. 236.

HUMAN OVARY, showing a
corpus luteum, nine weeks after
menstruation ; from a girl dead
of tubercular meningitis.

CORPUS LUTEUM <JF PKEGNANCY. 717

When, therefore, we examine the ovaries of a healthy female, in whom
the menses have recurred with regularity for some time previous to
death, several corpora lutea will be met with, in different stages of
growth. We have found, under such circumstances, four, five, six, and
even eight corpora lutea in the ovaries at the same time, perfectly dis-
tinguishable by their texture, though very small, and most of them in
a state of advanced retrogression. They finally disappear altogether,
and the number of those present in the ovary no longer corresponds
with that of the Graafian follicles which have been ruptured.

II. Corpus Lnteum of Pregnancy.

The process above described takes place at every menstrual period,
independently of impregnation and sexual intercourse. The mere pre-
sence of a corpus luteum, therefore, is no indication that pregnancy has
existed, but only that a Graafian follicle has been ruptured and its
contents discharged. It is found, nevertheless, that when pregnancy
takes place, the appearance of the corpus luteum becomes so modified as
to be readily distinguished from that which follows the ordinary men-
strual process.

The distinction between these two kinds of corpora lutea is not an
essential or fundamental difference ; since they both originate in the
same way, and are composed of the same structures. It is only a differ-
ence in the rapidity and degree of their development. While the corpus
luteum of menstruation passes rapidly through its different stages, and
is soon reduced to a condition of atroplrv, that of pregnancy continues
.its development for a longer time, attains a larger size and firmer
organization, and disappears at a much later period.

This variation in the history of the corpus luteum depends upon the
condition of the pregnant uterus. This organ exerts a sympathetic
action, during pregnancy, upon many other parts of the system. The
stomach becomes irritable, the appetite is capricious, and even the
mental faculties and the moral disposition are frequently more or less
affected. The ovaries feel the influence of gestation more decidedly
than other organs, since they are more closely connected with the uterus
in the ordinary performance of their function. The moment that preg-
nancy takes place, menstruation is arrested. No more eggs come to
maturity, and no more Graafian follicles are ruptured, during the whole
period of gestation. It is not surprising that the growth of the corpus
luteum should also be modified, by an influence which affects so pro-
foundly the system at large, as well as the ovaries in particular.

During the first three weeks of its formation the growth of the corpus
luteum is the same in the impregnated as in the unimpregnated condition.
But after that time a difference becomes manifest. Instead of com-
mencing a retrograde course during the fourth week, the corpus luteum
of pregnancy continues its development. The external wall grows
thicker, and its convolutions more abundant. Its color changes, as

718

CORPUS LUTEUM.

Fig. 237.

CORPUS LUTEUM of pregnancy, at the end
of the second month ; from a woman dead from
induced abortion.

Fig. 238.

previously described, to a bright yellow ; and there is a deposit of fatty
matter in the form of microscopic globules.

By the end of the second month, the corpus luteum has so increased
in size as to measure 22 millimetres in length by 12 or 13 millimetres
in depth (Fig. 23?). The central coagulurn has by this time become
almost entirely decolorized, and presents the appearance of a purely

fibrinous deposit. Sometimes
it is found that a part of the
serum, during its separation
from the clot, has accumulated
in the centre of the mass, as
was the case in Fig. 237,forn>
ing a little cavity containing a
clear fluid and inclosed by a
fibrinous layer, the remains of
the solid portion of the clot.
The existence of such a cavit}^
however, is only an occasional,
not a constant, phenomenon.
More frequently, the fibrinous
clot is solid throughout, the
serum being gradually ab-
sorbed, as it separates sponta-
neously from the coagulum.

During the third and fourth
months, the enlargement of the
corpus luteum continues ; and
at the end of that time it
may measure 22 millimetres
in length by 18 or 19 milli-
metres in depth. Its flattened
form is very manifest, so that,
in a longitudinal section, it
may present a nearly circular
outline, as in Fig. 238, while in a transverse section it is a narrow oval.
The convoluted wall is still more highly developed than before, having
a thickness, at its deepest part, of nearly 5 millimetres, or double that
presented at the same point in the corpus luteum of menstruation, when
at its largest size. Its color, however, has already begun to fade, and is
of a dull yellowish tinge. The central coagulum, perfectly colorless and
fibrinous in appearance, is often so much flattened by the lateral com-
pression of its mass, that it is hardly 2 millimetres in thickness. The
other relations between the different parts remain the same.

The corpus luteum has now attained its maximum of development,
and continues without any very perceptible alteration during the fifth
and sixth months. It then begins to retrograde, diminishing in size
during the seventh and eighth months. Its external wall fades still

CORPUS LUTKUM of pregnancy, at the end of
the fourth month ; from a woman dead by poison.

CORPUS LUTEUM OF PREGNANCY.

719

Fig. 239.

CORPUS LUTEUM of
pregnancy, at term, from a
woman dead in delivery
from rupture of the uterus.

more, becoming of a faint yellowish-white color, not unlike that pre-
sented at the end of the third week. Its texture is thick, soft, and
elastic, and it is strongly convoluted. An abundance of fine red vessels
can be seen penetrating from the exterior into
the interstices of its convolutions. The central
coagulum is reduced by this time to the condi-
tion of a whitish radiated cicatrix.

Its atrophy continues during the ninth month.
At the termination of pregnancy, it is reduced in
size to 12 or 13 millimetres in length and less
than 10 millimetres in depth. (Fig. 239.) It is
then of a faint indefinite hue, but little contrasted
with the remaining tissues of the ovary. The
central cicatrix has become very small, and ap-
pears only as a thin whitish lamina, with radi-
ating processes which penetrate between the in-
terstices of the convolutions. The whole mass
is still quite firm to the touch, and is readily
distinguishable, both from its size -and texture,
as a prominent feature in the ovarian tissue,
and a reliable indication of pregnancy. The
convoluted structure of the external wall is very
perceptible, and the point of rupture, with its external peritoneal cicatrix,
still distinctly visible.

After delivery, the corpus luteum retrogrades rapidly. At the end of
eight or nine weeks, it has become so much altered that its color is no
longer distinguishable, although indications of its convoluted structure
may still be discovered by close examination. These traces of its
existence remain for a long time afterward, more or less concealed in
the ovarian tissue. We have distinguished them, in one instance, so
late as nine and a half months after delivery. They finally disappear
entirely, together with the external cicatrix which previously marked
their situation.

During the existence of gestation, the process of menstruation being
suspended, no new Graafian follicles are ruptured, and no new corpora
lutea are produced ; and as the old ones, formed before the period of
conception, fade and disappear, the corpus luteum which marks the
occurrence of pregnancy after a time exists alone in the ovary. In
twin pregnancies, we of course find two corpora lutea in the ovaries ;
but these are precisely similar to each other, and, being evidently of the
same date, need not give rise to any confusion. Where there is but a
single foetus in the uterus, and the ovaries contain two corpora lutea of
similar appearance, one of them belongs to an embryo which has been
blighted in the early part of pregnancy, and has failed of its develop-
ment. The remains of the blighted embryo may sometimes be dis-
covered, in such cases, in some part of the Fallopian tube, where it has
been arrested in its descent toward the uterus.

720

COKPUS LUTEUM.

After lactation has come to an end, the ovaries resume their ordinary
function. The Graafian follicles mature and rupture in succession, as
before, and new corpora lutea follow each other in alternate develop-
ment and disappearance.

The corpus luteuin of menstruation, therefore, differs from that of
pregnancy in the extent of its development and the duration of its
existence. While the former passes through all the important phases
of its growth and decline in a period of two months, the latter lasts
from nine to ten months, and presents, during a great portion of the
time, a larger size and a more solid organization. Even in the corpus
luteum of pregnancy, the bright yellow color, which is so important a
characteristic, is only temporary in duration; not making its appearance
till about the end of the fourth week, and again disappearing after the
sixth month.

The following table contains, in a condensed form, the characters of
the corpus luteum, as belonging to the two different conditions of men-
struation and pregnancy, corresponding with different periods of its
development.

CORPUS LUTEUM OF MENSTRUATION. CORPUS LUTEUM OF PREGNANCY.

At the end of
three iveeks.
One month.

Two months.

Four months.

Six months.

Nine months.

Twelve by nineteen millimetres in diameter; central clot reddish;

convoluted wall pale.
Smaller ; convoluted wall bright

yellow ; clot still reddish.
Reduced to the condition of an

insignificant cicatrix.

Absent or unnoticeable.

Absent.

Absent.

Larger; convoluted wall bright
yellow; clot still reddish.

Twelve by twenty-two milli-
metres in diameter ; convo-
luted wall bright yellow ; clot
perfectly decolorized.

Eighteen by twenty-two millime-
tres in diameter ; clot pale and
fibrinous; convoluted wall dull
yellow.

Still as large as at the end of
the second month. Clot fibri-
nous. Convoluted wall paler.

Ten by thirteen millimetres in
diameter; central clot con-
verted into a radiating cica-
trix ; external wall tolerably
thick and convoluted, but
without any bright yellow
color.

CHAPTEE VII.

DEVELOPMENT OF THE IMPREGNATED EGG— SEG-
MENTATION OF THE VITELLUS — BLASTODERM-
FORMATION OF ORGANS IN THE FROG.

THE egg, while still contained within the ovarian follicle, passes
through a series of consecutive changes, by which it is finally brought
to the condition of maturity. During this period it increases in size,
from the insignificant dimensions which it presents in the earlier stages
of its formation, to those of its complete development as an ovarian
egg. The vitellus, at first transparent and colorless, is not only en-
larged, but becomes more or less granular and opaque by the deposit
of new material in a different form ; and in birds and reptiles it assumes
a distinctive hue, which is generally orange or yellow. These modifica-
tions are due to the spontaneous growth of the egg and the parts in
which it is inclosed ; and they mark a continuous process of develop-
ment taking place independently in the generative organs of the female.
The last change which occurs in the ovarian egg, and that which indi-
cates its complete maturity, is the disappearance of the germinative
vesicle. This body, which is in general a distinctive feature of the ova-
rian egg, disappears a short time previous to its expulsion, or even when
it is just on the point of leaving the Graafian follicle.

The egg, therefore, at the time of its discharge from the ovary, con-
sists solely of the mature vitellus, inclosed in the vitelline membrane ;
and in this condition it meets with the spermatozoa, usually in some
part of the Fallopian tube. By the contact of the male elements, and
their union with its own substance, a new stimulus is imparted to its
growth; and while, if unimpregnated, its vitality, on arriving at this
point, would have reached its termination, the fecundated egg, on the
contrary, starts upon a more extensive course of development, by which
it is finally converted into the body of the young animal.

Deposit of Albuminous Layers in the Fallopian Tube. — The egg, in
the first place, as it passes down the Fallopian tube, becomes covered
with an albuminous secretion. In birds, this secretion is very abun-
dant, and is deposited in successive layers around the vitellus, forming
the so-called " white of egg " In reptiles, it is also poured out in con-
siderable quantity, and serves for the nourishment of the egg during its
early growth. In mammalians, albuminous matter is supplied in the
same way, though in smaller quantity, by the mucous membrane of the
Fallopian tube, and envelops the egg in a layer of nutritious material.
This albuminous layer, although its absolute quantity is very small, is

(721)

722

DEVELOPMENT OF THE IMPREGNATED EGG.

Fig. 240.

sufficiently abundant, in proportion to the size of the mammalian -egg;

and it serves for the supply of organic material in the earlier stages of

development, before the egg has established its connection with the

uterine mucous membrane.

Segmentation of the Vitellus. — A very important change now takes

place in the impregnated egg, which is known as the division, or seg-
mentation, of the vitellus. A furrow
shows itself, running round the globular
mass of the vitellus in a vertical direction,
which gradually deepens until it has di-
vided the vitellus into two separate halves
or hemispheres (Fig. 240, a.) Almost at
the same time another furrow, running at
right angles with the first, penetrates the
substance of the vitellus, and cuts it in a
transverse direction. The vitellus is thus
divided into four equal portions (Fig. 240,
6), the edges and angles of which are
rounded off, and which are still contained
in the cavity of the vitelline membrane.
The spaces between them and the internal
surface of the vitelline membrane are oc-
cupied by a transparent fluid.

The process thus commenced goes on
by a successive formation of furrows and
sections, in various directions. The four
vitelline segments already produced are
subdivided into sixteen, the sixteen into
sixty-four, and so on ; until the whole vi-
tellus is converted into a mulberry-shaped
mass of minute, nearly spherical bodies,
called the "vitelline spheres." (Fig. 240, c.)
The vitelline spheres have a somewhat
firmer consistency than the original sub-
stance of the vitellus ; and this consistency
appears to increase as they multiply in
numbers and diminish in size. At last
they become so abundant as to be closely
crowded together and compressed into po-
lygonal forms. (Fig. 240, d.} They have
by this time been converted into a layer of
cells, surrounding the original central cav-
ity of the egg, and themselves enveloped
by the vitelline membrane.
The segmentation of the vitellus constitutes the primary act in the

development of the impregnated egg. It is this remarkable process

which is the sign that fecundation has taken place, and that the forma-

SEGMENTATION OF THE
VIT KLLUS.

DEVELOPMENT OF THE IMPREGNATED EGG. 723

tion of an embryo has commenced. It takes place in all species of
animals, although it varies in detail according to the special constitu-
tion of the egg, and the presence or absence of accessory parts. In all
the mammalia, as well as in many of the invertebrates, where the vitellus
is very small, and where the body of the embryo immediately after its
formation is to be supplied with nourishment from without, the process
is that described above. In the birds, in scaly reptiles, and in many
fish, where the vitellus or yolk is of large size, and contains additional
nutritive matter, segmentation takes place only in a thin layer which
occupies the surface of the great mass of the yolk ; and, beginning at
one spot, extends thence from within outward, so that it advances more
rapidly at the centre of the segmenting region than at its periphery.
But in all cases segmentation of the vitellus is the first change to occur
in the process of development, and its result is alwaj^s the same, namely,
to divide the vitellus, which was at first of uniform texture throughout,
into a great number of minute bodies, which soon present the character
of animal cells.

Blastoderm, or Germinal Membrane. — The cells which are formed, in
the manner above described, by the segmentation of the vitellus, become
more closely packed as they increase in number ; and finally, by their
mutual contact, and adhesion at their adjacent edges, they serve to form
a continuous organized membrane, known as the germinal membrane
or blastoderm.

During the formation of this membrane, moreover, the egg, while
passing through the Fallopian tube, increases in size. The albuminous
matter with which it is enveloped becomes liquefied ; and, being absorbed
by endosmosis through the vitelline membrane, furnishes the material
for the more solid and extensive growth of the newly-formed structures.
A certain quantity of fluid also accumulates in the central cavity of the

egg-

The next change which takes place consists in the division or splitting
of the blastoderm into two layers, which are known as the external and
internal blastodermic layers. They are both still composed exclusively
of cells ; but those of the external layer are smaller and more compact,
while those of the internal are larger and less consistent. The egg then
has the form of a globular sac, the walls of which consist of three con-
centric layers, tying in contact with and inclosing each other, namely :
1st, the structureless vitelline membrane on the outside; 2d,the external
blastodermic layer, composed of cells ; and 3d, the internal blastodermic
layer, also composed of cells. The cavity of the egg is occupied by an
albuminous fluid, absorbed from the exterior and destined to serve as
nutritious material.

It is by this process that the simple globular mass of the vitellus is
converted into an organized structure. For the blastoderm, although
consisting only of cells which are nearly uniform in size and shape, is
nevertheless an organized membrane, made up of anatomical elements.
It is the first sign of distinct organization which makes its appearance

124: DEVELOPMENT OF THE IMPREGNATED EGG.

in the egg ; and as soon as it is completed, the body of the foetus is
formed. The blastoderm is, in fact, the foetus in its earliest condition ;
for although its texture is at this time exceedingly simple, all the various
organs of the body will afterward be produced from it by the modifica-
tion of its different parts. The further process of formation is com-
paratively simple in some classes of animals, more complicated in
others ; and its general features are most easily understood by com-
mencing with the study of embryonic development as it takes place in
the frog.

Formation of Organs in the Embryo. — The egg of the frog, when dis-
charged and fecundated, is deposited in the water, enveloped in an elastic
cushion of albuminous matter. It is thus freely exposed to the light,
the air, and the moderate warmth of the sun's rays, and is supplied,
with an abundance of moisture and appropriate nutritious rftaterial.
Its development is distinguished accordingly by a character of great
simplicity ; since the whole of the vitellus is directly converted into the
body of the embryo. There are no accessory organs required, and con-
sequently no complications of the formative process.

The two blastodermic layers, above described, represent together the
commencement of the body of the embryo. They serve, however, for
the production of two different systems; and the entire process of their
development may be expressed as follows: The external blastodermic
layer produces the skin, the cerebro-spinal axis, and the organs of ani-
mal life ; while the internal layer produces the mucous membrane of
the alimentary canal, and the organs of nutrition.

The first sign of advancing organization in the external blastodermic
layer shows itself in a thickening and condensation of its structure.
The thickened portion has the form of an elongated oval spot, termed

the "embryonic spot" (Fig. 241), the wide
edges of which are somewhat more opaque
than the rest of the blastoderm. Inclosed
within these opaque edges is a narrower
colorless and transparent space, the " area
pellucida," and in its centre is a delicate
line, or furrow, running longitudinally from
front to rear, called the u primitive trace."
In the anterior portion of the area pel-
lucida, the substance of the blastoderm rises
up in such a manner as to form two nearly

Diagrammatic view of the IM- parallel ridges or plates, which approach
PKEGNATED E o o , showing the each other, from side to side, over what

SSSS^S-T1 *e"ucl"a' win be the dorsal '"i*0" of the embry°'

and are therefore called the " dorsal plates."

Between them is included a groove, termed the "medullary groove."
The dorsal plates gradually meet each other and coalesce upon the
median line, thus converting the intervening groove into a canal. The
coalescence of the edges of the two dorsal plates takes place first in the

DEVELOPMENT OF THE IMPREGNATED EGG.

725

anterior part of the,, are^pellucida and extends gradually backward •,
and when it is «jtoule)te throughout their length, the whole of the
medullary groove^BmbeenjKyiverted into a closed canal. This is the
"medullary canal ]^^d in its cavity will afterward be formed the cere-
bro-spinal axis, by a growth of nervous matter from its internal surface.
At its anterior extremity, the medullary canal is large and rounded, to
accommodate the brain and the medulla oblongata; its remainder is
narrow, and pointed posteriorly, and is destined to contain the spinal
cord.

In a diagrammatic section of the egg at this stage, made transversely
to the longitudinal axis of the embryo (Fig. 242), the dorsal plates may
be seen approaching each other above, on each side of the medullary
groove. At a more advanced period (Fig. 243) they are fairly united
with each other, and inclose the cavity of the medullary canal. At

Fi?. 242.

Fig. 243.

Diagrammatic section of the impregnated
EGG in an early stage of development.— 1.
External blastodermic layer. 2, 2. Dorsal
plates. 3. Internal blastodermic layer.

IMPREGNATED Eoo, at a somewhat
more advanced period. — 1. Point of union
between the abdominal plates. 2, 2. Dor-
sal plates united with each other on the
median line and inclosing the medullary
canal. 3,3. Abdominal plates. 4. Section
of the spinal column, with laminae and ribs.
6. Internal blastodermic layer.

the same time, the edges of the thickened portion of the blastoderm
grow outward and downward, extending over the lateral portions of the
vitelline mass. These are called the "abdominal plates;" and, as they
enlarge, they tend to approach each other below and inclose the abdo-
minal cavity, as the dorsal plates united above, and inclosed the medul-
lary canal. At last the abdominal plates actually unite on the median
line (at i, Fig. 243), embracing the whole of the internal blastodermic
layer ( 5 ), which incloses in turn the remains of the original vitellus and
the albuminous fluid accumulated in its cavity.

During this time, there is formed, in the thickened central part of
the blastoderm, immediately beneath the medullary canal, a longitudinal
cartilaginous cord, the "chorda dorsalis." Around the chorda dorsalis

726

DEVELOPMENT OF THE IMPREGNATED EGG.

are afterward developed the bodies of the vertebrae (Fig. 243,4), and.
the oblique processes of the vertebrae run upward from this point into
the dorsal plates, while the transverse processes and ribs run outward
and downward in the abdominal plates, to encircle more or less com-
pletely the corresponding portion of the body.

In a longitudinal section of the egg, made while this process is going
on, the thickened portion of the external blastodermic layer (Fig-. 244, i)
may be seen in profile. The anterior portion (2), which will form the
head, is thicker than the posterior ( 3 ), which will form the tail. As the
whole mass grows rapidly, both in the anterior and the posterior direc-
tion, the head becomes thick and voluminous, while the tail begins to
project backward, and the egg assumes an elongated form. (Fig. 245.)

Fig. 244.

Fig. 245.

Diagram of FROG'S EGO, in an early EGG OF FROG, in process of develop-

stage of development; longitudinal sec- ment.

tion. — 1. Thickened portion of external
blastodermic layer. 2. Anterior extremity
of the embryo. 3. Posterior extremity. 4.
Internal blastodermic layer. 6. Cavity of
vitellus.

The abdominal plates also meet upon its under surface, and complete
the closure of the abdominal cavity. The internal blastodermic layer
is seen, in the longitudinal section of the egg, embraced by the abdo-
minal plates, and inclosing, as before, the remains of the vitellus.

As development goes on (Fig. 246), the head becomes larger, and
shows traces of the formation of organs of special sense. The tail also

Fig. 246.

EGG OF FROG, farther advanced.

increases in size, and projects farther from the posterior extremity of
the embryo. The spinal cord runs in a longitudinal direction from front
to rear, and its anterior extremity enlarges, to form the brain and me-
dulla oblongata. In the mean time, the internal blastodermic layer,
which is subsequently converted into the intestinal canal, has been shut

DEVELOPMENT OF THE IMPREGNATED EGG. 727

in by the abdominal walls, and still forms a closed sac, of slightly
elongated figure, without inlet or outlet. Afterward, the mouth is
formed by means of a perforation, which takes place through both
external and internal layers at the anterior extremity; while a similar
perforation, at the posterior extremity, results in the formation of the
anus.

By a continuation of the same process, the different portions of the
external blastodermic layer are further developed, resulting in the com-
plete formation of the various parts of the skeleton, the integument,
the organs of special sense, and- the voluntary muscles and nerves. The
tail at the same time acquires sufficient size and strength to be capable
of acting as an organ of locomotion. (Fig. 247.) The intestinal canal,

Fig. 247.

TADPOLE, fully developed.

which has been formed from the internal blastodermic layer, is at first a
short, wide, and nearly straight tube, running directly from the mouth
to the anus. It soon, however, begins to grow faster than the abdominal
cavity which incloses it, becoming longer and narrower, and is at the
same time thrown into numerous curvilinear folds.

Arrived at this period, the young tadpole ruptures the vitelline mem-
brane, by which he has heretofore been inclosed, and leaves the cavity
of the egg. He at first fastens himself upon the remains of the albu-
minous matter deposited round the egg, and feeds upon it for a short
period. He soon^ however, acquires sufficient strength and activity to
swim about freely in search of other food, propelling himself by means
of his large, membranous, and muscular tail. The alimentary canal
increases in length and becomes spirally coiled up in the abdominal
cavity, attaining a length from seven to eight times greater than that of
the entire body.

After a time, a change takes place in the external form of the animal.
The posterior limbs are the first to make their appearance, by budding
or sprouting from the sides of the body at the base of the tail, (Fig.
248.) The anterior extremities are for a time concealed beneath the
integument, but afterward become liberated, and show themselves ex-
ternally. At first both the fore and hind legs are very small, incom-
plete in structure, and useless for purposes of locomotion. They soon,
however, increase in size and strength ; while the tail, on the contrary,
ceases to grow, and becomes shrivelled and atrophied. The limbs, in
fact, are destined finally to replace the tail as organs of locomotion ; and

728 DEVELOPMENT OF THE IMPREGNATED EGG.

a time at last arrives (Fig. 249) when the tail has altogether disappeared,
while the legs have become fully developed, muscular, and powerful.
Then the animal, heretofore confined to an aquatic mode of life, becomes
capable of living upon land, and a transformation is effected from the
tadpole into the frog.

Fig. 248. Fig. 249.

TA DPOLE, with limbs beginning to be formed. Perfect FROG.

During the same time, other changes of equal importance take place
in the internal organs. The tadpole at first breathes by gills ; but these
organs subsequently become atrophied, and are replaced by lungs. The
structure of the mouth, also, of the integument, and of the circulatory
system, is altered to correspond with the varying conditions and wants
of the growing organism ; and all these changes taking place, in part
successively and in part simultaneously, bring the animal at last to a
state of complete formation.

The process of development, as thus far described, may be recapitu-
lated as follows :

1. The germinal membrane or blastoderm, produced b}r the segmenta-
tion of the vitellus, consists of two cellular layers, namely, an external
and an internal blastodermic layer.

2. The external blastodermic layer incloses by its dorsal plates the
cerebro-spinal canal, and by its abdominal plates the abdominal or
visceral cavity.

3. The internal blastodermic layer forms the intestinal canal, which
becomes lengthened and convoluted, and communicates with the exterior
by a mouth and anus of secondary formation.

4. Finally, the cerebro-spinal axis and its nerves, the skeleton, the
organs of special sense, the integument, and the voluntar}^ muscles, are
developed from the external blastodermic layer ; while the anterior and
posterior extremities are formed from the same layer by a process of
sprouting, or continuous growth.

CHAPTEE VIII.

FORMATION OF THE EMBRYO IN THE FOWL'S EGG.

IN the preceding chapter a condensed description has been given of
the general phenomena of embryonic development, as illustrated in the
egg of the frog This species is useful as an example, to exhibit the
progressive alterations of form which lead to the final production of
a vertebrate animal out of the fecundated vitellus, uncomplicated by the
presence of any accessory organs. But the development of the chick, in
the egg of the fowl during incubation, has been found more favorable
for the study of certain important details. The readiness with which the
fowl's egg may be obtained in all the successive stages of incubation,
and the convenient size of the embryo in the earlier periods of its forma-
tion, have made it a favorite subject of investigation for embryologists ;
and some of the most valuable discoveries in this department of physi-
ology have resulted from observations upon the young chick and the
mode of formation of its different organs.

The Yolk and the Cicatricula. — The yolk of the fowl's egg represents
something more than the vitellus proper. Its principal mass consists
of an opaque, yellow, semifluid substance, the "yellow yolk," which
solidifies on boiling, owing to its large proportion of albuminous matter.
This substance contains a great abundance of soft, spherical, finely
granular bodies, from 25 to 100 mmm. in diameter.

The yellow yolk is surrounded everywhere by a thin layer of nearly
colorless appearance, the " white yolk," which contains, instead of the
granular spheres described above, smaller globular bodies with one or
more brightly refracting masses in their interior. The albuminous
matter of the white yolk, furthermore, does not solidify firmly on the
application of heat; so that in a boiled egg the thin outer stratum of this
substance remains semifluid. There is also a spot in the centre of the
yolk-sphere, which is occupied by the same material, and which conse-
quently remains soft in the boiled egg ; the central cavity thus left
communicating with the surface of the yolk by a narrow passage, like
the neck of a flask.

The whole yolk is thus formed of two substances, which are distin-
guished from each other by their microscopic characters and by their
comparative coagulability at the temperature of boiling water. Neither
of the two corresponds with the granular vitellus of the mammalian egg ;
and the yolk, as a whole, constitutes a deposit of nutritious material,
superadded to the vitellus proper, and destined to be absorbed for the
support of the embryonic tissues. This yolk, however, is formed, in.
47 ( 729 )

730 FORMATION OF THE EMBRYO.

birds, within the ovarian follicle, and is, in respect to its volume, the
main constituent of the ovarian egg.

At one point upon the surface of the yolk of the fowl's egg, while still
contained within the ovarian follicle, there is a whitish circular spot
about 5 millimetres in diameter, lying immediately beneath the vitelline
membrane. This is the cicatricula. It is a thin layer of uniformly
granular material, containing none of the spherical bodies found in the
white and yellow yolk. Its granules are imbedded in a homogeneous
substance of viscid consistency, by which they are agglutinated into a
disk-like mass. In its centre is contained the germinative vesicle,
which is distinctly visible by its transparency and well-defined outline,
until the mature egg is ready to leave the ovary, when it disappears,
as in other classes of animals. The cicatricula of the fowl's egg cor-
responds, therefore, in its structure, though not in its form, with the
entire vitellus of the mammalian egg. Its position is always exactly
above the tubular prolongation of white yolk, already described as
leading to the central cavity of the egg.

Formation of the Blastoderm. — The fowl's egg is fecundated soon
after leaving the ovary, and while in the upper portion of the ovi-
duct. The segmentation of the cicatricula then begins, by a furrow
which passes across its disk, and which is followed by others running
in different directions. By the continued multiplication of these fur-
rows, the substance of the cicatricula is divided successively into
smaller and smaller portions; the process beginning and proceeding
most rapidly at its centre, but extending thence outward to the peri-
phery. When these divisions have become reduced in size and increased
in number to a certain degree, they present, as in other instances, the
form and structure of distinct cells. The cells are in two layers. Those
of the upper layer are smaller, more numerous, cylindrical or prismatic

Fig. 250.

VERTICAL SECTION THROUGH A PORTION OF THE BLASTODERM of a fowl's
egg, at the commencement of incubation.— 1. Upper cellular layer. 2. Lower cellular layer.
3, 3. Larger cells, found in small number beneath those of the lower layer. (Foster and Bal-
four.)

in form, standing upright side by side, like the cells of columnar epithe-
lium, and adherent to each other by their adjacent surfaces. According
to Foster and Balfour1 they have a very uniform size of 9 mmm., and
most, if not all of them are provided with a distinct oval nucleus- The

1 Elements of Embryology. London, 1874, p. 17.

FORMATION OF THE EMBRYO. 731

cells of the lower layer are rather larger, more globular in form, and less
closely united with each other. The whole forms an organized cellular
membrane, the blastoderm, which, occupies the place of the original
cicatricula.

Thus the blastoderm, or germinal membrane, is formed in the impreg-
nated fowl's egg by a process of segmentation essentially similar to that
which takes place in eggs of other kinds. It presents the appearance of
a thin sheet, of uniform texture, composed of nothing but cells, lying
at one spot upon the surface of the yolk. Its formation, which begins
immediately after the impregnation of the egg, continues, under the
influence of the animal temperature, during the eighteen or twenty hours
that the egg is retained in the oviduct for the deposit of its albumen and
external envelopes. According to Foster and Balfour, it has reached the
condition of a distinct cellular membrane at the time of the expulsion
of the egg. If afterward kept at a low temperature it remains in this
state ; but, if subjected to natural or artificial incubation at a tempera-
ture of 38° (100° F.), it goes on to the further development of the body
of the embryo.

Folds of the Blastoderm. — The form of the body of the embryo and
of its different parts is sketched out, in all cases, by means of a series
of folds, which show themselves at various points in the blastoderm.
This membrane presents at first a flat surface ; or, i'f it have a certain
degree of convexity, corresponding with that of the }Tolk upon which it
lies, this convexity is perfectly uniform, and is too slightly pronounced
to be appreciable within the limits of the blastoderm. But as soon as
development begins to make a definite progress, this uniformity of sur-
face is broken by the appearance of folds or ridges, which are directed
longitudinally or transversely, and which thus mark the lines of separa-
tion between different parts of the blastoderm. Such a fold, running in
a curvilinear direction from side to side, marks the position of the head
of the embryo, and is called the " head-fold." The free border of this
mass, projecting forward and above the neighboring portion of the blas-
toderm, becomes in fact the head, which, as well as the neck, is curved
more and more forward and downward, in the subsequent stages of
embryonic growth, with the deepening of the fold which first gave origin
to it as a distinct part. A similar transverse curvilinear fold at the
posterior portion of the area pellucida, marks off the hinder extremity
of the embryo, and is called the " tail-fold." Longitudinal folds are
also formed in the same manner, one on each side, which fix the lateral
limits of the body of the embryo.

By this means, a certain portion of the blastoderm becomes distinctly
marked off from the rest. The part included within the transverse and
longitudinal folds is immediately recognizable as the body of the embryo;
while that which remains outside these limits becomes developed into
accessory organs, playing an important though secondary part in the
history of development. This forms a marked distinction between the
process as it takes place in the fowl's egg, and that already described in

732 FORMATION OF THE EMBRYO.

the egg of the frog. In the frog, the whole of the blastoderm serves for
the formation of the body of the embryo. In the fowl, only a portion
of it is immediately devoted to that object ; while the remainder extends
itself over the voluminous yolk, to be employed for the absorption of
nutritious material and its indirect transfer to the embryonic tissues.

But even within the limits of the body of the embryo, similar folds
of the blastoderm become visible, and are the principal means of forma-
tion for its different organs. The earliest permanent appearances of
this kind are the longitudinal ridges which include between them the
"medullary groove" (Fig. 252, I.), and which afterward, by coalescing
with each other along the median line of the back, inclose the medul-
lary canal (Fig. 252, II.). That these ridges or " dorsal plates," as well
as the groove between them, are produced by the formation of folds, is
plain from the fact that the surface of the groove, while still open, is
continuous, over its undulating borders, with that of the neighboring
part of the blastoderm ; and that after its closure, its cavity is lined
with a layer of cells identical in form with those on the free surface of
the blastoderm above. It is also shown, by transverse sections of the
embryo (His, Foster and Balfour), that the folds in question pass
through the whole thickness of the outer blastodermic layer. Accord-
ing to Foster and Balfour, the medullary canal, in the fowl's egg, is
completely closed at the region of the head on the second day of incu-
bation ; after which the coalescence of its edges goes on progressively
from before backward.

The closure of the abdomen in front, and the conversion of the inner
layer of the blastoderm into an intestinal canal, take place by a similar
production of lateral folds, approaching each other along the median
line. For, as the limits of the body of the embryo are marked off, on
each side, from the rest of the blastoderm by an inverted fold, when
this fold becomes deeper its borders are brought nearer to each other.
Thus the body of the embryo is at first spread out on the surface of the
vitellus, lying, as it were, upon the mucous membrane of its open alimen-
tary canal But as the folds which mark its lateral borders penetrate
more deeply below the surface (Fig. 252, IV.), the sides of the embryo
shut in between them a portion of this mucous membrane, and at last
completely inclose it in the abdominal cavity, in the same manner as the
dorsal folds inclose the medullary canal.

The folds of the blastoderm, which thus determine the configuration
of the embryo, are the result of a special activity of growth in par-
ticular parts of the blastodermic layers. If the blastoderm were to
grow only at its edges, these would simply extend farther and farther
over the vitellus, the central portion remaining as before. Or if it were
to increase at a uniform rate in all its parts at the same time, its form
would not necessarily be subjected to any special alteration. This is
what really takes place during the production of the blastoderm itself.
The segmentation of the vitellus, and the organization of the cellular
layers, go on with a similar activity in all directions, extending uni-

FORMATION OF THE EMBRYO. 783

formly from the centre outward. The blastoderm accordingly, when
completed, is a smooth, even membrane, having the same texture
throughout.

But when the process of incubation commences, the blastoderm grows
more rapidly at particular points, and along certain lines of direction,
than elsewhere. What may be the determining cause of such a con-
centration of growth in special situations, it is impossible to say ; but
its result is that the blastoderm, enlarging more rapidly in one direction
than another, is thrown into undulations, which indicate, by their posi-
tion and size, the unequal expansion of the blastodermic membrane.
Thus, if it grow more rapidly at one particular point than in any of the
surrounding parts, it will form at that spot a conical eminence or de-
pression, according as it meets with less resistance above or below. If
a similar rapidity of increase were to affect a considerable portion of the
membrane along a transverse line, the consequence would be a transverse
fold ; and if the same thing were to occur in an antero-posterior direc-
tion, it would cause a longitudinal fold. The subsequent history of em-
bryonic development shows continual repetitions of this process, often
on a much larger scale than that exhibited in the blastoderm. The
folds of the intestinal canal, the valvulae conniventes of its mucous
membrane, the convolutions of the brain, and the tubular windings of
the perspiratory glands, with many other analogous forms, are pro-
duced in a similar way. All these structures are at first smooth or
straight. They become thrown into folds or convolutions at some period
during the development of the embryo, whenever they grow more
rapidly than the surrounding parts.

Position of the Embryo in the Egg. — Although the blastoderm is at
first apparently of uniform structure throughout, yet each particular
part has from the beginning a physiological individuality, which leads
to its subsequent development into a special organ or part of an organ.
This is evident from the manner in which the local activity of nutrition
gives rise to the appearance of folds, running in definite directions, and
determining in this way the future location of the head, the tail, and
the sides of the body. But it is manifested still more remarkably in
the position assumed by the entire embtyo. The yolk of the fowl's egg
has a nearly regular spherical form ; and the cicatricula, as well as the
blastoderm into which it is converted, is a circular spot upon its surface.
The ovoid form presented by the whole egg, with one round and one
pointed extremity, is given to it by the deposit of albumen round the
yolk, in the middle and lower parts of the oviduct, after fecundation
has taken place. And yet, when the rudiments of the embryo first
become peceptible in the area pellucida, it is so placed as to lie cross-
wise to the long axis of the egg, with its right side toward the round
end and its left side toward the pointed end. The exceptions to this
rule are so few as to show that, even before incubation has commenced,
one particular portion of the circular blastoderm is destined to become

734 FORMATION OF THE EMBRYO.

the head and another portion the tail ; and consequently that every one
of the future organs of the embryo has its point of origin already fixed.

Division of the Blastodermic Layers. — The blastoderm when first
formed consists, as above described, of two layers of cells ; those of the
external layer being cylindrical and compact, those of the internal,
larger, rounded, and more loosely connected. The outer blastodermic
layer forms the tegumentary surface of the body and the cavity of the
cerebro-spinal axis ; the inner is converted into the mucous membrane
of the alimentary canal. But between the two there soon appears
another formation of cells, which is sometimes spoken of as the third
or " intermediate" blastodermic layer. The cells of this layer are in
immediate contact with, and more or less adherent to, those of the two
others ; but they are rounded in form and rather loosely united, in com-
parison both with those above and below. The intermediate layer, in
the blastoderm of the fowl's egg, is distinctly formed, according to
Foster and Balfour, in the first twelve hours of incubation.

The exact number and designation of the fundamental layers of the
blastoderm has been and still is the main point of discrepancy in the
writings of embryologists. There is no difference of opinion as to the
existence or destination of the two principal layers, namely, the external
and internal, which are the first to make their appearance, as above
described. They form respective^ thQ basis for the production of the
external sensitive integument and cerebro-spinal axis on the one hand,
and for the lining of the alimentary canal with its adjacent glandular
organs on the other. But the intermediate portion, formerly described
as the u vascular layer," is connected both with the organs of animal
life and with those of digestion and nutrition. It is, therefore, by some
regarded as an independent layer, equal in original importance to the
other two ; by others as an accessory formation, destined to aid in the
development of both the external and internal parts. According to
His,1 whose observations are among the most extensive and valuable
in the department of embryology, the most appropriate enumeration is
the older one, of an external and internal blastodermic layer ; since the
cells of the intermediate portion remain attached partty to the outer
and partly to the inner layer, when the separation between the two
takes place in the manner now to be described.

Immediately underneath the medullary canal, along the axial line of
the body of the embryo, there is formed in the intermediate layer of
the blastoderm a cylindrical cord, termed the "chorda dorsalis" (Fig.
252, 6), which marks the situation of the future spinal column. For
a certain distance on each side of the chorda dorsalis, the component
parts of the blastoderm remain in contact with each other throughout
its thickness. But farther outward, toward the edges of the embryo,
it separates, by a horizontal division or cleavage, into two laminae, an
outer and inner, or upper and lower. This cleavage takes place appa-

1 Unsere Korperform. Leipzig, 1875, p. 38.

FORMATION OF THE EMBRYO. 735

rently in consequence of an unequal rapidity of growth in the two blas-
todermic layers. Both layers are now extending outward, downward,
and inward, by the deepening of the lateral longitudinal folds ; tending
to approach the median line and thus shut in the abdomen and ali-
mentary canal. But the external layer, which is to form the walls of
the abdomen, grows more rapidly, and tends to inclose a larger space,
than the internal layer, which is to form the lining membrane of the
intestine. Wherever this happens, a separation takes place between
the two, at the expense of the intermediate layer, some of the cells of
which remain attached to the external and some to the internal blasto-
dermic Ia'er.

VERTICAL SECTION OF A PORTION OP THE BLASTODERM OF THE FOWL'S EGG,
in process of separation into two laminae.— 1. External blastodermic layer. 2. Internal
blastodermic layer. 3. Cells of the intermediate layer, partly drawn out into filamentous
extensions. Magnified 250 diameters. (His.)

The cleavage or division of the blastoderm into two laminae, as above
described, does not take place everywhere simultaneously. It occurs
here and there, as the process of growth becomes more. active in par-
ticular spots. But the general course of its extension is from without
inward, or from the lateral borders of the embryo toward the median
line. It does not, however, reach the median line, but leaves a con-
siderable space around the chorda dorsalis and on each side of it still
undivided, when the lateral portions of the blastoderm are already
completely separated into their two laminse.

By the separation of the laminse of the blastoderm thus effected, a
space or interval (Fig. 252, 5) is left between the two. This space, when
the closure of the abdominal walls is accomplished, becomes the perito-
neal cavity. The cells of the intermediate layer subsequently give rise
to the development of muscular tissue ; and that portion which, in the
separation of the two laminse, continues adherent to the external layer,
produces the voluntary muscles of the chest and abdomen. The por-
tion remaining adherent to the internal layer, on the other hand, pro-
duces the involuntary muscular coat of the alimentary canal. In Figure
252, II., III., and IV., these two portions of the intermediate la}?er,
which give rise respectively to voluntary and involuntary muscular
tissue, are seen shaded with parallel lines.

Primitive Vertebrae — Formation of the Spinal Column and it* Mus-
cles.— Already on the second day of incubation there have appeared,
on each side of the chorda dorsalis and medullary canal, a number

736

FORMATION OF THE EMBRYO.

of rectangular masses arranged in longitudinal series, almost exactly
similar to each other, and separated by regular transverse divisions.
They resemble strongly in their appearance the simpler component parts
of a spinal column, and, in fact, form the basis out of which this struc-

Fig. 252.

TRANSVERSE SECTION OF THE CHICK-EMBRYO, at different stages of development.
Magnified 40 diameters.

I. On the second day of incubation.

II. Between the second and third days.

III. On the third day.

IV. On the fourth day.

1. Medullary groove. 2. Medullary canal. 3. External blastodermic layer. 4. Internal
blastodermic layer. 5. Space of separation between the two laminae of the blastoderm;
future peritoneal cavity. 6. Chorda dorsalis. 7. Primitive vertebrae. 8. Aorta. 9. Cavity
of the intestine. (His.)

ture will afterward be developed. But they do not represent imme-
diately and exclusively the bodies of the vertebrae. They are to serve,
not only for the formation of these organs, but also for that of the spinal
muscles on the one hand and of the muscular layer of the aorta on the
other. They are therefore known as the primitive vertebras. In a
transverse section of these bodies (Fig. 252, 7 ) there is an evident dis-

FORMATION OF THE EMBRYO. 737

tinction between their central portion or nucleus, and their external
portion or shell. The nucleus is more transparent, and will afterward
supply the cartilaginous deposit for the permanent vertebrae ; the shell
has a radiating striated texture, and serves for the formation of mus-
cular tissue.

On the second day of incubation (Fig. 252, I.) the primitive verte-
brae, as seen in transverse section, have the form of a narrow oval, with
a small nucleus and a comparatively thick and perfectly continuous
shell. From the second to the third day (Fig. 252, II.) the nucleus
grows more rapidly than the outer parts, which it pushes upward and
downward ; and the shell begins to show indications of a separation
into upper and lower portions. On the third day (Fig. 252, III.) this
separation is complete ; and the upper portion of the shell, taking a
position more or less parallel with the outline of the body at this point,
will become the layer of voluntary muscles about the spinal column.
Its lower portion recedes farther from above downward, and approaches
the situation of the double aorta ( 8 ), which it will afterward supply with
its involuntary muscular layer. In a section of the embryo at the
fourth day (Fig, 252, IV.) the final position of these two muscular
layers is distinctly marked ; the projection of the spinal ridge, on the
one hand, having become higher and steeper, and, on the other, the
double aorta having been fused into a single vascular canal.

The nucleus of the primitive vertebra, in the mean time, extends
upward and inward, in such a manner as to surround both the medul-
lary canal and the chorda dorsalis, which it embraces in a tissue of new
formation. This tissue afterward supplies the cartilage, both of the
bodies of the vertebrae, and of the oblique processes which inclose the
spinal canal at its sides and behind. But when these cartilages are
formed, it is observed that they do not correspond in situation with the
original primitive vertebrae. A new segmentation takes place, by which
the lines of separation between the successive permanent vertebrae pass
through the middle of what were the primitive vertebrae j1 and conse-
quently each permanent vertebra is formed out of the adjacent halves
of two primitive vertebrae. The chorda dorsalis, included in the car-
tilaginous matrix of the bodies of the vertebrae, ceases to grow in a
corresponding ratio with the neighboring parts, becomes atrophied, and
disappears ; while the bodies of the vertebrae, which surround it, are
rapidly enlarged, and assume the form and size of the principal com-
ponent parts of the spinal column.

1 Foster and Balfour, Elements of Embryology. London, 1874, p. 153.

CHAPTEE IX.

DEVELOPMENT OF ACCESSORY ORGANS IN THE
IMPREGNATED EGG. UMBILICAL YESICLE, AM-
NION, AND ALLANTOIS.

THUS far, the process of development has been followed as it relates
to the primary formation of the principal parts of the body of the
emb^o. In some species of animals this includes all the important
structures which show themselves in the impregnated egg; the embryo
arriving ver}r soon at a stage of growth in which it is liberated by the
rupture of the vitelline membrane and is already capable of carrying on
an independent existence. But in many fish and reptiles, and in all
birds and mammalia, there are additional structures which aid in the
nutrition of the young animal during the middle and later periods of its
development. In these instances, the whole of the blastoderm is not
immediately converted into the tissues of the embryo. Certain por-
tions, both of its external and internal layers, remain outside the limits
of the body, and perform, in this situation, the function of accessory
organs. These organs are the umbilical vesicle, the amnion, and the
allantois.

Umbilical Vesicle.

In the frog's embryo (page 725), the abdominal plates, closing to-
gether in front, join each other upon the median line, and shut in directly
the whole of the vitellus, which is thus inclosed in the intestinal sac
formed by the internal blastodermic layer.

In other instances, the abdominal plates do not immediately embrace
the whole of the vitelline mass, but tend to close together at some inter-
mediate point ; so that the vitellus is con-
p' stricted, and divided into two portions, one

internal, and one external. (Fig. 253.) As
development proceeds, the body of the embryo
increases in size out of proportion to the
vitelline sac, and the constriction just men-
tioned becomes at the same time more strongly
marked; so that the separation between the
internal and external portions of the vitelline
EGG OF FISH, showing for- gac is near]y complete. The internal blasto-

mation of umbilical vesicle. J

dermic layer is by this means divided into

two portions, one of which forms the intestinal canal, while the other,
remaining outside, forms a sac-like appendage to the abdomen, known
by 'the name of the umbilical vesicle.
(738)

AMNION AND ALLANTOIS. 739

The umbilical vesicle is accordingly lined by a portion of the internal
blastodermic layei;, continuous with the mucous membrane of the intes-
tine ; and covered by a portion of the external blastodermic layer, con-
tinuous with the integument of the abdomen.

After the young animal leaves the egg, the umbilical vesicle in some
species becomes shrunken and atrophied by the absorption of its con-
tents ; while in others, the abdominal walls gradually extend over it,
and crowd it back into the abdomen; the nutritious matter which it
contains passing from the cavity of the vesicle into that of the intes-
tine by the narrow passage remaining open between them.

In the human species, on the other hand, as well as in quadrupeds,
the umbilical vesicle becomes more completely separated from the ab-
domen. There is at first a wide communication be-
tween the cavity of the umbilical vesicle and that of Fig. 254.

the intestine ; subsequently this communication is
gradually narrowed by the constriction of the ab-
dominal walls; and this constriction proceeds so far
that the opposite surfaces of the canal at least come
in contact with each other and adhere together, so
that the passage previously existing, between the
cavitjr of the intestine and that of the umbilical
vesicle, is obliterated, and the vesicle is then con-
nected with the abdomen only by an impervious
cord. This cord afterward elongates, and becomes with umbilical vesi-

converted into a slender pedicle (Fig. 254), emerging aou

from the abdomen of the foetus, and connected by its
farther extremity with the umbilical vesicle, which is filled with a trans-
parent, colorless fluid. The umbilical vesicle is distinctly visible in the
human foetus so late as the end of the third month. After that period
it diminishes in size, and is gradually lost in the advancing development
of the neighboring parts.

Amnion and Allantois.

The amnion and allantois are two organs which can be best studied
in connection with each other, since they are closely related in physio-
logical importance; the office of the first being to pro vide for the forma-
tion of the second. The amnion is developed from the external blasto-
dermic layer ; the allantois from the internal Ia3^er. The amnion is so
called probably from the Greek d.tm?, a young lamb ; on account of its
having been first observed as a foetal envelope in this animal. The
name of the allantois is also derived from the Greek axxayr <mSij>$, owing
to its elongated or sausage-like form in the pig, and some other of the
domestic animals.

In the frog's egg. the embryo is abundantly supplied with moisture,
air, and nourishment from without. The absorption of oxygen and of
albuminous liquids, and the exhalation of carbonic acid, so far as it
is produced, can readily take place through the simple membranes of

740 ACCESSORY ORGANS IN IMPREGNATED EGG.

the egg ; especially as the time occupied in the formation of the pri-
mary organs is very short, and the greater part of the process of de-
velopment remains to be accomplished after the young animal leaves
the egg.

But in birds and quadrupeds, the time required for the development
of the embryo within the egg is longer. The young animal acquires a
more perfect organization during the time that it remains inclosed by
its membranes ; and the processes of absorption and exhalation neces-
sary for its growth, being increased in activity to a corresponding
degree, require a special organ for their accomplishment. This organ,
destined to bring the blood of the foetus into relation with the atmo-
sphere and external sources of nutrition, is the allantois.

In the frog, the internal blastodermic layer, forming the intestinal
mucous membrane, is everywhere inclosed by the external layer, form-
ing the integument. But in the higher animals a portion of this internal
layer, which is the seat of the greatest vascularity, and which is des-
tined to produce the allantois, is brought into contact with the external
membrane of the egg for purposes of exhalation and absorption ; and
this can only be accomplished by opening a passage for it through the
external blastodermic layer. This is done in the following manner by
the formation of the amnion.

Soon after the body of the embryo has begun to be formed, by the
thickening and involution of the external blastodermic layer, a second-
ary fold of this layer rises up on all sides about
Fig. 255. the edges of the newly-formed embryo ; so that

its body appears as if sunk in a kind of depres-
sion, and surrounded with a membranous ridge,
as in Fig. 255. The embryo (c) is here seen in
profile, with the external membranous folds, above
mentioned, rising up in advance of the head, and
behind the posterior extremity. The same thing

takeS PlaCC On the tw° sides °f the foetllS> ^ the

formation of lateral folds simultaneously with the
*PP<^ance of those in front and behind. As
these folds are destined to form the amnion, they

*™ Called tlle " amni°tic folds'"

The amniotic folds continue to grow, extend-
ing forward, backward, and laterally, until they approach each other at
a point over the back of the embryo (Fig. 256): Their opposite edges
afterward come in contact with each other at this point, and adhere
together, so as to shut in a space (Fig. 256, b) between their inner sur-
face and the body of the embryo. This space, which contains a thin
layer of clear fluid, is the amniotic cavity.

There now appears a prolongation or diverticulum (Fig. 256, c),
growing from the posterior portion of the intestinal canal, and follow-
ing the course of the amniotic fold which has preceded it ; occupying,
as it gradually enlarges and protrudes, the space left vacant by the

AMNION AND ALLANTOIS.

741

Fig. 256.

Diagram of the FECUN-
DATED EGG, farther
advanced — a. Umbilical
vesicle, b. Amniotic cav-
ity, c. Allantois.

Fig. 257.

rising up of the amniotic fold. This diverticulum is the commencement
of the allantois. It is an elongated membranous sac, continuous with
the posterior portion of the intestine, and con-
taining bloodvessels derived from those of the
intestinal circulation. The cavity of the allantois
is also continuous with the cavity of the intes-
tine.

After the amniotic folds have approached and
touched each other, as above described, over the
back of the embryo, the adjacent surfaces, thus
brought in contact, fuse together, so that the
cavities of the two folds, coming respectively from
front and rear, are separated only by a single
membranous partition (Fig. 251, c) running from
the inner to the outer lamina of the amniotic
folds. This partition is soon afterward atro-
phied and disappears ; and the inner and outer laminae become conse-
quently separated from each other. The inner lamina (Fig. 257, a)
which remains continuous with the integument of the foetus, inclosing
the body of the embryo in a distinct cavity, is
called the amnion (Fig. 258, 6), and its cavity is
known as the amniotic cavity. The outer lamina
of the amniotic fold, on the other hand (Fig.
257, 6), recedes farther and farther outward,
until it comes in contact with the original vitel-
line membrane, still covering the exterior of the
egg. It at last fuses with the vitelline membrane
and unites with its substance, so that the two
form but one. This membrane, resulting from
the union and consolidation of two others, con-
stitutes then the external investing membrane of
the egg.

The allantois, in the mean time, increases in
size and vascularity. Following the course of
the amniotic folds as before, it insinuates itself
between them, and thus comes in contact with
the external membrane above described. It then
begins to expand laterally, enveloping more and

more the body of the embryo, and bringing its vessels into contact with
the external investing membrane of the egg.

By a continuation of this process, the allantois at last envelops com-
pletely the body of the embryo, together with the amnion; its two
extremities coming in contact with each other, and fusing together over
the back of the embryo, in the same manner as the amniotic folds had
previously done. (Fig. 258.) It lines, therefore, the whole internal
surface of the investing membrane with a flattened, vascular sac, the

Diagram of the FECTTN.
DATED EGG, with allan-
tois nearly complete.— a.
Inner lamina of amniotic
fold. 6. Outer lamina of
ditto, c. Point where the
amniotic folds come in
contact. The allantois is
seen penetrating between
the inner and outer lami-
nae of the amuiotic folds.

742 ACCESSORY ORGANS IN IMPREGNATED EGG.

vessels of which come from the interior of the body of the embryo, and
which still communicates with the cavity of the intestinal canal.

It is evident, accordingly, that there is a close connection between
the formation of the amnion and that of the
Fig. 258. allantois. For it is only by this means that

the allantois, which is an extension of the in-
ternal blastodermic layer, can come to be
situated outside the embryo and the amnion,
and thus brought into relation with surround-
in or media. The two laminae of the amniotic

O

folds, by separating from each other as above
described, open a passage for the allantois, and
allow it to come in contact with the external
Diagram of the FECUNDA- membranous investment of the egg.

TED EGG, with the allantois _. . , . _ . - ,7 . . mu

fully formed. — a. Umbilical Pnysiological Action of the Allantois. — Ihe

vesicle, b. Amnion. c. Allan- physiological action of the allantois, in its

simplest form, may be studied with advantage

in the fowl's egg, where it forms an extensive and highly vascular
organ, but does not present any important modifications of its original
structure.

The egg of the fowl contains, when first laid, an abundant deposit of
semi-solid albuminous matter in which the yolk is enveloped. This
affords, in connection with the yolk, a sufficient quantity of moisture
and organic nutriment for the growth of the embryo. The necessaiy
warmth is supplied by the body of the fowl in incubation ; and the
atmospheric gases can pass and repass without difficulty through the
porous shell and its lining membranes. On the commencement of incu-
bation, a liquefaction takes place in the albumen immediately above that
part of the yolk which is occupied by the blastoderm ; so that the vitel-
lus rises toward the surface, by virtue of its specific gravity, and the
blastoderm comes to be placed almost immediately underneath the
lining membrane of the egg-shell. The body of the embryo is thus
placed in the most favorable, position for the reception of warmth and
other necessary external influences. The liquefied albumen is absorbed
by the vitelline membrane, and the yolk thus becomes larger, softer, and
more diffluent than before the commencement of incubation.

As soon as the circulatory apparatus of the embryo has been fairly
formed, two minute arteries are seen to run out from its lateral edges
and spread into the neighboring parts of the blastoderm, breaking up
into inosculating branches, and covering the adjacent portions of the
yolk with a plexus of capillary bloodvessels. The space occupied in
the blastoderm by these vessels is called the area vasculosa. The blood
is returned from it to the body of the embryo by two veins which pene-
trate beneath its edges, one near the head and one near the tail.

The area vasculosa increases in extent as the development of the
embryo proceeds, and its circulation becomes more active. It covers
the upper half or hemisphere of the yolk ; and then, passing this point,

AMNION AND ALLANTOIS. 743

it embraces more and more of the inferior hemisphere, its vessels con-
verging toward the opposite pole of the yolk.

The function of the area vasculosa is to absorb nourishment from the
cavity of the vitelline sac. As the albumen liquefies during the process
of incubation, it passes by endosmosis into the vitelline cavity ; the
whole yolk growing constantly larger and more fluid in consistency.
The blood of the embryo, circulating in the vessels of the area vasculosa,
absorbs the oleagino-albuminous matters of the vitellus, and, carrying
them back to the embryo by the returning veins, supplies the tissues
and organs with appropriate nourishment.

During this period the amnion and the allantois have been also in
process of formation. At first the body of the embryo lies upon its
abdomen, as heretofore described ; but, as it increases in size, it alters
its position so as to lie upon its left side. The allantois, emerging from
the posterior portion of the abdominal cavity, turns upward over the
body of the embryo, and comes in contact with the shell membrane. It
then spreads out rapidly, extending toward the two extremities and down
the sides of the egg, enveloping the embryo and the vitelline sac, and
taking the place of the albumen which has been liquefied and absorbed.

The umbilical vesicle is at the same time formed by the separation of
part of the yolk from the abdomen of the chick ; and the vessels of the
original area vasculosa, which were at first distributed over the yolk,
now ramify upon the surface of the umbilical vesicle.

At last the allantois, by its continued growth, envelops nearly the
whole of the remaining contents of the egg ; so that toward the later
periods of incubation, at whatever point we open the egg, the internal
surface of the shell membrane is found to be lined with a vascular ex-
pansion. This expansion is the allantois, supplied by arteries emerging
from the body of the embryo.

The allantois is accordingly adapted, by its structure and position, to
perform the office of a respiratory organ. The air penetrates from the
exterior through the porous shell and its lining membranes, and acts
upon the blood in the vessels of the allantois much in the same manner
that the air in the lungs of the adult animal acts upon the blood in the
pulmonary capillaries. Examination of the egg, at various periods of
incubation, shows that changes take place in it which are entirely anal-
ogous to those of respiration.

The egg, in the first place, during the development of the embr}ro,
loses water by exhalation. This exhalation is not a simple effect of
evaporation, but is the result of the nutritive changes going on in the
interior of the egg ; since it does not take place, except in a compara-
tively slight degree, in unimpregated eggs, or in those which are not
incubated, though freely exposed to the air. The exhalation of fluid is
also essential to the processes of development ; since it has been found,
in hatching eggs ~by artificial warmth, that if the air of the hatching
chamber become unduly charged with moisture, so as to retard or pre-
vent further exhalation, the development of the embryo is arrested. The
loss of weight during natural incubation, mainly due to the exhalation

744 ACCESSORY ORGANS IN IMPREGNATED EGG.

of water, has been found by Baudrimont and St. Ange1 to be over 15
per cent, of the entire weight of the egg.

Secondly, the egg absorbs oxygen and exhales carbonic acid. The
two observers above mentioned, ascertained that during eighteen days'
incubation, the egg absorbs nearly 2 per cent, of its weight of oxygen,
while the quantity of carbonic acid exhaled from the sixteenth to the
nineteenth day amounts to nearly £ of a gramme in twenty-four hours.
It is also observed that in the egg during incubation, as well as in the
adult animal, more oxygen is absorbed than is returned by exhalation
under the form of carbonic acid.

The allantois, however, is not simply an organ of respiration; it
takes part also in the absorption of nutritious matter. As the process
of development advances, the skeleton of the young chick, at first carti-
laginous, begins to ossify. The calcareous matter, necessary for ossifi-
cation, is in great part derived from the shell. The shell is perceptibly
lighter and more fragile toward the end of incubation than at first ; and,
at the same time, the calcareous ingredients of the bones increase in
quantity. The lime-salts, requisite for ossification, are apparently ab-
sorbed from the shell by the vessels of the allantois, and thus transferred
to the skeleton of the growing chick ; so that, in the same proportion
that the former becomes weaker, the latter grows stronger. The dimi-
nution in density of the shell is connected not only with the develop-
ment of the skeleton, but also with the final escape of the chick from
the egg. This deliverance is accomplished mainly by the movements
of the chick itself, which become, at a certain period, sufficiently vigor-
ous to break out an opening in the attenuated shell. The first fracture
is generally accomplished by a stroke from the end of the bill ; and it
is precisely at this point that the solidification of the skeleton is most
advanced. The egg-shell, therefore, which at first serves for the pro-
tection of the embryo, afterward furnishes the materials which are used
to accomplish its own demolition, and at the same time to effect the
escape of the fully developed chick.

Toward the latter periods of incubation, the allantois becomes more
adherent to the internal surface of the shell-membrane. At last, when
the chick, arrived at the full period of development, escapes from its
confinement, the allantoic vessels are torn off at the umbilicus ; and the
allantois itself, cast off as an effete organ, is left behind in the cavity
of the abandoned shell.

Both the amnion and the allantois are, therefore, formations belong-
ing to the embryo, and constituting, for a time, accessory but essential
parts of its organization. Developed from the peripheral portions of
the outer and inner blastodermic layers, they are important organs
during the middle and latter periods of incubation ; but when the chick
lias become fully developed, and is ready to carry on an independent
existence, they are thrown off as obsolete structures, their place being
afterward supplied b}' organs belonging to the adult condition.

1 DSveloppement du Foetus. Paris, 1850, p. 143.

CHAPTEE X.

DEVELOPMENT OF THE IMPREGNATED EGG AND
ITS MEMBRANES IN THE HUMAN SPECIES. AM-
NION AND CHORION.

IN the human species, as well as in the lower animals, the foetus is
enveloped in two membranes, an inner and an outer, derived respec-
tively from extensions of the external and internal blastodermic layers,
and consequently parts of the emb^onic organism. While the inner
of these envelopes has the same characters as elsewhere, the outer one
presents such modifications of structure as to have received a distinct
name. In the lower animals, therefore, the foetal membranes are called
the amnion and the allantois; in man, they are known as. the amnion
and the chorion.

Amnion.

The formation of the amnion in the human species takes place in the
same manner as that already described (p. 740), namely, by the growth
of a circumvallation or fold of the external blastodermic layer, which
extends itself in such a way that its edges meet and coalesce over the
back of the embryo, thus inclosing it in a distinct cavity.

Fig. 259.

Fig. 260.

HUMAN EMBRYO AND ITS ENVEL-
OPES, about the end of the first month.
—1. Umbilical vesicle. 2. Amnion. 3,
Chorion.

HUMAN EMBRYO AND ITS ENVEL-
OPES, at the end of third month; showing
the enlargement of the amnion..

At the time of its formation, the amnion closely embraces the body
of the embryo, so that there is hardly any space between the two ; the
opposite surfaces lying in contact with each other, like those of the
48 ( 745 )

746 DEVELOPMENT OF THE IMPREGNATED EGG.

peritoneum in the adult. This space afterward enlarges somewhat and
becomes the amniotic cavity, containing a little colorless, transparent,
serous fluid, the amniotic fluid. But throughout the earlier periods of
development the cavity of the amnion is small, as compared with that
of the entire egg ; and the space between the amnion and the external
membrane, or chorion (Fig. 259;, is occupied by an amorphous gelati-
nous material, in which the umbilical vesicle and its stem lie imbedded.
Subsequent!}^ the amnion enlarges more rapidly, in comparison with
the remaining parts of the egg, and thus encroaches upon the layer of
gelatinous material by which it is surrounded. At the same time the
amniotic fluid increases in quantity (Fig. 260) ; so that a considerable
space is left around the embryo, which is supported by the uniform
pressure of the surrounding fluid. The amnion continues to enlarge at
this increased rate of growth until about the beginning of the fifth
month, when it comes in contact with the inner surface of the chorion ;
the gelatinous material previously intervening between them having
disappeared, or being reduced to a nearly imperceptible layer.

Chorion.

The chorion, in the human species, is the external enveloping mem-
brane of the embryo. It originates, like the corresponding envelope in
the lower animals, by a protrusion or outgrowth from the posterior por-
tion of the primitive alimentary canal, which, insinuating itself between
the two laminae of the amniotic fold, spreads gradually over and around
the inner lamina or amnion proper, so as to occupy finally a position out-
side of it. It there meets with the two thin layers which have preceded
it in this situation, namely the outer lamina of the amniotic fold, and
the original vitelline membrane of the egg. But these two layers, ceas-
ing to grow, while the new structures and the whole egg are rapidly
enlarging, disappear as distinct membranes, and their place is taken by
the chorion, which thus becomes, alone, the external investment of the
egg-

So far, the history of development of the chorion is the same with
that of the allantois. But the peculiarity which distinguishes it is that,
in expanding over and around the other parts, it does not present the
form of a double sac containing fluid, but of a single vascular sheet or
membrane, like that of the skin. It is on this account that in the
human species it is called the chorion, while in the lower animals it
retains the name of allantois.

Nevertheless, the chorion, like the allantois, is at its commencement
a hollow sac or canal with a blind extremity, the cavity of which is a
continuation of that of the intestine. But this cavity does not extend
i\t any time for more than a short distance outside the body of the
embryo. Beyond this point it becomes obliterated, its membranous
walls remaining in contact with and adherent to each other, forming a
solid membrane, as above described. Inside the body of the embryo,
on the other hand, it retains the form of a membranous sac ; and this

CHORION.

"47

Fig. 261.

portion afterward becomes, in the process of further development, the
urinary bladder. The rounded cord or "urachus," which, in the adult,
runs from the superior fund us of the bladder to the situation of the
umbilicus in the abdomen, is the vestige of the obliterated canal of the
primitive chorion.

The next peculiarity of the chorion is, that it becomes shaggy. Even.
while the egg is still very small, and has but recently found its way into
the uterine cavity, its exterior is already covered with transparent villi
(Fig. 259), which increase the extent of its surface, and, assist in the
absorption of fluids from without. The villi are at this time quite sim-
ple in form, and homogeneous in structure.

As the egg increases in size, the villi elongate, and become ramified
by the repeated budding of lateral offshoots. After this process has
continued for some time, the outer
surface of the chorion presents a uni-
formly shaggy appearance, owing to its
being covered everywhere with com-
pound villosities.

The villosities, when examined by
the microscope, have an exceedingly
characteristic appearance. They origi-
nate from the surface of the chorion by
a somewhat narrow stem, and divide
into secondary and tertiary branches
of varying size and figure; some of
them filamentous, others club-shaped,
many of them irregularly swollen at
various points. All terminate by
rounded extremities, giving to the
whole tuft a certain resemblance to
some varieties of sea-weed. The larger
trunks and branches of the villosity
are seen to contain minute nuclei, im-
bedded in a nearly homogeneous, or
finely granular substratum. The

smaller ones appear, under a low magnifying power, simply granular in
texture.

The villi of the chorion are quite unlike any other structure to be
met with in the body. Whenever we find, in the uterus, any portion of
a membrane having villosities of this character, it is certain that preg-
nancy has existed ; for such villosities can only belong to the chorion,
and the chorion itself is a part of the foetus. The presence of portions
of a shaggy chorion is therefore as satisfactory proof of the existence
of pregnancy, as if the body of the foetus itself had been found.

While the villosities just described are in process of formation, the
chorion receives a supply of bloodvessels from the interior of the body
of the embryo. The arteries, which are a continuation of those dis-

Compound villosity of the HUMAN
CHORION, ramified extremity. From
a three months' foetus. Magnified 30
diameters.

748 . DEVELOPMENT OF THE IMPREGNATED EGG.

tributed to the alimentary canal, pass out along the canal of communi-
cation to the chorion and ramify over its surface. The embryo at this
time has reached such an activity of growth that it requires to be sup-
plied with nourishment by means of vascular absorption, instead of the
slow process of imbibition hitherto taking place through the compara-
tively structureless villi of the chorion. The capillary bloodvessels, with

which the chorion is supplied, begin to pene-
Fig. 262. trate the substance of its villosities. They

enter the base or stem of each villus, and.
following the division of its compound rami-
fications, reach the rounded extremities of
its terminal offshoots. Here they turn upon
themselves in loops (Fig 262), and retrace
heir course, to unite finally with the venous
runks of the chorion.

The villi of the chorion are, accordingly, an-
alogous in structure and function to those of
the intestine ; their power of absorption cor-
responding with the abundance of their rami-
fications, and the extent of their vascularity.

Extremity of a VILLOSITY ,,,. , , -, , „ ,, , .

OP THE CHORION, magnified Hie bloodvessels of the chorion, further-
iso diameters; showing the ar- mOre, are all derived from the abdomen of

rangement of bloodvessels in its . _ ' . ,, .

interior. the foetus ; and all substances absorbed by

them are transported to the interior of the

body, and used for the nourishment of its tissues. The chorion, there-
fore, as soon as its villi and bloodvessels are completely developed, be-
comes an active organ in the nutrition of the fo3tus ; and constitutes
the only means by which new material is introduced from without.

The third event of importance in the history of the chorion is that
after being at first uniformly shaggy throughout, it afterward becomes
partially bald. (Fig. 260.) This change begins about the end of the
second month, commencing at a point opposite the insertion of the
foetal bloodvessels. The villosities of this region cease growing; and
while the entire egg continues to enlarge, they fail to keep pace with
the progressive expansion of the chorion. They accordingly become at
this part thinner and more scattered, leaving the surface of the chorion
comparatively bald. This baldness increases in extent, spreading over
the adjacent portions of the chorion, until at least two-thirds of its sur-
face have become nearly or quite destitute of villosities.

At the opposite pole of the egg, namely, that which corresponds with
the insertion of the foetal bloodvessels, the villosities of the chorion,
instead of becoming atrophied, continue to grow ; and this portion be-
comes even more shaggy and thickly set than before. The consequence
is that the chorion afterward presents a different appearance at different
parts of its surface. The greater part is smooth; but a certain portion,
constituting about one-third of the whole, is covered with a soft, spongy
mass of long, thicks-set, compound villosities. It is this thickened

CHORION. 749

portion which is afterward concerned in the formation of the placenta;
while the remaining smooth portion continues to be known under the
name of the chorion. The placental portion of the chorion becomes dis-
tinctly limited in outline by about the end of the third month.

The vascularity of the chorion keeps pace, in its different parts, with
the atrophy and development of its villosities. As the villosities shrivel
and disappear over a part of its extent, the bloodvessels with which they
were supplied diminish in abundance ; and the smooth portion of the
chorion finally shows only a few straggling vessels running over its sur-
face, but not connected with any abundant capillary plexus. In the
thickened portion, on the other hand, the bloodvessels lengthen and
ramify to an extent corresponding with that of the villosities in which
they are situated. The arteries, coming from the abdomen of the foetus,
divide into branches which enter the villi, and penetrate through their
whole extent ; forming, at the placental portion of the chorion, a mass
of tufted and ramified vascular loops, while the rest of the membrane
has a comparatively scanty vascular supply.

The chorion, accordingly, is the external investing membrane of the
egg, produced by an outgrowth from the body of the embryo ; and the
placenta, so far as it consists of the foetal membranes, is a part of the
chorion, distinguished from the rest by the local development of its villi
and bloodvessels.

CHAPTEE XI.

DEVELOPMENT OF THE DECIDUAL MEMBRANE,
AND ATTACHMENT OF THE EGG TO THE UTERUS.

IN the human species, where the development of the embryo is com-
pleted within the cavity of the uterus, the egg depends for its nutrition
and growth upon materials derived from the organism of the female
parent. The immediate source of supply for this purpose is the mucous
membrane of the uterus, which becomes unusually developed and in-
creased in functional activity during the period of gestation. The
uterine mucous membrane, when thus modified in structure, is known
as the decidual membrane, or the decidua. It has received this name
because it is exfoliated and discharged at the same time that the egg
itself is expelled from the uterus.

The mucous membrane of the body of the uterus, in the unimpreg-
nated condition, is thin and delicate, and presents a smooth internal
surface. There is no distinct layer of connective tissue between it and
the muscular substance of the uterus ; so that the mucous membrane
cannot here, as in most other

organs, be readily separated Fig. 264.

by dissection from the subja-
cent parts. The structure of
the mucous membrane, how-
ever, is sufficiently well
marked. It consists, through-
Fig. 263.

UTERINE Mucous MEM-
BRANE, from the unimpregnated
uterus, in vertical section, a. Free
surface, b. Attached surface. Mag-
nified about 10 diameters.

UTERINE TUBULES, from the mucous mem-
brane of an unimpregnated human uterus. Mag-
nified 125 diameters.

out, of tubular follicles, ranged side by side, and running perpendicu-
larly to its free surface. Near this surface, they are nearly straight ; but
toward the deeper part of the mucous membrane, where they terminate
in blind extremities, they become more or less wavy or spiral in their
( T50 )

DECIDUA REFLEXA. 751

course. The tubules are about 0.05 millimetre in diameter, and are
lined with columnar epithelium. They occupy the entire thickness of
the uterine mucous membrane, their closed extremities resting upon
the subjacent muscular tissue, while their mouths open into the cavity
of the uterus. A few fine bloodvessels penetrate the mucous membrane
from below, and, running upward between the tubules, encircle their
superficial extremities with a capillary network. There is no connective
tissue in the uterine mucous membrane, but only a few isolated nuclei
and spindle-shaped fibre-cells, scattered between the tubules.

Decidua Vera. — As the fecundated egg descends through the Fal-
lopian tube, the uterine mucous membrane takes on an increased
activity of growth. It becomes tumefied and vascular ; and, as it in-
creases in thickness, it projects, in rounded eminences or folds, into
the uterine cavity. (Fig. 265.) In .this process the uterine tubules in-
crease in length, and also become wider ; so that their open mouths may
be readily seen by the naked eye upon the uterine surface, as numerous
minute perforations. According to the observations of Kolliker, so
early as the end of the first week they have increased to three or four
times their original length and width, so that they measure at this time
on the average nearly 0.20 millimetre in diameter, The bloodvessels of
the mucous membrane also enlarge and communicate freely with each
other ; the vascular network between and around the tubules becoming
more extensive and abundant. The internal surface of the uterus, after
this process has been for some time going on, presents a thick, rich, soft,
velvety, and vascular lining, quite different in appearance from that
which is to be found in the unimpregnated condition. It is now known
as the decidua ; and in order to distinguish it from a similar growth of
subsequent formation, it has received the special name of the decidua
vera.

The production of the decidua is confined to the body of the uterus,
the mucous membrane of the cervix taking no part in the process, but
retaining its original appearance. The decidual membrane commences
above, at the orifices of the Fallopian tubes, and ceases below, at the
situation of the os intern um. The cavity of the cervix, meanwhile, is
filled with an abundant secretion of its peculiarly viscid mucus, which
blocks up its passage, and protects the internal cavity. If the uterus
be opened, therefore, in this condition, its internal surface will be seen
lined with the decidua vera, which is continuous, at the os internum,
with the unaltered mucous membrane of the cervix uteri.

Decidua Reflexa. — As the fecundated egg passes the lower orifice of
the Fallopian tube, it insinuates itself between the opposite surfaces of
the uterine mucous membrane, and becomes lodged in one of the furrows
or depressions between the folds of the decidua. (Fig. 265.) At this
situation an adhesion subsequently takes place between the external
membranes of the egg and the uterine decidua. At the point where
the egg thus becomes fixed, a still more rapid development takes place
in the uterine mucous membrane. Its projecting folds grow up around

752 DEVELOPMENT OF THE DEC1DUAL MEMBRANE.

the egg in such a manner as to partially inclose it in a kind of circum-
vallation, and to shut it off, mure or less completely, from the general

Fig. 265.

Fig-. 2(;«.

IMPREGNATED UTERUS; showingfor-
mation of decidua. The decidua is repre-
sented in black; and the egg is seen, at the
fundus of the uterus, engaged between two
of its projecting folds.

IMPREGNATED UTERUS, with project-
ing folds of decidua growing up around the
egg. The narrow opening, where the edges
of the folds approach each other, is seen
over the most prominent portion of the egg.

iif. 267.

cavity of the uterus. (Fig. 266.) The egg thus comes to be contained
in a special cavity of its own, which still communicates for a time with
the general cavity of the uterus, by an opening situated over its most

prominent portion. As the process of growth
goes on, this opening becomes narrower, while
the decidual folds approach each other OA^er
the surface of the egg. At last these folds
touch each other and unite, forming a kind of
cicatrix which remains for a certain time, to
mark the situation of the original opening.

When the development of the uterus has
reached this point (Fig. 267), the egg is com-
pletely inclosed in a cavity of its own ; being
everywhere covered with a decidual layer of
new formation, which has gradually enveloped
it, and by which it is concealed from view
when the uterine cavity is laid open. This
newly-formed layer, enveloping the projecting
portion of the egg, is called the Decidua
reflexa ; because it is reflected over the egg from the general surface
of the uterine mucous membrane. The orifices of the uterine tubules,
in consequence of the manner in which the decidua reflexa is formed,
are to be seen not only on its external surface, or that which looks
toward the cavity of the uterus, but also on its internal surface, or that
which looks toward the egg.

The decidua vera, therefore, is the original mucous membrane lining
the surface of the uterus. The decidua reflexa is a new formation,
which grows up around the egg and incloses it in a distinct cavity.

IMPREGNA.TKD UTERUS;
showing the egg completely in-
closed by the decidua reflexa.

ATTACHMENT OF EGG TO UTERUS. 753

If abortion occur at this time, the mucous membrane of the uterus,
that is, the decidua vera, is thrown off, and brings with it the egg and
the decidua reflexa. On examining the mass so discharged, the egg
will be found imbedded in the substance of the decidual membrane.
One side of the membrane, where it has been torn away from its attach-
ment to the uterus, is ragged ; the other side, corresponding to the cavity
of the uterus, is smooth or gently convoluted, and exhibits distinctly
the orifices of the uterine tubules; while the egg itself can only be
extracted by cutting through the decidual membrane, either from one
side or the other, and opening in this way the special cavity in which it
is inclosed.

During the formation of the decidua reflexa, the entire egg, as well
as the body of the uterus which contains it, has considerably enlarged.
That portion of the uterine mucous membrane situated immediately
underneath the egg, and to which it first became attached, has also con-
tinued to increase in thickness and vascularity. The remainder of the
decidua vera, however, ceases to grow as before, and no longer keeps
pace with the increasing size of the egg and of the uterus. It is still
thick and vascular at the end of the third month ; but after that period
it becomes comparatively thinner and less glandular, while the activity
of growth is concentrated in the egg, and in that portion of the uterine
mucous membrane with which it is in immediate contact.

Attachment of the Egg to the Uterus. — While the above changes are
taking place in the lining membrane of the uterus, the formation of the
embryo, and the development of the amnion
and chorion have been going on simultane- Fig. 268.

ously ; and soon after the entrance of the
egg into the uterine cavity, the chorion is
everywhere covered with projecting villosities.
These villosities insinuate themselves into the
uterine tubules, or between the folds of the
decidual surface ; penetrating in this way into
little cavities of the uterine mucous mem-
brane. When the formation of the decidua
reflexa is completed, the chorion has already
become uniformly shaggy ; and its villosities,
spreading in all directions from its external
surface, penetrate everywhere both into the

. , ,, IMPREGNATED UTERUS,

decidua vera beneath it and into the decidua showing the connection he-
reflexa witn which it is covered. In- this way tween the viiiositiea of the

c chorion and the decidual mem-

. ,

the egg becomes entangled with the decidua,

and cannot be readily separated from it with-

out rupturing some of the filaments which have grown from its surface,

and have penetrated the substance of the decidua. The nutritious fluids,

exuded from the glandular textures of the decidua, are now imbibed by

the villosities of the chorion ; and a more rapid supply of nourishment

754 DEVELOPMENT OF THE DECIDUAL MEMBRANE.

Fig. 269.

is thus provided, corresponding in abundance with the greater size of
the egg.

Yery soon the activity of absorption is still further increased. The
chorion becomes vascular, by the formation of bloodvessels emerging
from the body of the embryo and penetrating everywhere into the villo-
sities with which it is covered. Each villosity then contains a vascular
loop, imbedded with itself in the substance of the decidua, and serving
to absorb from the uterine, mucous membrane the materials for the
growth of the embryo.

Subsequently, the vascular tufts of the chorion, which are at first uni-
formly distributed over its surface, disappear throughout the greater

part of its extent, while they become still
further developed and concentrated at a
particular point, the situation of the
future placenta. This is the spot at
which the egg is in contact with the de-
cidua. Here, both the decidual membrane
and the tufts of the chorion continue to
increase in thickness and vascularity ;
while elsewhere, over the prominent por-
tion of the egg, the chorion not only be-
comes bare of villosities and compara-
tively destitute of bloodvessels, but the
decidua reflexa, which is in contact with
it, also loses its activity of growth and
becomes expanded into a thin layer, with-
out any remaining trace of glandular fol-
licles.

The uterine mucous membrane is there-
fore developed, during gestation, in such a way as to provide for the
nourishment of the embryo in the different stages of its growth. At first,
the whole of it is uniformly increased in thickness (decidua vera). Next,
a portion of it grows upward around the egg, and covers its projecting
surface (decidua reflexa). Afterward, both the decidua reflexa and the
greater part of the decidua vera diminish in the activity of their growth,
and lose their importance as a means of nourishment for the embryo ;
while that part which is in contact with the vascular tufts of the chorion
continues to grow, becoming excessively developed, and taking part in
the formation of the placenta.

PREGNANT UTERUS; showing
the formation of the placenta by
the united development of a portion
of the decidua and the villosities of
the chorion.

CHAPTER XII.

THE PLACENTA.

IN all instances in which, as in man and the mammalians, the em-
bryo is dependent, for the materials of its growth, upon nutritious fluids
supplied by the uterus, the communication between them is established
by means of two vascular membranes. One of these membranes, the
chorion or the allantois, is a part of the embryo; the other is the mucous
membrane of the uterus. By their more or less intimate juxtaposition,
the fluids transuded from the bloodvessels of the mother are absorbed
by those of the embryo, and thus a transfer of nutriment takes place
from the maternal to the foetal organism.

In some species of animals, the connection between the maternal and
foetal membranes is a simple one. In the pig, for example, the uterine
mucous membrane is everywhere uniformly vascular; its only pecu-
liarity consisting in the presence of transverse folds, which project
inward from its surface, like the valvulse conniventes of the small in-
testine. The external investing membrane of the egg, or the allantois,
is also smooth and uniformly vascular. No special development of
tissue or of vessels occurs at any part of these membranes, and no adhe-
sion takes place between them. The vascular allantois of the foetus is
simply in close apposition with the vascular mucous membrane of the
uterus; each of the two contiguous surfaces following the undulations

Fig. 270.

Diagram oftheFoiTAL PIG, with its membranes, in, the uterus; showing the relation of
the allantoic and uterine surfaces.— a, a, 6, 6. Walls of the uterus, c, c. Cavity of the uterus.
d. Amnion. e, e, Allantois.

presented by the other. (Fig. 2TO.) By this arrangement, transudation
and absorption take place from the bloodvessels of the mother to those
of the foetus, in sufficient quantity to provide for the nutrition of the
latter. When parturition takes place, a moderate contraction of the
uterus is sufficient to expel its contents. The egg, displaced from its
original position, slides forward over the surface, of the uterine mucous

( 755 )

756 THE PLACENTA.

membrane, and is discharged without any hemorrhage or laceration of
the parts.

In other instances, there is a more intimate connection, at certain
points, between the foetal and maternal structures. In the cow, the
sheep, and the ruminating animals generally, the external membrane of
the egg, beside being everywhere supplied with branching bloodvessels,
presents, scattered over its surface, a large number of distinct rounded
or oval spots, at each of which it is covered with thickly set, tufted,
vascular prominences. These spots are called cotyledons, or cups, be-
cause each one is surrounded by a raised rim or fold, which embraces a
corresponding rounded mass projecting from the internal surface of the
uterus. This projecting portion of the uterine mucous membrane is
also abundantly supplied with bloodvessels; and the tufted vascular
loops projecting from the surface of the foetal membrane (Fig. 271, 6, 6)
dip down into its substance and are entangled with those belonging to

Fig. 271.

COTYLEDON, from the pregnant uterus of the cow.-o. Internal surface of the allantois.
b, b. Foetal bloodvessels, c, c. Surface of uterine mucous membrane, d, d. Maternal blood-
vessels.

the uterus (d, d). There is no absolute adhesion between the two sets
of vessels, but only an interlacement of their ramified extremities ; and
by careful manipulation the foetal portion, with its villosities, may be
extricated from the maternal portion without the laceration of either.

In the carnivorous animals, a similar highly developed, vascular por-
tion of the allantois runs, in the form of a single broad belt or band,
round its middle part ; and this corresponds in situation with an equally
developed zone of the uterine mucous membrane. Here the foetal and
maternal structures are adherent to each other ; while, elsewhere,
toward the two extremities of the egg, they lie simply in contact.
When gestation comes to an end in these animals, and the foetus, with

THE PLACENTA.

757

its membranes, is expelled, the thickened zone of uterine mucous mem-
brane is detached at the same time, and its place is afterward made
good by a new growth.

In the human species, as shown in the preceding chapter, the perma-
nently thickened portions of the chorion and decidua, united with each
other by mutual interpenetration and growth, form a single, flattened,
cake-like mass of rounded form, oceupj'ing rather less than one-third
of the surface of the chorion, and corresponding to a similar extent of
the inner surface of the uterus. This mass, consisting of the foetal and
maternal elements combined, is the placenta.

The complete development of the placenta takes place in the follow-
ing manner :

The villi of the chorion, when first formed, penetrate into follicles
situated in the substance of the uterine mucous membrane; and after
becoming vascular, they are developed into tufted ramifications of
bloodvessels, each one of which turns upon itself in a loop at the ex-
tremity. At the same time the uterine follicle, into which the villus
has penetrated, enlarges to a similar extent ; sending out branching
diverticula, corresponding with the multiplied ramifications of the
villus. The growth of the follicle and that of the villus thus go on
simultaneously and keep pace with each other ; the latter constantly
advancing as the cavity of the former enlarges.

But it is not only the uterine follicles which increase in size and in
complication of structure at this period. The capillary bloodvessels,
which lie between them and ramify over their exterior, also become
unusually developed. They enlarge and inosculate freely with each
other ; so that every uterine folli-

cle is covered with a network of
dilated capillaries, derived from
the bloodvessels of the original
decidua.

As the formation of the pla-
centa goes on, the anatomical ar-
rangement of the foetal bloodves-
sels remains the same. They
continue to form vascular loops,
penetrating deeply into the de-
cidual membrane ; only they be-
come more elongated, and their
ramifications more abundant and
tortuous. The maternal capilla-
ries, however, on the outside of

Fig. 272.

Extremity of a FOETAL TUFT, from the
human placenta at term, in its recent condi-
tion.— a, a. Capillary bloodvessels. Magnified
135 diameters.

the uterine follicles, become con-
siderably altered in their anatomi-
cal relations. They enlarge in

all directions, and, by encroaching upon the spaces situated between
them, fuse successively with each other ; and, losing gradually in this

758 THE PLACENTA.

way the characters of a capillary network, become dilated into sinuses,
which communicate freely with the vessels in the muscular walls of the
uterus. As the original capillary plexus occupied the entire thickness
of the hypertrophied decidua, the vascular sinuses, into which it is thus
converted, are equally extensive. They commence at the external sur-
face of the placenta, where it is in contact with the muscular walls of
the uterus, and extend through its whole thickness, quite to the surface
of the foetal chorion.

As the maternal sinuses grow. inward, the vascular tufts of the cho-
rion grow outward, and extend also through the entire thickness of the
placenta. In the latter periods of pregnancy, the development of the
bloodvessels, both in the foetal and maternal portions of the placenta,
is so excessive that all the other tissues, which originally coexisted
with them, have nearly disappeared. If a villus from the foetal portion
of the placenta be examined at this time by transparency, in the fresh
condition (Fig. 272) it will be seen that its bloodvessels are covered
only with a layer of homogeneous, or finely
granular material, about 7 mmm. in thickness,
in which are imbedded small oval-shaped nu-
clei, similar to those seen at an earlier period
in the villosities of the chorion. The placental
villus is now, therefore, hardly anything more
than a congeries of ramified and tortuous vas-
cular loops ; its remaining substance having
been atrophied and absorbed in the excessive
growth of the bloodvessels, the abundance and
development of which can be readily shown by
injection from the umbilical arteries. (Fig.

Extremity of a FOSTAL ^^ The uterine follicles have at the same
TUFT of the human piacen- time lost their original structure, and have
become mere vascular sinuses, into which the
tufted foetal bloodvessels are received, as the
villosities of the chorion were at first received into the uterine fol-
licles.

Finally, the walls of the foetal bloodvessels having come into close
apposition with the walls of the maternal sinuses, the two become adhe-
rent and fuse together ; so that a time at last arrives when we can no
longer separate the foetal vessels, in the substance of the placenta, from
the maternal sinuses, without lacerating either the one or the other,
owing to the adhesion which has taken place between them.

The placenta, therefore, when perfectly formed, has the structure
which is shown in the accompanying diagram (Fig. 274), representing
a vertical section of the organ through its entire thickness. At a, a, is
seen the chorion, receiving the umbilical vessels from the body of the
foetus through the umbilical cord, and sending out its compound and
ramified vascular tufts into the substance of the placenta. At 6, 6, is
the attached surface of the decidua, or uterine mucous membrane ; and

THE PLACENTA. 759

at c, c, c, c, are the orifices of uterine vessels which penetrate it from
below. These vessels enter the placenta in an extremely oblique direc-
tion, though they are represented in the diagram, for the sake of dis-
tinctness, as nearly perpendicular. When they have once penetrated

Fig. 274

c

Vertical section of the PLACENTA, showing the arrangement of the maternal and festal
bloodvessels. — a. a. Chorion. 6,6. Decidua. c, c, c, c. Orifices of uterine sinuses.

the lower portion of the decidua, they immediately dilate into the pla-
cental sinuses (represented, in the diagram, in black), which extend
through the whole thickness of the organ, closely embracing all the
ramifications of the foetal tufts. It will be seen, therefore, that the pla-
centa, arrived at this stage of completion, is composed essentially of
nothing but bloodvessels. The other tissues which originally entered
into its structure have disappeared, leaving the bloodvessels of the foetus
entangled with and adherent to the bloodvessels of the mother.

There is, however, no direct communication between the foetal and
maternal vessels. The blood of the foetus is always separated from the
blood of the mother by a membrane which has resulted from the suc-
cessive union and fusion of four different membranes, namely : first, the
membrane of the foetal villus ; secondly, that of the uterine follicle ;
thirdly, the wall of the foetal bloodvessel ; and fourthly, the wall of the
uterine sinus. The membrane, however, thus produced, is of great
extent, owing to the abundant branching and subdivision of the foetal
tufts. These tufts, in which the blood of the foetus circulates, are bathed
everywhere, in the placental sinuses, with the blood of the mother; and
the processes of absorption and exhalation go on between the two with
a corresponding activity.

It is easy to demonstrate the arrangement of the foetal tufts in the
human placenta. They can be readily seen by the naked eye, and may

7(30 THE PLACENTA.

be traced from their attachment at the under surface of the chorion to
their termination near the uterine surface of the placenta. The ana-
tomical disposition of the placental sinuses is more difficult of examina-
tion. During life, and while the placenta is still attached to the uterus,
they are filled, of course, with the blood of the mother, and occupy fully
one-half the mass of the placenta. But when the placenta is detached,
the maternal vessels belonging to it are torn oif at their necks (Fig.
274, c, c, c, c), and the sinuses, being then emptied of blood by the com-
pression to which the placenta is subjected, are apparently obliterated ;
and the foetal tufts, falling together and lying in contact with each
other, appear to constitute the whole of the placental mass. The ex-
istence of the placental sinuses, however, and their true extent, may be
demonstrated in the following manner.

If we take the uterus of a woman who has died undelivered at the
full term or thereabout, and open it in such a way as to avoid wounding
the placenta, this organ will be seen remaining attached to the uterine
surface, with all its vascular connections complete. Let the foetus be
now removed by dividing the umbilical cord, and the uterus, with the
placenta attached, placed under water, with its internal surface upper-
most. If the end of a blowpipe be then introduced into one of the
divided vessels of the uterine walls, and air forced in by gentle insuffla-
tion, we can easily inflate, first, the vascular sinuses of the uterus, and
next, the deeper portions of the placenta ; and lastly, the bubbles of air
insinuate themselves every where between the foetal tufts, and appear in
the most superficial portions of the placenta, immediately underneath
the transparent chorion (a, a, Fig. 274) ; thus showing that the pla-
cental sinuses, which freely communicate with the uterine vessels, occupy
the entire thickness of the placenta, and are equally extensive with the
tufts of the chorion. We have verified this fact in the above manner,
on six different occasions, and in the presence of Prof. C. R. Oilman,
Prof. Geo. T. Elliot, Prof. Henry B. Sands, Prof. T. G. Thomas, Dr. T.
C. Finnell, and various other medical gentlemen of New York. The
same thing has been done by Prof. A. Flint, Jr.,1 with a similar result.

If the placenta be detached and examined separately, it will be found
to present upon its uterine surface a number of openings, which are ex-
tremely oblique in position, and bounded on one side by a very thin
crescentic edge. These are the orifices of the uterine bloodvessels,
passing into the placenta and torn off at their necks, as above described ;
and by carefully following them with the probe and scissors, they are
found to lead at once into extensive empty cavities (the placental
sinuses), situated between the foetal tufts. These cavities are filled
during life with the maternal blood ; and there is every reason to believe
that before delivery, while the circulation is going on, the placenta is at
least twice as large as after it has been detached and expelled from the
uterus.

1 Flint, Physiology of Man. New York, 18^4, vol. v. p. 382.

THE PLACENTA. 761

The placenta, accordingly, is a double organ, formed partly by the
chorion and partly by the decidua ; and consisting of maternal and foetal
bloodvessels, entangled and united with each other.

The part which this organ takes in the development of the foetus is
of primary importance. From the date of its formation, at about the
beginning of the fourth month, it constitutes the only channel through
which nourishment is conveyed from the mother to the foetus. The
nutritious materials, which circulate in the blood of the maternal
sinuses, pass through the intervening membrane, and enter the blood of
the foetus. The healthy or injurious regimen, to which the mother is
subjected, will accordingly exert an influence upon the child. Even
medicinal substances, taken by the mother and absorbed into the circu-
lation, may transude through the placental vessels, and thus exert a
specific effect upon the foetal organization.

The placenta is, furthermore, an organ of exhalation as well as of
absorption. The excrementitious matters, produced in the circulation
of the foetus, are undoubtedly in great measure disposed of by transu-
dation through the walls of the placental vessels, to be afterward dis-
charged by the excretory organs of the mother. The sj^stem of the
mother may therefore be affected in this manner by influences derived
from the foetus. It has been observed in the lower animals, that when
the female has two successive litters of young *by different males, the
young of the second litter will sometimes bear marks resembling those
of the first male. In these instances, the influence which produces the
external mark is transmitted by the first male to the foetus, from the
foetus to the mother, and from the mother to the foetus of the second
litter.

It is also through the placental circulation that those disturbing effects
are produced upon the nutrition of the foetus, which result from sud-
den shocks or injuries inflicted upon the mother. There is little room
for doubt that various deformities and deficiencies of the foetus, confor-
mably to the popular belief, originate, in certain cases, from nervous
impressions experienced b}* the mother. The mode in which these effects
may be produced is readily understood from the anatomy and functions
of the placenta. It is well known how easily nervous impressions will
disturb the circulation in the brain, the face, or the lungs; and the
uterine circulation is quite as readily influenced by similar causes, as
shown in cases of amenorrhcea and menorrhagia. If a nervous shock
may excite premature contraction in the muscular fibres of the pregnant
uterus and produce abortion, it is undoubtedly capable of disturbing
the circulation of the blood in the same organ. But the foetal circulation
is dependent, to a great extent, on the maternal. The two sets of vessels
are united in the placenta, and as the foetal blood has much the same
relation to the maternal, that the blood in the pulmonary capillaries has
to the air in the pulmonary air-cells, it must be liable to derangement
from similar causes. And lastly, as the nutrition of the foetus is pro-
vided for wholly by the placenta, it will suffer from any disturbance of
49

762 THE PLACENTA.

the placental circulation. These effects may be manifested either in the
general atrophy and death of the foetus, or in the imperfect develop-
ment of particular parts ; just as in the adult a morbid action may ope-
rate upon the entire system, or may show itself in some one organ, which
is more particularly sensitive to its influence.

CHAPTEE XIII.

DISCHARGE OF THE FCETUS AND PLACENTA.
REGENERATION OF THE UTERINE TISSUES.

DURING the growth of the embryo and its membranes, and the
development of the uterine mucous membrane into the decidua and
placenta, the muscular tissue of the uterus also increases in thickness,
while the whole organ enlarges, to accommodate the greater volume of
its contents. This increase of substance, which is mainly due to an un-
usual growth in the muscular walls of the organ, gives it a sufficient
degree of contractile power for the expulsion of the foatus at the time
of delivery.

The enlargement of the amniotic cavity, and the increased quantity
of the amniotic fluid, also provide the requisite space and freedom for
the intra-uterine movements of the foetus. These movements begin to
be perceptible about the fifth month, at which time the development of
the muscular system has become sufficient to allow it a certain amount
of functional activity. During the latter months of pregnancy they
become more frequent and vigorous, and may often be felt by the hand
of the observer applied to the abdomen over the region of the uterus.

The attachment of the embryo to the investing membranes of the egg
is at first by a very short and comparatively wide funnel-shaped con-
nection, consisting of the com-
mencement of the chorion, a part
of the amnion, and an abundant
deposit of gelatinous material
between the two, containing the
stem of the umbilical vesicle.
Subsequently, as the amniotic
cavity enlarges, the body of the
embiyo recedes farther from the
inner surface of the chorion, by
the elongation of its connecting
part ; and this part consequently
begins to present the appearance
of a cord (Fig, 275). It is still
surrounded with a thick layer of
gelatinous matter, by which it is
separated from its amniotic in-
vestment. As it emerges from

the abdomen of the embryo at a" point where the abdominal walls will
afterward close round it, to form the umbilicus, it is known by the

(763)

Fig. 275.

HUMAN EMBRYO AND ITS MEM-
BRANES, in the early period of gestation;
showing the commencement of formation of
the umbilical cord.

764

DISCHARGE OF FCETUS AND PLACENTA.

name of the umbilical cord. It contains the bloodvessels passing out
from the body of the embryo to the chorion and placenta.

After the third month the umbilical cord and its bloodvessels elongate
even more rapidly than is required by the increase in size of the amniotic
cavity. They consequently assume a twisted form, the two umbilical
arteries winding round the vein in a spiral direction.

The direction of the spiral is not always the same. Prof. McLane
has recorded observations made in regard to this point upon 260 um-
bilical cords at term, partty in his private practice and partly at the
Nursery and Child's Hospital, New York. Of this number, in 138
cases the direction of the spiral was from left to right ; in 112 cases,
from right to left; and in the 10 remaining instances it was doubtful,
the twist being too imperfectly marked for decision. This gives nearly
the following percentage as the result of all the observations :

DIRECTION OF THE SPIRAL TWIST OF THE HUMAN UMBILICAL CORD.

From left to right 53 per cent.

From right to left 43 "

Indeterminate 4 "

Fig. 276.

100

There is, accordingly, no
marked preponderance in fre-
quency of the twist in either
direction. Two cases of twins
are included in the above list ;
in the first of which both um-
bilical cords turned from right
to left ; in the second, one of
them turned from right to left,
the other from left to right.
In two instances, the cord
presented turns in opposite
directions in different parts of
its length.

The gelatinous matter, al-
ready described as existing
between the amnion and cho-
rion, and which disappears
elsewhere, accumulates, on
the contrary, in the cord in
considerable quantity, cover-
ing the vessels with a thick,
elastic envelope, which protects them from accidental compression or
obliteration. The whole is covered by an extension of the amnion,
which is continuous at one extremity with the integument of the abdo-
men, and invests the cord with an uninterrupted sheath, like the finger
of a glove.

PREGNANT HUMAN UTERUS AND ITS
CONTENTS, about the end of the seventh month ;
showing the relations of the cord, placenta, and
membranes.— 1. Decidua vera. 2. Decidua reflexa.
3. Chorion. 4. Amnion.

DISCHARGE OF FCETUS AND PLACENTA. 765

The cord also contains, for a certain period, the pedicle or stem of
the umbilical vesicle. The situation of this vesicle, necessarily, is
always between the chorion and the amnion. Its pedicle gradually
elongates with the growth of the umbilical cord ; and the vesicle itself,
which generally disappears soon after the third month,, sometimes re-
mains as late as the fifth, sixth, or seventh. According to Mayer, it
may even be found, by careful search, at the termination of pregnancy.
In the middle and latter periods of gestation, it presents itself as a
small, flattened vesicle, situated beneath the amnion, at a variable dis-
tance from the insertion of the umbilical cord. A minute bloodvessel
is often seen running to it from the cord, and ramifying upon its
surface.

The decidua reflexa, during the latter months of pregnancy, is con-
stantly distended by the increasing size of the egg, and finally pressed
against the opposite surface of the decidua vera. By the end of the
seventh month, the decidua vera and reflexa are in contact, though still
distinct and capable of being easily separated. After that time, they
become confounded with each other, forming at last only a single, thin,
friable, semi-opaque layer, in which no trace of glandular structure can
be discovered.

This is the condition of things at the termination of pregnancy.
Then, the time having arrived for parturition to take place, the hyper-
trophied muscular walls of the uterus contract upon its contents, and
the egg is discharged, together with the decidual membrane.

In the human species, as well as in most quadrupeds, the membranes
of the egg are usually ruptured during the process of parturition ; and
the foetus escapes first, the placenta and the rest of the appendages fol-
lowing a few moments afterward. Occasionally the egg is discharged
entire, and the foetus afterward liberated by the laceration of the mem-
branes. In each case the mode of separation and expulsion is essen-
tially the same.

The process of parturition, therefore, consists in a separation of the
decidual membrane, which, on being discharged, brings away the ovum
with it. The greater part of the decidua. vera, having fallen into a
state of atrophy during the latter months of pregnancy, is by this time
nearly destitute of vessels, and separates without perceptible hemor-
rhage. That portion which enters into the formation of the placenta is,
on the contrary, excessively vascular; and when the placenta is sepa-
rated, and its maternal vessels torn off at their insertion, a gush of
blood takes place, which accompanies or immediately follows the birth
of the foetus. This hemorrhage, which occurs at the'time of parturition,
does not come immediately from the uterine vessels. It consists of
blood which was contained in the placental sinuses, and which is ex-
pelled from them owing to the compression of the placenta by the
muscular walls of the uterus. Since the whole amount of blood thus
lost was previously employed in the placental circulation, and since the
placenta itself is thrown off at the same time, no unpleasant effect is-

766 DISCHARGE OF FCETUS AND PLACENTA.

produced upon the mother by such a hemorrhage, because the propor-
tion of blood in the rest of the vascular system remains the same.
Uterine hemorrhage at the time of delivery becomes injurious only
when it continues after complete separation of the placenta ; in which
case it is supplied by the mouths of the uterine vessels, left open by
failure of the uterine contractions. These vessels, in natural parturi-
tion, are instantly closed, after separation of the placenta, by the con-
traction of the uterine muscular fibres. They pass, as already men-
tioned, in an exceedingly oblique direction, from the uterus to the
placenta; and the muscular fibres, which cross them transversely above
and below, necessarily close their orifices by constriction as soon as
they are thrown into a state of functional activity

Regeneration of the Uterine Tissues after Delivery. — Both the mu-
cous membrane and muscular tissue of the uterus, which are the seat
of an unusual growth during pregnancy, are afterward replaced by
corresponding tissues of new formation. The mucous membrane, or
decidua, is discharged at the time of delivery ; and the hypertrophied
muscular tissue, which has served its purpose in the expulsion of the
foetus, undergoes soon afterward a process of retrogression and atrophy.

A remarkable phenomenon connected with the renovation of the ute-
rine tissues, is the appearance in the uterus, during pregnancy, of a
new mucous membrane, growing underneath the old, and ready to take
the place of the latter after its discharge.

If the internal surface of the body of the uterus be examined imme-
diately after parturition, it will be seen that at the spot where the pla-
centa was attached, every trace of mucous membrane has disappeared.
The muscular fibres of the uterus are here exposed and bare ; while the
mouths of the ruptured uterine sinuses are also visible, with their thin
edges hanging into the cavity of the uterus, and their orifices plugged
with bloody coagula.

Over the rest of the uterine surface the decidua vera has also disap-
peared. Here, however, notwithstanding the loss of the original mucous
membrane, the muscular fibres are not perfectly bare, but °re covered
with a semi-transparent film, of whitish color and soft consistency.
This film is an imperfect mucous membrane of new formation, which
begins to be produced, underneath the old decidua vera, as early as
the beginning of the eighth month. We have seen this very dis-
tinctly in the uterus of a woman who died undelivered at the above
period. The old mucous membrane, or decidua vera, is at this time
somewhat opaque, and of a slightly yellowish color, owing to partial
fatty degeneration. It is easily separated from the subjacent parts,
on account of the atrophy of its vascular connections ; and the new
mucous membrane, situated beneath it, is distinguishable by its fresh
color and semi-transparent aspect.

The mucous membrane of the cervix uteri, which takes no part in
the formation of the decidua, is not thrown off in parturition ; and after

DISCHARGE OF FCETUS AND PLACENTA.

767

MUSCULAR FIBRES OF THE UNIMPREG-
NATED HUMAN UTERUS; from a woman aged
40, dead of phthisis pulmonaiis.

Fig. 278.

delivery it may be seen to ter- Fig. 277.

minate at the os intern um by
an uneven, lacerated edge,
where it was formerly contin-
uous with the decidua vera.

Subsequent!}', a regeneration
of the mucous membrane takes
place over the whole extent of
the body of the uterus. The
mucous membrane of new for-
mation, which is already in
existence at the time of de-
livery, becomes thickened and
vascular ; and glandular tu-
bules are gradually developed
in its substance. At the end of
two months after delivery, ac-
cording to Longet1 and Heschl,2
it has regained the natural
structure of uterine mucous
membrane. It unites at the os
interum, by a linear cicatrix,
with the mucous membrane of
the cervix, and the traces of
laceration at this spot after-
ward cease to be visible. At
the point, however, where the
placenta was attached, the re-
generation of the mucous mem-
brane is less rapid ; and a cica-
trix-like spot is often visible
at this situation for several
months after delivery.

The corresponding change
in the muscular tissue of the
uterus consists in the fatty de-
generation of its fibres. The

muscular fibres of the unimpregnated uterus are pale, flattened, spindle-
shaped bodies (Fig. 277), homogeneous or faintly granular in appear-
ance, and measuring about 50 mmm. in length. During gestation these
fibres increase considerably in size. Their texture becomes more dis-
tinctly granular, and their outlines more strongly marked. An oval
nucleus also shows itself in the central part of each fibre. The entire

MUSCULAR FIBRES OF THE HUM.
RUS, ten days after parturition; from f
dead of puerperal fever.

UTE-
woman

1 Traitfc de Physiologic. Paris, 1850, G6n6ration, p. 173.

2 Zeitschrift der K. K. Gesellschaft der Aerzte, in Wien, 1852.

768

DISCHARGE OF FCBTUS AND PLACENTA.

Fig. 279.

walls of the uterus, at the time of delivery, are composed of such mus-
cular fibres, arranged in circular, oblique, and longitudinal bundles.

About the end of the first week after delivery, these fibres begin to
undergo a fatty degeneration. (Fig. 278.) Their granules become larger
and more prominent, and soon assume the appearance of fat granules,
deposited in the substance of the fibre. The deposit, thus commenced,

increases in abundance, and
the granules continue to en-
large until they become con-
verted into fully formed fat
globules, which fill the interior
of the fibre more or less com-
pletely, and mask, to a certain
extent, its anatomical charac-
ters. (Fig. 279.) The fatty
degeneration, thus induced,
gives to the uterus a softer
consistency, and a pale yellow-
ish color which is characteristic
of this period. The altered
muscular fibres are afterward
absorbed, and gradually give
place to others of new forma-
tion, which already begin to
show themselves before the
old ones have disappeared.

The process finally results in a complete renovation of the muscular
substance of the uterus. The organ becomes again reduced in size, com-
pact in tissue, and of a pale ruddy hue, as in the unimpregnated con-
dition. The entire renewal or reconstruction of the uterus is completed,
according to Heschl, about the end of the second month after delivery

MUSCULAR FIBRES OF HUMAN UTERUS^
three weeks after parturition; from a woman dead
of peritonitis.

CHAPTEE XIV.

Fig. 280.

DEVELOPMENT OF THE NERVOUS SYSTEM, ORGANS
OF SENSE, SKELETON, AND LIMBS.

THE first trace of the cerebro-spinal axis in the embryo consists of the
two longitudinal folds of the external blastoderraic layer, which include
between them the median furrow, known as the " medullary groove"
(page 724). The two folds, after uniting by their corresponding edges
on the median line, over the back of the embryo,
convert the groove into a canal, the " medullary
canal ;" and it is within this canal that the cerebro-
spinal axis is formed.

The mode of its formation is by the growth of
nervous matter upon the inner surface of the medul-
lary canal ; and this canal, which becomes the cerebro-
spinal canal, is accordingly lined with a secondary
internal sheath of nervous matter, which also has
the form of a tubular membranous canal, with a. con-
tinuous central cavity. This is the cerebro-spinal
axis, which thus forms a hollow cylindrical cord of
nervous matter, running in a longitudinal direction
within the cerebro-spinal canal. Anteriorly it ex-
pands into a bulbous enlargement corresponding to
the brain. Its middle portion, constituting the spinal
cord, is nearly cylindrical ; and posteriorly, at its
caudal extremity, it terminates by a pointed enlarge-
ment.

The next change which shows itself is a division of the anterior bul-
bous enlargement into three secondary compartments or vesicles, par-
tially separated from each other by incomplete transverse constrictions.
These are known as the cerebral vesicles, from which the different parts
of the encephalon are afterward to be developed. The first or most
anterior vesicle is destined to form the hemispheres ; the second or
middle, the tubercula quadrigemina ; the third, or posterior, the medulla
oblongata. All three vesicles are still hollow, and their cavities com-
municate freely with each other through the intervening orifices.

Very soon the anterior and posterior cerebral vesicles undergo a fur-
ther division, the middle one remaining undivided. The anterior vesicle
thus separates into two portions, of which the first, or larger, consti-
tutes the hemispheres, while the second, or smaller, becomes the optic

(769)

Formation of the

CEREBRO-SriNAL

Axis. — a, b. Spinal
cord c. Cephalic ex-
tremity, d. Caudal
extremity.

770

DEVELOPMENT OF THE NERVOUS SYSTEM.

thalami. The third vesicle also separates into two portions, of which
the anterior becomes the cerebellum, the posterior the medulla oblongata.

Fig. 281.

Fig. 282.

*

FOJTAL PlG, 1§ centimetre long, showing the condition
of the brain and spinal cord.— 1. Hemispheres. 2. Tubercula
quadrigemina. 3. Cerebellum. 4. Medulla oblongata.

There are, therefore, at this time five cerebral
vesicles, all of which communicate with each
other and with the central cavity of the spinal
cord. The entire cerebro-spinal axis also be-
comes strongly curved in an anterior direction,
corresponding with the anterior curvature of
the body of the embryo (Fig. 282) ; so that the
middle vesicle, or that of the tubercula quadri-
2. vesicle of the tubercula gemina, occupies a prominent angle at the upper

quadrigemina. 3. Vesicle

Formation of the CERK-

of the medulla oblongata.

part of the encephalon, while the hemispheres and
the medulla oblongata are situated below it, ante-
riorly and posteriorly. At first the relative size of the various parts
of the encephalon is very different from that presented in the adult
condition. The hemispheres are hardly larger than the tubercula quad-
rigemina; and the cerebellum is inferior in size to the medulla oblongata.
Soon afterward, the relative position and volume of the parts begin to
alter. The hemispheres and tubercula quadrigemina grow faster than
the posterior portions of the encephalon ; and the cerebellum becomes
doubled backward over the medulla oblongata. (Fig. 283.) Subse-

Fig. 283.

Fig. 284.

FCETAL P i o, three centimetres long.
— 1. Hemispheres. 2. Tubercula quadri-
gemina. 3. Cerebellum. 4 Medulla ob-
longata.

HEAD OF FCETAL PIG, nine centimetres
long.— 1 Hemispheres. 3. Cerebellum. 4. Me-
dulla oblongata.

quently, the hemispheres enlarge more rapidly, growing upward and
backward, so as to cover both the optic thalami and the tubercula

DEVELOPMENT OF THE NERVOUS SYSTEM. 771

quadrigemina (Fig. 284) ; the cerebellum tending in the same way to
grow backward, and projecting farther in this direction over the medulla
oblongata. The subsequent history of the development of the enceph-
alon is mainly a continuation of the same process ; the relative dimen-
sions of the parts constantly changing, so that the hemispheres become,
in the adult condition (Fig. 285), the largest division of the encephalon.

Fig. 285.

BRAIN OF ADULT PIG. — 1. Hemispheres. 3. Cerebellum. 4. Medulla oblongata.

while the cerebellum is next in size, and covers the upper portion of
the medulla oblongata. The surfaces of the hemispheres and cerebellum,
which are at first smooth, become afterward convoluted ; thus increasing
still farther the extent of their nervous matter. In the human foetus
the cerebral convolutions begin to appear about the beginning of the
fifth month (Longet), and grow deeper and more abundant during the
remainder of foetal life.

The lateral portions of the brain growing at the same time more
rapidly than that on the median line, they project on each side outward
and upward ; and by folding over against each other toward the median
line, they form the right and left hemispheres, separated by the longi-
tudinal fissure. A similar process of growth in the spinal cord results
in the formation of its two lateral halves, and the anterior and posterior
median fissures of the cord. Elsewhere the median fissure is less com-
plete, as, for example, between the two lateral halves of the cerebellum
or those of the medulla oblongata ; but it exists everywhere, and marks
more or less distinctly the division between the two sides of the nervous
centres, produced by the excessive growth of their lateral portions. In
this way the whole cerebro-spinal axis is converted into a double organ,
equally developed upon the right and left sides, and partially divided
by longitudinal median fissures.

Organs of Special Sense.— The eyes are formed by a diverticulum
which grows out on ench side from the first cerebral vesicle. This
diverticulum is at first hollow, its cavity communicating with that of
the hemisphere. Afterward, the passage between the two is filled with
a deposit of nervous matter, and becomes the optic nerve. The globular
portion of the diverticulnm, which is converted into the globe of the
eye, has a thin layer of nervous matter deposited upon its internal sur-

772 DEVELOPMENT OF THE NERVOUS SYSTEM.

face, which becomes the retina ; the rest of its cavity being occupied
by a gelatinous substance, the vitreous body. The crystalline lens is
formed in a distinct follicle, which is an ofl'shoot of the integument, and
becomes partially imbedded in the anterior portion of the eyeball. The
cornea also is originally a part of the integument, and remains some-
what opaque until a late period of development. It becomes nearly
transparent a short time before birth.

The iris is a muscular septum, formed in front of the crystalline lens.
Its central opening, which afterward becomes the pupil, is at first closed
by a vascular membrane, the pupillary membrane, passing across the
axis of the eye. The bloodvessels of this membrane, which are derived
from those of the iris, subsequently become atrophied. They disappear
first from its centre, and recede gradually toward its circumference ;
returning upon themselves in loops, the convexities of which are directed
toward the centre. The pupillary membrane itself finally becomes atro-
phied, following in this retrograde process the direction of its receding
bloodvessels, namely, from the centre outward. It has completely dis-
appeared by the end of the seventh month. (Cruveilhier.)

The eyelids are formed by folds of the integument, which project
from above and below at the situation of the eyeball. They grow so
rapidly during the second and third months that their free margins
come in contact and adhere together, so that at that time they cannot
be separated without some violence. They remain adherent from this
period until the seventh month (Guy), when their margins separate and
they become free and movable. In carnivorous animals (dogs and cats),
the eyelids do not separate from each other until eight or ten days after
birth.

The internal ear is formed in a somewhat similar manner with the
eyeball, by an offshoot from the third cerebral vesicle ; the passage
between them filling up by a deposit of white substance, which becomes
the auditory nerve. The tympanum and auditory meatus are botli
offshoots from the external integument.

Skeleton and Limbs. — At a very early period of development there
appears, immediately beneath the medullary canal, a cylindrical cord,
termed the chorda dorsalis (page 725). It consists of a tubular sheath
containing a mass cf simple cells, closely packed together and united
by adhesive material. It does not become a permanent part of the
skeleton, but is a temporary organ destined to disappear as development
proceeds.

On each side of the chorda dorsalis there is formed a series of rec-
tangular plates, the " primitive vertebrae," a portion of whose substance
is devoted to the formation of muscular tissue, while another portion
becomes the basis for the permanent vertebrae. The latter are de-
posited in the form of cartilaginous plates, which encircle the chorda
dorsalis in a series of rings, corresponding in number with the bodies
of the future vertebrae. The rings increase in thickness from without
inward, encroaching upon the substance of the chorda dorsalis, and

SKELETON AND LIMBS. 773

finally taking its place altogether. The thickened rings, thus solidified
by cartilaginous deposit, become the bodies of the vertebrae ; while their
transverse and articulating processes, with the laminae and spinous pro-
cesses, are formed by outgrowths from the bodies in various directions.

When the union of the dorsal plates upon the median line fails to
take place, the spinal canal remains open at that situation, and presents
the malformation known as spina bifida. This may consist simply in
a fissure of the spinal canal, more or less extensive, in which case it
may sometimes be cured, or may even close spontaneously ; or it may
be complicated with either an imperfect development or complete absence
of the spinal cord at the same spot, producing permanent paralysis of
the lower extremities.

The entire skeleton is at first cartilaginous. The first points of ossifi-
cation show themselves about the beginning of the second month, almost
simultaneously in the clavicle and the lower jaw. Then come, in the
following order, the femur, humerus, and tibia, the superior maxilla, the
bodies of the vertebrae, the ribs, the vault of the cranium, the scapula
and the pelvis, the metacarpus and metatarsus, and the phalanges of the
fingers and toes. The bones of the carpus are all cartilaginous at birth,
and do not begin to ossify until a year afterward. According to Cru-
veilhier, the calcaneum, the cuboid, and sometimes the astragalus, begin
their ossification during the latter periods of foetal life, but the remainder
of the tarsus is cartilaginous at birth. The lower extremity of the
femur, according to the same authority, shows a point of ossification at
birth ; all the other extremities of the long bones being still in a carti-
laginous condition at this time. The scaphoid bone of the tarsus and
the pisiform bone of the carpus are the last to commence their ossifica-
tion, several years after birth. Nearly all the bones ossify from several
distinct points ; the ossification spreading as the cartilage increases in
size, and the various bony pieces, thus produced, uniting with each
other at a later period, usually some time after birth.

The limbs appear by a budding process, as offshoots of the external
blastodermic layer. They are at first mere rounded 'elevations, without
any separation between the fingers and toes, or any distinction between
the different articulations. Subsequently the free extremity of each
limb becomes divided into the phalanges of the fingers or toes ; and
afterward the articulations of the wrist and ankle, knee and elbow,
shoulder and hip, appear successively from below upward.

The lower limbs in man are less rapid in development than the upper.
Both the legs and the pelvis are very slightly developed in the early
periods of growth, as compared with the spinal column, to which they
are attached. The inferior extremity of the spinal column, formed by
the sacrum and coccyx, projects at first beyond the pelvis, forming a
tail, which is curled forward toward the adbomen, and terminates in a
pointed extremity. The entire lower half of the body, with the spinal
column and appendages, is also twisted, from left to right ; so that the
pelvis is not only curled forward, but also faces at right angles to the

774:

DEVELOPMENT OF THE NERVOUS SYSTEM.

Fig. 286.

direction of the head and upper part of the body. Subsequently the
spinal column becomes straighter and loses its twisted form. At the

same time the pelvis and the muscular parts
seated upon it grow so much faster than the
sacrum and coccyx, that the latter become
concealed under the adjoining soft parts,
and the rudimentary tail disappears.

The integument of the embryo is at first
thin, vascular, and transparent. It after-
ward becomes thicker, more opaque, and
whitish in color. Even at birth, however,
it is considerably more vascular than in the
adult condition, and its ruddy color, due to
its transparency and the abundance of its
capillary bloodvessels, is strongly marked.
The hairs begin to appear about the middle
of intra-uterine life; showing themselves
first upon the eyebrows, afterward upon the
scalp, trunk and extremities. The nails are
in process of formation from the third to
the fifth month ; and, according to Kolliker,

are covered with a layer of epidermis until after the latter period. The
sebaceous matter of the cutaneous glandules accumulates upon the skin
after the sixth month, and forms a whitish, semi-solid, oleaginous layer,
the vernix caxeosa, which is most abundant in the flexures of the joints,
between the folds of the integument, behind the ears, and upon the scalp.

HUMAN EMBRYO, about one
month old. Showing the large
Bize of the head and upper parts
of the body; the twisted form of
the spinal column ; the rudiment-
ary condition of the upper and
lower extremities ; and the rudi-
mentary tail at the end of the
spinal column.

CHAPTBE XV.

DEVELOPMENT OF THE ALIMENTAEY CANAL
AND ITS APPENDAGES.

THE intestinal canal is formed, as already described (page 726), from
the internal blastodermic layer which curves downward and inward on
each side, and is thus converted into a cylindrical tube, terminating at
each extremity in a cul-de-sac, and inclosed by the external blastodermic
layer. The abdominal walls do not unite with each other upon the
median line until after the formation of the intestinal canal ; so that,
during a certain period, the abdomen of the embryo is widely open in
front, presenting a long oval excavation, in which the intestinal tube is
situated, running from its anterior to its posterior extremity.

Stomach and Intestine. — The formation of the stomach takes place in
the following manner : The alimentary canal, originally straight, soon
presents two lateral curvatures at the upper part of the abdomen ; the
first to the left, the second to the right. The first of these curvatures
becomes expanded into a wide sac, projecting laterally from the median
line into the left hypochondrium, forming the great pouch of the
stomach. The second curvature, directed to the right, marks the
boundary between the stomach and the duodenum ; and the tube at
that point, becoming constricted and furnished with an unusually thick
circular layer of muscular fibres, is converted into the pylorus. Im-
mediately below the pylorus, the duodenum turns to the left ; and these
curvatures, increasing in num-

ber and complexity, form the con-
volutions of the small intestine.
The large intestine assumes a
spiral curvature ; ascending on
the right side, then crossing
over to the left as the transverse
colon, and again descending on
the left side, to terminate by the
sigmoid flexure in the rectum.

The curvatures of the intes-
tinal canal, which take place in
an antero-posterior, as well as in
a lateral direction, may be best
studied in a profile view, as in
Fig. 287. The abdominal walls
are here still imperfectly closed,

Fig. 287.

Formation of the ALIMENTARY CANAL.—
a, b. Commencement of amnion. c, c. Intestine.
d. Pharynx, e. Urinary bidder. / Allantois
or chorion. g. Umbilical \esicle.

(775)

776 DEVELOPMENT OF THE ALIMENTARY CANAL

leaving a wide opening at a, 6, where the integument of the foetus is
continuous with the commencement of the amniotic membrane. The
intestine makes at first a single angular turn forward, and opposite the
most prominent portion of this angle is to be seen the stem of the um-
bilical vesicle (g). A short distance below this point the intestine sub-
sequently enlarges in calibre, and the situation of this enlargement
marks the commencement of the colon. The two portions of the intes-
tine, after this period, become widely different from each other. The
upper portion, which is the small intestine, grows most actively in
the direction of its length, and becomes a long, narrow, convoluted
tube ; while the lower portion, which is the large intestine, increases
rapidly in diameter, but elongates less than the former. The rectum is
the part of the large intestine which alters least its form and position.
It elongates comparatively little, retains its position for the most part
upon the median line, and as its name indicates, continues to follow a
nearly straight course; presenting only a moderate antero-posterior
curvature corresponding with the hollow of the sacrum, and a slight
lateral obliquity, from its upper portion which is placed a little toward
the left, to the anus which is situated upon the median line. At first
forming the blind extremity of the large intestine, it subsequently com-
municates with the exterior by a perforation which becomes the anus.
In the chick-embryo, according to Burdach,1 the perforation of the anus
appears on the fifth day of incubation ; in the human embryo it is
formed during the seventh week. In certain instances, this opening
fails to take place, and the rectum is still closed at birth; presenting
the malformation known as imperforate anus. If the rectum be other-
wise fully developed, it may sometimes be felt, distended with meconium,
immediately under the integument ; and an artificial opening may be
successfully made by an incision at the anal region. In other cases,
there is also a deficiency, more or less extensive, of the rectum itself,
the large intestine terminating in the upper portion of the pelvic cavity.

At the point of junction between the small and the large intestine, a
lateral diverticulum of the latter shows itself, and increases in extent,
until the ileum seems at last to be inserted obliquely into the side of the
colon. The diverticulum of the colon is at first conical in shape ; but
afterward that portion which forms its free extremity becomes narrow,
elongated, and sometimes twisted upon itself, forming the appendix
vermiformis ; while the remaining portion, which is continuous with the
intestine, becomes exceedingly enlarged, and forms the caput coli.

The caput coli and the appendix vermiformis are at first situated near
the umbilicus ; but between the fourth and fifth months (Cruveilhier)
their position is altered, and they become fixed in the right iliac region.
During the first six months the internal surface of the small intestine is
smooth. At the seventh month, the valvulae conniventes begin to ap-
pear, after which they increase slowly in size, but are still comparatively

1 Trait6 de Physiologie, traduit par Jourdan. Paris, 1838, tome iii. pp. 274, 468.

AND ITS APPENDAGES.

777

Fig. 288.

undeveloped at the time of birth. The division of the colon into sacculi
by longitudinal and transverse bands, is also an appearance which pre-
sents itself only during the last half of foetal life. Previous to that
time, the colon is smooth and cylindrical, like the small intestine.

After the small intestine is formed, it increases rapidly in length. It
grows, at this time, faster than the walls of the abdomen ; so that it
can no longer be contained in the abdominal
cavity, but protrudes, under the form of an
intestinal loop, or hernia, from the umbilical
opening. (Fig. 288.) In the human em-
bryo, this protrusion of the intestine can be
readily seen during the latter part of the
second month. At a subsequent period,
the walls of the abdomen grow more rapidly
than the intestine ; and, gradually envelop-
ing the hernial protrusion, at last reinclose
it in the cavity of the abdomen.

Owing to imperfect development of the
abdominal walls, and incomplete closure of
the umbilicus, the intestinal protrusion,
which is normal during the early stages of
foetal life, sometimes remains at birth, and
thus produces congenital umbilical hernia.
As the parts at this time have a natural
tendency to unite with each other, if the
hernial protrusion be returned within the abdomen, and retained by
simple pressure for a sufficient period, the defect is usually remedied,
and a permanent cure effected. The conditions are different in a hernia
in the adult, where it is due to pressure from within, and a gradual
yielding of the fibrous tissues. As the natural period for the closure
of the abdominal orifices has passed, the intestine may be retained
within the abdomen, in such cases, by mechanical means, but usually
escapes again when the pressure is taken off.

The contents of the intestine, which accumulate during foetal life, vary
in different parts of the alimentary canal. In the small intestine they
are semifluid in consistency, of a light yellowish or grayish-white color
in the duodenum, yellow, reddish-brown, and greenish-brown below. In
the large intestine they are dark greenish and pasty in consistency ;
and the contents of this portion of the alimentary canal have received
the name of meconium, from their resemblance to inspissated poppy-
juice. The meconium contains a large quantity of fat, as well as various
insoluble substances, probably the residue of epithelial and mucous
accumulations. It does not exhibit any trace of the biliary substances
proper (taurocholates and glycocholates) when examined by Petteni-
kofer's test ; and cannot therefore be regarded as resulting from the
accumulation of bile. In the contents of the small intestine, on the
contrary, according to Lehmann, slight traces of bile may be found, as
50

FCETAL Pio, showing the pro.
truding loop of intestine, forming
umbilical hernia; from a speci-
men in the author's possession.
From the convexity of the loop a
thin filament ia seen passing to
the umbilical vesicle, which, in
the pig, has a flattened, leaf-like
form.

778 DEVELOPMENT OF THE ALIMENTARY CANAL

early as between the fifth and sixth months. We have found distinct
traces of bile in the small intestine at birth, but it is even then in ex-
tremely small quantity, and is sometimes altogether absent.

The meconium, therefore, and the intestinal contents generally, are
not composed principally, or even to any measurable extent, of the
secretions of the liver. They appear rather to be derived from the
mucous membrane of the intestine. Even their yellowish and greenish
color does not depend on the presence of bile, since the yellow color
first shows itself about the middle of the small intestine, and not at its
upper extremity. The material which afterward accumulates appears
to extend from this point upward and downward, gradually filling the
intestine, and becoming, in the ileum and large intestine, darker colored
and more pasty as gestation advances.

It is, perhaps, of some importance in this connection, that the amni-
otic fluid, during the latter half of foetal life, finds its way, in greater or
less abundance, into the stomach, and through that into the intestinal
canal. Small cheesy-looking masses are sometimes to be found at birth
in the fluid contained in the stomach, which are seen on microscopic
examination to be portions of the vernix caseosa exfoliated from the
skin into the amniotic cavity, and afterward introduced through the
oesophagus into the stomach. According to Kolliker, the downy hairs
of the foetus, exfoliated from the skin, are often swallowed in the same
way, and may be found in the meconium.

The gastric juice is not secreted before birth ; the contents of the
stomach being generally in small quantity, clear, nearly colorless, and
neutral or alkaline in reaction.

Liver. — The liver is developed at a very early period. Its size in
proportion to that of the entire body is much greater in the early
months than at birth or in the adult condition. In the foetal pig we
have found, the relative size of the liver greatest within the first month,
when it amofliits to nearly 12 per cent of the entire weight of the body.
Afterward it grows less rapidly than other parts, and its relative
weight diminishes successively to 10 per cent, and 6 per cent.; being
reduced before birth to 3 or 4 per cent. In man, also, the weight of
the liver at birth is between 3 and 4 per cent, of that of the entire
body.

The glycogenic function of the liver commences during foetal life,
and at birth the tissue of the organ is abundantly saccharine. In the
early periods of gestation, however, sugar is produced in the foetus from
other sources than the liver. In very young foetuses of the pig, both
the allantoic and amniotic fluids are saccharine a considerable time
before glucose makes its appearance in the liver. Even the urine, in
half-grown foetal pigs, contains an appreciable quantity of sugar, and
the young animal is normally, at this period, in a diabetic condition.
The glucose disappears before birth, as shown by Bernard,1 from both

1 LeQons de Physiologie ExpSrimentale. Paris, 1855, p. 398.

AND ITS APPENDAGES. 779

the urine and the amniotic fluid ; while the liver begins to produce the
saccharine substance which it contains after birth.

Lungs, Thoracic Cavity, and Diaphragm. — The anterior portion of
the alimentary canal, which occupies the region of the neck, is the
oesophagus. It is straight, and, at first, very short ; but it subsequently
increases in length, simultaneously with the growth of the neighboring
parts. As the oesophagus lengthens, the lungs begin to be developed
by a protrusion from the anterior portion of the oesophagus, represent-
ing the commencement of the trachea. This protrusion soon divides
into two symmetrical branches, which themselves elongate and become
repeatedly subdivided, forming the bronchial tubes and their ramifica-
tions. At first, the lungs project into the upper part of the abdominal
cavity ; for there is still no distinction between the chest and abdomen.
Afterward, a horizontal partition begins to form on each side, at the
level of the base of the lungs, which gradually closes together to form
the diaphragm, and which finally shuts off the cavity of the chest from
that of the abdomen. Before the closure of the diaphragm is com-
plete, an opening exists by which the peritoneal and pleural cavities
communicate with each other. In some instances the development of
the diaphragm is arrested at this point, either on one side or the other,
and the opening remains permanent. The abdominal organs then par-
tially protrude into the cavity of the chest on that side, forming con-
genital diaphragmatic hernia. The lung on the affected side usually
remains in a state of imperfect development. Diaphragmatic hernia of
this character is more frequently found upon the left side than upon
the right, and may sometimes continue until adult life without causing
serious inconvenience.

Urinary Bladder and Urethra. — Soon after the formation of the
intestine a vascular outgrowth takes place from its posterior portion,
which gradually protrudes from the open walls of the abdomen, until it
comes in contact with the external investing membrane of the egg
(Fig. 287, f)] forming subsequently, by its continued growth and ex-
pansion, the allantois in the lower animals, the chorion in man.

The chorion, in the portion immediately connected with the body of
the embryo, has, like the allantois, the form of a hollow canal ; but as
it spreads out, to constitute the external investment of the egg, it takes
the shape of a continuous membrane, forming the chorion proper
(p. 746). The tubular cavity of its connecting portion, the umbilical
cord, subsequently becomes obliterated ; the obliteration commencing
at its outer extremity and gradually proceeding inward until it reaches
the umbilicus. Inside the umbilicus it still proceeds for a certain dis-
tance and then ceases. Thus the original protrusion of the intestinal
canal within the abdomen, which gave rise to the allantois and the cho-
rion, is divided into two portions. The first portion, or that imme-
diately connected with the intestine, remains hollow, and forms after-
ward the urinary bladder. The second portion, between the urinary

780 DEVELOPMENT OF THE ALIMENTARY CANAL

bladder and the umbilicus, is consolidated into a rounded cord, which
is termed the urachus.

The urinary bladder is at first, accordingly, a pyriform ' sac (Fig.
287, e), communicating at its base with the lower portion of the intes-
tinal canal, and continuous by its superior pointed extremity with the
solid cord of the urachus, by means of which it is attached to the inter-
nal surface of the abdominal walls at the situation of the umbilicus.
Afterward, the bladder loses this conical form, and its superior fundus
becomes in the adult rounded and bulging.

Development of the Mouth and Face — The intestinal canal is at first
a cylindrical tube, closed at its anterior as well as at its posterior
extremity. In the region of the abdomen, which in the earliest periods
of development constitutes nearly the whole length of the body, the
blastoderm separates, as previously described (p. 735), into two laminae,
an outer and an inner. The outer lamina, consisting of the external
integument and the subjacent voluntary muscles, forms the parietes of
the abdomen. The inner lamina forms the mucous membrane of the
alimentary canal, with its covering of involuntary muscular fibres.
Owing to the separation of these two laminae, there is formed the peri-
toneal cavity, between the intestine on the one side and the abdominal
walls on the other.

But in the anterior part of the body of the embryo, this separation
between the two laminae of the blastoderm does not take place. Con-
sequently, the corresponding portion of the alimentary canal, namely,
the oesophagus, remains in contact with the surrounding parts ; and its
anterior rounded extremity, the pharynx (Fig. 287, d), lies immediately
underneath the head, covered in front only by the tissues of the external
blastodermie layer.

At this time there are formed, on the sides and front of the neck, four
nearly transverse fissures, the cervical fissures, leading from the exte-
rior into the cavity of the pharynx. These fissures, or clefts, are analo-
gous to those which exist permanently at the same situation in fishes,
where the gills are located, and by which the water, taken in at the
mouth, is expelled through the sides of the neck. But in the mamma-
lian embryo they have only a temporary existence as continuous open-
ings. The three lower fissures disappear entirely by the subsequent
adhesion of their adjacent edges ; and in the chick, according to Foster
and Balfour, are completely closed by the seventh day of incubation.
The upper fissure is converted into a narrow canal, leading from the
exterior into the pharynx, but closed about its middle by a transverse
partition. The outer portion of this canal becomes the external audi-
tory meatus ; the inner portion, the Eustachian tube. The transverse
partition is the membrana tympani.

The cervical fissures in man are especially connected with the forma-
tion of the mouth and face. Between the fissures there are, of course,
bands or ridges of solid tissue, belonging to the external lamina of the
blastoderm; and these bands, especially the upper, increase in growth to

AND ITS APPENDAGES. 781

such an extent that they become more or less prominent folds, and have
received the name of the " visceral folds." The first visceral fold grows
rapidly forward, and divides into two somewhat diverging processes or
offshoots, which continue to become more and more prominent. The
corresponding processes from the right and left sides tend to approach
each other, and to unite upon the median line. Those of the lower pair
do so unite, and thus form the inferior maxilla. Those of the tipper
pair, which form the superior maxilla, unite, not with each other, but
with an intervening process which grows from above downward, upon
the median line, between them.

By this growth of folds or processes in an anterior direction, and by
their union, above and below, upon the median line, there is included
between them a depressed space, lined with a continuation of the exter-
nal blastodermic layer, and situated immediately in front of the extremity
of the pharynx. This excavation is the cavity of the mouth, inclosed
on each side by the processes of the superior and inferior maxillae, widely
open in front, but terminating at its bottom by a blind pit ; there being
as yet no communication between it and the interior.

Subsequently an opening is formed between the bottom or back part
of the mouth and the cavity of the pharj-nx, by a perforation through
the substance of both blastodermic layers at that point. This perfora-
tion takes place in the human embryo, according to Burdach,1 during
the sixth week. The opening thus formed marks the situation of the
fauces; and the alimentary canal is thus made to communicate with
the exterior. The lining membrane of the mouth is consequently de-
rived from the external blastodermic layer, is a continuation of the
external integument, and the muscles sur-
rounding it are voluntary muscles ; while the Fig. 289.

mucous membrane of the pharynx and oeso-
phagus is derived from the internal blasto-
dermic layer, and is surrounded by involun-
tary muscles.

The completion of the component parts
of the face about the mouth is accomplished
by the continuous development of the five
buds or processes, above described, which
grow together in such a way as to diminish
the size of the originally wide oral orifice, HUMAN EMBRYO, about one
and to modify its form in various directions, month old: showing the growth

/TT c\nf\ \ mi T of the frontal process downward,

(Fig. 289.) The process which grows di- and that of th; 8uperior anrt in!
rectly downward in the median line from the ferior maxillary processes from
frontal region, is called the frontal or inter- ^ .2SET" '" '"
maxillary process, because it afterward con-
tains, in its lower extremity, the intermaxillary bones, with the four
upper incisor teeth. The superior maxillary processes, coming from

1 TraitS de Physiologic ; traduit par Jourdan. Paris, 1838, tome iii. p. 468.

782

DEVELOPMENT OF THE ALIMENTARY CANAL

Fi<r. 290.

the sides, unite with the intermaxillary process, to form the upper jaw.
In quadrupeds the intermaxillary bones, containing the upper incisor
teeth, remain distinct from those of the superior maxilla, the line of
demarcation between them being indicated by a suture. In man, as a
general rule, they are consolidated with each other, the only permanent
suture being that on the median line, between the right and left halves
of the upper jaw. According to Geoffroy Saint-Hilaire,1 a permanent line
of suture sometimes remains between the intermaxillary and the superior
maxillary bones.

The two inferior maxillary processes unite with each other, making
the lower border of the cavity of the mouth, and form, by their union
upon the median line, the inferior maxilla. In quadrupeds the two

inferior maxillary bones remain perma-
nently divided by a median suture; but in
man they are consolidated into a single
piece during the first year after birth.

As the intermaxillary process grows
from above downward, it becomes double
at its lower extremity, and at the same
time gives origin to two lateral offshoots,
which curl round and inclose two circular
orifices, the anterior nares (Fig. 290); the
offshoots themselves becoming the alse
nasi. The external border of the ala nasi
subsequently adheres to the superior maxil-
lary process, leaving only a curved crease
or furrow at the side of the nose, which

marks the line of union between them. In many of the quadrupeds,
this furrow remains partially open, extending, as a curvilinear cleft, out-
ward and upward from the orifice of the nostril.

The mouth at this time is wide and gap-
ing, owing to the incomplete development
of the upper and lower jaw and the com-
parative insufficiency of the lips and
cheeks. The soft parts afterward increase
in growth, and thus gradually diminish
the size of the oral orifice (Fig. 291). The
lips and cheeks arise by folds of the in-
tegument and subjacent muscular layers,
which, projecting respectively from above
downward, from below upward, and from
behind forward, form the permanent bor-
ders of the opening of the mouth. The
upper lip in man presents a median furrow,
possession. bordered by two slightly elevated ridges,

HEAD OP HUMAN EMBRYO
at about the sixth week. From a
specimen in the author's possession.

1 Histoire des Anomalies de 1'Organization. Paris, 1832, tome i. p. 581.

AND ITS APPENDAGES. 783

corresponding with the union of the superior maxillary and the inter-
maxillary processes. The lower lip, like the inferior maxilla, is com-
pletely consolidated upon the median line, and usually shows no trace
of its double origin.

In some instances, the superior maxillary and the intermaxillary
processes fail to unite with each other, giving rise to the malformation
known as hare-lip. The fissure, in cases of hare-lip, is consequently
situated, as a general rule, not in the median line, but a little to one
side of it, corresponding with the outer edge of the intermaxillary pro-
cess. Sometimes the same deficiency exists on both sides, forming
u double hare-lip ;" in which case, if the fissure extend through the bony
structures, the central piece of the superior maxilla, detached from the
remainder, contains the upper incisor teeth, and corresponds with the
intermaxillary bone of the lower animals. In one instance, observed
by Wyman,1 the fissure of hare-lip was situated in the median line, the
two intermaxillary bones not having united with each other.

The eyes at an early period are upon the sides of the head (Fig. 289).
As development proceeds, they come to be situated farther forward
(Fig. 290), their axes being divergent and directed obliquely forward
and outward. At a still later period they are placed on the anterior
plane of the face (Fig. 291), and have their axes nearly parallel and
looking directly forward. This change in situation is effected by the
more rapid growth of the posterior and lateral portions of the head,
which enlarge in such a manner as to alter the relative position of the
parts seated in front.

The palate is formed by a septum between the mouth and nares,
which arises on each side as a horizontal offshoot from the superior
maxilla. The two plates afterward unite upon the median line, forming
a complete partition between the oral and nasal cavities. The right
and left nasal passages are separated from each other by a vertical
plate (vomer), which grows from above downward and fuses with the
palatal plates below. Fissure of the palate is caused by a deficiency
of one of the horizontal maxillary plates. It is accordingly situated a
little on one side of the median line, and is frequently associated with
hare-lip and fissure of the upper jaw. The fissures of the palate and of
the jaw are often continuous with each other.

The anterior and posterior arches of the palate are incomplete trans-
verse partitions which grow inward from the sides of the fauces, subse-
quently to the perforation of the pharynx and its communication with
the oral cavity. Owing to the muscular tissue which the}^ contain, the
orifice of the alimentary canal thus becomes capable of constriction or
enlargement, according to its condition of functional activity.

1 Transactions of the Boston Society for Medical Improvement, March 9th, 1863.

CHAPTEK XVI.

DEVELOPMENT OF THE WOLFFIAN
NEYS, AND INTERNAL ORGANS
TION.

BODIES, KID-
OF GENERA-

THE first trace of a urinary apparatus in tho embryo consists of two
long, fusiform organs, which make their appearance in the abdomen at
a very early period, one on each side the spinal column, and which are
known by the name of the Wolffian bodies. They are fully formed, in
the human subject, toward the end of the first month (Coste), at which
time they are the largest organs in the abdomen, extending from just
below the heart, nearly to the posterior extremity of the body. In the
foetal pig, when thirteen or fourteen millimetres in length, the Wolffian
bodies are rounded and kidney-shaped, and oc-
cupy a large part of the abdominal cavity. Their
combined weight is at this time a little over 3 per
cent, of that of the entire body ; a proportion
which is seven or eight times as large as that of
the kidneys in the adult condition. There are,
indeed, at this period only three organs of no-
ticeable size in the abdomen, namely, the liver,
which has begun to be formed at the upper part
of the abdominal cavity ; the intestine, which is
already somewhat convoluted, and occupies a
central position ; and the Wolffian bodies, which
project on each side the spinal column.

The Wolffian bodies, in their intimate structure,
closely resemble the adult kidney. They consist
of secreting tubules, lined with epithelium, run-
ning transversely from the inner to the outer edges
of the organs, and terminating at their extremities by rounded dilata-
tions. Into each of these dilated extremities is received a globular coil
of capillary bloodvessels, or glomerulus, similar to those of the kidney.
The tubules of the Wolffian body empty into a common excretory duct,
which leaves the organ at its lower extremity, and communicates with
the intestinal canal, at the point where the diverticulum of the allantois
is given off, and where the urinary bladder is afterward to be situated.
The principal distinction in structure, between the Wolffian bodies and
the kidneys, consists in the size of the tubules and of their glomernli ;
these elements being considerably larger in the Wolffian body than in

PIG, 13 milli-
metres long; from a spe-
cimen in the author's pos-
session.—1. Heart. 2. An-
terior limb. 3. Posterior
limb. 4. Wolffian body.
The abdominal walls have
been cut away, in order
to show the position of
the Wolfflan bodies.

the kidney. In the
( 784 )

foetal pig, when 3j or 4 centimetres in length,

DEVELOPMENT OF THE WOLFFIAN BODIES, ETC. 785

at which time both organs coexist, the diameter of the tubules of the
Wolffian body is 0.125 millimetre, while in the kidney of the same foetus,
the diameter of the tubules is only 0.034 millimetre. The glomeruli in
the Wolffian bodies measure 0.55 millimetre in diameter, while those of
the kidney measure only 0.14 millimetre. The Wolffian bodies are there-
fore urinary organs, so far as regards their anatomical structure, and
are sometimes known by the name of the " false kidneys." There is
little doubt that they perform, at this early period, a function analogous
to that of the kidneys, and separate from the blood of the embryo an
excrementitious fluid which is discharged into the cavity of the allantois.

Subsequently, the Wolffian bodies increase for a time in size, though
not so rapidly as the other organs. Their relative magnitude con-
sequently diminishes. Still later, they suffer an absolute atrophy, and
become gradually less perceptible. In the human embryo, they are
hardly to be detected after the end of the second month (Longet), and
in the quadrupeds they completely disappear long before birth.

The kidneys are formed just behind the Wolffian bodies, and are at
first entirely concealed by them in a front view, the kidneys being at
this time not more than one-fourth or one-fifth part the size of the
Wolffian bodies. (Fig. 293.) The kidneys
subsequently enlarging, while the Wolffian
bodies diminish, the proportion between the
two organs is reversed ; and the Wolffian
bodies appear as small rounded masses, sit-
uated on the anterior surface of the kidneys.
(Figs. 294 and 295). The kidneys, during
this period, grow more rapidly in an upward
than in a downward direction, so that the
Wolffian bodies come to be situated near
their inferior extremity.

The kidneys, during the succeeding pe-
riods of foetal life, become in turn very largely
developed in proportion to the rest of the author's possession.— i. Woif-
internal organs ; attaining a size, in the foetal fian body> 2> Kidney-
pig, equal to more than two per cent, in weight of the entire body.
This proportion again diminishes before birth, owing to the increased
development of other parts. In the human foetus at birth, the weight
of the two kidneys, taken together, is 6 parts per thousand of that of
the entire body.

Internal Organs of Generation. — About the same time that the kid-
neys are formed behind the Wolffian bodies, two oval-shaped organs
make their appearance in front, on the inner side of the Wolffian bodies
and between them and the spinal column. These bodies are the inter-
nal organs of generation ; namely, the testicles in the male, and the
ovaries in the female. At first they occupy the same situation and
present the same appearance, whether the foetus is afterward to be
male or female. (Fig. 294.)

786 DEVELOPMENT OF THE WOLFFIAN BODIES, ETC.

A short distance above the internal organs of generation there com-
mences, on each side, a narrow tube which runs from above downward

along the anterior border of the Wolffian body,

Fig. 294. immediately in front of, and parallel with

the excretory duct of this organ. The two
tubes then approach each other below ; and,
joining upon the median line, einpt}', together
with the ducts of the Wolffian bodies, into
the base of the allantois, or what will after-
ward be the urinary bladder. These tubes
serve as the excretory ducts of the internal
organs of generation ; and will afterward be-
come the vasa deferentia in the male, and

INTERNAL ORGAN a OP ., .„ ,, . , . ,, ,, -•

GENERATION, in a foetal pig the Fallopian tubes m the female. Accord-
iy2 centimetres long. From a ing to Coste, the vasa deferentia at an early

specimen in the author's pos- , -, .,, ., ,. -,

session - 1, i. Kidneys. 2, 2. period are disconnected with the testicles ;
Wolffian bodies. 3,3 internal and originate, like the Fallopian tubes, by
or^i>efsgerruHnarytbSildCder free extremities, presenting each an open
turned over in front. 5. intea- orifice. Afterward the vasa deferentia be-
come adherent to the testicles, and establish

a communication with the tubuli seminiferi. In the female, the Fallo-
pian tubes remain permanently disconnected with the ovaries, except by
the edge of the fimbriated extremity ; which in many of the lower ani-
mals becomes closely adherent to the ovary, and envelops it more or
less completely in a distinct sac.

Male Organs of Generation ; Descent of the Testicles. — In the male
foetus there now commences a change of place in the internal organs
of generation, which is known as the u descent of the testicles." Jr.
consequence of this change, the testicles, which are at first placed
near the middle of the abdomen and in front of the kidneys, come at
last to be situated in the scrotum, outside and below the abdominal
cavity. They also become inclosed in a distinct serous sac, the tunica
vaginalis testis. This apparent movement of the testicles is accom-
plished in the same manner as that of the Wolffian bodies, namely, by
a disproportionate growth of the middle and upper portions of the
abdomen and of the tissues above the testicles, so that the relative
position of the organs becomes altered.

By the upward enlargement of the kidneys, both the Wolffian bodies
and the testicles are soon found to occupy an inferior position. (Fig.
295.) At the same time, a slender rounded cord (not represented in the
figure) passes from the lower extremity of each testicle in an outward
and downward direction, crossing the vas deferens a short distance above
its union with its fellow of the opposite side. Below this point, the cord
spoken of continues to run obliquely outward and downward ; and,
passing through the abdominal walls at the situation of the inguinal
canal, is inserted into the subcutaneous tissue near the symphysis pubis.
The lower part of this cord becomes the gubernaculum testis. It con-

DEVELOPMENT OF THE WOLFFIAN BODIES, ETC. 787

Fiir. 295.

INTERNAL ORGANS OF (JKNEBA-
TION in a foetal pi£ nearly 10 centimetres
long. From a specimen in the author's
possession.— 1, 1. Kidneys. 2, 2. Wolffian
bodies. 3, 3. Testicles. 4. Urinary blad-
der. 6. Intestine.

tains muscular fibres, which may be easily detected, in the human foetus,

during the latter half of intra-uterine

life. At the period of birth, however,

or soon afterward, they have usually

disappeared.

That portion of the excretory tube
of the testicle which is situated out-
side the crossing of the gubernaculum,
is destined to become afterward con-
voluted, and converted into the epi-
didymis, That which is situated
inside the same point remains com-
paratively straight, but becomes con-
siderably elongated, and is finally
known as the vas deferens.

As the testicles descend still far-
ther in the abdomen, they continue to
grow, while the Wolffian bodies, on
the contrary, become smaller ; and at
last, when the testicles have arrived at the internal inguinal ring, the
Wolffian bodies have altogether disappeared, or have become so altered
that they are no longer recognizable. In the human foetus, the testicles
reach the internal inguinal ring about the termination of the sixth
month (Wilson).

During the succeeding month, a protrusion of the peritoneum takes
place through the inguinal canal, in advance of the testicle; the last-
named organ still continuing its descent. As it passes into the scrotum,
loops of muscular fibres are given off from the lower border of the in-
ternal oblique muscle of the abdomen, extending downward with the
testicle, upon it and upon the elongating spermatic cord. These con-
stitute afterward the cremaster muscle.

At last, the testicles descend quite to the bottom of the scrotum.
The convoluted portion of the efferent duct, namely, the epididymis,
remains attached to the body of the testicle ; while the vas deferens
passes upward, in a reverse direction, enters the abdomen through the
inguinal canal, again bends downward, and joins its fellow of the oppo-
site side ; after which they both open into the prostatic portion of the
urethra by distinct orifices, situated on either side of the median line.
At the same time, two diverticula arise from the median portion of the
vasa deferentia, and, elongating in a backward direction, beneath the
base of the bladder, become developed into sacculated reservoirs, the
vesiculse seminales.

The left testicle is a littler later in its descent than the right ; but it
afterward passes farther into the scrotum, and, in the adult condition,
usually hangs a little lower than the corresponding organ on the oppo-
site side.

After the testicle has passed into the scrotum, the serous pouch,

788 DEVELOPMENT OF THE WOLFFIAN" BODIES, ETC

Fig. 296.

Formation of the TUNICA
VAGINALIS TRSTIS.— 1.
Testicle nearly at the bottom
of the scrotum. 2. Cavity of
tunica vaginalis. 3. Cavity of
peritoneum. 4. Obliterated
neck of peritoneal sac.

which preceded its descent, remains for a time in communication with
the peritoneal cavity. In many of the quadrupeds, as, for example, the
rabbit, this condition is permanent ; and the testicle may be alternately
drawn downward into the scrotum, or retracted
into the abdomen, by the action of th& guber-
naculum and the cremaster muscle. In the
human foetus, the two opposite surfaces of the
peritoneal pouch approach each other at the
inguinal canal, forming at that point a con-
striction, which partly shuts off the testicle
from the cavity of the abdomen. By a con-
tinuation ot this process, the serous surfaces
come in contact, and, adhering together at
this situation (Fig. 296, 4), form a kind of
cicatrix, by which the cavity of the tunica va-
ginalis (2) is shut off from the general cavity
of the peritoneum(s). The tunica vaginalis
testis is, therefore, originally a part of the
peritoneum, from which it is subsequently
separated by the adhesion of its opposite
walls.

The separation of the tunica vaginalis testis from the peritoneum is
usually completed in the human foetus before birth. But sometimes it
fails to take place at the usual time, and the intestine is then liable to
protrude into the scrotum, in front of the spermatic cord, giving rise
to congenital inguinal hernia. (Fig. 297.)
The parts implicated in this malformation
have still, as in the case of congenital umbili-
cal hernia, a tendency to unite with each other
and obliterate the opening; and if the intes-
tine be retained by pressure in the cavity of
the abdomen, cicatrization usually takes place
at the inguinal canal, and a cure is effected.

Female Organs of Generation. — At an early
period of development, the ovaries have the
same external appearance, and occupy the
same position in the abdomen, as the testicles
in the opposite sex. The descent of the ovaries
also takes place, to a great extent, in the same
manner with the corresponding change of
When, in the early part of this descent, they
have reached the level of the lower edge of the kidneys, a cord, analogous
to the gubernaculum, may be seen proceeding from their lower extremity,
crossing the efferent duct on each side, and passing downward, to be
attached to the subcutaneous tissues at the situation of the inguinal
ring. That part of the duct situated outside the crossing of this cord,
becomes convoluted, and is converted into the Fallopian tube ; while

CONGENITAL INGUINAL
H K R N i A .—1. Testicle. 2, 2, 2.
Intestine.

position of the testicles.

DEVELOPMENT OF THE WOLFFIAN BODIES, ETC. 789

that which is inside the same point, is developed into the uterus. The
upper portion of the cord itself becomes the ligament of the ovary ; its
lower portion, the round ligament of the uterus.

As the ovaries continue their descent, they pass below and behind the
Fallopian tubes, which perform at the same time a movement of rota-
tion, from before backward and from above downward ; the whole,
together with the ligaments of the ovaries and the round ligaments,
being enveloped in double folds of peritoneum, which enlarge with the
growth of the parts included between them, and constitute finally the
broad ligaments of the uterus.

While these changes are taking place in the adjacent organs, the two
lateral halves of the uterus fuse with each other upon the median line,
and become covered with an abundant layer of muscular fibres. In the
quadrupeds, the uterus remains divided at its upper portion, running
out into two long conical tubes or cornua (Fig. 228), presenting the
form known as the uterus bicornis. In the human species, the fusion
of the two lateral halves of the organ is nearly complete ; so that the
uterus presents externally a somewhat rounded, flattened and triangular
figure (Fig. 229), with the ligaments of the ovary and the round liga-
ments passing off from its superior angles. Internally, the cavity of
the organ still presents a strongly marked triangular form, the vestige
of its original division.

Occasionally the human uterus in the adult condition remains divided
by a vertical septum, running from the middle of its fundus downward
toward the os internum. The organ may even present a partial external
division, corresponding with the situation of the internal septum, and
producing the malformation known as " uterus bicornis," or double
uterus.

The os internum and the os externum are produced by partial constric-
tions of the original generative passage ; and the anatomical distinctions
between the body of the uterus, the cervix, and the vagina, arise from
the different modes of development of the mucous membrane and mus-
cular tunic in its corresponding portions. During foetal life, the neck
of the uterus grows faster than its body; so that, at the period of birth,
the organ is far from presenting the form which it exhibits in the adult
condition. In the human foetus at term, the cervix uteri constitutes
nearly two-thirds of the entire length of the organ ; while the body
forms but little over one-third. The cervix, at this time, is larger in
diameter than the body; so that the 'whole organ presents a tapering
form from below upward. The arbor vitae uterina of the cervix is at
birth very fully developed, and the mucous membrane of the body is
also thrown into three or four folds which radiate upward from the os
internum. The cavity of the cervix is filled with transparent semi-solid
mucus.

The position of the uterus at birth is different from that which it
assumes in adult life; nearly the entire length of the organ being above
the level of the symphysis pubis, and its inferior extremity passing

790 DEVELOPMENT OF THE WOLFFIAN BODIES, ETC.

below that point only by about six millimetres. It is also slightly ante-
flexed at the junction of the body and cervix. After birth, the uterus,
together with its appendages, continues to descend ; and at the period
of puberty its fundus is situated just below the level of the symphysis
pubis.

The ovaries at birth are narrow and elongated in form. They contain
at this time an abundance of eggs ; each inclosed in a Graafian follicle,
and averaging .04 millimetre in diameter. The vitellus is imperfectly
formed in most of them, and in some is hardly to be distinguished. The
Graafian follicle at this period envelops each egg closely, there being no
fluid between its internal surface and the exterior of the egg, but only
the thin layer of cells forming the "membrana granulosa." Inside this
layer is to be seen the germinative vesicle, with the germinative spot,
surrounded by a faintly granular vitellus, more or less abundant in dif-
ferent parts. Some of the Graafian follicles containing eggs are as large
as .05 millimetre; others as small as .02 millimetre. In the very
smallest, the cells of the membrana granulosa appear to fill entirely the
cavity of the follicle, concealing the rudiments of the primitive egg.

CHAPTEE XVII.

DEVELOPMENT OF THE VASCULAR SYSTEM.

THERE are three distinct forms assumed by the circulatory system
during different periods of life. These different forms of the circulation
are connected with the manner in which nutrition and the renovation of
the blood are accomplished at different epochs ; and they follow each
other in the progress of development, as different organs are employed
in turn to accomplish the above functions. The first form is that of the
vitelline circulation, which exists at a period when the vitellus is the
source of nutrition for the embryo. The second is the placental circula-
tion, which lasts, in man and the mammalians, through the greater part
of foetal life, and is characterized by the existence of the placenta ; the
third is the complete or adult circulation, in which the renovation and
nutrition of the blood are provided for by the lungs and the intestinal
canal.

Vitelline Circulation. — When the body of the embryo has begun to
be formed in the centre of the blastoderm, a number of bloodvessels
shoot out from its sides and ramify over the neigh-
boring parts of the vitelline sac, forming by their Fig. 298.
inosculation an abundant vascular plexus. The area
occupied by this plexus around the foetus is the
" area vasculosa." In the egg of the fish (Fig. 298),
the area vasculosa occupies the whole surface of the
vitellus, outside the body of the embryo. A number
of arteries pass out from each side, supplying the
vascular network; and the blood is returned from EGG OP FISH
it to the embryo by a principal vein which is seen (Jarrabacca), show-

, , „ , , ing the vitelline cir-

passmg upward along the front of the egg, and enter- cuiation.
ing the body beneath the head.

In the egg of the fowl, the area vasculosa spreads gradually over the
vitelline sac from within outward. It is at first limited on its external
border by a terminal vein or sinus, which collects the greater part of
the blood from the vascular plexus on each side, and returns it to the
interior of the embryo by a double or single trunk, entering, as in the
fish, beneath the head. Another vein, of smaller size, enters the body
of the embryo near its posterior extremity; and a number of others,
still smaller, along the sides. All these vessels gradually change in
relative importance, as the development of the embryo proceeds.
Especially the terminal sinus becomes less distinct as the area vascu-
losa extends farther over the vitelline sac, and the anterior and pos-

(791)

792 DEVELOPMENT OF THE VASCULAR SYSTEM.

terior venous trunks disappear more or less completely, to be replaced
in importance by some of those which enter upon the sides. The area
vasculosa is therefore an appendage to the circulatory apparatus of the
embryo, spread out over the surface of the vitellus, and absorbing from
it the requisite materials for nutrition.

In man and the mammalians, the first formation of the area vasculosa
is not essentially different from that presented in fishes and birds. But
owing to the small size and rapid exhaustion of the vitellus as a source
of nourishment, this form of the circulation never acquires a high degree
of development, and soon becomes retrograde. It presents, however,
certain modifications, which are of importance as indicating the mode
of origin of various parts of the permanent vascular system.

These modifications relate mainly to the arrangement of the arteries
and veins distributing the blood to the external vascular plexus, and
returning it thence to the body of the embryo. As the embryo and the
entire egg increase in size, there are two arteries and two veins which
become larger than the others, and which subsequently do the whole
work of conveying the blood to and from the area vasculosa. The two
arteries emerge from the lateral edges of the embryo, on the right and
left sides ; while the two veins enter at about the same point and nearly
parallel with them. These four vessels are termed the omphalo-mesen-
teric arteries and veins.

The arrangement of the circulatory apparatus in the interior of the
body at this time is as follows : The heart is situated at the median
line, immediately beneath the head, and in front of the oesophagus. It
receives at its lower extremity the united trunks of the two omphalo-
mesenteric veins, and at its upper extremity gives off two vessels which
almost immediately divide into two sets of lateral arches, bending back-
ward along the sides of the neck, and again uniting into two trunks
near the anterior surface of the vertebral column. These trunks then
run from above downward, in a nearly similar direction, on each side
the median line. They are called the vertebral arteries, on account of
their situation, which is parallel with that of the vertebral column.
They give off, throughout their course, small lateral branches, which
supply the body of the foetus, and also two larger branches — the
omphalo-mesenteric arteries — which pass out, as above described, into
the area vasculosa. The two vertebral arteries remain separate in the
upper part of the body, but fuse with each other a little beneath
the level of the heart ; so that, below this point, there remains but one
large artery, the aorta, running from above downward along the median
line, giving off the omphalo-mesenteric arteries to the area vasculosa,
and supplying smaller branches to the body, the walls of the intestine,
and the other organs of the embryo.

This is the condition which marks the first or vitelline circulation.
A change now begins to be established, by which the vitellus is super-
seded, as an organ of nutrition, by the placenta ; and the second or pla-
cental circulation takes its place.

DEVELOPMENT OF THE VASCULAR SYSTEM.

793

Fig. 299.

Diagram of the YOUNG EMBRYO AND
ITS VESSELS, showing the circulation
of the umbilical vesicle, and also that of
the allantois, beginning to be formed.

Placental Circulation. — After the umbilical vesicle has been formed
by the process already described (page 738), a part of the vitellus re-
mains included in it, while the rest is retained in the abdomen and
inclosed in the intestinal canal. As
these two organs (umbilical vesicle
and intestine) are originally parts of
the same vitelline sac, they remain
supplied by the same vascular sys-
tem, namely, the omphalo-mesenteric
vessels. Those which remain within
the abdomen of the foetus supply the
mesentery and intestine; but the
larger trunks pass outward, and
ramify upon the walls of the um-
bilical vesicle. (Fig. 299.) At first
there are, as above mentioned, two
omphalo-mesenteric arteries emerg-
ing from the body, and two omphalo-
mesenteric veins returning to it ; but
afterward the two arteries are re-
placed by a common trunk, while a
similar change takes place in the two veins. Subsequently, therefore,
there remains but a single artery and a single vein, connecting the
internal and external portions of the vitelline circulation.

The vessels belonging to this system are called the omphalo-mesen-
teric vessels, because a part of them (omphalic vessels) pass outward,
by the umbilicus, or " omphalos," to the umbilical vesicle, while the
remainder (mesenteric vessels) ramify upon the mesentery and the
intestine.

At first, the circulation of the umbilical vesicle is more important
than that of the intestine ; and the omphalic artery and vein appear
accordingly as large trunks, of which the mesenteric vessels are small
branches. (Fig. 299.) Afterward the intestine enlarges, while the um-
bilical vesicle diminishes ; and the proportion between the two sets of
vessels is therefore reversed. The mesenteric vessels then come to be
the principal trunks, while the omphalic vessels are minute branches,
running out along the stem of the umbilical vesicle, and ramifying in a
few scanty twigs upon its surface. (Fig. 300).

In the mean time, the allantois is formed by a protrusion from the
lower extremity of the intestine, which, carrying with it two arteries
and two veins, passes out by the anterior opening of the body, and comes
in contact with the external membrane of the egg. The arteries of the
allantois, termed the umbilical arteries, are supplied by branches of the
abdominal aorta ; the umbilical veins, on the other hand, join the mesen-
teric veins, and empty with them into the venous extremity of the heart.
As the umbilical vesicle diminishes, the allantois enlarges ; and the lat-
ter is converted, in the human subject, into a vascular chorion, part of
51

794 DEVELOPMENT OF THE VASCULAR SYSTEM.

which is devoted to the formation of the placenta. (Fig. 300.) As the
placenta soon becomes the only source of nutrition for the foetus, its
vessels increase in size, and preponderate over all the other parts of the
circulatory system. During the early periods of the formation of the

Fig. 300.

Diagram of the EMBRYO AND ITS VESSEI/S; showing the second or placental circu-
lation. The intestine has become further developed, and the mesenteric arteries have
enlarged, while the umbilical vesicle and its vascular branches are reduced in size. The
large umbilical arteries are seen passing out to the placenta.

placenta, there are, as above mentioned, two umbilical arteries and two
umbilical veins. Subsequently one of the veins disappears, and the
whole of the blood is returned to the foetus by the other, which becomes
enlarged in proportion. For a long time previous to birth, there are,
therefore, in the umbilical cord two umbilical arteries, and but one
umbilical vein.

Adult Circulation — The placental circulation is exchanged, at the
period of birth, for the third or adult circulation. This is distinguished
by the disappearance of the placenta and the vessels connected with it,
and by the entrance into activity of the lungs and the alimentary canal,
as the organs of nutrition and aeration for the blood. A large propor-
tion of the blood is accordingly turned into different channels, and is
distributed to organs which were before but scantily supplied. This
change differs from that which preceded it mainly in its suddenness.
The transition from the first to the second form of circulation is a
gradual one ; the vitellus and umbilical vesicle diminishing as the pla-
centa enlarges, and the two organs, with their bloodvessels, coexisting

DEVELOPMENT OF THE VASCULAR SYSTEM. 795

for a certain period. But at the time of birth the placenta is detached,
and the lungs brought into play, with comparative suddenness; and
although the pulmonary circulation and respiration are not established
in full activity until an interval of some days has elapsed, yet the pla-
centa is at once withdrawn from the circulatory system, and its office is
assumed by the lungs, the skin, and the alimentary canal.

The comparatively sudden changes which take place at birth have,
however, been already provided for by the gradual development of the
necessary organs. This is accompanied by corresponding alterations in
both the arterial and venous systems.

Development of the Arterial System. — At an earl}7 period of develop-
ment, the main arterial trunks, after passing off from the anterior ex-
tremity of the heart, curve backward in two sets of nearly parallel
branches, toward the vertebral column, after which they again become
longitudinal, and receive the name of the "vertebral arteries." The
curved branches which pass along the sides of the neck, from front to
rear, are called the cervical arches. They run in the substance of the
visceral folds existing in this situation (page 781), and are separated
from each other by the intervening cervical fissures. In the chick-
embryo, according to Foster and Balfour, three cervical arches, in the
three upper visceral folds, have been formed by the end of the second
day of incubation. During the third and fourth days, the first and
second cervical arches become obliterated, but a fourth and a fifth be-
come developed at the same time, in the substance of the corresponding
visceral folds. Thus there are, in all, five vascular cervical arches ; but
only three are to be found coexisting at any one time.

In fishes, the cervical arches remain, as permanent bloodvessels sup-
plying the gills, generally four in number on each side, sometimes five.
In birds and mammalians, some of them disappear during the further
progress of development, or leave only certain arterial inosculations in
the adult, as vestiges of their existence during the embryonic condition.
Some of them, on the other hand, remain as permanent vascular trunks
or branches, forming important parts of the adult arterial system.

The details relating to the growth and subsequent modification of
the cervical arches are not all described in the same manner by different
observers ; and there seems to be some variation, in this respect, in the
mammalian embryo, as compared with that of birds. The general fea-
tures, however, of the process of transformation are as follows.

The two ascending trunks, on the anterior part of the neck, from
which the cervical arches are given off, become the carotid arteries.
The first and second, that is, the two upper cervical arches, on each
side, disappear as above mentioned, or remain only in the form of small
and inconstant arterial inosculations. The third arch becomes the sub-
clavian artery, giving off, in an upward direction, the permanent verte-
bral artery, and continuing outward as the axillary artery, to supply
the upper limb. The fourth cervical arch undergoes very different
changes on the two opposite sides. On the left side it becomes enor-

796 DEVELOPMENT OF THE VASCULAR SYSTEM.

mously enlarged, giving off, as secondary branches, all the arterial
trunks going to the head and upper limbs, and is thus converted into
the permanent arch of the aorta. On the right side the corresponding
arch grows smaller, and ultimately disappears ; so that at last there is
only a single aortic arch, situated to the left of the median line, and
continuous below with the thoracic aorta.

The fifth or last cervical arch becomes on each side the pulmonary
artery ; its external portion on the right side disappearing at a very
early period, but on the left remaining for a certain time, as the ductus
arteriosus, between the pulmonary artery and the aorta.

Notwithstanding that the cervical arches are at first, as their name
implies, all situated in the region of the neck, their remains or perma-
nent representatives in the complete form of the arterial system, come
to be placed farther downward, and are evejn found in the cavity of the
chest. This is due to the varying rapidity of growth in different parts,
at the successive periods of embryonic development. The thorax at
first has no existence as a distinct portion of the trunk ; the heart
being placed immediately beneath the head, and afterward changing its
relative position as the development of the lungs goes forward and the
walls of the chest expand to cover them. The neck, with the esopha-
gus and trachea, also elongates in an upward direction, so that the vas-
cular organs at first placed in the cervical region afterward occupy a
position lower down. In fishes, where the cervical arches are perma-
nent and where no lungs are developed, there is no thoracic cavity, and
the heart remains situated at the most anterior portion of the trunk, just
behind the gills.

Corresponding changes take place, during this time, in the lower part
of the body. Here the abdominal aorta runs undivided, upon the me-
dian line, quite to the end of the spinal column ; giving off on each side
lateral branches, which supply the intestine and the parietes of the body.
When the allantois begins to be developed, two of these lateral branches
accompany it, and become, consequently, the umbilical arteries. These
vessels increase so rapidly in size, that they soon appear as divisions
of the aortic trunk ; while the original continuation of the aorta,
running to the end of the spinal column, appears as a small branch
given off at the point of bifurcation. The lower limbs are supplied
by two small branches, given off from the umbilical arteries near their
origin.

Up to this time, the pelvis and posterior extremities are but slightly
developed. Subsequently they grow more rapidly, in proportion to the
rest of the body, and the arteries which supply them enlarge in a corre-
sponding manner. That portion of the umbilical arteries, lying between
the bifurcation of the aorta and the origin of the branches going to the
lower extremities, becomes the common iliac arteries, which in their
turn afterward divide into the umbilical arteries proper, and the femorals.
Subsequently, in accordance with the continued growth of the pelvis
and lower extremities, the relative size of their bloodvessels is still

DEVELOPMENT OF THE VASCULAR SYSTEM.

797

Fig. 301.

further increased ; and at last the arterial system in this part of the
body assumes the arrangement which belongs to the latter periods of
gestation. The aorta divides, as before, into the two common iliac
arteries. These divide into the external iliacs supplying the lower ex-
tremities, and the internal iliacs supplying the pelvis ; and this division
is so placed that the umbilical or hypogastric arteries arise from the
internal iliacs, of which they now appear to be secondary branches.

After the birth of the foetus and the separation of the placenta, the
hypogastric arteries become partially atrophied, and are converted, in
the adult condition, into solid cords, running upward to the umbilicus.
Their lower portion, however, remains pervious,
and gives off arteries supplying the urinary blad-
der. The terminal continuation of the original
abdominal aorta, is the arteria sacra media, which,
in the adult, runs downward on the anterior sur-
face of the sacrum, supplying branches to the
rectum and to the anterior sacral nerves.

Development of the, Venous System. — According
to the observations of Coste, the principal veins of
the body consist at first of two long venous trunks,
the vertebral veins (Fig. 301), which run along the
sides of the vertebral column, parallel with the
vertebral arteries. They receive in succession all
the intercostal veins, and empty into the heart by
two lateral trunks of equal size, the canals of Cu-
vier. When the inferior extremities become de-
veloped, their two veins, returning from below,
join the vertebral veins near the posterior portion
of the body ; and, crossing them, afterward unite
with each other, thus constituting another vein of
new formation (Fig. 302, a), which runs upward a
little to the right of the median line, and empties
by itself into the lower extremity of the heart.

The two branches, by means of which the veins of the lower extremi-
ties thus unite, become afterward the common iliac veins ; while the
single trunk (a) resulting from their union becomes the vena cava in-
ferior. Subsequently, the vena cava inferior becomes very much larger
than the vertebral veins ; and its two branches of bifurcation are after-
ward represented by the iliac veins.

Above the level of the heart, the vertebral and intercostal veins re-
tain their relative size until the development of the superior extremities
has commenced. Then, two of the intercostal veins increase in diameter
( Fig. 302), and become converted into the right and left subclavians ;
while those portions of the vertebral veins situated above the subcla-
vians become the right and left jugular veins. Just below the junction
of the jugulars with the subclavians, a small branch of communication
now appears between the two vertebrals (Fig. 302, 6), passing over from

Diagram of the VE-
NOUS SYSTEM in its
early condition ; show-
ing the vertebral veins
emptying into the heart
by two lateral trunks,
the " canals of Ouvier."

798

DEVELOPMENT OF THE VASCULAR SYSTEM.

Fig. 302.

VENOUS SYSTEM farther
advanced, showing the for-
mation of the iliac and sub-
clavian veins — a. Vein of
new formation, which he-
comes the inferior vena cava.
b. Transverse hr-inoh of new
formation, which afterward
becomes the left vena inno-
minata.

Fig. 303.

Further development of
the VENOUS SYSTEM.—
The vertebral veins are
much diminished in size,
and the canal of Cuvier, on
the left side, is gradually
disappearing, c. Transverse
branch of new formation,
which is to become the vena
azygos minor.

left to right, and emptying into the right verte-
brtil vein a little above the level of the heart ;
so that a part of the blood coming from the
left side of the head, and the left upper extre-
mity, still passes down the left vertebral vein
to the heart upon its own side, while a part
crosses over by the communicating branch (6),
and is finally conveyed to the heart b}7 the
right descending vertebral. Soon afterward,
this branch of communication enlarges so
rapidly that it preponderates over the left
superior vertebral vein, from which it origi-
nated (Fig. 303), and, serving then to convey
all the blood from the left side of the head and
left upper extremity to the right side above the
heart, it becomes the left vena innominata.

On the left side, that portion of the superior
vertebral vein, which is below the subclavian,
remains as a small branch of the vena innomi-
nata, receiving the six or seven upper inter-
costal veins ; while on the right side it becomes
excessively enlarged, receiving the blood of
both jugulars and both subclavians, and is con-
verted into the vena cava superior.

The left canal of Cuvier, by which the left
vertebral vein at first communicates with the
heart, is subsequently atrophied and obliterated,
while on the right side it becomes excessively
enlarged, and forms the lower extremity of the
vena cava superior.

The superior and inferior venae cavse, accord-
ingly, do not correspond with each other so far
as regards their mode of origin, and are not
to be regarded as analogous veins. The supe-
rior vena cava is one of the original vertebral
veins ; while the inferior vena cava is a vessel of
new formation, resulting from the union of two
lateral trunks coming from the inferior extre-
mities.

The remainder of the vertebral veins finally
assume the condition shown in Fig. 304, which
is the complete or adult form of the venous
circulation. At the lower part of the abdo-
men, the vertebral veins send inward small
transverse branches of communication to the
vena cava inferior, between the points at which
they receive the intercostal veins. These

DEVELOPMENT OF THE VASCULAR SYSTEM.

799

Fig. 304.

branches of communication, by increasing in size, become the lumbar
veins (7), which, in the adult condition, communicate with each other
by arched branches, a short distance to the side
of the vena cava. Above the level of the lumbar
arches, the vertebral veins retain their original
direction. That upon the right side still re-
ceives all the right intercostal veins, and becomes
the vena azygos major ( 8 ). It also receives a
small branch of communication from its fellow
of the left side (Fig. 303, c), and this branch
soon enlarges to such an extent as to bring
over to the vena azygos major all the blood of
the five or six lower intercostal veins of the left
side, becoming, in this way, the vena azygos
minor (9). The six or seven upper intercostal
veins on the left side still empty, as before, into
their own vertebral vein (10), which, joining the
left vena innominata above, is known as the
superior intercostal vein. The left canal of
Cuvier has by this time entirely disappeared ;
so that all the venous blood now enters the
heart by the superior and the inferior vena cava.
But the original vertebral veins are still con-
tinuous throughout, though much diminished in
size at certain points ; since both the greater
and lesser azygous veins inosculate below with
the superior lumbar veins, and the superior in-
tercostal vein inosculates below with the lesser
azygous, before it crosses to the right side.

There are still two parts of the circulatory
apparatus, the development of which presents

peculiarities sufficiently important to be described separately. These
are, first, the liver and the ductus venosus, and secondly, the heart and
ductus arteriosus.

The Hepatic Circulation and Ductus Ve-
nosus.— The liver appears at a very early
period, in the upper part of the abdomen, as
a mass of glandular and vascular tissue, de-
veloped around the upper portion of the
omphalo-mesenteric vein, just below its ter-
mination in the heart (Fig. 305). As soon
as the organ has attained a considerable
size, the omphalo-mesenteric vein ( i ) breaks
up in its interior into a capillary plexus, Earlv form of the HEPATIC

. J 1 CIKCULATION.- 1. Omphalo-

the vessels of Which again unite into a mesenteric vein. 2. Hepatic vein.

VenOUS trunk, which Conveys the blood to 3- Heart. The dotted line show*

, , m, . . . the situation of the future um-

the Heart. I he omphalo-mesenteric vein biiicai vein.

Adult condition of the
VENOUS SYSTEM. — 1.
Right auricle of the heart.
2. Vena cava superior. 3,3.
Jugular veins. 4, 4. Subcla-
vian veins. 5. Vena cava
inferior. 6, 6. Iliac veins.
7. Lumbar veins. 8. Vena
azygos major. 9. Vena
azygos minor. 10. Superior
intercostal vein.

Fig. 305.

800 DEVELOPMENT OF THE VASCULAR SYSTEM.

below the liver then becomes the portal vein ; while above the liver, and
between that organ and the heart, it receives the name of the hepatic
vein (2). The liver, accordingly, is at this time supplied with blood

entirely by the portal vein, coming from the
Fig. 306. umbilical vesicle and the intestine ; and all

the blood derived from this source passes
through the hepatic circulation before reach-
ing the venous extremity of the heart.

But soon afterward the allantois makes
its appearance, and becomes developed into
the placenta; and the umbilical vein re-
turning from it joins the omphalo-mesenteric
vein in the substance of the liver, and
takes part in the formation of the hepatic

HEPATIC Cuter NATION

farther advanced. - 1. Portal capillary plexus. Since the umbilical vesicle,
vein. 2 umbilical vein. 3. He- however, becomes atrophied, while the intes-

patic vein.

tine remains inactive, at the same time that

the placenta increases in size and in functional importance, a period
arrives when the liver receives more blood by the umbilical vein than by
the portal vein. (Fig. 306.) The umbilical vein then passes into the
liver at the longitudinal fissure, and supplies the left lobe entirely with
its own branches. To the right it sends off a large branch of communi-
cation, which opens into the portal vein, and partially supplies the right
lobe with umbilical blood. The liver is thus supplied with blood from
two different sources, the most abundant of which is the umbilical vein ;
and all the blood entering the liver circulates, as before, through its
capillary vessels.

But the liver is much larger, in proportion to the entiro body, at an
early period of foetal life than in the later months. In the foetal pig,
when very young, it amounts to nearly twelve per cent, of the weight
of the whole body; while before birth it diminishes to seven, six, and
even three or four per cent. For some time, therefore, during the
latter part of foetal life, much more blood returns from the placenta
than is required for the capillary circulation of the liver. Accordingly,
a vascular duct or canal is formed in its interior, by which a portion of
the placental blood is carried directly through the organ, and conveyed
to the heart without having passed through the hepatic capillaries. This
canal is the Ductus venosus.

The ductus venosus is formed by a gradual dilatation of one of the
hepatic capillaries (at 5 Fig. 307), which, enlarging excessively, be-
comes converted into a wide branch of communication, passing from the
umbilical vein below to the hepatic vein above. The circulation through
the liver, at this period, is as follows : A certain quantity of venous blood
still enters through the portal vein (i), and circulates in a part of the
capillary system of the right lobe. The umbilical vein (2), bringing a
much larger quantity of blood, enters the liver a little to the left, and
the blood which it contains divides into three principal streams. One of

DEVELOPMENT OF THE VASCULAR SYSTEM.

801

HEPATIC CIRCULATION during the
latter part of foetal life.— 1. Portal vein.
2. Umbilical vein. 3 Left branch of um-
bilical vein. 4. Eight branch of umbili-
cal vein. 5. Ductus venosus. 6. Hepatic
vein.

Fig. 308.

them passes through the left branch Fig. 307.

(3) into the capillaries of the left
lobe; another turns off through the
right branch (4), and, joining the
blood of the portal vein, circulates
through the capillaries of the right
lobe ; while the third passes directly
onward through the ductus venosus
(5) and reaches the hepatic vein with-
out having passed through any part
of the capillary plexus.
' This condition of the hepatic cir-
culation continues until birth. At
that time, two important changes
take place. First, the placental cir-
culation is cut off; and secondly, a
much larger quantity of blood than
before begins to circulate through the
vessels of the lungs and the intestine.

The superabundance of blood, previously coming from the placenta, is
now diverted to the lungs ; while the intestinal canal becomes the sole
source of supply for the hepatic venous
blood. The following changes, there-
fore, take place at birth in the vessels
of the liver. (Fig. 308.) First, the um-
bilical vein shrivels and becomes con-
verted into a solid cord ( 2 ). This cord
may be seen, in the adult condition,
running from the internal surface of the
abdominal walls, at the umbilicus, to
the longitudinal fissure of the liver. It
is then known under the name of the
round ligament. Secondly, the ductus
venosus also becomes obliterated.
Thirdly, the blood entering the liver by
the portal vein ( i ) passes off by its
right branch, as before, to the right lobe.
But in the left branch (* ) the course of
the blood is reversed. This was for-
merly the right branch of the umbilical
vein, its blood passing in a direction
from left to right. It now becomes the
left branch of the portal vein ; and its

blood passes from right to left, to be distributed to the capillary vessels
of the left lobe.

According to Guy, the umbilical vein is completely closed at the end
of the fifth dav after birth.

Adult form of HEPATIC CIRCU-
LATION.—1. Portal vein. 2. Oblite-
rated umbilical vein, forming the round
ligament ; the continuation of the dot-
ted lines through the liver shows the
situation of the obliterated ductus
venosus. 3. Hepatic vein. 4. Left
branch of portal vein.

802

DEVELOPMENT OF THE VASCULAR SYSTEM.

The Heart, and Ductus Arteriosus. — When the embryonic circulation
is first established, the heart is a simple tubular canal (Fig. 309), receiv-
ing the veins at its lower extremity, and giving off the arterial trunks at
its upper extremity. In the progress of growth, it soon becomes bent
upon itself; so that the entrance of the veins and the exit of the arte-
ries come to be placed more nearly upon the same horizontal level
(Fig. 310) ; but the entrance of the veins (i) is behind and a little
below, while the exit of the arteries (2) is in front and a little above.
The heart is then a simple twisted tube; and the blood passes through
it in a continuous stream, turning upon itself at the point of curvature,
and emerging by the arterial orifice.

Fig. 309. Fig. 310. Fig. 311.

f,

Earliest form of the
FCETAL HEART.— 1.
Venous extremity 2.
Arterial extremity.

FOITAL HEART, bent
upon itself.— 1. Venous ex-
tremity. 2. Arterial extre-
mity.

FCETAL HEART, divided
into right and left' cavities.
— 1. Venous extremity 2.
Arterial extremity. 3, 3.
Pulmonary branches.

Soon afterward, the single cardiac tube is divided into two parallel
canals, right and left, by a longitudinal partition, which grows from the
inner surface of its walls and follows the twisted course of the organ
itself. (Fig. 311.) This partition, which is indicated in the figure by a
dotted line, extends a short distance into the commencement of the
primitive arterial trunk, dividing it into two lateral halves, one of which
is in communication with the right side of the heart, the other with the
left.

The pulmonary branches (s, z) are given off from each side of the
arterial trunk near its origin; and the longitudinal partition, above
spoken of, is so placed that both these branches fall upon one side of it,
and are both, consequently, given off from that
division of the artery which is connected with
the right side of the heart.

The first portion of the arterial trunk is also
divided into two parallel vessels of nearly simi-
lar curvature, which join each other a short
distance beyond the origin of the pulmonary
branches. The left lateral division of the arte-
rial trunk is the commencement of the aorta (i );

HE ART still far- while its riSht lateral ^vision is the trunk of
ther developed. - 1. Aorta, the pulmonary artery (2), giving off the right
2 Pulmonary artery. 3, 3. anc] jeft pulmonary branches (s, a), at a short

Pulmonary branches. 4. .... m. ,. „ ,.

Ductus arteriosus. distance from its origin. That oortion of the

Fi

DEVELOPMENT OF THE VASCULAR SYSTEM.

803

Fig. 313.

HEART OF INFANT, showing
the mode of disappearance of the
arterial duct after birth. — 1. Aorta.
2. Pulmonary artery. 3, 3. Pulmo-
nary branches. 4. Ductus arterio-
fcus becoming obliterated.

pulmonary trunk (4) which is beyond the origin of the pulmonary
branches, and which communicates freely with the aorta, is the Ductus
arteriosus.

The ductus arteriosus is at first as large as the pulmonary trunk
itself; and nearly the whole of the blood coming from the right ven-
tricle, passes through the arterial duct,
and enters the aorta without going to the
lungs. But as the lungs become devel-
oped, the pulmonary branches increase in
proportion to the pulmonary trunk and to
the ductus arteriosus. At the termination
of fetal life in man, the ductus arteriosus
is about as large as either one of the pul-
monary branches ; and a considerable por-
tion of the blood, therefore, coming from
the right ventricle, still passes onward to
the aorta without being distributed to the
lungs.

But at the period of birth, the lungs
enter upon the performance of the func-
tion of respiration, and immediately re-
quire a greater supply of blood. The
right and left pulmonary branches then enlarge, so as to become the
two principal divisions of the pulmonary trunk. (Fig. 313.) The ductus
arteriosus at the same time contracts to such an extent that its cavity
is obliterated ; and it is finally converted into an impervious cord,
which remains until adult life, running from the point of bifurcation of
the pulmonary artery to the under side of the arch of the aorta. The
obliteration of the arterial duct is complete, at latest, by the tenth
week after birth. (Guy.)

The two auricles are separated from the two ventricles by transverse
septa which grow from the internal surface of the cardiac walls ; but
these septa remaining incomplete, the auriculo-ventricular orifices con-
tinue pervious, and allow the passage of the blood from the auricles to
the ventricles.

The interventricular septum, or that which separates the two ven-
tricles from each other, is completed at an early date ; but the inter-
auricular septum, or that situated between the two auricles, remains
incomplete for a long time, being perforated by an oval-shaped opening,
the foramen ovate, allowing, at this situation, a free passage from the
right to the left side of the heart. The existence of the foramen ovale
and of the ductus arteriosus gives rise to a peculiar crossing of the
streams of blood in passing through the heart, which is characteristic
of foetal life, and which may be described as follows :

The two venae cavse in the foetus do not open into the right auricle on
the same plane or in the same direction ; for while the superior vena
cava is situated anteriorly, and is directed downward and forward, the

804

DEVELOPMENT OF THE VASCULAR SYSTEM.

Fig. 314.

inferior is situated posteriorly, and passes into the auricle in a direction
from right to left, transversely to the axis of the heart. A nearly ver-
tical curtain or valve at the same time projects behind the orifice of the
superior vena cava and in front of the orifice of the inferior. This cur-
tain is formed by the lower and right hand edge of the septum of the
auricles, which, as above mentioned, is incomplete at this time, and which
terminates inferiorly and toward the right in a crescentic border, leaving
an oval opening, the foramen ovale. The stream of blood, coming from
the superior vena cava, falls in front of this curtain, and passes down-
ward, through the auriculo-ventricular orifice, into the right ventricle.
But the inferior vena cava, being farther back and directed transversely,
opens, properly speaking, not into the right auricle, but into the left ;
for its stream of blood, falling behind the curtain above mentioned,
passes across, through the foramen ovale, into the cavity of the left auri-
cle. This direction of the current
of blood, coming from the inferior
vena cava, is further secured by a
special membranous valve, which
exists at this period, termed the
Eustachian value. This valve,
which is very thin and transparent
(Fig. 314, /), is attached to the an-
terior border of the orifice of the
inferior vena cava, and terminates
by a crescentic edge, directed to-
ward the left ; thus standing as an
incomplete membranous partition
between the cavity of the inferior
vena cava and that of the right
auricle. A bougie, placed in the
inferior vena cava, as shown in Fig.
314, lies quite behind the Eusta-
chian valve, and passes through
the foramen ovale, into the left
auricle.

The two streams of blood, there-
fore, coming from the superior and
inferior venae cavse, cross each other
upon entering the heart. This
crossing does not take place in the
cavity of the right auricle ; but, owing to the position and direction of
the two veins, the stream coming from the superior vena cava enters the
right auricle, while that from the inferior passes almost directly into
the left.

It also appears, from the relative position of the aorta, pulmonary
artery, and ductus arteriosus, at this time, that the arteria innominata,
together with the left carotid and left subclavian arteries, are given off

HEART OF THE HUMAN F<ETITS, at
the end of the sixth month ; from a specimen
in the author's possession. — a. Inferior vena
cava. ft. Superior vena cava. c. Cavity of
the right auricle, laid open from the front.
d. Appendix auricularis. e. Cavity of the
right ventricle, also laid open. /. Eustachian
valve. The bougie which is placed in the in.
ferior vena cava, can be seen passing behind
the Eustachian valve, just below the point
indicated by /, then crossing behind the
cavity of the right auricle, through the
foramen ovale, to the left side of the heart.

DEVELOPMENT OF THE VASCULAR SYSTEM.

805

Fig. 315.

Diagram of the CIRCULATION

THROUGH THE FtETAL HEART,.

— a. Superior vena cava. b. Inferior
vena cava. c, c, c, c. Arch of the aorta
and its branches. d. Pulmonary
artery.

from the arch of the aorta, before its junction with the ductus arteriosus ;
and this arrangement causes the blood of the two venae cavae, not only
to enter the heart in different directions, but also to be distributed, after
leaving the ventricles, to different parts of the body. (Fig. 315.) The
blood of the superior vena cava passes
through the right auricle downward into
the right ventricle, thence through the
pulmonary artery and ductus arteriosus,
into the thoracic aorta ; while the blood
of the inferior vena cava, entering the
left auricle, passes into the left ventricle,
thence into the arch of the aorta, and is
distributed to the head and upper extre-
mities. The two streams, therefore, in
passing through the heart, cross each
other both behind and in front. The
venous blood, returning from the head
and upper extremities by the superior
vena cava, passes through the thoracic
and abdominal aorta and the umbilical
arteries, to the lower part of the body,
and to the placenta ; while that returning
from the placenta, by the inferior vena

cava, is distributed to the head, and upper extremities, through the
vessels given off from the arch of the aorta.

This division of the streams of blood, during a certain period of foetal
life, is so complete that Reid,1 on injecting the inferior vena cava with
red, and the superior with yellow, in a human foetus of seven months,
found that the red injection had passed through the foramen ovale into
the left auricle and ventricle and the arch of the aorta, and had filled
the vessels of the head and upper extremities ; while the yellow had
passed into the right ventricle, pulmonary artery, ductus arteriosus, and
thoracic aorta, with only a slight admixture of red at the posterior part
of the right auricle. All the branches of the thoracic and abdominal
aorta were filled with yellow, while the whole of the red had passed to
the upper part of the body.

We have repeated this experiment several times on the foetal pig,
when about one-half and three-quarters grown, first taking the precau-
tion to wash out the heart and large vessels with a watery injection,
immediately after the removal of the foetus, and before the blood had
been allowed to coagulate. The injections used were blue for the supe-
rior vena cava, and yellow for the inferior. The two syringes were
managed, at the same time, by the right and left hands ; their nozzles
being held in place b}' the fingers of an assistant. When the points of
the syringes were introduced into the veins, at equal distances from the

Edinburgh Medical and Surgical Journal, 1835, vol. xliii. p. 11.

80(3 DEVELOPMENT OF THE VASCULAR SYSTEM.

heart, and the two injections made with equal rapidity, it was found
that the admixture of the colors was so slight, that at least nineteen-
tvventieths of the yellow injection had passed into the left auricle, and
nineteen-twentieths of the blue into the right. The pulmonary artery
and ductus arteriosus contained a similar proportion of blue, and the
arch of the aorta of yellow. In the thoracic and abdominal aorta, how-
ever, there was always an admixture of the two colors, generally in
about equal proportions. This may be owing to the smaller size of the
head and upper extremities in the pig, as compared with those of the
human foetus, which would prevent their receiving all the blood coming
from the left ventricle ; or to some difference in the manipulation of
these experiments, in which it is not always easy to imitate exactly
the force and rapidity of the different currents of blood in the living
bod}'. These results, however, leave no doubt of the fact, that, up to
an advanced stage of foetal life, by far the greater portion of the blood
coming from the inferior vena cava passes through the foramen ovale,
into the left side of the heart; while by far the greater portion of that
coming from the head and upper extremities passes into the right side
of the heart, and thence outward by the pulmonary trunk and ductus
"arteriosus. Toward the latter periods of gestation, this division of the
venous currents becomes less complete, owing to the following causes.

First, the lungs increasing in size, the two pulmonary arteries, as well
as the pulmonary veins, enlarge in proportion ; and a greater quantity
of the blood coming from the right ventricle, instead of going onward
through the ductus arteriosus, passes to the lungs, and, returning thence
by the pulmonary veins to the left auricle and ventricle, joins the stream
passing out by the arch of the aorta.

Secondly, the Eustachian valve diminishes in size. This valve, which
is very large at the end of the sixth month, subsequently becomes
atrophied to such an extent that, at the end of gestation, it has either
disappeared, or is reduced to the condition of a narrow membranous
ridge, which can exert no influence on the current of the blood. Thus,
the cavity of the inferior vena cava, at its upper extremity, ceases to
be separated from that of the right auricle ; and a passage of blood from
one to the other may more readily take place.

Thirdly, the foramen ovale becomes partially closed by a valve which
passes across its orifice from behind forward. This valve, which begins
to be formed at a very early period, is the valve of the foramen ovale.
It consists of a thin, fibrous sheet, which grows from the posterior sur-
face of the auricular cavity, a little to the left of the foramen ovale, and
projects into the left auricle, presenting a thin crescentic border, at-
tached, b}' its two extremities, to the auricular septum upon the left
side. The valve does not at first interfere with the flow of blood from
right to left, since its edge hangs loosely into the cavity of the left
auricle. It only opposes regurgitation from left to right.

But as gestation advances, while the walls of the heart continue to
enlarge, and its cavities expand in every direction, the fibrous bundles,

DEVELOPMENT OF THE VASCULAR SYSTEM. 807

forming the valve, do not elongate in proportion. The valve, accord-
ing^, becomes drawn downward more closely toward the foramen ovale.
It thus comes in contact with the edges of the inter-auricular septum,
and unites with its substance ; the adhesion taking place first at the
lower and posterior portion, and proceeding gradually upward and for-
ward, so that the passage from the right auricle to the left becomes con-
stantly more oblique in direction.

At the same time there is an alteration in the position of the inferior
vena cava. This vessel, which at first looked transversely toward the
foramen ovale, becomes directed more obliquely forward ; and thus, the
Eustachian valve having nearly disappeared, a part of the blood of the
inferior vena cava enters the right auricle, while the remainder still
passes through the equally oblique opening of the foramen ovale.

At birth a change takes place, by which the foramen ovale is com-
pletely occluded, and all the blood coming through the inferior vena
cava is turned into the right auricle.

The change depends upon the commencement of respiration. When
this occurs, a much larger quantity of blood is sent to the lungs, and
of course returns from them to the left auricle. The left auricle,
being thus filled with blood from the lungs, no longer admits the
entrance of a further quantity from the right auricle through the fora-
men ovale ; and the valve of the foramen, pressed backward against the
edges of the septum, becomes after a time adherent throughout, and
thus obliterates the opening. The cutting off of the placental circula-
tion diminishes at the same time the quantity of blood arriving at the
heart by the inferior vena cava. It is evident that the same quantity
of blood which previously returned from the placenta by the inferior
vena cava on the right side of the inter-auricular septum, now returns
from the lungs, by the pulmonary veins, upon the left side of the same
septum ; and it is owing to all these circumstances combined, that, while
before birth a portion of the blood always passed from the right auricle
to the left through the foramen ovale, no such passage takes place after
birth, since the pressure is then equal on both sides of the auricular
septum.

The foetal circulation is then replaced by the adult circulation, repre-
sented in Fig. 316.

That portion of the inter-auricular septum, originally occupied by the
foramen ovale, is accordingly constituted, in the adult condition, by the
valve of the foramen ovale, which has become adherent to the edges of
the septum. The septum in the adult heart is, therefore, thinner at this
spot than elsewhere ; and presents, on the side of the right auricle, an
oval depression, termed the fossa ovalis, which indicates the site of the
original foramen ovale. The fossa ovalis is surrounded by a slightly
raised ring, the annulus ovalis, representing the curvilinear edge of the
original inter-auricular septum.

The foramen ovale is sometimes completely obliterated within a few
days after birth, but often remains partially pervious for several weeks

808

DEVELOPMENT OF THE VASCULAR SYSTEM.

or months. We have a specimen, taken from a child one year and nine
months old, in which the opening is still very distinct ; and it is not
unfrequent to find a small aperture existing even in adult life. In these

Fig. 316.

Diagram of the ADULT CIRCULATION THROUGH THE HEART.— a, a. Superior and
inferior venae cavse. b. Right ventricle, c. Pulmonary artery, dividing into right and left
branches, d. Pulmonary vein. e. Left ventricle. /. Aorta.

instances, although the adhesion and solidification of the inter-auricular
septum may not be complete, yet no admixture of blood takes place
between the right and left sides of the heart ; since the direction of the
passage is always very oblique, and its valvular arrangement prevents
any regurgitation from left to right. The complete filling of the left
auricle with arterial blood, returning from the lungs, also opposes a
complete obstacle to the entrance of venous blood from the right
auricle.

CHAPTEK XVIII.

DEVELOPMENT OF THE BODY AFTER BIRTH.

THE newly-born infant is still far from having arrived at a state of
complete development. The changes through which it has passed while
in the foetal condition are followed by others during the periods of
infancy, childhood, and adolescence. The anatomy of the organs, both
internal and external, their physiological functions, and even the morbid
derangements to which they are subject, continue to undergo gradual
and progressive alterations, throughout the entire course of subsequent
life. The history of development extends, properly speaking, from the
earliest organization of the embryonic tissues to the complete formation
of the adult body. The period of birth marks only a single epoch in a
constant series of changes, some of which have preceded, while many
others are to follow.

The weight of the newly-born infant is about seven pounds. The
middle point of the body is nearly at the umbilicus, the head and upper
extremities being still large, in proportion to the lower extremities and
the pelvis. The abdomen is larger and the chest smaller, in proportion,
than in the adult. The lower extremities are still partially curved in-
ward, so that the soles of the feet look obliquely toward each other,
instead of being directed horizontally downward, as at a subsequent
period. Both the arms and the legs are curled upward and forward
over the chest and the abdomen, and all the joints are in a semi-flexed
position.

The process of respiration is imperfectly performed for some time
after birth. The expansion of the pulmonary vesicles, and the changes
in the circulatory apparatus which take place at the time of birth, far
from being instantaneous, are always more or less gradual in character,
and require an interval of several days for their completion. Respira-
tion seems to be accomplished, during this period, to a considerable ex-
tent through the skin, whicli is remarkably soft, vascular, and ruddy.
The animal heat is less actively generated than in the adult, and re-
quires to be sustained by careful protection, and by contact with the
body of the mother. The young infant sleeps during the greater part
of the time ; and even when awake exhibits comparatively few mani-
festations of intelligence or perception. The special senses of sight
and hearing are dull and inexcitable, and even consciousness seems
present only to a limited extent. Voluntary motion and sensation are
52 ' ( 809 )

810 DEVELOPMENT OF THE BODY AFTER BIRTH.

nearly absent ; and the almost constant irregular movements of the
limbs, observable at this time, are mainly automatic. Nearly all the
nervous phenomena presented by the newly-born infant, are of a similar
nature. The motions of its hands and feet, the act of suckling, and even
its cries and the contortions of its face, are reflex in their origin, and do
not indicate the existence of active volition, or distinct perception of
external objects. There is at first but little nervous connection with
the external world, and the system is almost exclusively occupied with
the functions of nutrition and respiration.

The difference in organization between the newly-born infant and
the adult may be represented, to some extent, by the following list,
which gives the relative weight of the most important internal organs
at the period of birth and in adult age ; the weight of the entire body
being reckoned, in each case, as 1000. The relative weight of the adult
organs has been calculated from the estimates of Cruveilhier, Solly, and
Wilson, that of the organs in the foetus at term from our own observa-
tions.

Foetus at term. Adult.

Weight of the entire body . . . 1000.00 1000.00

" encephalon . . . 148.00 23.00

" liver .... 37.00 29.00

" heart .... 7.77 4.17

" " kidneys .... 6.00 4.00

" supra-renal capsules . 1.63 0.13

" thyroid gland . . . 0.60 0.51

" thymus gland . . . 3.00 0.00

It appears that most of the internal organs diminish in relative size
after birth, owing principally to the increased development of the osse-
ous and muscular systems, both of which are in an imperfect condition
throughout intra-uterine life, but come into activity during childhood
and youth.

The remains of the umbilical cord begin to wither within the first day
after birth, and become completely desiccated by about the third day.
A superficial ulceration then takes place at the point of its attachment,
and it is separated and thrown off within the first week. After the
separation of the cord, the umbilicus becomes completely cicatrized by
the tenth or twelfth day. (Guy.)

An exfoliation and renovation of the cuticle take place over the whole
body soon after birth. According to Kolliker, the eyelashes, and pro-
bably all the hairs of the body and head, are thrown off and replaced
by new ones within the first year.

The teeth in the newly-born infant are but partially developed, being
still inclosed in their follicles and concealed beneath the gums. They
are twenty in number, namely, two incisor, one canine, and two molar
teeth on each side of each jaw. At birth there is a thin layer of den-
tine and enamel covering their upper surfaces, but the body of the tooth
and its fangs are formed subsequently by progressive elongation and

DEVELOPMENT OF THE BODY AFTER BIRTH. 811

ossification of the tooth-pulp. The fully-formed teeth emerge from the
gums in the following order. The central incisors in the seventh month
after birth ; the lateral incisors in the eighth month ; the anterior molars
at the end of the first year; the canines at a year and a half; and the
second molars at two years (Kblliker). The eruption of the teeth in
the lower jaw generally precedes by a short time that of the correspond-
ing teeth in the upper jaw.

During the seventh year a change begins to take place by which the
first set of teeth are thrown off and replaced by the second or permanent
set, which are different in number, size, and shape from the preceding.
The anterior permanent molar tooth first shows itself just behind the
posterior temporary molar, on each side. This happens at about six
and a half years after birth. At the end of the seventh year the middle
incisors are thrown off and replaced by corresponding permanent teeth,
of larger size. At the eighth year a similar exchange takes place in the
lateral incisors. In the ninth and tenth years, the anterior and second
molars are replaced by the anterior and second permanent bicuspid
teeth. In the twelfth year, the canine teeth are changed. In the thir-
teenth year the second permanent molars show themselves ; and from
the seventeenth to the twenty-first year, the third molars, or " wisdom
teeth," emerge from the gums, at the posterior extremities of the dental
arch. (Wilson.) The jaw, therefore, in the adult condition, contains
three teeth on each side more than in childhood, making in all thirty-
two permanent teeth ; namely, on each side, above and below, two
incisors, one canine, two bicuspids, and three permanent molars.

The generative apparatus, which is still inactive at birth, begins to
enter upon a condition of functional activity from the fifteenth to the
twentieth year. The entire configuration of the body alters at this
period, and the distinction between the sexes becomes more marked.
The beard is developed in the male ; and in the female the breasts as-
sume the size and form characteristic of the condition of puberty. The
voice, which is shrill and sharp in infancy and childhood, becomes deeper
in tone, and the countenance assumes a more sedate expression. After
this period, the muscular system increases still further in size and
strength, and the consolidation of the skeleton also continues ; the bony
union of its various parts not being entirely accomplished until the
twenty-fifth or thirtieth year. Finally, all the different organs of the
body arrive at the adult condition, and the entire process of develop-
ment is then complete.

INDEX.

A BDOMEN, movement of, in inspira-
A tion, 276
Abdominal plates, 725
Abdominal pregnancy, 711
Abdominal respiration, 276
Abducens nerve, 538
Absorption, 189

by bloodvessels, 194

by lacteals, 19(3

of fat, 192

of liquids by animal substances, 359,
365

of oxygen in respiration, 281
Absorption-bands, 207
Accommodation, of the eye, for vision at

different distances, 629
Acid, carbonic, 60, 128, 129, 130, 283, 296,
744

lactic, 118, 158

cholic, 104, 105

glycocholic, 104

taurocholic, 105

hippuric, 111

meconic, 142

oxalic, 393

uric, 111, 385

phosphoric, 51

Acid and alkaline animal fluids, 50
Acid fermentation of urine, 393
Acidity, of gastric juice, 158

of urine, 382
Action of arrest, 568, 571
Adipose tissue, 72

digestion of, 168, 185
Adult circulation, 320, 794

establishment of, 807
Air, quantity of, used in respiration, 280

alterations of, in respiration, 280
Air-cells, of lungs, 274
Air-chamber, in fowl's egg, 691
Ala cinerea, 506, 557
Albumen, 86

vegetable, 87

in milk, 118

in saliva, 141

in the blood, 259

in urine, 385, 389

of the egg, how produced, 690, 721
Albuininose, 87, 160

produced in digestion, 160, 168

in the blood-plasma, 259

interference with Trommer's test, 87

with iodine-test for starch, 88
Albuminous matters, 79
Alimentary canal, 131

development of, 727, 775
Alkalies, effect of, on urine, 386
Alkaline carbonates, 51

Alkaline fluids, of the animal system, 50
Alkaline phosphates, 49
Alkaline fermentation, of the urine, 394
Alkalescence, of the blood, 50, 51, 260
Allantois, 739

formation of, 741

in fowl's egg, 742

function of, 743

in fcetal pig, 755

Ammonio-magnesian phosphate, in de-
composing urine, 395
Ammonium carbonate, in decomposing

urine, 394
Amnion, 739

formation of, 740

enlargement of, 745

contact of, with chorion, 746
Amniotic fluid, 746
Amniotic folds, 746
i Amoeba, 255
Amoeba princeps, 256
! Amoeboid movements of -white globules

of the blood, 255, 256
Amphioxus, 251
Amphiuma tridactylum, blood-globules

of, 252

Ampullre, of the semi-circular canals, 656
Analysis, of animal fluids, 35, 36
Animal charcoal, as a decolorizer, 94
Animal functions, 25
Animal heat, 300

quantity of, produced, 302

mode of generation of, 305

normal variations of, 303

local production of, 307
Animalcules, infusorial, 676
Annulus ovalis, 807
Anterior columns of spinal cord, 435,445,

450

Anterior pyramids, 438
Anus, formation of, 727, 779

imperforate, 776
Aorta, development of, 796
Aphasia, 485

Appetite, disturbed by anxiety, 171
Aquatic respiration, 272
Aqueous humor, 612
Arbor vitse uterina, 693
Arch of aorta, formation of, 796
Arches, cervical, 795
Area pellucida, 724
Area vasculosa, 742
Arrest, action of, 568, 571
Arteries, 330

pulsation of, 331

movement of blood in, 330, 338

omphalo-mesenteric, 792

vertebral, 79_', 795

(813)

814

INDEX.

Arteries, umbilical, 793
Arterial pressure, 338
Arterial system, 330

development of, 795
Articulation, conditions of, 485, 509, 545,

579

Arytenoid cartilages, 278
Asphyxia, 281
Ataxia, locomotor, 466
Attitude, 4G4
Auditory apparatus, 649
Auditory nerve, 551
Auditory hairs, 656
Auriculo-ventricular valves, 320
Axis cylinder, 403
Azygous veins, formation of, 799

BACTERIUM TEKMO, 83, 680
Batrachians, red blood-globules of,

252
Bile, 201

physical characters of, 205

spectrum of, 207

composition of, 211

quantity of, 218, 219

reactions of, with gastric juice, 159,
222

functions of, 221

alteration and reabsorption of, in in-
testine, 220, 223

secretion of, in the foetus, 777
Bile-test, Gmelin's, 98
Biliary matters, in urine, 388
Biliary salts, 106, 211
Bilifulvine, 98
Biliphseine, 98
Bilirubine, 98, 206
Biliverdine, 98, 206
Binocular vision, 637

Bladder, urinary, closure and evacuation
of, 468

formation of, in foetus, 779
Blastoderm, 723, 730

folds of the, 731
Blind spot, of the retina, 620
Blood, 243

red globules of, 243

spectrum of, 248, 250

diagnosis of, 253

white globules of, 254

plasma, 257

coagulation of, 260

quantity of, 267

alterations of, in respiration, 293

temperature of, 300, 308

cooling of, in lungs and skin, 308

circulation of, 318

occurrence of, in the urine, 392
Blood-stains, recognition of, 253
Bones, composition of, 45

ossification of, 45, 773

of the middle ear, 6^0
Brain, of reptile, 436

of bird, 437

of quadruped, 437

of man, 433, 441, 471

fissures and convolutions of, 472

rapidity of nervous action in, 430

remarkable cases of injury to, 479

of idiots, 481

development of, 769

Branchiae, 272

Bread, 119

Broad ligaments, of uterus, formation of,

789

Bronchi, division of, 273
Bronchial tubes, ultimate, 273
Brunner's glands, 180
Butter, 119
Butyrine, 119 „

pANAL, medullary, 725, 736, 769
\J Canal of Schlemm, 609
Canals, semicircular, 655

of Cuvier, 797
Cane sugar, 67
Capillary bloodvessels, 343

inosculation of, 345

motion of blood in, 346
Capillary circulation, 343

causes of, 348

rapidity of, 349

local variations in, 351

peculiarities of, in different parts,

353
Capsule, internal, 475

external, 476

Caput coli, formation of, 776
Carbo-hydrates, 55
Carbonate, lime, 46

ammonium, in decomposing urine,

394

Carbonates, alkaline, 51
Carbonic acid, 60, 128, 129, 130, 283, 287, 291

in the breath, 283

in the blood, 296

origin of, 297

mode of production of, 298

daily quantity of, 283

exhaled by the skin, 285

by the egg, during incubation, 744

absorbed by vegetables, 60, 131, 270
Cardiac circulation, in adult, 320, 808

in the foetus, 803
Carnivorous animals, respiration of, 286

urine of, 52, 112

Carotid arteries, formation of, 795
Caseine, 88
Catalytic action, 81
Catoptric images, in the eye, 632
Cellulose, of starch, 56
Centre, nervous, definition of, 415
Cereal grains, composition of, 119
Cerebellum, 493

effects of injury to, 494

function of, 499

development of, 770
Cerebral ganglia, 437, 476, 491
Cerebral vesicles, 769
Cerebrine, 103
Cerebro-spinal system, 432

development of, 769
Cerebrum, 471

development of, 770
Cervical arches, 795
Cervical fissures, 780
Cervix uteri, 693

in the foetus, 789
Chalazae, of fowl's egg, 690
Cheese, 118

Chest, movements of, in respiration, 276
Chiasma, of optic nerves, 516

INDEX.

815

Chick, development of, 729
Chloride, potassium, 49, 384
Chloride, sodium, 47, 384
Chlorophylle, 101
Cholepyrrhine, 98
Cholesterine, 76
Chondrine, 91

Chorda dorsalis, 725, 734, 736, 772
Chorda tympani, 549

influence of, on circulation in sub-
maxillary gland, 550

on the sense of taste, 550
Chordae vocales, movement of, in respira-
tion, 277

action of, in vocalization, 565

obstruction of glottis by, after section

of the pneumogastric nerves, 563
Chorion, 746

villosities of, 747

source of vascularity of, 748

union of, with decidua, 753
Choroid coat, of the eye, 610
Chyle, 73, 192, 367

absorption of, 192

in the lacteals, 197

in the blood, 199
Chyme, 169
Cicatricula, 689, 729

segmentation of, 730
Ciliary muscle, 610, 634
Ciliary nerves, 583
Circulation, 318

in the heart, 318

in the arteries, 330

in the veins, 340

in the capillaries, 343

rapidity of, 350

local variations of, 351

peculiarities of, in different parts, 353

placenta!, 759, 793

vitelline, 791

adult, 794
Circulatory apparatus, 318

development of, 791
Claustrum, 476
Clot, formation of, 262
Coagulation, 81

of fibrine, 81, 86, 258

of albumen, 86

of milk, 118

of pancreatine, 175

of pty aline, 141, 142

of blood, 260
Cochlea, 660
Cold, resistance to, by animals, 300, 314

effect of, when long continued, 312
Collagen, 91
Coloring matters, 94

of the blood, 95

of the skin, 97

of bile, 98, 99, 206

of urine, 99

of the corpus luteum, 100

of green plants, 101

Commissure, gray, of the spinal cord,
435

white, of the spinal cord, 435, 445

transverse, of the cerebrum, 477

of the cerebellum, 494, 500
Composition, of Fehling's liquor, 64

of different articles of food, 118

of the daily ration of food, 125

Composition, of saliva, 141

of human parotid saliva, 144

of gastric juice, 157

of pancreatic juice, 173

of intestinal juice, 183

of bile, 211

of the red blood-globules, 247

of blood-plasma, 257

of cutaneous perspiration, 316

of lymph, 367

of lymph and chyle, 369

of the urine, 378

Congenital diaphragmatic hernia, 779
Congenital inguinal hernia, 788
Congenital umbilical hernia, 777
Contraction, of stomach during digestion,
167

of the blood-clot, 261

of the diaphragm and intercostal
muscles in respiration, 275

of the posterior crico-arytenoid mus-
cles, 278

of the ventricles of the heart, 324

of the muscles after death, 419

of the sphincter ani, 467

of the rectum, 467

of the urinary bladder, 468

of the pupil, under the influence of

light, 400, 518, 524, 611, 634
Convolutions, of the human brain, 475
Cooking, effect of, on albuminous matters,
82

on meat, 121

on vegetables, 123
Cord, spinal, 433, 443

umbilical, 763
Cornea, 609

Corpora striata, 437, 476
Corpora Wolffiana, 784
Corpus callosum, 47"
Corpus dentatum, 493
Corpus geniculatum, internum and ex-

ternum, 516
Corpus luteum, 713

of menstruation, 713

of pregnancy, 717
Cbrti, organ of, 662
Cranial nerves, 511

classification of, 513

general arrangement and origin of,

579

Creatine, 106
Creatinine, 107, 382
Cremaster muscle, 787
Crossed action, of spinal cord, 454

of optic nerves, 521

of optic tubercles, 522

of the oculomotorius nerves, 523

of the facial nerves, 546
Crossing, of fibres in medulla oblongata,
439, 455

of sensitive fibres in spinal cord, 455

of fibres of optic nerves, 516

of streams of blood in the foetal heart,

803

Crystalline lens, 613
Crystallizable nitrogenous matters, 102
Crystals, of stearine, 70

of palmitine, 71

of cholesterine, 77

of sodium glycocholate, 105

of sodium taurocholate, 106

816

INDEX.

Crystals, of biliary matters, from small
intestine, 217

of creatine, 107

of creatinine, 107

of urea, 109

of sodium urate, 382

of uric acid, 385

of lime oxalate, 394

of ammonio-magnesian phosphate.

396

Cumulus proligerus, 706
Cupola, of the cochlea, 660
Cuticle, exfoliation of, after birth, 810
Cuvier, canals of, 797
Cysticercus cellulose, 673

DEATH, a necessary consequence of
life, 668
Decidua, 750

vera, 751

reflexa, 751

union of, with chorion, 753

vera and reflexa, contact of, 765
Decussation, of cerebro-spinal nerve fi-
bres, 433

of anterior columns of spinal cord,
444, 445

of anterior pyramids, 439, 454, 503

of sensitive fibres in the spinal cord,
455

of optic nerves, 440, 519

of the patheticus nerves, 525

of the facial nerves, 546
Degeneration, fatty, of the decidua, 766

of the uterine muscular fibres, after

delivery, 767
Deglutition, 151, 508, 579

retarded by division of Steno's duct,
148

reflex action of, 508, 555, 566
Dentition, first, 810

second, 811

Deposits, iu the urine, 390
Descent, of the testicles, 786

of the ovaries, 788

Development, of the impregnated egg,
721, 745

of allantois, 740, 741

of chorion, 746

of decidua, 750

of placenta, 793

of nervous system, 769

of eye, 771

of ear, 772

of skeleton, 772

of limbs, 773

of integument, 774

of alimentary canal, 775

of urinary passages, 779

of liver, 778

of face, 780

of Wolffian bodies, 784

of kidneys, 785

of internal organs of generation, 785

of circulatory apparatus, 791

of arterial system, 795

of venous system, 797

of hepatic circulation, 799

of the heart, 802

of the body after birth, 809
Dextrine, 59

Diabetes, 242

in the fetus, 778
Diaphragm, action of, 275

formation of, 779

Diaphragmatic hernia, congenital, 779
j Diagnosis, of blood, 253
I Diastase, 59, 142
I Dichroism, of bile, 206
| Dicrotic pulse, 335
Diet, influence of, on nutrition, 116

on the products of respiration, 2P6

on formation of urea, 110

on formation of sodium urate, 111
Digestion, 131

of starch, 60, 149, 150, 175

of fats, 168, 175

of sugar, 184

of albuminous matters, 160, 168. 177

of meat, 168

of milk, 169

of vegetable tissues, 169

time required for, 170
Digestive apparatus, of fowl, 132

of ox, 133

of man, 134
Dilator pupillse, 611
Direct and indirect vision, 628
Discus proligerus, 706
Distance and solidity, appreciation of, 640
Diurnal variation, in exhalation of car-
bonic acid, 283

in production of urea, 109

in density and acidity of the urine, 376
Dorsal plates, 724, 732
Double vision, 639, 640
Ductus arteriosus, 802, 803
Ductus cochlearis, 661
Ductus venosus, 799, 800
Duodenal fistula, 217
Duodenal glands, 180
Duration, of luminous impulses necessary
for sight, 644

of musical sounds necessary for hear-
ing, 666

EAR, external, 649
middle, 649

internal, 654

development of, 772
Earthy phosphates, 46

in urine, 47, 383, 390, 395
Egg, 685

contents of, 386

where formed, 687

pre-existence of, in ovary, 703

development of, at puberty, 704

ripening and discharge of, 705, 707

impregnation of, 698

development of, after impregnation,
721

attachment of, to uterine mucous
membrane, 753

discharge of, at delivery, 765

condition of, in fcetus at term, 790
, as food, 122
Elasticine, 92
Embryo, formation of, 721

position of, in the fowl's egg, 733
Embryonic spot, 724
Emulsion of fats, 68

by pancreatic juice, 176

INDEX.

817

Encephalon, 471
Endolymph, 658
Endosmosis, 360
Endosmonjeter, 361
Entozoa, 672

encysted and sexless, 673
reproduction of, 674, 675
Epilepsy, from injury of the spinal cord,

461

Epidermis, exfoliation of, after birth, 810
Epididymis, 698

formation of, 787

Epithelium, of salivary glands, 139
in saliva, 141

of gastric follicles, 153, 154
of intestine, during digestion, 193
of the membranous labyrinth, 656,

657

of the ductus cochlearis, 662
Equilibrium, sense of, 659
Eustachian tube, 654
Eustachian valve, 804
Evacuation, of the rectum and bladder,

467

Excrementitious substances, 374
Excretine, 188
Excretion, 374

Exfoliation, of cuticle after birth, 810
Exhalation, from the lungs, 43, 288
from the skin, 43, 316
from the fowl's egg, during incuba-
tion, 743
Exhaustion, of muscles and nerves, by

repeated irritation, 420
Exosmosis, 361
Experiments on living animals, 26

direct and indirect results of, 28
Expiration, movements of, 276
Eye, 608

inflammation of, after division of tri-

geminus nerve, 536
development of, 771

FACE, motor nerve of, 539
sensitive nerve of, 526

development of, 780
Facial paralysis, 541, 543
Fallopian tubes, 692

formation of, 786, 789
Farinaceous substances, 55

digestion of, 60, 149, 150, 175
Fat, 68

absorption of, 192

emulsion of, 68, 175

decomposition of, in the blood, 199

necessary, as an ingredient of the

food, 115
Fatty degeneration, of the decidua, 766

of uterine muscular fibres, after de-
livery, 767
Feces, 187

Fecundation, of the egg, 698, 711
Fehling's test for glucose, 64
Female generative organs, 685

development of, 788
Fenestra rotunda, 655
Fenestra ovalis, 655
Fermentation, 64

of bread, 120

of saccharine urine, 386

acid, of urine, 393

Fermentation, alkaline, of urine, 394
Fibrine, 85

of the blood, 257

coagulation of, 86, 258, 261

disappearance of in liver and kidneys,
266

usefulness of, 266
Fibrinogen, 265
I Fibrino-plastic matter, 265
1 Fifth pair of cranial nerves,. 526
! Fissure, frontal, 488

of Kolando, 473

of Sylvius, 472

parietal, 473

| Fissure of the palate, 783
! Fissures, cervical, 7&0
I Fistula, gastric, 156

pancreatic, 172

duodenal, 217
Fixation, point of, in vision with both

eyes, 638

Fluorescence, of the bile, 206
Fcetus, development of, 769
Follicles, salivary, 139

gastric, 152

of Lieberkuhn, 180

Graafian, 687

uterine, 750
Food, 113

daily quantity of, 124

effect of cooking on, 121, 123
Foramen ovale, 803

valve of, 806

closure of, 807
Force, nervous, rapidity of transmission

of, 425

Fossa ovalis, 807
Fovea centralis, 623-
Functions, 25

animal, 32

vegetative, 31

of the teeth, 136

of saliva, 147

of gastric juice, 160, 166"

of pancreatic juice, 174

of intestinal juice, 184

of bile, 221

of perspiration, 317

of the crystalline lens, 614

of the semicircular canals, 65&

of the cochlea, QQ3-

GALVANISM, action of, on muscles,
II 418

on nerves, 419
Ganglia, cerebral, 437, 476, 491

spinal, 446, 583

of the sympathetic system, 583
Ganglion, Gasserian, 528

geniculatum, 548

impar, 585

jugular, 557

ophthalmic, 583

otic, 584

petrosal, 553

semilunar, 585

sphenopalatine, 584

spiral, 663

submaxillary, 584

Ganglionic system of nerves, 432, 582
Gasserian ganglion, 528

818

INDEX.

Gastric fistula, 156

Gastric follicles, 152, 153, 154

Gastric juice, 152

mode of obtaining, 157

composition of, 157

action of, on the food, 159, 166

mode of secretion of, 161

daily quantity of, 164

reabsorption of, 170
Gelatine, 35

source of, 91

eft'ect of feeding animals on, 117
Generation, 668

spontaneous, 670

of infusoria, 679

of entozoa, 672

sexual, 682
Germ, 682

Germinal membrane, 723
Germinative vesicle, 686

disappearance of, in mature egg, 721
Germinative spot, 686
Gills, 272
Glands, of Brunner, 180

salivary, 138

peptic, 155

of small intestine, 190

lymphatic, 356

Glandulse, agminatse and solitariae, 190
Globules, red, of the blood, 243

appearance of, under the microscope,
244

mutual adhesion of, 245

action of water on, 246

composition of, 247

size of, in different animals, 250

function of, 254, 294
Globules, white, of the blood, 254

amoeboid movements of, 255
Globules, of lymph, 369
Glomeruli, of the Wolffian bodies and

kidneys, 784

Glosso-pharyngeal nerve, 553
Glottis, movements of, in respiration, 277

in vocalization, 565
Glottis, closure of, after division of the

pneumogastric nerves, 563
Glucose, 62

formation of, in the liver, 232

detection of, in the urine, 386
Gluten, in wheat, flour, 86
Glycerine, 69, 231
Glycine, 104

Glycocholate, sodium, 104
Glycocholic acid, 104
Glycogen, 61, 228

conversion of, into sugar, 232
Glycogenic function of liver, 228

' in the foetus, 778
Gmelin's bile-test, 98
Graafian follicles, 687

structure of, 706

rupture of, in ovulation, 707

in menstruation, 710

condition of, in foetus at term, 790
Granulose, of starch grains, 56
Gray substance, of the nervous system,

400, 413

Groove, medullary, 724, 732, 736, 769
Gubernarulum testis, 787
Gustatory nerves, 533, 554, 601

HAIES, auditory, 656
Hairs, formation of, in foetus, 774

exfoliation of, during intra-uterino
life, 778

exfoliation of, after birth, 810
Hare-lip, 783

Headache, pathology of, 531
Hearing, sense of, 648

organ of, 649
Heart, 318

of mammalians, 319

of man, 319

circulation of blood through, 320

sounds of, 322

movements of, 324

impulse of, 326

development of, 802
Heat, vital, of animals, 300

of plants, 301

how produced, 305
Hemaphaaine, 99
Hematoidine, 98
Hemianassthesia, 492
Hemiplegia, 457, 45S, 492

with aphasia, 486
Hemispheres, cerebral, 436, 471

cases of injury to, 479

effect of removal of, 482

effect of disease of, 481

functions of, 479

centres of motion in, 487

development of, 770
Hemoglobine, 95

spectrum of, 248, 250
Hemorrhage, arrest of, by coagulation of
fibrin e, 266

from the placenta, in parturition, 765
Hepatic circulation, 201

development of, 799
Herbivorous animals, respiration of, 286

urine of, 52, 112
Hernia, congenital, diaphragmatic, 779

inguinal, 788

umbilical, 777
Hibernation, 311

respiration in, 282

production of heat in, 305
Hippurate, sodium, 111
Hippuric acid, 111
Honey, composition of, 67
Hydrobilirubine, 99

Hydrocarbonaceous proximate princi-
ples, 55

source and destination of, 78
Hygroscopicity, of albuminous matters, 80
Hyperaesthesia, after injury to spinal

cord, 456
Hypoglossal nerve, 574

TDIOTS, brain of, 481

1 Images, catoptric, in the eye, 632

Images, negative, 646

Im perforate anus, 776

Impregnation, of the egg, 698, 711

of the female, 700
Impulse, of the heart, 326
Incisor teeth, 136, 138
Incus, 650

Infant, newly born, condition of, 809
Infusoria, 676

reproduction of, 679

INDEX.

819

Inguinal hernia, congenital, 788
Inorganic proximate principles, 40

source and destination of, 54
Inosculation, of veins, 341

of capillaries, 345

of nerves, 405, 406
Inspiration, movements of, 275, 278
Instinct, nature of, 501
Integument, respiration by, 285, 809

development of, 774
Intellectual powers, 484
Intestine, of fowl, 132

of man, 134

secretions of, 180

digestion in, 184

epithelium of, 193

development of, 727, 775
Intestinal juice, 180
Iodine, action of, on starch, 58

in the urine, 389
Iris, 610

movements of, 400, 518, 524, 611, G34

formation of, 772
Iron, in hemoglobine, 96

in the food, 97

in melanine, 98
Irritability, nervous, 417

muscular, 418
Island of Keil, 473

TACOBSON, nerve of, 553
U Jaundice, yellow color of urine in, 388
Judgment, 484
Jugular ganglion, 557

TfERATINE, 92

IV Kidneys, circulation in, 352, 353

elimination of medicinal substances
by, 389

development of, 785

T ABYRINTH, 654

JJ Laeteals, 197

Lactic acid, in souring milk, 118

in gastric juice, 158
Lactose, 66

Lamina, spiral, of the cochlea, 661
Language, articulate, 485, 509, 545, 579
Large intestine, 186

development of, 775, 776
Larynx, action of, in respiration, 277

in vocalization, 565

nerves of, 557, 558

Layers, blastoclermic, external and in-
ternal, 723, 730

intermediate, 734
Lecithine, 102
Legumine, 89
Lens, crystalline, 613
Leucine, 104

Lieberkiikn, follicles of, 180, 181
Ligament, broad, of the uterus, 789

round, of the uterus, 789

round, of the liver, 801

of the ovary, 789
Limbs, formation of, 727, 773
Lime carbonate, 46

oxalate, 394

Lime phosphate, 43

Line of direct vision, 628

Lingual nerve, 530, 532

Liver, 201

secretion of bile in, 216
formation of glycogen in, 228
production of sugar in, 232
development of, 778, 799

Liver-cells, 202

Liver-sugar, formation of, 232

accumulation of, after death, 234
proportion of, during life, 236
production of, in the foetus, 778

Lobules, of the liver, 201
of the lung, 273

Locomotion, 464

Locomotor ataxia, 466

Lungs, structure of, 272, 273
development of, 779

Luteine, 100

Lymph, 367

Lymph-globules, 369

Lymphatic system, 354

MACULA AUDITIVA, 656
Macula lutea, 623
Magnesium phosphate, 46
Male organs of generation, 695

development of, 786
Malleus, 650
Mastication, 136, 533, 579

unilateral, in rumination, 145

retarded by suppression of saliva, 148
Meat, as food, 121
Meconic acid, 142
Meconium, 777
Medulla oblongata, 439, 440, 502

reflex action of, 505, 507

development of, 770
Medullary canal, 725, 736, 769
Medullary groove, 724, 732, 736, 769
Medullary layer, of nerve fibres, 402
Melanine, 97
Membrana basilaris, 661
Membrana granulosa, 706
Membrana tympani, 649
Membrane, pupillary, 772
Membranous labyrinth, 655
Memory, 484
Menobranchus, blood-globules of, 252

gills of, 272

spermatozoa of, 696
Menstruation, 708

corpus luteum of, 713
Mesenteric glands, 358
Metalbumen, 259, 264
Micropyle, 685, 699
Middle ear, 649

bones of, 650
Milk, 73, 118
Milk-sugar, 66

conversion of, into lactic acid, 118
Molar teeth, 137, 138
Motor nerve fibres, 409
Mouth, 134

development of, 780, 782
Movements, of bacterium cells, 84, 680

of stomach, 166

of intestine, 191

of white blood-globules, 255, 256

of chest, in respiration, 275

820

INDEX.

Movements of glottis, in respiration, 277

of the heart, 324

of spermatozoa, 096

of the iris, 400, 518, 524, 611, 634

of the foetus in utero. 764

of the newly-born infant, 810
Mucosine, 90
Mucous membrane, of stomach, 152

of intestine, 180, 189

of the uterus, 693, 750
Mucus, in the urine, 392
Muscles, irritability of, 419
Musical notes, production and perception

of, 665

Myeline-forms, 102
Myopic eye, 636
Myosiue, 90

NAILS, development of, 774
Negative images, 646
Nerve, abducens, 538

auditory, 551

facial, 539

great superficial petrosal, 548

glossopharyngeal, 553

hypoglossal, 574

lingual, 530, 532

oculomotorius, 522

olfactory, 513

optic, 516

patheticus, 524

pneumogastric, 557

small superficial petrosal, 549

spinal accessory, 571

stapedius, 549

sympathetic, 582

trigeminus, 526
Nerve cells, 413
Nerve fibres, 400

medullated, 402

non-medullated, 404

division of, 406, 407

termination of, 408

sensitive and motor, 409

effect of division on, 410

union and regeneration of, 411

connection of, with nerve cells, 414
Nerves, 405

spinal, 434, 445

cranial, 511, 579
Nervous force, 419

nature of, 423

rapidity of transmission of, 425
Nervous irritability, 417

duration of, after death, 419

exhausted by excitement, 420
Nervous system, 399

development of, 769
Nervous tissue, two kinds of, 400
Network, capillary, 346
Nitrogen, a constituent of albuminous

rnatters, 79
Non-nitrogenous proximate principles,

55
Nucleus, caudate, 476

lenticular, 476

olivary, 504

of the abducens and facial nerves, 538

of the auditory nerve, 551

of the glossopharyngeal nerve, 553

of the hypoglossal nerve, 574

Nucleus of the oculomotorius and path*

ticus nerves, 522
of the optic nerve, 516
of the pneumogastric nerve, 557
of the spinal accessory, 571
of the trigeiniuus, 526

Nutrition, 33

OBLITERATION, of ductus venosus,
801

of ductus arteriosus, 803

of foramen ovale, 807
Oculomotorius nerve, 522
(Esophagus, 134

paralysis of, after division of the

pneumogastric nerves, 566
(Estruation, phenomena of, 708
Oleaginous substances, 68

importance of, as ingredients of the
food, 115, 116

in the blood, 199, 260
Oleine, 70

Olfactory apparatus, 604
Olfactory bulb, 514
Olfactory ganglia, 436
Olfactory lobes, 515
Olfactory nerves, 513
Olfactory tubercle, 514
Olivary bodies, 439, 504
Omphalo-mesenteric vessels, 792, 799
Ophthalmic ganglion, 583
Ophthalmoscope, 615
Optic ganglia, 436
Optic nerves, 516

decussation of, 519

crossed action of, 521

physiological properties of, 620, 626

development of, 771
Optic thalami, 437, 476

development of, 769
Optic tract, 516
Optic tubercles, 436
Ora serrata, 616
Organ of Corti, 662
Organs, 25
Organization, of the animal solids and

fluids, 34

Origin, of plants and animals, 667
Ossicles, auditory, 650
Ossification, of the skeleton, 45, 773
Otic ganglion, 584
Otoconia, 657
Ovarian pregnancy, 711
Ovaries, 683

of tsenia, 683

of frog, 687

of fowl, 689

of human female, 692

development of, 785, 788

condition of, in fcetus at term, 790
Oviducts, 687

Oviparous and viviparous animals, 703
Ovulation, 703, 710
Ovum, 683, 685

Oxalic acid, produced in urine, 393
Oxygen, absorbed in respiration, 281

solution of, in the blood, 248, 254, 294

absorption of, by the tissues, 295

exhalation of, by plants, 60, 131, 270

absorption of, by the fowl's egg.
during incubation, 744

INDEX.

821

pACINIAN bodies, 407
JT Pain, sensations of, 597
Palate, formation of, 783
Palmitine, 70
Pancreas, 172
Pancreatic juice, 171

mode of obtaining, 172

composition of, 173

action of, on starch and fat, 175

on albuminous matters, 177

daily quantity of, 179
Pancreatiue, 89

in pancreatic juice, 174
Paralysis, muscular, 422

nervous, 423

after division of anterior spinal nerve
root, 447

direct, after lateral injury of spinal
cord, 455

crossed, after lateral injury of brain,
455

various forms of, 457

facial, 543

glosso-labio-laryngeal, 510

of motor nerves, by woorara, 422

of voluntary motion and sensation by
destruction of tuber annulare, 502

of larynx, pharynx, and oesophagus,
by division of the pneumogastric
nerves, 564, 566

of muscular coat of stomach, 569

of the external muscles of the eye-
ball, 523

of levator palpebrse superioris, 523

of the muscles of mastication, 533

of the sphincter ani, 468

of the urinary bladder, 470
Paraplegia, 457

reflex action of the spinal cord in,

463

Parasites, internal, 672
Parotid saliva, 143, 144 .
Parturition, 765
Par vagum, see Pneumogastric Nerve,

557

Patheticus nerve, 524
Pelvis, development of, 596
Pepsine, 59

in gastric juice, 158
Pepsine cells, 155
Peptic glands, 155
Perception, of sensations, 483, 501
Perilymph, 655
Periodical ovulation, 703, 710
Peristaltic action, of stomach, 166

of intestine, 191

of oviduct, 688, 689

Personal error, in the observation of phe-
nomena, 431
Perspiration, 316

function of, in regulating tempera-
ture, 317

Petrosal ganglion, 553
Petrosal nerve, 548, 549
Pettenkofer's test for bile, 212
Peyer's patches, 190
Pharynx, action of, in swallowing, 555
Phenomena, vital, 29
Phonation, 509

Phosphate, amrnonio-mapnesian, in de-
composing urine, 395

lime, 44

Phosphates, alkaline, 49, 51, 383

earthy, 46,. 47, 260, 383, 390, 395
Phosphorized fat, 102
Phosphorus, not a proximate principle,
35

a constituent of lecithine, 103

oxidation of, in the body, 51, 103
Physiology, definition of, 25

method of study of, 26, 31
Placenta, 755

formation of, 757

foetal tufts of, 758

maternal sinuses of, 759

injection of, from uterine bloodves-
sels, 760

function of, 761

separation of, in delivery, 765
Placental circulation, 793
Plasma, of the blood, 243, 257
Plasmine, 264
Plates, dorsal, 724

abdominal, 725

Plexus, capillary, 152, 189, 190, 194, 202,
274, 346

peripheral, of nerves, 406

laryngeal, 558

cesophageal, 559

pulmonary, 559

solar, 585
Pneumogastric nerve, 557

physiological properties of, 559

connection of, with respiration, 560

with phonatiou, 565

with deglutition, 566

with the stomach and digestion, 568

influence of, on the heart, 569
Point of distinct vision, 629
Point of fixation, in vision with both eyes,

638

Polarity, of nerve fibres in action, 424
Polarized light, rotation of, by organic

fluids, 59

Pons Varolii, 439, 500
Portal blood, temperature of, 308
Portal vein, distribution of, in the liver,
201, 202

evelopment of, 800
Posterior columns of the spinal cord, 435,

445, 449, 453, 465
Potassium chloride, 49, 384
Potassium sulphate, 52, 53, 384
Potassium urate, 382
Presbyopic eye, 635
Pressure, arterial, 338
Primitive trace, 724
Primitive vertebrae, 735, 772
Protagon, 102

Proteus anguinus, blood-globules of, 252
Proximate principles, 33

definition of, 35

mode of extraction of, 36

varying proportion of, 37

classification of, 38
Ptyaline, 89, 141, 142
Puberty, signs of, 704
Pulsation, of heart, 322

of arteries, 330
Pulse, arterial, 330

dicrotic, 335
Pupil, action of, 400, 518, 524, 611, 634,

588
Pupillary membrane, 772

822

INDEX.

Pus, in the urine, 393
Putrefaction, 82

arrested by gastric juice, 161
Pyramids, anterior, of medulla oblon-
gata, 438

decussatiou of, 439, 455

QUANTITY, daily, of air used in res-
piration, 280

of albuminous matter, starch, and
fat in the food, 128

of bile, 219

of biliary acids, 106

of carbonic acid exhaled, 283

of creatinine, 108

of earthy posphates in the urine, 47

of feces, 187

of fluids secreted and reabsorbed,
373

of food, 124

of gastric juice, 164

of lime phosphate, in the urine, 46

of lymph and chyle, 371

of magnesium phosphate, in the urine,
46

of materials absorbed and discharged,
397

of mineral matter introduced and dis-
charged, 114

of oxygen consumed, 281

of pancreatic juice, 179

of perspiration, 316

of saliva, 146

of sodium chloride discharged, 49

of sodium and potassium phosphates,
in the urine, 51

of sodium and potassium sulphates,
in the urine, 53

of solid matters, in the urine, 377

of urea, 109

of urine, 376

Quantity, entire, of blood in the body,
267

of iron in the blood, 96

of lime phosphate in the body, 44

of sodium chloride in the body, 47

of sulphur in the albuminous ingre-
dients of the body, 63

RABBIT, brain of, 437
Rapidity, of movements of respira-
tion, 279

of the arterial current, 338

of the venous current, 349

of the circulation in general, 350

of nervous action, 425
Reactions, of the bile, 205

of fat, 68

of gastric juice, 157

of intestinal juice, 184

of milk, 118

of pancreatic juice, 173

of saliva, 141

of starch, 58

of sugar, 62

of urine, 384
Reasoning powers, 484
Rectum, 134

evacuation of, 467

development of, 776

Red globules of the blood, 243
Reflex action, 416

of the spinal cord, 459

of the brain, 485

of tubercula quadrigemina, 518, 522

of tuber annulare, 500

of medulla oblongata, 507
Refraction, of light, by the crystalline

lens, 613

Regeneration, of divided nerve fibres,
411

of the uterine tissues, after pregnan

cy, 766, 768
Reil, island of, 473
Rennet, 118, 133
Reproduction, 667

by generation, 668
Resinous matters, of the bile, 105
Respiration, 270

in vegetables, 270

organs of, 271

by gills, 272

by lungs, 272

by the skin, 285, 809

movements of, 275

thoracic, 276

abdominal, 276

internal phenomena of, 280, 293

in the newly-born infant, 809
Respiratory movements, of the chest, 275

of the abdomen, 276

of the glottis, 277

after division of the pneumogastric
nerves, 560, 563

after injury of the spinal cord, 458
Restiform bodies, 494
Retina, 616

Rhythm, of the heart's action, 328
Round ligament, of the uterus, 789

of the liver, 801

Ruminating animals, stomach of, 133
Rumination, movements of, 133, 145
Rutting condition, of the lower animals,
708

QACCHARINE SUBSTANCES, 61
U in the liver, 232
in the blood, 240
in the urine, 240, 386
Saccharomyces cerevisise, 65
Saccharose, 67

Sacculus. of the internal ear, 655
Saliva, 138

composition of, 141

different kinds of, 143

secretion of, 145

daily quantity of, 146

physiological action of, 147
Salivary glands, 138
Salivary tubes, 139
Salts, biliary, 104, 105

of the blood, 260

of the urine, 386
Saponification, of fat, 69
Scala tympani, 661
Scala vestibuli, 661
Schlemm, canal of, 609
Sclerosis, of posterior columns of the

spinal cord, 466

Sclerotic coat, of the eyeball, 609
Secretion, of saliva, 145

INDEX.

823

Secretion of gastric juice, 161
of intestinal juice, 180

of pancreatic juice, 179

of bile, 216

of perspiration, 316

of ineconium, bile, and gastric juice

in the foetus, 777, 778
Segmentation, of the vitellus, 722

of the cicatricula, 730
Semicircular canals, 655
Seminal fluid, 695
Sensation, 409

dependence of, on the tuber annulare,
500

channels of transmission for, in
spinal cord, 452, 455

loss of, in paraplegia and hemiplegia,

457, 458, 492
Sensations, of touch, 593

of temperature, 597

of pain, 597
Sense, of taste, 600

of smell, 604

of sight, 607

of hearing, 618
Senses, the, 593

mode of action of, 598
Sensibility, general, 593

of different regions, 595

of nerves to electric current, 419

of posterior spinal nerve roots, 448

of posterior and lateral columns of
the spinal cord, 449, 450

of the facial nerve, 547

of the hypoglossal nerve, 578

of the spinal accessory nerve, 572

stereoscopic, 642
Seriue, 259

Serum, of the blood, 252
Sexes, distinctive characters of, 684

union of, 700
Sexual generation, 683
Shock, nervous, 420
Sight, sense of, 607

organ of, 608

physiological conditions of, 627
Single and double vision, 639
Sinuses, vascular, of the placenta, 758,

759

Skeleton, ossification of, 45, 772
Skin, perspiratory secretion of, 316

respiration by, 285, 809

development of, 774
Smell, sense of, 604

nerves of, 513, 605
Sodium biphosphate, 382

carbonate, 51

chloride, 47, 384

glycocholate, 104

hippurate, 111

phosphate, 49

sulphate, 52, 384

sulphocyanide, 141, 142

taurocholate, 105

urate, 111, 382, 391

Solar plexus, of sympathetic nerve, 585
Solid bodies, vision of, with two eyes,

640
Sound, how produced, 649

how perceived, 657
Sounds, of the heart, 322

vocal, 565, 566, 573

Special senses, 599
Species, 668

continuation of, 669
Specific gravity, of the saliva, 144

of gastric juice, 157

of bile, 205

of the blood, 243

of lymph, 367

of the urine, 376
Spectrum, of bile, 207

of chlorophylle, 210

of Pettenkofer's test, 213, 214, 215

of blood, 248, 250
Spermatozoa, 695

formation of, 697

entrance of, into the egg, 699
Sphincter aui, 467
Sphincter vesicse, 468
Sphincter pupillse, 611
Sphygmograph, 331
Spina bifida, 773
Spinal accessory nerve, 571
Spinal column, formation of, 726, 735
Spinal cord, 433, 443

commissures of, 435

anterior, lateral, and posterior col-
umns of, 435

origin of nerves from, 434, 445

gray substance of, 443

white substance of, 445

sensibility and excitability of, 449

transmission of nervous impulses in,
429, 449, 452

crossed action of, 454

reflex action of, 459

protective action of, 463

influence of, on sphincters, 467

development of, 726
Spinal nerves, origin of, 434, 445

transmission of motor and sensitive

impulses in, 447
Spiral ganglion, of the cochlear nerve,

663

Spiral lamina, of the cochlea, 661
Spontaneous generation, 670
Stapedius muscle, 652
Starch, 55

action of saliva on, 142

digestion of, 60, 149, 150, 175
Stearine, 70
Stercorine, 188
Stereoscope, 642
Stereoscopic sensibility, 642
Stomach, 133, 134, 152

digestion in, 150, 166

influence of pneumogastric nerve on,
568

formation of, 775

Strabismus, from paralysis of oculomo-
torius nerve, 523

of abducens nerve, 539
Striated bodies, 437
Strychnine, effect of, on the spinal cord,

461

Sublingual saliva, 143
Submaxillary ganglion, of the sympa-
thetic, 584
Submaxillary gland, 140

influence of nerves on the circulation

in, 550, 591

Submaxillary saliva, 143
Sugar, 61

824

INDEX.

Sugar, varieties of, 62

tests for, 62

fermentation of, 64

source and destination of, 67, 68

production of, in liver, 232

discharge of, by the urine, 240, 386
Sulphates, alkaline, 52, 53

in the urine, 384

Sulpho-cyanide, sodium, in saliva, 141, 142
Sulphur, in albuminous matters, 53

in biliary matters, 105

in excretine, 188

in the feces, 224

oxidation of, in the body, 53
Swallowing, 151, 508, 579

retarded by suppression of the saliva,
148

by division of the pneumogastric
nerves, 566

reflex action of, 508, 555, 566
Sympathetic nerve, 582

physiological properties of, 585

influence of, on movement and sensi-
bility, 586

on the special senses, 586

on the circulation, 589

on the temperature of parts, 590

on reflex actions, 592

mACTILE corpuscle, 407, 408, 594
1 Tactile sensibility, of different re-
gions, 595
Tadpole, development of, 724

transformation of, into frog, 728
Tsenia, 674

single articulation of, 683
Tapeworm, 674

production of, from cysticercus, 675
Taste, 600

nerves of, 533, 554, 601

conditions of, 603

injury of, by paralysis of facial nerve,

550

Taurine, 105

Tauro-cholate, sodium, 105, 106
Tauro-cholic acid, 105
Teeth, 136, 138

first and second sets of, 810, 811
Temperature, animal, 300, 308

in different species, 301

of the blood in different organs, 308

regulation of, 311

elevation of, after division of the
sympathetic nerve, 590

sensations of, 597
Tensor tympani, 651
Terminal bulb, of a sensitive nerve, 408,

594
Termination, peripheral, of nerve fibres,

406, 407, 408
Tests, for starch, 58

for sugar, 62, 386

for bile, 98, 211, 212

for sulpho-cyanides, 142
Testicles, 683

periodical activity of, in fish, 700

development of, 785

descent of, 786
Tetanus, pathology of, 461
Thalami, optic, 437, 441, 476, 491
formation of, 769

Thaumatrope, 643
Thoracic duct, 197, 198
Thoracic respiration, 276
Tic douloureux, 532
Tongue, 601

motor nerve of, 574

sensitive nerve of, 532, 554
Toothache, 532
Touch, sensations of, 593
Trace, primitive, 724
Tract, optic, 516

Transmission, of nerve force, rapidity of,
425

in motor nerves, 428

in sensitive nerves, 429

in the spinal cord, 429

in the brain, 420
Transudation, 359, 365
Trichina spiralis, 675
Tricuspid valve, 320
Trigeminus nerve, 526
Trommer's test for glucose, 62

in the urine, 63

interfered with by albuminose, 87
Tubal pregnancy, 711
Tube, Eustachian, 654
Tuber annulare, 439, 499

action of, 500
Tubercula bigemina, 517
Tubercula quadrigemina, 436, 516

reflex action of, 518

crossed action of, 521

development of, 770
Tubes, Fallopian, 692

salivary, 139
Tubules, gastric, 152

uterine, 750

Tufts, placental, 757, 758, 759
Tunica vaginalis testis, formation of,

788
Tympanum, of the ear, 649

UMBILICAL CORD, 763
separation of, after birth, 810
Umbilical hernia, 777
Umbilical vesicle, 738, 745, 776
Umbilical veins, formation of, 794

obliteration of, 801
Urachus, 780
Urate, sodium, 111, 382
Urates, deposits of, in the urine, 390
Urea, 108, 379

daily quantity of, 109

conversion of, into ammonium car-
bonate, 108, 394
Uric acid, 111

deposited from urine, 385, 392
Urine, 374

general character of, 52, 112, 374

physical properties of, 376

composition of, 378

ingredients of, 379

reactions of, 384

interference of, with Trommer's test,
63

abnormal ingredients of, 386

deposits in, 390

acid fermentation of, 393

alkaline fermentation of, 394
Urinary bladder, closure and evacuation
Of, 468

INDEX.

825

Urinary bladder, development of, 779

Urobiline, 99

Urochrome, 99

Urohematine, 99

Urosaciue, 99

Urosine, 99

Uterus, 692, 693

mucous membrane of, 750
changes in, after impregnation, 751
regeneration of, after delivery, 766
development of, 789
position of, at birth, 790

Uterus bicornis, 789

Utricle, of the internal ear, 655

yALVE, Eustachian, 804
V of the foramen ovale, 806

of Vieussens, 525
Valves, of the heart, 320, 323

of the veins, 342

of the lymphatics, 355, 370
Valvulse conniventes, 135

formation of, 776
Vasa deferentia, 698

formation of, 786, 787
Vascular system, development of, 791
Vapor, watery, exhalation of, 43

from the lungs, 288

from the skin, 316

Vegetable food, necessary to man, 114
Vegetables, as food, 122

production of organic matter in, 60

production of fat in, 69

green coloring matter of, 101

absorption of carbonic acid and ex-
halation of oxygen by, 60, 131, 270

respiration in, 270

production of heat in, 301, 302
Vegetative functions, 31
Veins, 340

motion of the blood in, 341

action of the valves of, 342

rapidity of blood-current in, 313

omphalo-mesenteric, 792

umbilical, 794

vertebral, 797

Vena azygos, major and minor, forma-
tion of, 799

Venje cavse, formation of, 797, 798
Venous system, development of, 797
Ventricles, of the heart, situation of, 319

action of, 320

muscular fibres of, 328
Vernix caseosa, 774
Vertebral arteries, 792, 795
Vertebral veins, 797
Vertebrae, primitive, 735

permanent, formation of, 737, 772
Vesicle, umbilical, 738, 745, 776
Vesicles, adipose, 72

cerebral, 769

Vesicles, pulmonary, 274

seminal, 698
Vesiculfe seminales, 698

formation of, 787
Vestibule, of the internal ear, 654
Vieussens, valve of, 525
Villi, of stomach, 152

of intestine, 189, 194

of chorion, 747
Visceral folds, 781
Vision, sense of, 607

acuteness of, 626

field of, 627

line of direct, 628

point of distinct, 629

erect, 638

binocular, 639
Vital phenomena, 29
Vitellus, 685, 686

segmentation of, 722

formation of, in foetus, 790
Vitelline circulation, 791
Vitelline membrane, 685
Vitelline spheres, 722
Vitreous body, of the eye, 612
Voice, formation of, in the larynx, 565

loss of, after division of the pneumo-
gastric nerves, 566

of the spinal accessory nerves, 573
Volition, seat of, in the tuber annulare,

501
Vomiting, how produced, 556

WATER, as a proximate principle, 40
proportion of, in the tissues and

fluids, 41
probable formation of, in the system,

42
discharge of, from the body, 43, 288,

316
Weight of organs, comparative, in the

foetus at term and adult, 810
Wheaten bread, composition of, 121
White globules of the blood, 254
amoeboid movements of, 255
sluggish movement of, in the circula-
tion, 348
White substance of the nervous system,

409
Wolflfian bodies, 784

atrophy and disappearance of, 785
Woorara, action of, on motor nerves,
422

YEAST-FUNGUS, 65
Yolk, 686, 689, 729

17 ON A pellucida, 685

53

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RAMSBOTHAM'S MIDWIFERY. In one imperial octavo volume of 650 pages, many plates

and cuts. Leather 7 00

SWAYNE'S OBSTETRIC APHORISMS. From the 5th English edition. In one small 12mo.

volume. Cloth 1 2.3

SURGERY,

ASH HURST'S PRINCIPLES AND PRACTICE OF SURGERY. In one large octavo volume

of 1000 pages, and 550 illustrations. Cloth, $6.50 ; leather 7 50

BRYANT'S PRACTICE OF SURGERY. In one handsome Svo. volume of over 1000 pages,

and many illustrations. Cloth, $6.25 ; leather 7 2.5

DRUITT'S SURGERY. From the 8th English edition. In one handsome octavo volume of about

700 pages, and 432 illustrations. Cloth, $4 ; leather 500

ERICHSEN'S SCIENCE AND ART OF SURGERY. From the 6th English edition. In two

large octavo volumes of over 1700 pages, with more than 700 illustrations. Cloth, $') ;

leather 11 00

GROSS' SYSTEM OF SURGERY. Fifth and enlarged edition. In two imperial octavo vols.

of over 2200 pages, and 1403 illustrations. Leather 15 00

MILLER'S PRINCIPLES OF SURGERY. In one large Svo. volume, with 240 illustrations.

Cloth 3 75

MILLER'S PRACTICE OF SURGERY. la one large Svo. vol., with 364 illustrations. Cloth 3 75
HAMILTON ON FRACTURES AND DISLOCATIONS. Fifth and revised edition. In one

handsome octavo volume of 831 pages, and 344 illustrations. Cloth, $5.75; leather 6 75

OPHTHALMOLOGY.

LAWRENCE & MOON'S OPHTHALMIC SURGERY. Second edition. In one Svo. volume.

Cloth 2 75

LAWSON ON INJURIES OF THE EYE. In one octavo vol., many illustrations. Cloth.... 3 50
WELLS ON DISEASES OF THE EYE. Second revised and enlarged edition. In one large

octavo volume of over 750 pages, and many illustrations. Plates. Cloth, $5 ; leather. , . . 6 00

JTJRISPBUDENCE.

TAYLOR'S MANUAL OF MEDICAL JURISPRUDENCE. Seventh American edition. Edited
by John J. Reese, M.D. In one large octavo volume of nearly 900 pages. Cloth, $5;
leather 6 00

TAYLOR'S PRINCIPLES AND PRACTICE OF MEDICAL JURISPRUDENCE. Second edition.

In two large octavo volumes. Cloth, $10; leather 12 00

TAYLOR ON POISONS. Third edition. In one Svo. volume of 850 pages, and many illus-
trations. Cloth, $5.50; leather 6 5)

DICTIONARIES AND MANUALS.

DUNGLISON'S MEDICAL LEXICON. A new and revised edition. Edited by Richard J.

Dunglison, M.D. In one royal octavo volume of over 1100 pages. Cloth, $6.50; leather 7 50
HOBLYN'S MEDICAL DICTIONARY. In one handsome 12mo. volume of over 500 pages.

Cloth, $1.50; leather 2 00

HARTSHORNE'S CONSPECTUS OF THE MEDICAL SCIENCES. Second and revised edition.

In one large 12mo. volume of over 1000 page,, and 477 illustrations. Cloth, $1.25 ; leather 5 00
LUDLOW'S MANUAL OF EXAMINATIONS. Third edition. In one large 12mo. volume,

many cuts. Cloth, $3.25 ; leather 3 75

NEILL & SMITH'S COMPENDIUM OF THE MEDICAL SCIENCES. In one handsome octavo

volume of about 1000 pages, with 374 illustrations. Cloth, $t ; leather 4 75

TANNER'S MANUAL OF CLINICAL MEDICINE. From the second English edition. In one

12mo. vol. of 375 pages. Cloth I 50

HENRY C. LEA— Philadelphia.

O.

(LATE LEA & BLANCHARD'S)

OIF

MEDICAL AND SURGICAL PUBLICATIONS.

In asking the attention of the profession to the works advertised in the following
pages, the publisher would state that no pains are spared to secure a continuance of
the confidence earned for the publications of the house by their careful selection and
accuracy and finish of execution.

The printed prices are those at which books can generally be supplied by booksellers
throughout the United States, who can readily procure for their customers any works
not kept in stock. Where access to bookstores is not convenient, books will be sent
by mail post-paid on receipt of the price, but no risks are assumed either on the
money or the books, and no publications but my own are supplied. Gentlemen will
therefore in most cases find it more convenient to deal with the nearest bookseller.

An ILLUSTRATED CATALOGUE, of 64 octavo pages, handsomely, printed, will be for-
warded by mail, post-paid, on receipt of ten cents.

HENRY C. LEA.

Nos. 706 and 708 SANSOM ST., PHILADELPHIA, September, 1875.

ADDITIONAL INDUCEMENT FOR SUBSCRIBERS TO

THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES.

THEEE MEDICAL JOURNALS, containing over 2000 LAEGE PAGES,
Free of Postage, for SIX DOLLAES Per Annum,

TERMS FOR 1875:

THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES, and ) Five Dollars per annum,
THE MEDICAL NEWS AND LIBRARY, both free of postage, j in advance.

THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES, published quar- "] q- -r\ -\-\

terly (llnO pages per annum), with

THE MEDICAL NEWS AND LIBRARY, monthly (384 pp. per annum), and }• per annum,
THE MONTHLY ABSTKACT OF MEDICAL SCIENCE (592 pages per | ina(jvan,

annum),

SEPARATE SUBSCRIPTIONS TO

THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES, when not paid for in advance,

Five Dollars.

THE MEDICAL NEWS AND LIBRARY, free of postage, in advance, One Dollar.
THE MONTHLY ABSTRACT OF MEDICAL SCIENCE, free of postage, in advance, Two

Dollars and a Half.

It is manifest that only a very wide circulation can enable so vast an amount of
valuable practical matter to be supplied at a price so unprecedentedly low. The pub-
lisher, therefore, has much gratification in stating that the very great favor with which
these periodicals are regarded by the profession promises to render the enterprise a
permanent one, and it is with especial pleasure that he acknowledges the valuable
assistance spontaneously rendered by so many of the old subscribers to the "JOUR-
NAL," who have kindly made known among their friends the advantages thus offered,
and have induced them to subscribe. Relying upon a continuance of these friendly
exertions, he hopes to be able to maintain the unexampled rates at which these works

(For "THE OBSTETRICAL JOURNAL," see p. 22.)

2 HENRY C. LEA'S PUBLICATIONS — (Am. Journ. Med. Sciences).

are now offered, and to succeed in his endeavor te place upon the table of every
reading practitioner in the United States the equivalent of three large octavo volumes,
at the comparatively trifling cost of Six DOLLARS per annum.

These periodicals are universally known for their high professional standing in their
several spheres.

I.

THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES,
EDITED BY ISAAC HAYS, M.D.,

is published Quarterly, on the first of January, April, July, and October. Each num-
ber contains nearly three hundred large octavo pages, appropriately illustrated wher-
ever necessary. It has now been issued regularly for over FIFTY years, during nearly
the whole of which time it has been under the control of the present editor. Through-
out this long period, it has maintained its position in the highest rank of medical
periodicals both at home and abroad, and has received the cordial support of the en-
tire profession in this country. Among its Collaborators will be found a large number
of the most distinguished names of the profession in every section of the United
States, rendering the department devoted to

ORIGINAL COMMUNICATIONS

full of varied and important matter, of great interest to all practitioners. Thus, during
1874, articles have appeared in its pages from nearly one hundred gentlemen of the
highest standing in the profession throughout the United States.*

Following this is the "REVIEW DEPARTMENT," containing extended and impartial
reviews of all important new works, together with numerous elaborate "ANALYTICAL
AND BIBLIOGRAPHICAL NOTICES" of nearly all the medical publications of the day.

This is followed by the "QUARTERLY SUMMARY OF IMPROVEMENTS AND DISCOVERIES
IN THE MEDICAL SCIENCES," classified and arranged under different heads, presenting
a very complete digest of all that is new and interesting to the physician, abroad as
well as at home.

Thus, during the year 1874, the "JOURNAL" furnished to its subscribers 85 Orig-
inal Communications, 113 Reviews and Bibliographical Notices, and 305 articles in
the Quarterly Summaries, making a total of about FIVE HUNDRED articles emanating
from the best professional minds in America and Europe.

That the efforts thus made to maintain the high reputation of the "JOURNAL" are
successful, is shown by the position accorded to it in both America and Europe as a
national exponent of medical progress: —

America continues to take a great place in this
class of journals (quarterlies), at, the head of which
the great work of Dr. Hays, the American Journal
of the Medical Sciences, still holds its ground, as our
quotations have often proved. — Dublin Med. Press
uitd Circular, Jan. 31, 1872.

Of English periodicals the Lancet, and of American
the Am. Journal of the Medical Sciences, are to be
regarded as necessities to the reading practitioner. —
Ji Y. Medical Gazette, Jan. 7, 1871.

The American Journal of the Medical Sciences

rowed matter it contains, and has established for
itself a reputation in every country where medicine
is cultivated as a science. — Brit, and For. Med.-Chi-
rurg. Review, April, 1S71.

This, if not the best, is one of the best-conducted
medical quarterlies in the English language, and the
present number is not by any means inferior to its
predecessors. — London Lancet, Aug. 23, 1873.

Almost the only one that circulates everywhere,
all over the Union and in Europe. — London Medical
Times, Sept. 5, 1868.

yields to none in the amount of original and bor-

And that it was specifically included in the award of a medal of merit to the Pub-
lisher in the Yienna Exhibition" in 1873.

The subscription price of the " AMERICAN JOURNAL OF THE MEDICAL SCIENCES" has
never been raised during its long career. It is still FIVE DOLLARS per annum ; and
when paid for in advance, the subscriber receives in addition the "MEDICAL NEWS AND
..LIBRARY," making in all about 1500 large octavo pages per annum, free of postage.

II.

THE MEDICAL NEWS AND LIBRARY

is a monthly periodical of Thirty-two large octavo pages, making 384 pages per
annum. Its "NEWS DEPARTMENT" presents the current information of the day, with
Clinical Lectures and Hospital Gleanings; while the "LIBRARY DEPARTMENT" is de-
voted to publishing standard works on the various branches of medical science, paged

* Communications are invited from gentlemen in all parts of the country. Elaborate articles inserted
<by the Editor are paid for by the Publisher.

HENRY C. LEA'S PUBLICATIONS— (Am. Journ. Med. Sciences). 3

separately, so that they can be removed and bound on completion. In this manner
subscribers have received, without expense, such works as " WATSON'S PKACTICE,"
" TODD AND BOWMAN'S PHYSIOLOGY," "WEST ON CHILDREN," " MALGAIGNE'S SUR-
GERY," &c. &c. With Jan. 1875, was commenced the publication of Dr. WILLIAM
STOKES'S new work on FEVER (see p. 14), rendering- this a very desirable time for new
subscriptions.

As stated above, the subscription price of the " MEDICAL NEWS AND LIBRARY" is
ONE DOLLAR per annum in advance ; and it is furnished without charge to all advance
paying subscribers to the ''AMERICAN JOURNAL OF THE MEDICAL SCIENCES."

III.

THE MONTHLY ABSTRACT OF MEDICAL SCIENCE,

The publication in England of Banking's " HALF-YEARLY ABSTRACT OF THE MEDI-
CAL SCIENCES" having ceased with the volume for January, 1874, its place has been
supplied in this country by a monthly "ABSTRACT" containing forty-eight large octavo
pages each month, thus furnishing in the course of the year about six hundred pages,
the same amount of matter as heretofore embraced in the Half-Yearly Abstract.
As the discontinuance of the "Ranking" arose from the multiplication of journals
appearing more frequently and presenting the same character of material, it has been
thought that this plan of monthly issues will better meet the wants of subscribers,
who will thus receive earlier intelligence of the improvements and discoveries in the
medical sciences. The aim of the MONTHLY ABSTRACT will be to present a careful
condensation of all that is new and important in the medical journalism of the world,
and all the prominent professional periodicals of both hemispheres will be at the dis-
posal of the Editors.

Subscribers desiring to bind the ABSTRACT will receive, on application at the end
of each year, a cloth cover, gilt lettered, for the purpose, or it will be sent free by
mail on receipt of the postage, which, under existing laws, will be six cents.

The subscription to the " MONTHLY ABSTRACT," free of postage, is Two DOLLARS
AND A HALF a year, in advance.

As stated above, however, it will be supplied in conjunction with the "AMERICAN
JOURNAL OF THE MEDICAN SCIENCES" and the "MEDICAL NEWS AND LIBRARY," making
in all about rJ VENTY-ONE HUNDRED pages per annum, the whole free of postage, for
Six DOLLARS a year, in advance.

The first volume of the " MONTHLY ABSTRACT," from July to December, 1874, can
be had by those who desire to have complete sets, if early application be made, for
$1 50, forming a handsome octavo volume of 300 pages, cloth.

In this effort to bring so large an amount of practical information within the reach
of every member of the profession, the publisher confidently anticipates the friendly
aid of ail who are interested in the dissemination of sound medical literature. He
trusts, especially, that the subscribers to the "AMERICAN MEDICAL JOURNAL" will call
the attention of their acquaintances to the advantages thus offered, and that he will
be sustained in the endeavor to permanently establish medical periodical literature
on a footing of cheapness never heretofore attempted.

PEEMIUM POR NEW SUBSOKIBEES TO TEE " JOUKNAL,"

Any gentleman who will remit the amount for two subscriptions for 1875, one of
which must be for a new subscriber, will receive as a PREMIUM, free by mail, a copy of
"FLINT'S ESSAYS ON CONSERVATIVE MEDICINE" (for advertisement of which see p. 15),
or of "STURGES'S CLINICAL MEDICINE" (see p. 14), or of the new edition of "SWAYNE'S
OBSTETRIC APHORISMS" (see p. 24), or of "TANNER'S CLINICAL MANUAL" (see p. 5),
or of " CHAMBERS'S RESTORATIVE MEDICINE" (see p. 16), or of " WEST ON NERVOUS.
DISORDERS OF CHILDREN" (see page 21).

%* Gentlemen desiring to avail themselves of the advantages thus offered will do
well to forward their subscriptions at an early day, in order to insure the receipt of
complete sets for the year 1875, as the constant increase in the subscription list
almost always exhausts the quantity printed shortly after publication.

10^* The safest mode of remittance is by bank check or postal money order, drawn
to the order of the undersigned. Where these are not accessible, remittances for the
"JOURNAL" may be made at the risk of the publisher, by forwarding in REGISTERED
letters. Address,

HENRY C. LEA,
Nos. 706 and 708 SANSOM ST., PHILADELPHIA, PA.

u. IAEA'S

ruBLicATiONS — (JJictionames).

J^UNGLISON (ROBLEY), M.D.,

Late Professor of Institutes of Medicine in Jefferson Medical College, Philadelphia.

MEDICAL LEXICON; A DICTIONARY OP MEDICAL SCIENCE: Con-
taining a concise explanation of the various Subjects and Terms of Anatomy, Physiology,
Pathology, Hygiene, Therapeutics, Pharmacology, Pharmacy, Surgery, Obstetrics, Medical
Jurisprudence, and Dentistry. Notices of Climate and of Mineral Waters; Formulae for
Officinal, Empirical, and Dietetic Preparations; with the Accentuation and Etymology of
the Terms, and the French and other Synonymes ; so as to constitute a French as well as
English Medical Lexicon. A New Edition. Thoroughly Revised, and very greatly Mod-
ified and Augmented. By RICHARD J. DUNGLISON, M.D. In one very large and hand-
some royal octavo volume of over 1100 pages. Cloth, $6 50; leather, raised bands, $7 50.
(Just Issued.)

The object of the author from the outset has not been to make the work a mere lexicon or
dictionary of terms, but to afford, under each, a condensed view of its various medical relations,
and thus to render the work an epitome of the existing condition of medical science. Starting
with this view, the immense demand which has existed for the work has enabled him, in repeated-
revisions, to augment its completeness and usefulness, until at length it has attained the position
of a recognized and standard authority wherever the language is spoken.

Special pains have been taken in the preparation of the present edition to maintain this en-
viable reputation. During the ten years which have elapsed since the last revision, the additions
to the nomenclature of the medical sciences have been greater than perhaps in any similar period
of the past, and up to the time of his death the author labored assiduously to incorporate every-
thing requiring the attention of the student or practi'ioner. Since then, the editor has been
equally industrious, so that the additions to the vocabulary are more numerous than in any pre-
vious revision. Especial attention has been bestowed on the accentuation, which will be found
marked on every word. The typographical arrangement has been much improved, rendering
reference much more easy, and every care has been taken with the mechanical execution. The
work has been printed on new type, small but exceedingly clear, with an enlarged page, so that
the additions have been incorporated with an increase of but little over a hundred pages, and
the volume now contains the matter of at least four ordinary octavos.

A book well known to our readers, and of which
every American ought to be proud. When the learned
author of the work passed away, probably all of us
fen ml lest the book should net maintain its place
iu the advancing science whose terms it defines. For-
tnna-tely, Dr. Kichard J. Dunglison, having assisted his
father iu the revision of several editions of the work,
and having been, therefore, trained in the methods and
imbued with the spirit of the book, has been able to
edit it, not in the patchwork manner so dear to the
heart of book editors, so repulsive to the taste of intel-
ligent book readers, but to edit it as a work of the kind
should be edited — to carry it on steadily, without jar
or interruption, along the grooves of thought it has
travelled during its lifetime. To show the magnitude
of the task which Dr. Dunglison has assumed and car-
ried through, it is only necessary to state that more
than six thousand new subjects have been added in the
present edition. Without occupying more space with the
theme, we congratulate the editor on the successful
completion of his labors, and hope he may reap the well-
earned reward of profit and honor. — Ph-da. Med. Times.
Jan. 3, 1874.

About the first book purchased by the medical stu-
dent is the Medical Dictionary. The lexicon explana-
tory of technical terms is simply a sine qua non. In a
science so extensive, and with such collaterals as medi-
cine, it is as much a necessity also to the practising
physician. To meet the wants of students and most
physicians, the dictionary must be condensed while
comprehensive, and practical while perspicacious. Jt
was because Dunglison's met these indications that it
became at once the dictionary of general use wherever
medicine was studied in the English language. In no
i';L-iiier revision have tlie alterations and additions been
s< > great. More than six thousand new subjects and terms
have been added. The chief terms have been set in black
letter, while the derivatives follow in small caps; an
arrangement which greatly facilitates reference. WTe
may safely confirm the hope ventured by the editor
'• that the work, which possesses for him a filial as well
as an individual interest, will be found worthy a con-
tinuance of the position so long accorded to it as a I references. — London Medical Gazette.
standard authority." — Cincinnati Clinic, Jan. 10, 1874. |

We are glad to see a new edition of this invaluable
work, and to find that it has been so thoroughly revised,
and so greatly improved. The dictionary, iu its pre-
sent form, is a mtdical library in itself, and one of
which every physician should be possessed.— A". 1". Med.
Journal, Feb. 1874.

With a history of forty years of unexampled success
and universal indorsement by the medical profession of
the western continent, it would be presumption in any
living medical American to essay its review. No re-
viewer, however able, can add to its fame; no captious
critic, however caustic, can remove a single stone from
its firm and enduring foundatipn. It is destined, as a
colossal monument, to perpetuate the solid and richly
deserved fame of Kobley Dunglison to coming genera-
tions. The large additions made to the vocabulary, we
think, will be welcomed by the profession as supplying
the want of a lexicon fully up with the march of sci-
ence, which has been increasingly felt for some years
past. The accentuation of terms is very complete, and,
as far as we have been able to examine it, very excel-
lent. WTe hope it may be the means of securing greater
uniformity of pronunciation among medical men. — At-
lanta Med. and Surg. Journ., Feb. 1874.

It would be mere waste of words in us to express
our admiration of a work which is so universally
and deservedly appreciated. The most admirable
work of its kind in the English language. — Glasgow
Medical Journal, January, 1866.

A work to which there is no equal in the English
language. — Edinburgh Medical Journal.

Few works of the class exhibit a grander monument
i)f patient research and of scientific lore. The extent
of the sale of this lexicon is sufficient to testify to its
asefulness, and to the great service conferred by Dr.
Robley Dunglison on the profession, and indeed on
ithers, by its issue. — London Lancet, May 13, 1865.

It has the rare merit that it certainly has no rival
in the English language for accuracy and extent of

fJOBLYN (RICHARD D.), M.D.

A DICTIONARY OF THE TERMS USED IN MEDICINE AND

THE COLLATERAL SCIENCES. Revised, with numerous additions, by ISAAC HATS,
M.D., Editor of the "American Journal of the Medical Sciences." In one large royal
12mo. volume of over 500 double-columned pages; cloth, $1 50 ; leather, $2 00.
It is the best book of definitions we have, and ought always to be aponthe •Indent's table.— Southern
.Med. and Surg. Journal.

HENRY 0. LEA'S PUBLICATIONS — (Manuals).

WEILL (JOHN], M.D., and &MITH (FRANCIS G.), M.D.,

Prof, of the Institutes of Medicine hi the Univ. of Penna.

AN ANALYTICAL COMPENDIUM OF THE VARIOUS

BRANCHES OF MEDICAL SCIENCE; for the Use and Examination of Students. A
new edition, revised and improved. In one very large and handsomely printed royal 12mo.
volume, of about one thousand pages, with 374 wood cuts, cloth, $4; strongly bound in
leather, with raised bands, $4 75.

The Compend of Drs. Neill and Smith is incompara-
bly tke most valuable work of its class ever published
*.n this country. Attempts have been made in various
ijnarters to squeeze Anatomy, Physiology, Surgery,
the Practice of Medicine, Obstetrics, Materia Medica,
*nd Chemistry into a single manual; but the opera-
tion has signally failed in the hands of all up to the
advent of "Neill and Smith's" volume, which is quite
». miracle of success. The outlines of the whole are
:«,dffiirably drawn and illustrated, and the authors
are eminently entitled to the grateful consideration
of the student of every class. — N. 0. Med. and Surg.
Journal.

There are but few students or practitioners of me-
dicine unacquainted with the former editions of this
anassnming though highly instructive work. The
whole science of medicine appears to have been sifted,
»s the gold-bearing sands of El Dorado, and the pre-

cious facts treasured up in this little volume. A com-
plete portable library so condensed that the student
may make it his constant pocket companion. — West-
ern Lancet.

In the rapid course of lectures, where work for the
students is heavy, and review necessary for an exa-
mination, a compend is not only valuable, but it is
almost a sine qua non. The one before us is, in most
of the divisions, the most unexceptionable of all books
of the kind that we know of. Of course it is useless
for us to recommend it to all last course students, but
there is a class to whom we very sincerely commend
tnis cheap book as worth its weight in silver— that
class is the graduates in medicine of more than ten
years' standing, who have not studied medicine
since. They will perhaps find out from it that the
science is not exactly now what it was when they
left it off.— The Stethoscope.

IffARTSHORNE (HENRY], M. D.,

Professor of Hygiene in the University of Pennsylvania.

A CONSPECTUS OF THE MEDICAL SCIENCES; containing

Handbooks on Anatomy, Physiology, Chemistry, Materia Medica, Practical Medicine
Surgery, and Obstetrics. Second Edition, thoroughly revised and improved. In one large
royal 12mo. volume of more than 1000 closely printed pages, with 477 illustrations on
wood. Cioth, $4 25; leather, $5 00. (Lately Issued.)

The favor with which this work has been received has stimulated the author in its revision to
render it in every way fitted to meet the wants of the student, or of the practitioner desirous to
refresh his acquaintance with the various departments of medical science. The various sections have
been brought up to a level with the existing knowledge of the day, while preserving the condensa-
tion of form by which so vast an accumulation of facts have been brought within so narrow a
eompnss. The series of illustrations has been much improved, while by the use of a smaller type
the additions have been incorporated without increasing unduly the size of the volume.

The work before us has already successfully assert- | and the clear and instructive illustrations in some
ed its claim to the confidence and favor of the profes- parts of the work.— American Journ. of Pharmacy
siou ; it but remains for us to say that in the present j Philadelphia, July, 1874.

The volume will be found useful, not only to stu-
dents, but to many others who may desire to refresh
their memories with the smallest possible expendi-
ture of time.— N. Y. Med. Journal, Sept. 1874.

The student will find,this the most convenient and
useful book of the kind on which he can lay his
hand.— Pacific Med. and Surg. Journ., Aug. 1874.

edition the whole work has been fully overhauled
and brought up to the present status of the science. —
Atlanta Med. and Surg. Journal, Sept. 1874.

The work is intended as an aid to the medical stu-
dent, and as such appears to admirably fulfil its ob-
ject by its excellent arrangement, the full compilation
of facts, the perspicuity and terseness of language,

fUDLOW (J.L.), M.D.
A MANUAL OF EXAMINATIONS upon Anatomy, Physiology,

Surgery, Practice of Medicine, Obstetrics, Materia Medica, Chemistry, Pharmacy, and
Therapeutics. To which is added a Medical Formulary. Third edition, thoroughly revised
and greatly extended and enlarged. With 370 illustrations. In one handsome royal
12mo. volume of 816 large pages, cloth, $3 25; leather, $3 75.

The arrangement of this volume in the form of question and answer renders it especially suit-
fcbla for the office examination of students, and for those preparing for graduation.

WANNER (THOMAS HA WKES), M. D., frc.

A MANUAL OF CLINICAL MEDICINE AND PHYSICAL DIAG-
NOSIS. Third American from the Second London Edition. Revised and Enlarged by
TILBURY Fox, M. D., Physician to the Skin Department in University College Hospital,
Ac. In one neat volume small 12mo., of about 375 pages, cloth, $1 50.

*** By reference to the " Prospectus of Journal" on page 3, it will be seen that this work is
offered as a premium for procuring new subscribers to the "AMERICAN JOURNAL OP THE MEDICAL
SCIENCES."

Taken as a whole, it is the most compact vade me-
cum for the use of the advanced student and junior
practitioner with which we are acquainted. — Boston
Med. and Surg. Journal, Sept. 22, 1870.

It contains so much that is valuable, presented in
so attractive a form, that it can hardly be spared
even in the presence of more full and complete works.
Its convenient size makes it a valuable companion
to the country practitioner, and if conitantly car-
ried by him, would often render him good service,
and relieve many a doubt and perplexity. — Leaven-

The objections commonly, and justly, urged against
the general run of "compends," "conspectuses," and
other aids to indolence, are not applicable to this little
volume, which contains in concise phrase just those
practical details that are of most use in daily diag-
nosis, but which the young practitioner finds it diffi-
cult to carry always in his memory without some
quickly accessible means of reference. Altogether,
the book is one which we can heartily commend to
those who have not opportunity for extensive read-
ing, or who, having read much, still wish an occa-
sional practical reminder. — N. T. Med. Gazette, NOT.

HENRY C. LEA'S PUBLICATIONS — (Anatomy).

(HENRY), F.R.S.,

Lecturer on Anatomy at St. George's Hospital, London.

ANATOMY, DESCRIPTIVE AND SURGICAL. The Drawings by

H. V. CARTER, M. D., late Demonstrator on Anatomy at St. George's Hospital ; the Dissec-
tions jointly by the AUTHOR and DR. CARTER. A new American, from the fifth enlarged
and improved London edition. In one magnificent imperial octavo volume, of nearly 906
pages, with 465 large and elaborate engravings on wood. Price in cloth, $6 00 ; lea-
ther, raised bands, $7 00. (Just Issued.)

The author has endeavored in this work to cover a more extended range of subjects than is cus-
tomary in the ordinary text-books, by giving -not only the details necessary for the student, but
also the application of those details in the practice of medicine and surgery, thus rendering it both
a guide for the learner, and an admirable work of reference for the active practitioner. The en -
gravings form a special feature in the work, many of them being the size of nature, nearly all
original, and having the names of the various parts printed on the body of the cut, in place of
figures of reference, with descriptions at the foot. They thus form a complete and splendid series,
which will greatly assist the student in obtaining a clear idea of Anatomy, and will also serve to
refresh the memory of those who may find in the exigencies of practice the necessity of recalling
the details of the dissecting room; while combining, as it does, a complete Atlas of Anatomy, with
a thorough treatise on systematic, descriptive, and applied Anatomy, the work will be found of
essential use to all physicians who receive students in their offices, relieving both preceptor and
pupil of much labor in laying the groundwork of a thorough medical education.

Notwithstanding the enlargement of this edition, it has been kept at its former very moderate
price, rendering it one of the cheapest works now before the profession.

The illustrations are beautifully executed, and ren-
der this work an indispensable adjunct to the library
of the surgeon. This remark applies with great force

From time to time, as successive editions have ap-
peared, we have had much pleasure in expressing
the general judgment of the wonderful excellence of

to those surgeons practising at a distance from our j Gray's Anatomy. — Cincinnati Lancet, July, 1870.
large cities, as the opportunity of refreshing their Altogether, it is unquestionably the most complete

and serviceable text-book in anatomy that has evov
been presented to the student, and forms a striking
contrast to the dry and perplexing volumes on the
same subject through which their predecessors strug-
gled in days gone by. — N. Y. Med. Record, June 15,
1870.

To commend Gray's Anatomy to the medical pro-
fession is almost as much a work of supererogation
as it would be to give a favorable notice of the Bible
in the religious press. To say that it is the most
complete and conveniently arranged text-book of its
kind, is to repeat what each generation of students
has learned as a tradition of the elders, and verified
by personal experience. — N Y. Med. Gazette, Dec.
17,1870.

memory by actual dissection is not always attain-
able.— Canada Med. Journal, Aug. 1870.

The work is too well known and appreciated by the
profession to need any comment. No medical man
can afford to be without it, if its only merit were to
serve as a reminder of that which so soon becomes
forgotten, when not called into frequent use, viz., the
relations and names of the complex organism of the
human body. The present edition is much improved.
—California Med. Gazette, July, 1870.

Gray's Anatomy has been so long the standard of
perfection with every student of anatomy, that we
need do no more than call attention to the improve-
ment in the present edition. — Detroit Review of Med.
and Pharm., Aug. 1870.

VMITH (HENRY H.), M.D., and JJORNER ( WILLIAM E.},M.D.,

Prof, of Surgery in the Univ. of Penna., &c. LateProf. of Anatomy in the Univ. ofPenna., Ac.

AN ANATOMICAL ATLAS, illustrative of the Structure of the

Human Body. In one volume, large imperial octavo, cloth, with about six hundred and

fifty beautiful figures. $4 50.

The plan of this Atlas, which renders it so pecn- 1 the kind that has yet appeared ; and we must add,
liarly convenient for the student, and its superb ar- | the very beautiful manner in which it is "got up,"
tistical execution, have been already pointed out. We ! is so creditable to the country as to be flattering to
must congratulate the student upon the completion our national pride. — American Medical Journal.
of this Atlas, as it is the most convenient work of I

VHARPEY ( WILJjIAM], M.D., and Q VAIN (JONES fr RICHARD).
HUMAN ANATOMY. Revised, with Notes and Additions, by JOSEPH

LEIDT, M. D., Professor of Anatomy in the University of Pennsylvania. Complete in two
large octavo volumes, of about 1300 pages, with 511 illustrations; cloth, $6 00.
The very low price of this standard work, and its completeness in all departments of the subject,
should command for it a place in the library of all anatomical students.

fTO DOES (RICHARD M.}, M.D.,

Late Demonstrator of Anatomy in the Medical Department of Harvard University.

PRACTICAL DISSECTIONS. Second Edition, thoroughly revised. In

one neat royal 12mo. volume, half-bound, $2 00.

The object of this work is to present to the anatomical student a clear and concise description
of that which he is expected to observe in an ordinary couise of dissections. The author has
endeavored to omit unnecessary details, and to present the subject in the form which many years'
experience has shown him to be the most convenient and intelligible to the student. In the
revision of the present edition, he has sedulously labored to render the volume more worthy of
the favor with which it has heretofore been received.

HOENER'S SPECIAL ANATOMY AND HISTOLOGY. I In 2 vols. 8vo., of over 1000 pages, with more tha»
Eighth edition, extensively revised and modified. 1 300 wood-cuts; cloth, $6 00.

HBNRY C. LEA'S PUBLICATIONS— (Anatomy).

\XTILSON (ERASMUS), F.R.S.

A SYSTEM OF HUMAN ANATOMY, General and Special. Edited

by W. H. GOBRECHT, M. D., Professor of General and Surgical Anatomy in the Medical Col-
lege of Ohio. Illustrated with three hundred and ninety-seven engravings on wood. In
one large and handsome octavo volume, of over 600 large pages; cloth, $4 00; leather,
$5 00.

The publisher trusts that the well-earned reputation of this long-established favorite will be
more than maintained by the present edition. Besides a very thorough revision by the author, it
has been most carefully examined by the editor, and the efforts of both have been directed to in-
troducing everything which increased experience in its use has suggested as desirable to render it
a complete text-book for those seeking to obtain or to renew an acquaintance with Human Ana-
tomy. The amount of additions which it has thus received may be estimated from the fact that
i,he present edition contains over one-fourth more matter than the last, rendering a smaller type
9>n<l an enlarged page requisite to keep the volume within a convenient size. The author has not
only thus added largely to the work, but he has also made alterations throughout, wherever there
appeared the opportunity of improving the arrangement or style, so as to present every fact in its
taost appropriate manner, and to render the whole as clear and intelligible as possible. The editor
lj.aa exercised the utmost caution to obtain entire accuracy in the text, and has largely increased
the number of illustrations, of which there are about one hundred and fifty more in this edition
than in the last, thus bringing distinctly before the eye of the student everything of interest or
Importance.

fJEATH (CHRISTOPHER), F.'R. C. S.t

Teacher of Operative Surgery in University College, London.

PRACTICAL ANATOMY: A Manual of Dissections. From the

Second revised and improved London edition. Edited, with additions, by W. W. KKSN,
M. D., Lecturer on Pathological Anatomy in the Jefferson Medical College, Philadelphia.
In one handsome royal 12ino. volume of 578 pages, with 247 illustrations. Cloth, $3 50 j
leather, $4 00. (Lately Published.)

lining its hold upon the slippery slopes of anatomy.

-St. Louis Med. and Surg. Journal, Mar. 10, 1871.
It appears to us certain that, as a guide in dissec-

,ion, and as a work containing facts of anatomy in

brief and easily understood form, this manual is

}>r. Keen, the American editor of this work, in his
preface, says: "In presenting this American edition
«f • Heath's Practical Anatomy,' I feel that I have
keon instrumental in supplying a want long felt for
a real dissector's manual," and this assertion of its

editor we deem is fully justified, after an examina- j ^plete. This work contains, also, very perfect
tion of its contents, for it is really an excellent worft. | nustrations of parts which can thus be more easily
Indeed, we do not hesitate to say, the best of its class
with which we are acquainted ; resembling Wilson
In terse aud clear description, excelling most of the
ao-called practical anatomical dissectors in the scope
<?f the subject aud practical selected matter. . . .
In reading this work, one is forcibly impressed with
Uie great pains the author takes to impress the sub-
ject upon the mind of the student. He is full of rare
e.ud pleasing little devices to aid memory in main-

inderstood and studied; in this respect it compares
'avorably with works of much greater pretension.
Such manuals of anatomy are always favorite works
with medical students. We would earnestly recom-
mend this one to their attention; it has excellences
which make it valuable as a guide in dissecting, as
well as in studying anatomy. — Buffalo Medical and
Surgical Journal, Jan. 1871.

f>ELLAMY(E.), F.R.C.S.

THE STUDENT'S GUIDE TO SURGICAL ANATOMY: A Text-

Book for Students preparing for their Pass Examination. With engravings on wood. In.
ono handsome royal 12nio. volume. Cloth, $2 25. (Just Issued.)

We welcome Mr. Bellamy's work, as a contribu-
tion to the study of regional anatomy, of equal value
to the student and the surgeon. It is written in a
clear and concise style, and its practical suggestions
add largely to the interest attachiug to its technical
details —Chicago Med. Examiner, March 1, 1874.

We cordially congratulate Mr. Bellamy upon hav-
ing produced it. — Med. Times and Qaz.

We cannot too highly recommend it. — Student's
Journal.

Mr. Bellamy has spared no pains to produce a real-
ly reliable student's guide to surgical anatomy — one
which all candidates for surgical degrees may con-
sult with advantage, and which posseses much ori-
ginal matter — Mad. Press and Circular.

MACLISE (JOSEPH).

SURGICAL ANATOMY. By JOSEPH MACLISE, Surgeon. In one

volume, very large imperial quarto ; with 68 large and splendid plates, drawn in the best
style and beautifully colored, containing 190 figures, many of them the size of life; together
with copious explanatory letter-press. Strongly and handsomely bound in cloth. Price
$14 00.

We know of no work on surgical anatomy which
nan compete with it. — Lancet.

The work of Maclise on surgical anatomy is of the

feighest value. In some respects it is the best publi-
cation of its kind we have seen, and is worthy of a
place in the library of any medical man, while the
student could scarcely make a better investment than
t h is. — The Western Journal of Medicine and Siirgery.
No such lithographic illustrations of surgical re-

$ions have hitherto, we think, been given. While
bhe operator is shown every vessel and nerve where
in operation is contemplated, the exact anatomist is
refreshed by those clear and distinct dissections,
which every one must appreciate who has a particle
of enthusiasm. The English medical press has quits
exhausted the words of praise, in recommending this
admirable treatise, — Boston Med. and Surg. Journ.

fJARTSHORNE (HENRY), M.D.,

•*•-*• Professor of Hygiene, etc , in the Univ. ofPenna.

HANDBOOK OF ANATOMY AND PHYSIOLOGY. Second Edi-
tion, revised. In ane ro.yal 12mo. volume, with 220 wood-cuts; cloth, $1 75. (Just Issued.)

HENRY C. LEA'S PUBLICATIONS — (Physiology).

MARSHALL (JOHN), F. R. S.,

fLuL Professor of Surgery in University College, London, &c.

OUTLINES OF PHYSIOLOGY, HUMAN AND COMPARATIVE.

With Additions by FRANCIS GURNEY SMITH, M. D., Professor of the Institutes of Medi-
cine in the University of Pennsylvania, &c. With numerous illustrations. In one large
and handsome octavo volume, of 1026 pages, cloth, $6 50 ; leather, raised bands, $7 50.
In fact, in every respect, Mr. Marshall has present- , tive, with which we are acquainted. To speak ol

this work in the terms ordinarily used on snch occa-
sions would not be agreeable to ourselves, and would
fail to do justice to its author. To write such a boofc
requires a varied and wide range of knowledge, con-
siderable power of analysis, correct judgment, ski}.}

ed us with a most complete, reliable, and scientific
work, and we feel that it is worthy our warmest
commendation. — St. Louis Med. Reporter, Jan. 1869.

We doubt if there is in the English language any
compend of physiology more useful to the student
than this work.— St. Louis Med. and Surg. Journal,
Jan. 1869.

It quite fulfils, in our opinion, the author's design
of making it truly educational in its character— which

in arrangement, and conscientious spirit. — London
Lancet, Feb. 22, 1868.

rp^,^r^^

asked.— Am. Journ. Med. Sciences, Jan. 1869.

We may now congratulate him on having com-
pleted the latest as well as the best summary of mod-
ern physiological science, both human and compara-

joyed the highest reputation as a teacher of physiol-
ogy, possessing remarkable powers of clear exposition
and graphic illustration. We have rarely the plea-
sure of being able to recommend a text-book so unre-
servedly as this.— British Med. Journal, Jar . 25, 1868.

CARPENTER (WILLIAM B.), M.D., F.R.S.,

V/ Examiner in Physiology and Comparative Anatomy in the University of London.

PRINCIPLES OF HUMAN PHYSIOLOGY; with their chief appli-
cations to Psychology, Pathology, Therapeutics, Hygiene and Forensic Medicine. A ne^
American from the last and revised London edition. With nearly three hundred illustrations.
Edited, with additions, by FRANCIS GTJRNEY SMITH, M. D., Professor of the Institutes o!
Medicine in the University of Pennsylvania, &c. In one very large and beautiful octavo
volume, of about 900 large pages, handsomely printed; cloth, $5 50 ; leather, raised bands,
$6 50.

With Dr. Smith, we confidently believe "that the
present will more than sustain the enviable reputa-
tion already attained by former editions, of being
one of the fullest and most complete treatises on the
subject in the English language." We know of none
from the pages of which a satisfactory knowledge of
the physiology of the human organism can be as well
obtained, none better adapted for the use of such as
take up the study of physiology in its reference to
the institutes and practice of medicine. — Am. Jour.
Med. Sciences.

We doubt not it is destined to retain a strong hold
on public favor, and remain the favorite text-book ia
our colleges. — Virginia Medical Journal.

. The above is the title of what is emphatically the
great work on physiology ; and we are conscious that
it would be a useless effort to attempt to add any-
thing to the reputation of this invaluable work, and
can only say to all with whom our opinion has any
influence, that it is our authority.— Atlanta Med..
Journal.

T>T THE SAME AUTHOR.

PRINCIPLES OF COMPARATIVE PHYSIOLOGY. New Ameri-
can, from the Fourth and Revised London Edition. In one large and handsome octavo
volume, with over three hundred beautiful illustrations. Pp. 752. Cloth, $5 00.
As a complete and condensed treatise on its extended and important subject, this work becomes
a necessity to students of natural science, while the very low price at which it is offered places it
within the reach of all.

JTIRKES ( WILLIAM SENHOUSE), M.D.

A MANUAL OF PHYSIOLOGY. Edited by W. MORRANT BAKER,

M.D., F.R.C.S. A new American from the eighth and improved London edition. With
about two hundred and fifty illustrations. In one large and handsome royal 12mo. vol-
ume. Cloth, $3 25; leather, $3 75. (Lately Issued.)

Kirkes' Physiology has long been known as a concise and exceedingly convenient text-book,
presenting within a narrow compass all that is important for the student. The rapidity with
which successive editions have followed each other in England has enabled the editor to keep it
thoroughly on a level with the changes and new discoveries made in the science, and the eighth
edition, of which the present is a reprint, has appeared so recently that it may be regarded as
the latest accessible exposition of the subject.

On the whole, there is very little in the book
which either the student or practitioner will nottind
of practical value and consistent -with our present
knowledge of this rapidly changing science ; and we
have no hesitation in expressing our opinion that
this eighth edition is one of the best handbooks on
physiology which we have in our language. — N. Y.
Med. Record, April 15, 1873.

This volume might well be used to replace many
of the physiological text-books in use in this coun-
try. It represents more accurately than the works
of Dalton or Flint, the present state of our knowl-
edge of most physiological questions, while it is
much less bulky and far more readable than the lar-

ger text-books of Carpenter or Marshall. The book
is admirably adapted to be placed in the hands of
students. — Boston Med. and Surg. Journ., April 10,
1873.

In its enlarged form it is, in our opinion, etill the
best book on physiology, most useful to the student.
—Phila. Med. Timed, Aug. 30, 1873.

This is undoubtedly the best work for students of
physiology extant. — Cincinnati Med. News, Sept. '73.

It more nearly repi'esents the present condition of
physiology than any other text-book on the subject. —
Detroit Rev. of Med. Pharm., Nov. 1873.

HENRY C. LEA'S PUBLICATIONS— (Physiology). 9

f)ALTON (J. (7.), M.D.,

-U Professor of Physiology in the College of Physicians and Surgeons, New York, &c.

A TREATISE ON HUMAN PHYSIOLOGY. Designed for the use

of Students and Practitioners of Medicine. Sixth edition, thoroughly revised and enlarged,
with three hundred and sixteen illustrations on wood. In one very beautiful octavo vol-
ume, of over 800 pages. (Nearly Ready.)

From the Preface to the Sixth Edition.

In the present edition of this book, while every part has received a careful revision, the ori-
ginal plan of arrangement has been changed only so far as was necessary for the introduction of
new material. Although the whole field of physiology has been cultivated, of late years, with
unusual industry and success, perhaps the most important advances have been made in the two
departments of Physiological Chemistry and the Nervous System. The number and classification
of the proximate principles, more especially, and their relation to each other in the process of
nutrition, have become, in many respects, better understood than formerly ; though it is evident
that this fundamental part of physiology is to receive, in the future, modifications and additions
of the most valuable kind.

The additions and alterations in the text, requisite to present concisely the growth of positive
physiological knowledge, have resulted in spite of the author's earnest efforts at condensation,
in an increase of fully fifty per cent, in the matter of the- work. A change, however, in the ty-
pographical arrangement has accommodated these additions without undue enlargement in the
bulk of the volume.

The new chemical notation and nomenclature are introduced into the present edition, as hav-
ing now so generally taken the place of the old, that no confusion need result from the change.
The centigrade system of measurements for length, volume, and weight, is also adopted, these
measurements being at present almost universally employed in original physiological investiga-
tions and their published accounts. Temperatures are given in degrees of the centigrade s ale,
usually accompanied by the corresponding degrees of Fahrenheit's scale, inclosed in brackets.
NEW YORK, September, 1875.

A few notices of the previous edition are subjoined.

The fifth edition of this truly valuable work on
Human Physiology comes to us with many valuable
Improvements and additions. As a text-book of
physiology the work of Prof. Dalton has long been
well known as one of the best which could be placed
In the hands of student or practitioner. Prof. Dalton
has, in the several editions of his work heretofore
published, labored to keep step with the advancement
5a science, and the last edition shows by its improve-
ments on former ones that he is determined to main-
tain the high standard of his work. We predict for
the present edition increased favor, though this work
has long been the favorite standard. — Buffalo Med.
and Surg. Journal, April, 1872.

An extended notice of a work so generally and fa-
vorably known as this is unnecessary. It is justly
regarded as one of the most valuable text-books on
the subject in the English language. — St. Louit Med.
Archives, May, 1872.

We know no treatise in physiology so clear, com-
plete, well assimilated, and perfectly digested, as
Dalton's. He never writes cloudily or dubiously, or
in mere quotation. He assimilates all his material,
and from it constructs a homogeneous transparent

irgument, which is always honest and well informed,
ind hides neither truth, ignorance, nor doubt, so far
is either belongs to the subject in hand. — Brit. Med.
Journal, March 23, 1872.

Dr. Dalton's treatise is well known, and by many
highly esteemed in thiscountry. It is, indeed, a good
elementary treatise on the subject it professes to
teach, and may safely be put into the hands of Eng-
lish students. It has one great merit — it is clear, and,
on the whole, admirably illustrated. The part we
have always esteemed most highly is that relating
to Embryology. The diagrams given of the various
stages of development give a clearer view of the sub-
ject than do those in general use in this country ; and
the text may be said to be, upon the whole, equally
clear. — London Med. Times and Gazette, March 23,
1872.

Professor Dalton is regarded j ustly as the authority
in this country on physiological subjects, and the
fifth edition of his valuable work fully justifies the
exalted opinion the medical world has of his labors.
This last edition is greatly enlarged. — Virginia Clin-
ical Record, April, 1872.

J)UNGLISON (ROBLEY), M.D.,

Professor of Institutes of Medicine in Jefferson Medical College, Philadelphia.

HUMAN PHYSIOLOGY. Eighth edition. Thoroughly revised and

extensively modified and enlarged, with five hundred and thirty-two illustrations. In two
large and handsomely printed octavo volumes of about 1500 pages, cloth, $7 00.

TEHMANN (C. 6?.).

PHYSIOLOGICAL CHEMISTRY. Translated from the second edi-
tion by GEORGE E. DAY, M. D., P. R. S., Ac., edited by R. E. ROGERS, M. D., Professor of
Chemistry in the Medical Department of the University of Pennsylvania, with illustrations
selected from Funke's Atlas of Physiological Chemistry, and an Appendix of plates. Com-
plete in two large and handsome octavo volumes, containing 1200 pages, with nearly two
hundred illustrations, cloth, $6 00.

THE SAME AUTHOR.

MANUAL OF CHEMICAL PHYSIOLOGY. Translated from the

German, with Notes and Additions, by J. CHESTON MORRIS, M. D., with an Introductory
Essay on Vital Force, by Professor SAMUEL JACKSON, M. D., of the University of Pennsyl-
vania. With illustrations on wood. In one very handsome octavo volume of 336 pages,
oloth, $2 25.

10

HENRY C. LEA'S PUBLICATIONS — (Chemistry).

A TTFIELD (JOHN), Ph. D.,

"^ Professor of Practical Chemistry to the Pharmaceutical Society of Great Britain, Ac.

CHEMISTRY, GENERAL, MEDICAL, AND PHARMACEUTICAL ;

including the Chemistry of the U. S. Pharmacopoeia. A Manual of the General Principles
of the Science, and their Application to Medicine and Pharmacy. Fifth Edition, revised
by the author. In one handsome royal 12mo. volume ; cloth, $2 75 ; leather, $3 25.
(Lately Issued.)

No other American publication with which we are
acquainted covers the same ground, or does it so well.
In addition to an admirable expose" of th« facts and
principles of general elementary chemistry, the au-
thor has presented us with a condensed mass of prac-
tical matter, just such as the medical student and
practitioner needs. — Cincinnati Lancet, Mar. 1874.

We commend the work heartily as one of the best
text-books extant for the medical student. — Detroit
Rev. of Med. and Pharm., Feb. 1872.

The best work of the kind in the English language.
— N. T. Psychological Journal, Jan. 1872.

The work is constructed with direct reference to
the wants of medical and pharmaceutical students;
and, although an English work, the points 'of differ-
ence' between the British and United States Pharma-
copoeias are indicated, making it as useful here as in
England. Altogether, the book is one we can heart-
ily recommend to practitioners as well as students.
— N. Y. Med. Journal, Dec. 1871.

It differs from other text-books in the following
particulars: first, in the exclusion of matter relating
to compounds which, at present, are only of interest
to the scientific chemist; secondly, in containing the
chemistry of every substance recognized officially or
in general, as a remedial agent. It will be found a
most valuable book for pupils, assistants, and others

engaged in medicine and pharmacy, and we heartily
commend it to our readers. — Canada Lancet, Oct.
1871.

When the original English edition of this work was
published, we had occasion to express our high ap-
preciation of its worth, and also to review, in con-
siderable detail, the main features of the book. As
the arrangement of subjects, and the main part of
the text of the present edition are similar to the for-
mer publication, it will be needless for us to go over
the ground a second time ; we may, however, call at-
tention to a marked advantage possessed by the Ame-
rican work— we allude to the introduction of the
chemistry of the preparations of the United States
Pharmacopoeia, as well as that relating to the Britisli
authority. — Canadian Pharmaceutical Journal,
Nov. 1871.

Chemistry has borne the name of being ahard sub-
ject to master by the student of medicine, am),
chiefly because so much of it consists of compounds
only of interest to the scientific chemist ; in this work
such portions are modified or altogether left out, and
in the arrangement of the subject-matter of the work,
practical utility is sought after, and we think fully
attained. We commend it for its clearness and ord&r
to both teacher and pupil. — Oregon Med. and Surg.
Reporter, Oct. 1871.

F

OWNES (GEORGE), Ph.D.

A MANUAL OF ELEMENTARY CHEMISTRY; Theoretical and

Practical. With one hundred and ninety-seven illustrations. A new American, from the
tenth and revised London edition. Edited by ROBERT BRIDGES, M. D. In one large
royal 12mo. volume, of about 850 pp., cloth, $2 75 ; leather, S3 25. (Lately Issued.)
This work is so well known that it seems almost other work that has greater claims on the physician,

superfluous for us to speak about it. It has been a pharmaceutist, or student, than this. We cheerfully

favorite text-book with medical students for years, recommend it as the best text-book on elementary

and its popularity has in no respect diminished, chemistry, and bespeak for it the careful attention

Whenever we have been consulted by medical stu-

dents, as has frequently occurred, what treatise on

chemistry they should procure, we have always re-

commend^d Fownes', for we regarded it as the best.

' students of pharmacy. — Chicago Pharmacist, Aug.

There is no work that combines so many excellen

Here is a new edition which has been long watched
for by eager teachers of chemistry. In its new garb,

ces. It is of convenient size, not prolix, of plain and under the editorship of Mr. Watts, it has resumed
perspicuous diction, contains all the most recent its old place as the most successful of text-books.—
discoveries, and is of moderate price.— Cincinnati, Indian Medical. Gazette, Jan. 1, 1869
Med. Repertory, Aug. 1869. It wm continae? as heretofore) to boid the flr8t raa)t

Large additions have been made, especially in the %s a text-book for students of medicine.— Chtcnpe
department of organic chemistry, and we know of no Wed. Examiner, Aug. 1869.

0

DLTNG ( WILLIAM),

Lecturer on Chemistry at St. Bartholomew's Hospital, Ac.

A COURSE OF PRACTICAL CHEMISTRY, arranged for the Use

of Medical Students. With Illustrations. Prom the Fourth and Revised London Edition.
In one neat royal 12mo. volume, cloth, $2.

riALLOWAY (ROBERT), F.C.S.,

Prof, of Applied Chemistry in the Royal College of Science for Ireland, &c.

A MANUAL OF QUALITATIVE ANALYSIS. From the Fifth Lon-
don Edition. In one neat royal 12mo. volume, with illustrations,- cloth, $2 50. (Ju&
Issued.)

The success which has carried this work through repeated editions in England, and its adoption
as a text-book in several of the leading institutions in this country, show that the author has suo-
oeeded in the endeavor to produce a sound practical manual and book of reference for the che-
mical student.

Prof. Galloway's books are deservedly in high
esteem, and this American reprint of the fifth edition
(1869) of his Manual of Qualitative Analysis, will be
acceptable to many Amer^pan students to whom the
English edition is not accessible.— Am. Jour, of Sci-
tnc6 and Arts, Sept. 1872.

We regard this volume as a valuable addition to
the chemical text-books, and as particularly calcu-
lated to instruct the student in analytical researches
of the inorganic compounds, the important vegetable
acids, and of compounds and various secretions and
excretions of animal origin. — Am. Journ.
Sept. 1873.

HENRY C. LEA'S PUBLICATIONS— ( Chemistry).

11

T>LOXAM (C. L.},

•*-* Professor of Chemistry in King's College, London.

CHEMISTRY, INORGANIC AND ORGANIC. From the Second Lon-
don Edition. In one very handsome octavo volume, of 700 pages, with about 300 illustra-
tions. Cloth, $4 00 ; leather, $5 00. (Lately Issued.)

It has been the author's endeavor to produce a Treatise on Chemistry sufficiently comprehen-
sive for those studying the science as a branch of £, neral education, and one which a student
may use with advantage in pursuing his chemical stud s at one of the colleges or medical schools.
The special attention devoted to Metallurgy and some other branches of Applied Chemistry renders
the work especially useful to those who are being educated for employment in manufacture.

We have in this work a complete aud most excel- experiment have been worked up with especial care,
lent text-book for the use of schools, and can heart-
ily recommend it as such. — Boston Med. and Surg.
Journ., May 28, 1874.

Of all the numerous works upon elementary chem-
istry that have been published within the last few
years, we can point to none that, in fulness, accuracy,
and simplicity, can surpass this; while, in the num-
ber and detailed descriptions of experiments, as also
in the profuseness of its illustrations, we believe it
stands above any similar work publ ished in this coun-
try The statements made are clear and con-
cise, and every step proved by an abundance of ex-
periments, which excite our admiration as much by
their simplicity as by their direct conclusiveness.—
Chicago Med. Examiner, Nov. 15, 1873.

It is seldom that in the same compass so complete
and interesting a compendium of the leading facts of
chemistry is offered. — Druggists' Circular, Nov. '73.

The above is the title of a work which we can most
conscientiously recommend to students of chemistry.
It is as easy as a work on chemistry could be made,
at the same time that it presents a full account of that
Rcience as it now stands. We have spoken of the
workasadmirably adapted to the wants of students ;
it is quite as well suited to the requirements of prac-
titioners who wish to review their chemistry, or have
occasion to refresh their memories on any point re-
lating to it. In a word, it is a book to be read by all
who wish to know what is the chemistry of the pre-
sent day. — American Practitioner, Nov. 1873.

Among the various works upon general chemistry
issued, we know of none that will supply the average
wants of the student or teacher better than this. —
Indiana, Jour n. of Med., Nov. 1873.

We cordially welcome this American reprint of a
work which has already won for itself so substantial
a reputation in England. Professor Bloxam has con-
densed into a wonderfully small com >ass all the im-
portant principles and facts of chemical science.
Thoroughly imbued with an enthusiastic love for the
science he expounds, he has stripped it of ail need-
less technicalities, and rounded out its hard outlines
by a fulness of illustration that cannot fail to attract
and delight the student. The details of illustrative

and many of the experiments described ai-e both nex
aud striking. —Detroit Rev. of Med. and Pharm.,
Nov. 1873.

One of the best text-books of chemistry yet pub-
lished.— Chicago Med. Journ., Nov. 1873.

This is an excellent work, well adapted for the be-
ginner and the advanced student of chemistry. — Am.
Journ. of Pharm., Nov. 1873.

Probably the most valuable, and at the same time
practical, text-book on general chemistry extant in
our language. — Kansas City Med. Journ., Dec. 1873.

Prof. Bloxam possesses pre-eminently the inestima-
ble gift of perspicuity. It is a pleasure to read his
books, for he is capable of making very plain what
other authors frequently have left very obscure. —
Va. Clinical Record, Nov. 1873.

It would be difficult for a practical chemist and
teacher to find any material fault with this most ad-
mirable treatise. The author has given us almost a
cyclopedia within the limits of aconvenient volume,
and has done so without penning the useless para-
graphs too commonly making up a great part of the
bulk of many cumbrous works. The progressive sci-
entist is not disappointed when he looks for the record
of new and valuable processes and discoveries, while
the cautious conservative does not find its pages mo-
nopolized by uncertain theories and speculations. A
peculiar point of excellence is the crystallized form of
expression in which great truths are expressed in
very short paragraphs. One is surprised at the brief
space allotted to an important topic, and yet, after
reading it, he feels that little, if any more, should
have been said. Altogether, it is seldom you see a
text-book so nearly faultless.— Cincinnati Lancet,
Nov. 1873.

Professor Bloxam has given us a most excellent
and useful practical treatise. His 666 pages are
crowded with facts and experiments, nearly all well
chosen, ajid many quite new, even to scientific men.
. . . It is astonishing how much information he often
conveys in a few paragraphs. We might quote fifty
instances of this. — Chemical News.

IXTOHLER AND FITTIG.

OUTLINES OF ORGANIC CHEMISTRY. Translated with Ad-
ditions from the Eighth German Edition. By IRA REMSEN, M.D., Ph.D., Professor of
Chemistry and Physics in Williams College, Mass. In one handsome volume, royal 12mo.
of 550 pp., cloth, $3.

As the numerous editions of the original attest, this work is the leading text-book and standard
Authority throughout Germany on its important and intricate subject — a position won for it by
the clearness and conciseness which are its distinguishing characteristics. The translation has
been executed with the approbation of Profs. Wohler and Fittig, and numerous additions and
alterations have been introduced, so as to render it in every respect on a level with the most
advanced condition of the science.

JgOWMAN (JOHN E.),M. D.

PRACTICAL HANDBOOK OF MEDICAL CHEMISTRY. Edited

by C. L. BLOXAM, Professor of Practical Chemistry in King's College, London. Sixth
American, from the fourth and revised English Edition. In one neat volume, royal 12mo.,
pp. 351, with numerous illustrations, cloth, $2 25.
J£Y THE SAME AUTHOR. (Lately Issued.)

INTRODUCTION TO PRACTICAL CHEMISTRY, INCLUDING

ANALYSIS. Sixth American, from the sixth and revised London edition. With numer-
ous illustrations. In one neat vol., royal 12mo., cloth, $2 25.

KBTAPP'S TECHNOLOGY ; or Chemistry Applied to
tse Art*, and to Manufactures. With American
additions, by Prof. WALTER B. JOHHSOS. In. two

very handsome octavo volumes, with 600 wood
engravings, cloth, $6 00.

12 HENRY 0. LEA'S PUBLICATIONS — (Mat. Med. and Therapeutics}. .

PARRISH (EDWARD],

Late Professor of Materia Medica in the Philadelphia College of Pharmacy.

A TREATISE ON PHARMACY. Designed as a Text-Book for the

Student, and as a Guide for the Physician and Pharmaceutist. With many Formulae and
Prescriptions. Fourth Edition, thoroughly revised, by THOMAS S. WIEGAND. In one
handsome octavo volume of 977 pages, with 280 illustrations; cloth, $5 50; leather, $6 50.
(Just Issued.)

The delay in the appearance of the new U. S. Pharmacopoeia, and the sudden death of the au
thor, have postponed the preparation of this new edition beyond the period expected. The notes
and memoranda left by Mr. Parrish have been placed in the hands of the editor, Mr. Wiegand,
who has labored assiduously to embody in the work all the improvements of pharmaceutical sci-
ence which have been introduced during he last ten years. It is therefore hoped that the new
edition will fully maintain the reputation which the volume has heretofore enjoyed as a standard
text-book and work of reference for all engaged in the preparation and dispensing of medicines.
Of Dr Parrish's great work on pharmacy it only an honored place on our own bookshelves. — Dublin
remains to be said that the editor has accomplished j Med. Prexs and Circular, Aug. 12, 1S74.
his work so well as to maintain in this fourth edi- We expressed our Opin5on of a former edition in
tion, the high standard of excellence which it bad terms of unquallfied pralRe and we are in no ,nood
attained in previous editions, under the editorship of , to detract from tnat opinlon in reference to the pre-

its accomplished author. This has not been accom

seat edition, the preparation of which has fallen into

plished without much labor, and many additions and competem hands. It is a book with which uopharma-
improvemeuts, involving changes in the arrangement 1 cist cau dispense, and from which no physician can
of the several parts of the work, and the addition o\ fail to derive mnch informa,ion of THiue 10 him in
much new matter. With the modifications thus et practjce,— Pacific Mtd. and Sura. Journ., June '74.
fected it constitutes, as now presented, a compendium j
of the science and art indispensable to the pharma- | With these few remarks we heartily commend the

cist, and of the utmost value to every practitioner
of medicine desirous of familiarizing himself with
the pharmaceutical preparation of the articles which
he prescribes for his patients. — Chicago Med. Journ.,
July, 1874.

The work is eminently practical, and has the rare
merit of being readable and interesting, while it pre-
serves a striciJy scientific character. The whole work
reflects the greatest credit on author, editor, and pub-
lisher It will convey some idea of i he liberality which
has been bestowed upon its production when we men-
tion that there are no less than 2SO carefully executed
illustrations. In conclusion, we heartily recommend
the work, not only to pharmacists, but also to the
multitude of medical practitioners who are obliged
to compound their own medicines. It will ever hold

work, and have no doubt that it will maintain its
old reputation as a text book for the student, and a
work of reference for the more experienced physi-
cian and pharmacist . — Chicago Med. Examiner,
June 1-3, 1874.

Perhaps one, if not the most important book upon
pharmacy which has appeared in the English lan-
guage has emanated from the transatlantic press.
"Parrish's Pharmacy'' is-
side of the water, and tin

useful work never becomes merely local in ics fame.
Thanks to the judicious editing of Mr. Wiegaiid, the
posthumous edition of "Parrish" has been saved to
the public with all the mature experience of its au-
thor, an.i perhaps none the worse for a dash of aew
blood.— Lond. Pharm. Journal, Oct. 17, 1874.

a well-known work on this
fact shows us that a really

&TILLE (ALFRED), M.D.,

*3 Professor of Theory and Practice of Medicine in the University of Penna.

THERAPEUTICS AND MATERIA MEDICA; a Systematic Treatise

on the Action and Uses of Medicinal Agents, including their Description and History.

Fourth edit., revised and enlarged. In two large and handsome 8vo. vols. of about 2000

pages. Cloth, $10; leather, $12. (Now Ready.)

The care bestowed by the author on the revision of this edition has kept the work out of the
market for nearly two years, and has increased its size about two hundred and fifty pages. Not"
withstanding this enlargement, the price has been kept at the former very moderate rate. A few
notices of former editions are subjoined.

Dr. iSlille's splendid work on therapeutics and ma-
teria medica. — London Med. Times, April 8, 1865.

Dr. Still6 stands to-day one of the best and most
honored representatives at home and abroad, of Ame-
rican medicine ; and these volumes, a library in them-
selves, a treasure-house for every studious physician,
assure his fame even had he done nothing more. — The
Western Journal of Medicine, Dec. 1868.

We regard this work as the best one on Materia
Medica in the English language, and as such it de-
serves the favor it has received. — Am. Journ. Medi-
cal Sciences, July 1868.

We need not dwell on the merits of the third edition
of this magnificently conceived work. It is the work
on Materia Medica, in which Therapeutics are prima-
rily considered — the mere natural history of drugs

abroad its reputation as a standard treatise on Materin
Medica is securely established. It is second to no
work on the subject in the English tongue, and, in-
deed, is decidedly superior, in some respects, to any
other. — Pacific Med. and Surg Journal, July, 1S68,

Stille~'s Therapeutics is incomparably the best work
on the subject.— N. Y. Med. Gazette, Sept. 26, 1868.

Dr. Still's work is becoming the best known of any
of our treatises on Materia Medica. . . . One of the
most valuable works in the language on the subjects
of which it treats.— jy. Y. Med. Journal, Oct. 1868.

The rapid exhaustion of two editions of Prof. Stille'n
scholarly work, and the consequent necessity for &
third edition, is sufficient evidence of the high esti-
mate placed upon it by the profession. It is no exag-
geration to say that there is no superior work upon

briefly disposed of. To medical practitioners I the subject in the English language. The present
this Is a very valuable conception. It is wonderful \ edition is fully up to the most recent advance in the

'

how much of the riches of the literature of Materia
Medica has been condensed into this book. The refer-
ences alone would make it worth possessing. But it
is not a mere compilation. The writer exercises a
#ood judgment of his own on the great doctrines and
points of Therapeutics. For purposes of practice,

Still6's book is almost unique as a repertory of in- for itself. As a work of great research, and scholar-
formation, empirical and scientific, on the actions and | ship, it is safe to say we have nothing superior. It i»
uses of medicines. — London Lancet, Oct. 31, 1868. exceedingly full, and the busy practitioner will find
Through the former editions, the professional world ' ample suggestions upon almost every important point
is well acquainted with this work. At home and j of therapeutics. — Cincinnat i Lancet, Aug. 1868.

science and art of therapeutics. — Leavenworth Medi-
cal Herald, Aug 1868.

The work of Prof. Still6 has rapidly taken a high
place in professional esteem, and to say that a third
edition is demanded and now appears before us, suffi-
ciently attests the firm position this treatise has made

HENRY C. LEA'S PUBLICATIONS — {Mat. Med. and Therapeutics). 13

/GRIFFITH (ROBERT E.), M.D.

A UNIVERSAL FORMULARY, Containing the Methods of Prepar-
ing and Administering Officinal and other Medicines. The whole adapted to Physician* and
Pharmaceutists. Third edition, thoroughly revised, with numerous additions, bj JOHN M.
MAISCH, Professor of Materia Medica in the Philadelphia College of Pharmacy. In one large
andhandsome octavo volume of aboutSOO pages, cloth, $4 50 ; leather, $5 50. (Just Issued.)
This work has long been known for the vast amount of information which it presents in a con-
densed form, arranged for easy reference. The new edition has received the most careful revi-
sion at the competent hands of Professor Maisch, who has brought the whole up to the standard of
the most recent authorities. More than eighty new headings of remedies have been introduced,
the entire work has been thoroughly remodelled, and whatever has seemed to be obsolete has been
omitted. As a comparative view of the United States, the British, the German, and the French
Pharmacopoeias, together with an immense amount of unofficinal formulas, it affords to the prac-
titioner and pharmaceutist an aid in their daily avocations not to be found elsewhere, while three
indexes, one of "Diseases and their Remedies," one of Pharmaceutical Names, and a General
Index, afford an easy key to the alphabetical arrangement adopted in the text.

The young practitioner will find the work invalu-
able in suggesting eligible modes of administering
many remedies. — Am. Journ. of Pharm., Feb. 1874.

Our copy of Griffith's Formulary, after long use,
first in the dispensing shop, and afterwards in our
medical practice, had gradually fallen behind in the
onward march of materia medica, pharmacy, and
therapeutics, until we had ceased to consult it as a
daily book of reference. So completely has Prof.
Maisch reformed, remodelled, and rejuvenated it in
the new edition, we shall gladly welcome it back to
our table again beside Duuglison, Webster, and Wood
& Bache. The publisher could not have been more
fortunate in the selection of an editor. Prof. Maisch
is eminently the man for the work, and he has done
it thoroughly and ably. To enumerate the altera-
tions, amendments, and additions would be an end-
less task; everywhere we are greeted with the evi-
dences of his labor. Following the Formulary, is an
addendum of useful Recipes, Dietetic Preparations,
List of Incompatibles, Posological table, table of
Pharmaceutical Names, Officinal Preparations and
Directions, Poisons. Antidotes and Treatment, and
copious indices, which afford ready access to all parts
of the work. We unhesitatingly commend the book
as being the best of its kind, within our knowledge.
— Atlanta Med. and Surg. Journ., Feb. 1874.

To the druggist a good formulary is simply indis-
pensable, and perhaps no formulary has been more
extensively used than the well-known work before
us. Many physicians have to officiate, also, as drug-
gists. This is true especially of the country physi-
cian, and a work which shall teach him the means
by which to administer or combine his remedies in
the most efficacious and pleasant manner, will al-
ways hold its place upon his shelf. A formulary of
this kind is of benefit also to the city physician in
largest practice.— Cincinnati Vlinic, Feb. 21, 1874.

The Formulary has already proved itself accepta-
ble to the medical profession, and we do not hesitate
to say that the third edition is much improved, and
of greater practical value, in consequence of the care-
ful revision of Prof Maisch.— Chicago Med. Exam-
iner, March 15, 1874.

A more complete formulary than it is in its pres-
ent form the pharmacist or physician, could hardly
desire. To the first some such work is indispensa-
ble, and it is hardly less essential to the practitioner
who compounds his own madiciaes. Much of what
is contained in the introduction^ought to be com-
mitted to memory by every student of inedijiae.
As a help to physiciaus it will be found invaluable,
and doubtless will make its way into libraries not
already supplied with a standard work of the kind.
— The American Practitioner, Louisville, July, '74.

E.

'LLIS (BENJAMIN], M.D.

THE MEDICAL FORMULARY: being a Collection of Prescriptions

derived from the writings and practice of many of the most eminent physicians of America
and Europe. Together with the usual Dietetic Preparations and Antidotes for Poisons. The
whole accompanied with a few brief Pharmaceutic and Medical Observations. Twelfth edi-
tion, carefully revised and much improved by ALBERT H. SMITH, M.D. In one volume 8v@.
of 376 pages, cloth, $3 00.

iEREIRA (JONATHAN), M.D., F.R.S. and L.S.

MATERIA MEDICA AND THERAPEUTICS; being an Abridg-
ment of the late Dr. Pereira's Elements of Materia Medica, arranged in conformity with
the British Pharmacopoeia, and adapted to the use of Medical Practitioners, Chemists and
Druggists, Medical and Pharmaceutical Students, &c. By F. J. FARRE, M.D., Senior
Physician to St. Bartholomew's Hospital, and London Editor of the British Pharmacopoeia ;
assisted by ROBEHT BENTLEY, M.R.C.S., Professor of Materia Medica and Botany to the
Pharmaceutical Society of Great Britain; and by ROBERT WARINGTON, F.R.S., Chemical
Operator to the Society of Apothecaries. With numerous additions and references to the
United States Pharmacopoeia, by HORATIO C. WOOD, M.D., Professor of Botany in the
University of Pennsylvania. In one large and handsome octavo volume of 1040 closety
printed pages, with 236 illustrations, cloth, $7 00; leather, raised bands, $8 00.

DDNGLISON'S NEW REMEDIES, WITH FORMULA
FOR THEIR PREPARATION AND ADMINISTRA-
TION. Seventh edition, with extensive additions.
One vol. 8vo., pp. 770; cloth. $4 00.

EOYLE'S MATERIA MEDICA AND THERAPEU-
TICS. Edited by JOSEPH CAKSON, M. D. With
ninety-eight illustrations. 1 vol. 8vo., pp. 700,
cloth. $3 00.

CARSON'S SYNOPSIS OF THE LECTURES ON MA-
TERIA MEDICA AND PHARMACY, delivered in
the University of Pennsylvania. Fourth and re-
vised edition. Cloth, $3.

'HRISTISON'S DISPENSATORY. With copious ad
^U.irttifi, and 9.1 3 lar«« wood-«n«rravin«s Bv R.
EGLESFELD GRIFFITH, M. D. One vol. 8vo., pp. 1000 ;
cloth. $4 00.

CARPENTER'S PRIZE ESSAY ON THE USE OP
ALCOHOLIC LIQUORS IN HEALTH AND DISEASE. New
edition, with a Preface by D. F. CONDIE. M.D., and
explanations of scientific words. In one neat 12mo.
volume, pp. 178, cloth. 60 cents.

DE JONGH ON THE THREE KINDS OF COD-LIVEB
OIL, with their Chemical and Therapeutic Pro-
perties. 1 vol. 12rno., cloth. 75 cents.

14

HENRY C. LEA'S PUBLICATIONS — (Pathology -, <£<?.).

flENWICK (SAMUEL], M.D.,

-*- Assistant Physician to the London Hospital.

THE STUDENT'S GUIDE TO MEDICAL DIAGNOSIS. From the

Third Revised and Enlarged English Edition. With eighty-four illustrations on wood.

In one very handsome volume, royal ]2mo., cloth, $2 25. (J^(,st Issued.}

The very great success which this work has obtained in England, shows that it has supplied an
admitted want among elementary books for the guidance of students and junior practitioners.
Taking up in order each portion of the body or class of disease, the author has endeavored to
present in simple language the value of symptoms, so as to lead the student to a correct appreci-
ation of the pathological changes indicated by them. The latest investigations have been care-
fully introduced into the present edition, so that it may fairly be considered as on a level with
the most advanced condition of medical science.

Of the many guide-books on medical diagnosis, | else, practical manner, well calculated to assist the

claimed to be written for the special instruction of
students, this is the best. The author is evidently a
well-read and accpmplished physician, and he knows
how to 'each practical medicine. The charm of sim-
plicity is not the least interesting feature in the man-
ner in which Dr. Fenwick conveys instruction. There
are few books of this size on practical medicine that
contain so much and convey it so well as the volume
before us. It, is a book we can sincerely recommend
to the student for direct instruction, and to the prac-
titioner as a ready and useful aid to his memory. —
Am. Jo urn. of Syphilography, Jan. 1874.

It covers the ground of medical diagnosis in a con-

student in forming a correct, thorough, and system-
atic method of examination and diagnosis of disease.
The illustrations are numerous, and finely executed.
Those illustrative of the microscopic appearance of
morbid tissue, &c., are especially clear and distinct..
— Chicago Med. Examiner, Nov. 1£73.

So far superior to any offered to students that the
colleges of this country should recommend it to their
respective classes. — 27. 0. Med. and Surg. Journ.,
March, 1874.

This little book ought to be in the possession of
every medical student. — Boston Medical and Surg.
Journ., Jan. 15, 1874.

SCREEN (T. HENRY), M.D.,

Lecturer on Pathology and Morbid Anatomy at Charing-Gross Hospital Medical School.

PATHOLOGY AND MORBID ANATOMY. With numerous Illus-
trations on Wood. In one very handsome octavo volume of over 250 pages, cloth, $2 50.
(Lately Published.)

We have been very much pleased by our perusal of thology and morbid anatomy. The author shows that
this little volume. It is the only one of the kind with he has been not only a student of the teachings of his
which we are acquainted, and practitioners as well
as students will find it a very useful guide ; for the
information is up to the day, well and compactly ar-
ranged, without being at all scanty. — London Lan-
cet, Oct. 7, 1871.

It embodies in a comparatively small space a clear
statement of the present state of our knowledge of pa-

zonfrtres in this branch of science, but a practical
and conscientious laborer in the post-mortem cham-
ber. The work will provea useful one to the great
mass of students and practitioners whose time for de-
votion to this class of studies is limited.— Am. Journ,
of Syphilography, April, 1872.

GLUGE'S ATLAS OF PATHOLOGICAL HISTOLOGY.
Translated, with Notes and Additions, by JOSEPH
LEIDT, M. D. In one volume, very large imperial
quarto, with 320 copper-plate figures, plain and
colored, cloth. $4 00.

JONES AND SIEVEKING'S PATHOLOGICAL ANA-
TOMY. With 397 wood-cuts. 1 vol. Svo., of nearly
750 pages, cloth. $3 50.

HOLLAND'S MEDICAL NOTES AND .REFLEC-
TIONS. 1 vol. 8vo., pp. 500, cloth. $3 50.

WHATTO OBSERVE ATTHE BEDSIDE AND AFTEE
DEATH IN MEDICAL CASES. Published under the
authority of the London Society for Medical Obser-
vation. From the second London edition. 1 vol.
royal 12mo., cloth. $1 00.

LA ROCHE ON YELLOW FEVER, considered in its
Historical, Pathological, Etiological, and Therapeu-
tical Relations. In two large and handsome octavo
volumes of nearly 1500 pages, cloth. $7 00.

LAYCOCK'S LECTURES ON THE PRINCIPLES
AND METHODS OF MEDICAL OBSERVATION AND RE-
SEARCH. For the use of advanced students and
junior practitioners. In one very neat royal 12mo.
volume, cloth. $1 00.

BARLOW'S MANUAL OF THE PRACTICE OP
MEDICINE. With Additions by D. F. CONDIE,
M. D. 1 vol. 8vo., pp. 600, cloth. $2 50.

TODD'S CLINICAL LECTURES ON CERTAIN ACUTE
DISEASES. In one neat octavo volume, of 320 pages,
cloth. $2 60.

&TURGES (OCTAVIUS], M.D. Cantab.,

*-J Fellow of the Royal College of Physicians, &c. &c.

AN INTRODUCTION TO THE STUDY OP CLINICAL MED-

ICINE. Being a Guide to the Investigation of Disease, for the Use of Students. In one
handsome 12mo. volume, cloth, $1 25. (Just Issued.)

D

AVIS (NATHAN S.},

Prof, of Principles and Practice of Medicine, etc., in Chirago Med. College.

CLINICAL LECTURES ON VARIOUS IMPORTANT DISEASES;

being a collection of the Clinical Lectures delivered in the Medical Wards of Mercy Hos-
pital, Chicago. Edited by FRANK H. DAVIS, M.D. Second edition, enlarged. In one
handsome royal 12mo. volume. Cloth, $1 75. (Now Ready.)

&TOKES (WILLIAM], M.D., D.C.L., F.R.S.,

'A3 Reyius Professor of Physic in the Univ. of Dublin, &c.

LECTURES ON FEVER, delivered in the Theatre of the Meath Hos-
pital and County of Dublin Infirmary. Edited by JOHN WILLIAM MOORE, M.D , Assistant
Physician to the Cork Street Fever Hospital. In one neat octavo volume. (Preparing.)

j^*^ To appear in the " MEDICAL NEWS AND LIBRARY" for 1875.

HENRY C. LEA'S PUBLICATIONS — (Practice of Medicine).

15

F

rLINT (AUSTIN], M.D.,

Professor of the Principles and Practice of Medicine in Bellevue Med. College, N. T.

A TREATISE ON THE PRINCIPLES AND PRACTICE OF

MEDICINE ; designed for the use of Students and Practitioners of Medicine. Fourth
edition, revised and enlarged. In one large and closely printed octavo volume of about 1 100
pages; cloth, $6 00 ; or strongly bound in leather, with raised bands, $7 00. (.Just Issued.)
By common consent of the English and American medical press, this work has been assigned
to the highest position as a complete and compendious text-book on the most advanced condition
of medical science. At the very moderate price at which it is offered it will be found one of the
cheapest volumes now before the profession. A few notices of previous editions are subjoined.

Admirable and unequalled. — Western Journal of
Medicine, Nov. 1869.

Dr. Flint's work, though claiming no higher title
than that of a text-book, is really more. He is a man
of large clinical experience, and his book is fnll of
such masterly descriptions of disease as can only be
drawn by a man intimately acquainted with their
various forms. It is not so long since we had the
pleasure of reviewing his first edition, and we recog-
nize a great improvement, especially in the general
part of the work. It is a work which we can cordially
recommend to our readers as fully abreast of the sci-
ence of the day. — Edinburgh Me.d. Journal, Oct. '69.

One of the best works of the kind for the practi-
tioner, and the most convenient of all for the student.
—Am. Journ. Med. Sciences, Jan. 1869.

This work, which stands pre-eminently as the ad-
vance standard of medical science up to the present
time in the practice of medicine, has for its author
one who is well and widely known as one of the
leading practitioners of this continent. In fact, it is
•eldora that any work is ever issued from the press
more deserving of universal recommendation. — Do-
minion Med. Journal, May, 1869.

The third edition of this most excellent book scarce-
ly needs any commendation from us. The volume,
as it stands now, is really a marvel : first of all, it is

sxcellently printed and bound — and we encounter
that luxury of America, the ready-cut pages, which
the Yankees are 'cute enough to insist upon — nor are
these by any means trifles ; but the contents of the
book are astonishing. Not only is it wonderful that
iny one man can have grasped in his mind the whole
scope of medicine with that vigor which Dr. Flint
shows, but the condensed yet clear way in which
this is done is a perfect literary triumph. Dr. Flint
is pre-eminently one of the strong men, whose right
to do this kind of thing is well admitted ; and we say
10 more than the truth when we affirm that he is
very nearly the only living man that could do it with
mch results as the volume before us. — The London
Practitioner, March, 1869.

This is in some respects the best text-book of medi-
cine in our language, and it is highly appreciated on
the other side of the Atlantic, inasmuch as the first,
edition was exhausted in a few months. The second
sdition was little more than a reprint, but the present
has, as the author says, been thoroughly revised.
Much valuable matter has been added, and by mak-
ing the type smaller, the bulk of the volume is not
much increased. The weak point in many American
works is pathology, but Dr. Flint has taken peculiar
pains on this point, greatly to the value of the book.
—London Med. Times and Gazette, Feb. 6, 1869.

T>Y THE SAME AUTHOR.

ESSAYS ON CONSERVATIVE MEDICINE AND KINDRED

TOPICS. In one very handsome royal 12ino. volume. Cloth, $1 38. (Just Issued.")

CONTENTS,

I. Conservative Medicine. II. Conservative Medicine as applied to Therapeutics. III. Con-
servative Medicine as applied to Hygiene. IV. Medicine in the Past, the Present, and the Fu-
ture. V. Alimentation in D sease. VI. Tolerance of Disease. VII. On the Age cy of the
Mind in Etiology, Prophylaxis, and Therapeutics. VIII. Divine design as exemplified in the
Natural History of Disease.

"ATSON (THOMAS], M. D., &c,

LECTURES ON THE PRINCIPLES AND PRACTICE OF

PHYSIC. Delivered at King's College, London. A new American, from the Fifth re-
vised and enlarged English edition. Edited, with additions, and several hundred illustra-
ations, by HENRY HARTSHORNE, M.D., Professor of Hygiene in the University of Pennsylv-
nia. In two large and handsome Svo.vols. Cloth, $9 00 ; leather, $11 00. (Lately Published.)

W:

It is a subject for congratulation and for thankful-
ness that Sir Thomas Watson, during a period of com-
parative leisure, after a long, laborious, and most
honorable professional" career, while retaining full
possession of his high mental faculties, should have
employed the opportunity to submit his Lectures to
a more thorough revision than was possible during
the earlier and busier period of his life. Carefully
passing in review some of the most intricate and im-
portant pathological and practical questions, there-
suits of his clear insight and his calm judgment are
now recorded for the benefit of mankind, in language
which, for precision, vigor, and classical elegance, has
rarely been equalled, and never surpassed The re-
vision has evidently been most carefully done, and
the results appear in almost every page. — Brit. Med.
Journ., Oct. 14, 1871.

The lectures are so well known and so justly
appreciated, that it is scarcely necessary to do
more than call attention to the special advantages
of the last over previous editions. The author's

rare combination of great scientific attainments com-
bined with wonderful forensic eloquence has exerted
extraordinary influence over the last two generations
of physicians. His clinical descriptions of most dis-
eases have never been equalled ; and on this score
at least his work will live long in the future. The
work will be sought by all who appreciate a great
book. — Amer. Journ. of Syphilography, July, 1872.
We are exceedingly gratified at the reception of
this new edition of Watson, pre-eminently the prince
of English authors, on "Practice." We, who read
the first edition shall never forget the great pleasure
and profit we derived from its graphic delineations
of disease, its vigorous style and splendid English.
Maturity of years, extensive observation, profound
research, and yet continuous enthusiasm, have com-
bined to give us in this latest edition a model of pro-
fessional excellence in teaching with rare beauty in
the mode of communication. But this classic needs
no eulogium of ours. — Chicago Med. Journ., July,
1872.

D

UNGLISON, FORBES, TWEEDIE, AND CONOLLY.

THE CYCLOPAEDIA OF PRACTICAL MEDICINE: comprising

Treatises on the Nature and Treatment of Diseases, Materia Medica and Therapeutics,
Diseases of Women and Children, Medical Jurisprudence, <fcc. <fec. In four large super-royal
octavo volumes, of 3254 double-columned pages, strongly and handsomely bound in leather,
$15 j cloth, $J1.

16 HENRY C. LEA'S PUBLICATIONS — (Practice of Medicine).

fTARTSHORNE (HENRY), M.D.,

•*-*• Professor of Hygiene in the University of Pennsylvania.

ESSENTIALS OF THE PRINCIPLES AND PRACTICE OF MEDI-

CINE. A handy-book for Students and Practitioners. Fourth edition, revised and im-
proved. With about one hundred illustrations. In one handsome royal 12mo. volume,
of about 550 pages, cloth, $2 63 ; half bound, $2 88. (Just Ready.)

The thorough manner in which the author has labored to fully represent in this favorite hand-
book the most advanced condition of practical medicine is shown by the fact that the present
edition contains more than 250 additions, representing the investigations of 172 authors not re-
ferred to in previous editions. Notwithstanding an enlargement of the page, the size has been
increased by sixty pages. A number of illustrations have been introduced which it is hoped
will facilitate the comprehension of details by the reader, and no effort has been spared to make
the volume worthy a continuance of the very great favor with which it has hitherto been received.
The work is brought fully up with all the recent j Without doubt the best hook of tLekind published
advances in medicine, is admirably condensed, and in the English language. — St. Louis Mtd. andSurg.
yet sufficiently explicit for all the purposes intended, Journ., Nov. 1874.

thus making it by far the be?t work of its character
ever published.— Cincinnati Clinic, Oct. 24, 1874.

We have already had occasion to notice the previ-
ous editions of this work. It is excellent of its kind.
The author has given a very careful revision, in view
of the rapid progress of medical science.— N. Y. Med.
Journ., JNTov. 1874.

As a handbook, which clearly sets forth the ESSEN-
TIALS Of the PRINCIPLES AND PRACTICE OF MEDICINE, W8

do not know of its equal.— Va. Mc.d. Monthly.

As a brief, condensed, but comprehensive hand-
book, it cannot be improved upon. — Chicago Med.
Examiner, Nov. 35, 1874.

f>AVY(F. W.),M.D.,F.R.S.,

-*• Senior Asst. Physician to and Lecturer on Physiology, at Guy's Hospital, Ac.

A TREATISE ON THE FUNCTION OF DIGESTION; its Disor-

ders and their Treatment. From the second London edition. In one handsome volume,
small octavo, cloth, $2 00.
T>J THE SAME AUTHOR. (Just Ready.

A TREATISE ON FOOD AND DIETETICS, PHYSIOLOGI-
CALLY AND THERAPEUTICALLY CONSIDERED. In one handsome octavo volume
of nearly 600 pages, cloth, $4 75.

SUMMARY OF CONTENTS.

Introductory Remarks on the Dynamic Relations of Food — On the Origination of Food — The
Constituent Relations of Food — Alimentary Principles, their Classification, Chemical Relations,
Digestion, Assimilation, and Physiological Uses — Nitrogenous Alimentary Principles — Non-Ni-
trogenous Alimentary Principles — The Carbo-Hydrates — The Inorganic Alimentary Principles —
Alimentary Substances — Animal Alimentary Substances — Vegetable Alimentary Substances —
Beverages — Condiments — The Preservation of Food — Principles of Dietetics — Practical Dietetics
— Diet of Infants — Diet for Training — Therapeutic Dietetics — Dietetic Preparations for the Inva-
lid— Hospital Dietaries.

riHAMBERS (T. K.}, M.D. (Now Ready.}

V^ Consulting Physician to St. Mary n Hospital, London, &c.

A MANUAL OF DIET AND REGIMEN IN HEALTH AND SICK-

NESS. In one handsome octavo volume. Cloth, $2 75.

The aims of this handbook are purely practical, and therefore it has not been thought right
to increase its size by the addition of the chemical, botanical, and industrial learning which
rapidly collects round the nucleus of every nrticle interesting as an eatable. Space has been
thus gained for a full discussion of many matters connecting food and drink with the daily cur-
rent of social life, which the position of the author as a practising physician has led him to
believe highly important to the present and future of our race. — Preface.

SUMMARY OF CONTENTS.

PARTl. General Dietetics. CHAP. I. Theories of Dietetics. II. On the Choice of Food. III.
On the Preparation of Food. IV. On Digestion and Nutrition.

PART II. Special Dietetics of Health. CHAP. I. Regimen of Infancy and Motherhood. II.
Regimen of Childhood and Youth. III. Commercial Life. IV. Literary and Professional Life.
V. Noxious Trades. VI. Athletic Training. VII. Hints for Healthy Travellers. VIII. Effects
of Climate. IX. Starvation, Poverty, and Fasting. X. The Decline of Life. XI. Alcohol.

PART III. Dietetics in Sickness. CHAP. I. Dietetics and Regimen in Acute Fevers. II. The
Diet and Regimen of certain other Inflammatory States. III. The Diet and Regimen of Weak
Digestion. IV. Gout and Rheumatism. V. Gravel, Stone, Albuminuria, and Diabetes. VI.
Deficient Evacuation. VII. Nerve Disorders. VIII. Scrofula, Rickets, and Consumption. IX.
Diseases of Heart and Arteries.

T)Y THE SAME AUTHOR. (Lately Published.)

RESTORATIVE MEDICINE. An Harveian Annual Oration. With

Two Sequels. In one very handsome volume, small 12mo., cloth, $1 00.

TyRINTON (WILLIAM), M.D., F.R.S.
-^LECTURES ON THE DISEASES OF THE STOMACH; with an

Introduction on its Anatomy and Physiology. From the second and enlarged London edi-
tion. With illustrations on wood In one handsome octavo volume of about 300 pages
cloth, $3 25.

HENRY C. LEA'S PUBLICATIONS.

(AUSTIN), M.D.,

Professor of the Principles and Practice of Medicine in Bellevue Hospital Med. College, N. T.

A PRACTICAL TREATISE ON THE DIAGNOSIS, PATHOLOGY,

AND TREATMENT OF DISEASES OF THE HEART. Second revised and enlarged
edition. In one octavo volume of 550 pages, with a plate, cloth, $4.

Dr. Flint chose a difficult subjectfor his researches, i able for purposes of illustration, in connection with
and has shown remarkable powers of observation cases which have been reported by other trustworthy

and reflection, as well as great industry, in his treat-
ment of it. His book must be considered the fullest
aud clearest practical treatise on those subjects, and
should be in the hands of all practitioners and stu-
dents. It is a credit to American medical literature.
— Amer. Journ. of the Med. Sciences, July, 1860.

We question the fact of any recent American author
In our profession being more extensively known, or
more deservedly esteemed in this country than Dr.

observers.— Brit, and For. Med.-Chirurg. Review.

In regard to the merits of the work, we have no
hesitation in pronouncing it full, accurate, aud judi-
cious. Considering the present state of science, such
a work was much needed. It should be in the hands
of every practitioner. — Chicago Med. Journ.

With more than pleasure do we hail the advent of
this work, for it fills a wide gap on the list of text-

Flint. We willingly acknowledge his success, more j books for our schools, and is, for the practitioner, the
particularly in the volume on diseases of the heart, most valuable practical work of its kind.— N. 0. Med.
jn making an extended personal clinical study avail- I News.

>Y THE SAME AUTHOR.

A PRACTICAL TREATISE ON7 THE PHYSICAL EXPLORA-
TION OF THE CHEST AND THE DIAGNOSIS OF DISEASES AFFECTING THE
RESPIRATORY ORGANS. Second and revised edition. In one handsome octavo volume
of 595 pages, cloth, $4 50.

which pervades his whole work lend an additional

Dr. Flint's treatise is one of the most trustworthy
guides which we can consult. The style is clear and
distinct, and is also concise, being free from that tend-
ency to over-refinement and unnecessary minuteness
which characterizes many works on the same sub-
ject.— Dublin Medical Press, Feb. 6, 1867.

The chapter on Phthisis is replete with interest ;
and his remarks on the diagnosis, especially in the
early stages, are remarkable for their acumen and
great practical value. Dr. Flint's style is ciear and
elegant, and the tone of freshness and originality

force to its thoroughly practical character, which
cannot fail to obtain for it a place as a standard work
on diseases of the respiratory system. — London
Lancet, Jan. IP, 1867.

This is an admirable book. Excellent in detail and
execution, nothing better could be desired by the
practitioner. Dr. Flint enriches his subject with
much solid and not a little original observation.—
Ranking' s Abstract, Jan. 1867.

gY THE SAME AUTHOR.

A PRACTICAL TREATISE ON PHTHISIS— DIAGNOSIS, PROG-

NOSIS, AND TREATMENT. IN A SERIES OF CLINICAL STUDIES. A new work,
in preparation for early publication. In one handsome octavo volume.
A brief table of contents is subjoined: —

CHAP. I. Morbid Anatomy. II. Etiology. III. Symptomatic Events and Complications.
IV. Fatality and Prognosis. V. Treatment. VI. Physical Signs and Diagnosis.

PULLER (HENRY WILLIAM], M. D.,

Physician to St. George's Hospital, London.

ON DISEASES OF THE LUNGS AND AIR-PASSAGES. Their

Pathology, Physical Diagnosis, Symptoms, and Treatment. From the second and revised
English edition. In one handsome octavo volume of about 500 pages, cloth, $3 50.

(c. j. B.},

Senior Consulting Physician to the Hospital for Consumption, Brompton, and

(CHARLES T.}, M.D.,

Physician to the Hospital for Consumption.

PULMONARY CONSUMPTION; Its Nature, Yarieties, and Treat-

ment. With an Analysis of One Thousand Cases to exemplify its duration. In one neat
octavo volume of about 350 pages, cloth, $250. (Lately Published.}

He can still speak from a more enormous experi-
ence, and a closer study of the morbid processes in-
volved in tuberculosis, than most living men. He
owed it to himself, and to the importance of the sub-
ject, to embody his views in a separate work, and
we are glad that he has accomplished this duty.

After all, the grand teaching which Dr Williams has
for the profession is to be found in his therapeutical
chapters, and in the history of individual cases ex-
tended, by dint of care, over ten, twenty, thirty, and
aven forty years.— London Lancet, Oct. 21, 1871.

LA ROCHE ON PNEUMONIA. 1 vol. 8vo., cloth,

of 500 pages. Price $3 00.
SMITH ON CONSUMPTION ; ITS EARLY AND RE-

MEDIABLE STAGES. 1 vol. 8vo., pp. 254. $2 25.

WALSHE ON THE DISEASES OF THE HEART AND
GREAT VESSELS. Third American edition. In
1 vol. 8vo., 420 pp., cloth. $3 00.

FOX ( WILSON), M.D.,

•*- Holme Prof, of Clinical Med., University Coll., London.

THE DISEASES OF THE STOMACH: Being the Third Edition of

the "Diagnosis and Treatment of the Varieties of Dyspepsia." Revised and Enlarged.
With illustrations. In one handsome octavo volume, cloth, $2 00. (Now Ready.)
Dr. Fox has put forth a volume of uncommon ex- I rank among works that treat of the stomach.— Am-
cellence, which we feel very sure will take a high | Practitioner, March, 1873.

18

HENRY C. LEA'S PUBLICATIONS — (Practice of Medicine).

•*-b

A

OBERTS ( WILLIAM], M. D.,

Lecturer on Medicine in the Manchester School of Medicine, &c.

PRACTICAL TREATISE ON URINARY AND RENAL DIS-

EASES, including Urinary Deposits. Illustrated by numerous cases and engravings. Sec-
ond American, from the Second Revised and Enlarged London Edition. In one large
and handsome octavo volume of 616 pages, with a colored plate ; cloth, $4 50. (Lately
Published.)

The author has subjected this work to a very thorough revision, and has sought to embody in
it the results of the latest experience and investigations. Although every effort has been made
to keep it within the limits of its former size, it has been enlarged by a hundred pages, many
new wood-cuts have been introduced, and also a colored plate representing the appearance of the
different varieties of urine, while the price has been retained at the former very moderate rate.

diseases we have examined. It is peculiarly adapted
to the wants of the majority of American practition-

The plan, it will thus be seen, is very complete,
and the manner in which it has been carried out is
in the highest degree satisfactory. The character*
of the different deposits are very well described, and
the microscopic appearances they present are illus-
trated by numerous well executed engravings. It
only remains to us to strongly recommend to our
readers Dr. Roberts's work, as containing an admira-
ble r<'xum6 of the present state of knowledge of uri-
nary diseases, and as a safe and reliable guide to the
clinical observer. — Edin. Med. Jour.

The most complete and practical treatise upon renal

ers from its clearness and simple announcement of the
facts in relation to diagnosis and treatment of urinary
disorders, and contains in condensed form the investi-
gations of Bence Jones, Bird, Beale, Hassall, Prout,
and a host of other well-known writers upon this sub-
ject. The characters of urine, physiological and pa-
thological, as indicated to the naked eye as well as by
microscopical and chemical investigations, are con-
cisely represented both by description and by well
executed engravings. — Cincinnati Journ. of Med.

B

ASSAM (W.R.), M.D.,

Senior Physician to the Westminster Hospital, &c.

RENAL DISEASES : a Clinical Guide to their Diagnosis and Treatment.

With illustrations. In one neat royal 12mo. volume of 304 pages, cloth, $2 00.

ieUll* of larger books here acquire a new interest
from the author's arrangement. This part of the
book is full of good work. — Brit, and For. Medico-
Jhirurgival Review, July, 1870.

The chapters on diagnosis and treatment are very
good, and the student and young practitioner will
find them full of valuable practical hints. The third
part, on the urine, is excellent, and we cordially
recommend its perusal. The author has arranged
his matter in a somewhat novel, and, we think, use-
ful form. Here everything can be easily found, and,
what is more important, easily read, for all the dry

The easy descriptions and compact modes of state-
ment render the book pleasing and convenient. — Am.
Journ. Med. Sciences, July, 1870.

INCOLN (D. F.). M.D.,

Physician to the Department of Nervous Diseases, Boston Dispensary.

ELECTRO THERAPEUTICS ; A. Concise Manual of Medical Electri-

city. In one very neat royal 12mo. volume, cloth, with illustrations, $1 50. (Just Ready.)

The work is convenient in size, its descriptions of
methods and appliances are sufficiently complete for
the general practitioner, and the chapters on Electro-
physiology and diagnosis are well written and read-
able. For those who wish a handy-book of directions
for the employment of galvanism in medicine, this
will serve as a very good and reliable guide. — New
Remedies, Oct. 1874.

It is a well written work, and calculated to meet
the demands of the busy practitioner. It contains
the latest researches in this important branch of med-
icine.— Peninsular Journ. of Med., Oct. 1874.

Eminently practical in character. It will amply
repay any one for a careful perusal. — Leavenworth
Med. Herald, Oct. 1874.

This little hook is, considering its size, one of the
very best of the English treatises on its subject that
has come to our notice, possessing, among others, the
rare merit of dealing avowedly and actually with
principles, mainly, rather than with practical details,
thereby supplying a real want, instead of helping
merely to flood the literary market Dr. Lincoln's
style is usually remarkably clear, and the whole
book is readable and interesting. — Boston Med. and
Surg. Journ., July 23, 1874.

We have here in a small compass a great deal of
valuable information upon the subject of Medical
Electricity. — Canada Med. and Surg. Journ.. Nov.
1874.

TEE (HENRY).

Prof, of Surgery at the Riyal College of Surgeons of England, etc.

LECTURES ON SYPHILIS AND ON SOME FORMS OF LOCAL

DISEASE AFFECTING PRINCIPALLY THE ORGANS OF GENERATION. In one
handsome octavo volume.

c o isr T IE nxr T s .

LECTURES I., II., III. General. — IV. Treatment of Syphilis — V. Treatment of Particular
and Modified Syphilitic Affections — VI. Second Stage of Lues Venerea; Treatment — VII. Lo-
cal Suppurating Venereal bore ; Syphilization ; Lymphatic Absorption ; Physiological Absorp-
tion ; Twofold Inoculation — VIII. Urethral Discharges : different kinds; Treatment; Conclu-
sions of Hunter and Ricord — IX. Prostatic Discharges — X. Lymphatic Absorption continued ;
Local Affections ; Warts and Excrescences.

DIPHTHERIA ; its Nature and Tr<>at nent, with an
account of the History of its Prevalence in vari-
ous Countries. By D. D. SLADK, M.D. Second and
revised edition. In one neat royal 12mo. volume,
cloth, $1 25.

LECTURES ON THE STUDY OF FEVER. By A.
HUDSON, M.D., M.R.I.A., Physician to the Meath
Hospital. In one vol. 8vo., cloth, $2 50.

A TREATISE ON FEVER. By ROBERT D. LYONS,
K C C. In one octavo volume of 362 pages, cloth,
$2 25.

CLINICAL OBSERVATIONS ON FUNCTIONAL
NERVOUS DISORDERS ByC. HANDFIELD JONKS,
M.D., Physician to St. Mary's Hospital, &c. Sec-
ond American Edition. In one handsome octavo
volume of 348 pages, cloth, $3 25. ;

HENRY C. LEA'S PUBLICATIONS — ( Venereal Diseases, etc.).

19

~DUMSTEAD (FREEMAN J.}, M.D.,

•*-* Professor of Venereal Diseases at the Col. of Phys. and Surgr., New York, &c.

THE PATHOLOGY AND TREATMENT OF VENEREAL DIS-

EASES. Including the results of recent investigations upon the subject. Third edition,
revised and enlarged, with illustrations. In one large and handsome octavo volume of
over 700 pages, cloth, $5 00 ; leather, $6 00.

In preparing this standard work again for the press, the author has subjected it to a very
thorough revision. Many portions have been rewritten, and much new matter added, in order to
bring it completely on a level with the most advanced condition of syphilography, but by careful
compression of the text of previous editions, the work has been increased by only sixty-four pages.
The labor thus bestowed upon it, it is hoped, will insure for it a continuance of its position as a
complete and trustworthy guide for the practitioner.

It is the most complete book with which we are ac-
quainted in the language. The latest views of the
best authorities are put forward, and the information
IR well arranged — a great point for the student, and

more for the pi-actitioner. The subjects of vis-
C' -val syphilis, syphilitic affections of the eyes, and
t '•!'.: treatment of syphi/is by repeated inoculat'ons, are
very fully discussed. — London Lancet, Jan. 7, 1871.

Dr. Bumstead's work is already so universally
known as the best treatise in the English language on
venereal diseases, that it may seem almost superflu-
ous to say more of it than that a new edition has been
Issued. But the author's industry has rendered this
new edition virtually a new work, and so merits as

much special commendation as if its predecessors had
not been published. As a thoroughly practical book
on a class of diseases which form a large share of
nearly every physician's practice, the volume before
us is by far the best of which we have knowledge. —

N. Y. Medical Gazette, Jan. 28, 1871.

It is rare in the history of medicine to find any one
book which contains all that a practitioner needs to
know; while the possessor of "Bumstead on Vene-
real" has no occasion to look outside of its covers for
anything practical connected with (he diagnosis, his-
tory, or treatment of these affections.— N. Y. Medical
Journal, March, 1871.

rtULLERIER (A.}, and

*~S Surgeon to the Hdpital du Midi.

ftUMSTEAD (FREEMAN J.},

•*-* Professor of Venerea I Diseases in the College of
Physicians and Surgeons, N. Y.

AN ATLAS OF VENEREAL DISEASES. Translated and Edited by

FREEMAN J. BUMSTEAD. In one large imperial 4to. volume of 328 pages, double-columns,
with 26 plates, containing about 150 figures, beautifully colored, many of them the size of
life; strongly bound in cloth, $17 00 ; also, in five parts, stout wrappers for mailing, at $3
per part.

Anticipating a very large sale for this work, it is offered at the very low price of THREE DOL-
LARS a Part, thus placing it within the reach of all who are interested in this department of prac-
tice. Gentlemen desiring early impressions of the plates would do well to order it without delay.
A specimen of the plates and text sent free by mail, on receipt of 25 cents.

which for its kind is more necessary for them to have.
-California Med. Gazette, March, 1869.

The most splendidly illustrated work in the lan-
guage, and in our opinion far more useful than the
French original. — Am. Journ. Med. Sciences, Jan. '69.

The fifth and concluding number of this magnificent
work has reached us, and we have no hesitation in
saying that its illustrations surpass those of previous
numbers. — Boston Med. and Surg. Journal, Jan. 14,
1869.

Other writers besides M. Cullerier have given us a
good account of the diseases of which he treats, but
no one has furnished us with such a complete series
of illustrations of the venereal diseases. There is,
however, an additional interest and value possessed
by the volume before us ; for it is an American reprint
and translation of M. Cullerier's work, with inci-
dental remarks by one of the most eminent American
syphilographers, Mr. Bumstead. — Brit, and For.
Medico-Chir. Review, July, 1869.

We wish for once that our province was not restrict-
•d to methods of treatment, that we might say some-
thing of the exquisite colored plates in this volume.
—London Practitioner, May, 1869.

As a whole, it teaches all that can be taught by
means of plates and print. — London Lancet, March
13, 186S.

Superior to anything of the kind ever before issued
on this continent. — Canada Med. Journal, March, '69.

The practitioner who desires to understand this
branch of medicine thoroughly should obtain this,
the most complete and best work ever published. —
Dominion Med. Journal, May, 1869.

This is a work of master hands on both sides. M.
CuHerier is scarcely second to, we think we may truly
«ay is a peer of the illustrious and venerable Ricord,
frVnle in this country we do not hesitate to say that
Dr. Bumstead, as an authority, is without a rival
A..SUI ing our readers that these illustrations tell the
•wholo history of venereal disease, from its inception
to its end, we do not know a single medical work,

(BERKELEY],

Surgeon to the Lock Hospital, London.

ON SYPHILIS AND LOCAL

one handsome octavo volume ; cloth, $3
Bringing, as it does, the entire literature of the dis-
ease down to the present day, and giving with great
ability the results of modern research, it is in every
respect a most desirable work, and one which should
find a place in the library of every surgeon. — Cali-
fornia Med. Gazette, June, 1869.

Considering the scope of the book and the careful
attention to the manifold aspects and details of its
subject, it is wonderfully concise. All these qualities
render it an especially valuable book to the beginner,

CONTAGIOUS DISORDERS. In

25.

to whom we would most earnestly recommend its
study ; while it is no less useful to the practitioner.—
St. Louis Med. and Surg. Journal, May, 1869.

The most convenient and ready book of i-eference
we have met with.— A1'. Y. Med. Record, May 1,1869.

Most admirably arranged for both student and prac-
titioner, no other work on the subject equals it ; it i»
more simple, more easily studied. — Buffalo Med. and
Surg. Journal, March, 1869.

M.D.

A COMPLETE TREATISE ON VENEREAL DISEASES. Trans-

lated from the Second Enlarged German Edition, by FREDERIC R. STURGIS, M.D In one
octavo volume, with illustrations. (Preparing.)

HENRY C. LEA'S PUBLICATIONS — (Diseases of the Skin).

WILSON (ERASMUS), F.R.S.

ON DISEASES OF THE SKIN. With Illustrations on wood. Sev-

enth American, from the s\xth and enlarged English edition. In one large octavo volume
of over 800 pages, $5.

A SERIES OF PLATES ILLUSTRATING "WILSON ON DIS-
EASES OF THE SKIN;" consisting of twenty beautifully executed plates, of which thir-
teen are exquisitely colored, presenting the Normal Anatomy and Pathology of the Skin,
and embracing accurate representations of about one hundred varieties of disease, most of
them the size of nature. Price, in extra cloth, $5 50.

Also, the Text and Plates, bound in one handsome volume. Cloth, $10.

No one treating skin diseases should be without
a copy of this standard work. — Canada Lancet.

We can safely recommend it to the profession at
the best work on the subject now in existence ir
the English language. — Medical Times and Gazette

Mr. Wilson's volume is an excellent digest of the
actual amount of knowledge of cutaneous diseases :
it includes almost every fact or opinion of importanc€
connected with the anatomy and pathology of the
skin. — British and Foreign Medical Review.

Such a work as the one before us is a most capital

ind acceptable help. Mr. Wilson has long been held
is high authority in this department of medicine, and
his book on diseases of the skin has long been re-
jarded as one of the best text-books extant on the
subject. The present edition is carefully prepared,
ind brought up in its revision to the present time. In
his edition we have also included the beautiful series
of plates: illustrative of the text, and in the last edi-
tion published separately. There are twenty of these
plates, nearly all of them colored to nature, and ex-
hibiting with great fidelity the various groups of
diseases. — Cincinnati Lancet.

F THE SAME AUTHOR.

THE STUDENT'S BOOK OF CUTANEOUS

EASES OP THE SKIN.

MEDICINE and Dis-

In one very handsome royal 12mo. volume. $3 50.

TtfELIGAN (J.MOORE}, M.D., M.R.I. A.

A PRACTICAL TREATISE ON DISEASES OF THE SKIN.

Fifth American, from the second and enlarged Dublin edition by T. W. Belcher, M.B.
In one neat royal 12mo. volume of 462 pages, cloth, $2 25.

Fully equal to all the requirements of students and
young practitioners. — Dublin Med. Press.

Of the remainder of the work we have nothing be-
yond unqualified commendation to offer. It is so far
the most complete one of its size that has appeared,
and for the student there can be none which can com-
pare with it in practical value. All the late disco-
veries in Dermatology have been duly noticed, and
Y THE SAME AUTHOR.

their value justly estimated; in a word, the work is
fully up to the times, and is thoroughly stocked with
most valuable information. — New York Med. Record,
Jan. 15, 1867.

The most convenient manual of diseases of the
skin that can be procured by the student. — Chicago
Med. Journal, Dec. 1866.

ATLAS OF CUTANEOUS DISEASES. In one beautiful quarto

volume, with exquisitely colored plates, &c., presenting about one hundred varieties of
disease. Cloth, $5 50.

The diagnosis of eruptive disease, however, under I inclined to consider it a very superior work, corn-
all circumstances, is very difficult. Nevertheless, | bining accurate verbal description with sound view*

Dr. Neligau has certainly, "as far as possible," given
a faithful and accurate representation of this class of
diseases, and there can be no doubt that these plates
will be of great use to the student and practitioner in
drawing a diagnosis as to the class, order, and species
to which the particular case may belong. While

looking over the
examine also the

Atlas" we have been induced to
'Practical Treatise," and we are

of the pathology and treatment of eruptive diseases.
— Glasgow Med. Journal.

A compend which will very much aid the practi-
tioner in this difficult branch of diagnosis. Taken
with the beautiful plates of the Atlas, which are re-
markable for their accuracy and beauty of coloring,
it constitutes a very valuable addition to the library
of a practical man. — Buffalo Med. Journal.

pflLLIER (THOMAS], M.D.,

Physician to the Skin Department of University College Hospital, &c .

HAND-BOOK OF SKIN DISEASES, for Students and Practitioners.

Second American Edition. In one royal 12mo. volume of 358 pp. With Illustrations.
Cloth, $2 25.

We can conscientiously recommend it to the stu-
dent; the style is clear and pleasant to read, the
matter is good, and the descriptions of disease, with
the modes of treatment recommended, are frequently
illustrated with well-recorded cases. — London Med.
Times and Gazette, April 1, 1865.

It is a concise, plain, practical treatise on the vari-
ous diseases of the skin ; just such a work, indeed,
as was much needed, both by medical students and
practitioners. — Chicago Medical Examiner, May,
1865.

A NDERSON (McCALL], M.D.,

•^*~ Physician to the Dispensary for Skin Diseases, Glasgow, &c.

ON THE TREATMENT OF DISEASES OF THE SKIN. With an

Analysis of Eleven Thousand Consecutive Cases. In one vol. 8vo. $1. (Lately Published.)

GUERSANT'S SURGICAL DISEASES OF INFANTS I DT5WEES ON THE PHYSICAL AND MEDICAL
AND CHILDREN. Translated by R. J. DUNGLI- TREATMENT OF CHILDREN. El wventh edition.
BOX, M.D. 1 vol. 8vo. Cloth, $2 50. 1 TO!. 8vo. of 548 pages. Cloth, $2 80.

HENRY C. LEA'S PUBLICATIONS — (Diseases of Children). 21

GMITH(J. LEWIS], M. D.,

O Professor of Morbid Anatomy in the Bellevue Hospital Med. College, N. T.

A COMPLETE PRACTICAL TREATISE ON THE DISEASES OP

CHILDREN. Second Edition, revised and greatly enlarged. In one handsome octavo
volume of 742 pages, cloth, $5; leather, $6. (Lately Published.)
FROM THE PREFACE TO THE SECOND EDITION.

In presenting to the profession the second edition of his work, the author gratefully acknow-
ledges the favorable reception accorded to the first. He has endeavored to merit a continuance
of this approbation by rendering the volume much more complete than before. Nearly twenty
additional diseases have been treated of, among which may be named Diseases Incidental to
Birth Rachitis, Tuberculosis, Scrofula, Intermittent, Remittent, and Typhoid Fevers, Chorea,
and the various forms of Paralysis. Many new formulae, which experience has shown to be
useful, have been introduced, portions of the text of a less practical nature have been con-
densed, and other portions, especially those relating to pathological histology, have been
rewritten to correspond with recent discoveries. Every effort has been made, however, to avoid
an undue enlargement of the volume, but, notwithstanding this, and an increase in the size of
the page, the number of pages has been enlarged by more than one hundred.

227 WEST 49TH STREET, NEW YORK, April, 1872.

The work will be found to contain nearly one-third more matter than the previous edition, and
It is confidently presented as in every respect worthy to be received as the standard American
text-book on the subject.

Eminently practical as well as judicious in its
teachings.— Cincinnati Lancet and Obs., July, 1S72.

A standard work that leaves little to be desired.—
Indiana Journal of Medicine, July, 1872.

We know of no book on this subject that we can
more cordially recommend to the medical student
and the practitioner. — Cincinnati Clinic, June 29, '72.

We regard it as superior to any other single work
on the diseases of infancy and childhood. — Detroit
Rev. of Med. and Pharmacy, Aug. 1872.

We confess to increased enthusiasm in recommend-
ing this second edition.— St. Louis Med. and Surg.
Journal, Aug. 1872.

rtONDIE (D. FRANCIS), M.D.

A PRACTICAL TREATISE ON THE DISEASES OF CHILDREN.

Sixth edition, revised and augmented. In one large octavo volume of nearly 800 closely-
printed pages, cloth, $5 25 ; leather, $6 25.

The present edition, which is the sixth, is fully up
to the times in the discussion of all those points in the
pathology and treatment of infantile diseases which
kave been brought forward by the Germa u and French

teachers. As a whole, however, the work is the best
American one that we have, and in its special adapta-
tion to American practitioners it certainly has no
equal.— New York Med. Record, Marci 2, 1868.

TXTEST (CHARLES], M.D.,

Physician to the Hospital for Sick Children, &c.

LECTURES ON THE DISEASES OP INFANCY AND CHILD-
HOOD. Fifth American from the sixth revised and enlarged English edition. In one large
and handsome octavo volume of 678 pages. Cloth, $4 50 ; leather, $5 50. (Just Issued.)
The continued demand for this work on both sides of the Atlantic, and its translation into Ger-
man, French, Italian, Danish, Dutch, and Russian, show that it fills satisfactorily a want exten-
sively felt by the profession. There is probably no man living who can speak with the authority
derived from a more extended experience than Dr. West, and his work now presents the results of
nearly 2000 recorded cases, and 600 post-mortem examinations selected from a.mong nearly 40,000
cases which have passed under bis care. In the preparation of the present edition he has omitted
much that appeared of minor importance, in order to find room for the introduction of additional
matter, and the volume, while thoroughly revised, is therefore not increased materially in size.

Of all the English writers on the diseases of chil- I living authorities in the difficult department of medi-
dren, there is no one so entirely satisfactory to us as | cal science in which he is most widely known. —
Dr. West. For years we have held his opinion as I Boston Med. and Surg. Journal.
judicial, and have regarded him as one of the highest |

DF THE SAME AUTHOR. (Lately Issued.)

ON SOME DISORDERS OF THE NERVOUS SYSTEM IN CHILD-

HOOD; being the Lumleian Lectures delivered at the Royal College of Physicians of Lon-
don, in March, 1871. In one volume, small 12mo., cloth, $1 00.

J3MITH (E USTA CE), M. D^~

Physician to the Northwest London Free Dispensary for Sick Children.

A PRACTICAL TREATISE ON THE WASTING DISEASES OF

INFANCY AND CHILDHOOD. Second American, from the second revised and enlarged
English edition. In one handsome octavo volume, cloth, $2 50. (Lately Issued.)

This is in every way an admirable book. The
modest title which the author has chosen for it scarce-
ly conveys an adequate idea of the many subjects
upon which it treats. Wasting is so constant an at-
tendant upon the maladies of childhood, that a trea-
tise upon the wasting diseasesof childrenmust neces
garily embrace the consideration of many affections
of which it is a symptom ; and this is excellently well
done by Dr. Smith. The book might fairly be de-

scribed as a practical handbook of the common dis-
eases of children, so numerous are the affections con-
sidered either collaterally or directly. We are
acquainted with no safer guide to the treatment of
children's diseases, and few works give the insight
into the physiological and other peculiarities of chil-
dren that Dr. Smith's book does.— Brit. Med. Journ.,
April 8, 1871.

22

HENRY C. LEA'S PUBLICATIONS — (Diseases of Women).

mRE OBSTETRICAL JOURNAL. (Free of postage for 1875.)

THE OBSTETRICAL JOURNAL of Great Britain and Ireland;

Including MIDWIFERY, and the DISEASES OF WOMEN AND INFANTS. With an American
Supplement, edited by WILLIAM F. JENKS, M.D. A monthly of about 80 octavo pages,
very handsomely printed. Subscription, Five Dollars per annum. Single Numbers, 50
cents each.

Commencing with April, 1873, the Obstetrical Journal consists of Original Papers by Brit-
ish and Foreign Contributors ; Transactions of the Obstetrical Societies in England and abroad ;
Reports of Hospital Practice; Reviews and Bibliographical Notices; Articles and Notes, Edito-
rial, Historical, Forensic, and Miscellaneous; Selections from Journals; Correspondence, Ac.
Collecting together the vast amount of material daily accumulating in this important and ra-
pidly improving department of medical science, the value of the information which it pre-
sents to the subscriber may be estimated from the character of the gentlemen who have already
promised their support, including such names as those of Drs. ATTHILL, ROBERT BARNES, HENRY
BENNET, THOI^AS CHAMBERS, FLEETWOOD CHURCHILL, MATTHEWS DUNCAN, GRAILY HEWITT,
BRAXTON HICKS, ALFRED MEADOWS, W. LEISHMAN, ALEX. SIMPSON, TYLER SMITH, EDWARD J.
TILT, SPENCER WELLS, &c. <fcc. ; in short, the representative men of British Obstetrics and Gynae-
cology.

In order to render the OBSTETRICAL JOURNAL fully adequate to the wants of the American
profession, each number contains a Supplement devoted to the advances made in Obstetrics and
Gynaecology on this side of the Atlantic. This portion of the Journal is under the editorial
charge of Dr. WILLIAM F. JENKS, to whom editorial communications, exchanges, books for re-
view, Ac., may be addressed, to the care of the publisher.

**.* Complete sets from the beginning can no longer be furnished, but subscriptions can com-
mence with January, 1875, or with Vol. II., April, 1874.

fTHOMAS (T. GAILLARD),M.J).,

Professor of Obstetrics, &c., in the College of Physicians and Surgeons, N. T., &c.

A PRACTICAL TREATISE ON THE DISEASES OF WOMEN. Fourth

edition, enlarged and thoroughly revised. In one large and handsome octavo volume of
800 pages, with 191 illustrations. Cloth, $5 00; leather, $6 00. (Now Ready.)
The author has taken advantage of the opportunity afforded by the call for another edition of
this work to render it worthy a continuance of the very remarkable favor with which it has been
received. Every portion has been subjected to a conscientious revision, and no labor has been
spared to make it a complete treatise on the most advanced condition of its important subject.

A few notices of the previous editions are subjoined : —

No general practitioner can afford to be without
it.— St. Louis Mud. and Surg. Journal, May, 1872.

Professor Thomas fairly took the Profession of the
United States by storm when his book first made its
appearance early in IS'.iS. Its reception was simply
enthusiastic, notwithstanding a few adverse criti-
cisms from our transatlantic brethren, the first large
edition was rapidly exhausted, and in six mouths a
second one was issued, and in two years a third one
was announced and published, and we are now pro-
mised the fourth. The popularity of this work was
not ephemeral, and its success was unprecedented in
the annals of American medical literature. Six years
is a long period in medical scientific research, but
Thomas's work on "Diseases of Women" is still the
leading native production of the United States. The
order, the matter, the absence of theoretical disputa-
tU-eness, the fairness of statement, and the elegance
of diction, preserved throughout the entire range of
the book, indicate that Professor Thomas did not
overestimate his powers when he conceived the idea
and executed the work of producing a new treatise
upon diseases of women. — PROF. PALLEX, in Louis-
mile Med. Journal, Sept. 1874.

Briefly, we may say that we know of no book
which so completely and concisely represents the
present state of gynaecology; none so full of well-
digested and reliable teaching ; none which bespeaks
an author more apt in research and abundant in re-
sources.— N. Y. Med. Record, May 1, 1872.

Its able author need not fear comparison between
it and any similar work in tlie English language;
nay more, as a text-hoek for students and as a guide
for practitioners, we believe it is unequalled. If
either student or practitioner can get but ^ne book
on diseasesof women, that hook should be "Thomas."
—Amer. Jour. Med. Sciences, April, ' 872

To students we unhesitatingly recommend it as
the best text-book on diseases of females extant.—
Sf. Louis Med. Reporter, June, 1869.

Of all the army of books that nave appeared of late
years, on the diseases of the uterus and its appendages,
we know of none that is so clear, comprehensive, and
practical as this of Dr. Thomas', or one that we should
more emphatically recommend to the young practi-
tioner, as his guide.— California Med. Gazette) June,
1869.

It would he superfluous to give an extended review
of what is now firmly established as the American
text-hook of Gynaecology.— N. Y. Med. Gazette, July
17, 1869.

This is a new and revised edition of a work which
we recently noticed at some length, and earnestly

We shou.d not be doing onr duty to the profession i g^**** *' tt^on "pace""? tT^'K.

r^n-er^^^

^0?e^^^

__i :»„!.:„„: , „ „„ j ; „ „ r»r. Th/\ma c'o •nr^flr u ,s I LanCet, AUK. 1OD9.

no hesitation in recommending Dr. Thomas's work as
one of the most complete of its kind ever published.
It should be in the possession of every practitioner
for reference and for study.— London Lancet, April
27, 1872.

We are free to say that we regard Dr. Thomas the
best American authority on diseases of women. —
Cincinnati Lancet and' Observer, May, 1S72.

Lancet, Aug.

It is so short a time since we gave a full review of
the first edition of this book, that we deem it only
necessary now to call attention to the second appear-
ance of the work. Its success has been remarkable,
and we can only congratulate the author on the
brilliant reception his book has received.—/?". Y.-Med.
Journal, April, 1869.

HENRY C. LEA'S PUBLICATIONS — (Diseases of Women).

TTODGE (HUGH Z/.), M.D.,

•O- Emeritus Professor of Obstetrics, Ac., in the University of Pennsylvania.

ON DISEASES PECULIAR TO WOMEN; including Displacements

of the Uterus. With original illustrations. Second edition, revised and enlarged. ID
one beautifully printed octavo volume of 531 pages, cloth, $4 50.

From PROF. W. H. BTPORD, of the Riish Medical
College, Chicago.

The book bears the impress of a master hand, and
must, as its predecessor, prove acceptable to the pro-
fession. In diseases of women Dr. Hodge has estab-
lished a school of treatment that has become world-
wide in fame.

Professor Hodge's work is truly an original one
from beginning to end, consequently no one can pe-
ruse its pages without learning something new. The
book, which is by no means a large oue, is divided into
two grand sections, so to speak : first, that treating of
the nervous sympathies of the uterus, and, secondly,

chat which speaks of the mechanical treatment of dis-
placements of that organ. He is disposed, as a non-
Seliever In the frequency of inflammations of the
uterus, to take strong ground against many of the
highest authorities iu this branch of medicine, and
the arguments which he offers in support of his posi-
tion are. to say the least, well put. Numerous wood-
cuts adorn this portion of the work, and add incalcu-
lably to the proper appreciation of the variously
shaped instruments referred to by our author. As s
contribution to the study of women's diseases, it i« o*
great value, and is abundantly able to stand on its
own merits.— .V. Y. Medical Record, Sept. 15, 1868.

W

•EST (CHARLES), M.D.

LECTURES ON THE DISEASES OF WOMEN. Third American,

from the Third London edition. In one neat octavo volume of about 550 pages, cloth,
$3 75 ; leather, $4 75.

seeking truth, and one that

As a writer. Dr. West stands, in our opinion, se-
eoud only to Watson, the "Macaulay of Medicine;'
he possesses that happy faculty of clothing instruc-
tion in easy garments ; combining pleasure with
profit, he leads his pupils, in spite of the ancient pro-
verb, along a royal road to learning. His work is one
which will not satisfy the extreme on either side, but
It is one that will please the great majority wko are

0 , ill convince the student

that he has committed himself to a candid, safe, and
valuable guide.— jr. A. Med.-Chirurg Review.

We have to say of it, briefly and decidedly, that it
is the best work on the subject in any language, and
that it stamps Dr. West as the facile princeps of
British obstetric authors.— Edinburgh Med.

PARNES (ROBERT], M.D., F.R. C.P.,

•*-* Obstetric Physician to St. Thomas'* Hospital, Ac.

A CLINICAL EXPOSITION OF THE MEDICAL AND SURGI-
CAL DISEASES OF WOMEN. In or,« hnmlsome octavo volume of about 800 pages, with
169 illustrations. Cloth, $5 00, leather, $6 00. (Just Issued.}

The very complete scope of this volume and the manner in which it has been filled out, may
be seen by the subjoined Summary of Contents.

INTRODUCTION. CHAPTER I. Ovaries ; Corpus Luteum. II. Fallopinn Tubes. III. Shape of
Uterine Cavity. IV. Structure of Uterus. V. The Vagina. VI. Examinations and Diagnosis.
VII. Significance of Leucorrhoea. VIII. Discharges of Air. IX. Watery Discharges. X. Puru-
lent Discharges. XI. Hemorrhagic Discharges. XII Significance of Pain. XIII. Significance
of Dyspareunia. XIV. Significance of Sterility. XV. Instrumental Diagnosis and Treatment.
XVI. Diagnosis by the Touch, the Sound, the' Speculum. XVII. Menstruation and its Disor-
ders. XVIII. Amenorrhcea. XIX. Amenorrhcea (continued). XX. Dysuienorrhoea. XXI.
Ovarian Dysmenorrhoea, Ac. XXII. Inflammatory Dysmenorrhoea. XXIII. Irregularities of
Change of Life. XXIV. Relations between Menstruation and Diseases. XXV. Disorders of Old
Age. XXVI. Ovary, Absence and Hernia of. XXVII. Ovary, Hemorrhage, Ac., of. XXVIII.
Ovary, Tubercle, Cancer, Ac., of. XXIX. Ovarian Cystic Tumors. XXX. Dermoid Cvsts of
Ovary. XXXI. Ovarian Tumors, Prognosis of. XXXII. Diagnosis of Ovarian Tumors. XXXIII.
Ovarian Cysts, Treatment of. XXXIV. Fallopian Tubes. Diseases of. XXXV. Broad Liga-
ments, Diseases of. XXXVI. Extra-uterine Gestation. XXXVII. Special Pathology of Ute
rus. XXXVIII. General Uterine Pathology. XXXIX. Alterations of Blood Supply. XL.
Metritis, Endometritis, Ac. XLI. Pelvic Cellulitis and Peritonitis, Ac. XLII. Haematocele, Ac
XLIII. Displacements of Uterus. XLIV. Displacements (continued). XLV. Retroversion and
Retroflexion. XLVI. Inversion. XLVII. Uterine Tumors. XLVIII. Polypus Uteri. XLIX.
Polypus Uteri (continued). L. Cancer. LI. Diseases of Vagina. LIT. Diseases of the Vulva.

mas, and Peaslee, as if these eminent men were his

Embodying the long experience and personal obser-
vation of one of the greatest of living teachers in dis-
eases of women, it seems pervaded by the presence
of the author, who speaks directly to the reader, and
speaks, too, as one having authority. And yet, not-
withstanding this distinct personality, there is noth-
ing narrow as to time, place, or individuals, in the
views presented, and in the instructions given ; Dr.
Barnes has been an attentive student, not only of Eu-
ropean, but also of American literature, pertaining to
diseases of females, and enriched\his own experience
by treasures thence gathered ; he seems as familiar,
for example, with the writings of Sims, Emmet, Tho-

countrymen and colleagues, and gives them a credit
which must be gratifying to every American physi-
cian.— Am. Journ. Med. Set., April, 1874.

Throughout the whole book it is impossible not to
feel that the author has spontaneously, conscientious-
ly, and fearlessly performed his task. He goes direct
to the point, and does not loiter on the way to gossip
or quarrel with other authors. Dr. Barnes's book
will be eagerly read all over the world, and will
everywhere be admired for its comprehensiveness,
honesty of purpose, and ability. — The Obstet. Journ.
of Great Britain and Ireland, March, 1874.

CHURCHILL ON THE PUERPERAL FEVER AND
OTHER DISEASES PECULIAR TO WOMEN. 1 vol.
Svo., pp. 450, cloth. $2 50.

MEIGS ON WOMAN: HER DISEASES AND THEIR
REMEDIES. A Series of Lectures to his Class.
Fourth and Improved Edition. 1 vol. Svo., over
700 pages, cloth, $5 00 ; leather, *6 00.

MEIGS ON THE NATURE, SIGNS, AND TREAT-
MENT OF CHILDBED FEVER. 1 vol. 8vo., pp
3SS, cloth. $2 00.

ASHWELL'S PRACTICAL TREATISE ON THE DIS-
EASES PECULIAR TO WOMEN. Third American,
from the Third and revised London edition. 1 vol.
8vo., pp. 528, cloth. $3 50.

DEWEES'S TREATISE ON THE DISEASES OF FE-
MALES. With illustrations. Eleventh Edition,
with the Author's last improvements and correc-
tions. In one octavo volume of 536 pages, with
plates, cloth. $3 00.

HENRY C. LEA'S PUBLICATIONS — (Midwifery).

fTODGE (HUGH L.}, M.D.,

•*--*- Emeritus Professor of Midwifery, &c., in the University of Pennsylvania, Ac.

THE PRINCIPLES AND PRACTICE OF OBSTETRICS. Illus-
trated with large lithographic plates containing one hundred and fifty-nine figures from
original photographs, and with numerous wood-cuts. In one large and beautifully printed
quarto volume of 550 double-columned pages, strongly bound in cloth, $14.

The work of Dr. Hodge is something more than a
simple' presentation of his particular views in the de-
partment of Obstetrics; it is something more than an
ordinary treatise on midwifery; it is, in fact, a cyclo-
paedia of midwifery. He has aimed to embody in a
single volume the whole science and art of Obstetrics.
An elaborate text is combined with accurate and va-
ried pictorial illustrations, so that no fact or principle
Is left unstated or unexplained. — Am. Med. Times,
Sept. 8, 1864.

We should like to analyze the remainder of this
excellent work, but already has this review extended
beyond our limited space. We cannot conclude this
aotice without referring to the excellent finish of the
work. In typography it is not to be excelled ; the
paper is superior to what is usually afforded by our
American cousins, quite equal to the best of English

books. The engravings and lithographs are most j —0 t

beautifully executed. ^ The Work recommends itself instructive, and in the main, we believe" correct. "The

great attention which the author has devoted to the

for its originality, and is in every way a most valu-
able addition to those on the subject of obstetrics.--
Canada Med. Jorirnal, Oct. 1864.
It is very large, profusely and elegantly illustrated,

We have examined Professor Hodge's work with
great satisfaction ; every topic is elaborated most
fully. The views of the author are comprehensive,
and concisely stated. The rules of practice are judi-
cious, and will enable the practitioner to meet every
emergency of obstetric complication with confidence.
— Chicago Med. Journal, Aug. 1864.

More time than we have had at our disposal since
we received the great work of Dr. Hodge is necessary
to do it justice. It is undoubtedly by far the most
original, complete, and carefully composed treatise
on the principles and practice of Obstetrics which has
ever been issued from the American press. — Pacific
Med. and Surg. Journal, July, 1864.

We have read Dr. Hodge's book with great plea-
sure, and have much satisfaction in expressing our
commendation of it as a whole. It is certainly highly

mechanism of parturition, taken along with the con-
clusions at which he has arrived, point, we think,
conclusively to the fact that, in Britain at least, the

and is fitted to take its place near the works of great ; doctrines of Naegele have been too blindly received.

obstetricians. Of the American works on the subject

—Glasgow Med. Joiirnal, Oct. 1864.

It is decidedly the best.— Edinb. Med. Jour., Dec. '64.

#*# Specimens of the plates and letter-press will be forwarded to any address, free by mail,
en receipt of six cents in postage stamps.

BANNER (THOMAS H.}, M. D.
ON THE SIGNS AND DISEASES OF PREGNANCY. First American

from the Second and Enlarged English Edition. With four colored plates and illustrations
on wood. In one handsome octavo volume of about 500 pages, cloth, $4 25.

The very thorough revision the work has undergone
has added greatly to its practical value, and increased
materially its efficiency as a guide to the student and
to the young practitioner.— Am. Journ. Med. Sci.,
April, 1868.

With the immense variety of subjects treated of
and the ground which they are made to cover, the im-
possibility of giving an extended review of this truly
remarkable work must be apparent. We have not a
single fault to find with it, and most heartily com-
mend it to the careful study of every physician who
would not only always be" sure of his diagnosis of

pregnancy, but always ready to treat all the nume-
rous ailments that are, unfortunately for the civilized
women of to-day, so commonly associated with the
function.—^. T. Med. Record, March 1U, 1S68.

We recommend obstetrical students, young and
old, to hav* this volume in their collections. It con-
tains not on! j
and diseases of pregnancy,
much interesting relative matter that is not to be
found in any other work that we can name. — Edin-
burgh Med Journal, Jan. 1868.

a fair statement of the signs, symptoms,
f renanc, but comprises in addition

Sf WAYNE (JOSEPH GRIFFITHS), M. D.,

Physician- Accoucheur to the British General Hospital, &c.

OBSTETRIC APHORISMS FOR THE USE OF STUDENTS COM-

MENCING MIDWIFERY PRACTICE. Second American, from the Fifth and Revised
London Edition, with Additions by E. R. HUTCHINS, M. D. With Illustrations. In one
neat 12mo. volume. Cloth, $1 25. (Lately Issued.)

* ,.* See p. 3 of this Catalogue for the terms on which this work is offered as a premium to
subscribers to the " AMERICAN JOURNAL OP THE MEDICAL SCIENCES."

It is really a capital little compendium of the sub- answers the purpose. It is not only valuable for

ject, and we recommend young practitioners to buy it
and carry it with them when called to attend cases of
labor. They can while away the otherwise tedious
hours of waiting, and thoroughly fix in their memo-
ries the most important practical suggestions it con-
tains. The American editor has materially added by
his notes and the concluding chapters to the com-
pleteness and general value of the book. — Chicago
Med. Journal, Feb. 1870.

The manual before us containsin exceedingly small
compass — small enough to carry in the pocket — about
all there is of obstetrics, condensed into a nutshell of
Aphorisms. The illustrations are well selected, and
serve as excellent reminders of the conduct of labor —
regular and difficult. — Cincinnati Lancet, April, '70.

TMs is a mostadmirable little work, and completely

young beginners, but no one who is not a proficient
in the art of obstetrics should be without it, because
it condenses all that is necessary to know for ordi-
nary midwifery practice. We commend the book
most favorably. — St. Louis Med. and Surg. Journal,
Sept. 10, 1870.

A studied perusal of this little book has satisfied
us of its eminently practical value. The object of the
work, the author says, in his preface, is to give the
student a few brief and practical directions respect-
ing the management of ordinary cases of labor ; and
also to point out to him in extraordinary cases when
and how he may act upon his own responsibility, and
when he ought to send for assistance.—^. Y. Medical
Journal, May, 1870.

VfTINCKEL (F.),

Professor and Director of the Gyncecological Clinic in the University of Rostock.

A COMPLETE TREATISE ON THE PATHOLOGY AND TREAT-
MENT OF CHILDBED, for Students and Practitioners. Translated, with the consent of
the author, from the Second German Edition, by JAMES READ CHADWICK, M D. In one
octavo volume. (Preparing.)

HENRY C. LEA'S PUBLICATIONS— (Midwifery).

25

^EISHMAN (WILLIAM], M.D.,

' Regius Professor of Midwifery in the University of Glasgow, &c.

A SYSTEM OF MIDWIFERY, INCLUDING THE DISEASES OF

PREGNANCY AND THE PUERPERAL STATE. In one large and very handsome oc-
tavo volume of over 700 pages, with one hundred and eighty-two illustrations. Cloth,
$5 00 ; leather, $6 00. (Lately Published.)

This is one of a most complete and exhaustive cha-
racter. We have gone carefully through it, and there
Is no subject in Obstetrics which ha> not- been con-
sidered well and fully. The result is a work, not
only admirable as a text-book, but valuable as a work
of reference to the practitioner in the various emer-
gencies of obstetric practice. Take it all in all, we
have no hesitation in saying that it is in our judgment
the best English work on the subject. — London Lan-
cet, Aug. 23, 1873.

The work of Leishman gives an excellent view of
modern midwifery, and evinces its author's extensive
acquaintance with British and foreign literature ; and
not only acquaintance with it, but wholesome diges-
tion and sound judgment of it. He has, withal, a
manly, free style, and can state a difficult and Compli-
cated matter with remarkable clearness and brevity.
—Kdin. Med. Journ., Sept. 1873.

The author has succeeded in presenting to the pro-
fession an admirable treatise, especially in its practi-
cal aspects ; one which is, iu general, clearly written,
and sound in doctrine, and one which cannot fail to
add to his already high reputation. In concluding
our examination of this work, we cannot avoid again
saying that Dr. Leishman has fully accomplished
that difficult task of presenting a good text-book upon
obstetrics. We know none better for the use of the stu-
dent or junior practitioner.— Am. Practitioner, Mar.
1874.

It proposes to offer to practitioners and students

"A Complete System of the Midwifery of the Present
Day," and well redeems the promise. In all that
relates to the subject of labor, the teaching is admi-
rably clear, concise, and practical, representing not
alone British practice, but the contributions of Con-
tinental and American schools. — N. T. Med. Record,
March 2, 1874.

The work of Dr. Leishman is, in many respects,
not only the best treatise on midwifery that we have
seen, but one of the best treatises on any medical sub-
ject that has been published of late years. — Lond.
Practitioner, Feb. 187-4.

It was written to supply a desideratum, and we will
be much surprised if it does not fulfil the purpose of
its author. Taking it as a whole, we know of no
work on obstetrics by an English author in which the
student and the practitioner will find the information
so clear and so completely abreast of the present state
of our knowledge on the subject.— Glasgow Med.
Journ., Aug. 1873.

Dr. Leishman's System of Midwifery, which has
only just been published, will go far to supply the
want which has so long been felt, of a really good
modern English text-book. Although large, as is in-
evitable in a work on so extensive a subject, it is so
well and clearly written, that it is never wearisome
to read. Dr. Leishman's work may be confidently
recommended as an admirable text-book, and is sure
to be largely used.— Lond. Med. Record, Sept. 1873.

ffAMSBOTHAM (FRANCIS H.), M.D.

THE PRINCIPLES AND PRACTICE OF OBSTETRIC MEDI-
CINE AND SURGERY, in reference to the Process of Parturition. A new and enlarged
edition, thoroughly revised by the author. With additions by W. V. KEATING, M. D.,
Professor of Obstetrics, &c., in the Jefferson Medical College, Philadelphia. In one large
and handsome imperial octavo volume of 650 pages, strongly bound in leather, with raised
bands ; with sixty-four beautiful plates, and numerous wood-cuts in the text, containing in
all nearly 200 large and beautiful figures. $7 00.

We will only add that the student will learn from
it all he need to know, and the practitioner will find
it, as a book of reference, surpassed by none other. —
Stethoscope.

The character and merits of Dr. Ramsbotham's
work are so well known and thoroughly established,
that comment is unnecessary and praise superfluous.
The illustrations, which are numerous and accurate,
are executed in the highest style of art. We cannot
too highly recommend the work to our readers. — St.
Louis Med. and Surg. Journal.

To the physician' s library it is indispensable, while
to the student, as a text-book, from which to extract
the material for laying the foundation of an education
on obstetrical science, it has no superior.— Ohio Med.
and Surg. Journal.

When we call to mind the toil we underwent in
acquiring a knowledge of this subject, we cannot but
envy the student of the present day the aid which
this work will afford him.— Am. Jour, of the Med.
Sciences.

rjHURCHILL (FLEETWOOD), M.D., M.R.I. A.

ON THE THEORY AND PRACTICE OF MIDWIFERY. A new

American from the fourth revised and enlarged London edition. With notes and additions
by D. FRANCIS CONDIE, M. D., author of a "Practical Treatise on the Diseases of Chil-
dren," <fcc. With one hundred and ninety-four illustrations. In one very handsome octavo
volume of nearly 700 large pages. Cloth, $4 00; leather, $5 00.

These additions render the work still more com-
plete and acceptable than ever ; and we can com-
mend it to the profession with great cordiality and
pleasure. — Qinnnnati Lancet.

Few work? on this branch of medical science are
equal to it, certainly none excel it, whether in regard
to theory or practice — Brit. Am. Journal.

No treatise on obstetrics with which we are ac-

quainted can compare favorably with this, in re'
spect to the amount of material which has been gath-
ered from every source. — Boston Med. and Siirg
Journal .

There is no better text-book for students, or work
of reference and study for the practising physician
than this. It should adorn and enrich every medical
library. — Chicago Med. Journal.

MONTGOMERY'S EXPOSITION OF THE SIGNS i aiQBY'S SYSTEM OF MIDWIFERY,. With Notes
AND SYMPTOMS OF PREGNANCY. With two and Additional Illustrations. Second American
exquisite colored plates, and numerous wood-cats. ' edition. One volume octavo, cloth, 422 pages.
In 1vol. 8vo., of nearly 600 pp., cloth. $375. 1 $260.

26

HENRY C. LEA'S PUBLICATIONS — (Surgery).

flROSS (SAMUEL D.), M.D.,

" Professor of Surgery in the Jefferson Medical College of Philadelphia.

A SYSTEM OF SURGERY: Pathological, Diagnostic, Therapeutic,

and Operative. Illustrated by upwards of Fourteen Hundred Engravings. Fifth edition,
carefully revised, and improved. In two large and beautifully printed imperial octavo vol-
umes of about 2300 pages, strongly bound in leather, with raised bands, $15. ( Just Issued.)
The continued favor, shown by the exhaustion of successive large editions of this great work,
proves that it has successfully supplied a want felt by American practitioners and students. In the
present revision no pains have been spared by the author- to bring it in every respect fully up to
the day. To effect this a large part of the work has been rewritten, and the whole enlarged by
nearly one-fourth, notwithstanding which the price has been kept at its former very moderate
rate. By the use of a close, though very legible type, an unusually large amount oi matter ie
condensed in its pages, the two volumes containing as much as four or five ordinary octavos.
This, combined with the most careful mechanical execution, and its very durable binding, renders
it one of the cheapest works accessible to the profession. Every subject properly belonging to the
domain of surgery is treated in detail, so that the student who possesses this work' may be said to
have in it a surgical library. A few notices of the previous edition are subjoined : —

It must long remain the most comprehensive work
on this important part of medicine. — Boston Medical
and Stirgical Journal, March 23, 1865.

We have compared it with most of our standard
works, such as those of Erichsen, Miller, Fergusson,
Syme, and others, and we must, in justice to our
author, award it the pre-eminence. As a work, com-
plete in almost every detail, no matter how minute
or trifling, and embracing every subject known in
the principles and practice of surgery, we believe it
stands without a rival. Dr. Gross, in his preface, re-
marks "my aim has been to embrace the whole do-
main of surgery, and to allot to every subject its
legitimate claim to notice;" and, we assure our
readers, he has kept his word. It is a work which
we can most confidently recommend to our brethren,
for its utility is becoming the more evident the longer
It is upon the shelves of our library. — Canada Med.
Journal, September, 1865.

The first two editions of Professor Gross' System of
Surgery are so well known to the profession, and so
highly prized, that it would be idle for us to speak in
praise of this work.— Chicago Medical Journal,
September, 1865.

We gladly indorse the favorable recommendation
of the work, both as regards matter and style, which
we made when noticing its first appearance.— British
and Foreign Medico- Chirurgical Review, Oct. 1865.

The most complete work that has yet issued from
the press on the science and practice of surgery.—
London Lancet.

This system of surgery is, we predict, destined to
take a commanding position in our surgical litera-
ture, and be the crowning glory of the author's well
earned fame. As an authority on general surgical
subjects, this work is long to occupy a pre-eminent
place, not only at home, but abroad. We have no

DY THE SAME AUTHOR.

A PRACTICAL TREATISE ON FOREIGN BODIES IN THE

AIR-PASSAGES. In 1 vol. 8vo., with illustrations, pp. 468, cloth, $2 75.

hesitation in pronouncing it without a rival in onr
language, and equal to the best systems of surgery in
any language.—^. Y. Med. Journal.

Not only by far the best text-book on the subject,
as a whole, within the reach of American students,
but one which will be much more than ever likely
to be resorted to and regarded as a high authority
abroad. — Am. Journal Med. Sciences, Jan. 1865.

The work contains everything, minor and major,
operative and diagnostic, including mensuration and
examination, venereal diseases, and uterine manipu-
lations and operations. It is a complete Thesaurus
of modem surgery, where the student and practi-
tioner shall not seek in vain for what they desire.—
San Francisco Med. Press, Jan. 1865.

Open it where we may, we find sound practical in-
formation conveyed in plain language. 'This book i»
no mere provincial or even national system of sur-
gery, but a work which, while very largely indebted
to the past, has a strong claim on the gratitude of tha
future of surgical science. — Edinburgh Med. Journal,
Jan. 1865.

A glance at the work is sufficient to show that the
author and publisher have spared no labor in making
it the most complete "System of Surgery" ever pub-
lished in any country. — St. Louis Med. and Surg.
Journal, April, 1865.

A system of surgery which we think unrivalled in
our language, and which will indelibly associate his
name with surgical science. And what, in our opin-
ion, enhances the value of the work is that, while the
practising surgeon will find all that he requires in it,
it is at the same time one of the most valuable trea-
tises which can b£ put into the hands of the student
seeking to know the principles and practice of this
branch of the profession which he designs subse-
quently to follow. — The Brit. Am.Journ., Montreal.

SKET'S OPERATIVE SURGERY. In 1 vol. 8vo.

cloth, of over 650 pages ; with about 100 wood-cuts.

$3 25.
COOPER'S LECTURES ON THE PRINCIPLES AND

PRACTICE OF SURGERY. In 1 vol. 8vo. cloth, 750 p. $2. j

GIBSON'S INSTITUTES AND PRACTICE OF SUB-
GERY. Eighth edition, improved and altered. With
thirty-four plates. In two handsome octavo vol-
umes, about 1000 pp., leather, raised bandt. $6 60.

M

ILL EH (JAMES),

Late Professor of Surgery in the University of Edinburgh, &c.

PRINCIPLES OF SURGERY. Fourth American, from the third and

revised Edinburgh edition. In one large and very beautiful volume of 700 pages, with
two hundred and forty illustrations on wood, cloth, $3 76.

DY THE SAME AUTHOR.

THE PRACTICE OF SURGERY. Fourth American, from the last

Edinburgh edition. Revised by the American editor. Illustrated by three hundred and
sixty-four engravings on wood. In one large octavo volume of nearly 700 pages, cloth,
$3 75.

UARGENT (F. W.), M.D.
® ON BANDAGING AND OTHER OPERATIONS OF MINOR

SURGERY, New edition, with an additional chapter on Military Surgery. One handsome
royai 12mo. volume, of nearly 400 pages, with 184 wood-cuts. Cloth, $1 76.

HENRY C. LEA'S PUBLICATIONS — (Surgery).

27

ASHHURST (JOHN, Jr.), M.D.,

Surgeon to the Episcopal Hospital, Philadelphia.

THE PRINCIPLES AND PRACTICE OF SURGERY. In one

very Large and handsome octavo volume of about 1000 pages, with nearly 550 illustrations,
cloth, $6 50; leather, raised bands, $7 50. (Lately Published.)

The object of the author has been to present, within as condensed a compass as possible, a
complete treatise on Surgery in all its branches, suitable both as a text-book for the student and
a work of reference for the practitioner. So much has of late years been done for the advance-
ment of Surgical Art and Science, that there seemed to be a want of a work which should present
the latest aspects of every subject, and which, by its American character, should render accessible
to the profession at large the experience of the practitioners of both hemispheres. This has been
the aim of the author, and it is hoped that the volume will be found to fulfil its purpose satisfac-
torily. The plan and general outline of the work will be seen by the annexed

CONDENSED SUMMARY OF CONTENTS.

CHAPTER I. Inflammation. II. Treatment of Inflammation. III. Operations in general:
Anaesthetics. IV. Minor Surgery. V. Amputations. VI. Special Amputations. VII. Effects
of Injuries in General : Wounds. VIII. Gunshot Wounds. IX. Injuries of Bloodvessels. X.
Injuries of Nerves, Muscles and Tendons, Lymphatics, Bursae, Bones, and Joints. XI. Fractures.
XII. Special Fractures. XIII. Dislocations. XIV. Effects of Heat and Cold. XV. Injuries
of the Head. XVI. Injuries of the Back. XVII. Injuries of the Face and Neck. XVIII.
Injuries of the Chest. XIX. Injuries of the Abdomen and Pelvis. XX. Diseases resulting from
Inflammation. XXI. Erysipelas. XXII. Pyaemia. XXIII. Diathetic Diseases: Struma (in-
eluding Tubercle and Scrofula); Rickets. XXIV. Venereal Diseases ; Gonorrhoea and Chancroid.
XXV. Venereal Diseases continued : Syphilis. XXVI. Tumors. XXVII. Surgical Diseases of
Skin, Areolar Tissue, Lymphatics, Muscles, Tendons, and Bursae. XXVIII. Surgical Disease
of Nervous System (including Tetanus). XXIX. Surgical Diseases of Vascular System (includ-
ing Aneurism). XXX. Diseases of Bone. XXXI. Diseases of Joints. XXXII. Excisions.
XXXIII. Orthopaedic Surgery. XXXIV. Diseases of Head and Spine. XXXV. Diseases of the
Eye. XXXVI. Diseases of the Ear. XXXVII. Diseases of the Face and Neck. XXXVIII.
Diseases of the Mouth, Jaws, and Throat. XXXIX. Diseases of the Breast. XL. Hernia. XLI.
Special Hernias. XLII. Diseases of Intestinal Canal. XLIII. Diseases of Abdominal Organs,
and various operations on the Abdomen. XLIV. Urinary Calculus. XLV. Diseases of Bladder
and Prostate. XLVI. Diseases of Urethra. XLVII. Diseases of Generative Organs. INDEX.

Its author has evidently tested the writings and
experiences of the past and present in the crucible
of a careful, analytic, and honorable mind, and faith-
fully endeavored to bring his work up to the level of
the highest standard of practical surgery. He is
frank and definite, and gives us opinions, and gene-
rally sound ones, instead of a mere resume of the
opinions of others. He is conservative, but not hide-
bound by authority. His style is clear, elegant, and
scholarly. The work is an admirable tex-tbook, and
a useful book of reference It is a credit to American
professional literature, and one of the first ripe fruits
of the soil fertilized by the blood of our late unhappy
war.— N. Y. Med. Record, Feb. 1, 1872.

Indeed, the work as a whole must be regarded as
an excellent and concise exponent of modern sur-
gery, and as such it will be found a valuable text-
book for the student, and a useful book of reference
for the general practitioner. — N. Y. Med. Journal,
Feb. 1872.

It gives us great pleasure to call the attention of the
profession to this excellent work. Our knowledge of
its talented and accomplished author led us to expect
from him a very valuable treatise upon subjects to
which he has repeatedly given evidence of having pro-
fitably devoted much time and labor, and we are in no
way disappointed.— Phila. Med. Times, Feb. 1, 1872.

pIRRIE ( WILLIAM), F. R. S. E.,

•*- Professor of Surgery in the University of Aberdeen.

THE PRINCIPLES AND PRACTICE OF SURGERY. Edited by

JOHN NEILL, M. D., Professor of Surgery in the Penna. Medical College, Surgeon to the
Pennsylvania Hospital, &c. In one very handsome octavo volume of 780 pages, with 316
illustrations, cloth, $3 75.

TJAMILTON (FRANK H.}, M.D.,

Professor of Fractures and Dislocations, &c., in Bellevue Hosp. Med. College, New York.

A PRACTICAL TREATISE ON FRACTURES AND DISLOCA-
TIONS. Fourth edition, thoroughly revised. In one large and handsome octavo volume
of nearly 800 pages, with several hundred illustrations. Cloth, $5 75; leather, $6 75.

It is not, of course, our intention to review in ex-
Censo, Hamilton on "Fractures and Dislocations."
Eleven years ago such review might not have been
out of place ; to-day the work is an authority, so well,
so generally, and so favorably known, that it only
remains for the reviewer to say that a new edition is
just out, and it is better than either of its predeces-
sors.— Cincinnati Clinic, Oct. 14, 1871.

Undoubtedly the best work on Fractures and Dis-
locations in the English language.— Cincinnati Med.
Repertory, Oct. 1871.

We have once more before us Dr. .Hamilton's admi-

rable treatise, which we have always considered the
most complete and reliable work on the subject. As
a, whole, the work is without an equal in the litera-
ture of the profession. — Boston Med. and Surg.
Journ., Oct. 12, 1871.

It is unnecessary at this time to commend the book,
except to such as are beginners in the study of this
particular branch of surgery. Every practical sur-
geon in this country and abroad knows of it as a most
trustworthy guide, and one which they, in common
with us, would unqualifiedly recommend as the high-
est authority in any language.—^. Y. Med. Record,
Oct. 16, 1871.

28 HENRY C. LEA'S PUBLICATIONS — (Surgery).

&RICHSEN (JOHN E.),

*-^ Professor of Surgery in University College, London, etc.

THE SCIENCE AND ART OF SURGERY; being a Treatise on Sur-

gical Injuries, Diseases, and Operations. Revised by the author from the Sixth and
enlarged English Edition. Illustrated by over seven hundred engravings on wood. In
two large and beautiful octavo volumes of over 1700 pages, cloth, $9 00 ; leather, $11 00.
(Lately Issued.)

Author's Preface to the New American Edition.

" The favorable reception with which the ' Science and Art of Surgery' has been honored by the
Surgical Profession in the United States of America has been not only a source of deep gratifica-
tion and of just pride to me, but has laid the foundation of many professional friendships that
are amongst the agreeable and valued recollections of my life.

"I have endeavored to make the present edition of this work more deserving than its predecessors
of the favor that has been accorded to them. In consequence of delays that have unavoidably
occurred in the publication of the Sixth British Edition, time has been afforded to me to add to this
one several paragraphs which I trust will be found to increase the practical value of the work."
LONDON, Oct. 1S72.

On no former edition of this work has the author bestowed more pains to render it a complete and
satisfactory exposition of British Surgery in its modern aspects. Every portion has been sedu-
lously revised, and a large number of new illustrations have been introduced. In addition to the
materinl thus added to the English edition, the author has furnished for the American edition such
material as has accumulated since the passage of the sheets through the press in London, so that
the work as now presented to the American profession, contains his latest views and experience.

The increase in the size of the work has seemed to render necessary its division into two vol-
umes. Great care has been exercised in its typographical execution, and it is confidently pre-
sented as in every respect worthy to maintain the high reputation which has rendered it a stand-
ard authority on this department of medical science.

These are only a few of the points in which the states in his preface, they are not confined to any one
present edition of Mr. Erichsen's work surpasses its j portion, but are distributed generally through the
predecessors. Throughout there is evidence of a ! subjects of which the work treats. Certainly one of
laborious care and solicitude in seizing the passing: the most valuable sections of the book seems to us to
knowledge of the day, which reflects the greatest bo that which treats of the diseases of the arteries
credit on the author, and much enhances the value and the operative proceedings which they necessitate
of his work. We can only admire the industry which In few text-books is so much careful I/ arranged in-
has enabled Mr. Erichsen thus to succeed, amid the formation collected. — London Med. Times and Gaz.,
distractions of active practice, in producing emphatic- ! Oct. 26, 1872.

ally THE book of reference and study for British prac- I The entire work complete, as the great English
titioners of surgery.— London Lancet, Oct. 26, 1872. ! treatise on Surgery of our own time, is, we can assure
Considerable changes have been made in this edi- our readers, equally well adapted for the most junior
lion, and nearly a hundred new illustrations have student, and, as a book of reference, for the advanced
been added. It is difficult in a small compass to point practitioner. — Dublin Quarterly Journal.
out the alterations and additions; for, as the author I

D

RUITT (EGBERT), M.R.C.S., frc.

THE PRINCIPLES AND PRACTICE OF MODERN SURGERY.

A new and revised American, from the eighth enlarged and improved London edition. Illus-
trated with four hundred and thirty -two wood engravings. In one very handsome octavo
volume, of nearly 700 large and closely printed pages, cloth, $4 00; leather, $5 00.

practice of surgery are treated, and so clearly and

All that the surgical student or practitioner could
desire. — Dublin Quarterly Journal.

It is a most admirable book. We do not know
when we have examined one with more pleasure. —
Boston Med. and Surg. Journal.

In Mr. Druitt's book, though containing only some
seven hundred pages, both the principles and the

perspicuously, as to elucidate every important topic.
We have examined the book most thoroughly, and
can say that this success is well merited. His book,
moreover, possesses the inestimable advantages of
having the subjects perfectly well arranged and clas-
sified, and of being written in a style at once clear
and succinct. — Am. Journal of Med. Sciences.

ASHTON (T. /.).
ON THE DISEASES, INJURIES, AND MALFORMATIONS OP

THE RECTUM AND ANUS ; with remarks on Habitual Constipation. Second American,
from the fourth and enlarged London edition. With handsome illustrations. In one very
beautifully printed octavo volume of about 300 pages, cloth, $3 25.

T>1GELOW (HENRY J.), M.D.,

-*-* Professor of Surgery in the Massachusetts Med. College.

ON THE MECHANISM OF DISLOCATION AND FRACTURE

OF THE HIP. With the Reduction of the Dislocation by the Flexion Method. With
numerous original illustrations. In one very handsome octavo volume. Cloth, $2 50.

LA WSON (GEORGE), F. R. C. S., EngL,
Assistant Surgeon to the Royal London Ophthalmic Hospital, Moorflelds, Ac.

INJURIES OF THE EYE, ORBIT, AND EYELIDS: their Imme-
diate and Remote Effects. With about one hundred illustrations. In one very hand-
some octavo volume, cloth, $3 50.

It is an admirable practical book in the highest and best sense of the phrase.— London Medical Times
•and Gazette, May 18, 1867.

HENRY C. LEA'S PUBLICATIONS — (Surgery).

29

J3RYANT (THOMAS], F.R.C.S.,

•£•* Surgeon to Guy's Hospital.

THE PRACTICE OF SURGERY. With over Five Hundred En-

gravings on Wood. In one large and very handsome octavo volume of nearly 1000 pages,
cloth, $6 25 ; leather, raised bands, $7 25. (Lately Pubiisked.)

Again, the author gives us his own practice, his
own beliefs, and illustrates by his own cases, or those
treated in Guy's Hospital. This feature adds joint
emphasis, and a solidity to his statements that inspire
confidence. One feels himself almost by the side of
the surgeon, seeing his work aud hearing his living
words. The views, etc., of other surgeons are con-
sidered calmly and fairly, but Mr. Bryant's are
adopted. Thus the work is not a compilation of
other writings; it is not an encyclopaedia, but the
plain statements, on practical points, of a man who
has lived and breathed and had his being in the
richest surgical experience. The whole profession
owe a debt of gratitude to Mr. Bryant, for his work
in their behalf. We are confident that the American
profession will give substantial testimonial of their
feelings towards both author and publisher, by
speedily exhausting this edition. We cordially and
heartily commend it to our friends, aud think that
no live'surgeou can afford to be without it — Detroit
Review of Med. and Pharmacy, August, 1873.

As a manual of the practice of surgery for the use
of the student, we do not hesitate to pronounce Mr.
Bryant's book a first-rate work. Mr. Bryant has a
g'.,,d deal of the dogmatic energy which goes with
die clear, pronounced opinions of a man whose re-
flections aud experience have moulded a character
uot wanting in firmness aud decision. At the same
time he teaches withythe enthusiasm of one who has
faith in his teaching ;\he speaks as one having au-
thority, and herein lies the charm and excellence of
his work. He states the opinions of others freely

and fairly, yet it is no mere compilation. The book
combines much of the merit of the manual with the
merit of the monograph. One may recognize in
almost every chapter of the ninety-four of which the
work is made up the acuteness of a surgeon who has
seen much, and observed closely, and who gives forth
the results of actual experience. In conclusion we
repeat what we stated at first, that Mr. Bryant's book
is one which we can conscientiously recommend both
to practitioners and students as an admirable work.
— Dublin Journ. of Med. Science, August, 1873.

Mr. Bryant has long been known to the reading
portion of the profession as an able, clear, and graphic
writer upon surgical subjects. The volume before
us is one eminently upon the practice of surgery and
not one which treats at length on surgical pathology,
though the views that are entertained upon tnis sub-
ject are sufficiently interspersed through the work
for all practical purposes. As a text-book we cheer-
fully recommend it, feeling convinced that, from the
subject-matter, and the concise and true way Mr.
Bryant deals with his subject, it will prove a for-
midable rival among the numerous surgical text-
books which are offered to the student. — N. Y. Med.
Record, June, 1S73.

This is, as the preface states, an entirely new book,
and contains in a moderately condensed form all the
surgical information necessary to a general practi-
tioner. It is written in a spirit consistent with the
present improved standard of medical and surgical
science. — American Journal of Obstetrics, August,
1873.

\XTELL8 (J. SOELBERG),

Professor of Ophthalmology in King's College Hospital, &c.

A TREATISE ON DISEASES OF THE EYE. Second American,

from the Third and Revised Lpndon Edition, with additions; illustrated with numerous
engravings on wood, and six colored plates. Together with selections from the Test-types
of Jaeger and Snellen. In one large and very handsome octavo volume of nearly 800
pages ; cloth, $5 00 ; leather, $6 00. (Lately Published.)

The continued demand for this work, both iu England and this country, is sufficient evidence
that the author has succeeded in his effort to supply within a reasonable compass n full practical
digest of ophthalmology in its most modern aspects, while the call for repeated editions has en-
abled him in his revisions to maintain its position abreast of the most recent investigations and
improvements. In again reprinting it, every effort has been made to adapt it thoroughly to the
wants of the American practitioner. Such additions as seemed desirable have been introduced
by the editor, Dr. I. Minis Hays, and the number of illustrations has been largely increased. The
importance of test-types as an aid to diagnosis is so universally acknowledged at the present day
that it seemed essential to the completeness of the work that they should be added, and as the
author recommends the use of those both of Jaeger and of Snellen for different purposes, selec-
tions have been made from each, so that the practitioner may have at command all the assist-
ance necessary. Although enlarged by one hundred pages, it has been retained at the former
very moderate price, rendering it one of the cheapest volumes before the profession.
A few notices of the previous edition are subjoined.

On examining it carefully, one is not at all sur- lucid and flowing, therein differing materially from
priced that it should meet with universal favor. It \ some of the translations of Continental writers on this

-, iu fact, a comprehensive and thoroughly practical
treatise 011 diseases of the eye, setting forth the prac-
tice of the leading oculists of Europe and America,
a u d giving the author's own opinions aud preferences,
which are quite decided and worthy of high consid-
eration. The third English edition, from which this
i.-j taken, having been revised by the author, com-
prises a notice of all the more recent advances made
in ophthalmic science. The style of the writer is

subject that are in the market. Special paius are
taken to explain, at length, those subjects which are
particularly difficult of comprehension to the begin-
ner, as the use of the ophthalmoscope, the interpre-
tation of its images, etc. The book is profusely and
ably illustrated, and at the end are to be found 16
excellent colored ophthalmoscopic figures, which are
copies of some of the plates of Liebreich's admirable
atlas.— Kansas City Med. Journ., June, 1874.

r A URENCE (JOHN Z.), F. R. C. S.,

Editor of the Ophthalmic Review, &c.

A HANDY-BOOK OF OPHTHALMIC SURGERY, for the use of

Practitioners. Second Edition, revised and enlarged. With numerous illustrations,
one very handsome octavo volume, cloth, $3 00.

In

For those, however, who must assume the care of
diseases and injuries of the eye, and who are too
much pressed for time to study the classic works on
the subject, or those recently published by Stellwag,
Wells, Bader, aud others, Mr. Laurence will prove a
safe and trustworthy guide. He has described in thib

editiou those novelties which have secured the confi-
dence of the profession since the appearance of his
last. The volume has been considerably enlarged
and improved by the revision and additions of its
author, expressly for the American edition. — Am.
Journ. Med. Sciences, Jan. 1870.

30 HENRY C. LEA'S PUBLICATIONS— (Surgery, &c.).

THOMPSON (SIR HENR F),

J- Surgeon and Professor of Clinical Surgery to University College Hospital.

LECTURES ON DISEASES OF THE URINARY ORGANS. With

illustrations on wood. Second American from the Third English Edition. In one neat

octavo volume. Cloth, $2 25. (Now Ready.)

My aim has been to produce in the smallest possible compass an epitome of practical knowl-
edge concerning the nature and treatment of the diseases which form the subject of the work ;
and I venture to believe that my intention has been more fully realized in this volume than in
either of its predecessors. — Authors Preface.

•D7 THE SAME AUTHOR.

ON THE PATHOLOGY AND TREATMENT OF STRICTURE OF

THE URETHRA AND URINARY FISTULA. With plates and wood-cuts. From the
third and revised English edition. In one very handsome octavo volume, cloth, $3 50.
(Lately Published.)
T>Y THE SAME AUTHOR. (Just Issued.)

THE DISEASES OF THE PROSTATE, THEIR PATHOLOGY

AND TREATMENT. Fourth Edition, Revised. In one very handsome octavo volume of
355 pages, with thirteen plates, plain and colored, and illustrations on wood. Cloth, $3 75.

/TAYLOR (ALFRED £.), M.D.,

Lecturer on Med. Jurisp. and Chemistry in Guy^s Hospital

MEDICAL JURISPRUDENCE. Seventh American Edition. Edited

by JOHN J. REESE, M.D., Prcf. of Med. Jurisp. in the Univ. of Penn. In one large
octavo volume of nearly 900 pages. Cloth, $5 00; leather, $6 00. (Just Issued.)

In preparing for the press this seventh American edition of the " Manual of Medical Jurispru-
dence" the editor has, through the courtesy of Dr. Taylor, enjoyed the very great advantage of
consulting the sheets of the new edition of the author's larger work, " The Principles and Prac-
tice of Medical Jurisprudence," which is now ready for publication in London. This has enabled
him to introduce the author's latest views upon the topics discussed, which are believed to bring
the work fully up to the present time.

The notes of the former editor, Dr. Hartshorne, as also the numerous valuable references to
American practice and decisions by his successor, Mr. Penrose, have been retained, with but few
slight exceptions ; they will be found inclosed in brackets, distinguished by the letters (H.) and
(P.). The additions made by the present editor, from the material at his command, amount to
about one hundred pages; and his own notes are designated by the letter (R.).

Several subjects, not treated of in the former edition, have been noticed in the present one,
and the work, it is hoped, will be found to merit a continuance of the confidence which it has so
long enjoyed as a standard authority.

1D¥ THE SAME AUTHOR. (Now Ready.)

THE PRINCIPLES AND PRACTICE OF MEDICAL JURISPRU-

DENCE. Second Edition, Revised, with numerous Illustrations. In two large octavo
volumes, cloth, $10 00; leather, $12 00.

This great work is now recognized in England as the fullest and most authoritative treatise on
every department of its important subject. In laying it. in its improved form, before the Ameri-
can profession, the publisher trusts that it will assume the same position in this country.

jgF THE SAME AUTHOR. New Edition— Nearly Ready.

POISONS IN RELATION TO MEDICAL JURISPRUDENCE AND

MEDICINE. Third American, from the Third and Revised English Edition. In one

large octavo volume of 850 pages.

This work, which has been so long recognized as a leading authority on its important subject,
has received a very thorough revision at the hands of the author, and may be regarded as a
new book rather than as a mere revision. He has sought to bring it on all points to a level
with the advanced science of the day; many portions have been rewritten, much that was of
minor importance has been omitted, and every effort made to condense a complete view of the
subject within the limits of a single volume. Dr. Taylor's position as an expert has brought
him into connection with nearly all important cases in England for many years. He thus speaks
with an authority that few other living men possess, while his intimate acquaintance with the
literature of toxicology on both sides of the Atlantic, renders his work equally adapted as a
text-book in this country as in Great Britain.

Poisons. — Absorption and Elimination — Detection — Action — Influence of Habit — Classifica-
tion of Poisons — Evidence of Poisoning — Diseases resembling Poisoning — Inspection of the Dead
Body — Objects of Chemical Analysis — Moral and Circumstantial Evidence in Poisoning, Ac. &c.

Irritant Poisons. — Mineral Irritants — Acid Poisons — Alkaline Poisons — Non-Metallic Irri-
tants — Metallic Irritants — Vegetable Irritants — Animal Irritants.

Neurotic Poisons. — Cerebral or Narcotic Poisons — Spinal Poisons — Cerebro-Spinal Poisons —
Cerebro-Cardiac Poisons.

HENRY C. LEA'S PUBLICATIONS — (Psychological Medicine, &c.). 31

WUKE (DANIEL HACK], M.D.,

JL Joint author of " The Manual of Psychological Medicine," &c.

ILLUSTRATIONS OF THE INFLUENCE OF THE MIND UPON

THE BODY IN HEALTH AND DISEASE. Designed to illustrate the Action of the
Imagination. In one handsome octavo volume of 416 pages, cloth, $3 25. (Just Issued.)
The object of the author in this work has been to show not only the effect of the mind in caus-
ing and intensifying disease, but also its curative influence, and the use which may be made of
the imagination and the emotions as therapeutic agents. Scattered facts bearing upon this sub-
ject have long been familiar to the profession, but no attempt has hitherto been made to collect
and systematize them so as to render them available to the practitioner, by establishing the seve-
ral phenomena upon a scientific basis. In the endeavor thus to convert to the use of legitimate
medicine the means which have been employed so successfully in many systems of quackery, the
author has produced a work of the highest freshness and interest as well as of permanent value.

ftLANDFORD (G. FIELDING], M. D., F. R. C P.,

Lecturer on Psychological Medicine at the School of St. George's Hospital, &c.

INSANITY AND ITS TREATMENT: Lectures on the Treatment,

Medical and Legal, of Insane Patients. With a Summary of the Laws in force in the
United States on the Confinement of the Insane. By ISAAC RAY, M. D. In one very
handsome octavo volume of 471 pages; cloth, $3 25.

This volume is presented to meet the want, so frequently expressed, of a comprehensive trea-
tise, in moderate compass, on the pathology, diagnosis, and treatment of insanity. To render it of
more value to the practitioner in this country, Dr. Ray has added an appendix which affords in-
formation, not elsewhere to be found in so accessible a form, to physicians who may at any moment
b« called upon to take action in relation to patients.

It satisfies a want which must have been sorely j actually seen in practice and the appropriate treat
felt by the busy general practitioners of this country.
It takes the form of a manual of clinical description
of the various forms of insanity, with a description
of the mode of examining persons suspected of in-
aanity. We call particular attention to this feature
of the book, as giving it a unique value to the gene-
ral practitioner. If we pass from theoretical conside-
rations to descriptions of the varieties of insanity as

ment for them, we find in Dr. Blandford's work
considerable advance over previous writings on the
subject. His pictures of the various forms of mental
disease are so clear and good that no reader can fail
to be struck with their superiority to those given in
ordinary manuals in the English language or (so far
as our own reading extends) in any other.— London
Practitioner, Feb. 1871.

w-

'INSLOW (FORBES], M.D., D.C.L., frc.

ON OBSCURE DISEASES OF THE BRAIN AND DISORDERS

OF THE MIND; their incipient Symptoms, Pathology, Diagnosis, Treatment, and Pro-
phylaxis. Second American, from the third and revised English edition. In one handsome
octavo volume of nearly 600 pages, cloth, $4 25.

T EA (HENRY (7.).
•^SUPERSTITION AND FORCE: ESSAYS ON THE WAGER OF

LAW, THE WAGER OF BATTLE, THE ORDEAL, AND TORTURE. Second Edition,
Enlarged. In one handsome volume royal 12mo. of nearly 500 pages; cloth, $2 75.
(Lately Published.)

We know of no single work which contains, in so i interesting phases of human society and progress. . .
•mall a compass, so much illustrative of the strangest The fulness and breadth with which he has carried
operations of the human mind. Foot-notes give the out his comparative survey of this repulsive field of
authority for each statement, showing vast research history [Torture], are such as to preclude our doing
and wonderful industry. We advise our confreres j justice to the work within our present limits. But
to read this book and ponder its teachings. — Chicago \ here, as throughout the volume, there will be found
Mvd. Journal, Aug. 1870. a w

As a work of curious inquiry on certain outlying
points of obsolete law, "Superstition and Force" is
one of the most remarkable books we have met with.
—London Athenceum, Nor. 3, 1866.

He has thrown a great deal of light upon what must
be regarded as one of the most instructive as well as

wealth of illustration and a critical grasp of the
philosophical import of facts which will render Mi.
Lea's labors of sterling value to the historical stu-
dent.— London Saturday Review, Oct. 8, 1870.

As a book of ready reference on the subject, it is of
the highest value. — Westminster Review, Oct. 1867.

I THE SAME AUTHOR. (Lately Published.)

STUDIES IN CHURCH HISTORY— THE RISE OF THE TEM-
PORAL POWER— BENEFIT OF CLERGY— EXCOMMUNICATION. In one large royal
12mo. volume of 516 pp. cloth, $2 75.

literary phenomenon that the head of one of the first
American houses is also the writer of some of its most
original books. — London Athenceum, Jan. 7, 1871.

Mr. Lea has done great honor to himself and this
country by the admirable works he has written on
ecclesiologicaland cognate subjects. We have already
had occasion to commend his "Superstition and
Force" and his "History of Sacerdotal Celibacy."
The present volume is fully as admirable in its me-
thod of dealing with topics and in the thoroughness —
a quality so frequently lacking in American authors —
with which they are investigated. — N. ¥. Journal of
Psychol. Medicine, July, 1870.

The story was never told more calmly or with
greater learning or wiser thought. We doubt, indeed,
If any other study of this field can be compared with
this for clearness, accuracy, and power. — Chicago
Examiner, Dec. 1870.

Mr. Lea's latest work, "Studies in Church History,"
fully sustains the promise of the first. It deals with
cnree subjects — the Temporal Power, Benefit of
Clergy, and Excommunication, the record of which
has a peculiar importance for the English student, and
is a chapter on Ancient Law likely to be regarded as
final. We can hardly pass from our mention of such
works as these — with which that on "Sacerdotal
Celibacy" should be included — without noting the

HENRY C. LEA'S PUBLICATIONS.

INDEX TO CATALOGUE.

American Journal of the Medical Sciences
Abstract, Half-Yearly, of the Med. Sciences
Anatomical Atlas, by Smith and Homer .
Anderson on Diseases of the Skin .
Ashton on the Rectum and Anus . . .

PAGE

. 1
. 3
. 6
. 20
.28
Attfleld's Chemistry ...... 10

Ashwell on Diseases of Females . . . .23

Ashhurst's Surgery ...... 27

Barnes on Diseases of Women . . . .23

Bellamy's Surgical Anatomy .... 7

Bryant's Practical Surgery ..... 29

Bloxam's Chemistry • ..... 11

Blandford on Insanity ...... 31

Basham on Renal Diseases ..... IS

Brinton on the Stomach ..... 16

Bigelo-w on the Hip .... .28

Barlow's Practice of Medicine . . . . 14

Bowman's (John E.) Practical Chemistry . . 11
Bowman's (John E.) Medical Chemistry . . II
Bumstead on Venereal ...... 19

Bumstead and Cullerier's Atlas of Venereal . 19
Carpenter's Human Physiology .... 8

Carpenter's Comparative Physiology ... 8
Carpenter on the Use and Abuse of Alcohol . 13
Carson's Synopsis of Materia Medica . . .13
Chambers on Diet and Regimen . . . .16

Chambers's Restorative Medicine . . 16

Christison and Griffith's Dispensatory . ' 13
Churchill's System of Midwifery . . [ 25

Churchill on Puerperal Fever . . . '23
Condie on Diseases of Children . . . ' 21
Cooper's (B. B.) Lectures on Surgery . '26

Cullerier's Atlas of Venereal Diseases . ' 19
Cyclopedia of Practical Medicine . . * 15

Dalton's Human Physiology . 9

Davis' Clinical Lectures • 14

De Jongh on Cod-Liver Oil . . . . • 13

Dewees on Diseases of Females . . . '23
Dewees on Diseases of Children . . . -20
Druitt's Modern Surgery • 28

Dunglison's Medical Dictionary ...» 4
Dunglison's Human Physiology 9

Dunglison on New Remedies . . . -13
Ellis's Medical Formulary, by Smith . . • 13
Erichsen's System of Surgery . . . • 28
Fenwick's Diagnosis ..... • 14

Flint on Respiratory Organs ..... 17

Flint on the Heart . . . . , -17

Flint's Practice of Medicine . . . . .15

Flint's Essays ...... -15

Flint on Phthisis ....... 17

Fownes's Elementary Chemistry . . . - 10
Fox on Diseases of the Stomach . . . • 17
Fnlleron the Lungs, &c ..... • 17

Green's Pathology and Morbid Anatomy . • 14
Gibson's Surgery ...... -26

G luge's Pathological Histology, by Leidy . . 14
Galloway's Qualitative Analysis . . . 10

Gray's Anatomy ....... 6

Griffith's (R. E.) Universal Formulary . . 13
Gross on Foreign Bodies in Air-Passages . . 26
Gross's Principles and Practice of Surgery . . 26
Guersant on Surgical Diseases of Children . . 20
Hamilton on Dislocations and Fractures . . 27
Hartshorne's Essentials of Medicine . . .16
Hartshorne's Conspectus of the Medical Sciences 5
Hartshorne's Anatomy and Physiology . . 7
Heath's Practical Anatomy ..... 7

Hoblyn's Medical Dictionary .... 4

Hodge on Women ....... 23

Hodge's Obstetrics ....... 24

Hodges' Practical Dissections .... 6

Holland's Medical Notes and Reflections . . 14
Homer's Anatomy and Histology ... 6
Hudson on Fevers ...... 18

Hill on Venereal Diseases ..... 19

Hillier's Handbook of Skin Diseases . . 20

Jones and Sieveking's Pathological Anatomy . 14
Jones (C. Handfield) on Nervous Disorders . 18

PAGB

8

.11
.31
. 31
18

.18
. 25

Kirkes' Physiology

Knapp's Chemical Technology . .

Lea's Superstition and Force . .

Lea's Studies in Church History ..

Lee on Syphilis

Lincoln on Electro-Therapeutics . .

Leishman's Midwifery ....

La Roche on Yellow Fever ..... 14

La Roche on Pneumonia, &c. . . . .17

Laurence and Moon's Ophthalmic Surgery . . 29
Lawson on the Eye ...... 28

Laycock on Medical Observation . . . .14

Lehmann's Physiological Chemistry, 2 vols. . 9
Lehmann's Chemical Physiology ....<>

Ludlow's Manual of Examinations ... 6
Lyons on Fever ....... 18

Maclise's Surgical Anatomy ..... 7

Marshall's Physiology ...... 8

Medical News and Library ..... 2

Meigs's Lectures on Diseases of Women . . 23
Meigs on Puerperal Fever ..... 23

Miller's Practice of Surgery ..... 26

Miller's Principles of Surgery . . . .26

Montgomery on Pregnancy ..... 25

NeilL and Smith's Compendium of Med. Science . fi
Neligan's Atlas of Diseases of the Skin . . 20
Neligan on Diseases of the Skin . ... 2

Obstetrical Journal ...... 22

Odling's Practical Chemistry .... 10

Pavy on Digestion ...... 16

Pavy on Food .......

Parrish' s Practical Pharmacy .... 12

Pirrie's System of Surgery . . . .27

Pereira's Mat. Medica and Therapeutics, abridged 1 3
Quain and Sharpey's Anatomy, by Leidy .
Roberts on Urinary Diseases ..... 1

Ramsbotham on Parturition ..... 26

Rigby's Midwifery ....... 26

Royle's Materia Medica and Therapeutics . . 13
Swayne's Obstetric Aphorisms . ... 2

Sargent's Minor Surgery ..... 26

Sharpey and Quain's Anatomy, by Leidy .

Skey's Operative Surgery ..... 26

Slade on Diphtheria ...... 18

S^nith (J.L.) on Children ..... 2]

Smith (H. H.) and Homer's Anatomical Atlas .
Smith (Edward) on Consumption . . . .17

Smith on Wasting Diseases *. Children . . 21
Still's Therapeutics ...... 12

Sturges on Clinical Medicine . . . .14

Stokes on Fever ....... 14

Tanner's Manual of Clinical Medicine ... 6
Tanner on Pregnancy . ... 24

Taylor's Medical Jurisprudence . . . .30

Taylor's Principles and Practice of Med Jurisp •
Taylor on Poisons ....... 3G

Tuke on the Influence of the Mind . . .31
Thomas on Diseases of Females . . . .22

Thompson on Urinary Organs . . . .30

Thompson on Stricture ...... 30

Thompson on the Prostate ..... 30

Todd on Acute Diseases ...... 14

Walshe on the Heart ...... 17

Watson's Practice of Physic ..... 15

Wells on the Eye ....... 29

West on Diseases of Females ... 23

West on Diseases of Children ... 21

West on Nervous Disorders of Children . 21

What to Observe in Medical Cases . . 14

Williams on Consumption .... 17

Wilson s Human Anatomy .... 7

Wilson on Diseases of the Skin ... 20

Wilson's Plates on Diseases of the Skin . 20

Wilson's Handbook of Cutaneous Medicine 20

Winslow on Brain and Mind ... 31

Wohler's Organic Chemistry ... 11

Winckel on Childbed ...... 4

Zeissl on Venereal ....... 19

For "THE OBSTETRICAL JOURNAL," FIVE DOLLARS a year, see p. 22.

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